不同形貌低维纳米／微米CdSe／ZnSe的溶剂热法合成

利用溶剂热法．通过添加不同种类的溶剂及改变反应温度、反应时间．成功合成了具有片状、棒状、球技，圆锥花序状等不同形貌的纳米/微米级硒化镉、硒化锌半导体材料.简单讨论了表面活性剂、反应温度及反应时间对产物形貌及尺寸的影响。所得产物进行了扫描电子显微镜（SEM）、透射电子显微镜（TEM）、能谱（EDS）、X射线折射（XRD）等表征.     

不同形貌低维纳米/微米CdSe/ZnSe的溶剂热法合成

利用溶剂热法,通过添加不同种类的溶剂及改变反应温度、反应时间,成功合成了具有片状、棒状、球状、圆锥花序状等不同形貌的纳米/微米级硒化镉、硒化锌半导体材料.简单讨论了表面活性剂、反应温度及反应时间对产物形貌及尺寸的影响.所得产物进行了扫描电子显微镜(SEM)、透射电子显微镜(TEM)、能谱(EDS)、X射线衍射(XRD)等表征.     

CdSe 在玻璃中的核化过程

用高分辨电镜、X-射线衍射研究了 CdSe 在玻璃中的成核和生长过程.首次观察到,伴随着这种成核和生长过程,玻璃的光吸收限、光吸收限的温度系数,以及光吸收系数和光子能量的依从关系都发生变化.     

ZnSe单晶CVT法生长与系统优化

采用热力学数值计算的方法, 分析了ZnSe-I₂、H₂、HCl和NH₄Cl化学气相输运系统的特性. 对比计算结果表明, ZnSe-NH₄Cl系统具有压力高、输运反应焓变适中的特点. NH₃分解产生的H₂起着调节输运组分H₂Se分压的作用. 以ZnSe-I₂输运系统中实际输运组分分压值为参考, 确定了ZnSe-NH₄Cl系统中单晶生长工艺参数范围: 温度在1000℃左右, NH₄Cl的浓度范围在0.5~1.0mg/mL之内. 采用该工艺生长了尺寸约为8mm×6mm×4mm的ZnSe单晶, 生长态(111)面摇摆曲线半峰宽为60.48’’, 蚀坑密度(EPD)为(4.5~5.0)×10⁴/cm².     

不同形貌CdSe纳米晶的合成及其形成机理研究

采用水热反应法,通过调节反应时间制备得到了不同形貌的CdSe纳米晶材料,并用TEM、XRD、EDS、XPS等分析手段对其形貌结构进行表征。研究表明,在反应温度为180℃的条件下,所得产物均为六方晶相的CdSe纳米晶,形貌随着反应时间的改变而发生变化:当控制反应时间为2h、5h、10h时,得到的CdSe纳米晶的形貌分别为树枝状、由树枝状到棒状过渡的簇状及棒状。分析了CdSe纳米晶形成的化学反应原理,并运用结晶学原理和相关模型理论对CdSe纳米晶的形成机理及其形貌变化进行了探讨。     

ZnSe体单晶生长技术

简述了ZnSe体单晶熔体生长，气相生长、溶液生长和固相再结晶技术以及ZnSe的基本理化性质，分析并认为这些基本理化性质对Znse单晶生长过程控制存在不同程度的影响，理解这些性质并将其应用于ZnSe晶体生长过程工艺参数的控制，对获得高质量大尺寸ZnSe单晶十分重要，分析了不同方法的工艺与相应ZnSe单晶研究现状及发展趋势。     

嵌段聚合物模板合成CdSe纳米粒子及表征

以羟基化SBS(SBS-OH)为模板,N,N-二甲基甲酰胺(DMF)为溶剂,硒代硫酸钠及乙酸镉为前驱物,"原位反应"制备了CdSe纳米粒子.通过紫外-可见吸收光谱、荧光光谱(PL)和透射电子显微镜(TEM)等方法对CdSe纳米粒子的光学性质及形貌进行了表征.结果表明,利用SBS-0H的两亲性质,可以在DMF中得到具有明...     

N-Bi2O2CO3/CdSe量子点光催化氧化NO及原位红外光谱研究

本实验成功制备了氮掺杂碳酸氧铋(N-Bi₂O₂CO₃, N-BOC)/硒化镉量子点(CdSe QDs)复合光催化剂, 并将其运用于光催化降解室内空气污染物一氧化氮(NO)。X射线衍射、透射电子显微镜和光电子能谱测试结果表明N-BOC光催化剂在保持原有纳米片结构和形貌的基础上成功负载了CdSe QDs。光催化氧化NO实验结果显示CdSe QDs的引入可显著提高N-BOC的NO去除率, 并且二次毒副产物NO₂生成率大幅度降低至1%, 表明复合光催化剂具有极强的毒副产物抑制特性。固体紫外漫反射吸收光谱和发光光谱测试表明CdSe QDs拓宽并提升了N-BOC的光响应范围和能力, 并有效抑制了光生电子-空穴的复合效率。通过原位漫反射傅里叶变换红外光谱技术(DRIFTS)分析, 发现在N-BOC/CdSe QDs光催化氧化NO反应过程中没有NO₂信号产生, 仅观测到NO₃ ^-相关信号。机理分析表明超氧自由基(O₂ ^-)和光生空穴(h ⁺)是体系中可能存在的活性物种, 实现了对NO到NO₃ ^-的彻底氧化。     

CVD法制备单层二硒化钨薄膜及其生长机制研究

二硒化钨(WSe₂)是一种具有较高带隙的半导体材料,其结构类似于石墨烯,具有优异的光电特性,在互补逻辑电路、场效应晶体管以及气敏传感器等领域具有潜在的应用价值。本实验采用化学气相沉积法(CVD)实现了大面积、高质量单层WSe₂薄膜的制备,利用XPS、AFM、Raman对薄膜进行了表征,探究了基片到钨源的距离和生长温度对样品的形貌、尺寸及形核密度的影响。从晶体生长学的角度,用不同n(W):n(Se)(■0.5,>0.5,=0.5)生长模型解释了不同形貌WSe₂薄膜的生长机制,为可调控二维半导体单层薄膜制备工艺的优化提供了参考。     

GaN单晶的HVPE生长与掺杂进展

相比于第一代和第二代半导体材料,第三代半导体材料具有更高的击穿场强、电子饱和速率、热导率以及更宽的带隙,更适用于制备高频、大功率、抗辐射、耐腐蚀的电子器件、光电子器件和发光器件。氮化镓(GaN)作为第三代半导体材料的代表之一,是制作蓝绿激光、射频微波器件和电力电子器件的理想衬底材料,在激光显示、5G通信、相控阵雷达、航空航天等领域具有广阔的应用前景。氢化物气相外延(Hydride vapor phase epitaxy, HVPE)方法因生长设备简单、生长条件温和和生长速度快而成为制备GaN晶体的主流方法。由于普遍使用石英反应器,HVPE法生长获得的非故意掺杂GaN不可避免地存在施主型杂质Si和O,使其表现出n型半导体特性,但载流子浓度高和电导率低限制了其在高频大功率器件中的应用。掺杂是改善半导体材料电学性能最普遍的方法,通过掺杂不同掺杂剂可以获得不同类型的GaN单晶衬底,提高其电化学特性,从而满足市场应用的不同需求。本文介绍了GaN半导体晶体材料的基本结构和性质,综述了近年来采用HVPE法生长高质量GaN晶体的主要研究进展;对GaN的掺杂特性、掺杂剂类型、生长工艺以及掺杂原子对电学性...     

硒化镉(CdSe)单晶体的变温霍尔效应研究

通过变温（20～300K）霍尔效应测量,研究了CdSe单晶体的电阻率ρ（T）、载流子浓度n（T）、霍尔系数RH（T）和霍尔迁移率μH（T）的温度依赖关系.实验结果表明CdSe单晶体的导电类型总为n型,且它的电阻率与载流子浓度的温度依赖关系与n-Si单晶类似.通过拟合禁带宽度约为1.7eV.本文还进一步研究了本征区、饱和区、弱电离区内电子浓度的变化和霍尔因子γ随温度变化关系,并由此计算出杂质电离能（24.7meV）与补偿度（23.7%）.上述结果表明CdSe单晶体具有优良的电学特性,是制作室温核辐射探测器的理想材料.     

气相生长硒化镉单晶体的生长速度研究

以晶体生长理论为基础，计算了气相提拉生长CdSe晶体时的生长速率。结果表明用提拉法气相生长CdSe晶体时，晶体的气相生长速率将会随着时间的延长以指数关系快速的趋近于提拉速度，以后不再变化。由此，在选定温场的前提下，对CdSe单晶体的气相生长速度进行了优化，确定了3mm／d的生长速度，得到了平界面生长的尺寸为Ф20mm×30mm，电阻率高达10^9Ω·cm，且未观察到深能级陷阱的优质CdSe大单晶体.     

Growth and physico chemical characterization of lanthanum neodymium oxalate single crystals

Single crystals of lanthanum neodymium oxalate (LNO) are grown in sodium meta silicate gels, by the diffusion of a mixture of aqueous solutions of lanthanum nitrate and neodymium nitrate into the test tube having the set gel containing oxalic acid. The bluish pink coloured tabular crystals of LNO having well defined hexagonal basal planes appear either as ‘foggy’ or ‘clear’, the latter at the greater depths inside the gel. The colouration of LNO visually observed is evidenced in UV-visible spectrum, by the revelation of well pronounced characteristic peaks in the visible region (500–900 nm). X-ray diffraction (XRD) of powdered LNO is ordered, meaning crystalline in nature, besides its ‘isostructurality’ with similarly grown lanthanum samarium oxalate crystals. The single crystallinity of LNO is established by its oscillation XRD pattern. Thermogravimetric analysis (TGA) and differential scanning colorimetry (DSC) support that LNO loses water of crystallization around 120°C and CO and CO₂ around 350–450°C, while the infrared absorption (IR) spectrum of LNO establishes the presence of oxalate (C₂O₄)²⁻ ions. Energy dispersive X-ray analysis (EDAX) confirms the presence of La and Nd in the sample. X-ray photoelectron spectroscopic (XPS) studies of LNO establish the presence of La and Nd in their respective oxide states. An empirical structure for LNO has been proposed on the basis of these findings. The ‘smokiness’ in the foggy LNO crystal has been attributed due to the ‘gel inclusion’ during the growth process.     

Structural characterization of gel-grown neodymium copper oxalate single crystals

Sparingly soluble neodymium copper oxalate (NCO) single crystals were grown by gel method, by the diffusion of a mixture of neodymium nitrate and cupric nitrate into the set gel containing oxalic acid. Tabular crystal, revealing well-defined dissolution figures has been recorded. X-ray diffraction studies of the powdered sample reveal that NCO is crystalline. Infrared absorption spectrum confirmed the formation of oxalato complex with water of crystallization, while energy dispersive X-ray analysis established the presence of neodymium dominant over copper in the sample. X-ray photoelectron spectroscopic studies established the presence of Nd and Cu in oxide states besides (C₂O₄)²⁻ oxalate group. The intensities of Nd (3d _5/2) and Cu (2p _3/2) peaks measured in terms of maximum photoelectron count rates also revealed the presence of Nd in predominance. The inductively coupled plasma analysis supports the EDAX and XPS data by the estimation of neodymium percentage by weight to that of copper present in the NCO sample. On the basis of these findings, an empirical structure for NCO has been proposed. The implications are discussed.     

Growth of low dislocation density single crystals of nickel

Low dislocation density single crystals of nickel have been grown at high ambient pressure by the Czochralski method. X-ray Laue picture shows that the crystals are strain-free. The dislocation density was determined to be <10³/cm² by the etching procedure. It was found that the necking and cone regions are very critical in the dislocation introduction in the crystals. An increase in the ambient pressure used during the growth seems to aid the crystal quality.     

Growth and characterization of rare-earth mixed single crystals of samarium barium molybdate

Molybdate crystals doped with rare-earth ions are finding immense use as laser materials. Rare-earth mixed single crystals of samarium barium molybdate grown in silica gel are important for use in optical equipment and electronic and acoustic studies. These octahedral bipyramidal crystals of samarium barium molybdates are characterized by IR, EDAX and thermal analyses.     

Vapor growth of CdSe:Cr and CdS:Cr single crystals for mid-infrared lasers

Single crystals of CdSe:Cr and CdS:Cr with the doping level up to 10¹⁹ cm⁻³ were grown by a vapor phase contact-free technique. An efficient room-temperature pulsed and continuous wave (CW) lasing with the CdSe:Cr crystal was achieved. First a pulsed lasing with the CdS:Cr crystal was also demonstrated. The slope efficiency on the absorbed energy was as high as 46.5% for Cr²⁺:CdSe and 39% for Cr²⁺:CdS lasers. Using an intra-cavity prism, the Cr²⁺:CdSe laser wavelength was continuously tuned from 2.26 to 3.61 μm while the Cr²⁺:CdS laser from 2.2 to 3.3 μm. For the laser wavelength, the crystal passive loss coefficient was estimated to be smaller than 0.045 cm⁻¹ for CdSe:Cr crystals and 0.039 cm⁻¹ for CdS:Cr crystals. For the Cr²⁺:CdSe laser, the CW output power up to 1.07 W was achieved.     

Growth of larger and more perfect single crystals of KClO4 in silica gel

As part of a continuing effort on crystal growth in gels, this paper describes the growth of large transparent single crystals of KClO₄ by the improved design. The effect of various anionic and cationic components on nucleation, growth and quality of these crystals has been studied. It has been found that a combination of KNO₃ and HClO₄ as the reactants resulted in the best crystals in terms of crystal size, quality and inter-crystalline separation. The effect of various impurities on nucleation, growth and quality of these crystals has been studied. It has been found that the impurities which enhance the solubility of KClO₄ have a positive effect on the size and quality of the crystals. A new etchant, consisting of concentrated HCl and H₂SO₄ in the volume ratio 2:3 has been found to reveal as-grown as well as freshly introduced dislocations.     

Growth by SR method and characterization of hippuric acid single crystals

The potential organic nonlinear optical material of hippuric acid (HA) has been grown by novel unidirectional solution growth method using dimethyl formamide (DMF) as the solvent. The crystal system has been identified and lattice dimensions have been measured from the single crystal X-ray diffraction analysis. The crystalline perfection has been evaluated by high resolution X-ray diffraction (HRXRD) technique and found that the crystal quality is reasonably good. However, it contains a low angle structural grain boundary. The relative second harmonic generation (SHG) has been tested using Kurtz powder technique and found to be 1.54 times higher than that of potassium dihydrogen phosphate (KDP) single crystal. Its optical character has been assessed by UV-Vis. analysis and found that there is no absorption in the entire visible region.     

Growth and characterization of 4-methyl benzene sulfonamide single crystals

Single crystals of 4-methyl benzene sulfonamide (4MBS) were successfully grown from aqueous solution by low temperature solution growth technique. The grown crystal was characterized by single crystal XRD and powder XRD methods to obtain the lattice parameters and the diffraction planes of the crystal. UV–vis–NIR absorption spectrum was used to measure the range of optical transmittance and optical band gap energy. The optical transmission range was measured as 250–1200 nm. FTIR spectral studies were carried out to identify the presence of functional groups in the grown crystal. The thermal behavior of the crystal was investigated from thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC) study. The absence of SHG was noticed by Kurtz and Perry powder technique. The third order NLO behavior of the material was confirmed by measuring the nonlinear optical properties using Z-scan technique and it was found that the crystal is capable of exhibiting saturation absorption and self-defocusing performance.