氧分压对ZnO纳米结构的形貌及光学性能的影响

利用未采用催化剂的真空热蒸发法合成了不同形貌的硅基ZnO纳米结构,研究了氧分压对纳米ZnO结构及光学性能的影响.研究结果表明氧分压对ZnO纳米结构的形貌及光学性能具有明显的影响,在氧分压为25;、10;和5;时制得的纳米ZnO结构分别为纳米线、纳米带和纳米梳.X射线衍射测试表明制得的不同ZnO纳米材料均为六方纤锌矿结构,并具有明显的c轴择优取向性.采用PL谱对制备纳米结构的光学性能进行了测试.     

P型微晶硅氧薄膜光电性能研究

本工作采用甚高频等离子体化学气相沉积(VHF-PECVD)技术制备了P型微晶硅氧窗口层薄膜,讨论了P型微晶硅氧的光电特性随硼烷掺杂率的变化.采用紫外-可见透射光谱,拉曼光谱,傅立叶变换红外吸收光谱(FTIR),暗电导测量对薄膜的光电特性进行了表征.结果表明,P型微晶硅氧材料均表现为微晶态,随着硼烷掺杂率增加,晶化程度逐步降低,暗电导率快速减小,光学带隙持续降低.该结果可归因于硼烷掺杂的增加抑制晶化使得非晶成分增多,有效掺杂率降低导致薄膜电导率下降,另一方面,对硅氧物相分离的阻碍作用导致薄膜带隙下降.硼烷掺杂率为0.4;样品的电导率高达0.158 S/cm且光学带隙为2.2 eV,兼具高透射性和良好电导率,可作为高效硅基太阳电池的窗口层.     

硼协同掺杂金刚石单晶的高温高压合成

金刚石是一种具有优异性能的极限性超硬多功能材料。人工合成的金刚石可通过掺杂的方式使其具有各种独特的性质。掺硼金刚石兼具p型半导体的导电特性和金刚石自身优良的物理和化学性能,在国防、医疗、勘探、科研等领域具有极高的应用价值。本文基于本课题组高温高压(HPHT)法合成的系列掺硼金刚石以及硼协同掺杂金刚石单晶,进行了硼掺杂金刚石、硼氢协同掺杂金刚石以及硼氮协同掺杂金刚石的合成和性能特征等方面的研究。通过表征合成样品在光学、电学方面的性能,探讨了不同掺杂添加剂对合成金刚石性能的影响,为合成高性能的半导体金刚石提供了思路。     

Network connectivity in aluminoborosilicate glasses: A high-resolution 11B, 27Al and 17O NMR study

O-17 enriched calcium and potassium aluminoborosilicate glasses with compositions similar (or analogous) to commercial E-glass were made and studied by ¹¹B, ²⁷Al and ¹⁷O NMR in order to explore the network speciation and mixing. Fractions of non-bridging oxygens associated with silicon and boron can be obtained simply from ¹⁷O magic angle spinning (MAS) NMR, while bridging oxygen populations result from complete peak assignment of high-resolution ¹⁷O triple quantum magic angle spinning (3QMAS) NMR spectra. Dramatic differences between the two samples in boron and oxygen speciation demonstrate a large effect of the charge of the modifier cation on mixing behavior and on the stabilization of non-bridging oxygens. The observed oxygen speciation is compared with that calculated from two models: random mixing of Si, B, and Al, and mixing with avoidance of linkages between tetrahedral aluminum and tetrahedral boron groups. Mixing of B and Al in the K-containing glass tends to follow the latter, while the network speciation in the Ca-containing glass is closer to the random model. The effects of Al and Si on boron speciation are discussed, and indicate that the maximum fractions of four-coordinated boron observed in a wide range of glass compositions are closely related to tetrahedral B and Al ‘avoidance’. A modified ‘Dell and Bray’ model is proposed which seems to accurately approximate boron speciation in many alkali aluminoborosilicate glasses. The higher field strength modifier cation (Ca²⁺ vs. K⁺) promotes the formation of non-bridging oxygen, trigonal over tetrahedral boron, and at least minor amounts of five-coordinated aluminum.     

Flexible Structures Based on a Short Pitch Cholesteric Liquid Crystals

We report on the realization and characterization of electro-responsive and pressure sensitive polydimethylsiloxane (PDMS) conductive photonic structures combined with the reconfigurable properties of short pitch cholesteric liquid crystals (aligned in Grandjean configuration). By combining ion-implantation process and surface chemistry functionalization, we have overcome the insulating properties of PDMS and induced long range organization of cholesteric liquid crystals, thus controlling both diffraction and selective Bragg reflection of light by means of external perturbations (electric field, pressure). We have characterized our devices in terms of morphological, optical and electro-optical properties.     

水基流延成型和热压烧结制备碳化硼陶瓷及性能研究

以工业碳化硼粉末为原料、采用Si3N4磨球磨损法引入Si3N4烧结助剂,采用水基流延成型和热压烧结方法制备了碳化硼陶瓷.研究了氧含量、分散剂、pH值等因素对B4C陶瓷浆料分散性能的影响,采用XRD、SEM等对碳化硼陶瓷的物相、显微结构和第二相分布进行了表征,并测试了样品的维氏硬度、断裂韧性、抗弯强度和弹性模量.结果表明:经醇洗后的碳化硼粉末中氧化硼含量降低,有利于B4C陶瓷浆料的分散稳定.采用球磨磨损引入了Si3N4粉,在B4C基体中通过原位反应形成第二相SiC和BN,SiC和BN第二相颗粒在B4C基体中弥散分布均匀.在2100 ℃热压烧结样品的维氏硬度、抗弯强度、断裂韧性和弹性模量分别达到30.2 GPa、596.5 MPa、3.36 MPa·m1/2和362.3 GPa.     

Influence of thermal annealing ambient on Ga-doped ZnO thin films

The effect of thermal annealing on the structural, chemical, electrical, and optical properties of Ga-doped ZnO (GZO) films was investigated in various ambients, such as oxygen, nitrogen, and forming gas (95% N₂ 5% H₂). The variation of these properties is thought to be related to the chemisorption and removal of adsorbed oxygen on the GZO film surface. The carrier concentration of the GZO films increased with heat treatment in the forming gas ambient. However, the carrier concentration of the GZO films decreased with heat treatment in oxygen and nitrogen. Annealing under forming gas, oxygen weakly absorbed on the GZO film was removed. Annealing under N- and O-rich conditions, chemisorption of oxygen was dominant. These results were clarified by comparatively analyzing the chemical states of oxygen on the surface of the GZO films.     

氧对饵掺杂硅纳米晶粒电子结构和光学性质的影响

采用第一性原理,对O与Er共掺杂硅纳米晶粒的电子结构及光学性质进行了计算.计算结果表明:O原子的掺杂没有影响Er掺硅纳米晶粒的禁带宽度;Er掺硅纳米晶粒结构在紫外区的吸收峰因O原子的掺入明显加强,红外区源于Er原子的吸收峰峰值减小.     

LPE生长GaN的不同极性面的光学性质

极化效应会导致GaN基发光器件的效率降低,因此关于非极性和半极性GaN单晶的研究受到了广泛关注.为了进一步探究不同极性GaN的发光特性和杂质掺入的内在机理,本文利用钠助熔剂法侧向生长出的不同极性面的GaN单晶作为研究对象,对比了不同极性面的光学性质及杂质掺入特点,讨论了黄光带(YL)峰的起源及其影响因素.首先利用阴极荧...     

Ag掺杂ZnO薄膜结构和光学特性研究

采用脉冲激光沉积技术制备出了Ag掺杂的ZnO薄膜.研究了Ag含量、衬底温度及氧压对ZnO结构和光学性能的影响.结果表明:Ag以替位形式存在于ZnO晶格中,Ag掺杂浓度较低时,样品具有高度c轴择优取向.衬底温度越高,薄膜的结晶质量越好,光学带隙越接近纯ZnO的带隙,而其紫外荧光峰在衬底温度为300 ℃时最强.氧压为10 Pa时,薄膜的结晶质量最好,紫外峰最强,其带隙则随氧压的增大呈先变窄后加宽的趋势.     

直流磁控溅射陶瓷靶制备ITO薄膜及性能研究

以10%质量分数SnO2和90%质量分数In2O3烧结成的ITO氧化物陶瓷为靶材,采用直流磁控反应溅射法在玻璃基片上制备ITO透明导电薄膜,研究了基片温度和氧分压条件对ITO薄膜的物相结构和光电性能的影响。实验结果表明:ITO薄膜的方块电阻随衬底温度的升高而下降,而可见光透过率增大;ITO薄膜可见光透过率和方块电阻随氧分压的增加而增大。     

Structure and Optical Properties of dc Reactive Magnetron Sputtered Zinc Oxide Films

Zinc oxide films were deposited on glass substrates in argon and oxygen atmosphere by dc reactive magnetron sputtering using a metallic zinc target. The influence of oxygen pressure and substrate temperature on the structure and optical properties of the films were systematically investigated and optimised the deposition parameters to prepare single phase zinc oxide films with preferred (002) orientation. At an optimum oxygen pressure of 1x10^-3 mbar and substrate temperature of 663 K, the films exhibited an optical transmittance of 83% with a band gap of 3.28 eV.     

Thermal expansion and transition temperature of glasses in the systems BeO–Al2O3–B2O3 and MgO–Al2O3–B2O3

Researches were conducted for glasses in the systems BeO–Al₂O₃–B₂O₃ and MgO–Al₂O₃–B₂O. The following characteristics have been determined: thermal expansion coefficient within 20–300 °C, structural thermal expansion coefficient (STEC) and glass transition temperature. The discussed properties of Be-aluminoborate and Mg-aluminoborate glasses have been compared with those of Ca-, Sr- and Ba-aluminoborate glasses. TEC of studied glasses gets higher going from Be-aluminoborate glasses to Ba-aluminoborate ones, but T_g decreases under the same succession. The dependence of STEC on the nature of a given cation is more complicated. The pattern of dependence of the properties on composition is due to changing the boron coordination number with respect to oxygen, which is the main network-former, and to competition between the aluminium and boron for the oxygen brought by an ion-modifier. The difference between the effect of one ion-modifier and that of another is determined by decreasing the radius of an ion and increasing its electric field strength in the succession from Ba²⁺ to Be²⁺. The ions of Be and Mg can also act as network-former to some extent.     

Substrate effect on microstructure and optical performance of sputter‐deposited TiO2 thin films

This study deals with the role of the different substrates on the microstructural, optical and electronical properties of TiO₂ thin films produced by conventional direct current (DC) magnetron sputtering in a mixture of pure argon and oxygen using a Ti metal target with the aid of X–ray diffractometer (XRD), ultra violet spectrometer (UV–vis) and atomic force microscopy (AFM) measurements. Transparent TiO₂ thin films are deposited on Soda lime glass, MgO(100), quartz and sitall substrates. Phase purity, surface morphology, optical and photocatalytic properties of the films are compared with each other. It is found that the amplitude of interference oscillation of the films is in a range of 77‐89%. The transmittance of the film deposited on Soda lime glass is the smallest while the film produced on MgO(100) substrate obtains the maximum transmittance value. The refractive index and optical band gap of the TiO₂ thin films are also inferred from the transmittance spectra. The results show that the film deposited on Soda lime glass has the better optical property while the film produced on MgO(100) substrate exhibits much better photoactivity than the other films because of the large optical energy band gap. As for the XRD results, the film prepared on MgO(100) substrate contains the anatase phase only; on the other hand, the other films contain both anatase and rutile phases. Furthermore, AFM images show that the regular structures are observed on the surface of all the films studied. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and optical properties of vapour‐etching based porous silicon

The structural and optical properties of porous silicon (PS) layers prepared by Vapour‐Etching (VE) of moderately and heavily boron‐doped Si substrates are investigated. The VE technique produces rough PS layers that are essentially formed of interconnected cluster‐like structures. Optical investigations indicate that this surface roughness enables the PS layers to be used as antireflection coatings in silicon based devices. These optical characteristics are investigated by optical reflectivity and light scattering. The local chemical state and the microstructure of the PS layers are studied by electron energy loss spectroscopy (EELS) in transmission electron microscopy (TEM), and are correlated to the red photoluminescence (PL). TEM studies point out that the cluster‐like interconnected structures are composed of luminescent nanocrystallites. PL measurements display that both quantum confinement and surface passivation determine the electronic states of the silicon nanocrystallites. The complex dielectric function is calculated from the experimental single‐scattering distribution spectrum using a Kramers Kronig analysis. The first resonance peak in the imaginary part is observed at 2.3 eV; two other broadened features appear at 4.7 and 8.8 eV. The latter is generally related to an interface plasmon resulting from the silicon‐silicon oxide interface. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoacoustic studies on optical and thermal properties of p‐type and n‐type nanostructured porous silicon for (100) and (111) orientations

Nanostructured p‐type and n‐type porous silicon samples were prepared for (100) and (111) orientations and a systematic study is carried out on the effects of orientations, dopant type (boron and phosphorous), current density (20 and 30mA/cm²) and etching time on the formation, optical and thermal properties by photoacoustic spectroscopy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dependence of RF power on the phase transformation for boron nitride films deposited on graphite at room temperature

Cubic boron nitride (cBN) thick films deposited on mainly c-axis-oriented graphite substrate at room temperature and zero bias by radio frequency (RF) magnetron sputtering were studied. In the growth process, RF power plays a key role in determining the content of cubic phase in films, while the conventional substrate heating and biasing have been neglected. With increase in RF power, the dominated content of films converts from explosion boron nitride (eBN) to cBN. The transformation mechanism has been discussed. The unique structural properties of the “soft” graphite are favorable to propose simple conditions for growing “hard” cBN films. Furthermore, the optical band gap of BN films having ∼90% cubic phase is of ∼5.8 eV obtained from ultraviolet–visible optical transmission measurement. The electron field emission examination shows that cBN film on graphite has a high emission current density of 2.8×10⁻⁵ A/cm² at an applied field of ∼30 V/μm.     

New aluminium precursors for MOMBE (CBE): a comparative study

Recently different new Al precursors have been developed to improve the electrical and optical quality of AlGaAs layers grown by MOMBE (CBE), since AlGaAs layers still suffer from the high incorporation of oxygen and carbon. Three approaches are introduced and results obtained from Al_xGa_1−xAs layers (0 < x ≤ 1) are discussed. APAH, a double ring structure molecule, was found to yield AlGaAs layers with high contents of carbon and nitrogen. The use of an Alane-adduct decreases impurity concentrations and improves optical properties. However, TIBAl is superior and provides highest PL response together with carrier concentrations below p = 10¹⁶ cm^-3. Even though the concept of coordinative saturation is promising, results achieved by TIBAl showed that trialkyls could also be well suited for AlGaAs, assuming that they are properly synthesized.     

Investigation of semi-insulating oxygen-doped GaAs

We found Oxygen-doped GaAs crystals to be suitable materials for CO₂ laser optical component preparation, with application at 10.6 μm. An optical transmission of 55% in the IR spectrum range, between 2 and 15 μm has been reached for such a GaAs type material. The GaAs crystals that we have analysed were grown by two procedures: Horizontal Bridgman (HB) and Liquid Encapsulated Czochralski (LEC). The HB method has been used for obtaining pure (undoped) crystals, while the oxygen-doped GaAs ingots were grown by LEC technique. The two types of samples processed in the same manner as regards mechanical polishing and chemical etching, which were investigated by Hall measurements, optical transmission spectrometry and elastic recoil detection analysis (ERDA) technique. The GaAs:O (LEC) has near semi-insulating properties as can be observed from the results of the electrical resistivity and Hall effect measurements. The ERDA spectrum shows an intense signal of oxygen in the bulk of GaAs:O (LEC) crystals, while the oxygen signal is not present in the ERDA spectrum of the undoped GaAs (HB). We consider that these results could recommend the ERDA technique as a possible qualitative and quantitative analysis in an ion-beam accelerator for oxygen content in oxygen-doped GaAs crystals. The analysis is not sensitive to the native oxide, as could be seen by measuring GaAs (HB) undoped crystals.     

Na0.5Pb2[B5O9]Cl(OH)0.5, a new polar variety of hilgardite containing Na+ cations in the cavities of the framework. The OD-family of the 5: 2Δ 3⧄ pentaborates: Hilgardites, heidornite, probertite, and ulexite

A new orthorhombic polar variety of Pb-hilgardite containing Na⁺ and HOCl^2? ions in the cavities of the framework has been prepared by hydrothermal synthesis. A correlation between the structural features and nonlinear-optical properties of the crystals is discussed. Similar to the hexaborate group, pentaborates with different degrees of condensation of the boron—oxygen radical are characterized by close structural similarity, which is described within the _OD theory with distinguishing structural units (blocks or modules) of different dimensionality—bricks, rods, and layers. Consideration of the variants of their connection allows us to describe the diversity of the pentaborate family including hypothetical structures.