晶体生长机理.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,非平衡材料研究室,西安理工大学,晶体生长基础,郭 学 锋,材料科学与工程学院,内容简介,晶体生长过程相平衡,晶体形核理论,界面运动学,晶体生长过程的输运,生长过程中界面稳定性,界面动力学问题,目 录,第一章 单晶体,第二章 晶体生长方法,第三章 相平衡状态图,第四章 晶体生长过程中的输运问题,第五章 界面稳定性理论,第六章 晶体形核理论,第七章 界面结构与运动学理论,第八章 界面动力学理论,第九章 晶体生长的基本问题,第十章 晶体的品质鉴定,第一章 单 晶 体,1.1,新材料技术与单晶体,材料的分类（按照用途分）,2.,晶体,BBO Crystal,晶体材料在功能材料中占有重要地位，这是由于它具有一系列,独特的物理性能,所决定的。,常见的晶体材料有：,（,1,）激光晶体,固体激光器的发光材料，通常被称为激光晶体。,早期的红宝石：,(Al,2,O,3,:Cr,3+,),目前的掺钕钇铝石榴石：,(YAG:Nd,3+,),目前在,350,多种基质晶体和,20,多种激活离子的约,70,个跃迁波段上实现了受激发射。,Nd:YVO,4,Crystal,Nd:YVO,4,crystal is one of the most excellent laser host materials,it is suitable for diode laser-pumped solid state laser.,A,）基质晶体（载体）中掺入激活离子（发光中心,Nd,3+,，,Cr,3+,，,Ho,3+,，,Dy,2+,）。输出的波长从紫外（,0.17,m,）到中红外（,5.15,m,）。如：红宝石,Al,2,O,3,:Cr,3+,，掺钕钇铝石榴石,YAG:Nd,3+,等。,B,）化学计量激光晶体，这种晶体的激化离子就是晶体组成之一。其特点：高效、低值，功率小。,分类（按组分分）,（,2,）非线性光学晶体,定义：,晶体当受到强电磁场作用时，由于非线性极化引起非线性光学效应。,目的：,是实现光频率的转化：由于非线性光学晶体可以通过其倍频、和差、光参量放大和多光子吸收等非线性过程改变入射光和发射光频率的变化。,KDP and DKDP crystals,Potassium Dihydrogen Phosphate(KDP)and Potassium Dideuterium Phosphate(DKDP)are currently used for electro-optical modulation and frequency conversion.CORETECH KDP and DKDP have high nonlinear coefficient and high optical damage threshold,and can be used electro-optical modulator,Q switches and shutters for high speed photography.,KH,2,PO,4,KD,2,PO,4,应用,激光频率转换、四波混频、光束转向、图象放大光信息处理、激光对抗和核聚变等研究领域,。,现状：,我国该领域领先,（,3,）电光晶体,定义：,光通过有外加场的晶体时，光随着外加场的变化发生如偏转、偏振面旋转等而达到控制光传播的目的。这类晶体为电光晶体。,应用：,光通讯、光开关、大屏幕显示、光储存、光雷达和光计算机等。,要求：,在使用的波长范围内，对光的吸收和散射要小、电阻率要大、介电损耗角要小、化学稳定、机械和热性能好、半波电压低等。,（,4,）声光晶体,定义：,超声波通过晶体时，在晶体中产生随时间变化的压缩和膨胀区域，使晶体的折射率发生周期性变化，形成超声导致的折射率光栅，当光通过折射率周期性变化的晶体时，将受到光栅的衍射，产生声光相互作用。这类晶体为声光晶体。,应用：,高速激光印刷系统、激光雷达、光计算机等。,（,5,）磁光晶体,定义：,当光通过组成原子有一定磁性的被磁性晶体反射（克耳效应）或透射（法拉第效应）时，其偏振面状况将发生变化，这类晶体为磁光晶体。,应用：,激光快速开关、调制器、循环器及隔离器；计算机储存器等。,（,6,）热释电晶体,定义：,当温度发生变化时，晶体某一结晶学方向上正负电荷相对重心位移而引起自发极化效应，这类晶体为热释电晶体。,应用：,红外热释电探测器、红外热释电摄像管等。,（,7,）压电晶体,定义：,通过拉伸或压缩使晶体产生极化，导致晶体表面电荷的现象称为压电效应，这类晶体为压电晶体。,应用：,滤波器、谐振器、光偏转器、测压元件等。,（,8,）闪烁晶体,定义：,当射线或放射性粒子通过晶体时，晶体会发出荧光脉冲，这类晶体为闪烁晶体。,应用：,核医学、核技术、空间物理等。,（,9,）半导体晶体,定义：,电阻率处于导电体（,10,-5,.cm,）和绝缘体（,10,10,.cm,）之间的晶体为半导体晶体。,应用：,声、光、电等。,（,10,）薄膜晶体,定义：,1,m,或以下厚度的,晶体。,应用：,电子管和超大规模集成电路等。,（,11,）,晶体,除了以上谈到的晶体以外，尚有：铁电、硬质、绝缘、敏感、热光、超导体、快离子导体等等,。,1.2,晶体生长单晶时原料（母相）状态对生长方法进行分类：,气相,液相,固相,晶体生长方法分类,晶体生长方法,溶液生长法,熔液生长法,气相生长法,固相生长法,薄膜生长法,降温，恒温蒸发，温差水热，循环流动，凝胶等,提拉，下降，焰熔，导模，冷坩埚，助熔剂区熔，浮区，基座等,真空蒸发镀膜，升华，气相外延，化学气相沉积等,高压，再结晶等,真空蒸发，分子束外延，溅射，粒子束外延，液相外延，离子注入，,LB,膜等,科学发展要求晶体材料的数量、品质、品种等越来越高。晶体生长方法各有其特点，生产中采用哪一种完全要根据要求来确定。,2.,晶体生长方法发展动向,晶体生长技术发展动向,完整性,利用性,功能性,重复性,杂质、缺陷的控制，特殊环境下生长等,大尺寸、异形、薄膜等,极端条件下生长，结构、组织的控制生长,自动化，程序化，原材料规范化等,3.,晶体生长研究方法,晶体生长研究方法同其它材料的研究方法相同，除了严格控制晶体生长原材料之外，对晶体的结构、晶体的生长方法和晶体的性质进行研究是晶体生长研究的重点。由此可见：研究晶体生长必然以,（,1,）晶体生长,（,2,）晶体物理,（,3,）晶体化学,为基础。,简言之：,晶体生长,控制,生长工艺,生长设备,生长理论,生长方法,晶体物理,晶体化学,形貌,缺陷,物性,应用,结构,组成,化学键,相关系,图,1.1,晶体学研究的基础内容及相互关系,1.4,材料科学研究与发展方向,（,1,）材料复合化,（,2,）纳米材料,（,3,）智能材料,（,4,）生物医学材料,（,5,）,C,60,系列材料,非平衡材料,C,CARBON,Carbon is an element that exists in various polymorphic forms,as well as in the amorphous state.,This group of materials does not really fall within any one of the traditional metal,ceramic,polymer classification schemes.,1.DIAMOND,Diamond is a metastable carbon polymorph at room temperature and atmospheric pressure.Its crystal structure is a variant of the zinc blende,in which carbon atoms occupy all positions(both Zn and S),as indicated in the unit cell shown in Figure 3.4.,Figure,A unit cell for the diamond cubic crystal structure.,2.GRAPHITE,Graphite has a crystal structure distinctly different from that of diamond and is also more stable than diamond at ambient temperature and pressure.,The graphite structure is composed of layers of hexagonally arranged carbon atoms;within the layers,each carbon atom is bonded to,three coplanar neighbor atoms,by strong covalent bonds.The fourth bonding electron participates in a weak van der Waals type of bond between the layers.,Figure,The structure of graphite.,covalent bond,Weak van der Waals type,3.FULLERENES,Another polymorphic form of carbon was discovered in 1985.It exists in discrete molecular form,and consists of a hollow spherical cluster of sixty carbon atoms.,A single molecule is denoted by C,60,.,Each molecule is composed of groups of carbon atoms that are bonded to one another to form both hexagon(six-carbon atom)and pentagon(five-carbon atom)geometrical configurations.,One such molecule is found to consist of 20 hexagons and 12 pentagons,which are arrayed such that no two pentagons share a common side;the molecular surface thus exhibits the symmetry of a soccer ball.,The material composed of C,60,molecules is known as,buckminsterfullerene,named in honor of R.Buckminster Fuller,who invented the geodesic dome.,C,60,is often referred to as buckyball for short.,The term,fullerene,is used to denote the class of materials that are composed of this type of molecule.,Here we are!,Figure,The structure of a C,60,molecule.,As a pure crystalline solid,this material is electrically insulating.However,with proper impurity additions,it can be made highly conductive and semiconductive.,As a final note,molecular,shapes,other than the ball clusters recently have been discovered;these include nanoscale tubular and polyhedral structures.,It is anticipated that,with further developments,the fullerenes will become technologically important materials.,1.5,材料科学,