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Controlling the Aspect Ratio of Inorganic Nanorods and Nanowires
Advanced Materials
Abstract
Semiconductors and metals exhibit unusual optical, electronic, and magnetic properties on the nanometer scale. Chemists and materials scientists are developing methods to make non-spherical shapes of semiconductors and metals on the nanometer scale. We use a seed-mediated growth approach to make metallic nanorods and nanowires in homogeneous solution. Control of the ratio of metallic spherical seeds to metal salt in the reduction reaction controls the aspect ratio of the resulting rods and wires.
... In particular, NWs have lengths in the range of micrometers and high aspect ratios of 20 or higher. Their cross-sections are usually round [2][3][4]. NWs generally have high crystalline quality, have tunable composition and properties, and, due to their morphology, they can also be incorporated in different devices with different designs [5,6]. ...
... In 1964, Wagner [18] presented a vapor-liquid-solid (VLS) mechanism for the synthesis of Si whiskers on a Au-deposited Si substrate using SiCl 4 and H 2 source materials. By Catalyst alloy formation for two-and three-valence metal oxides such as ZnO and In2O3 can be described as follows [36]. ...
Metal oxide nanowires (NWs) with a high surface area, ease of fabrication, and precise control over diameter and chemical composition are among the best candidates for the realization of resistive gas sensors. Among the different techniques used for the synthesis of materials with NW morphology, approaches based on the vapor-liquid-solid (VLS) mechanism are very popular due to the ease of synthesis, low price of starting materials, and possibility of branching. In this review article, we discuss the gas-sensing features of metal oxide NWs grown by the VLS mechanism, with emphasis on the growth conditions and sensing mechanism. The growth and sensing performance of SnO2, ZnO, In2O3, NiO, CuO, and WO3 materials with NW morphology are discussed. The effects of the catalyst type, growth temperature, and other variables on the morphology and gas-sensing performance of NWs are discussed.
... AgNWs suspension solution of 1% was well re-dispersed using ultrasonication for 10 min. The AgNWs were made into formulated AgNWs ink using 0.1% by weight of chitosan (MW~10,000) as a thickening agent, and the clean AgNWs suspension (0.2%) was Materials 2023, 16, 5501 3 of 22 then diluted to (0.05% by weight). The final AgNWs suspension (ink) was then coated by using a spin coater at different steering speeds for one minute on a clean glass substrate. ...
... Materials 2023,16, 5501 ...
A growing number of people are interested in using silver nanowires (AgNWs) as potential transparent and conductive materials. The production of high-performance and high-throughput AgNWs was successfully optimized in this work using a one-step, straightforward, and reproducible modified polyol approach. The factors influencing the morphology of the silver nanowires have undergone extensive research in order to determine the best-optimized approach for producing AgNWs. The best AgNW morphology, with a length of more than 50 m and a diameter of less than 35 nm (aspect ratio is higher than 1700), was discovered to be produced by a mixture of 44 mM AgNO3, 134 mM polyvinylpyrrolidone (PVP) (Mo.Wt 40,000), and 2.4 mM KCl at 160 °C with a stirring rate of 100 rpm. With our improved approach, the overall reaction time was cut from almost an hour with the conventional polyol method to a few minutes. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and ultraviolet (UV) spectroscopy were used to characterize AgNWs. The resultant AgNWs’ dispersion was cleaned using a centrifuge multiple times before being deposited on glass and PET substrates at room temperature. In comparison to commercial, delicate, and pricey indium-doped tin oxide (ITO) substrates, the coated samples displayed exceptionally good sheet resistance of 17.05/sq and optical haze lower than 2.5%. Conclusions: Using a simple one-step modified polyol approach, we were able to produce reproducible thin sheets of AgNWs that made excellent, flexible transparent electrodes.
... Therefore, over the past decade great research efforts have been made on characterizing mechanical properties of NWs. But due to the NWs' small physical size, with typical diameters from 10 nm to 500 nm and high aspect ratios from 1 to 300 or even larger than 1000 [3], [4], experimental work has been so far limited to specially prepared individual NWs, e.g., using atomic force microscopy (AFM), in which the tested NWs must be removed from their substrate and fixed on a special one [5]. However, next-generation energy-harvesting (photovoltaics, thermoelectrics, etc.) and storage devices (Li ion battery, super capacitor, etc.) or metal bumps for low-resistance room-temperature fine-pitch bonding on flexible substrates rely on large-scale vertically-aligned NW arrays (NWAs), which have to be characterized without releasing them from their substrates [6], [7]. ...
Dimensional and contact resonance (CR) images of nanowire (NW) arrays (NWAs) are measured using our newly developed microprobe CR imaging (CRI) setup. Then a reference method is employed to calculate the indentation modulus of NWs ( M i , NW ) representing the elasticity of NWs, by measuring NWAs and reference samples at the same static probing force. Furthermore, topography is imaged in combination with CR and M i , NW separately by software, in which the z values indicate the topography of the NWs and the color bars show its CR or M i , NW . Then NWs’ topography relation to M i , NW is visualized. As typical examples, 3D imaging of topography and measurement of M i , NW is performed with Si<111> pillar arrays as well as Cu and ZnO NWAs. The novel method enables fast mechanical performance measurements of large-scale vertically-aligned NWAs without releasing them from their respective substrates. For instance, the diameter and pitch of the Si<111> pillars and the diameter of the Cu NWAs are in good agreement with the values measured by scanning electron microscopy (SEM). The position of ZnO NWs bunches grown at arbitrary sites on silicon can be identified with the help of combined topography and indentation modulus images. Furthermore, M i , NW measured by our homemade CRI setup agrees well with bulk values. Differences between the measured M i , NW and bulk M i values may be related to a size effect in NW elasticity.
... The synthesis of anisotropic gold nanoparticles in surfactant solutions has been performed by the seed-mediated method, using cetyltrimethylammonium bromide (CTAB) micelles as templates (Murphy and Jana 2002;Gole and Murphy 2004). The rationale of this method is associated with the influence of the cationic anisotropic CTAB micelles, directing the growth of pre-synthesized isotropic AuNPs (the seeds) (Gole and Murphy 2004). ...
Hyperspectral imaging can provide accurate information on the distribution of the chemical species in materials and biological samples, based on the analysis of their electronic and vibrational profiles. In special, confocal Raman microscopy is one of the best ways to access the chemical distribution of molecules, especially under resonance Raman or SERS conditions. On the other hand, enhanced dark field optical microscopy can be employed for hyperspectral imaging in the visible and near-IR region, while extending the optical resolution up to the nanoscale dimension. It allows the detection of gold or silver single nanoparticles, as well as spectral monitoring from the characteristic surface plasmon bands. The two hyperspectral microscopies can be conveniently combined to provide nanoscale electronic and vibrational information of the species present in a wide variety of chemical and biological systems. Case studies, including the classical spot-test analysis of nickel(II) ions with dithizone are here reported. A great enhancement of sensitivity in the detection of nickel(II) ions, by at least 4 orders of magnitude, has been observed in this work. Hyperspectral measurements allowed the mapping of the gold nanoparticles (AuNP) distribution on cellulose fibers and on glass, and the evaluation of their extinction and SERS spectra for analytical purposes. Spot tests analysis metal ions with pentacyanidoferrate(II) complexes have also been examined from the point of view of electronic and Raman spectral images. Differentiation of the chemical and electromagnetic mechanisms in the SERS spectra of substituted terpyridine iron(II) complexes with gold nanoparticles has been reported. Characterization of Turkevich nanodisks, and ranelate induced gold nanoparticles formation have also been conducted in this thesis. Finally, hyperspectral techniques have been successfully employed to probe the interaction of gold nanoparticles with microtubules associated with molecular machines.
... Murphy and Jana, 2002 AgCl . Wang et al., 2005DNA AgNW Hong et al., 2001Ijiro and Mitomo, 2017 AgNW HCl AgCl R 1. ...
We report a novel method for the synthesis of silver nanowires (AgNWs). In this method, silver chloride (AgCl) and N, N-dimethyl-dodecylamine hydrochloride (C12H25NMe2·HCl) are used as a silver source and a protecting agent, respectively. Heating of both reagents in N, N-dimethyldodecylamine forms silver chlorocomplex, AgCl n1– ⁿ solving homogeneously in the melting C12H25NMe2·HCl. The addition of the reducing agent, N, N-dibenzylhydroxyamine to the reaction mixture in order to reduce AgCl n1– ⁿ to silver atom (Ag⁰) gives firstly multiplied twinned nanoparticles (MTPs), and then uniform silver nanowires (AgNWs) with the dimension of 50–100 nm in thickness and >20 µm in length. Thermogravimetric analysis of the product reveals that highly pure AgNWs containing less organic residues are obtained. We investigate the effects of loading ratios of tertiary amine hydrochlorides to AgCl, the molecular structures of amines, and reaction temperature on the morphologies and yields of the generated AgNWs. We demonstrate that the MTPs are efficiently generated by the reduction reaction of AgCl n1– ⁿ in the presence of tertiary amine hydrochlorides, and that tertiary amine hydrochlorides also play an important role in anisotropic crystal growth of Ag⁰ to AgNWs through the formation of the MTPs.
... Therefore, the SPR parameters can be adapted to specific applications [9]. This fact favored the development of new methods for synthesizing nano-objects of various shapes such as rods, bipyramids, bicones, dodecahedrons, triangles, cubes, and stars [10][11][12][13][14][15][16]. ...
В роботi в рамках пiдходу еквiвалентного сфероїда дослiджуються оптичнi характеристики металевих наночастинок бiконiчної та бiпiрамiдальної форм. Проведено розрахунки частотних залежностей дiагональних компонент тензора поляризовностi, перерiзiв поглинання та розсiювання i частот поздовжнього та поперечного поверхневого плазмонного резонансу частинок вказаних форм. Встановлено, що положення поверхневого плазмонного резонансу суттєво залежить вiд аспектного вiдношення, коли плазмоннi коливання вiдбуваються вздовж бiльшого розмiру наночастинки i не залежить вiд аспектного вiдношення для плазмонних коливань вздовж меншого розмiру. Показано, що положення й амплiтуда максимумiв перерiзу поглинання залежать не лише вiд аспектного вiдношення, а i вiд форми поперечного перерiзу частинки (коло або п’ятикутник). В свою чергу, змiна матерiалу наночастинок має наслiдком лише зсув спектральних кривих зi збереженням вiдносних положень i величин максимумiв перерiзiв поглинання.
... The assessment of GNR cytotoxicity is a crucial aspect of in vitro and in vivo PTT studies. The cytotoxicity of GNRs is influenced by the presence of hexadecyltrimethylammonium bromide (CTAB), which is used in the synthesis of GNRs [34,35]. However, when GNRs are modified with polyethylene glycol (PEG) on their surfaces, this leads to a reduction in cytotoxicity in in vitro experiments compared to non-PEGylated GNRs [36]. ...
Gold nanorods are the most commonly used nanoparticles in photothermal therapy for cancer treatment due to their high efficiency in converting light into heat. This study aimed to investigate the efficacy of gold nanorods of different sizes (large and small) in eliminating two types of cancer cell: melanoma and glioblastoma cells. After establishing the optimal concentration of nanoparticles and determining the appropriate time and power of laser irradiation, photothermal therapy was applied to melanoma and glioblastoma cells, resulting in the highly efficient elimination of both cell types. The efficiency of the PTT was evaluated using several methods, including biochemical analysis, fluorescence microscopy, and flow cytometry. The dehydrogenase activity, as well as calcein-propidium iodide and Annexin V staining, were employed to determine the cell viability and the type of cell death triggered by the PTT. The melanoma cells exhibited greater resistance to photothermal therapy, but this resistance was overcome by irradiating cells at physiological temperatures. Our findings revealed that the predominant cell-death pathway activated by the photothermal therapy mediated by gold nanorods was apoptosis. This is advantageous as the presence of apoptotic cells can stimulate antitumoral immunity in vivo. Considering the high efficacy of these gold nanorods in photothermal therapy, large nanoparticles could be useful for biofunctionalization purposes. Large nanorods offer a greater surface area for attaching biomolecules, thereby promoting high sensitivity and specificity in recognizing target cancer cells. Additionally, large nanoparticles could also be beneficial for theranostic applications, involving both therapy and diagnosis, due to their superior detection sensitivity.
... At 464 nm, the absorption peak suggests that the electron transition involved is primarily a dipole transition. In a dipole transition, the conduction electrons of the AgNPs are excited from the ground state to a higher energy state by absorbing a photon with a specific energy corresponding to the wavelength of 464 nm [50][51][52]. FT-IR analysis of AgNPs is a technique utilized to determine the chemical composition and bonding properties of these nanoparticles. This technique is based on principle of the interaction of infrared radiation with the molecular vibrations of the nanoparticles [53]. ...
In recent years, bacterial pathogens have developed resistance to antimicrobial agents that have created a global threat to human health and environment. As a novel approach to combating antimicrobial resistance (AMR), targeting bacteria’s virulent traits that can be explained by quorum sensing (QS) is considered to be one of the most promising approaches. In the present study, biologically synthesized silver nanoparticles derived from Lactobacillus rhamnosus (AgNPs-LR) were tested against three Gram-negative bacteria to determine whether they inhibited the formation of biofilms and triggered the virulence factors controlled by QS. In C. violaceum and S. marcescens, a remarkable inhibition (>70%) of QS-mediated violacein and prodigiosin production was recorded, respectively. A dose-dependent decrease in virulence factors of P. aeruginosa (pyocyanin, pyoverdine, LasA protease, LasB elastase and rhamnolipid production) was also observed with AgNPs-LR. The biofilm development was reduced by 72.56%, 61.70%, and 64.66% at highest sub-MIC for C. violaceum, S. marcescens and P. aeruginosa, respectively. Observations on glass surfaces have shown remarkable reductions in biofilm formation, with less aggregation of bacteria and a reduced amount of extra polymeric materials being formed from the bacteria. Moreover, swimming motility and exopolysaccharides (EPS) was also found to reduce in the presence of AgNPs-LR. Therefore, these results clearly demonstrate that AgNPs-LR is highly effective in inhibiting the development of biofilms and the QS-mediated virulent traits of Gram-negative bacteria. In the future, AgNPs-LR may be used as an alternative to conventional antibiotics for the treatment of bacterial infections after careful evaluation in animal models, especially for the development of topical antimicrobial agents.
... For decades, the structure-property correlations and their corresponding mechanistic principles of formation were extensively elucidated. The guiding principles and factors that affect size-and shape-control of a material, including crystal growth mechanism, phase transformation, and kinetics, have been explored for anisotropic onedimensional (1D) nanostructures, such as nanorods, nanotubes, and nanowires [1][2][3][4]. The 1D electronic pathways to accumulate effective charge transportation and larger surface area of anisotropic nanostructures provide a profound impact in nanoelectronics and nanodevices [5]. ...
One-dimensional (1D) inorganic metal/metal oxide nanostructures are of significant interest due to their distinctive physical and chemical properties that are beneficial for various applications. A fundamental understanding of the guiding principles that control the anisotropy and the size of the nanostructures is essential toward developing the building blocks for the fabrication of leading-edge miniaturized devices. Oriented attachment (OA) crystal growth mechanism has been recognized as an effective mechanism for producing 1D anisotropic nanostructures. However, a limited understanding of the OA mechanism could impede the controlled fabrication of 1D nanostructures. This chapter provides a comprehensive summary on recent advances of the OA mechanism and the current state of the art on various in-situ, ex-situ, and theoretical investigations of OA-based crystal growth dynamics as well as the shape and size-controlled kinetics. Other competing crystal growth mechanisms, including seed-mediated growth and Ostwald ripening (OR), are also described. Further, we thoroughly discuss the knowledge gap in current OA kinetic models and the necessity of new kinetic models to elucidate the elongation growth of anisotropic nanostructures. Finally, we provide the current limitations, challenges for the understanding of crystal growth dynamics, and future perspectives to amplify the contributions for the controlled self-assembled 1D nanostructures. This chapter will lay the foundation toward designing novel complex anisotropic materials for future smart devices.
... To solve this problem, it was proposed to include photothermal nanoparticles in greenhouse photoconversion covers. Photothermal nanoparticles can be based on noble metals: Au, Ag, Cu and Pt [163], which have intensive bands of localized surface plasmon resonance-a phenomenon caused by the collective oscillation of surface electrons after exposure to incident light. [164]. ...
Modern agriculture cannot be imagined without the introduction of smart and efficient technologies. These, undoubtedly, include technologies for directed regulation of the illumination of agricultural plants. Depending on the climatic conditions of cultivation, farmers shade or additionally illuminate the plants, and also change the spectrum of the light reaching the plants. The aim of this review is to provide an overview of solar light conversion methods and approaches for agricultural applications and discuss their advantages and limitations.
... The color of the mixture is constantly changing until the reaction is complete and the color of the mixture is murky dark green. [18][19][20] With PVP protecting the surface of the silver nanoparticles, each nanoparticle can be easily dispersed in solution with other nanoparticles. ...
Nano‐silver conductive inks have attracted the attention of researchers due to their high electrical conductivity, good chemical stability, and wide applicability. As the mainstream conductive ink, it is mostly used in inkjet printing, but its application is limited due to the high sintering temperature. In this paper, silver nanoparticles were synthesized by reducing silver nitrate with sodium borohydride. Using silver nanoparticles as basic conductive fillers and graphene or copper nanoparticles as auxiliary conductive fillers, silver conductive inks, silver/graphene conductive inks and silver/copper conductive inks suitable for micro‐direct writing printing were prepared. Electrode patterns were printed on photo paper by micropen writing printing. The prepared paper electrode can detect nitrate using electrochemical analysis. The results show that the paper electrodes prepared by the three conductive inks can be used for the analysis of potassium ferricyanide and potassium nitrate. The minimum square resistance of paper electrodes prepared with silver conductive ink is 0.11Ω/sq. It can be cycled 60 times in electrochemical applications with small standard deviation and high reproducibility and stability. Analysis and detection can also be performed in nitrate concentrations ranging from 60 μM to 1000 μM. This low silver content, green, and low resistivity flexible electrode offers a solution for the simplicity and economy of electronic devices.
... The role of oleylamine in the evolution of NRs was examined by synthesizing three samples containing an exact composition of Pb and Sn precursors with or without ligands. Aspect ratio ranging from 1 to 20 corresponds to NRs, and greater than 20 corresponds to the NWs [40]. The long-chain ligands get intercalated into bulk perovskites resulting in low dimensional structures [29]. ...
Stable mixed cation (tin-lead) perovskite nanorods results from intercalating long-chain organic ligand- oleylamine into perovskite 3D (CH3NH3PbBr3) structure using the ligand-assisted re-precipitation method. A spin-coated nanorod film works as an active layer for resistive memory devices by sandwiching nanorod film between two electrodes with a switching voltage of 1.4 V. A poly(methyl methacrylate) passivated nanorod film results in better resistive memory properties by exploiting advantages of both insulating poly(methyl methacrylate) and semiconducting perovskite nanorods. The passivation enhances the stability of the device, protecting electrodes from reacting with the perovskite layer. The structure lowers the current in the high resistance state, increasing the ON-OFF current ratio to ∼ 10⁵. The device exhibits non-volatile rewritable resistive switching characteristics with a switching voltage ∼ 0.5 V. The conduction mechanism involved in the switching action is explained from the relation between current-voltage as space charge limited conduction.
... Among different morphologies, nanowires (NWs) with aspect ratios greater than 20 [28] are highly popular for sensing applications, owing to their high surface area, straightforward preparation methods, ease of gas sensor fabrication, high and rapid response to the target gas, long-term stability, and high crystallinity [29,30]. Accordingly, several studies have realized the enhanced gas-sensing capacity of NW-based gas sensors [31,32]. ...
There is an increasing need for the development of low-cost and highly sensitive gas sensors for environmental, commercial, and industrial applications in various areas, such as hazardous gas monitoring, safety, and emission control in combustion processes. Considering this, resistive-based gas sensors using metal oxide semiconductors (MOSs) have gained special attention owing to their high sensing performance, high stability, and low cost of synthesis and fabrication. The relatively low final costs of these gas sensors allow their commercialization; consequently, they are widely used and available at low prices. This review focuses on the important MOSs with different morphologies, including quantum dots, nanowires, nanofibers, nanotubes, hierarchical nanostructures, and other structures for the fabrication of resistive gas sensors.
... To load drug molecules on AMRs, the surface of the AMRs was modified by sodium citrate and allowed to bind to positively changed DOX molecules via electrostatic interactions. It has been reported that sodium citrate has plentiful active carboxyl groups, often used as stabilizers to modify Gold (Au), Ti, and magnetic nanoparticles for improved biocompatibility (Kang et al., 2018;Murphy and Jana, 2002;Raza et al., 2016). Figure 4A shows the schematic of the surface functionalization of AMRs. ...
To realize the potential to use micro/nanorobots for targeted cancer therapy, it is important to improve their biocompatibility and targeting ability. Here, we report on drug-loaded magnetic microrobots capable of polarizing macrophages into the anti-tumor phenotype to target and inhibit cancer cells. In vitro tests demonstrated that the microrobots have good biocompatibility with normal cells and immune cells. Positively charged DOX were loaded onto the surface of microrobots via electrostatic interactions and exhibited pH-responsive release behavior. The nano-smooth surfaces of the microrobots activated M1 polarization of macrophages; thus, activating their intrinsic targeting and anti-tumor abilities towards cancer cells. Through dual targeting from magnetic guidance and M1 macrophages, the microrobots were able to target and kill cancer cells in a 3D tumor spheroid culture assay. These findings demonstrate a way to improve the tumor-targeting and anti-tumor abilities of microrobots through the combined use of magnetic control, macrophages, and pH-responsive drug release.
... Metallic NWs have been synthesized by a range of methods, including the template method (Bera et al., 2004), hydrothermal method (Liu et al., 2003), electrochemical deposition (Tian et al., 2003), chemical vapor deposition (Kim et al., 2008), physical vapor deposition (Richter et al., 2009;Yoo et al., 2010), and polyol method (solution phase) (Murphy and Jana, 2002;Sun et al., 2002;Wiley et al., 2005;Wiley et al., 2007). The last two methods are known to produce high-quality single-crystalline and penta-twinned NWs, respectively, with uniform diameter, smooth surfaces, and well-defined defect structures if any (e.g., TBs). ...
Mechanical properties of nanowires (NWs) can be different from those of their bulk counterparts, manifesting so-called size effect. Measuring their mechanical properties and understanding their deformation mechanisms are of critical relevance. This article reviews the mechanical properties of three types of NWs – metallic, ionic, and covalent NWs categorized by their bonding types – including Young’s modulus, strength, plasticity and fracture. Major mechanical testing methods for NWs such as bending, resonance, and uniaxial tension are also summarized along with key experimental challenges such as sample preparation and effect of boundary conditions. A brief summary and outlook for future research directions are provided.
... 45 Moreover, small-sized spherical Ag nanoparticles give resonance bands at 350-500 nm region with peaks positioned at approximately 410 nm. 46,47 Similarly, the small Au nanoparticles (approximately from 9 nm) typically show peaks at around 520 nm and move towards redshift as the size increases. 48 As a result of the observed peaks, the Ag(NP) and Au(NP) are ascertained to be spherical and small in size. ...
Micro-pollutants, especially antibiotics contamination in water bodies, are a serious concern, and their detection at a low level is important for human health and even aquatic life at large. The present investigation aims to obtain the novel nanocomposite material precursor to clay and silane. The nanocomposite material is decorated with Ag or Au nanoparticles as obtained indigenously by a green route using natural phytochemicals. The materials were extensively characterized by advanced analytical methods. The nanocomposite materials (Ag(NP)/TCBN and Au(NP)/TCBN) are employed in the selective and efficient trace measurement of sulfamethoxazole (SMZ) in aqueous solutions using the differential pulse anodic stripping voltammetry. The cyclic voltammetric and electrochemical impedance spectroscopic methods showed an increased electroactive surface area as well as faster electron transfer reactions compared to the glassy carbon electrode (GCE). The DPASV measurements at the concentration range of 0.25 mg/L to 30.0 mg/L showed that the novel nanocomposites provide the LOD of 0.022 and 0.036 mg/L, respectively, for the Ag(NP)/TCBN/GCE and Au(NP)/TCBN/GCE for sulfamethoxazole. Further, the application of the method for the detection of sulfamethoxazole in real water samples resulted in an acceptable recovery percentage of 93.08 to 103.7.
Nanotechnology refers to nanomaterials of different dimensions, ranging in size from 1 to 100 nm. Shape and size, as well as properties of nanomaterials, depend on the materials based on their production. Nanomaterials are classified according to the type of substrate into carbon-based nanomaterials, metal-based nanomaterials, ceramic nanomaterials, lipid-based nanomaterials, semiconductor nanomaterials, and polymer nanomaterials. There are many physical methods that are widely used to produce nanomaterials, among these methods are inert gas condensation (IGC), physical evaporation, electric arc discharge, sputtering, and laser methods. Many characterization analysis techniques of nanomaterials, including ultraviolet–visible (UV–V) spectroscopy, XRD (X-ray diffraction), BET (Brunauere emmette teller), FESEM (Field emission scanning electron microscopy), FTIRS (Fourier transform infrared spectroscopy), TEM (Transmission electron microscopy) and Zeta size analysis. The unique properties that distinguish nanomaterials, allows them to penetrate many applications that directly serve the world. Nanomaterials have been utilized in various applications in the environment, agriculture, food industries, medical industries, chemical processing, and military industries.
The research aimed to observe the influence of the storage conditions of silver colloidal solutions prepared by biological (green) and chemical methods on their long-term stability. Green methods for reducing and stabilizing silver nanoparticles (AgNPs) use natural substances. The rosemary leaf extract was used for AgNPs synthesis, and prepared nanoparticles were spherical (average size of 12 nm). In the chemical method, commercial chemicals (NaBH4, TSC, PVP, and H2O2) were used, and two colloids were prepared; the first contained spherical nanoparticles with an average size of 8 nm, and the second triangular prisms with an average size of 35 nm. The prepared colloids were stored under four conditions: at room temperature in the light and the dark, and at a temperature of 5 °C (refrigerator) in the light and the dark. The results confirmed the influence of storage conditions on the stability of nanoparticles. Colloids stored at 5 °C in the dark show the best stability. However, differences in stability dependent on the shape of nanoparticles prepared by chemical method were also observed; triangular nanoparticles showed the least stability. Methods such as UV–vis spectrophotometry, TEM, and EDX were used to analyze the nanoparticles before and after storage.
Silver, a precious metal, can be recovered as a by-product of the processing of non-ferrous metals such as lead. In this work, silver crystals grown from the controlled cooling of a 10% silver–90% lead melt have been examined to quantify crystal morphologies developed under industrial conditions. X-ray tomography (XCT) is adapted to quantify the size and morphology of silver crystal structures grown from the Ag-Pb melt. The examination utilized high X-ray energies and small sample sizes to mitigate attenuation and enhance image quality. Examination of single crystal dendrites under high magnification demonstrates that silver crystals, even those grown under commercial conditions, yield a Face-Centered Cubic (FCC) crystalline lattice, which could be important for the practical extension of this work to the commercial production of Ag nano-crystals and crystalline supra-molecular structures. The crystals observed are composed of multiple twinned euhedral grains in a variety of dendritic to acicular arrangements, yielding a substantial heterogeneity of crystalline forms. XCT data were used to generate size and shape descriptors for the individual crystals. The results were compared to an equivalent set of descriptors generated from laser sizing examination of a sample of unconsolidated crystals from the same experimental run. The correspondence to within 9% of the crystal equivalent diameters determined independently by the XCT and laser sizing demonstrates a favorable outcome in particle sizing as achieved by visual inspection of XCT results. XCT examination of crystal assemblages identifies small octahedral crystals and larger triangular platelets. The structures expected for FCC crystals grown at thermodynamically controlled conditions are not observed in our systems, suggesting the possibility of the first crystal nuclei form at such conditions, but their growth transition to kinetically controlled mechanisms occurs as their size increases above a threshold cutoff. Based on literature observations, this size threshold is much smaller than the resolution of the XCT instrumentation employed herein. Our characterization data are in fact consistent with thermodynamics/kinetics—and then kinetics-controlled mechanisms—as the crystal size increases. This observation is important because the systems considered here are representative of commercial processes. As such, this work extends prior crystal growth concepts, which were explored in aqueous systems often probed by electrodeposition.
Goldbeating is the ancient craft of thinning bulk gold into gossamer leaves. Pioneered by ancient Egyptian craftsmen, modern mechanized iterations of this technique can fabricate sheets as thin as ∼100 nm. We take inspiration from this millennia-old craft and adapt it to the nanoscale regime, using colloidally-synthesized 0D/1D gold nanoparticles (AuNPs) as highly ductile and malleable nanoscopic gold ingots and subjecting them to solid-state, uniaxial compression. The applied stress induces anisotropic morphological transformation of AuNPs into 2D leaf form and elucidates insights into metal nanocrystal deformation at the extreme length scales. The induced 2D morphology is found to be dependent on the precursor 0D/1D nanoparticle morphology, size (0D nanosphere diameter and 1D nanorod diameter and length), and their on-substrate arrangement (e.g., interparticle separation, packing order) prior to compression. Overall, this versatile and generalizable solid-state compression technique enables new pathways to synthesize and investigate the anisotropic morphological transformation of arbitrary nanoparticles and their resultant emergent phenomena.
Nanostructured materials with high aspect ratios have been widely studied for their unique properties. In particular, nanosheets have safety, dispersibility, and nanosized effects, and nanosheets with exceptionally small thicknesses exhibit unique properties. For non‐exfoliable materials, the bottom‐up nanosheet growth using various interfaces as templates have been investigated. This review article presents the synthesis of nanosheets at the interfaces and layered structure; it explains the features of each interface type, its advantages, and its uniqueness. The interfaces work as templates for nanosheet synthesis. We can easily use the liquid‐liquid and gas‐liquid interfaces as the templates; however, the thickness of nanosheets usually becomes thick because it allows materials to grow in thickness. The solid‐gas and solid‐liquid interfaces can prevent nanosheets from growing in thickness. However, the removal of template solids is required after the synthesis. The layered structures of various materials provide two‐dimensional reaction fields between the layers. These methods have high versatility, and the nanosheets synthesized by these methods are thin. Finally, this review examines the key challenges and opportunities associated with scalable nanosheet synthesis methods for industrial production.
Nanotechnology has been hailed as one of science’s most important breakthroughs in recent decades. Its numerous applications and rapidly increasing demand have paved the way for novel approaches to the production of higher-quality nanomaterials. Traditional synthesis methods were used in the early stages, and they focused on carcinogenic chemicals as well as a high-energy input to produce nano-sized material. Traditional synthesis procedures cause pollutants, necessitating the development of ecologically friendly alternatives. As evidence of the effects of climate change grows, scientists continue to look for ways to mitigate the havoc caused by harmful industrial practices. Natural biological systems are used to produce nanomaterials using greenways. Green synthesis is a technology that is equally as effective, if not even more, than traditional synthesis; it uses naturally available starting materials and relies on low-energy procedures to provide a sustainable solution to nanomaterial fabrication. Active compounds have recently been used to synthesize diverse nanoparticle systems in biological systems like fungi, yeast, and bacteria. As a result, integrating green synthesis into mass production and scientific research could give a potential answer to standard synthesis methods’ shortcomings. The history of green synthesizing nanoparticles and their applications is discussed in this chapter, starting with conventional methods and progressing to green approaches.
When plasmonic metal nanoparticles become smaller and smaller, a new class of nanomaterials-metal nanoclusters of atomic precision-comes to light and has become an attractive research topic in recent years. These ultrasmall nanoparticles (or nanoclusters) are unique in that they are molecularly uniform and pure, often possess a quantized electronic structure, and can grow into single crystals as do protein molecules. Exciting achievements have been made by correlating their properties with the precise structures at the atomic level, which has provided a profound understanding of some mysteries that could not be elucidated in the studies on conventional nanoparticles, such as the critical size at which plasmons are emergent. While most of the reported nanoclusters are spherical or quasi-spherical owing to the reduced surface energies (and hence stability), some anisotropic nanoclusters of high stability have also been obtained. Compared to the anisotropic plasmonic nanoparticles, the nanocluster counterparts such as rod-shaped nanoclusters can provide insights into the growth mechanisms of plasmonic nanoparticles at the early stage (i.e., nucleation), reveal the evolution of properties (e.g., optical), and offer new opportunities in catalysis, assembly, and other themes. In this Review, we highlight the anisotropic nanoclusters of atomic precision obtained so far, primarily gold, silver, and bimetallic ones. We focus on several aspects, including how such nanoclusters can be achieved by kinetic control, and how the anisotropy gives rise to new properties over the isotropic ones. The anisotropic nanoclusters are categorized into three types, (i) dimeric, (ii) rod-shaped, and (iii) oblate-shaped nanoclusters. For future research, we expect that anisotropic nanoclusters will provide exciting opportunities for tailoring the physicochemical properties and thus lead to new developments in applications.
A quick and sensitive colorimetric method for the determination of mercury (Hg(II)) has been addressed in this article. Differential centrifugation based monodispersed silver nanoparticles (AgNPs) were synthesized from mature green tea leaves with an average particle size of 14.708 ± 2.4 nm. The obtained AgNPs were analyzed with several spectroscopy and image analysis methods such as UV–Vis spectrophotometry, X-ray diffractometer (XRD), field emission transmission electron microscopy (FETEM), and X-ray photoelectron spectroscopy (XPS). The specific novelty refers to ambient temperature synthesis followed by centrifugal differentiation of highly sensitive, and selective monodispersed AgNPs. The efficacy of the developed sensor was optimum at a pH of 4 and was due to the interfering effect of OH– ions with the Hg(II). The successful Hg(II) detection in aqueous solutions in the 0.001 to 8 mg/L concentration range confirmed upon the applicability of the developed colorimetric sensor in real-time scenarios such as tap water system. Further, AgNPs were analyzed to interact with Hg(II) ions and form a Hg − Ag alloy (amalgam) that allowed a color alteration from brown to no color in the sample. UV − Vis spectrophotometry confirmed that the limit of detection (LOD) and limit of quantification (LOQ) of the sensing system were 0.01 mg/L and 0.04 mg/L, respectively. These findings verily demonstrate the efficacy of the mentioned process to achieve functional AgNPs for the Hg(II) colorimetric sensing application.
A series of novel phenomena such as optical nonlinear enhancement effect, transmission enhancement, orientation effect, high sensitivity to refractive index, negative refraction and dynamic regulation of low threshold can be generated by the control of surface plasmon (SP) with metal micro-nano structure and metal/material composite structure. The application of SP in nano-photonics, super-resolution imaging, energy, sensor detection, life science, and other fields shows an important prospect. Silver nanoparticles are one of the commonly used metal materials for SP because of their high sensitivity to refractive index change, convenient synthesis, and high controllable degree of shape and size. In this review, the basic concept, fabrication, and applications of silver-based surface plasmon sensors are summarized.
The gold nanobipyramids (Au NBPs) are widely used in the analytical detection of biochemistry due to their unique localized surface plasmon resonance (LSPR) properties. In our developed approach, I- in kelp was detected by etching Au NBPs in the presence of IO3-. Under acidic conditions, IO3- reacted rapidly with I- to form I2, subsequently I2 reacted with I- to form the intermediate I3-. In the presence of CTAB, Au NBPs were etched by I2 derived from I3-, resulting in a decrease in the aspect ratio of Au NBPs, to form a significant blue shift of LSPR longitudinal peak and color variation of colloid which changed from blue-green to magenta and could be employed to quantitatively detect the concentration of I- with the naked eye. A linear relationship can be found between the LSPR peak changes with the I- concentration in a wide range from 4.0 μM to 15.0 μM, and the sensitive limit of detection (LOD) was 0.2 μM for UV-vis spectroscopy and the obvious color changes with a visual LOD was 4.0 μM for the naked eye. Benefiting from the high specificity, the proposed colorimetric detection of I- in kelp samples was achieved, indicating the available potential of the colorimetric detection for the determination of I- in real samples. What's more, this detection procedure was time-saving and could avoid tedious procedures.
Nanocrystals offer a unique platform for tailoring the physicochemical properties of solid materials to enhance their performances in various applications. While most work on controlling their shapes revolves around symmetrical growth, the introduction of asymmetrical growth and thus symmetry breaking has also emerged as a powerful route to enrich metal nanocrystals with new shapes and complex morphologies as well as unprecedented properties and functionalities. The success of this route critically relies on our ability to lift the confinement on symmetry by the underlying unit cell of the crystal structure and/or the initial seed in a systematic manner. This Review aims to provide an account of recent progress in understanding and controlling asymmetrical growth and symmetry breaking in a colloidal synthesis of noble-metal nanocrystals. With a touch on both the nucleation and growth steps, we discuss a number of methods capable of generating seeds with diverse symmetry while achieving asymmetrical growth for mono-, bi-, and multimetallic systems. We then showcase a variety of symmetry-broken nanocrystals that have been reported, together with insights into their growth mechanisms. We also highlight their properties and applications and conclude with perspectives on future directions in developing this class of nanomaterials. It is hoped that the concepts and existing challenges outlined in this Review will drive further research into understanding and controlling the symmetry breaking process.
In this work we demonstrate a new approach towards the electroless deposition of tellurium nanowires in deep eutectic solvents. Unlike most electroless deposition where the substrate is sacrificed to drive the reduction, our process uses immobilised silver epoxy islands on gold films to give localised galvanic displacement of the silver, resulting in an even growth of wires across the entire gold electrode surface. We demonstrate the strong dependence of the nanostructure on the experimental conditions, with changes in bath temperature, tellurium concentration and the halide component of the solvent leading to sizeable alterations in the nanowire geometry. This demonstrates electroless deposition as a promising synthetic route towards low-dimensional tellurium nanostructures.
Atomic and molecular sizes are reaching nanoscale dimensions. All matter may be reduced to its constituent atoms. Due to the growing exposure to nanoparticles, it is essential to analyze the toxicity of NPs-based compounds. Since the physicochemical properties of nanomaterials impact the characteristics of NPs, assessing the physicochemical properties of nanomaterials is more critical than ever. Size-dependent effects may be detected in a more prominent way at the nanoscale. In the 1–10 nm range, the electronic properties of semiconductors are determined by quantum mechanical considerations. Quantum dots are thus characterized as nanospheres with a diameter between one and ten nanometers. The sizes and forms of nanomaterials have a considerable effect on their optical properties; quantum dots are one example. The optical properties of a material are intimately related to its electrical and electronic properties, and they may be altered by altering its shape, surface chemistry, or aggregation state. There is a one-to-one relationship between the particle size and the degree of optical absorption they possess. It is known that the optical properties of semiconductors and a number of metals experience considerable changes as a function of particle size. This is easily seen by the colors of the different nanoparticle solutions. The magnetic properties of the nanostructures are diverse from one another. It is conceivable for the energy of magnetic anisotropy in magnetic nanoparticles to be so low that it induces thermal variation in the magnetization vector, resulting in the phenomenon known as superparamagnetism. Mechanically, nanoparticles vary significantly from microparticles and bulk materials. The basic mechanical properties of NPs, such as their hardness and elastic modulus, will help in the design of NPs for specific applications and the assessment of their functions and action mechanisms. In comparison with microcomposites, copper-based nanocomposites have a very high hardness. The thermal conductivities of metal nanoparticles are substantially higher than those of solid fluids. As a direct result of their improved understanding of the underlying nanostructure of materials, scientists are getting a deeper understanding of the crucial factors that regulate the activity, selectivity, reaction processes, and lifetimes of nanocatalysts. In compared to their bulk counterparts, nanoparticle catalysts exhibit greatly enhanced reactivities, giving them distinctive catalytic properties.
As a new type of light-collecting and luminescent material, all-inorganic cesium lead halide CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) are expected to have a wide range of applications in the fields of photovoltaics, optoelectronics, and fluorescence anti-counterfeiting, etc. Therefore, improving the fluorescence performance and stability of CsPbX3 perovskite NCs to prompt their applications would promise both fundamental and practical significance for in-depth research in the field of halide perovskites. In this paper, we developed a modification strategy to introduce a halogen source, zinc bromide (ZnBr2) in hexane, to CsPbX3 perovskite that can be conducted under atmospheric conditions with reduced reaction cost and easier operation. The first work in this paper was to apply the modification strategy to CsPbI3 nanowires (NWs). Compared with the untreated NWs, the ZnBr2/hexane modified CsPbI3 NWs exhibited better fluorescence properties. Subsequently, based on the study of perovskite NWs, we investigated perovskite nanocrystal-CsPbI3 nanorods (NRs) with different morphologies and sizes. It was found that the luminescence properties of nanorods (NRs) were superior. Later, we infiltrated the modified NRs into the aramid/polyphenylene sulfide (ACFs/PPS) composite paper yielded from our previous work to study its fluorescence performance for anti-counterfeiting. Their luminescence properties under ultraviolet light irradiation enable better performance in fluorescence anti-counterfeiting. The ZnBr2/hexane modification strategy and the applications studied in this work will expand the scope of perovskite research, laying the foundation for the applications of fluorescent anti-counterfeiting, nano-photoelectric devices, and fluorescent composite materials.
Triangular silver nanoplates (TSNPs) have attracted much attention for their tunable plasmonic properties. In this letter, TSNPs have been synthesized by the improved light-driven seed growth method with only trisodium citrate (TSC) as both photoreducing reagent and capping reagent. By means of this high efficient method, TSNPs could be produced in high yield. As a kind of promising material, TSNPs will be used for chemical and biological sensing, and they can also be applied in optical limiters against high intensity laser pulse.
Using liquid metals to grow Ag nanostructures
Ultrathin two-dimensional (2D) nanostructures attract increasing attention due to their unique properties and resultant applications in diverse fields, yet the controllable synthesis of ultrathin 2D nanostructures without capping agents remains...
The proposal of the research mainly employs the surface plasmon resonance of gold (Au) and silver (Ag) nanoparticles (NPs) to stabilized induction current of hybrid cuprous oxide (Cu2O)/aluminum doped zinc oxide nano-rods (AZO NRs) for non-enzymatic glucose sensor. This research investigation concerns the mechanism of formation and surface plasmon resonance. There were mainly three synthesis processes for the hybrid electrode. The first involved the hydrothermal growth of AZO NRs, and the seed layer of AZO was sputtered with different thickness from 35 to 105 nm. The second concerned the deposition of Cu2O on AZO NRs by the method of electrochemical deposition, and the Cu2O films were prepared with different pH value from 3 to 10. The third was concerned with Au and Ag NPs, and they were formed with the hydrothermal method and the seed reduction method, respectively. These NPs were dripped uniformly on the surface of Cu2O/AZO NRs through Nafion dispersants. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and chronoamperometry (CA) were used to verify these formation performances for the Au or Ag NPs/Cu2O/AZO NRs hybrid electrodes. The results showed that the linear range changed from 70.5 to 37.5 and 54.5 mg/dL, and linear regression coefficients (R²) also increased from 0.982 to 0.9965 and 0.997, respectively for Au and Ag NPs modified Cu2O/AZO NRs electrodes.
Thermoelectric technology is very promising to the development of global sustainable energy and carbon neutrality. Understanding the thermoelectric transport, in low dimensions, may provide a potential route to achieve high thermoelectric conversion efficiency of thermoelectric materials. In the past decade, low-dimensional thermoelectric materials, including their hybrids, have gradually attracted more and more attentions due to their unique electronic structures and potentially high thermoelectric performance. They are expected to play an increasingly significant role in power generation and solid-state cooling systems. In this chapter, we briefly review recent advances in their electronic structures, thermoelectric performance, and characterization techniques.
Semiconductor/electrolyte interfaces are of great interest to numerous scientific fields including renewable energy, (photo)electrochemistry, and energy storage. The semiconductor flatband potential is a key parameter in locating the conduction band minimum or valence band maximum of the semiconductor material in electrolyte. Despite its importance for quantifying the energetic location of the semiconductor bands, literature reports for the same material demonstrate significant variability in the flatband potential. In this compendium and meta-analysis, reported flatband potentials of the common semiconductor materials TiO2, SnO2, and ZnO in aqueous electrolyte were compiled and assessed to quantify the spread in literature flatband potentials as well as determine the factors that lead to the significant spread. For TiO2, SnO2, and ZnO, literature flatband potentials referenced to the reversible hydrogen electrode span a range of nearly 2 V each. Flatband potential tabulations were separated by variables such as the solution pH, the crystalline polymorph, the crystal facet, the morphology, and the dimensions or combinations of these variables to assess the factors that contribute to the observed spread. Important and surprising findings from these categorizations are summarized: (1) Even for the narrowest categorizations, the spread in flatband potential is still large. (2) Flatband potentials of TiO2 and SnO2 follow the expected Nernstian dependence with solution pH. ZnO materials deviate from this Nernstian dependence. (3) In the aggregate, there is no statistically significant difference in the reported flatband potentials of anatase and rutile TiO2. Single crystal tabulations were the only distributions to have statistically significant differences in the flatband potential between anatase and rutile TiO2. (4) Anatase TiO2 materials with a nanotube morphology appear to have a +400 mV difference in mean flatband potential compared to all other morphologies, but we argue that this is likely due to widespread misuse of the Mott–Schottky analysis. Other interesting findings are revealed within the spread of literature flatband potentials, and possible explanations are provided to generate discussion. We also briefly review and discuss common techniques that were used to determine the flatband potential and the pitfalls/criticisms of these techniques. Last, we discuss some ways in which future research on the determination of the flatband potential can be performed to improve the reliability of reported values and the quality of the work. In total, the results from this meta-analysis suggest multiple factors can affect the measured flatband potential and that an abundance of caution should be applied when attempting to quantify the flatband potential of complex or nanostructured systems.
The present study aims to synthesized nano gold with chemical method with two shape sphere and rod with multi diameter and aspect ratio and then characterize the synthesized material with Atomic Force Microscope (AFM), Transmission Electron Microscope (TEM) and Ultraviolet-visible (UV–Visible ) spectrophotometer. The AFM and TEM characterization result of three samples for each sphere and rods show that the synthesized material are in nano range with diameter 31.9 nm, 36.19 nm and 79.37 nm respectively for nano sphere and diameters 39.9nm, 36.05 nm and 28 nm respectively for nano-rods samples and the UV-Visible spectrophotometer show that peak of surface plasmon resonance of nano-sphere are at wavelengths 532 nm, 535 nm and 546 nm and all are in the visible range and nano-rod have two peaks one in the visible range at wavelengths 525nm,518nm and 531nm and the other peak is in the near infrared range at wavelengths 633nm, 680nm and 875 nm respectively.
In this chapter we provide an overview of the fundamental thermodynamic and kinetic parameters governing the growth of colloidal nanoparticles. We also give a phenomenological description of shape control of nanostructures, along with several examples drawn from the literature.
Using a seed-mediated growth approach in a rodlike micellar
media, silver nanorods of varied aspect ratio were prepared from nearly
spherical 4 nm silver nanoparticles.
Colloidal inorganic nanoparticles have size-dependent optical, optoelectronic and material properties that are expected to lead to superstructures with a range of practical applications. Discrete nanoparticles with controlled chemical composition and size distribution are readily synthesized using reverse micelles and microemulsions as confined reaction media, but their assembly into well-defined superstructures amenable to practical use remains a difficult and demanding task. This usually requires the initial synthesis of spherical nanoparticles, followed by further processing such as solvent evaporation, molecular cross-linking or template-patterning. Here we report that the interfacial activity of reverse micelles and microemulsions can be exploited to couple nanoparticle synthesis and self-assembly over a range of length scales to produce materials with complex organization arising from the interdigitation of surfactant molecules attached to specific nanoparticle crystal faces. We demonstrate this principle by producing three different barium chromate nanostructures-linear chains, rectangular superlattices and long filaments-as a function of reactant molar ratio, which in turn is controlled by fusing reverse micelles and microemulsion droplets containing fixed concentrations of barium and chromate ions, respectively. If suitable soluble precursors and amphiphiles with headgroups complementary to the crystal surface of the nanoparticle target are available, it should be possible to extend our approach to the facile production of one-dimensional `wires' and higher-order colloidal architectures made of metals and semiconductors.
Nanometre-size inorganic dots, tubes and wires exhibit a wide range of electrical and optical properties(1,2) that depend sensitively on both size and shape(3,4), and are of both fundamental and technological interest. In contrast to the syntheses of zero-dimensional systems, existing preparations of one-dimensional systems often yield networks of tubes or rods which are difficult to separate(5-12). And, in the case of optically active II-YI and III-V semiconductors, the resulting rod diameters are too large to exhibit quantum confinement effects(6,8-10). Thus, except for some metal nanocrystals(13), there are no methods of preparation that yield soluble and monodisperse particles that are quantum-confined in two of their dimensions. For semiconductors, a benchmark preparation is the growth of nearly spherical II-VI and III-V nanocrystals by injection of precursor molecules into a hot surfactant(14,15). Here we demonstrate that control of the growth kinetics of the II-VI semiconductor cadmium selenide can be used to vary the shapes of the resulting particles from a nearly spherical morphology to a rod-like one, with aspect ratios as large as ten to one. This method should be useful, not only for testing theories of quantum confinement, but also for obtaining particles with spectroscopic properties that could prove advantageous in biological labelling experiments(16,17) and as chromophores in light-emitting diodes(18,19).
Semiconductor nanocrystals were prepared for use as fluorescent probes in biological staining and diagnostics. Compared with
conventional fluorophores, the nanocrystals have a narrow, tunable, symmetric emission spectrum and are photochemically stable.
The advantages of the broad, continuous excitation spectrum were demonstrated in a dual-emission, single-excitation labeling
experiment on mouse fibroblasts. These nanocrystal probes are thus complementary and in some cases may be superior to existing
fluorophores.
Scanning probe microscopy has become a powerful tool to detect structural changes in small clusters of atoms. Herein, we use an atomic force microscope to measure the length of gold nanowire structures during extension and compression cycles. We have found that nanowires elongate under force in quantized steps of up to three integer multiples of 1.76 A and that they shorten spontaneously in steps of 1.52 A. Our results can be explained by the sliding of crystal planes within the gold nanowires creating stacking faults that change the local structure from face-centered cubic to hexagonal close packed. Our data also show that there can be up to three simultaneous slip events, in good agreement with the tetrahedral arrangement of slip planes in a gold crystal. These experiments provide direct evidence for the mechanism underlying the plastic deformation of a nanowire. A similar approach can be used to examine the atomic events underlying the plastic failure of other metals and their alloys.
The optical electronic, and catalytic properties of semiconductor Q-particles differ significantly from those of either the bulk materials or of the molecules, as the nanometer-size particles exhibit effects due to quantum confinement. The methods of preparing these materials, their characterization, their properties, and their applications are reviewed, and the requirements for future progress, even the extension of the work to nanometer-sized metal particles, are discussed.
Specific organization of gold nanorods into anisotropic
3D-aggregates is obtained by DNA hybridisation.
The primary process in the photographic emulsion is interfacial electron transfer. The electron is transferred from the excited state of a dye species to empty electron acceptor states in silver bromide. There have been no detailed measurements of the rate constants of this commercially important process. The fluorescence decay curves of thiocarbocyanine dye (see figure) yield these rate constants.
We investigate numerically the plasmon resonances of 10–50 nm nanowires with a non-elliptical section. Such wires have a much more complex behavior than elliptical wires and their resonances span a larger frequency range. The field distribution at the surface of these wires exhibits a dramatic enhancement, up to several hundred times the incident field amplitude. These strongly localized fields can provide an important mechanism for surface enhanced Raman scattering (SERS).
We report the band gaps of rodlike CdSe quantum dots with diameter varying from 3.0 to 6.5 nm and length from 7.5 to 40 nm. A qualitative explanation for the dependence of band gap on width and length is presented.
Gold nanorods with different aspect ratios are prepared in micelles by the electrochemical method and their absorption spectra are modeled by theory. Experimentally, a linear relationship is found between the absorption maximum of the longitudinal plasmon resonance and the mean aspect ratio as determined from TEM. It is shown here that such a linear dependence is also predicted theoretically. However, calculations also show that the absorption maximum of the longitudinal plasmon resonance depends on the medium dielectric constant in a linear fashion for a fixed aspect ratio. Attempts to fit the calculations to the experimental values indicate that the medium dielectric constant has to vary with the aspect ratio in a nonlinear way. Chemically, this suggests that the structure of the micelle capping the gold nanorods is size dependent. Furthermore, comparison with the results obtained for rods of different aspect ratios made by systematic thermal decomposition of the long rods further suggests that the medium dielectric constant is also temperature dependent. This is attributed to thermal annealing of the structure of the micelles around the nanorods.
Aqueous solutions containing a high yield of suspended gold nanorods have been successfully synthesized via an electrochemical method. The control of preparing gold nanorods with different aspect ratios can be attained. Their absorption spectral features show a dominant surface plasma band corresponding to the longitudinal resonance, SPl, and its λmax shifts markedly to the red as the aspect ratio is increased. Meanwhile, the dependence of λmax for longitudinal resonance on the mean aspect ratio shows a deviation from the classical electrostatic model prediction at mean aspect ratios around 4 ± 1, where it limits the validity of the classical electrostatic approximation.
Gold nanorods with aspect ratios of 4.6 ± 1.2, 13 ± 2, and 18 ± 2.5 (all with 16 ± 3 nm short axis) are prepared by a seeding growth approach in the presence of an aqueous miceller template. Citrate-capped 3.5 nm diameter gold particles, prepared by the reduction of HAuCl4 with borohydride, are used as the seed. The aspect ratio of the nanorods is controlled by varying the ratio of seed to metal salt. The long rods are isolated from spherical particles by centrifugation.
In the present Letter we demonstrate that particle shape can be controlled even if the macroscopic structure of the self-assembly used as a template remains unchanged. We demonstrate that the control of nanocrystal shape is influenced by the addition of salt while the same template is kept.
We have prepared nanoscopic gold cylinders of controlled radius and aspect ratio via electrodeposition of the metal within the pores of anodically-grown porous aluminum oxide membranes. The nanocylinder radii are determined by the pore dimensions of the host alumina which, in turn, depend on anodization conditions. The particle aspect ratios were controlled by varying the amount of Au deposited within the pores. The optical spectra of the gold nanocylinder/alumina composites exhibit strong absorption bands in the visible spectrum. The extinction maxima (lambda(max)) values for gold particles approaching spherelike geometry agree well with Mie theory calculations. The blue shift of lambda(max) as the particle aspect ratio is increased is in qualitative agreement with Maxwell-Garnett theory. We propose a simple modification of Maxwell-Garnett theory that addresses both size and shape effects.
Central to the concept of seed-mediated growth of nanoparticles is that small nanoparticle seeds serve as nucleation centers to grow nanoparticles to a desired size. We have examined this common assumption in a model system, the wet chemical synthesis of gold nanoparticles via reduction of a gold salt, by transmission electron microscopy and electronic absorption spectroscopy. We find that changing the seed concentration does affect the size of the product nanoparticles, but the method of reagent addition drastically affects the outcome even more. For fast addition of reducing agent, the presence of seeds appears to promote the formation of more seeds instead of growth. The observed nucleations are drastically enhanced (99%) compared to particle growth. For slow addition of reducing agent, the seeds do grow, but the product nanoparticle's degree of homogeneity in shape is compromised. For higher concentrations of seeds, nanoparticle growth is better controlled for slow addition of reducing agent compared to fast addition of reducing agent. We propose a mechanistic step to explain the commonly observed size distribution.
A seed-mediated growth approach to improved monodispersity of nanoparticles that involves controlling nucleation and growth in solution is presented. Using this approach, spheroidal and rod-like gold particles (see Figure) could be prepared in the presence of a rod-like micellar template. The aspect ratio of the particles could be varied from 1 to 10 by varying the ratio of preformed seed to metal salt.
Deoxyribonucleic acid (DNA)-derivatized gold nanowires were discussed as the building blocks of surface assemblies. Oligonucleotides were adsorbed as monolayer coatings on the wires through gold-thiol linkages. Absorption and fluorescence spectroscopy were employed to quantify the amount of DNA bound. The nanowires were modified with single stranded (ss) DNA at specific sites with the remaining wire covered by passivating monolayers. The modification resulted in easy implementation of the site-specific DNA directed assembly.
A first key step in the control of biomineralization is the self assembly of an appropriate microstructure template, within which minerals of a required structure and shape might be induced to form under controlled conditions. This templating strategy is proven valid when the initial surfactant self-assembled microstructure is well defined. A direct relationship is demonstrated between shape and size of template and synthesis of copper metal particles. Not only the microstructures be predicted, but further that these microreactors act as genuine templates in generating nanoparticles of controlled size and anisometry.
A Boolean logic, nonreversible computing machine should, in principle, be capable of 10 18 bit operations per second at a power consumption of 1 W. In order to build such a machine that can even approach this benchmark for efficiency, the development of a robust quantum-state switch capable of ambient operation, as well as a bottom–up manufacturing technology, will be necessary. My group, in collaboration with Hewlett Packard, has developed much of the architecture for such a machine, which we call a chemically assembled electronic nanocomputer (CAEN). More recently, in a collaborative effort with Fraser Stoddart's group at UCLA, we have begun to build it. The fundamental unit of the machine is a field-programmable molecular switch, and the fundamental architecture is a hierarchical organization of wire/switch lattices called crossbars. Electronically, singly configurable molecular-based switch devices based on rotaxane molecular compounds have been fabricated in high yield. These switches were used to construct simple molecular-based logic structures and read-only memory elements.
Current research into semiconductor clusters is focused on the properties of quantum dots-fragments of semiconductor consisting
of hundreds to many thousands of atoms-with the bulk bonding geometry and with surface states eliminated by enclosure in a
material that has a larger band gap. Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability
to join the dots into complex assemblies creates many opportunities for scientific discovery.
The development of optical gain in chemically synthesized semiconductor nanoparticles (nanocrystal quantum dots) has been
intensely studied as the first step toward nanocrystal quantum dot lasers. We examined the competing dynamical processes involved
in optical amplification and lasing in nanocrystal quantum dots and found that, despite a highly efficient intrinsic nonradiative
Auger recombination, large optical gain can be developed at the wavelength of the emitting transition for close-packed solids
of these dots. Narrowband stimulated emission with a pronounced gain threshold at wavelengths tunable with the size of the
nanocrystal was observed, as expected from quantum confinement effects. These results unambiguously demonstrate the feasibility
of nanocrystal quantum dot lasers.
We show a simple, robust, chemical route to the fabrication of ultrahigh-density arrays of nanopores with high aspect ratios
using the equilibrium self-assembled morphology of asymmetric diblock copolymers. The dimensions and lateral density of the
array are determined by segmental interactions and the copolymer molecular weight. Through direct current electrodeposition,
we fabricated vertical arrays of nanowires with densities in excess of 1.9 × 1011 wires per square centimeter. We found markedly enhanced coercivities with ferromagnetic cobalt nanowires that point toward
a route to ultrahigh-density storage media. The copolymer approach described is practical, parallel, compatible with current
lithographic processes, and amenable to multilayered device fabrication.
The properties of a material depend on the type of motion its electrons can execute, which depends on the space available for them (i.e., on the degree of their spatial confinement). Thus, the properties of each material are characterized by a specific length scale, usually on the nanometer dimension. If the physical size of the material is reduced below this length scale, its properties change and become sensitive to its size and shape. In this Account we describe some of the observed new chemical, optical, and thermal properties of metallic nanocrystals when their size is confined to the nanometer length scale and their dynamical processes are observed on the femto- to picosecond time scale.
Colloidal quantum rods of cadmium selenide (CdSe) exhibit linearly polarized emission. Empirical pseudopotential calculations
predict that slightly elongated CdSe nanocrystals have polarized emission along the long axis, unlike spherical dots, which
emit plane-polarized light. Single-molecule luminescence spectroscopy measurements on CdSe quantum rods with an aspect ratio
between 1 and 30 confirm a sharp transition from nonpolarized to purely linearly polarized emission at an aspect ratio of
2. Linearly polarized luminescent chromophores are highly desirable in a variety of applications.
Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated. The self-organized, <0001> oriented
zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process.
These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and
lengths up to 10 micrometers. Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with
an emission linewidth less than 0.3 nanometer. The chemical flexibility and the one-dimensionality of the nanowires make them
ideal miniaturized laser light sources. These short-wavelength nanolasers could have myriad applications, including optical
computing, information storage, and microanalysis.
- B Trosken
- F Willig
- K Schwarzburg
- A Ehret
- M Spitler
B. Trosken, F. Willig, K. Schwarzburg, A. Ehret, M. Spitler, Adv. Mater.
1995, 7, 448.
- H Weller
H. Weller, Adv. Mater. 1993, 5, 88.
- M A El-Sayed
M. A. El-Sayed, Acc. Chem. Res. 2001, 34, 257.
- Y Y Yu
- S S Chang
- C L Lee
- C R C Wang
Y. Y. Yu, S. S. Chang, C. L. Lee, C. R. C. Wang, J. Phys. Chem. B 1997,
101, 6661.
- T Thurn-Albrecht
- J Schotter
- G A Kastle
- N Emley
- T Shibauchi
- L Krusin-Elbaum
- K Guarini
- C T Black
- M T Tuominen
- T P Russell
T. Thurn-Albrecht, J. Schotter, G. A. Kastle, N. Emley, T. Shibauchi,
L. Krusin-Elbaum, K. Guarini, C. T. Black, M. T. Tuominen, T. P. Russell,
Science 2000, 290, 2126.
- E Dujardin
- L B Hsin
- C R C Wang
- S Mann
E. Dujardin, L. B. Hsin, C. R. C. Wang, S. Mann, Chem. Commun. 2001,
1264.
- X G Peng
- L Manna
- W D Yang
- J Wickham
- E Scher
- A Kadavanich
- A P Alivisatos
X. G. Peng, L. Manna, W. D. Yang, J. Wickham, E. Scher, A. Kadavanich,
A. P. Alivisatos, Nature 2000, 404, 59.
- M Li
- H Schnablegger
- S Mann
M. Li, H. Schnablegger, S. Mann, Nature 1999, 402, 393.
- X Duan
- C M Lieber
X. Duan, C. M. Lieber, Adv. Mater. 2000, 12, 298.
- N R Jana
- L Gearheart
- C J Murphy
N. R. Jana, L. Gearheart, C. J. Murphy, Chem. Mater. 2001, 13, 2313.
- C A Foss
- G L Hornyak
- J A Stockert
- C R Martin
C. A. Foss, G. L. Hornyak, J. A. Stockert, C. R. Martin, J. Phys. Chem.
1994, 98, 2963.
- A Filankembo
- M P Pileni
A. Filankembo, M. P. Pileni, J. Phys. Chem. B 2000, 104, 5865.
- S Link
- M B Mohamed
- M A Sayed
S. Link, M. B. Mohamed, M. A. El-Sayed, J. Phys. Chem. B 1999, 103,
3073.
- M Bruchez Jr
- M Moronne
- P Gin
- S Weiss
M. Bruchez Jr., M. Moronne, P. Gin, S. Weiss, A. P. Alivisatos, Science
1998, 281, 2013.
- M H Huang
- S Mao
- H Feick
- H Q Yan
- Y Y Wu
- H Kind
- E Weber
- R Russo
- P D Yang
M. H. Huang, S. Mao, H. Feick, H. Q. Yan, Y. Y. Wu, H. Kind, E. Weber,
R. Russo, P. D. Yang, Science 2001, 292, 1897.
- V I Klimov
- A A Mikhailovsky
- S Xu
- A Malko
- J A Hollingsworth
- C A Leatherdale
- H J Eisler
- M G Bawendi
V. I. Klimov, A. A. Mikhailovsky, S. Xu, A. Malko, J. A. Hollingsworth,
C. A. Leatherdale, H. J. Eisler, M. G. Bawendi, Science 2000, 290, 314.
- M Bruchez
- M Moronne
- P Gin
- S Weiss
- A P Alivisatos
M. Bruchez Jr., M. Moronne, P. Gin, S. Weiss, A. P. Alivisatos, Science
1998, 281, 2013.
- S Link
- M B Mohamed
- M A El-Sayed
S. Link, M. B. Mohamed, M. A. El-Sayed, J. Phys. Chem. B 1999, 103,
3073.
- N R Jana
- L Gearheart
- C J Murphy
N. R. Jana, L. Gearheart, C. J. Murphy, Chem. Commun. 2001, 617.
- N R Jana
- L Gearheart
- C J Murphy
N. R. Jana, L. Gearheart, C. J. Murphy, J. Phys. Chem. B 2001, 105, 4065.
- J P Kottmann
- O J F Martin
- D R Smith
- S Schultz
J. P. Kottmann, O. J. F. Martin, D. R. Smith, S. Schultz, Chem. Phys. Lett.
2001, 341, 1.
- J K N Mbindyo
- B D Reiss
- B R Martin
- C D Keating
- M J Natan
- T E Mallouk
J. K. N. Mbindyo, B. D. Reiss, B. R. Martin, C. D. Keating, M. J. Natan,
T. E. Mallouk, Adv. Mater. 2001, 13, 249.
- J R Heath
J. R. Heath, Pure Appl. Chem. 2000, 72, 11.
- M P Pileni
- B W Ninham
- T Gulik-Kryzwicki
- J Tanori
- I Lisiecki
- A Filankembo
M. P. Pileni, B. W. Ninham, T. Gulik-Kryzwicki, J. Tanori, I. Lisiecki,
A. Filankembo, Adv. Mater. 1999, 11, 1358.