Increase In Dopant Level Research Articles

Promoting Active Electronic States in LaFeO3 Thin-Films Photocathodes via Alkaline-Earth Metal Substitution.

The effects of alkaline-earth metal cation (AMC; Mg2+, Ca2+, Sr2+, and Ba2+) substitution on the photoelectrochemical properties of phase-pure LaFeO3 (LFO) thin-films are elucidated by X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflectance, and electrochemical impedance spectroscopy (EIS). XRD confirms the formation of single-phase cubic LFO thin films with a rather complex dependence on the nature of the AMC and extent of substitution. Interestingly, subtle trends in lattice constant variations observed in XRD are closely correlated with shifts in the binding energies of Fe 2p3/2 and O 1s orbitals associated with the perovskite lattice. We establish a scaling factor between these two photoemission peaks, unveiling key correlation between Fe oxidation state and Fe-O covalency. Diffuse reflectance shows that optical transitions are little affected by AMC substitution below 10%, which are dominated by a direct bandgap transition close to 2.72 eV. Differential capacitance data obtained from EIS confirm the p-type characteristic of pristine LFO thin-films, revealing the presence of sub-bandgap electronic state (A-states) close to the valence band edge. The density of A-states is decreased upon AMC substitution, while the overall capacitance increases (increase in dopant level) and the apparent flat-band potential shifts toward more positive potentials. This behavior is consistent with the change in the valence band photoemission edge. In addition, capacitance data of cation-substituted films show the emergence of deeper states centered around 0.6 eV above the valence band edge (B-states). Photoelectrochemical responses toward the hydrogen evolution and oxygen reduction reactions in alkaline solutions show a complex dependence on alkaline-earth metal incorporation, reaching incident-photon-to-current conversion efficiency close to 20% in oxygen saturated solutions. We rationalize the photoresponses of the LFO films in terms of the effect sub-bandgap states on majority carrier mobility, charge transfer, and recombination kinetics.

Influence of nitrogen doping on TiO2 nanoparticles synthesized by pneumatic spray pyrolysis method

Improving the photon harvesting efficiency of dye sensitized solar cells (DSSCs) employing TiO2 photo-anode has been the major issue since 1991. So it is very important to discover new techniques that will enhance the properties of TiO2 nanoparticles (NPs) which will then prevent recombination of the photo-generated electron hole pairs and as well as improving the visible absorption properties of the TiO2. This will in turn improve the performance of the DSSC photo-electrode. The optical, electronic and structural properties of TiO2 NPs rely on factors like morphology, surface area, particle size and the presence of beneficial defects caused by dopants. This study focuses on the fabrication and characterization of nitrogen doped TiO2 (NPs) prepared by pneumatic spray pyrolysis (PSP) technique. The un-doped and nitrogen doped TiO2 NPs were prepared using titanium butoxide as a precursor and urea as the dopant. The morphological and structural properties of PSP synthesized NPs were evaluated using SEM, EDX, Raman Spectroscopy (RS), XRD and FTIR. SEM analysis revealed that the presence of nitrogen dopant results in a significant change in the surface morphology of the PSP synthesized NPs. RS revealed the presence of Raman vibrational modes and symmetry at 158 (Eg(1)), 208 (Eg(2)), 258 (B1g), 255 (B1g) 396 (B1g), 514 (A1g + B1g(2)) and 640 (Eg(3)) belonging to a mixed Anatase-Rutile phase. XRD analysis revealed that the PSP synthesized NPs have particles sizes of 10.90 nm, 11.31 nm, 11.93 nm and 14.14 nm for un-doped TiO2, 0.005 M TiO2, 0.015 M TiO2 and 0.025 M TiO2 NPs respectively. FTIR spectra of the PSP fabricated samples exhibited a peak at 616.22 cm−1 that is assigned to Ti–O vibrational stretching of the anatase phase of TiO2. UV–vis spectroscopy revealed a decrease in energy band gap with increase in dopant level for the TiO2 samples prepared.

Doping of metastable Cu3N at different Ni concentrations: Growth, crystallographic sites and resistivity

Copper nitride, Cu3N, is a metastable material whose properties can be changed considerably by doping with metals which opens for a variety of applications in several areas (sensors, electrical connects, batteries, memories, etc.). The present work is a systematic study in the system Cu-Ni-N of preferences regarding occupation of interstitial and substitutional crystallographic sites in the Cu3N structure as the metal dopant level increases and how the occupation influences growth behavior, texture, microstructure and resistivity. Ni doped Cu3N films of different chemical composition were grown by a gas-pulsed Chemical Vapor Deposition technique. The occupation of the different crystallographic sites of the Cu3N by the Ni atoms was obtained from analysis of X-ray diffraction data. At low Ni content, less than about 21% in metal content, Ni replaced the Cu atoms in the structure. In the intermediate Ni metal content range from about 21 to 40% the vacant centre position became available. After filling the centre position, substitution of Cu for Ni occurred up to a Ni content of about 80% (Cu0.8Ni3.2N) which is the solid solubility limit of Ni in Cu3N. The film resistivity decreased rapidly by adding nickel to the Cu3N structure from about 109μΩ·cm without any Ni doping to about 100μΩ·cm with 80% Ni in the metal content. After filling the centre position the change in resistivity when Cu atoms were substituted for Ni was very small. Finally, the growth mechanism, texture and microstructure changed significantly with the uptake of Ni atoms in the structure.

Structural, optical and electrical properties of Ni doped ZnO nanostructures synthesized by solution combustion method

In this work, pure and Ni-doped ZnO nanostructures (NSs) with different concentrations of Ni (2, 4, 6%) were successfully prepared via solution combustion method. The TEM photograph shows the formation of flake-like structures with the decrease in size of NSs as the dopant concentration is increased. XRD investigation shows the hexagonal wurtzite structure of doped and undoped ZnO nanostructures with a NiO peak (200) as secondary phase for 4 and 6% dopant concentration level. Broadening of spectra of ZnO around 480 cm−1 in FTIR spectra is observed with the increase of dopant concentration. UV–Visible spectra show the increase in absorbance when the dopant level (Ni2+) is increase from 2 to 4% in ZnO and decrease in absorbance with further increase in dopant level to 6%. An increase in energy band gap is observed in Ni (6%)-doped ZnO due to due to the sp–d interactions taking place between the band electrons and the localised d electrons of Ni2+ ions (Burstein-Moss effect). I–V characteristics reveal the increase in current with the increase in dopant level from 2 to 4% and decrease in current when the dopant level is further increased to 6% which is in agreement with the Burstein-Moss effect.

Room temperature variation in dielectric and electrical properties of Mn doped SnO2 nanoparticles

Pure and Mn doped SnO2 nanoparticles of the composition MnxSn(1-x)O2 where (x = 0.0, 0.03, 0.05, 0.07) were synthesized by sol gel auto combustion method. Structural studies performed by XRD and EDS suggest that the crystal system remains pure rutile with a tetragonal structure even after the doping of Mn. The EDS analysis reveals that both Sn and Mn elements are present in the sample which confirmed the successful doping of Mn in the SnO2 host structure. The identification of the various chemical bonds present in the pure and Mn doped samples has been carried out through Fourier Transform Infrared spectroscopy. FTIR spectrum has been recorded in solid phase using KBr pellets technique in the regions of 4000–400 cm-1. The complex dielectric constant, complex impedance, and a.c. conductivity have been studied as function of frequency and composition using LCR meter. Dielectric constant and loss was found to decrease with the increase in frequency and the obtained results have been explained on the basis of Maxwell-Wagner model. A.C. conductivity was found to increase with the increase in frequency due to hopping between charge carriers. It increases with the increase in dopant level which may be due to the free electron density and crystalline size.

CSA-doped PANI semiconductor nanofilms: synthesis and characterization

Camphorsulfonic acid doped polyaniline (PANI-CSA) prepared by chemical oxidative polymerization is dip coated on glass plates with three different PANI:CSA weight ratios (1:0.5, 1:1 and 1:2). Films of thickness being <100 nm are termed as nanofilms. Fourier transform infrared spectroscopy indicated the presence of dopant and increase in degree of polymerization with increase in dopant level. X-ray diffraction studies revealed the amorphous nature of the films. Scanning electron microscopy showed very smooth morphology without any crack or pores. Hall-effect analysis showed that the increase in CSA weight ratio appreciably increases the conductivity of PANI-CSA films due to increase in carrier concentration and it also represents the semiconductivity (P-type) nature in all the films. UV–visible absorption spectra and photoluminescence spectra revealed that high intense absorption and emission peaks occur for the PANI-CSA film with PANI:CSA weight ratio (1:2). This appreciable increase is due to increase in charge carriers. Photoluminescence study of PANI-CSA films excited using 300 nm shows high intense peaks at 361 and 494 nm and a weak peak at 410 nm which confirmed the semiconducting nature of the film.

Effect of Dopants and Surface Morphology on the Absorption Edge of ZnO Films DOPED with in, Al, and Ga

We have studied the surface morphology and intrinsic absorption spectra for zinc oxide thin fi lms with different levels of doping by indium, aluminum, or gallium, deposited by high-frequency magnetron sputtering on glass substrates. We show that as the dopant concentration increases (indium >5 wt.%, aluminum >0.3 wt.%, and gallium >2.2 wt.%) in ZnO films, a decrease may occur in the average sizes of the crystallites and accordingly there may be an increase in the concentration of structural defects in the form of intercrystallite boundaries. We have established that in ZnO films, with an increase in the indium dopant concentration from 1.7 to 6.6 wt.%, the optical bandgap width decreases from 3.30 to 3.27 eV due to the increase in the number of structural defects. We estimate the concentration of free charge carriers and show that the shift in the fundamental absorption edge in thin fi lms of ZnO:Al and ZnO:Ga as the dopant level increases is due to the Burstein–Moss effect.

Deposition and Characterization of Chromium Doped Tin Oxide Transparent Conducting Thin Films Prepared by Spray Pyrolysis Technique

Emergenceof innovative technological deposition technique of spray pyrolysis enabled the enhancement of structural, optical, and electrical properties of Sn1-xCrxO2 (x=0.0, 0.02, 0.04, 0.06, 0.10, 0.15) transparent semiconductors thin films in the present study. To evaluate these properties, X-Ray diffraction (XRD) spectroscopy were usedto study the elemental component and the crystalline nature of the materials while the optical properties and structure of the samples were evaluated using UV—vis spectroscopy and field emission scanning electron microscopy (FE-SEM).Finding showed that the Cr-doped SnO2 films were tetragonal in shape. Transmission spectra of the deposited films showed high transparency of ~ 70-90% in visible region with optical edge of 3.7eVfor SnO2. Resistivity of pure tin oxide samples was 0.01 Ω-Cm and increases with increase in dopant level. The Hall voltage showed that the type of semiconductor changed with increasing of dopant.

Development of FeNiMoB thin film materials for microfabricated magnetoelastic sensors

MetglasTM 2826MB foils of 25–30 μm thickness with the composition of Fe40Ni38Mo4B18 have been used for magnetoelastic sensors in various applications over many years. This work is directed at the investigation of ∼3 μm thick iron-nickel-molybdenum-boron (FeNiMoB) thin films that are intended for integrated microsystems. The films are deposited on Si substrate by co-sputtering of iron-nickel (FeNi), molybdenum (Mo), and boron (B) targets. The results show that dopants of Mo and B can significantly change the microstructure and magnetic properties of FeNi materials. When FeNi is doped with only Mo its crystal structure changes from polycrystalline to amorphous with the increase of dopant concentration; the transition point is found at about 10 at. % of Mo content. A significant change in anisotropic magnetic properties of FeNi is also observed as the Mo dopant level increases. The coercivity of FeNi films doped with Mo decreases to a value less than one third of the value without dopant. Doping the FeNi with B together with Mo considerably decreases the value of coercivity and the out-of-plane magnetic anisotropy properties, and it also greatly changes the microstructure of the material. In addition, doping B to FeNiMo remarkably reduces the remanence of the material. The film material that is fabricated using an optimized process is magnetically as soft as amorphous MetglasTM 2826MB with a coercivity of less than 40 Am−1. The findings of this study provide us a better understanding of the effects of the compositions and microstructure of FeNiMoB thin film materials on their magnetic properties.

Effect of Mn-Doping on Structural, Optical, and Dielectric Properties of SnO2 Nanoparticles by Coprecipitation Method

Pure and Mn-doped SnO2 nanoparticles are prepared by co-precipitation method. The structural analysis reveals the presence of tetragonal system of SnO2. Fourier transform infrared spectroscopy (FTIR) spectra of pure SnO2 show the occurrence of O-Sn-O vibrational mode at around 671 cm−1. It is observed that the wavenumber is shifted to lower region with the increase in Mn dopant concentration. As the Mn content is increased, a clear indication of red shift is observed in the UV-vis absorption spectra. From the scanning electron microscope (SEM) image, the surface morphology of the sample shows uniformly dispersed particles, which are spherical in shape. From dielectric studies, the dielectric constant suddenly drops to 0.5 × 106 Hz, and thereafter, it shows a constant behavior. Dielectric loss plot of the prepared samples exhibits a linear behavior at higher frequency region, which suggests the samples possess a lossless nature. The ac conductivity value drops linearly with the increase in dopant level. This is due to the particle size effect and screening effect caused by the impurities.

Spectroscopic Studies of “Exciplex Tuning” for Dicyanoaurate(I) Ions Doped in Potassium Chloride Crystals

Photoluminescence and Raman results for single crystals of KCl doped with KAu(CN)2 with different Au content are presented and compared with results for pure KAu(CN)2 crystals. Photoluminescence spectra of the doped crystals show three major UV−vis bands that can be resolved by varying the excitation wavelength. Spectroscopic and computational evidence suggests the formation of Au−Au bonded excimers and exciplexes in this doped system. The excimer/exciplex luminescence bands can be tuned in a given crystal by site-selective excitation and their relative intensities tuned by varying the dopant concentration. Microsecond lifetimes were observed for the various luminescence bands, suggesting Au-centered phosphorescent emissions. Raman spectral analysis was used successfully to correlate with the luminescence bands observed in pure and doped crystals of [Au(CN)2-] and [Ag(CN)2-] systems. The Raman νCN bands corresponding to various sites of [Au(CN)2-]n and [Ag(CN)2-]n clusters in various crystals correlated well with the luminescence spectra, in terms of both the number of peaks and their relative frequencies. The results have illustrated interesting differences in the clustering of [Au(CN)2-] versus [Ag(CN)2-] ions in the host lattice. As the dopant level increases, the extent of metal−metal interactions increases due to larger oligomers or shorter metal−metal separation, in either case leading to decreased back-bonding and higher νCN frequencies. The νCN Raman frequencies in [Au(CN)2-]/KCl crystals with increasing doping level increased beyond the value for pure KAu(CN)2 crystals, presumably due to a shorter Au−Au distance in the highest doped crystal than the distance in the pure crystal. In contrast, increasing the doping level in [Ag(CN)2-]/KCl systems resulted in the appearance of νCN Raman peaks with correspondingly higher frequencies but the values remained lower than those for pure KAg(CN)2 crystals, as expected.

Optical anisotropy of phosphorescence from photoselected benzophenone molecules in polystyrene matrices

Benzophenone present as a dopant in polystyrene matrices has been photoexcited at 406 nm and 77 K using a polarized beam from a dye laser. Polarization ratios of the phosphorescence from these directly produced triplet states were measured at delay times from 0.5 to 5.0 ms and at various dopant concentrations. At three different phosphorescence wavelengths the polarization ratios decrease as the dopant level increases. The major mechanism for emission depolarization is, evidently, energy migration. An observed dependence of the polarization ratio upon emission wavelength was tentatively ascribed to preferential coupling of triplet sublevels to upper vibrational states of the electronic ground state.

Summary of the plenary session B

The static defect structure of the oxygen ion conductor Y203 stabilized zirconia has been studied at room temperature by coherent diffuse neutron scattering from single crystal samples containing nominally 9.4, 12, 15 and 18 mol% Y203. There are two principal contributions to the observed diffuse intensity. The first arises from tetrahedral distortions in small vacancy free regions of the crystal which decrease in volume as the dopant level increases. The second arises from correlated vacancies and their associated relaxed ions in the remainder of the crystal. The 9.4 mol% sample has been studied at elevated temperatures. The scattering becomes partly quasielastic, but the correlations persist to the highest temperatures studied (1900°C). The temperature and Q-dependence of the energy width has been studied at selected positions in reciprocal space.

The defect structure of yttria-stabilized zirconia, studied by quasielastic diffuse neutron scattering

The static defect structure of the oxygen ion conductor Y 2 0 3 stabilized zirconia has been studied at room temperature by coherent diffuse neutron scattering from single crystal samples containing nominally 9.4, 12, 15 and 18 mol% Y 2 0 3 . There are two principal contributions to the observed diffuse intensity. The first arises from tetrahedral distortions in small vacancy free regions of the crystal which decrease in volume as the dopant level increases. The second arises from correlated vacancies and their associated relaxed ions in the remainder of the crystal. The 9.4 mol% sample has been studied at elevated temperatures. The scattering becomes partly quasielastic, but the correlations persist to the highest temperatures studied (1900°C). The temperature and Q -dependence of the energy width has been studied at selected positions in reciprocal space.

The defect structure of yttria-stabilized zirconia, studied by quasielastic diffuse neutron scattering

The static defect structure of the oxygen ion conductor Y203 stabilized zirconia has been studied at room temperature by coherent diffuse neutron scattering from single crystal samples containing nominally 9.4, 12, 15 and 18 mol% Y203. There are two principal contributions to the observed diffuse intensity. The first arises from tetrahedral distortions in small vacancy free regions of the crystal which decrease in volume as the dopant level increases. The second arises from correlated vacancies and their associated relaxed ions in the remainder of the crystal. The 9.4 mol% sample has been studied at elevated temperatures. The scattering becomes partly quasielastic, but the correlations persist to the highest temperatures studied (1900°C). The temperature and Q-dependence of the energy width has been studied at selected positions in reciprocal space.

Intergranular fracture, corrosion susceptibility, and impurity segregation in sensitized type 304 stainless steel

(1) Charpy impact values are a function of dopant and sensitization conditions. The impact energies are reduced especially in specimens sensitized at 750 ‡C. The reduction in impact energy is far greater in phosphorus-doped heats than in sulfur-doped heats. The fracture surfaces are transgranular for the sulfur-doped heats and intergranular for the phosphorus-doped heats. (2) The modified Strauss test shows an increase in corrosion rate when the heats are sensitized at 650 ‡C. The corrosion rate is linear with sensitization time and increases as the dopant level increases. Specimens treated at 650 ‡C separate along the grain boundaries while heat treating at other temperatures results in plastic deformation. (3) Auger spectroscopy of grain boundaries reveals that the phosphorus in the P-doped heats is segregated within 75 nm and the boundaries are saturated within 45 minutes of sensitizing at 750 ‡C.

Dependence of resistivity on the doping level of polycrystalline silicon

The electrical resistivity of polycrystalline silicon films has been studied as a function of doping concentration and heat treatment. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity of the as−deposited films was widely scattered but independent of dopant atom concentration at the lightly doped levels and was strong function of dopant level in the more heavily doped regions. Postdeposition heat treatments in an oxidizing atmosphere remove scatter in the data. The resultant resistivity for dopant levels less than 1016 atoms/cm3 was approximately equal to that of intrinsic silicon. In the next 2 orders of magnitude increase in dopant level, the resistivity dropped 6 orders of magnitude. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.