Substrate Room Temperature Research Articles

Room-Temperature Photochemical Copper-Mediated Fluorination of Aryl Iodides.

This report describes a method for the photochemical Cu-mediated fluorination of aryl iodides with AgF via putative aryl radical (Ar•) intermediates. It involves irradiating an aryl iodide with UVB light (λmax = 313 nm) in the presence of a mixture of CuI and CuII salts and AgF. Under these conditions, fluorination proceeds at room temperature for substrates containing diverse substituents, including alkoxy and alkyl groups, ketones, esters, sulfonate esters, sulfonamides, and protected amines. This method has been translated to radiofluorination using a combination of K18F, K3PO4, and AgOTf.

Effect of the Dielectric Barrier Discharge Plasma on the Optical Properties of CDS Thin Film

Cadmium sulphide CdS films with 200 nm have been prepared by thermal evaporation technique on glass substrate at substrate room temperature under vacuum of 10-5mbar.In this paper, the effect of Dielectric Barrier Discharge plasma on the optical properties of the CdS film. The prepared films were exposed to different time intervals (0, 3, 5, 8) min. For every sample, the Absorption A, absorption coefficient α , energy gap Eg ,extinction coefficient K and dielectric constant ε were studied. It is found that the energy gap were decreased with exposure time, and absorption , Absorption coefficient, refractive index, extinction coefficient, dielectric constant increased with time of exposure to the plasma. Our study considers the first investigation of the effect of cold atmospheric plasma on the optical properties of CdS film.

Spatial structure of radio frequency ring-shaped magnetized discharge sputtering plasma using two facing ZnO/Al2O3 cylindrical targets for Al-doped ZnO thin film preparation

Spatial structure of high-density radio frequency ring-shaped magnetized discharge plasma sputtering with two facing ZnO/Al2O3 cylindrical targets mounted in ring-shaped hollow cathode has been measured and Al-doped ZnO (AZO) thin film is deposited without substrate heating. The plasma density has a peak at ring-shaped hollow trench near the cathode. The radial profile becomes uniform with increasing the distance from the target cathode. A low ion current flowing to the substrate of 0.19 mA/cm2 is attained. Large area AZO films with a resistivity of 4.1 – 6.7×10-4 Ω cm can be prepared at a substrate room temperature. The transmittance is 84.5 % in a visible region. The surface roughnesses of AZO films are 0.86, 0.68, 0.64, 1.7 nm at radial positions of r = 0, 15, 30, 40 mm, respectively, while diffraction peak of AZO films is 34.26°. The grains exhibit a preferential orientation along (002) axis.

Embedded silver nanoparticle multilayers fabricated by femtosecond pulsed laser deposition

Deposits of exposed and embedded silver nanoparticles were grown on Si(100) and silica substrates by laser ablating high-purity silver and SiO2 targets in vacuum using a femtosecond Ti:sapphire laser delivering 45 fs pulses at 804 nm and 1 kHz repetition rate. The effect of the laser fluence and irradiation time on the obtained nanostructures was investigated using several fluences between 650 mJ/cm2 and 3.2 J/cm2 and deposition times in the range of 1-20 minutes. Optical response of the deposits was characterized using optical absorption spectroscopy and the surface morphology was studied by scanning electron microscopy (SEM). Samples with the optimal optical response were obtained by depositing three successive Ag/SiO2 bilayers at the main laser wavelength (804 nm) under vacuum at substrate room temperature. They were composed of silver nanoparticles with an average diameter of 6 nm and a narrow size distribution; each layer of these nanoparticles was then separated by silica layers of approximately 100 nm. The laser fluence and deposition time for Ag (SiO2) were 650 mJ/cm2 (3.2 J/cm2) and 1 min (10 min), respectively.

Influence of adsorption or desorption and surface diffusion on the formation kinetics of open half-monolayer coverage.

The formation kinetics of open half-monolayer films on solid substrates is studied by the deposition of particles from a gaseous (vapor) phase to a cold substrate (room temperature) provided the lateral interaction between the particles of adsorbed layer (adlayer) is attractive. A detailed analysis of two limiting cases is presented: when the half-monolayer film formation rate is limited by the adsorption of particles from the gas phase and when the formation of the half-monolayer film surface is determined by the rate of surface diffusion of the adsorbed particles. The asymptotic analysis of the coverage dispersion evolution and the characteristic spatial scale of coverage inhomogeneities at the early and late stages of relaxation of a submonolayer film after quenching under the spinodal is carried out. It is found that separation of the adlayer occurs, so inhomogeneities of submonolayer films at the later stages of the process tend to equilibrium values of coverage in any case. However, asymptotic and numerical analysis shows that in the second case for some relationship between the kinetic and thermodynamic parameters of the adlayer an intermediate asymptotic relaxation process can be observed. It testifies to a kinetic slowdown of the separation process at the spinodal values of coverages. This fact manifests as the appearance of the intermediate plateau in the evolution curves for the coverage dispersion and nonmonotonic change of the characteristic spatial scale of coverage inhomogeneities. Moreover, at the early stages of the coverage evolution, the incubation period is revealed in the development of its inhomogeneities. It is shown that at the later stages of the separation of the half-monolayer film, the characteristic spatial scale of coverage inhomogeneities increases with time according to the law τ {1/2} and the width of the transition region between enriched and depleted regions of adlayer decreases as 1/τ {1/2}.

Effect of Annealing Temperature on Structural and Electrical Properties of a-Ga as: Zn Films

GaAs:Zn films with different thickness (0.25, 0.5, 0.75 and 1.0) µm have been prepared by flash evaporation technique on glass substrate at substrate room temperature under vacuum of 10 -5 mbar. These films have been annealed at different annealing temperatures Ta (373and 473) K. The d.c. conductivity for all deposited films decreases with increases of annealing temperatures. The electrical activation energies (Ea1and Ea2) increase with increasing of annealing temperatures. Hall measurements showed that all the films are p- type with carrier's concentration increase with thickness increase and decreases from with increasing of annealing temperature from RT to 473K. Also we observe that the mobility increase with increasing of annealing temperature and decreasing with thickness. the structural characteristic of GaAs:Zn have been studied by using X-ray diffraction which show that the films have amorphous structure for sample annealed at Ta> 473K.The samples were annealed at 473 K showed a polycrystalline with Face-center cubic system preferred orientation along (111).

Femtosecond pulsed laser deposition of nanostructured TiO 2 films

Nanostructured deposits of TiO 2 were grown on Si (1 0 0) substrates by laser ablating a TiO 2 sintered target in vacuum or in oxygen using a Ti:sapphire laser delivering 80 fs pulses. The effect of the laser irradiation wavelength on the obtained nanostructures, was investigated using 800, 400 and 266 nm at different substrate temperatures and pressures of oxygen. The composition of the deposits was characterized using X-ray photoelectron spectroscopy (XPS) and the surface morphology was studied by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM). Deposits are absent of microscopic droplets in all conditions explored. The best deposits, constituted by nanoparticles of an average diameter of 30 nm with a narrow size distribution, were obtained at the shorter laser wavelength of 266 nm under vacuum at substrate room temperature.

Controlled growth of high-quality poly-silicon thin films with huge grains on glass substrates using an excimer laser

As the best results reported to date, high-quality poly-silicon thin film materials with huge grains have been fabricated on large-area glass substrates using the technique of excimer laser re-crystallization. It has been shown that the nucleation and growth of grains in poly-silicon films were well controlled. A uniform distribution of grains has been achieved at room temperature for substrates. Using a substrate temperature of 650°C, films with grains over 60 μm have been demonstrated. The excellent quality of the re-crystallized films was demonstrated using the evidence from transmission electron microscopy and secondary ion mass spectroscopy, respectively.

Thermal and catalytic decomposition of Si 2H 6 on a Ge(100)2 × 1 surface: Photoemission and LEED studies

We present photoemission and LEED results concerning the thermal and catalytic decomposition of disilane Si 2H 6 on a monocrystalline Ge(100)2 × 1 surface. The catalytic decomposition of disilane was obtained with a hot tungsten filament. Germanium substrates were heated by the Joule effect in the 20–500°C temperature range and exposed to either catalytically decomposed or undecomposed disilane. The thicknesses of the Si deposited layers were estimated from X-ray photoelectron spectroscopy (XPS) measurements. The crystalline quality of the deposited films could be controlled by angle resolved ultraviolet photoelectron spectroscopy (ARUPS), X-ray photoelectron diffraction (XPD) and low energy electron diffraction (LEED). For a substrate temperature around 350°C, the exposures to undecomposed or catalytically decomposed disilane lead to deposition of well-ordered Si thin films. At this substrate temperature, the Si growth rate was found to be 2–3 times higher when disilane was catalytically decomposed. At substrate room temperature, while some authors claimed the adsorption of undecomposed disilane on a Ge(100)2 × 1 surface, our results seem to show that no reaction occurs between undecomposed disilane and a Ge(100)2 × 1 surface. For substrate temperature above 400°C, the decrease of the Si photoemission intensities can be explained by an indiffusion of Si into Ge.

STUDIES OF LATTICE DAMAGE CAUSED BY 1MeV Si+ IMPLANTATION INTO Al0.3Ga0.7As/GaAs SUPERLATTICES AND GaAs AT ELEVATED SUBSTRATE TEMPERATURE

Rutherford backscattering/channeling technique has been used to investigate the lattice damage caused by 1MeV Si+ implantation into Al0.3Ga0.7As/GaAs superlattices and GaAs at elevated substrate temperature and room temperature for different doses. For elevated substrate temperature irradiation, a dose range for balance between defect production and dynamic annealing, and a critical dose for unbalance between them are observed for both Al0.3Ga0.7As/GaAs superlattices and GaAs. The superlattices are more difficult to be damaged than GaAs, and the critical dose for the former is also larger than that for the latter. The hot spot and knock-on model is used to interpret the temperature and dose dependence of damage accumulation in the two materials. The ralative bona strength in GaAs and ＡｌxＧａ1-xAs are calculated using CNDO/2 quantum chemistry method to explain the differences of damage accumulation in Al0.3Ga0.7As/GaAs superlattices and GaAs.