Glancing Angle X-ray Diffraction Studies Research Articles

Effect of Capping-Agent Concentration on Size and Size Dispersity of Palladium Nanoparticles for Resistive-Type Hydrogen Sensors

The size attributes in palladium nanoparticle yield were found to influence the hydrogen sensor response in resistive devices, and the sensing mechanism was correlated with the variation of particle size from large to small in a particular synthesis product. The quantity of polyvinylpyrrolidone (PVP), the stabilizer used in this study, was varied during synthesis, and the resulting sizes were determined by high-resolution transmission electron microscopy (HRTEM). The size tuning by the capping agent PVP was also confirmed by UV–Vis spectroscopy via a detailed analysis of the experimental spectra, which revealed an interesting shift of the major absorption peaks with the increase in PVP. Glancing-angle x-ray diffraction (GAXRD) studies were undertaken to highlight the face-centred cubic crystallinity of the drop-cast nanofilms on thin glass substrates, as well as to evaluate the variation in crystallite cluster size by analyzing the major diffraction peaks. The size variation from HRTEM and GAXRD studies was found to match within the limits of experimental accuracy. The hydrogen sensor studies showed good room temperature response with typical size-dependent characteristics. The mechanistic control of the hydrogen activity over the mixed sized nano-films at room temperature (RT) and beyond RT is elaborately discussed.

Optical properties of amorphous Na2O-WO3-B2O3 thin films deposited by electron beam evaporation

Thickness dependencies of the optical properties of as-deposited amorphous 30Na2O-10WO3-60B2O3 prepared by electron beam evaporation on glass substrates at a base pressure of 9×10−7Torr have been studied. Glancing angle X-ray diffraction studies were performed to confirm the amorphous nature of the prepared films. The absorption coefficient α, therefore extinction coefficient k, have been determined from the reflectance and transmission spectra at the strong absorption region. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple – DiDomenico model. The optical constants such as optical band gap, Urbach energy, the average excitation energy Eo and Ed the dispersion energy of thin films were determined. The optical data revealed the existence of allowed indirect transitions.

Optical properties of amorphous Li2O–WO3–B2O3 thin films deposited by electron beam evaporation

Thickness dependencies of the optical properties of as-deposited amorphous 30Li2O–10WO3–60B2O3 thin films prepared by electron beam evaporation on glass substrates at a base pressure of 9×10−7Torr were studied. Glancing angle X-ray diffraction studies were performed to confirm the amorphous nature of the prepared films. The absorption coefficient α (and therefore the extinction coefficient k) was determined from the reflectance and transmission spectra in the strong absorption region. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. The optical constants, such as optical band gap, Urbach energy, the average excitation energy Eo and the dispersion energy Ed, of the thin films were determined. The optical data revealed the existence of allowed indirect transitions.

Swift heavy ion induced topography changes of Tin oxide thin films

Monodisperse tin oxide nanocrystalline thin films are grown on silicon substrates by electron beam evaporation method followed by 100MeV silver ion bombardment with varying ion fluence from 5×1011 ionscm−2 to 1×1013 ionscm−2 at constant ion flux. Enhancement of crystallinity of thin films with fluence is observed from glancing angle X-ray diffraction studies. Morphological studies by atomic force microscopy reveal the changes in grain size from 25nm to 44nm with variation in ion fluence. The effect of initial surface roughness and adatom mobility on topography is reported. In this work correlation between ion beam induced defect concentration with topography and grain size distribution is emphasized.

Swift heavy ion induced surface modification for tailoring coercivity in Fe–Ni based amorphous thin films

Fe–Ni based amorphous thin films were prepared by thermal evaporation. These films were irradiated by 108 MeV Ag8+ ions at room temperature with fluences ranging from 1×1012 to 3×1013 ions/cm2 using a 15 UD Pelletron accelerator. Glancing angle x-ray diffraction studies showed that the irradiated films retain their amorphous nature. The topographical evolution of the films under swift heavy ion (SHI) bombardment was probed using atomic force microscope and it was noticed that surface roughening was taking place with ion beam irradiation. Magnetic measurements using a vibrating sample magnetometer showed that the coercivity of the films increases with an increase in the ion fluence. The observed coercivity changes are correlated with topographical evolution of the films under SHI irradiation. The ability to modify the magnetic properties via SHI irradiation could be utilized for applications in thin film magnetism.

ALD Approach toward Electrodeposition of Sb2Te3 for Phase-Change Memory Applications

This paper describes various studies undertaken to devise a deposition cycle for the formation of , a phase-change memory material, by electrochemical atomic layer deposition (EC-ALD). The importance of deposition potentials to the formation of deposits of Sb and Te, were investigated. The resulting potentials were then used in an EC-ALD cycle to form deposits one atomic layer at a time, using a sequence of surface limited reactions. The optimal deposition potentials for the EC-ALD cycle, on a Au substrate, consisted of for Sb deposition, and for Te. Bulk Te stripping at was performed at . The conditions using a TiN substrates included Sb deposition at , Te deposition, and bulk stripping at and , respectively. The deposits obtained were stoichiometric, with a atomic ratio of 1.5 from electron probe microanalysis. Glancing angle X-ray diffraction studies showed a (015) preferred orientation for the deposit. was shown to grow successfully on patterned TiN substrates with vias.

Synthesis of GaN phase by ion implantation

GaN phase is synthesized using systemic implantation of nitrogen ions of multiple energies (290, 130 and 50 keV) into Zn-doped GaAs (1 0 0) at room temperature and subsequent annealing at 850 °C for 30 min in Ar + H 2 atmosphere. The implanted doses of nitrogen ions are 5 × 10 16 and 1 × 10 17 ions-cm −2. Glancing angle X-ray diffraction studies show that hexagonal phase of GaN were formed. The photoluminescence studies show the emission from the band edge as well as from point defects.

Optimization of CdTe nanofilm formation by electrochemical atomic layer epitaxy (EC-ALE)

This paper concerns optimization studies of the growth of cadmium telluride, an important II–VI compound semiconductor, using electrochemical atomic layer epitaxy (EC-ALE). The importance of the potentials used to deposit atomic layers of Cd and Te, as well as the potential used to strip excess Te, were investigated. These potentials were used in a cycle, an EC-ALE cycle, to form deposits one atomic layer at a time, using a sequence of surface limited reactions. The optimal potentials for the CdTe EC-ALE cycle included Cd deposition at − 0.65 V, Te deposition at − 0.35 V and bulk Te stripping at − 0.70 V. The deposits obtained were stoichiometric, with a Te/Cd atomic ratio of 1.01 from electron probe microanalysis (EPMA). Electrochemical quartz crystal microbalance (EQCM) studies of the optimal condition indicated that about a third of the deposited Cd was oxidatively stripped at the potential used to deposit Te. Glancing angle X-ray diffraction studies showed a (111) preferred orientation for the deposit, while room temperature near infrared absorption measurements indicated a direct band gap of 1.5 eV.

Characterizations of porous titania thin films produced by electrochemical etching

Porous titania templates were prepared by thermal oxidation followed by electrochemical etching. A thin layer (10 nm) of Ti–2 wt%Al was deposited on 0.25 mm titanium substrates having a thick (100 nm) gold coating on the back surface. The substrates were then thermally oxidized at 800 °C in 1% O 2/Ar ambience. Aluminium was used to dope the titanium dioxide films in order to increase the non-stoichiometry in the oxide matrix and hence the conductivity. The as-grown oxide was then electrochemically etched in 0.1 M dilute sulphuric acid medium under 10 V potentiostatic bias for 30 min. For photo-electrochemical etching the oxide samples were exposed to 400-W UV radiations. The crystalline composition of the as-oxidized and electrochemically etched samples was analyzed by glancing angle X-ray diffraction studies (GAXRD) at different incident angles (0.2°, 0.5°, 1.0° and 10°). The surface morphology was studied by scanning electron microscopy (SEM) and the rms roughness of the porous surfaces was obtained from atomic force microscopy (AFM) studies. Resistivity and Hall Effect experiments at room temperature revealed n-type semiconducting nature of the grown oxide. The sensor study with palladium catalytic contact showed high sensitivity and fast response in 500 and 1000 ppm hydrogen. The calculated response time in 1000 ppm hydrogen was 5 s at 300 °C.

Effect of mechanical stress on the absorption band tail of cubic boron nitride thin films synthesized by inductively coupled radio-frequency plasma chemical vapour deposition

Thin films of cubic boron nitride were deposited on silica and Si substrates by inductively coupled radio-frequency plasma chemical vapour deposition (IPCVD) technique using a B2H6 + N2 + Ar gas mixture. Cubic phase formation was confirmed by glancing-angle X-ray diffraction studies, which showed reflections up to (311). Fourier-transform infrared (FTIR) spectra also indicated the predominantly cubic nature of the deposited films. The optical properties of the films were studied in the wavelength range 200–1000 nm. Both direct and indirect transitions were found to be present. Mechanical stress in the grain-boundary region of the films seems to contribute significantly to the optical absorption below the band gap. The intercrystalline barrier height (E b) and the trap state density (Q t ) were obtained from an analysis of the effects of grain boundaries on the optical properties of the samples.

QUANTUM CONFINEMENT EFFECT IN HgTe NANOCRYSTALS AND VISIBLE LUMINESCENCE

Mercury Telluride ( HgTe ) nanocrystals with a mean size of 5.35 nm have been synthesized by an electrochemical technique. Structural analysis by transmission electron microscopy and glancing angle X-ray diffraction studies indicate the presence of cubic phase HgTe nanocrystals in the deposit. Optical absorption measurements reveal two well resolved excitonic peaks around 578.5 nm and 550 nm attributed to heavy hole valence band (HVB)–conduction band (CB) and light hole valence band (LVB)–CB transitions, respectively, and suggest a band opening of bulk inverted narrow band gap HgTe as a result of strong quantum confinement effect (QCE). Visible photoluminescence (PL) of HgTe nanocrystals indicates free exciton transition around 579.5 nm as observed from the PL measurement at 300 K along with a bound exciton dominated band around 588 nm. Micro-Raman measurements at 300 K indicate the 1LO vibrational mode at 142.6 cm-1 shifted by 6 cm-1 from its standard bulk value and confirm the QCE.

Low-resistance and thermally stable Pd/Re ohmic contacts to p-type GaN

We have investigated a low-resistance thermally stable Pd/Re ohmic contact on moderately doped p-GaN:Mg (1.1 × 1017 cm−3). It is shown that the I–V characteristic of the as-deposited sample is improved upon annealing at 550 °C for 1 min under N2 ambient. However, annealing the sample at 650 °C results in the degradation of the I–V behaviour. Specific contact resistance as low as 8.7 × 10−4 Ω cm2 is obtained from the Pd(20 nm)/Re(25 nm) contact annealed at 550 °C. It is also shown that the contact exhibits thermal stability during annealing at 550 °C. Auger electron microscopy and glancing angle x-ray diffraction studies are carried out to characterize interfacial reactions between the Pd/Re contacts and the GaN.

A novel route of synthesis of aluminium nano-aggregates: an ion beammodification in metal-organic complex

A novel route for the formation of nano-aggregates of aluminium by ionirradiation of a spin-cast metal-organic thin film of aluminium acetylacetonate [((CH3CO)2CH)3Al] is reported. Glancingangle x-ray diffraction studies on an irradiated sample show the formation of fccaluminium clusters. Microstructural studies using transmission electronmicroscopy show the formation of aggregated branched nanoclusters of diameter≈5-60 nm, which on increasing fluences interconnect through branchesand form a network-like structure. Networked structures of aggregated Alclusters might have formed due to overlapping of multiple ion tracks atrelatively higher fluences.

Effect of fluorine-ion implantation on buried nitride silicon-on-insulator structures

Effect of fluorine-ion (19F+) implantation on the buried silicon nitride silicon-on-insulator (SOI) structures was investigated. Fluorine was introduced before and after the synthesis of buried Si3N4 layers in silicon by high-dose nitrogen ion (14N+) implantation. Infrared transmission spectropscopy and glancing angle x-ray diffraction studies show that 19F+ implantation before SOI synthesis inhibits the growth of larger-size polycrystalline Si3N4 grains, whereas after the synthesis it removes undesired polycrystalline silicon and helps to obtain larger-grain-size α-polycrystalline silicon nitride in few preferred planes.

High-temperature annealing characteristics of tungsten and tungsten nitride Schottky contacts to GaAs under different annealing conditions

We have systematically investigated the structural and electrical characteristics of thin-film tungsten and reactively sputtered tungsten nitride (WNx) Schottky contacts to GaAs under high-temperature annealing conditions (with annealing temperatures ranging from 700 to 850 °C) in an arsenic-overpressure and flowing nitrogen ambient with and without a silicon dioxide capping layer. Compositions of the WNx films measured by Rutherford backscattering spectrometry and proton resonant scattering techniques indicate a linear relationship between x and the nitrogen partial pressure during sputtering. Glancing angle x-ray diffraction studies revealed that for nonzero nitrogen partial pressure, the as-deposited films were amorphous, and after annealing these films converted to polycrystalline W2 N and W phases. A surface layer of W2 As3 phase was also observed after As-overpressure capless annealing and was believed to be the result of reactions between W and the ambient As gas. Electrical measurements showed that all WNx /GaAs contacts (with x=0–0.5) were thermally stable up to an annealing temperature of 850 °C. A diode edge effect is observed for WNx /GaAs diodes cap annealed in As overpressure at temperatures higher than 800 °C. The maximum achievable Schottky barrier heights for these contacts were found to be independent of the nitrogen content in the films but are influenced by the annealing conditions. We also explored the role played by nitrogen on the thermal stability and barrier height of the contacts.