Growth of ZnO single crystals by an induced nucleation from a high temperature solution of the ZnO‐PbF2 system

To grow ZnO single crystals from a high temperature solution of the ZnO‐PbF₂ system, a gas cooling system was assembled at the bottom of the crucible to induce nucleation in the initial growth stage. The growth experiments were carried out in a homemade vertical Bridgman furnace and Pt crucible of 28 mm in diameter was used. The furnace temperature was set to 1100°C and the flow rate of the oxygen gas was optimized as 3.0 l/min. ZnO crystal up to 5∼8mm in the thickness was obtained with the lowering rate of 0.3 mm/h. XRD patterns showed that the as‐grown crystal was pure ZnO Wurtzite phase. The impurity ions were analyzed by the glow discharge mass spectroscopy (GDMS) as 390.0 ppm and 40.0 ppm for Pb²⁺ and F^‐, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

氧化锌晶体生长基元模拟

本文利用Hyperchem分子模拟软件对氧化锌晶体生长基元Zn(OH)42-进行了系统的模拟.通过模拟分析生长基元的结合方式,提出了生长基元的结合规律.结果表明:Zn原子数(生长基元)与共用O原子数(O桥)的比例越大所形成的络合物越稳定;当分子中Zn原子和共用O原子比例一定时,羟基数目越少则越稳定.并且通过计算机模拟生长基元直线状结合情况解释了单晶ZnO纳米线状或纳米棒状的结构很难在实验中获得的原因.     

微管ZnO可控生长的研究

本文采用水热法在玻璃基片上生长出了微米级六棱管状ZnO.采用X射线衍射(XRD)、扫描电子显微镜(SEM)对所制备的样品进行物相结构及表面形貌的分析.结果显示所制备的样品为六角晶系纤锌矿结构的ZnO.通过在基片上预先生长不同尺度中空ZnO球的方法能够成功的生长出不同尺寸微米管状ZnO,初步实现了水热合成微米管状ZnO的可控生长.     

助熔剂法生长ZnO晶体

采用Bi4B2O9、CdB2O4和BaB2O4为助熔剂,获得了毫米级的氧化锌单晶.Muiliken的电负性理论和Viting的平均轨道电负性提供了一个选择晶体生长所采用的助熔剂的有效方法.实验结果表明ZnO晶体的生长温度比文献报道的均低,从而有效地减少了ZnO以及助熔剂的挥发.本文给出了几种有望获得大尺寸ZnO单晶的助熔剂.     

化学气相输运法制备ZnO晶体

本文采用化学气相输运法在常压开放系统中以(0001)蓝宝石为基片制备出定向生长的ZnO晶体.以ZnO粉体为原料,NH4Cl为输运气体,O2和H2O为反应气体,加入适量的HCl作刻蚀性气体,通过调节NH4Cl输运量,获得两种不同生长方向的ZnO晶体,分别为(1010)方向和(0002)方向.(0002)方向上生长的晶体呈现六角片状,a、b轴生长速度明显高于c轴方向,晶体在基片上呈外延生长,大面积显露c面,且和蓝宝石c面平行.文中对O2、H2O、NH4Cl、HCl在晶体的生长中的作用和生长机制进行了讨论.     

Growth behaviour of bulk GaN single crystals grown with various flux ratios using solvent‐thermal method

Bulk GaN single crystals were grown using a solvent‐thermal method. They were grown for 200 h at 600 °C and 800 °C using 8 MPa of N₂ gas and 1–3 mm sized pyramid GaN single crystals. Pure Na, NaN₃ and Ca were used as the flux. The mole fraction of the [flux]/([flux] + [Ga]) was 0.30–0.67. The growth behavior differed according to the flux ratio. The quality of the bulk GaN single crystals was improved by increasing the flux ratio. The bulk GaN single crystals formed by spontaneous nucleation were deposited on the BN crucible wall and bottom during the first step of synthesis. The wurtzite structure of the GaN grown single crystal was confirmed by x‐ray diffration. The chemical composition was analyzed by electron probe microanalysis. The quality and optical properties of the GaN single crystal were examined by Raman spectroscopy and photoluminesence analysis. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bridgman growth of Bi4Si3O12 scintillation crystals and doped effects on radiation resistance

Ce, Nd and Eu doped BSO crystals 20×20× 100mm³ in size have been gown by vertical Bridgman method, and the doped effects on radiation resistance of BSO have also been studied for the first time. Nd and Eu dopns were found to improve the radiation resistance of BSO. However, Cc and Nd dopings degrade the light output of BSO except that Eu doping has almost no effect on it. Therefore, Eu may be the most promising dopant candidate for improving the scintillation properties of BSO crystal.     

Growth and dissolution of equally‐sized insulin crystals

A protocol for growing sets of nearly uniform size crystals was devised and tested experimentally. The experiments were centered on insulin because of its medical significance however the method is applicable to other substances as well (C.N. Nanev, V.D. Tonchev, F.V. Hodzhaoglu, Protocol for growing insulin crystals of uniform size, J. Cryst. Growth 375 (2013)10–15). Now, both growth and dissolution of equally‐sized crystals are described quantitatively by a common analytical model. In our model the emphasis is put on the dissolution case when crystals number and/or size are sufficiently large to secure reaching solubility, while some non‐dissolved crystalline substance is still remaining. Quantitative results are obtained for the relations between dimensionless values of crystal size, solution concentration and time elapsed, the assumption simplifying our calculations being that the crystals retain their shape during the entire dissolution process.     

ZnO晶体的功能梯度分析

分析n-ZnO薄膜和硼掺杂p型金刚石薄膜在{111}面金刚石衬底上制作n-ZnO/p-金刚石p-n异质结的应用,ZnO体晶微观结构和缺陷分布及电阻、载流子浓度、迁移率分布特征,探讨了应用功能梯度材料理论研究ZnO晶体材料的方法.从而提出应系统地建立ZnO晶体内部组成和结构的梯度分布特性数据库,从不同的应用角度来进行ZnO晶体材料设计和研究.     

ZnO∶Al衬底上低温生长GaN薄膜

利用射频磁控溅射在普通玻璃上制备了(0002)择优取向的ZnO:Al薄膜.采用电子回旋共振-等离子体增强金属有机物化学气相沉积(ECR-PEMOCVD)技术,在ZnO:Al薄膜衬底上沉积了厚度为320 nm的GaN薄膜.利用高能电子衍射(RHEED)、X射线衍射(XRD)、原子力显微镜(AFM)和光透射谱等表征方法,研究了沉积温度对GaN薄膜的结晶性、表面形貌和透射率的影响.     

ZnO纳米棒在Si衬底上外延生长研究

运用热蒸发ZnO粉末法,以金做催化剂,分别在Si(100)和Si(111)两种基片上外延生长了ZnO纳米棒(样品分别标为1#和2#).通过X射线衍射(XRD)和扫描电子显微镜(SEM)分析,结合ZnO与Si的晶格结构特征,从理论上得出了两个样品的晶格匹配关系.1#样品:[0001]ZnO∥[114]Si,[0001]ZnO∥[1-1-4]Si,[0001]ZnO∥[11-4]Si,[0001]ZnO∥[1-14]Si,失配度为1.54;;2#样品:[0001]ZnO∥[111]Si,[21-1-0]ZnO∥[11-0]Si,[1-21-0]ZnO∥[1-01]Si ,[1-1-20]ZnO∥[011-]Si,失配度为18.12;.研究表明Si衬底对ZnO纳米棒生长方向具有调控作用.     

单质直接气相生长ZnMgSe单晶

采用高纯Zn、Mg、Se2单质为原料,以NH4Cl作为反应输运剂,用化学气相输运(CVT)的方法一步成功生长出ZnMgSe单晶。通过XRD、RO-XRD、EDS、紫外可见分光光度计和光致发光(PL)技术研究了ZnMgSe晶体的结构、成份以及光学特性。结果表明:ZnMgSe单晶具有良好的结晶性能,在400～800 nm范围内透过率达到40%～50%,在2.2～2.6 eV范围内存在与深能级电子复合相关的发光带。研究证明由Zn、Mg、Se2单质在输运剂NH4Cl辅助下一步直接合成ZnMgSe单晶是可行的。     

Shape evolution of detached Bridgman crystals grown in microgravity

Detached (or dewetted) Bridgman crystal growth defines that process in which a gap exists between a growing crystal and the crucible wall. In microgravity, the parameters that influence the existence of a stable gap are the growth angle of the solidifying crystal, the contact angle between the melt and the crucible wall, and the pressure difference across the meniscus. During actual crystal growth, the initial crystal radius will not have the precise value required for stable detached growth. Beginning with a crystal diameter that differs from stable conditions, numerical calculations are used to analyze the transient crystal growth process. Depending on the initial conditions and growth parameters, the crystal shape will either evolve towards attachment at the crucible wall, towards a stable gap width, or inwards towards eventual collapse of the meniscus. Dynamic growth stability is observed only when the sum of the growth and contact angles exceeds 180°.     

Growth of GaSe and GaS single crystals

The paper describes principal manipulations to prepare single crystals of GaSe and GaS. A new simple method of synthesis with single‐zone heating furnace is proposed. Growth of crystals was performed by modified Bridgman method with the use of rotating heat field. Raman and optical depth spectra show high structural and optical quality of obtained crystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Template effects on the morphology of ZnO via colloidal crystals with different functional groups

ZnO is an important wide bandgap compound semiconducting material and exhibits a wide range of novel structures that can be grown by tuning the growth rates along its fast growth directions. Highly ordered macroporous materials by using colloidal crystal template method are of great interest in many fields including photonic crystals and catalysts. In this study, ZnO with highly ordered porous structure was deposited by different electrochemical method. Nanomeshes, inverse opal structures, and spherical/ellipsoidal particles with pore arrays are fabricated by the colloidal crystals with different functional groups. The template effects on the morphology of the macroporous structures for different surface groups are studied. All the nanomeshes grows along the {111} plane family by colloidal crystals without functional groups. Disordered arrangements of the nanomeshes are induced by colloidal crystals with hydroxyl groups. The inverse opal structures fabricated by template with carboxyl groups are smoother in surface.     

Vacancy defects in bulk ammonothermal GaN crystals

We have applied positron annihilation spectroscopy to study in-grown vacancy defects in bulk GaN crystals grown by the ammonothermal method. We observe a high concentration of Ga vacancy related defects in n-type samples in spite of the low growth temperature, suggesting that oxygen impurities promote the formation of vacancies also through other mechanisms than a mere reduction of thermodynamical formation enthalpy. On the other hand, no positron trapping at vacancy defects is observed in Mg-doped p-type samples, as expected when the Fermi level is close to the valence band and intrinsic defects are dominantly positively charged. Annealing of the samples at temperatures well above the growth temperature is found to change significantly the defect structure of the material.     

温度对气相传输法制备氧化锌晶体生长机制影响研究

为提高气相传输法制备微纳结构样品形貌的可控性,进行了生长温度调控下氧化锌晶体生长机制及其变化的实验研究.实验中的样品制备,以高纯度锌粉末为原料,在无模板、无催化条件下,通过加热蒸发-氧化冷却-生长晶体过程实现.其中,蒸发温度固定于750℃,反应区气体氛围保持稳定,生长区温度在450～ 600℃变化,制备出不同生长温度下样品.对所制备出诸样品,应用扫描电子显微镜、X-射线衍射仪和透射电子显微镜等方法,进行形貌与结构表征.基于表征结果,观察、分析、研究生长温度变化的影响,结合理论分析,得出了生长温度通过对生长过程中锌蒸汽过饱和度的影响,决定着不同生长机制,从而有着不同的形貌结构的样品.     

Sn掺杂对ZnO晶体形貌和磁性的影响

采用水热法,在ZnO中添加SnCl2.2H2O作前驱物,3M KOH作矿化剂,温度430℃,填充度35%,反应24h,合成了掺杂Sn的ZnO晶体。当前驱物中添加SnCl2.2H2O可以明显影响部分晶体形态,使正极面c轴方向的生长速度受到抑制,较大面积显露正极面c{0001},同时也显露负极面-c{000 1}、正锥面p{10 10}、负锥面-p{101 1}和柱面m{10 10}。磁性测量结果显示Sn可微量掺入ZnO晶格中,且呈现顺磁性特征。X射线衍射和X光荧光能谱分析表明,SnCl2.2H2O的添加量较大时,还伴随生成金红相SnO2棒状晶体。     

MOCVD生长温度对氧化锌薄膜结构及发光性能的影响

利用甲醇做氧源,采用金属有机物化学气相沉积(MOCVD)工艺在硅(111)衬底上生长了一系列的氧化锌薄膜,生长温度为400～600 ℃.薄膜的表面形貌及晶体质量分别利用场发射扫描电镜及X射线衍射仪进行了测量.研究表明:随着生长温度的降低,在X射线衍射图谱中氧化锌(101)峰取代了(002)峰成为了主峰.这可能是由于温度过低使得甲醇未完全分解,而甲醇分子抑制了氧化锌沿c轴极性过快的生长所致.室温光致发光光谱结果表明在较高生长温度下获得的样品具有良好的光学性质,发光强度随着温度的降低而降低.