Energy Dispersive X-ray Measurements Research Articles

Synthesis of Ni-Fe thin films by electrochemical deposition technique and characterization of their microstructures and surface morphologies

Microstructural features and surface morphologies of Ni-Fe thin films fabricated by the electrochemical deposition technique have been experimentally studied. Ni-Fe thin films have been deposited under different deposition potentials and FeSO$_{4}$ concentrations. Energy dispersive X-ray measurements demonstrate that the Fe content decreases (increases) as the deposition potential (FeSO$_{4}$ concentration) is enhanced. All of the produced films exhibit an anomalous codeposition behavior. The effects of deposition potential and FeSO$_{4}$ concentrations on the degree of anomalous codeposition have been also characterized. X-ray diffraction studies reveal that the films have face-centered cubic crystallographic structures with [111] preferred crystallographic orientation regardless of the applied deposition conditions. However, the crystallization and the crystallite size of the films are affected by changing of the FeSO$_{4}$ concentration and the deposition potential. The results of scanning electron microscopy analyses verify that the surface structure of the film electroplated from the electrolyte with higher FeSO$_{4}$ concentration under higher deposition potential exhibits a more homogeneous and dense structure with smaller grain sizes.

Ex-situ evaluation of PTFE coated metals in a proton exchange membrane fuel cell environment

Metallic-based bipolar plates exhibit several advantages over graphite-based plates, including higher strength, lower manufacturing cost and better electrical conductivity. However, poor corrosion resistance and high interfacial contact resistance (ICR) are major challenges for metallic bipolar plates used in proton exchange membrane (PEM) fuel cells.Corrosion of metallic parts in PEM fuel cells not only increases the interfacial contact resistance but it can also decrease the proton conductivity of the Membrane Electrode Assembly (MEA), due to catalyst poisoning phenomena caused by corrosive products. In this paper, a composite coating of polytetrafluoroethylene (PTFE) was deposited on stainless steel alloys (SS304, SS316L) and Titanium (G-T2) via a CoBlast™ process. Corrosion resistance of the coated and uncoated metals in a simulated PEM fuel cell environment of 0.5M H2SO4+2ppm HF at 70°C was evaluated using potentiodynamic polarisation. ICR between the selected metals and carbon paper was measured and used as an indicator of surface conductivity. Scanning Electron Microscopy (SEM), 3D microscopy, Energy Dispersive X-ray (EDX), X-Ray Diffraction (XRD), and contact angle measurements were used to characterise the samples. The results showed that the PTFE coating improved the hydrophobicity and corrosion resistance but increased the ICR of the coated metals due to the unconductive nature of such coating. Thus, it was concluded that it is not fully feasible to use the PTFE alone for coating metals for fuel cell applications and a hybrid coating consisting of PTFE and a conductive material is needed to improve surface conductivity.

Growth and optical properties of In x Ga1−x P nanowires synthesized by selective-area epitaxy

Ternary III–V nanowires (NWs) cover a wide range of wavelengths in the solar spectrum and would greatly benefit from being synthesized as position-controlled arrays for improved vertical yield, reproducibility, and tunable optical absorption. Here, we report on successful selective-area epitaxy of metal-particle-free vertical InxGa1−xP NW arrays using metal–organic vapor phase epitaxy and detail their optical properties. A systematic growth study establishes the range of suitable growth parameters to obtain uniform NW growth over a large array. The optical properties of the NWs were characterized by room-temperature cathodoluminescence spectroscopy. Tunability of the emission wavelength from 870 nm to approximately 800 nm was achieved. Transmission electron microscopy and energy dispersive X-ray measurements performed on cross-section samples revealed a pure wurtzite crystal structure with very few stacking faults and a slight composition gradient along the NW growth axis. [Figure not available: see fulltext.] (Less)

Samarium colloids prepared in organic solvents and active solids

Samarium colloids in organic solvents (2-methoxyethanol, 2-propanol, 2-propanone, and 1,2-dimethoxyethane) were obtained by the chemical liquid deposition (CLD) method at 77 K. The colloids were characterized by electron diffraction, energy-dispersive X-ray (EDX), UV-Vis spectroscopy, kinetic stability, and electrophoretic measurements. The colloid stability depends on the solvent used and the metal concentration. The higher stability was obtained in 2-methoxyethanol, which is in agreement with previous results for other lanthanide colloids. The zeta potential (ζ) of the colloids ranges between 0.138 and 1.945 mV. The UV-Vis spectra exhibit bands characteristic of the solvent. The 2-methoxyethanol shows bands at 205 and 234 nm very similar to the 2-propanol which exhibits bands at 202 and 253 nm for 2.5E−4 M concentration. However, bands for 1,2-dimethoxyethane and 2-propanone colloids were impossible to determine due to their highest extinction coefficient values. A dependence of the UV/Vis spectral properties of these new sol materials with Sm(III) is described. In all cases, the EDX analyses confirm the presence of metal in the colloids. The electron diffraction gives the most common (hkl) planes corresponding to Sm and Sm2O3 (211) and (100), respectively. As shown by the particle size distribution determined from transmission electron microscopy (TEM), the Sm-2-methoxyethanol colloids exhibit ranges from 1.6 and 2.9 nm, but the Sm-2-propanol colloids show ranges from 2.3 to 2.5 nm; the medium particle size of Sm-1,2-dimetoxyethane colloid is 0.8 nm, and the Sm-2-propanone colloids have a range from 1.0 and 4.3 nm, exhibiting a solvent polarity dependence. Also, active solids from the evaporation of the colloids which have been fully characterized by several chemical and physical techniques have been obtained.

Effects of annealing on elemental composition and quality of CZTSSe thin films obtained by spray pyrolysis

The spray pyrolysis was used for the deposition of Cu2ZnSn(S, Se)4 (CZTSSe) kesterite thin films. The basic spray pyrolysis solution was prepared from two precursor solutions containing thiourea and cooled to a temperature near 1°C, which leads to minimizing the number of insoluble hydrates of copper chloride. The optimal substrate temperature was 350°C and the distance from the sprayer nozzle 30 cm. The as-deposited Cu2ZnSnS4 layers were annealed in S2 atmosphere for the compensation of the sulfur deficiency and with the addition of Sn in order to avoid tin loss. Cu2ZnSn(S, Se)4 thin films were obtained after the annealing of as-deposited films in the (S2 + Se2) atmosphere. The surface morphology and composition of obtained thin films were investigated using the energy dispersive X-ray (EDX) microanalysis and Raman spectroscopy measurements. The structural characterization by the grazing incidence X-ray diffraction (GIXRD) showed the presence of Cu2–xS phases in all of the annealed thin films. For the Se/(S + Se) ratio of the thin films annealed in the (S + Se) atmosphere was established from EDX measurements and analysis of GIXRD data, the results are in satisfactory agreement.

Uniform phosphorus doping of untapered germanium nanowires

One of the major challenges in the growth of vapor–liquid–solid (VLS) nanowires is the control of dopant incorporation in the structures. In this work, we study the n-type doping and morphology of nanowires grown by chemical vapor deposition when HCl is introduced. We obtain fully untapered nanowires with a growth temperature up to 410 °C and measure their resistivity using the 4-probe technique to be 2.0 mΩ cm. We perform energy dispersive x-ray measurements showing a concentration of dopants in the (5–7) × 1018 cm−3 range, being radially and axially uniform. The combination of these two measurements shows that the mobility is the same as for bulk germanium, demonstrating that the VLS mechanism has no detrimental effect for the electron transport in these nanowires.

Investigation of Dynamics of Perovskites using Chemically, Spatially and Temporally Resolved 2D Mapping

Currently, there is an ongoing strong discussion regarding the nature of organometallic CH3NH3PbI3-xClx perovskites for solar cells. In this work, perovskites have been investigated using chemically, spatially, and temporally resolved measurements. To investigate the carrier dynamics of perovskites, perovskite (CH3NH3PbI3-xClx) films were prepared using hot casting technique in which perovskite (CH3NH3PbI3-xClx) solution was prepared by dissolving equimolar ratios of lead iodide (PbI2, Sigma-Aldrich, 99%) and methylamine hydrochloride (MACl, Sigma-Aldrich) in N, N-dimethylformamide (DMF, Sigma-Aldrich, anhydrous, 99.8%) in 11% concentration. A lower hot-casting temperature (100 °C) resulted in smaller grain size, with typical grain sizes of 1~2µm. Hot-casting temperatures higher than 100 °C produced perovskite samples with larger grains of ~ more than tens of micrometers, which was confirmed by high-resolution scanning electron microscopy (SEM). The PL intensity and peak-position mapping image of submicron-scale were performed using confocal micro-spectroscopy. In-plane spatial resolution of ~380nm was indicated by an objective lens with numerical aperture of 0.7 and a solid-state laser with 405nm wavelength for the excitation. The signal collected by the objective lens was detected by a thermoelectrically cooled CCD detector. For the analysis of time resolved PL (TRPL), multifunctional confocal microscopy including a time-correlated single photon counting (TCSPC) system was employed. In addition, 2-D energy-dispersive X-ray (EDS) measurement was performed to elucidate the distribution of chemistries for the surface of perovskites, which were correlated to spatially and temporally resolved PL. Particularly, the carrier dynamics between grain interiors and grain boundaries were systematically investigated.

Influence of Surface Oxygen Non-Stoichiometry on Oxygen Electrochemical Properties of Perovskite-Type Oxides

Introduction Much attention has been paid to oxygen electrochemical reactions in alkaline electrolytes such as alkaline fuel cell, alkaline rechargeable metal-air battery and water-splitting devices. Many researchers have been exploring highly-active and cost-effective oxygen electrode catalysts, and one example of good oxygen electrocatalysts is perovskite-type oxide with the general formula of ABO3. Our group focuses on observing intrinsic electrochemical properties of perovskite when used as an oxygen electrode catalyst, using a carbon-free and binder-free perovskite electrode.1, 2 One of our research findings was that whereas oxygen evolution reaction activity of model electrodes were as high as that of composite electrodes consisting of perovskite powder, carbon and binder, oxygen reduction reaction activity of model electrodes was much lower than that of composite electrodes. This contrasting behavior motivated us to conduct further experiments such as hydrogen peroxide reduction reaction activity and cyclic characteristics of oxygen electrochemical reactions by using the model electrode and the composite electrode in terms of surface oxygen non-stoichiometry, which is our present research topic. Experimental section Synthesis and fabrication of La0.8Sr0.2CoO3 (LSCO) crystal electrodes were described in our previous literature.2 Perovskite powders were also synthesized by hydroxide-acid aided process3 and solid state process. The resultant oxide crystals and powders were characterized by using X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, Brunauer-Emmett-Teller for oxide powders, and iodometry for oxide powders. Electrochemical measurements were conducted by using a rotating disk electrode (RDE) in a three-electrode cell. For a working electrode, RDE of LSCO crystal electrodes were assembled by mounting a LSCO crystal in a Teflon disk holder. As for composite electrodes, a catalyst layer consisting of 250 μg cm-2 perovskite powder, 50 μg cm-2 Vulcan XC-72 (Cabot), and 50 μg cm-2 anion conductive ionomer (AS-4, Tokuyama) was formed on glassy carbon (GC) RDE. 50 μg cm-2 Pt(40wt%)/Vulcan (E-TEK) and 50 μg cm-2 anion conductive ionomer on GC RDE was also used as benchmarking of oxygen electrochemical reactions. Pt wire and reversible hydrogen electrode (RHE) were used as counter and reference electrodes, respectively. Oxygen electrochemical activity measurements were conducted using a solution of oxygen-saturated 1.0 mol dm-3 KOH for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and argon-purged 1 mol dm-3 KOH containing ca. 5 mmol dm-3 H2O2 for hydrogen peroxide reduction reaction (PRR). For qualitative electronic conductivity measurement, ferricyanide reduction reaction (FRR) was observed in a solution of argon-purged 1.0 mol dm-3 KOH containing 20 mmol dm-3 K3[Fe(CN)6]. Results and discussions XRD and EDX measurements confirmed that resultant LSCO crystals and perovskite powders had perovskite structure and the atomic compositions were quite similar as the desired composition. Figure 1 shows PRR activity on LSCO crystal. In the initial cycles, it shows clear rotation dependence indicating that LSCO crystal was active toward PRR. However, as the cycle number of cyclic voltammetry increased, reduction currents were decreased and finally showed no dependence on rotation. Similar results were observed for solid-state-synthesized LSCO composite electrode suggesting that obtained results by model electrodes were universal for practical electrodes. The decrease in activities was also observed for ORR, while the decrease in OER activity on LSCO crystal was not observed. FRR after PRR and ORR showed that electronic conductivity of LSCO crystal was decreased. The reason of activity decrease in ORR and PRR, and the influence of B-site cation in ORR and PRR in terms of surface oxygen non-stoichiometry will be discussed in the conference.

Rechargeable Batteries Using Molecular Ions As a Charge Carrier

Is it possible to exceed the lithium redox potential in electrochemical systems? One may think the answer to be “No” because among all the elements the redox potential of the elemental lithium is the lowest, which leads to the high voltage characteristics of the widely used lithium ion batteries. However, the answer should turn “Yes” in principle when we use a molecule-based ion which is not reduced even at the lithium potential. Here we examined a model battery system using a few molecular ion charge carriers such as PF6 – and Me4N+with organic active materials. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that molecular ions can work as a “rocking chair” type charge carrier in a battery [1]. There are so far a few studies [2-5] describing the use of a molecular ion as the charge carrier; however, its stoichiometery has rarely been analyzed. To construct a “rocking chair” type molecular ion battery using, for instance, an anion charge carrier, we used a PF6 –-based electrolyte solution with two redox polymers (poly(N-vinylcarbazole): PVK, poly(1,1'-pentyl-4,4'-bipyridinium dihexafluorophosphate): PBPy) (Fig. 1a) as active materials. As for the molecular ion battery which uses a cation charge carrier, we chose a Me4N+-based electrolyte with some low molecular weight quinone type organic active materials. As shown in Fig.1b, the prepared sealed full cell using a PF6 –-based electrolyte system exhibited the potential difference of about 1.8 V with about 100 mAh/g(PVK). The cell exhibited a fairly good cycle stability; the cell maintained about 65% of the initial capacity after 100 cycles. The cell using the Me4N+-based electrolyte system also showed a repeatable charge/discharge behavior. The concept of these molecular ion batteries was proved by energy dispersive X-ray (EDX) measurement: we evaluated the change in stoichiometry of PF6 – in the electrode of the former cell ex situ by EDX and found that the charge carrier in this system is PF6 – and the prepared system is certainly a PF6 –-based “rocking chair type” battery. When succeeded in further developing the molecular ion battery, the benefits we would gain are: Breaking through the Li potential limitation, High ion conductivity in the electrolyte solution, Free from the dendrite risk, Minor metal free, and so on. To enjoy these benefits, the development in the active materials of both the positive- and negative-electrodes is indispensable. Searching for a negative electrode active material with a low redox potential is especially significant, which, we believe, will pave the way for the progress of this new battery system.

Keggin heteropolyacids supported on TiO2 used in gas-solid (photo)catalytic propene hydration and in liquid-solid photocatalytic glycerol dehydration

(Photo)catalytic propene hydration to 2-propanol and glycerol dehydration to acrolein were carried out by using Keggin heteropolyacids (HPAs) supported on TiO2. Binary materials have been prepared by impregnation of H3PW12O40, H3PMo12O40 and H4SiW12O40, on TiO2 Evonik P25. Moreover, a binary material consisting of H4SiW12O40 and TiO2 was prepared via a hydrothermal treatment and tested for the same reactions. All the materials were characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM) coupled with energy dispersive X-ray (EDX) measurements, diffuse reflectance spectroscopy (DRS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The supported Keggin HPA species played a key role both for the catalytic and for the photo-assisted catalytic reactions due to their strong acidity and ability to form strong oxidant species under UV irradiation.

Evaluation of corrosion, mechanical and structural properties of new Ni–W–PCTFE nanocomposite coating

Abstract Polychlorotrifluoroethylene (PCTFE) particles were co-deposited with nickel–tungsten (Ni–W) coatings through electro-deposition process. The nanocomposite coatings have been prepared in four different concentrations (0, 4, 8 and 20 g/l). Corrosion performance of the coatings was examined using potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). Surface morphology and composition of the composite coatings were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDAX) measurements and X-ray Diffraction (XRD) analysis. The tribological properties of a surface have been investigated in ambient condition by Atomic Force Microscopy (AFM). Results show that, there is a significant shift in corrosion potential towards the noble direction, decrease in corrosion current density, and increase in charge transfer resistance and decrease in double-layer capacitance values with the incorporation of PCTFE particles in the Ni–W matrix. Higher PCTFE contents, however, negatively affected the corrosion behavior of the coatings. Co-deposition of the PCTFE particles into the Ni–W coating changed the structure and morphology of the deposited coating and decreased the nodules and crystalline size. By increasing the PCTFE concentration of coatings, microhardness decreased and the elastic behavior of coating, increased. The coatings with 4 and 8 g l − 1 PCTFE shows the low friction force in comparison with other samples.

Review of carbon nanotubes production by thermal chemical vapor deposition technique

ABSTRACTWe have reviewed carbon nanotubes (CNTs) production on a silicon wafer by thermal chemical vapor deposition (TCVD) using acetylene as a carbon source, cobalt as a catalyst and ammonia as a reactive gas. The DC-sputtering system was used to prepare cobalt thin films on Si substrates. Energy Dispersive X-ray (EDX) measurements were used to investigate the elemental composition of the Co nanocatalyst deposited on Si substrates. Atomic Force Microscopy (AFM) was used to characterize the surface topography of the Co nanocatalyst deposited on Si substrates. The as-grown CNTs were characterized under Field Emission Scanning Electron Microscopy (FESEM) to study the morphological properties of CNTs.

An alternative experimental approach to produce rare-earth-doped SiOx films

Rare-earth (RE) doped silicon-oxide (SiOx) films were prepared by sputtering a combined Si + RE2O3 target with argon ions. The study comprised the neodymium (Nd) and samarium (Sm) rare-earth species and the Si + RE2O3 targets were obtained by partially covering a solid disc of Si with area-defined thin layers of Nd2O3 or Sm2O3 powders. The films were investigated by energy-dispersive x-ray, Raman scattering, optical transmission, and photo-luminescence measurements. According to the experimental results, in the as-deposited form, the films were amorphous and presented RE and oxygen concentrations that scaled with the RE2O3 target area. Additional compositional-structural changes were obtained by thermal annealing the films under a flow of oxygen. Within these changes, one can mention: increase of oxygen concentration, optical bandgap widening, partial Si crystallization, and the development of RE-related light emission. The main aspects associated to the production and structural-optical properties of the films, as determined either by the deposition conditions or by the annealing treatments, are presented and discussed in detail.

Mg-doped Li2FeSiO4/C as high-performance cathode material for lithium-ion battery

Mg-doped Li2FeSiO4/C is synthesized by using Fe2O3 nanoparticle as iron source. Through Rietveld refinement of X-ray diffraction data, it is confirmed that Mg-doped Li2FeSiO4 owns monoclinic P21/n structure and Mg occupies in Fe site in the lattice. Through energy dispersive X-ray measurement, it is detected that Mg element is distributed homogenously in the resulting product. The results of transmission electron microscopy measurement reveal that the effect of Mg-doping on Li2FeSiO4 crystallite size is not obvious. As a cathode material for lithium-ion battery, this Mg-doped Li2FeSiO4/C delivers high discharge capacity of 190 mAh g−1 (the capacity was with respect to the mass of Li2FeSiO4) at 0.1C and its capacity retention of 100 charge-discharge cycles reaches 96% at 0.1C. By the analysis of electrochemical impedance spectroscopy, it is concluded that Mg-doping can help to decrease the charge-transfer resistance and increase the Li+ diffusion capability.

Spectroscopic Characterization of Dust-Fall Samples Collected from Greater Cairo, Egypt.

This work aimed to characterize dust-fall samples collected from street's trees in Greater Cairo (GC), Egypt, and its surroundings by different spectroscopic techniques, namely; X-ray diffraction (XRD), attenuated total-reflection Fourier transform infrared (ATR-FTIR), particle-size analyzer, and scanning electron microscopy (SEM) combined with energy dispersive X-ray measurements. Samples were collected from 19 different locations inside and outside of GC. Quantitative phase analysis of the dust-fall samples was performed using the Rietveld method. Results showed that the most frequently observed phases in the dust-fall samples were calcite (CaCO3), dolomite (CaMg(CO3)2), gypsum (CaSO4·2H2O), and quartz (SiO2) with average concentrations of 39 ± 16, 8 ± 7, 22 ± 13, and 33 ± 14 wt%, respectively. The occurrence of these constituents referred to a combination of different anthropogenic and natural sources. The ATR-FTIR results are in good agreements with XRD data of the different observed phases. Based on the SEM and particle-size measurements, quantitative determination of the particle-size distribution was described. It was found that not only the large-sized particles are deposited but also the small-sized ones (PM10 and PM2.5). In addition, the particle size of the collected dust-fall samples varied from 0.1 to 200 µm with an average particle size of 17.36 µm; however, the particle size ranged from 2.5 to 40 µm predominated in all of the dust-fall samples.

Cellulose biotemplates for layered double hydroxides networks

Synthesis of porous network structures of layered double hydroxides (LDH) has been studied using microcrystalline cellulose (MCC) as a hard template. LDH was synthesized using cellulose as biotemplate and post treated by microwave hydrothermal treatment (MWHT). The prepared LDHs were thoroughly characterized by Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy, X-ray Diffraction (XRD) studies, and Thermogravimetric (TGA) analysis, which proved the formation of LDH structure in the presence and absence of MCC as templates. The morphological structures of the composite materials were analyzed by Scanning Electron Microscopy (SEM), which showed that the LDH formed in the presence of cellulose had porous network structures, while LDH particles synthesized in the absence of the MCC exhibited a hexagonal platelet-like morphology. Energy Dispersive X-ray (EDX) measurements confirmed the presence of essential elements in the particles. TEM showed the fibrillar nature and size reduction of the particles. The surface area of the material was measured by Brunauer–Emmett–Teller (BET) analysis, exhibiting a twofold increase in surface area and increased specific pore volume in comparison with particles synthesized in absence of cellulose and thus showcasing the potential of MCC as templates for production of porous LDH with high surface area (152 m2/g). Further, the adsorption capacities of the materials were evaluated with orange II dye.

Temperature-Dependent Photoluminescence Property of Self-Assembly ZnO Nanowires via Chemical Vapor Deposition Combined with Hydrothermal Pretreatment

Vertically aligned ZnO nanowires with high aspect ratio were prepared by chemical vapor deposition on Si substrate, which had been catalyzed by the polar plane in [0001] direction of ZnO nanorods prepared by the hydrothermal method. Morphology and structure characterizations showed that the as-grown nanowires had the single-crystal hexagonal wurtzite structure with a [0001] growth direction. Energy Dispersive X-ray (EDX) measurement indicated the as-grown ZnO nanowires had a good deal of oxygen vacancies owing to the high operation temperature. Temperature-dependent photoluminescence measurement revealed that the peak of near-band-edge emission shifted from 380 to 387 nm with the increase of temperature from 150 to 300 K. The high intensity of the green peak at 525 nm highlighted the potential application in visible light emitting diodes.

Sulfurization temperature dependence of the structural transition in Cu2FeSnS4-based thin films

Cu2FeSnS4 (CFTS)-based thin films have been prepared on Mo-coated glass substrates by magnetron sputtering technique combined with a post-sulfurization processing. Energy dispersive X-ray measurement indicates that the Sn content decreases with the increasing sulfurization temperature, and all samples are in Cu-poor and Fe-rich states. X-ray photoelectron spectroscopy and X-ray diffraction show that all phases belong to the CFTS and no impure phase, e.g. Cu2SnS3, can be discovered in thin films. However, samples exhibit a phase transition behavior from rhodostannite to stannite structure with the increasing sulfurization temperature. The frequency of A1 mode of CFTS with rhodostannite structure is estimated to be 323.8cm−1 by using the empirical model, which coincides with the experimental value as measured by Raman spectra analysis. These results are helpful to understand the properties of CFTS-based thin films.

RETRACTED: Synthesis of carbon nanotubes using the cobalt nanocatalyst by thermal chemical vapor deposition technique

Abstract The three main synthesis methods of Carbon nanotubes (CNTs) are the arc discharge, the laser ablation and the chemical vapour deposition (CVD) with a special regard to the latter one. CNTs were produced on a silicon wafer by Thermal Chemical Vapor Deposition (TCVD) using acetylene as a carbon source, cobalt as a catalyst and ammonia as a reactive gas. The DC-sputtering system was used to prepare cobalt thin films on Si substrates. A series of experiments was carried out to investigate the effects of reaction temperature and deposition time on the synthesis of the nanotubes. The deposition time was selected as 15 and 25 min for all growth temperatures. Energy Dispersive X-ray (EDX) measurements were used to investigate the elemental composition of the Co nanocatalyst deposited on Si substrates. Atomic Force Microscopy (AFM) was used to characterize the surface topography of the Co nanocatalyst deposited on Si substrates. The as-grown CNTs were characterized under Field Emission Scanning Electron Microscopy (FESEM) to study the morphological properties of CNTs. Also, the grown CNTs have been investigated by High Resolution Transmission Electron Microscopy (HRTEM) and Raman spectroscopy. The results demonstrated that increasing the temperature leads to increasing the diameter of CNTs. The ideal reaction temperature was 850 °C and the deposition time was 15 min.

Investigation of characteristics of ZnO:Ga nanocrystalline thin films with varying dopant content

In this study, undoped and Ga doped ZnO thin films were synthesized by the sol–gel spin coating technique. The effect of Ga contribution on the structural, morphological and optical properties of the ZnO thin films was examined. XRD results showed that all films had a hexagonal wurtzite crystal structure with polycrystalline nature. The intensity of the (002) peak changed with the variable Ga content. The scanning electron microscopy (SEM) results revealed that the surface morphology of the ZnO thin films was affected by Ga content. Moreover, it consisted of nanorods as a result of the increased function of the Ga content. Additionally, the presence of Ga contributions was evaluated by energy dispersive x-ray (EDX) measurements. Although the transparency and the optical band gap of the ZnO thin films increased with Ga contribution, Urbach energy values decreased from 221meV to 98meV. In addition, these steepness parameters increased with the increased Ga content from 0% to 6%. The correlation between structural and optical properties was investigated and significant consistency was found.