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Raman spectra of aluminum doped zinc oxide, as-synthesized (black) and after annealing (red). After annealing,
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A combined experimental and first-principles study is performed to study the origin of conductivity in ZnO:Al nanoparticles synthesized under controlled conditions via a reflux route using benzylamine as a solvent. The experimental characterization of the samples by Raman, nuclear magnetic resonance (NMR) and conductivity measurements indicates tha...
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Context 1
... the AZO and pure ZnO samples (the as-synthesized as well as the annealed ones) were characterized by Raman spectroscopy. The measured Raman modes shown in Figure 4 and 5 ...
Context 2
... ease of interpretation, the Raman spectra were first normalized with respect to the E2 Low peak, which is attributed to the zinc sublattice. First, we consider the Raman measurement results for the AZO samples in Figure 4. After annealing, there is a decrease in intensity of the E2 high peak, and simultaneous increase in intensity of E1(LO) peak. ...
Citations
... For the Al-doped ZnO nanoparticles, the peak at 328 cm − 1 is produced by the second-order Raman spectrum from zone boundary phonons, with the pronounced, intense peak at 433 cm − 1 related to the E2 high mode. Additionally, the observation of a peak at 572 cm − 1 is attributed to a longitudinal optical (LO) scattering mode, which is a result of the increased carrier concentration due to doping [16,17]. The incorporation of Al into ZnO results in noticeable shifts in phonon mode frequencies as detected by Raman spectroscopy. ...
The electrical and optical characteristics of pure and Al-doped zinc oxide (ZnO) nanoparticles were analyzed. The
work function of these nanoparticles was investigated using Kelvin Probe Force Microscopy (KPFM). The work
function of the Al-doped ZnO nanoparticles was found to be lower than that of undoped ZnO nanoparticles.
Electrostatic Force Microscopy (EFM) was employed to map the distribution of charges and conductivity in both
ZnO and Al -doped ZnO, revealing enhanced charge trapping and increased conductivity in the Al-doped ZnO
nanoparticles compared to the undoped ones. XRD analysis verified that both pure ZnO and Al-doped ZnO
nanoparticles exhibited a hexagonal wurtzite crystal structure. Additionally, Raman spectroscopy revealed new
vibrational modes at 572 cm− 1
, which were attributed to E1 (LO) in Al-doped ZnO. UV–visible spectroscopy
indicated that the band gap of Al -doped ZnO nanoparticles is wider than that of pure ZnO nanoparticles,
Additionally, photoluminescence spectroscopy demonstrated a blue shift in the emission spectrum of the Aldoped ZnO nanoparticles, accompanied by a reduction in green emission defects.
... However, a slight shift to lower values is noted for E 2 low (92 cm −1 ) and LO (572 cm −1 ) indicating an increase in the quantity of ZnO-defects. 65 The reason behind the existence of defects is perhaps the suppression of zinc oxide formation. Even though the oxidation of zinc is favored over copper, there is a potential concurrence between both due to the higher copper content. ...
In recent decades, antibiotic resistance has become a crucial challenge for human health. One potential solution to this problem is the use of antibacterial surfaces, i.e., copper and copper alloys. This study investigates the antibacterial properties of brass that underwent topographic surface functionalization via ultrashort pulsed direct laser interference patterning. Periodic line-like patterns in the scale range of single bacterial cells were created on brass with a 37% zinc content to enhance the contact area for rod-shaped Escherichia coli (E. coli). Although the topography facilitates attachment of bacteria to the surface, reduced killing rates for E. coli are observed. In parallel, a high-resolution methodical approach was employed to explore the impact of laser-induced topographical and chemical modifications on the antibacterial properties. The findings reveal the underlying role of the chemical modification concerning the antimicrobial efficiency of the Cu-based alloy within the superficial layers of a few hundred nanometers. Overall, this study provides valuable insight into the effect of alloy composition on targeted laser processing for antimicrobial Cu-surfaces, which facilitates the thorough development and optimization of the process concerning antimicrobial applications.
... The electrical conductivity is higher for n-type semiconductors due to the high mobility of electrons. Being an extrinsic dopant, Aluminium is found to further increase the ntype conductivity by acting as a shallow donor and thereby resulting in increased carrier concentration and mobility [13,14]. ...
WO3 nanoparticles co-doped with Al and Mo were prepared via hydrothermal method and were characterized by
XRD, FTIR spectra, Raman spectra, UV-DRS, SEM microscopy combined with EDS techniques. The XRD peak
patterns confirmed the monoclinic structure for both the pristine and doped samples. The surface characterizations
performed using SEM and EDS analyses revealed the morphologies and particle sizes. The local molecular
structure of the crystal was obtained from FTIR and Raman spectra. The absorption spectra reveal the
decrease in optical band gap energy after doping with an increase in the width of Urbach tail states. The Al-Mo
co-doping enhanced the temperature dependent AC and DC conductivities of WO3 proving that there has been a
significant improvement in the electrical properties of WO3 as a result of co-doping with aluminium and molybdenum
ions.
... These latter sites procure possible dopant sites. n-type and p-type doped ZnO materials have been extensively studied because they exhibit interesting properties for industrial applications [18,19]. Undoped ZnO displays n-type conductivity, traditionally attributed to intrinsic defects such as zinc excess at the interstitial positions and the lack of oxygen. ...
... In this work, aluminum was selected as a dopant for the ZnO semiconductor material because of its abundancy, low price and suitability. Several articles have been published regarding the conductivity enhanced through n-type doping when Al is incorporated into the zinc oxide crystal lattice [19][20][21]29]. Some authors [30] also noticed that the electronic properties of the doped oxide are influenced by the crystallographic position of the aluminum dopant in the ZnO lattice. ...
... Thus, the strategy consisted in synthesizing undoped and Al-doped ZnO particles in the nanoscale to achieve large surface areas with consequent benefits for its performance. To this end, a method previously described by Momot et al. [19] was followed, where the authors presented an applicable solvothermal route to nanocrystalline Al-doped ZnO based on the reaction between zinc (II) acetylacetonate and aluminum (III) acetylacetonate as precursors and benzylamine used as solvent and reactant, Figure S1. The dopant concentrations range from 0 at% to 5 at% with respect to Zn. ...
Quasi-spherical undoped ZnO and Al-doped ZnO nanoparticles with different aluminum content, ranging from 0.5 to 5 at% of Al with respect to Zn, were synthesized. These nanoparticles were evaluated as photocatalysts in the photodegradation of the Rhodamine B (RhB) dye aqueous solution under UV-visible light irradiation. The undoped ZnO nanopowder annealed at 400 °C resulted in the highest degradation efficiency of ca. 81% after 4 h under green light irradiation (525 nm), in the presence of 5 mg of catalyst. The samples were characterized using ICP-OES, PXRD, TEM, FT-IR, 27Al-MAS NMR, UV-Vis and steady-state PL. The effect of Al-doping on the phase structure, shape and particle size was also investigated. Additional information arose from the annealed nanomaterials under dynamic N2 at different temperatures (400 and 550 °C). The position of aluminum in the ZnO lattice was identified by means of 27Al-MAS NMR. FT-IR gave further information about the type of tetrahedral sites occupied by aluminum. Photoluminescence showed that the insertion of dopant increases the oxygen vacancies reducing the peroxide-like species responsible for photocatalysis. The annealing temperature helps increase the number of red-emitting centers up to 400 °C, while at 550 °C, the photocatalytic performance drops due to the aggregation tendency.
... The increase of grain size by reducing the sputtering power could also lead to the increase of electrical conductivity [17]. Post-annealing of sputtered AZO films has successfully been demonstrated to improve the properties of the films [6,[18][19][20][21][22][23]. Annealing of AZO thin films under Ar + 10% H 2 ambient in Zn blanket style could greatly improve the conductivity which was explained by the decrease of acceptor defects caused by the diffusion of Zn into V Zn [20]. ...
... A combined first-principles study and experimental techniques using Raman and nuclear magnetic resonance (NMR) spectroscopies were performed to investigate the origin of conductivity in AZO by studying the defects in AZO nanoparticles before and after annealing, suggesting the migration of Al i which leads to the formation of Al Zn defect. This subsequently kicks the Zn atoms from the local sites to be the Zn interstitials (Zn i ), which is responsible for the observed increased conductivity of AZO after annealing [21]. The conductivity of AZO thin films can also be enhanced by annealing under hydrogen atmosphere because of the desorption of oxygen. ...
... Raman spectra from ZnO samples that have been etched with 5%, 10%, 15% and 20% etchant concentrations. The annotated peaks (1) to(6) are originated from E second-order Raman process), A 1 transverse optical mode (TO), E High 2 phonon mode, A 1 longitudinal optical mode (LO) and E 1 longitudinal optical mode (LO)[37][38][39]. ...
Zinc oxide (ZnO) is an attractive material for microscale and nanoscale devices. Its desirable semiconductor, piezoelectric and optical properties make it useful in applications ranging from microphones to missile warning systems to biometric sensors. This work introduces a demonstration of blending statistics and chemical etching of thin films to identify the dominant factors and interaction between factors, and develop statistically enhanced models on etch rate and selectivity of c-axis-oriented nanocrystalline ZnO thin films. Over other mineral acids, ammonium chloride (NH 4 Cl) solutions have commonly been used to wet etch microscale ZnO devices because of their controllable etch rate and near-linear behaviour. Etchant concentration and temperature were found to have a significant effect on etch rate. Moreover, this is the first demonstration that has identified multi-factor interactions between temperature and concentration, and between temperature and agitation. A linear model was developed relating etch rate and its variance against these significant factors and multi-factor interactions. An average selectivity of 73 : 1 was measured with none of the experimental factors having a significant effect on the selectivity. This statistical study captures the significant variance observed by other researchers. Furthermore, it enables statistically enhanced microfabrication processes for other materials.
... Figure 7 shows the Raman spectra of the commercial ZnO NPs and those of 0.075, 0.125, and 0.250 M H 2 O 2 treated/annealed ZnO NPs. Four Raman modes were observed at 331, 381, 440, and 584 cm −1 , associated with the ZnO wurtzite structure [38,39]. The sharp and strong peak at 440 cm −1 can be assigned to the nonpolar optical phonon E 2 (high) mode [40]. ...
... The Raman spectra were normalized with respect to the E 2 (high) − E 2 (low) peak for the ease of interpretation (Fig. 8). The ratio between A 1 (LO) and E 2 (high) peak intensities (I(A 1 (LO))/I(E 2 (high)) indicates the number of oxygen vacancies in the sample [38,39]. The contents of oxygen vacancies increase in the 0.125 M Fig. 7). ...
ZnO has been studied intensely for chemical sensors due to its high sensitivity and fast response. Here, we present a simple approach to precisely control oxygen vacancy contents to provide significantly enhanced acetone sensing performance of commercial ZnO nanopowders. A combination of H2O2 treatment and thermal annealing produces optimal surface defects with oxygen vacancies on the ZnO nanoparticles (NPs). The highest response of ~27,562 was achieved for 10 ppm acetone in 0.125 M H2O2 treated/annealed ZnO NPs at the optimal working temperature of 400 ℃, which is significantly higher than that of reported so far in various acetone sensors based on metal oxide semiconductors (MOSs). Furthermore, first-principles calculations indicate that pre-adsorbed O formed on the surface of H2O2 treated ZnO NPs can provide favorable adsorption energy, especially for acetone detection, due to strong bidentate bonding between carbonyl C atom of acetone molecules and pre-adsorbed O on the ZnO surface. Our study demonstrates that controlling surface oxygen vacancies by H2O2 treatment and re-annealing at optimal temperature is an effective method to improve the sensing properties of commercial MOS materials.
... 37 An anomalous mode (AM) was also observed at 275 cm À1 , which is related to interstitial zinc clusters. 38 The other peaks on the Raman spectra marked by "#" belong to the cotton fabric. 39 The peaks of the CNTs that normally appeared at 1340 and 1580 cm À1 were absent. ...
Wearable electronic devices such as health monitors, sensors, and e-skin can be powered by lightweight, high-power supercapacitors. Using a binder-free and low-temperature hydrothermal method, polyhedral ZnO nanoparticles were grown on carbon nanotube (CNT)-decorated cotton fabric, which is friendly to human skin and highly wearable, inexpensive, and thus commercially viable. The concentration of the starting material, zinc acetate, was varied to optimize the electrochemical performance. The evenly spaced polyhedral ZnO facilitated efficient permeation of the electrolyte into the active material. The fabric filaments were decorated with CNTs to enhance electron transfer and the overall electrochemical processes. The symmetric cell comprised of cotton fabric decorated with ZnO polyhedron/CNT showed no discernible change in the cyclic voltammetry curves even after 500 bending cycles, demonstrating the mechanical durability of the electrode. The potential window of 1.6 V using a Na2SO4/K2SO4 aqueous dual-ion electrolyte improved the long-term electrochemical stability and increased the energy storage capacity. The capacitance retention was 94% after 5000 cycles at a current density of 1 A·g⁻¹, indicating long-term electrochemical stability. A specific capacitance of 375 F·g⁻¹ at a current density of 5 A·g⁻¹ and energy density of 33.3 Wh·kg⁻¹ at a power density of 2000 W·kg⁻¹ were recorded for the optimized electrode. Highlights: Polyhedral ZnO was grown on cotton fabric using a hydrothermal process. The electrochemical performance was optimized by varying the zinc acetate concentration. The highest specific capacitance was 375 F·g⁻¹ at a current density of 5 A·g⁻¹. Under optimal conditions, the capacitance retention was 94% at N = 5000 cycles. The energy density of the electrode was as high as 33.3 Wh·kg⁻¹.
... The structural characterization of the synthesized ZnO nanocrystals was further carried out by Raman spectroscopic analysis. The attained Raman spectra for the prepared sample are depicted in Figure 4 and are consistent with previous studies [43]. For the wurtzite-like perfect structure, only the optical phonons are involved in first-order Raman scattering at the Γ point of the Brillouin zone, which can be expressed by the following equation: Among the different modes represented in Equation (2), only A 1 , E 1 and E 2 modes are Raman-active, whereas the B1 modes are Raman-silent. ...
In this work, ZnO nanocrystals (NCs) have been effectively synthesized by a simple, efficient and cost-effective method using coconut husk extract as a novel fuel. The synthesized NCs are characterized by UV-Vis, XRD, FT-IR, SEM, EDX, Raman and PL studies. The obtained ZnO were found to be UV-active with a bandgap of 2.93 eV. The X-ray diffraction pattern confirms the crystallinity of the ZnO with hexagonally structured ZnO with a crystallite size of 48 nm, while the SEM analysis reveals the hexagonal bipyramid morphology. Photocatalytic activities of the synthesized ZnO NCs are used to degrade methylene blue and metanil yellow dyes.
... The structural characterization of the synthesized ZnO nanocrystals was further carried out by Raman spectroscopic analysis. The attained Raman spectra for the prepared sample are depicted in Figure 4 and are consistent with previous studies [43]. For the wurtzite-like perfect structure, only the optical phonons are involved in first-order Raman scattering at the Γ point of the Brillouin zone, which can be expressed by the following equation: Among the different modes represented in Equation (2), only A 1 , E 1 and E 2 modes are Raman-active, whereas the B1 modes are Raman-silent. ...
