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1.
The non-resonant third-order non-linear optical properties of amorphous Ge20As25Se55 films were studied experimentally by the method of the femtosecond optical heterodyne detection of optical Kerr effect. The real and imaginary parts of complex third-order optical non-linearity could be effectively separated and their values and signs could be also determined, which were 6.6 × 10−12 and −2.4 × 10−12 esu, respectively. Amorphous Ge20As25Se55 films showed a very fast response in the range of 200 fs under ultrafast excitation. The ultrafast response and large third-order non-linearity are attributed to the ultrafast distortion of the electron orbitals surrounding the average positions of the nucleus of Ge, As and Se atoms. The high third-order susceptibility and a fast response time of amorphous Ge20As25Se55 films makes it a promising material for application in advanced techniques especially in optical switching.  相似文献   

2.
刘启明  何漩  干福熹  钱士雄 《物理学报》2009,58(2):1002-1006
利用飞秒激光超外差光Kerr(OHD-OKE)技术研究了As2S3, As2Se3, GeS2, GeSe2, Ge20As25S55, Ge20As25Se55, Ge10As40S20关键词: 全光开关 硫系非晶半导体薄膜 飞秒激光超外差光Kerr(OHD-OKE) 三阶非线性  相似文献   

3.
Reversible photo-induced volume changes have been observed accompanying reversible optical absorption edge shift produced by successive cycles of band gap illumination and annealing for well-annealed evaporated As2S3 and As4Se5Ge1 films. The As2S3 film shows an increase in its volume by illumination, while As4Se5Ge1 film shows a decrease. Qualitative discussion has been given in connection with pressure-induced optical constant change.  相似文献   

4.
The effect of heat treatment on the optical and electrical properties of Ge15Sb10Se75 and Ge25Sb10Se65 thin films in the range of annealing temperature 373-723 K has been investigated. Analysis of the optical absorption data indicates that Tauc's relation for the allowed non-direct transition successfully describes the optical processes in these films. The optical band gap (Egopt.) as well as the activation energy for the electrical conduction (ΔE) increase with the increase of annealing temperature (Ta) up to the glass transition temperature (Tg). Then a remarkable decrease in both the Egopt. and ΔE values occurred with a further increase of the annealing temperature (Ta>Tg). The obtained results were explained in terms of the Mott and Davis model for amorphous materials and amorphous to crystalline structure transformations. Furthermore, the deduced value of Egopt. for the Ge25Sb10Se65 thin film is higher than that observed for the Ge15Sb10Se75 thin film. This behavior was discussed on the basis of the chemical ordered network model (CONM) and the average value for the overall mean bond energy 〈E〉 of the amorphous system GexSb10Se90−x with x=15 and 25 at%. The annealing process at Ta>Tg results in the formation of some crystalline phases GeSe, GeSe2 and Sb2Se3 as revealed in XRD patterns, which confirms our discussion of the obtained results.  相似文献   

5.
Structural, magnetic, heat capacity, electrical and thermal transport properties are reported on polycrystalline Ba8Ni6Ge40. Ba8Ni6Ge40 crystallizes in a cubic type I clathrate structure with unit cell a=10.5179 (4) Å. It is diamagnetic with susceptibility χdia=−1.71×10-6 emu/g Oe. An Einstein temperature 75 K and a Debye temperature 307 K are estimated from heat capacity data. It exhibits n-type conducting behavior below 300 K. It shows high Seebeck coefficients (−111×10-6 V/K), low thermal conductivity (2.25 W/K m), and low electrical resistivity (8.8 mΩ cm) at 300 K.  相似文献   

6.
The second-order optical nonlinearity of poled Ge25Sb10S65 chalcogenide glass was found to be 40-50% larger after femtosecond laser irradiation. The highest χ(2) was 11.4 pm/V. Raman spectral change indicated that centrosymmetric defects were created by fs light. These defects promoted the third-order optical nonlinearity of the glass and as a result, its second-order nonlinearity was also enhanced. The study shows that fs laser modification is an effective method of increasing the optical nonlinearity of photonic materials.  相似文献   

7.
Ultrafast third-order nonlinear optical responses of GeS2-In2S3-CsI chalcohalide glasses have been measured by using the femtosecond time-resolved optical Kerr effect (OKE) technique at a wavelength of 820 nm. The third-order nonlinear susceptibility was estimated to be as large as 5.12×10−13 esu. The full width at half maximum of the Kerr signal was 120 fs and its response was dominantly assigned to the ultrafast distortion of the electron cloud. The relationship between the structural units and the third-order nonlinear optical responses was analysed by Raman spectra. It is suggested that the covalent bonds of S-Ge or S-In constituting the tetrahedral units [GeS4/2] or [InS4−xIx], respectively, play an important role in the ultrafast third-order nonlinear optical responses of these chalcohalide glasses.  相似文献   

8.
Magnetic properties of amorphous Ge1−xMnx thin films were investigated. The thin films were grown at 373 K on (100) Si wafers by using a thermal evaporator. Growth rate was ∼35 nm/min and average film thickness was around 500 nm. The electrical resistivities of Ge1−xMnx thin films are 5.0×10−4∼100 Ω cm at room temperature and decrease with increasing Mn concentration. Low temperature magnetization characteristics and magnetic hysteresis loops measured at various temperatures show that the amorphous Ge1−xMnx thin films are ferromagnetic but the ferromagnetic magnetizations are changing gradually into paramagnetic as increasing temperature. Curie temperature and saturation magnetization vary with Mn concentration. Curie temperature of the deposited films is 80-160 K, and saturation magnetization is 35-100 emu/cc at 5 K. Hall effect measurement at room temperature shows the amorphous Ge1−xMnx thin films have p-type carrier and hole densities are in the range from 7×1017 to 2×1022 cm−3.  相似文献   

9.
The ultrafast nonlinear optical properties of Bi2O3-B2O3-SiO2 oxide glass were investigated using a femtosecond optical Kerr shutter (OKS) at wavelength of 800 nm. The nonlinear response time of this Bi2O3-doped glass was measured to be <90 fs. The nonlinear refractive-index n2 was estimated to be 1.6 × 10−14 cm2/W. Measurements for the dependence of Kerr signals on the polarization angle between the pump and probe beams showed that the Kerr signals induced by 30-fs pulse laser arose mainly from the photoinduced birefringence effect.  相似文献   

10.
Amorphous Ge1−xCrx thin films are deposited on (1 0 0)Si by using a thermal evaporator. Amorphous phase is obtained when Cr concentration is lower than 30.7 at%. The electrical resistivities are 1.89×10−3–0.96×102 Ω cm at 300 K, and decrease with Cr concentration. The Ge1−xCrx thin films are p-type. The hole concentrations are 5×1016–7×1021 cm−3 at 300 K, and increase with Cr concentration. Magnetizations are 7.60–1.57 emu/cm3 at 5 K in the applied field of 2 T. The magnetizations decrease with Cr concentration and temperature. Magnetization characteristics show that the Ge1−xCrx thin films are paramagnetic.  相似文献   

11.
(Ba0.7Sr0.3)TiO3 (BST) ferroelectric thin films with perovskite crystal structure were fabricated by soft solution processing on a quartz substrate. The third-order nonlinear optical properties were investigated by using Z-scan technique. Positive nonlinear refractive index and nonlinear absorption coefficient were determined to be 4×10−7 esu and 1.2×10−6 m/w, respectively. The real part and imaginary part of third-order optical nonlinear susceptibility were calculated and the values were 6.43×10−8 and 5.14×10−8 esu, respectively. All of these results show ferroelectric BST thin film is promising for applications in nonlinear optical devices.  相似文献   

12.
Optical properties of ternary chalcognide amorphous Ge10AsxSe(90−x) (with 10?x?25 at%) thin films prepared by thermal evaporation have been measured in visible and near-infrared spectral region. The straightforward analysis proposed by Swanepoel has been successfully employed, and it has allowed us to determine the average thickness , and the refractive index, n, of the films, with high accuracy. The refractive index, n and the average thickness has been determined from the upper and lower envelopes of the transmission spectra measured at normal incidence, in the spectral range 400-2500 nm. The absorption coefficient α, and therefore extinction coefficient k, have been determined from the transmission spectra in the strong-absorption region. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple-DiDomenico model, and the optical absorption edge is described using the ‘nondirect transition’ model proposed by Tauc. Likewise, the optical energy gap is derived from Tauc's extrapolation. The relationship between the optical gap and chemical composition in Ge10AsxSe(90−x) amorphous system is discussed in terms of the average heat of atomization Hs and average coordination number Nc. Finally, the chemical bond approach has been also applied successfully to interpret the decrease of the glass optical gap with increasing As content.  相似文献   

13.
Thermal conductivity, k, of GexAs40−xS60 glasses has been measured between 4.5 and 300 K. A variation of k with the composition is found and dependences of its parameters on the mean coordination numbers are established. Analyses have been made within but also independently of the soft-potential model. Some correlations and scaling laws are proposed.  相似文献   

14.
In this work, we report the formation of CuInS2 thin films on glass substrates by heating chemically deposited multilayers of copper sulfide (CuS) and indium sulfide (In2S3) at 300 and 350 °C in nitrogen atmosphere at 10 Torr. CIS thin films were prepared by varying the CuS layer thickness in the multilayers with indium sulfide. The XRD analysis showed that the crystallographic structure of the CuInS2 (JCPDS 27-0159) is present on the deposited films. From the optical analysis it was estimated the band gap value for the CIS film (1.49 eV). The electrical conductivity varies from 3 × 10−8 to 3 Ω−1 cm−1 depending on the thickness of the CuS film. CIS films showed p-type conductivity.  相似文献   

15.
Thin chalcogenide films of Ge1−xSe2Pbx (x=0, 0.2, 0.4, 0.6 and 0.8) have been prepared by the thermal evaporation technique, from previously synthesized bulk samples. The X-ray diffraction showed the amorphous nature for the as-deposited films and the partially crystalline for the annealed films. The optical constants (the refractive index, n, and absorption index k) were determined for as-deposited and annealed Ge1−xSe2Pbx films of different thicknesses by using spectrophotometeric measurements of the transmittance and reflectance at normal incidence in the spectral range 200-2500 nm. The obtained values of both n and k were found to be independent of the film thickness. The optical absorption edges are described using both the Urbach rule and the indirect transition. In transparent region, the spectral dependences of refractive index were interpreted in the frame of a single oscillator model.  相似文献   

16.
The morphology of materials resulting from laser irradiation of the single-layer and the multilayer amorphous Ge2Sb2Te5 films using 120 fs pulses at 800 nm was observed using scanning electron microscopy and atomic force microscopy. For the single-layer film, the center of the irradiated spot is depression and the border is protrusion, however, for the multilayer film, the center morphology changes from a depression to a protrusion as the increase of the energy. The crystallization threshold fluence of the single-layer and the multilayer film is 22 and 23 mJ/cm2, respectively.  相似文献   

17.
Anatase phase TiO2 films have been grown on fused silica substrate by pulsed laser deposition technique at substrate temperature of 750 °C under the oxygen pressure of 5 Pa. From the transmission spectra, the optical band gap and linear refractive index of the TiO2 films were determined. The third-order optical nonlinearities of the films were measured by Z-scan method using a femtosecond laser (50 fs) at the wavelength of 800 nm. The real and imaginary parts of third-order nonlinear susceptibility χ(3) were determined to be −7.1 × 10−11esu and −4.42 × 10−12esu, respectively. The figure of merit, T, defined by T=βλ/n2, was calculated to be 0.8, which meets the requirement of all-optical switching devices. The results show that the anatase TiO2 films have great potential applications for nonlinear optical devices.  相似文献   

18.
Bismuth sulfide (Bi2S3) and antimony sulfide (Sb2S3) nanorods were synthesized by hydrothermal method. The products were characterized by UV-vis spectrophotometer, X-ray powder diffraction (XRD) and transmission electron microscope (TEM). Bi2S3 and Sb2S3 nanorods were measured by Z-scan technique to investigate the third-order nonlinear optical (NLO) properties. The result of NLO measurements shows that the Bi2S3 and Sb2S3 nanorods have the behaviors of the third-order NLO properties of both NLO absorption and NLO refraction with self-focusing effects. The third-order NLO coefficient χ(3) of the Bi2S3 and Sb2S3 nanorods are 6.25×10−11 esu and 4.55×10−11 esu, respectively. The Sb2S3 and Bi2S3 nanorods with large third-order NLO coefficient are promising materials for applications in optical devices.  相似文献   

19.
Five-layered Si/SixGe1−x films on Si(1 0 0) substrate with single-layer thickness of 30 nm, 10 nm and 5 nm, respectively were prepared by RF helicon magnetron sputtering with dual targets of Si and Ge to investigate the feasibility of an industrial fabrication method on multi-stacked superlattice structure for thin-film thermoelectric applications. The fine periodic structure is confirmed in the samples except for the case of 5 nm in single-layer thickness. Fine crystalline SixGe1−x layer is obtained from 700 °C in substrate temperature, while higher than 700 °C is required for Si good layer. The composition ratio (x) in SixGe1−x is varied depending on the applied power to Si and Ge targets. Typical power ratio to obtain x = 0.83 was 7:3, Hall coefficient, p-type carrier concentration, sheet carrier concentration and mobility measured for the sample composed of five layers of Si (10 nm)/Si0.82Ge0.18 (10 nm) are 2.55 × 106 /°C, 2.56 × 1012 cm−3, 1.28 × 107 cm−2, and 15.8 cm−2/(V s), respectively.  相似文献   

20.
We have grown MnxGe1−x films (x=0, 0.06, 0.1) on Si (001) substrates by magnetron cosputtering, and have explored the resulting structural, morphological, electrical and magnetic properties. X-ray diffraction results show there is no secondary phase except Ge in the Mn0.06Ge0.94 film while new phase appears in the Mn0.1Ge0.9 film. Nanocrystals are formed in the Mn0.06Ge0.94 film, determined by field-emission scanning electron microscopy. Hall measurement indicates that the Mn0.06Ge0.94 film is p-type semiconductor and hole carrier concentration is 6.07×1019 cm−3 while the MnxGe1−x films with x=0 has n-type carriers. The field dependence of magnetization was measured using alternating gradient magnetometer, and it has been indicated that the Mn0.06Ge0.94 film is ferromagnetic at room temperature.  相似文献   

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