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A great deal of interest has been dawn on the colloidal chemistry based semiconductor nanocrysallites, also known as quantum dots (QDs). Because of the strong quantum confinement, quantum dots have unique size-dependent optical properties, which are much more superior to the conventional organic fluorescence materials. In addition, strong chemical...
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There is a growing interest in using technology to provide diagnostics, therapeutics, and measured drug delivery to individuals suffering from a myriad of issues. Many of these biotechnological devices need to interact with the human body indefinitely, and it has therefore become a priority that these devices interact with the body with an increase...
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... CdSe quantum dots are quantum dots that are used as biomarkers in experimental fields in medicine and biology because they have luminescence properties and could cover all visible wavelength so they are very important for visualizing tissues and cells [14]. Salem et al. synthesized CdSe NPs by the heat treatment method at different temperatures (450-700)ᶱC in O 2 and N 2 environment. ...
... Bubbles formed by the argon gas in the second flask will agitate the CdSe solution thus H 2 S would react with Cd +2 to cap the CdSe QDs. The quantity of H 2 S provided to the second flask was regulated by the number of H 2 SO 4 drops added into the first flask ( the final reaction event was carried out at room temperature).The method adapted in this work was that of Xu [14]. Figure 3 shows the XRD patterns of CdSe nanoparticles and CdSe/CdS core/shell quantum dots prepared by the chemical bath method. ...
CdSe/CdS Core/shell nanostructures were prepared through the chemical synthesis method. XRD ,FESEM and TEM investigations confirmed the formation of core/shell structure for the sample. The AFM measurement was employed to reveal the morphology of the prepared thin films. Optical characterizations of the quantum dots were done by UV-visible and photoluminescence spectra. It was found that the quantum dots prepared has good optical properties. Due to the presence of shell coating on core CdSe, the energy gap of the core/shell nanomaterial were increased from 2.2 to 2.3eV. The resulted QDs are a promising candidate for photovoltaic and biosensor applications.
... [37] The hump from 20° to 35° along with the unmarked peaks are attributed to the presence of amorphous SiO2 (glass slide). [38] The XRD pattern of powdered NiO is presented in Fig. 6. As observed, three major peaks are observed at 2θ = 38°, 43°, and 62° which is in good agreement with the JCPDS data (JCPDS card No. . ...
... This can be attributed to the surface defects dominated emission. Fig. 1 UV-Vis absorption spectra and photoluminescence spectra of undoped (S1) and doped samples (S6, S13 and S16) [30,31]. In the present study, the ratio is 1:1 for the co-doped samples. ...
Undoped and Mn/Cu/(Mn+Cu) doped CdSe colloidal quantum dots embedded in Starch matrix have been synthesized by adopting single-step chemical bath deposition method. X-ray diffraction (XRD) results show cubic zinc blende structures in both doped and undoped samples. The estimated particle sizes from the XRD are found to be in the range (6.9–10.3) nm. The HRTEM images exhibit irregular shaped nanoparticles with size in the range (6–10.2) nm. Thus, the particle sizes estimated from XRD results roughly agree with those from HRTEM measurements. The UV–Vis absorption spectra for both doped and undoped samples show blue shift, suggesting quantum confinement. All the undoped and doped samples show PL emission in the range 510–653 nm. PL intensity is found to increase due to doping. Two terminal electrochemical devices are fabricated with the as-prepared doped and undoped samples as the active layer with ITO coated glass slide and aluminum (Al) as electrodes. I–V characteristics of the as-fabricated devices exhibit pinched hysteresis loops having memristive, memcapacitive and meminductive nature. A new parameter is conceptualized which is found to be sensitive to doping material as well as doping concentration. Schottky emission mechanism is found to be dominant in both low resistance state and high resistance state. ON/OFF switching features favour Coulomb Blockade phenomenon.
... Then more and more of the solid product deposits onto the nuclei, so the sizes of the crystallites grow slowly till the desired size is reached, at which time the reaction must be quenched. Otherwise, the dots could keep growing under a process, known as Ostwald ripening, which is the growth of larger dots through the transfer of material from smaller ones, which have a higher solubility [11,12]. ...
Key words In this study, an easy, low-cost, green, and environmentally friendlier reagents have been used to prepare CdS QDs, in chemical reaction method by mixed different ratio of CdO and sulfur in paraffin liquid as solvent and oleic acid as the reacting media in different concentration to get the optimum condition of the reaction to formation CdS QDs. The results give an indication that the behavior is at small concentration of 4ml of the oleic acid is best concentration which give CdS QDs of small about to 9.23 nm with nano fiber configuration. Quantum dots, Cd;S ratio, oleic acid concentration. Article info.
... In the last few years a great effort has been devoted to the study of low dimensional semiconductor structures. The reduction of the dimensionality causes several changes in the electronic and excitonic wave functions and these features can be used, at least in principle, to produce novel microelectronics [38] . ...
This thesis describes the synthesis of self-organized titanium dioxide nanotube layers by an electrochemical anodization of Ti at different conditions (time, voltage, concentration of NH4F in electrolyte with glycerol, conductivity and water content) at room temperature (~25ºC) were investigated.
In the current study, self-organized, vertically-oriented TiO2 nanotubes were successfully prepared by anodization method of a pure Titanium sheet (99.5%) using anodization cell is designed for first time in Iraq (Homemade) from Teflon material according to our knowledge to produce self-ordered Titanium nanotube in organic based electrolytes (glycerol based electrolyte) an electrolyte solution containing (0.5, 1, 1.5 and 2 wt.% NH4F) then added water (2 and 5Wt.% H2O) to (0.5wt.% NH4F) only with 15V. The range of anodizing time and potential were between 1-4hr. and 5-40V, where Wt.% represent weight percentage.
Scanning electron microscopy (SEM), Atomic force microscopy (AFM) and (XRD) X-Ray diffraction were employed to characterize the morphology and structure of the obtained Titania templates, optical interferometer (Fizeau frings) method to tubes length measurement.
For TiO2 nanotubes fabricated in non-aqueous electrolyte, the influence of the NH4F concentration on characteristics of nanotubes was studied. The results showed that when the NH4F concentration increased from 0.5 to 2wt.%NH4F, the tubes diameter, tubes length and roughness of TiO2 surface increased.
Also the effects of the anodizing time and anodizing potential were studied. The formation of TiO2 nanotubes was very sensitive to the anodizing time. Length of the tube increases with increasing anodizing time and anodizing potential significantly.
Either water content (2 and 5wt.%) with 0.5wt.% NH4F and the conductivity of electrolyte it is increasing the diameter, tube length and roughness of TiO2 surface increased, but simple increasing and formation of less homogenized TiO2 nanotube.
The optimal conditions for TiO2 formation was found 15V at 4hr with 0.5wt.% NH4F due to we obtain on best results for tube diameter, tube wall thickness, tube length and more homogenized of TiO2 nanotubes.
... The wave function is squeezed due to strong confinement and the electron, and the hole individually occupy the lowest energy state in a confined potential [1] . The dimension of a quantum dot is smaller than the De Broglie wavelength of thermal electrons, which is [15] An important property of a quantum dot is its large surface to volume ratio. The consequence of this feature is that quantum dots have pronounced surface-related phenomena [15,16] . ...
... The dimension of a quantum dot is smaller than the De Broglie wavelength of thermal electrons, which is [15] An important property of a quantum dot is its large surface to volume ratio. The consequence of this feature is that quantum dots have pronounced surface-related phenomena [15,16] . ...
... The photocurrent gain is calculated using equation (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) for the polymer coated and uncoated ZnO UV photoconductive sample. The average value of the gain registered for the polymer coated UV ZnO photoconductive detectors under the same measurement conditions is found to be about 200 ,whereas the gain without polymer ≈ 20 ...
The work concentrate on the improvement of the ZnO photoconductive detector in the UV region. The improvement is based on two mechanisms : The first is the functionlization of the detector surface by specific polymer material and the second mechanism is to improve the structure of the film on the silicon layer through developing the porous layer on n-type silicon substrate.The creation of the nanospikes silicon layer provides strong carrier - carrier interaction. The strong interaction leads to new energy relaxation and recombination channels associated with the electron – hole energy transfer. This new recombination mechanism may help in the fabrication of fast response photoconductive detector.
... Overall revision of the different methods of nanocrystal fabrication is shown in Table 1. But for QD syntheses, we most use of organometallic technique (Jiang 2008;Yang 2005;Protie're and Reiss 2006), which this technique and its sub-methods are illustrated and reviewed in Fig. 3. In this method, dimethyl cadmimum was considered as the precursor for the syntheses of highquality QD (Hwang and Cho 2005). ...
In this article, the syntheses and optical properties of core/shell quantum dot (CdSe/ZnS) and their applications are reviewed.
Nevertheless, the main focus is to provide an overview on biological applications of quantum dots that contain imaging, targeting,
and sensing. We discuss the different synthetic methods, optical properties (photoluminescence intensity, absorption, and
fluorescence spectra), and their dependence on shape, size, and inner structure of quantum dots. Also, the different mechanisms
of quantum dots bio-targeting (passive and active mechanisms) are discussed. The impact of quantum dots in bioimaging is reviewed
regarding its photoluminescence intensity, absorption and emission spectrum, and photo-stability on high-quality and sensitivity
imaging. Further, the difference between near infrared and visible emission quantum dots in deep tissue imaging will be reviewed
and some of done works are considered and compared with each other. And finally, the biosensing potential/application of quantum
dots in medical diagnosis is going to be highlighted.
... Three different types of confinement that have been realized among semiconductors materials are described below. [5]. ...
... A quantum wire is a structure in which the electrons and holes are confined in two dimensions, as in figure (1)(2)(3) such confinement allows free electron and hole behavior in only one direction, along the length of the wire [5]. This properties give rise to produce many nanoproduction which can be considered an a quantum wire (λ F > L x, L y and L x , L y <<L z ), carbon nanotubes and cold nanowire for connection are example of this type of confinement [7]. ...
... Where me is chosen to be equal to 9.1e-31kg .An important property of a quantum dot its large surface to volume ratio. The consequence of this feature is that QDs have pronounced surface -related phenomena [5]. ...
... [33] .The wave function is squeezed due to strong confinement and the electron and the hole individually occupy the lowest energy state in a confined potential [1] . The dimension of a quantum dot is smaller than the De Broglie wavelength of thermal electrons, which is [34] An important property of a quantum dot is its large surface to volume ratio. The consequence of this feature is that quantum dots have pronounced surfacerelated phenomena [34] . ...
... The dimension of a quantum dot is smaller than the De Broglie wavelength of thermal electrons, which is [34] An important property of a quantum dot is its large surface to volume ratio. The consequence of this feature is that quantum dots have pronounced surfacerelated phenomena [34] . ...
Abstract :
The aim of this research is to prepare CdS quantum dot and to study its structural and spectroscopic properties.
Two methods were used for the preparation: the first is a chemical spray pyrolysis and the second is the chemical method.
- Chemical spray pyrolysis
The first method for preparation of CdS quantum dot is based on chemical spray pyrolysis. The sample were prepared by spray a mixture of CdCl2 solution with CS(NH2)2 solution on glass slides containing nanometer defects (La2O3and dust).
The energy band gap was calculated from the absorption spectrum and we notices an increase in energy gap by (0.19 and 0.3) eV respectively which gives the quantum dot size of CdS quantum dot to be about (6.3 and 5) nm. Also the emission spectrum was measured to calculate the change in energy gap by (0.15 and 0.4) eV respectively. This means that the size of CdS quantum dot obtained was (7 and 4.34) nm respectively.
The second method for preparation of CdS quantum dot was by chemical spray pyrolysis using a mixture of CdCl2 solution with CS(NH2)2 solution and La2O3 nanoparticles and the absorption spectrum was measured to calculate the energy gap . Also we noticed an increase in energy gap by (0.18) eV and the calculated quantum dot size of CdS quantum dot was (6.4) nm.
As well as the calculation of energy gap was done by emission spectrum which gives a increase in energy gap by (0.19) eV and the calculated CdS quantum dot size was (6.3) nm. All the tests by optical microscope, using visible and UV to illuminate the sample and photographed by color digital camera, shows a yellow color which represents the formation of CdS quantum dot and selectivity PL calculated gives a blue dots which represent the quantum dot of the energy gap.
- The chemical method
The first method for preparation of CdS quantum dot was performed by reaction of solutions of CdCl2 and CS(NH2)2 on nanoparticles as a base for the reaction. The reaction was done in an alkaline medium.
Form the absorption spectrum, the calculated energy gap was creased in by (0.26) eV and the quantum dot size of the prepared CdS quantum dot was (5.38) nm. Also an increase of the energy gap was noticed, by using emission spectrum, by (0.25) eV and the quantum dot size (4.49) nm.
By using X-ray spectrum the calculated quantum dot size was (7.3) nm
The image of the samples were viewed by transmission electron microscope (TEM) and from the shape of the formed CdS quantum dot.
The second method for preparation of CdS quantum dot was by chemical method using reaction of S with CdCl2 in oleylamine as a support for the reaction. The energy band gap was calculated from the absorption spectrum and we noticed an increase in energy gap by (0.18) eV which gives the quantum dot size of CdS of (6.47) nm. Also the emission spectrum was measured to calculate the increase in energy gap by (0.19) eV. This mean that the size of CdS quantum dot is (6.29) nm.
By using X-ray spectrum the calculated quantum dot size was (5.27) nm.
The formation of CdS quantum dot was checked by TEM image.
... Thus, quantum confinement effects determine an emission signature which may be 'tuned' by simply varying the size of the QD assembly. This makes QDs applicable for medical application, where cell or tissue visualization can reveal important transport behavior [62]. ...
... Epitaxial QDs can be grown using molecular beam epitaxy or metal organic chemical vapor deposition [64]. A gelatin may be introduced to slow the chemical reaction providing regulation of growth rate and provide a biocompatible coating for in-vivo applications [62]. ...
... Thus, the inter-band transition energy approaches that of the bulk material when the QD diameter increases towards λ [62]. The band gap energy can be influenced at these length scales because their physical diameter is less the exciton Bohr radius (EBR). ...
Thermally-related, minimally invasive therapies are designed to treat tumors while minimizing damage to the surrounding tissues. Adjacent tissues become susceptible to thermal injury to ensure the cancer is completely destroyed. Destroying tumor cells, while minimizing collateral damage to the surrounding tissue, requires the capacity to control and monitor tissue temperatures both spatially and temporally. Current devices measure the tumor's tissue temperature at a specific location leaving the majority unmonitored. A point-wise application can not substantiate complete tumor destruction. This type of surgery would be more effective if volumetric tissue temperature measurement were available. On this premise, the feasibility of a quantum dot (QD) assembly to measure the tissue temperature volumetrically was tested in the experiments described in this dissertation. QDs are fluorescence semiconductor nanoparticles having various superior optical properties. This new QD-mediated thermometry is capable of monitoring the thermal features of tissues non-invasively by measuring the aggregate fluorescence intensity of the QDs accumulated at the target tissues prior to and during the surgical procedure. Thus, such a modality would allow evaluation of tissue destruction by measuring the fluorescence intensity of the QD as a function of temperature. The present study also quantified the photoluminescence intensity and attenuation of the QD as a function of depth and wavelength using a tissue phantom. A prototype system was developed to measure the illumination through a tissue phantom as a proof of concept of the feasibility of a noninvasive thermal therapy. This prototype includes experimental hardware, software and working methods to perform image acquisition, and data reduction strategic to quantify the intensity and transport characteristics of the QD. The significance of this work is that real-time volumetric temperature information will prove a more robust tool for use in thermal surgery. The thermal ablation zone is extremely diffusive and current imaging techniques and/or equipment may not accurately monitor portions of the tumor surviving the ablation process. Used in conjunction with other volumetric measuring systems, i.e., fluorescence or bioluminescence tomography, this platform will have the capacity to produce direct three dimensional intraoperative monitoring of the thermal surgical procedure. Lastely, realization of system requirements will aid in the automation of imaging to ease data acquisition, maximize exposure, and control test bed temperature.
