Increase In O2 Pressure Research Articles

Tailoring pulsed laser deposition of phosphorus doped WOx films from (PO2)4(WO3)4 target by space-resolved optical emission spectroscopy.

Phosphorus doped WOx films were deposited on fused silica substrates from a target of monophosphate tungsten bronze (PO2)4(WO3)2 m with m = 2. Different conditions of O2 pressures and substrate temperature depositions were performed in parallel to plasma investigations during the depositions step. Changes were observed in the film stoichiometries affecting the film properties while the increase of the O2 pressure. Optical bandgap was shifted from 3.39 eV to 3.86 eV as a function of the deposition pressure from 7.5 Pa to 20 Pa. In situ optical emission spectroscopy was carried out in all the O2 atmosphere conditions. With an increase in the oxygen pressure to 5 Pa, a change in the spectral composition of the plasma with a deficit of the phosphorus lines was observed. A complex plasma containing atoms and multiple ionized ions attributed to each composing species was observed at high O2 pressures of deposition. The increase in O2 pressure led to strong thermalization of the plasma and strong scattering of the plasma particle which created a favourable environment for the WO3 formation.

Stoichiometric dependent optical limiting in PLD SiOx thin films

In this letter, optical limiting property of the insufficiently oxidized silicon oxide (SiOx) thin films is reported. Films were deposited by Pulsed Laser Deposition technique using Q-switched Nd: YAG laser (532 nm) onto fused silica substrate at a substrate temperature of 400 °C by varying the O2 pressure in the range of 5×10 -5 to 0.5 mbar. Energy Dispersive X-Ray spectra showed the increase in oxygen content with increasing O2 pressure. Raman spectra of SiOx films depicted the presence of micron sized clusters composed of nanocrystalline Silicon embedded in uniform matrix of oxidized amorphous Silicon. The open Z-scan of the thin films, under cw He-Ne laser irradiation, showed strong reverse saturation absorption (RSA) features and non linear absorption (NLA) coefficient, β, was found to be decreasing from 23.5 cm/W to 1.64 cm/W, with increase in O2 pressure from 5×10 -5 to 10 -1 mbar, respectively. Also, the SiOx films except that with maximum oxygen content showed optical limiting, where limiting threshold increases with increasing transparency controlled by oxygen content. The key feature of the present work is the tunability in linear absorption, nonlinear RSA and optical limiting in the SiOx films which can be used as novel material for optical switching application.

Effect of oxygen partial pressure on structural and optical properties of pulsed laser deposited CaBi4Ti4O15 thin films

The influence of oxygen partial pressure (OPP) on the structural and optical properties of CaBi4Ti4O15 (CBTi) thin films deposited by pulsed laser deposition have been investigated in the range of 0.1mbar to 7.8×10−3mbar. The structural properties show all the films are polycystlline in nature with orthorombic structure. The optical transmission of the films is in the range of 60–90%. A slight shift in transmission threshold towards higher wavelength region with an increase in O2 pressure reveals the systematic reduction in the optical band gap energy (3.69 to 3.59eV) of the films. Raman studies confirm the phase formation and presence of stresses in the films. It is suggested that the OPP played a key role in controlling crystallinity, morphology, chemical composition and optical properties in CBTi thin films.

The influence of oxygen partial pressure on material properties of Eu3+-doped Y2O2S thin film deposited by Pulsed Laser Deposition

Eu3+-doping has been of interest to improve the luminescent characteristics of thin-film phosphors. Y2O2S:Eu3+ films have been grown on Si (100) substrates by using a Pulsed Laser Deposition technique. The thin films grown under different oxygen deposition pressure conditions have been characterized using structural and luminescent measurements. The X-ray diffraction patterns showed mixed phases of cubic and hexagonal crystal structures. As the oxygen partial pressure increased, the crystallinity of the films improved. Further increase of the O2 pressure to 140mtorr reduced the crystallinity of the film. Similarly, both scanning electron microscopy and Atomic Force Microscopy confirmed that an increase in O2 pressure affected the morphology of the films. The average band gap of the films calculated from diffuse reflectance spectra using the Kubelka–Munk function was about 4.75eV. The photoluminescence measurements indicated red emission of Y2O2S:Eu3+ thin films with the most intense peak appearing at 619nm, which is assigned to the 5D0–7F2 transition of Eu3+. This most intense peak was totally quenched at higher O2 pressures. This phosphor may be a promising material for applications in the flat panel displays.

Influence of gas atmosphere during laser surface treatment of CNT cathode

An ultraviolet laser was used to irradiate the screen-printed carbon nanotube (CNT) cathodes in air, N2, and O2 atmospheres in various pressures. The emission current density of CNT cathodes at a field of 6.6V∕μm was increased by a factor of 400 after laser irradiation in an O2 atmosphere, which was enhanced by the increase in O2 pressure. On the other hand, N2 has less influence on the laser irradiation effect. The enhancement in electron emission by laser irradiation in air was found to be 20% of that in an O2 atmosphere with the same pressure, because of the partial pressure of the oxygen in air.

Properties of hafnium oxide films grown by atomic layer deposition from hafnium tetraiodide and oxygen

Polycrystalline monoclinic HfO2 films were atomic layer deposited on Si(100) substrates by a nonhydrous carbon-free process of HfI4 and O2. The oxygen to hafnium ratio corresponded to the stoichiometric dioxide within the limits of accuracy of ion beam analysis. A 1.5–2.0 nm thick SiO2 interface layer formed between the HfO2 films and Si substrates. Hysteresis of the capacitance–voltage curves was observed in Al/HfO2/p-Si(100) structures with oxide grown in the substrate temperature range of 570–755 °C. The hysteresis ceased with an increase in O2 pressure. The effective permittivity of the dielectric layers varied between 12 and 16. The breakdown voltages were found to be lower in the case of higher oxygen doses and higher HfO2 deposition temperatures.

Effects of Oxygen on the Electron Current from a Heated Tungsten Field Emission Tip

The emission current from a tungsten tip was measured as a function of O2 pressure (9.4×10-11∼3.9×10-9 Torr) and of tip temperature (1170∼1530°K). Following results have been shown: (1) With the elapse of time, a sequence of a minimum and a maximum appears in the emission current. (2) The minimum and the maximum decrease with increase in O2 pressure. (3) The maximum decreases as the tip temperature is lowered or raised from 1290°K. (4) The time t0 at which the maximum appears decreases as the O2 pressure p increases. Linear relations hold between log p and log t0; the slope of the straight line decreases with increase in the tip temperature. It is shown that a combined consideration of O2 adsorption and build-up of tungsten oxides may account for the results.