Second-harmonic generation in UV-pulsed laser poled amorphous 80GeS2-15Ga2S3-5CdS chalcogenide film

With the pulsed laser deposition （PLD） method, amorphous 80GeS2-15Ga2S3-5CdS chalcogenide film was deposited on glassy substrate. Obvious second harmonic generation （SHG） was observed in the ultraviolet （UV）-polarized film and the SHG intensity increased with the increase in single pulse energy and irradiation time. Through Raman spectra and transmission spectra, the mechanism of SHG was studied. The experimental results demonstrated that effective electron traps and hole traps were generated in the UV- polarized film. The energy of electrons and holes was using up due to the collision with other particles and crystal fields during their movement and finally they were captured by the traps and fixed, which made the electric charge distribution nonuniform in the film and destroyed the spatial isotropy. In the meantime, the center of positive and negative charges separated and a built-in electric field was formed which generated the optical second-order nonlinearity of the film.     

Photo-induced phenomena in GeS4 glasses

GeS4 bulk glasses were prepared by the melt-quench technique and the samples were irradiated by 532-nm linearly polarized light. After the laser treatment, the photo-induced changes of the samples were investigated by UV-1601 speetrophotometer and optical second-order nonlinear tester. The results show that the transmittance of the samples around 532 nm obviously decreases and Bragg reflector forms, which is due to the production of photon-generated carriers. With the increase of laser pulse energy or the extension of irradiation duration, the Bragg reflector increases and gradually tends to be stable. These can be ascribed to the excitation- capture process of the carriers. After irradiation, the relaxation phenomenon results from the release of part of the absorbed energy in the glass matrix. And the fitting equation of the relaxation process is consistent with a conventional Kohlrausch stretched exponential function. The origin of the second harmonic generation （SHG） is because of the dipole reorientation caused by the photo-induced anisotropy in the glass.     

Laser-induced phase transformation in chalcogenide glasses investigated by micro-Raman spectrometer

A 488 nm continuous wave （CW） laser was employed in Raman spectrometer to both induce and characterize phase transformation in chalcogenide glasses. Laser-induced Raman inactive changes, structural evolution, and crystallization were observed at laser-irradiated region in GeS2-Sb2S3 glasses. The composition dependence of laser-induced phase transformation was discussed in terms of thermal stability and microstructural modification. It is strongly suggested from these results that fabrication of passive and active chalcogenide glass waveguides, such as refractive index change and nonlinear optical crystal line, is controllable by selecting appropriate glass composition, and convenient by using common CW lasers.     

Microstructure and Optical Properties of the （1-x）GeS2-xP2S5 Glasses

To find materials with larger second-order nonlinearity, the Ge-P-S chalcogenide glasses with various ratios of GeS2 ： P2S5 were prepared by the melt-quenching method. The microstructure and optical properties of these glasses were characterized by XRD, Raman, Vis- NIR speetroscopy and Maker fringe technique. The second harmonic generation （SHG） was observed in the as-prepared chalcogenide glasses which was ascribed to the thermal stress gradient and/ or the rnicroanisotropic defects （ such as the lone-pair orbital or the valence alternative pairs ） prefer-orientation of the as-prepared glasses.     

Study on the thermal stability and electrical properties of the high-k dielectrics (ZrO2)x(SiO2)1?x

(ZrO₂) _x (SiO₂)_1−x (Zr-Si-O) films with different compositions were deposited on p-Si(100) substrates by using pulsed laser deposition technique. X-ray photoelectron spectra (XPS) showed that these films remained amorphous after annealing at 800°C with RTA process in N₂ for 60 s. The XPS spectra indicated that Zr-Si-O films with x=0.5 suffered no obvious phase separation after annealing at 800°C, and no interface layer was formed between Zr-Si-O film and Si substrate. While Zr-Si-O films with x >0.5 suffered phase separation to precipitate ZrO₂ after annealing under the same condition, and SiO₂ was formed at the interface. To get a good interface between Zr-Si-O films and Si substrate, Zr-Si-O films with bi-layer structure (ZrO₂)_0.7(SiO₂)_0.3/(ZrO₂)_0.5(SiO₂)_0.5/Si was deposited. The electrical properties showed that the bi-layer Zr-Si-O film is of the lowest equivalent oxide thickness and good interface with Si substrate. Supported by the National Nature Science Foundation of China (Grant No. 60636010) and the National Basic Research Program of China (“973” Program) (Grant No. 2004CB619004)     

Corrosion and irradiation behavior of Fe-based amorphous coating in lead-bismuth eutectic liquids

Lead-bismuth eutectics (LBE) have considerable potential as a candidate material for accelerator-driven sub-critical systems (ADS). However, LBE corrosion and irradiation damage are two urgent challenges remaining to be solved for impellers of primary pumps. In this study, we have explored the possibility of using Fe-based amorphous coatings to overcome LBE corrosion and concurrently to sustain irradiation damage. Specifically, the Fe₅₄Cr₁₈Mo₂Zr₈B₁₈ amorphous coating was prepared by high-velocity oxygen-fuel (HVOF) spraying on 316L steel and exposed to saturated oxygen static LBE for 500 h at 400°C. The coating with high thermal stability (T_g=615°C and T_x=660°C) effectively prevented the substrate steel from being corroded by LBE owing to its unique long-range disordered atomic packing. The coating also exhibited strong irradiation resistance when being subjected to 45 dpa (displacement per atom) Au ion irradiation at room temperature, with no sign of crystallization even at the maximum implantation depth of 300 nm. Consequently, the hardness of the coatings before and after irradiation increased slightly. The current findings shed new insights into understanding corrosion mechanism and irradiation behavior of amorphous solids in LBE and expand the application range of amorphous materials.

     

Preparation and characterization of SrTiO<Subscript>3</Subscript> thin film on functional organic self-assembled monolayers

SrTiO₃ thin film was successfully prepared on the functionalized organic self-assembled monolayers (SAMs) by the Liquid Phase Deposition (LPD) method. The as-prepared samples were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscopy (SEM) and metallographic microscope. Measurement of contact angle showed that the hydrophobe substrate was changed into hydrophile by UV irradiation. AFM photographs of octadecyl-trichloro-silane self-assembled monolayer (OTS-SAM) surface approved that UV irradiation did change the morphology of OTS monolayer and provided evidence for the conversion of hydrophilic characteristic. Photographs of Metallographic Microscope showed that OTS-SAM had an active effect on the deposition of SrTiO₃ thin film. XRD and SEM indicated that the thin film was of pure cubic phase SrTiO₃ and composed of nanosized grains with a size in the range of 100–500 nm. The formation mechanism of the SrTiO₃ film was proposed.     

Properties and Microstructure of GeS2-Ga2S3-CdS Glasses

The samples of the GeS2-Ga2 S3-CdS pseudo-ternary glassy sysem were prepared by comventional melt-quenching techniques.The microstructure of the GeS2-Ca2 S3-CdS glasses was analyzed thoroughly using Raman spectra and the relationships among the composition,microstructure and properties（such as thermal properties,densities,optical properties）were probed.The experimental results indicate that the GeS2 acts as the network former,the Ga2S3 as the net intermediate,and the CdS as the net modifier,The GeS2 and Ga2S3 exist in the form of [GeS4/2],[GaS4/2]tetrahedra or S3G3（Ga）-（Ga）GeS3 ethane-like units within the glassy network,and the addition of CdS mainly breaks the Ge（Ga）-（Ga）Ge bonds among the ethane -like units,leading to the formation of [GeS4/2].[GaS4/2]tetrahedra.The Tg and Tx have tight relations on the congregated degree of glassy network,however,λvis,n and d are hardly involved into the connectional dependence of the space arrangement.     

铁电极化调控SnSe薄膜光电性质研究

利用脉冲激光沉积(PLD)技术在铌酸锂基片上沉积SnSe薄膜,研究了不同极化方向的铁电基片对SnSe薄膜光电性质的影响.控制PLD沉积时间,在铌酸锂基片上沉积出不同厚度的SnSe薄膜.X射线衍射和X射线光电子能谱的结果显示制备了高取向的单相SnSe薄膜.薄膜横截面高分辨透射电镜结果显示了薄膜具有较高的结晶质量.在无光照情况下,当铁电极化方向指向薄膜时,极化场可向SnSe薄膜中注入电子,使p型SnSe薄膜的电阻增加;当极化方向背离薄膜时,极化场可向SnSe薄膜中注入空穴,使p型SnSe薄膜的电阻降低.当用仅能使SnSe薄膜发生电子-空穴分离的632 nm激光照射时,不同极化方向的样品都表现出光电导增加的现象.当用405 nm激光照射时,不同极化方向的铌酸锂与薄膜界面处发生的电子-空穴分离使SnSe薄膜表现出完全不同的光电导效应.利用能带模型解释了不同铁电极化方向的铁电基片对SnSe薄膜光电导性质调控的机理.     

Influence of heat treatment temperature on microstructure and bonding of TiO<Subscript>2</Subscript> film coated on diamond particles surface

TiO₂ films were coated on the surface of diamond particles using a sol-gel method. The effects of heat treatment temperature on the morphology, phase composition and chemical bond of diamond particles coated with TiO₂ films were investigated through SEM, TEM, X-ray diffraction analysis, Raman spectroscopy, FTIR, and XPS. The results showed that when being heat-treated at 600 °C, the amorphous TiO₂ film transfered to the anatase film which bonded well with diamond substrate. Meanwhile, the Ti-O-C bond formed between TiO₂ film and diamond substrate. When being heat-treated at 800 °C, TiO₂ film was still anatase, and partial diamond began to graphitize. The graphitizated carbon could also form the Ti-O-C bond with TiO₂ film, although TiO₂ film would tend to crack in this case.     

Preparation and Properties of IrO2 Thin Films Grown by Pulsed Laser Deposition Technique

Highly conductive IrO2 thin films were prepared on Si （100） substrates by means of pulsed laser deposition technique from an iridium metal target in an oxygen ambient atmosphere. Emphasis was put on the effect of oxygen pressure and substrate temperature on the structure, morphology and resistivity of IrO2 films. It was found that the above properties were strongly dependent on the oxygen pressure and substrate temperature. At 20 Pa oxygen ambient pressure, pure polycrystalline IrO2 thin films were obtained at substrate temperature in the 300-500℃ range with the preferential growth orientation of IrO2 films changed with the substrate temperature. IrO2 films exhibited a uniform and densely packed granular morphology with an average feature size increasing with the substrate temperature. The room-temperature resistivity variations of IrO2 films correlated well with the corresponding film morphology changes. IrO2 films with the minimum resistivity of （42 ±6）μΩ·cm was obtained at 500℃.     

激光化学气相沉积非晶硅

本文报道了CO_2激光化学气相沉积非晶硅的实验结果,硅薄膜的沉积速率与硅烷气压、基片温度和激光光强密切有关。 利用不同方法测量了硅薄膜样品的各种特性,证实了薄膜确为非晶硅。 作者也研究了激光化学沉积非晶硅的机理,并给出了理论讨论以解释实验结果。     

Corrosion behavior of amorphous/nanocrystalline Al-Cr-Fe film deposited by double glow plasmas technique

In order to improve the corrosion resistance of AZ31 magnesium alloy, the amorphous/nanocrystal Al-Cr-Fe film has been successfully prepared on AZ31 magnesium alloy by double glow plasma technology. The amorphous/nanocrystalline consists of two different regions, i.e., an amorphous layer on outmost surface and an underlying lamellar nanocrystalline layer with a grain size of less than 10 nm. The corrosion behavior of amorphous/nanocrystalline Al-Cr-Fe film in 3.5% NaCl solution is investigated using an electrochemical polarization measurement. Compared with the AZ31 magnesium alloy, the amorphous/nanocrystalline Al-Cr-Fe film exhibits more positive corrosion potentials and lower corrosion current densities than that of AZ31 magnesium alloy. XPS measurement reveals that the passive film formed on the Al-Cr-Fe film after the anodic polarization tests is strongly enriched in Cr₂O₃, Fe₂O₃ and Al₂O₃ at outer surface of the film and in the inner layer consists of Cr₂O₃, FeO and Al₂O₃. Supported by the National Natural Science Foundation of China (Grant Nos. 50571045 and 50704022) and the Natural Science Foundation of Jiangsu Province, China (Grant No. BK2007591)     

Microstructural Probing of （1-x） GeS2- x Ga2S3 System Glasses By Raman Scattering

Roman scattering measurement of （ 1 - x ） GeS2-x Ga2S3 system glasses was conducted in order to understand the microstructural change caused by the addition of Ga2S3 . According to the change of Raman spectra with the addition of Ga2S3, two main structural transformations were deduced ： the gradual enhancement of ethane- like structural units S3 Ge- GeS3 （ 250 cm ^- 1） and S3 Ga- GaS3 （270 cm ^- 1 ） and the appearance of charge imbalanced units [ Ga2 S2 （ S1/2 ）4 ]^2- and [Ga（ S1/2 ）4 ]^- . And this change of structural aspect seems to give as a clue to understanding the cause of the increased rare-earth solubility.     

Crystallization and Electrical Properties of （Ba0.4Pb0.3）Sr0.3TiO3 Thin Film by Pulsed Laser Deposition

（Ba0.4Pb0.3）Sr0.3TiO3 thin films were fabricated via pulsed laser deposition （PLD） technique on Pt/TiO2/SiO2/Si substrate. The crystallization of the films was characterized by XRD and FSEM, and the experimental results suggested deposition parameters, especially the deposition temperature was the key factor in forming the perovskite structure. The dielectric properties of the film deposited with optimized parameters were studied by an Agilent 4294A impedance analyzer at 1 MHz. The dielectric constant was 772, and the loss tangent was 0.006. In addition, the well-shaped hysteresis loop also showed that the film had a well performance in ferroelectric. The saturated polarization P, remnant polarization Pr and coercive field E were about 4.6 μC/cm2, 2.5 μC/cm2 and 23 kV/cm （the coercive voltage is 0.7 V）, respectively. It is suggested the film should be a promising candidate for microwave applications and nonvolatile ferroelectric random access memories （NvFeRAMs）.     

Laser cladding Al-Si/Al2O3-TiO2 composite coatings on AZ31B magnesium alloy

To improve the wear resistance and corrosion resistance of magnesium alloys, a 5 kW continuous wave CO₂ laser was used to investigate the laser surface cladding on AZ31B magnesium alloys with Al-Si/Al₂O₃ -TiO₂ composite powders. A detailed microstructure, chemical composition, and phase analysis of the composite coatings were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The laser cladding shows good metallurgical bonding with the substrate. The composite coatings are composed of Mg₁₇Al₁₂, Al₃Mg₂, Mg₂Si, Al₂O₃, and TiO₂ phases. Compared to the average microhardness (50HV_0.05) of the AZ31B substrate, that of the composite coatings (230HV_0.05) is improved significantly. The wear resistances of the surface layers were evaluated in detail. The results demonstrate that the wear resistances of the laser surface-modified samples are considerably improved compared to the substrate. It also show that the composite coatings exhibit better corrosion resistance than that of the substrate in 3.5wt% NaCl solution.     

Correlations between the Optical Properties and the Microstructure of TiO2 Thin Films Prepared by Reactive Electron-beam Evaporation

High refractive index TiO₂ thin films were deposited on BK7 glass by reactive electron—beam (REB) evaporation at pressure of 2×10⁻² Pa, deposition rate of 0.2 nm/s and at various substrate temperatures from 120°C to 300°C. The refractive index and the thickness of the films were measured by visible spectroscopic ellipsometry (SE) and determined from transmission spectra. Optical properties and structure features were characterized by UV-VIS, SEM and XRD, respectively. The measurement and analysis on transmission spectra of all samples show that with the substrate temperature increasing from 120°C to 300°C, the refractive indices of thin films increase from 1.7 to 2.1 and the films after heat treatment have higher refractive indices due to its crystallizing. The XRD analysis results indicate that the structure of TiO₂ thin films deposited on BK7 glass at substrate temperatures of 120°C, 200°C and 300°C is amorphous, after post-annealing under air condition at 400°C for 1 hour, the amorphous structure is crystallized, the crystal phase is of 100% anatase with strong preferred orientation (004) and the grain size of crystalline is within 3.6–8.1 nm, which is consistent with results from SEM observation. WANG Xue-hua: Born in 1976. Funded by the Youth Project Foundation of Hubei Provincial Education Department (No. 2003B00)     

Photocatalytic performance of TiO<Subscript>2</Subscript> thin films connected with Cu micro-grid

Aiming at reducing the recombination of photo-induced carriers in semiconductor photocatalytic process, we prepared TiO₂ thin film with its surface modified by a connected Cu micro-grid via a microsphere lithography strategy, which showed higher photocatalytic activity than the pure TiO₂ film. The improvement of photocatalytic activity of Cu micro-grid to the TiO₂ film is due to the charge carrier separation and electron transfer by the conducting metal grid. The photocatalytic activity was improved as metal loading increased, which obtained the best performance at a certain loading amount, and then decreased at higher loading amount. This phenomenon was attributed to the metal’s bulk effect which could be explained by the relationship between the energetic positions and the metal cluster size. Supported by the National Natural Science Foundation of China (Grant Nos. 50672003, 50872005) and the National Basic Research Program of China (“973” Project) (Grant No. 2007CB613302) and the Fok Ying Tong Education Foundation (Grant No. 111050)     

A direct atomic layer deposition method for growth of ultra-thin lubricant tungsten disulfide films

We describe a direct atomic layer deposition method to grow lubricant tungsten disulfide (WS₂) films. The WS₂ films were deposited on a Si (100) substrate and a zinc sulfide (ZnS) film coated the Si (100) substrate using tungsten hexacarbonyl and hydrogen sulfide as precursors. The ZnS film served as an intermediate layer to facilitate the nucleation and growth of the WS₂ films. The thickness of the WS₂ films was measured via scanning electron microscope, the microstructure was probed with an X-ray diffractometer and a transmission electron microscope. The friction coefficient was measured with a ball-on-disk tester under dry nitrogen. The results reveal that the WS₂ films deposited on both substrates are ~175 nm and have (002) and (101) crystal orientations. The WS₂ film deposited on the ZnS coated Si substrate exhibits a stronger (002) orientation and a denser crystal structure than that deposited on the Si substrate. The WS₂ films on both substrates have low friction coefficients. However, due to the stronger (002) orientation and denser crystal structure, the friction coefficient of the WS₂ film deposited on ZnS coated Si substrate is smaller with longer wear life.     

Study on BaTiO<Subscript>3</Subscript> films prepared by AC power microarc oxidation

BaTiO₃ films were prepared by microarc oxidation (MAO) with an in-house built alternating current (AC) power supply in Ba(OH)₂ solution in this study. The surface morphology, combinability with the substrate and phase composition of the films were investigated by XRD, SEM and TEM. The BaTiO₃ films were annealed at a temperature range of 900 to 1200°C and phase compositions were tested thereafter. The results showed that the BaTiO₃ films were mainly composed of the primitive hexagonal phase with relatively small amount of tetragonal and amorphous phases. Moreover, the amount of amorphous phase decreased with the time of annealing. The transformation of BaTiO₃ from hexagonal structure to tetragonal stucture became obvious until the annealing temperature reached 1200°C. The film consisted mainly of BaTiO₃ tetragonal structure with ferroelectric property. The influence of annealing on surface morphology and mechanism of phase transformation of the films were also discussed. Supported by Guangdong Natural Science Foundation (Grant No. 0500649)