Yousong Jiang

Substrate temperature effect on the refractive index and a two-step film method to detect small inhomogeneities in optical films

Nb2O5 films were deposited by a reactive magnetron sputtering technique. The average refractive index was found to increase with the rise of substrate temperature. Modulated interference transmittance spectra were observed in the two-step films, which were prepared by stopping the deposition process in the middle of the designed sputtering time, and then, after a full cooling down to room temperature, starting the same deposition process again to complete the whole preparation of the films. A linearly graded-index model was used to explain the interference behavior. It was proved that the two-step film method was sensitive to the small inhomogeneity in the films. We also suggest that the inhomogeneity of sputtered films can be minimized by controlling the substrate temperature at a constant value.

Resputtering of zinc oxide films prepared by radical assisted sputtering

Sputtering losses of zinc oxide films prepared by radical assisted sputtering were studied. It was found that the sputtering loss can be very severe in oxygenous sputtering processes of zinc oxide films. In general, resputtering caused by negative oxygen ions dominates the sputtering loss, while diffuse deposition plays a minor role. Resputtering is strongly correlated with the sputtering threshold energy of the deposited films and the concentration of O− in the sputtering zone. The balance between the oxygen concentration in the sputtering zone and the oxidation degree of the growing films depends on the sputtering rate. Our research suggests that a lower oxygen concentration in the sputtering zone and a higher oxidation degree of the growing films are favorable for reducing the resputtering losses. The sputtering loss mechanisms discussed in this work are also helpful for understanding the deposition processes of other magnetron sputtering systems.

Small copper clusters studied by x-ray absorption near-edge structure

The local structure of copper nanoparticles grown in organic solution by reducing Cu(II) hexafluoroacetylacetonate [Cu(hfac)2] was studied as-grown by the Cu K-edge x-ray absorption near-edge structure (XANES). Comparison of the experimental XANES spectra with reference materials indicated small copper clusters are formed by ligand-exchange with oleylamine and subsequent reducing by diphenylsilane. The multiple-scattering (MS) calculation for various model clusters consisting of 13–135 atoms suggests that small (13–19 atom) Cu clusters are stabilized without a large deformation.

Graded refractive-index SiOx infrared filters prepared by reactive magnetron sputtering

Dense, uniform SiOx (0⩽x⩽2) films were deposited by reactive magnetron sputtering. By controlling the oxygen flow rate and/or sputtering power during deposition, the refractive index of SiOx films can be continuously tuned from 1.44 to 3.69 at λ=1550nm. The authors fabricated an 11-layer bandpass filter of SiOx∕SiO2 with high refractive-index contrast (nH∕nL=1.91 at λ=1550nm) and a 35-layer SiOx optical filter with a graded refractive-index profile. The measured reflectance and transmittance spectra correlate well with the designed spectra. This work demonstrates that SiOx material can be used to make infrared optical filters with graded refractive index and high refractive-index contrast.

Exactly solvable model for metal-insulator-metal stepped boundary tunnel junctions

An exactly solvable model, which treats the effective barrier potential of the biased metal–insulator–metal tunnel junctions as a trapezoidal potential with an ideal stepped boundary, is presented.Thus, the exact analytic expressions for the electron wave functions and the tunneling probabilities were obtained by solving Schrodinger’s equation strictly.It is found that if the ¨ longitudinal kinetic energy of the electron, E , is greater than the shorter side of the trapezoidal potential, in the barrier region x Schrodinger’s equation has to be solved in the two subregions: where E is lower and higher than the barrier height, respectively. x ¨ In order to compare the ideal stepped boundary model to Brinkman’s two approximation models (J.Appl.Phys.89 (1970) 1915), the graded diffuse boundary and perfectly sharp boundary model, the trapezoidal barrier parameters were determined by fitting the calculated I–V curves to the experimental ones at 77 K.The results show that for three types of junctions (with Au, Ag, and Cu top electrodes), the variations in barrier parameters with the metal electrodes are in agreement with each other. 2002 Elsevier Science B.V. All rights reserved.

Scatterless SiO 2 /TiO 2 multi-layered thick UV-IR cut filter prepared by EPD system

Scatterless SiO2/TiO2 multi-layered thick UV-IR cut filter can be prepared by the new IAD method called EPD (Effective Physical vapor Deposition).

RAS Bias Voltage Coating

In SiO2 bias voltage coating, it was suggested that densification of SiO2 occurred at high bias power. This technique shows promise for the application of electric devices such as surface acoustic wave (SAW) filter.

High-rate AR Coating for Plastic Substrate by EPD

These results indicate that EPD is the most relevant technique for AR coating on the plastic substrates and applicable to industrial production.

Structural and optical properties of titanium dioxide films produced by RAS (Radical Assisted Sputtering) coater

Titanium dioxide films were prepared by a previously described RAS (radical assisted sputtering) coater. Structural and optical properties of the films were investigated. Absorption-less multilayered optical filters were reached through 410nm to 700nm wavelength range.