Materials Science Forum Vols. 663-665

Abstract: Light amplification panel (LAP) based on laser principle is put forward in this paper. The LAP is coupled between the camera and eyepiece of the night vision devices to realize image intensification. The quality of imaging in low level light is gained enhancement. After analysis on principle of LAP, its gain, detection capability, imaging performance, noise and bandwidth are calculated theoretically. Laser media arranged alternately amplifies signals of different wavelength, broadening the bandwidth and also realizing night vision color imaging by physical mode.

Abstract: In this work, the crystallization of different silicon based thin films as the precursor of crystallization was investigated by femto-second laser with 800 nm wavelength. The linear absorption coefficient of a-Si films at that wavelength is quit lower than the other structures of Si-based thin film, which has no related with the incident light energy. However, we found that the crystallization of a-Si films was better than μc-Si films as the precursor. We use Z-scan techniques to prove that the two-photon absorption effect would be responsible for the crystallization. And unlike the linear absorption, the two-photon absorption effect is correlated with the incident light energy, as well as the micro-structure of the silicon based film. At the end of the paper, the crystallization by laser with wavelength longer than the absorption limit was discussed.

Abstract: As thin metal films are known to act as wide-band absorbers for infrared radiation, in this paper Ni metal films are prepared on the Ge surface of double-sided polishing, The results showed the absorbing properties of the metal layer are strongly influenced by the dielectric function of the sensor material. This paper also describes one multi-layers structure as absorber. The structure included a reflector layer of 100-nm-thick Ti (e-beam evaporation), 2-µm-thick polyimide(spin-coating), and 14.9-nm-thick Ni film (e-beam evaporation). These contain a half transmissive thin metal film, a total reflective thin metal film and a quarter-wave polyimide film. The results showed that, measured performance matches well with theoretical predictions.

Abstract: GaN nanowires have been successfully grown on Si (111) substrates by magnetron sputtering through ammoniating Ga2O3/V thin films. The influence of ammoniating temperature on the growth of GaN nanowires was analyzed in particular. The results demonstrate that ammoniating temperature has great influence on the growth of GaN nanowires. GaN nanowires are single crystal GaN with a hexagonal wurtzite structure and high crystalline quality after ammoniation at 900 oC for 15 min, which are straight and smooth with uniform thickness along the spindle direction and high crystalline quality, 50 nm in diameter and several tens of microns in length with good emission properties, and the growth direction of the nanowire is along the preferred (002) plane. A clear red-shift of the band-gap emission has occurred. The growth mechanism is also discussed briefly.

Abstract: Al doped Er2O3 films were deposited on Si(001) substrates by radio frequency magnetron technique. X-ray diffraction and atomic force microscopy show the Al doped Er2O3 films obtained are amorphous and uniform. The optical constants are studied which shows a proper value of refractive index and a lower reflectivity, indicating it could be a usefully material for solar cells.

Abstract: Photoreflectance (PR) spectra of a GaN thin film and an AlGaN/GaN heterostructure were measured by using a HeCd laser or a mercury lamp as a pump beam. The wavelengths (λ) of the HeCd laser and the mercury lamp are 325 nm and 253.7 nm, respectively. The energy of the HeCd laser is lower than band-gap energy of AlxGa1-xN (x > 0.2), so electron-hole pairs cannot be generated in the AlGaN layer. Hence, the PR of the AlGaN was measured by using Argon ion laser (λ =300 nm) or quadrupled Nd:YAG (λ =266 nm) rather than HeCd laser in the previous works. In this work, the mercury lamp was used as the pump beam. Although the mercury lamp is a diffused source, it is not a hindrance to the PR measurements. The signal to noise ratio is improved by using defocused pump and probe beams in the PR measurement.

Abstract: In order to develop novel electrochromic materials, 2,3′:4′,2″-terthiophene (I3T), 5,5′-biformyl- 2,2′:5′,2″:5″,2″′-quaterthiophene (4T-2CHO), and 2,5-(5′-cyano)thienyl-3,4-thienyl-t- hiophene (XT-2CN) were synthesized, and their electrochromic properties were studied. It was found that I3T, 4T-2CHO and XT-2CN as solid films showed reversible, clear color changes on electrochemical doping and dedoping. These oligothiophene derivatives constitute a new class of potential electrochromic materials.

Abstract: For RbTiOPO4 (RTP) crystal, the second harmonic generation (SHG) properties of 1064nm are discussed, including phase matching (PM) direction, effective nonlinear optical coefficient (deff), walk-off angle, and angular acceptance. For the frequency doubling of nano-second and pico-second Nd:YAG laser, the conversion efficiency of RTP crystal can reach 51 % and 57 %, respectively. The laser damage threshold of RTP crystal is measured.

Abstract: The aim of this study is to obtain high-quality zinc oxide thin films by reactive radiofrequency (rf) magnetron sputtering. The thin films were prepared at constant total gas pressure, with different oxygen and argon contents. The ZnO samples were characterized by several methods. From XRD measurements it was confirmed that ZnO films are c-axis oriented, the line width and intensity are sensitive to O2/Ar gas pressure. All films exhibited excellent transmission (in excess of 70 %) in the visible range with a steep fall off in transmission at 425 nm. From the absorbance measurements the optical band-gap energy was extrapolated according the transmission spectrum. It shows that the optical band gap of the films increased from 3.233 eV to 3.288 eV with increase in the oxygen concentrations from 20 % to 70 %. Refractive indexes of the obtained thin films were carried out in this study.

Abstract: Up-conversion luminescent materials of Y2O2S:Yb, Er with different doping concentrations of Er3+ ion (1 mol%–6 mol%) and Yb3+ ion (4 mol%–16 mol%) were prepared by flux method. As Yb3+ doping concentration was fixed at 8 mol%, when Er3+ doping concentration was 2 mol%, the green and red up-conversion luminescent intensity reached the maximum. As Er3+ doping concentration was fixed at 2 mol%, when Yb3+ doping concentration was 4 mol%, the green and red emission intensity reached the maximum. The up-conversion luminescent colours were adjustable.