Ultrasonic Assisted Chemical Vapor Deposition Research Articles

Synthesis of thin single-crystalline α-Cr-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- layers on sapphire substrates by ultrasonic-assisted chemical vapor deposition

Single-crystalline α-Cr2O3 layers were synthesized on a sapphire substrate with a basal orientation in a laboratory reactor using ultrasonic-assisted chemical vapor deposition in the temperature range of 700-850oC. The influence of the growth temperature on the structural quality of the layer was studied by X-ray diffraction. At a growth temperature of 800oC, continuous layers with a thickness of about 1 μm were obtained. The layers were transparent in the visible region with a slightly greenish tint and showed some light transmission up to wavelengths of ~ 350 nm. The full width at half maximum of the rocking curve for reflection 0006 was ~ 300 arcsec. Keywords: chromium oxide, CVD epitaxy, wide-bandgap semiconductor.

Тонкие монокристаллические слои α-Cr-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-, выращенные на подложках сапфира в реакторе ультразвуковой паровой химической эпитаксии

Single-crystalline α-Cr2O3 layers were synthesized on a sapphire substrate with a basal orientation in a laboratory reactor using ultrasonic-assisted chemical vapor deposition in the temperature range of 700-850°C. The influence of the growth temperature on the structural quality of the layer was studied by X-ray diffraction. At a growth temperature of 800°C, continuous layers with a thickness of about 1 μm were obtained. The layers were transparent in the visible region with a slightly greenish tint and showed some light transmission up to wavelengths of ~350 nm. The full width at half maximum of the rocking curve for reflection 0006 was ~ 300 arcsec.

Optimization of Synthesis Conditions of Carbon Nanotubes via Ultrasonic-Assisted Floating Catalyst Deposition Using Response Surface Methodology.

The growing use of carbon nanotubes (CNTs) in a plethora of applications has provided to us a motivation to investigate CNT synthesis by new methods. In this study, ultrasonic-assisted chemical vapor deposition (CVD) method was employed to synthesize CNTs. The difficulty of controlling the size of clusters and achieving uniform distribution—the major problem in previous methods—was solved by using ultrasonic bath and dissolving ferrocene in xylene outside the reactor. The operating conditions were optimized using a rotatable central composite design (CCD), which helped optimize the operating conditions of the method. Response surface methodology (RSM) was used to analyze these experiments. Using statistical software was very effective, considering that it decreased the number of experiments needed to achieve the optimum conditions. Synthesis of CNTs was studied as a function of three independent parameters viz. hydrogen flow rate (120–280 cm3/min), catalyst concentration (2–6 wt %), and synthesis temperature (800–1200 °C). Optimum conditions for the synthesis of CNTs were found to be 3.78 wt %, 184 cm3/min, and 976 °C for catalyst concentration, hydrogen flow rate, and synthesis temperature, respectively. Under these conditions, Raman spectrum indicates high values of (IG/ID), which means high-quality CNTs.

Influence of compactness and formation of metallic secondary phase on the thermoelectric properties of Cu2ZnSnS4 thin films

Thermoelectric studies of Cu2ZnSnS4 (CZTS) thin films deposited at different substrate temperatures by ultrasonic assisted chemical vapor deposition technique have been carried out. In order to identify the effect of compactness, crystallinity and formation of secondary phases (Cu2−xS and SnS2) on the thermoelectric properties of CZTS thin films, the films were deposited at different substrate temperatures. Detailed analysis of temperature dependent electrical resistivity (ρ) and Seebeck coefficient (S) have been carried out. Significant enhancement in the value of thermoelectric power factor (S2/ρ) is achieved in CZTS film deposited at 375°C substrate temperature, which is correlated to the compactness of thin films, improved crystallinity and presence of metallic secondary phase. Furthermore, Surface topography and surface potential studies also carried out to study the roughness and distribution of interfaces between CZTS and secondary phases (Cu2−xS and SnS2) in CZTS thin films.

Electrical conduction noise and its correlation with structural properties of Cu2ZnSnS4 thin films

Cu2ZnSnS4 (CZTS) thin films have been deposited by ultrasonic assisted chemical vapor deposition in a single step process at different substrate temperatures and structural, morphological, electrical and conduction noise characteristics of the CZTS thin films have been studied. Single phase CZTS thin films are formed at 275 °C and 325 °C deposition temperatures, whereas the CZTS thin film deposited at 375 °C showed secondary phase also. The crystallinity of the films improves and resistivity decreases with the increases of the deposition temperature. The temperature dependent electrical conductivity of the films reveals that in the temperature range 300–250 K, thermally activated conduction is observed. The conduction noise in the CZTS thin films, exhibits 1/f noise in the low frequency region and found to be strongly dependent on the film deposition temperatures. The film deposited at 275 °C and 375 °C shows larger conduction noise, whereas the film deposited at 325 °C shows smaller noise. For the low frequency 1/f noise, the value of α is also found to be the minimum for the film deposited at 325 °C. The higher value of conduction noise in the film deposited at 275 °C is related to poor crystallinity and less compact morphology. For the film deposited at 375 °C, crystallinity and compactness improves, but the presence of the secondary phases seems to be responsible for generating higher noise. The smallest conduction noise of the film deposited at 325 °C is due to single phase film with better crystallinity and smaller trap density ∼5.1 × 1015 cm−2 eV−1.

Magnetically tunable bandpass filter using cobalt ferrite thin film

Abstract Cobalt ferrite thin film based low loss magnetically tunable bandpass filter in the flip chip configuration is fabricated. Cobalt ferrite thin film was synthesized by ultrasonic assisted chemical vapor deposition technique on the quartz substrate. This was overlaid on a resonator appropriately coupled to 50 Ω feed lines. The initial operating frequency (resonance frequency) of the bandpass filter was 13.8 GHz which was shifted to 12.82 GHz when a small magnetic field (~150 Oe) was applied showing a tunability of ~7%. A large variation in the tunability of the coupled filter is attributed to change in the permeability of the CFO thin film on the application of magnetic field.

Thermally activated band conduction and variable range hopping conduction in Cu2ZnSnS4 thin films

The temperature dependence of electrical conductivity of the Cu2ZnSnS4 (CZTS) thin films has been measured in order to identify the dominant conduction mechanism. These CZTS film have been deposited by ultrasonic assisted chemical vapor deposition method at different substrate temperatures in a single step process. All the films exhibit p-type semiconducting behaviour. In the high temperature range (> 250 K), the dominance of thermally activated band conduction is observed, whereas in the lower temperature region (250−70 K), the hopping conduction is present. Detailed analysis of the temperature dependence of conductivity of the films reveals that in the temperature range from 250–170 K, nearest neighbour hopping dominates, whereas in the lower temperature region (170–70 K), the dominant hopping conduction is Mott's 3D variable range hopping and not Efros-Shklovskii variable range hopping. The value of Mott's temperature is found to decrease for the CZTS films deposited at higher temperature, which has been attributed to enhanced density of states at the Fermi level.

Tuning of optical bandgap and magnetization of CoFe2O4 thin films

Single phase CoFe2O4 thin films are deposited on quartz substrates at 400 °C using ultrasonic assisted chemical vapor deposition, and the tuning of optical bandgap and saturation magnetization of films is demonstrated by varying the post deposition annealing temperature. The optical band gap varies from 1.58 to 1.41 eV and saturation magnetization increases from 4 to 46 emu/g as the post deposition annealing temperature is increased from 500 °C to 700 °C. The observed change in optical bandgap and the magnetic properties is attributed of the shifting of Co2+ from the octahedral to the tetrahedral site with the increase in the annealing temperature. Raman studies of the films support the redistribution of Co2+ among the octahedral and tetrahedral sites in CoFe2O4 films with the increase in the annealing temperature.

Temperature dependence of conduction mechanism of ZnO and Co-doped ZnO thin films

ZnO and Co-doped ZnO thin films have been deposited on the sapphire substrate by ultrasonic assisted chemical vapor deposition technique. The films were annealed in vacuum at 450 °C. All the films were highly c-axis orientated and contained no impurity phase. The temperature dependence of the electrical conductivity has been measured in order to identify the dominant conduction mechanism. In the higher temperature region the dominance of thermally activated band conduction was observed whereas in the low temperature region the hopping conduction was found to dominate. The hopping conduction mechanism in the lower temperature range in the film was Mott's Variable Range Hopping and not the Nearest Neighbor Hopping. The temperature region, where hopping conduction was dominant found to increase by Co doping in ZnO film. The localization length was found to be larger in the Co-doped ZnO film.