Structural and optical properties of epitaxial ZnO thin films on 4H–SiC (0 0 0 1) substrates prepared by pulsed laser deposition

Epitaxially grown ZnO thin films on 4H–SiC (0 0 0 1) substrates were prepared by using a pulsed laser deposition (PLD) technique at various substrate temperatures from room temperature to 600 °C. The crystallinity, in-plane relationship, surface morphology and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) measurements, respectively. XRD analysis showed that highly c-axis oriented ZnO films were grown epitaxially on 4H–SiC (0 0 0 1) with no lattice rotation at all substrate temperatures, unlike on other hexagonal-structured substrates, due to the very small lattice mismatch between ZnO and 4H–SiC of ～5.49%. Further characterization showed that the substrate temperature has a great influence on the properties of the ZnO films on 4H–SiC substrates. The crystalline quality of the films was improved, and surfaces became denser and smoother as the substrate temperature increased. The temperature-dependent PL measurements revealed the strong near-band-edge (NBE) ultraviolet (UV) emission and the weak deep-level (DL) blue-green band emission at a substrate temperature of 400 °C.     

GROWTH OF β-SiC BY rf SPUTTERING ON SILICON SUBSTRATES

1. IlltroductiollSili(.oll t.arbide (SiC) llas beell il1vestigated as a nlaterial with great poteIltial il1 high-p()xxer. high teulperature. and high-f1equel1c} devices, sil1ce it has feat[tres of high break-(l()ttll voltage, l1igll satllratioll t.elocit}…     

α-Si3N4单晶纳米带的光致发光及激发光谱研究

采用催化裂解有机前驱体方法制备出单晶a-Si3N4纳米带,研究了纳米带的吸收光谱、光致发光(PL)及激发(PLE)光谱.吸收光谱表明约5.0eV禁带宽度的纳米带是间接带半导体吸收.室温下纳米带的PL光谱在1.8eV, 2.3eV和3.0eV处有3个宽峰.PLE光谱显示在能隙中存在多个能级.     

Micro-Raman Spectroscopy for Stress Evaluation of 3C-SiC Epitaxially Grown on Si Substrate by Hot Wall CVD

GROWTH of large area3C-SiC films on Si hasattracted great interest since the early report onhetero-epitaxial growth by means of chemical vapordeposition(CVD)[1],due to its outstanding thermal,chemical and electrical properties for deviceapplications,such as,wide-band gap(2.3eV),highthermal conductivity(4.9W/cmK),high electronmobility(lOOOcmVVs)and high electron saturationdrift velocity(2.7xl07cm/s)[l,2].To our knowledge,the reports on the growth of SiC involved largely on the(100)Si,wi…     

热处理对TiO2溅射薄膜结构和光谱性能的影响

用直流反应磁控溅射法制备了TiO2薄膜,并对热处理前后试样的紫外可见光谱（UV-Vis spectrum）和荧光发射光谱（PL Spectrunm）做了研究。发现热处理后试样的紫外可见光谱在496nm处出现了一个较为明显的吸收峰，荧光发射光谱496．5nm处出现一个荧光发射带肩。X射线光电予能谱（XPS）的分析结果表明，热处理可使薄膜中晶格氧扩散出去，生成Ti^3＋离子和氧空位。结合XPS的分析结果和理论计算，可推断热处理后出现的位于496nm处的吸收峰和496．5nm处的荧光带肩可被指认为薄膜中Ti^3＋离子的d电子跃迁产生。     

热处理对TiO_2溅射薄膜结构和光谱性能的影响

用直流反应磁控溅射法制备了TiO2薄膜,并对热处理前后试样的紫外可见光谱(UV-Visspectrum)和荧光发射光谱(PLSpectrunm)做了研究。发现热处理后试样的紫外可见光谱在496nm处出现了一个较为明显的吸收峰,荧光发射光谱496.5nm处出现一个荧光发射带肩。X射线光电子能谱(XPS)的分析结果表明,热处理可使薄膜中晶格氧扩散出去,生成Ti3+离子和氧空位。结合XPS的分析结果和理论计算,可推断热处理后出现的位于496nm处的吸收峰和496.5nm处的荧光带肩可被指认为薄膜中Ti3+离子的d电子跃迁产生。     

Evidence of triplet–triplet interaction in crystalline sexithiophene

Optically detected magnetic resonance (ODMR) experiments are performed at room temperature on crystalline sexithiophene (6T) photoluminescence (PL). The observed spectra are interpreted in terms of microwave induced transitions between spin sublevels of triplet–triplet pairs states. These triplets are produced by intersystem crossing and their mutual annihilation which leads to delayed fluorescence (DF) is modulated by the high power microwave and enhance the PL process.     

白光发射材料的制备和光学性能研究

用溶胶-凝胶法,在ZnS基质中直接掺杂过渡金属元素Cu,Mn,并适当调整Cu,Mn的掺杂量,获得白光发射且操作工艺简单的纳米ZnS：Cu,Mn荧光粉,使用XRD,UV和PL等方法研究了粉粒的粒径、结构及荧光特性。     

长余辉发光粒子与光催化剂在SiC晶圆化学机械抛光中的协同作用

目的 获得一种可改善单晶SiC晶圆化学机械抛光(CMP)效率的复合增效技术，实现单晶SiC晶圆高效率和低成本的加工要求，并对其增效机理进行深入研究。方法 通过抛光实验和原子力显微镜测试，探究长余辉发光粒子(LPPs)与不同光催化剂的协同作用对SiC–CMP的材料去除速率和表面粗糙度的影响。结合扫描电子显微镜(SEM)、紫外–可见漫反射光谱仪(UV–vis)、光致发光光谱仪(PL)和X射线光电子能谱仪(XPS)等仪器的测试结果，研究LPPs与光催化剂的协同增效机理。结果 与传统CMP的条件相比，在光催化条件下采用LPPs(质量分数0.5%)+TiO2(质量分数0.5%)+ H2O2(质量分数1.5%)+Al2O3(质量分数2%)的抛光液时，SiC的材料去除速率(MRR)由294 nm/h提高到605 nm/h，同时获得的晶圆表面粗糙度(Ra)为0.477 nm。然而，采用含有LPPs和ZrO2的抛光液抛光SiC时，其材料去除速率和表面粗糙度都未得到明显改善。XPS测试结果表明，LPPs与光催化剂的协同作用增强了抛光液对SiC的氧化作用。UV–vis和PL测试结果显示，LPPs与不同光催化剂协同效果的差异主要与其光学性能有关。结论 在光催化条件下，LPPs和TiO2对单晶SiC–CMP具有协同增效的作用，然而LPPs和ZrO2没有展现出协同增效的作用，即LPPs与光催化剂的协同作用可以改善SiC–CMP的性能，但是光催化剂的选择需要考虑LPPs的发光特性。     

Tunable photoluminescence of poly(phenylene vinylene) nanofibers by doping of semiconductor quantum dots and polymer

In this paper, we report the effects of polyvinyl alcohol (PVA) and CdS quantum dots (QDs) on the photoluminescence (PL) properties of poly(phenylene vinylene) (PPV) nanofibers. The composite nanofibers were fabricated by coupling self-assembly and electrospinning method. A significant blue shift in both PL spectra and fluorescence images of PPV fibers was observed after doping of CdS QDs and PVA in succession. It was found that the changes in PL spectra of PPV originated from the chemical interactions between PPV and PVA, and the changes in the crystallization of PPV itself. A possible PL mechanism was proposed accordingly.     

(SiCW+B4Cp)/MB15 Mg基复合材料的微观结构

利用高分辨电镜研究了(SiCw+B4Cp)/MB15 Mg合金基复合材料的微观结构.SiC晶须的表面附着呈截角八面体形状的MgO纳米颗粒.此外,MgB2和MgO共生在SiC晶须的表面,三者之间存在固定的晶体学取向关系[110]SiC∥[110]MgO∥[1120]MgB2和(111SiC∥(111MgO∥(0001MgB2.MgB2相呈六角盘状几何外形,在Mg合金中其界面能的各向异性显著.此外,还发现了SiC和Mg存在的一种晶体学取向关系[111]siC∥[0001]Mg和(202)siC∥(1120)Mg.研究结果表明,在Mg合金复合材料中,SiC比B4C更加稳定.     

Fluorene and silafluorene conjugated copolymer: A new blue light-emitting polymer

A novel series of soluble blue light-emitting conjugated random and alternating copolymers derived from 9,9′-dioctylfluorene (FO) and 3,6-dimethoxyl-9,9-dimethyl-9-silafluorene (DMSiF) were successfully synthesized by Suzuki coupling polymerization. The feed ratios of FO to DMSiF were 90:10, 80:20, 75:25, and 50:50. Chemical structures and optoelectronic properties of the copolymers were characterized by NMR, UV absorption, photoluminescence, and cyclic voltammetry. The ¹H NMR spactra of the copolymers indicated that DMSiF content in the copolymers was slightly lower than its feed composition. The random copolymers exhibited PFO-segment-dominated UV absorption and PL spectra in THF solution, in comparison with significantly blue-shifted spectra of the alternating copolymer. The blue shift of the spectra became more remarkable in cast film and increased with the increment of DMSiF content. The changes of the UV absorption and PL spectra in solution and film were ascribed to the effect of methoxyl substituents which can hinder the chain rotation and influence the polymer comformation espercially in the solid film. The systematic invesetigations on the solubility, thermostability, electrochemical property, and photophysical property of the copolymers showed that silafluorene was an attractive building unit for optoelectronic materials.     

Stable blue-emitting molecular material derived from calix[4]arene and pyrazoline: Synthesis, optical and electrochemical properties

A novel blue-emitting molecular material derived from calix[4]arene and pyrazoline was designed and synthesized. Its photophysical properties were investigated in CHCl₃ solution and solid film by UV–vis and photoluminescent (PL) spectra. The maximum peaks are almost at the same positions both in UV–vis and PL spectra indicated that the grafted pyrazoline on calix[4]arene by chemical bond can help to disperse emitting pyrazoline chromophores in host material of calix[4]arene and tend to reduce the interaction of each pyrazoline molecule. Light-emitting diodes (LEDs) using this material as active layer were fabricated by a wet process. The turn-on voltage of the typical LED based on calix[4]arene-pyrazoline was about 6.6 V, and the maximum EL efficiency of the device was determined to be 1.52%. The homogeneous film based the resulting material was obtained even after keeping for three months. The primary results indicate that this novel material is a promising candidate as pure blue and stable light-emitting material for display.     

Catalyst-free synthesis of ZnO microrod arrays on SiC substrate and their tunable photoluminescence by erosion process

We present here the results on the preparation and characterization of highly oriented ZnO microrods fabricated on SiC substrate via a vapor solid route. These ZnO microrods grow along the c-axis perpendicularly to the substrate and are well separated from each other. Photoluminescence (PL) due to the band-gap emission (centered at 380 nm) and defect-related deep band emission (centered at 530 nm) were observed. Tunable PL intensities of these two bands were achieved by acid etching for varying durations.     

Characterization of GaSb Films by Metalorganic Chemical Vapour Deposition

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Comparative study of microwave and conventional methods for the preparation and optical properties of novel MgO-micro and nano-structures

Magnesium oxide (MgO) was synthesised by a simple microwave-assisted combustion route without using any template, catalyst or surfactant. For the purpose of comparison, it was also prepared using conventional method. The as-synthesized MgO was characterized by powder X-ray diffraction (XRD), Fourier Transform infrared spectra (FT-IR), high resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), Energy Dispersive X-ray analysis (EDX), diffuse reflectance spectroscopy (DRS) and Photoluminescence (PL) spectroscopy. The XRD results confirmed the formation of cubic phase MgO. FT-IR was used to investigate the adsorption of water and CO₂ on MgO surface and confirm the formation of Mg-O phase. The formation of MgO micro cubes structures was confirmed by HR-SEM. The formation of MgO nanosheets was confirmed by HR-SEM and TEM and their possible formation mechanisms were also proposed. The optical absorption and photoluminescence emissions were determined by DRS and PL spectra respectively. An attempt has been made to compare the lattice parameter and the PL intensity.     

A comparison of transmittance properties between ZnO∶Al films for transparent conductors for solar cells deposited by sputtering of AZO and cosputtering of AZO/ZnO

Aluminum-doped zinc oxide (AZO) thin films were deposited on sapphire (002) andglass substrates by two different sputtering techniques radio frequency magnetron cosputtering of AZO and ZnO targets and sputtering of an AZO target. The dependence of the photoluminescence (PL) and transmittance properties of the AZO films deposited by cosputtering and sputtering on the AZO/ZnO target power ratio, R and the O2/Ar flow ratio, r were investigated, respectively. Only a deep level emission peak appears in the PL spectra of cosputtered AZO films whereas both UV emission and deep level emission peaks are observed in the PL spectra of sputtered AZO films. The absorption edges in the transmittance spectra of the AZO films shift to the lower wavelength region as R and r increase. Effects ofcrystallinity, surface roughness, PL on the transmittance of the AZO films werealso explained using the X-ray diffraction (XRD), atomic force microscopy (AFM), and PL analysis results.     

Effect of the dilution in polypropylene on photophysical properties of poly(3-alkylthiophenes)

Optical properties on the basis of absorption and photoluminescence (PL) have been examined for regioregular (RR-) poly(3-octylthiophene) (P3OT) and regiorandom (RRa-) P3OT diluted in polypropylene (PP). RR-P3OT gives blue-shifted spectra in both absorption and PL against the ones in the spin coated (SC) film, contrary to the case when diluted in poly-(methyl methacrylate) (PMMA). Spectroscopic features indicate that isolated species are primarily generated for RR-P3OT by the dilution using PP. The comparison in PL spectra between in the SC film and in diluted sample demonstrates that the species responsible for PL in the SC film are interchain excitons in RR-P3OT and intrachain excitons in RRa-P3OT. We further identified the enhancement in the PL quantum efficiency of RRa-P3OT as well as RR-P3OT by the dilution using PP, indicating that PL of conjugated polymers can be enhanced in the solid state by dilution using moderate inert polymers. We infer that RR-P3OT takes a highly rod-like structure in PP and that RRa-P3OT primarily takes a much less linear conformation in PP.     

电磁泵用碳化硅材料表面致密化

针对电磁泵用碳化硅耐火材料发生铝液的渗透破坏问题,采用负压液相浸渍技术使碳化硅耐火材料表面致密化.利用静力天平、SEM与ImageJ,对比研究了浸渍剂、浸渍工艺对碳化硅试体表面致密化效果的影响,并对浸渍剂和浸渍工艺进行了优化.结果表明:采用Ca_3(PO_4)_2、AlPO_4与纳米SiO_2饱和混合溶液浸渍、浸渍-干燥-烧结重复4次的浸渍工艺可得到最佳的表面致密化效果:表面孔隙率由9.3%降为0.1%、表面最大孔径由182 μm降为3.8 μm,吸水率由11.15%降为1.89%.     

Displacement deposition of gold nanoparticles and electroless deposition of nickel films on silicon-carbide (4H-SiC) wafers

Metallisation of silicon carbide (SiC) wafers is a key technology for producing efficient power devices. Conventional autocatalytic electroless deposition cannot produce adherent metal films directly on SiC substrates. The authors applied their recently developed surface-activation process for electroless metal-film deposition on silicon wafers to SiC wafers. Gold nanoparticles were produced on 4H-SiC substrates by displacement deposition after immersing the substrates in a tetrachloroauric(III) acid solution that includes hydrofluoric acid or potassium hydroxide. The size and the particle density of the deposited gold are changed with deposition parameters such as the surface condition of the substrates, the solution composition, and the UV-light illumination. The gold nanoparticles work not only as catalysts to initiate autocatalytic electroless deposition but also as binding-points between the metal film and the SiC surface. Adherent and uniform nickel-phosphorus alloy films are produced on such SiC substrates by autocatalytic electroless deposition without any further treatments.