富Te条件下CdTe晶体中的点缺陷研究

基于缺陷化学理论,考虑到富Te的CdTe晶体中可能存在的点缺陷,建立了在Te气氛下退火时,热力学平衡态晶体中的点缺陷模型,其中包括Cd间隙(Cdi)、Cd空位(VCd)、Te间隙(Tei)和Te反位(TeCd).利用质量作用定律和伪化学平衡方程计算了富Te情况下本征CdTe晶体中的点缺陷浓度和费米能级.计算结果系统的揭示了点缺陷浓度、费米能级、Te压以及退火温度之间的关系,发现只有TeCd浓度足够大时才能对费米能级产生钉扎作用.     

稀释磁性半导体Cd0.9Mn0.1Te晶体的退火改性

运用缺陷化学原理近似计算了Cd0.9Mn0.1Te晶体的点缺陷浓度,得到了晶体成分与理想化学计量比偏离最小时的退火条件.利用该退火条件,指导了Cd0.9Mn0.1Te晶体的两温区退火实验,并分析了退火对晶片性能的影响.结果表明:在973 K,Cd气氛下对Cd0.9Mn0.1Te晶片退火140 h后,晶片(111)面的X射线回摆曲线的FWHM值由退火前的168.8' 降至108',红外透过率由退火前48;提升到64;,接近晶体的理论透过率,电阻率也由退火前的2.643×105 Ω·cm提高到4.49×106 Ω·cm.由此可见,对生长态的Cd0.9Mn0.1Te晶体进行退火实验能提高晶体的结晶质量,补偿晶体的Cd空位点缺陷,使晶体成分接近理想的化学计量比.     

直流电弧等离子体区域电弧分布特征对自支撑金刚石膜性质的影响

直流电弧等离子体喷射法制备自支撑金刚石膜时,电弧区域可分为弧心、弧干和弧边三个区域.本文运用扫描电子显微镜(SEM)、X射线衍射(XRD)、激光Raman光谱、正电子湮没寿命谱(PAL)和力学性能实验机研究了同一块自支撑金刚石膜不同区域的生长面形貌、晶体取向、内应力、空位缺陷和断裂强度.结果表明:随着与直流电弧等离子体弧心距离增加金刚石膜生长更稳定,(220)取向晶粒减少,平均空位缺陷减少,内应力和断裂强度呈现先增大后减小的趋势.     

退火处理对CdZnTe晶体光电性能的影响

研究了生长态CdZnTe晶体在经历了不同温度和时间的Cd/Zn和Te气氛退火后,其光电性能的变化规律.研究表明,在Cd/Zn气氛下退火180 h后,CdZnTe晶体中直径在5μm以上的Te夹杂的密度减小了1个数量级,晶体的体电阻率由1010 Ω·cm减小至～107 Ω· cm.同时发现,Cd/Zn源区的温度决定了退火后晶体在500～4000cm-1范围内红外透过率曲线的平直状态,这可能与晶体中的Cd间隙缺陷浓度相关,而与晶体中的载流子浓度和夹杂/沉淀相状态无关.在Te气氛下退火时,发现晶体的红外透过率的平直状态与晶体电阻率的对数lg(ρ)呈近似线性关系,同样可归因于退火过程中Cd间隙缺陷的浓度变化.     

退火温度对Zn0.93Fe0.07O薄膜微结构和铁磁性能的影响

用射频磁控溅射方法在硅片上制备了Zn0.93Fe0.07O薄膜,并在空气中用不同温度进行热处理,利用X射线衍射仪和扫描电子显微镜对其微结构、表面和断面形貌进行测试.结果表明,薄膜沿c轴方向择优生长,呈六角纤锌矿结构,空气中450℃退火的样品XRD谱中出现最强的(002)衍射峰,晶粒尺寸变大,薄膜结晶和取向明显变好.用振动样品强磁计对样品铁磁特性进行测试,发现当退火温度的升高时,饱和磁化强度有所增加,并经分析认为这可能是薄膜中晶粒间的晶界缺陷引起的.     

多晶Si薄膜表面金催化Si纳米线生长

以Au膜作为催化剂和大晶粒多晶Si薄膜为衬底,利用固-液-固生长机制,制备出直径在30～ 100 nm和长度为几百微米的高密度Si纳米线.实验研究了退火温度、生长时间和N2流量对Si纳米线生长的影响.结果表明,随着退火温度的升高,生长时间的延长和N2流量的增加,Si纳米线的长度和密度都显著增加.对不同生长时间下获得的Si纳米线样品进行了X射线衍射测量,结果显示随着生长时间的延长,多晶Si薄膜和表面的Au膜成分都在减少.光致发光谱则显示出弱的蓝光发射和强的红光发射特性,前者应是由非晶SiOx壳层中的氧空位发光中心引起,后者则应归因于Si纳米线芯部与非晶SiOx壳层之间界面区域附近中的Si =O双键态或非桥键氧缺陷中心.     

空位浓度对纤锌矿CdS电子结构和光学性质影响的第一性原理研究

本文基于密度泛函理论的平面波超软赝势方法,采用第一性原理研究了含Cd空位缺陷CdS和含S空位缺陷纤锌矿CdS的几何结构、能带结构、电子态密度及光学性质。通过计算分析可知,含Cd空位缺陷的CdS体系均为p型半导体,含S空位缺陷的CdS体系跃迁方式均由直接跃迁变为间接跃迁。Cd、S空位缺陷的CdS体系的态密度总能量降低。空位CdS体系相较于本征CdS体系的静介电常数均有提高,并随着空位浓度的增大而增大,Cd空位缺陷体系更为明显,极化能力得到显著提升。空位Cd的CdS体系相较于本征CdS体系在红外波段存在明显的吸收,空位S的CdS体系相较于本征CdS体系在可见光波段存在明显的吸收。     

基于沉积温度优化和后退火工艺改善a-Si∶H/c-Si界面钝化质量的研究

a-Si∶H薄膜作为钝化层,在提高硅异质结太阳能电池效率方面发挥关键作用,工业化生产中通常采用PECVD法制备制备a-Si∶H薄膜.在本文中,首先对关键工艺参数如沉积温度进行了优化,并在160℃下获得了最佳的钝化效果.接着,通过傅里叶变换红外光谱法对a-Si∶H薄膜的微结构进行表征,以探索其钝化机理:低温下制备的a-Si∶H薄膜氢浓度高并有微空洞,从而影响钝化效果;高温下制备的a-Si∶H薄膜消除了微空洞而明显改善钝化质量.但是,过高的沉积温度又会导致a-Si∶H薄膜中微空位的产生从而影响钝化效果.此外,对比了两种典型后退火工艺对钝化效果的影响:一种是基于200℃退火10 min,一种是基于450℃退火30 s,并对相关钝化机理进行了研究.结果表明,第二种退火方式明显改善样品的钝化效果,主要原因是该退火消除了低温沉积样品中的微空洞和高温沉积样品中的微空位.最后,通过透射电镜研究了退火后的a-Si∶ H/c-Si界面微结构,并未观察到影响钝化效果的外延生长.     

基于光谱测试的纯净金刚石品质与缺陷研究

本文利用低温拉曼与光致发光光谱对纯净金刚石晶片的结晶质量、晶体应力分布进行表征分析,并结合电子辐照和快速退火对晶片的杂质缺陷结构开展研究。通过拉曼光谱对金刚石特征峰的表征分析发现,由于金刚石生长机制以及晶片的切割、抛光等因素影响,晶片的边缘与表面应力分布较高。光致发光光谱中的零声子线具有明显的温度依赖性,根据Jahn-Teller效应与电子-声子耦合理论阐明了测试温度变化引起中性单空位缺陷零声子线分裂与红移的机理。对晶片做电子辐照与退火调控处理后,晶片中氮-空位(NV)缺陷显著增多,表明在纯净晶片中氮主要以替代位氮杂质的形式存在。     

氧化锡纳米晶的合成与生长

采用水热法制备了氧化锡纳米晶,通过X射线衍射仪(XRD)和高分辨透射电镜(HRTEM)对氧化锡纳米晶样品的晶体结构、晶粒形貌进行了表征,并研究了氧化锡纳米晶生长和位错的产生机制.结果表明:在退火温度低于500 ℃时,晶粒生长依靠着周围的非晶成分而长大,纳米晶内部无晶格缺陷;退火温度高于500 ℃时,晶粒通过相互粘结的方式而长大.晶粒之间的不完全取向粘结导致了缺陷与位错的产生.     

Palladium(II) and platinum(II) tetrakisthiourea dichloride bis(7-hydroxy-5-methyl[1,2,4]triazolo[1,5a]pyrimidine) dihydrate solvates

The title compounds palladium(II) and platinum(II) tetrakisthiourea dichloride bis(7-hydroxy-5-methyl[1,2,4]triazolo[1,5a]pyrimidine (Hmtpo)) dihydrate solvates, have been synthesized by reacting thecis-[MCl₂(Hmtpo)₂] (where M=Pt(II), Pd(II)) complexes with an excess of thiourea (tu) and the structure of the palladium compound was solved by X-ray diffraction. Crystals of [Pd(tu)₄]Cl₂·2Hmtpo·2H₂O are triclinic with space groupP and unit cell dimensionsa=7.972(1),b=9.049(1),c=11.808(2)Å, =88.20(1), =75.15(1), =76.54(1)^o. The cation [Pd(tu)₄]²⁺ is centrosymmetric involving four sulfur thiourea atoms in a near square planar environment. The triazolopyrimidine molecules, chloride anions and water molecules do not take part in the metal center coordination but interact by hydrogen bonding between them and the thiourea moieties. A comparison between powder diffraction data of palladium(II) and platinum(II) compounds clearly indicates that both compounds are isomorphous.     

Structures of Bis(1-ethylbenzimidazol-2-yl)alkyl Copper(II) Dichlorides: An Unusual Cocrystallization

Abstract  Two structures containing pseudo-tetrahedral Cu(II)N₂Cl₂ coordination complexes are reported. The first molecular structure (A) of the compound, 1,1′bis(1-ethylbenzimidazol-2-yl)propane copper(II) dichloride (triEtBBIM)Cu(II)Cl₂, 1, is reported. The complex crystallized in the triclinic space group P-1 with a = 8.616(3) ?, b = 9.302(3) ?, c = 14.314(4) ?, α = 85.613(6)°, β = 85.170(6)°, γ = 66.117(6)° and V = 1044.1(5) ?³ with Z = 2. The second structure (B) contains 1 and (3,3′bis(1-ethylbenzimidazol-2-yl)pentane) copper(II) dichloride (tetEtBBIM)Cu(II)Cl₂, 2, both of which, cocrystallize in an equal molar ratio with a nitromethane solvate molecule. The complex crystallized in the monoclinic space group P2₁/c with a = 18.876(4) ?, b = 14.975(3) ?, c = 18.344(4) ?, β = 116.75(3)°, and V = 4630.3(16) ?³ with Z = 4. The cocrystallization of such discrete complexes has been coined a chemical Janus. Graphical Abstract  The title complexes contain pseudo-tetrahedral Cu(II)N₂Cl₂ coordination. One of the structures is the result of an unusual cocrystallization, in which two different discrete Cu(II) molecules cocrystallize in an equimolar ratio with a nitromethane solvate molecule.      

Crystal structure of bis(4-dimethylaminopyridinium) tribromocuprate(I) and bis(4-dimethylaminopyridinium) tetrabromocuprate(II)

The synthesis and crystal structures of two copper bromide salts of the 4-dimethylaminopyridinium (4DMAP⁺) cation are reported. The Cu(I) salt, (4DMAP)₂CuBr₃, crystallizes in the monoclinic space group C2/c, with a = 11.724(2), b = 11.055(3), c = 15.763(3) Å, = 107.64(3)°, and Z = 4. It contains isolated planar 4DMAP⁺ cations and trigonal planar CuBr₃ ^2– anions. Small distortions from idealized D _3h symmetry are observed for the anion. For the Cu(II) salt, (4DMAP)₂CuBr₄, a triclinic cell is observed with a = 8.2373(2), b = 9.2428(2), c = 14.4391(1) Å, = 93.760(1), = 94.576(1), = 105.249(1)°, and Z = 2. This compound contains discrete planar 4DMAP⁺ cations and flattened tetrahedral CuBr₄ ^2– anions. Small distortions are observed for ideal D _2d symmetry.     

The syntheses and crystal structures of two chromium(III) and molybdenum(III) coordination compounds with 4-ethylpyridine

The structures of trichlorotris(4-ethylpyridine)chromium(III), [CrCl₃(C₇H₉N)₃] (I), and trichlorotris(4-ethylpyridine)molybdenum(III), [MoCl₃(C₇H₉N)₃] (II), consist of neutral molecules where three 4-ethylpyridine and three chloro ligands coordinate to the metal with a meridional configuration. Compound I crystallizes in a trigonal space group P3₁ with a = 11.515(2) Å and c = 15.378(3) Å. Compound II crystallizes in a monoclinic space group C2/c with a = 24.200(3) Å, b = 18.089(3) Å, c = 22.6004(7) Å and = 106.7137(6)°.     

Magnetotransport In (TMTSF)2PF6 and (TMTSF)2C104 Under Pressure

We have shown from the magnetotransport that the Fermi surface of (TMTSF)₂PF₆ is effectively closed two-dimensionally and is compensated in the metallic state at low temperature. These results are inconsistent with a broad regime of one-dimensional superconducting fluctuations.

Independent electron theory is seen to be inadequate to explain either the Fermi surface or the threshold field for oscillations, thereby implying that correlation effects are still important in the metallic state. Finally, an anomaly has been observed in the magnetotransport of (TMTSF)₂C10₄ which is analogous to the threshold field in (TMTSF)₂PF₆.     

Synthesis and characterization of ternary L-histidine complexes. Crystal structure of (2,2′-dipyridyl)-(L-histidinato-N,N′,O)copper(II) perchlorate 1.5 hydrate

A series of ternary complexes of copper(II), cobalt(II) and zinc(II) with L-histidine, 1,10-phenanthroline, 2,2-dipyridyl or imidazole having perchlorate or acetate as counterions were synthesized and characterized by conventional methods and for [Cu(bipy)(L-hist)]ClO₄·1.5H₂O and X-ray crystal structure was determined. The crystals belong to the monoclinic space groupC2 witha=18.843(3),b=10.582(2),c=11.020(2), =115.20(10)°,Z=4,R=0.0535. The structure is consistent of [Cu(bipy)(L-hist)]⁺ cations, perchlorate ions and water molecules. The geometry around copper is trigonal bipyramidal with one N,N,O tridentate L-histidine molecule and one 2,2-dipyridyl ligand, the apical sites are occupied by the -amino nitrogen [Cu–N(71) 1.995(8)] and by N(11) of 2,2-dipyridyl [Cu–N(11) 1.983(7)], the equatorial plane is formed by the N(3) imidazole -nitrogen [Cu–N(3) 2.140(6)], O(82) carboxylic oxygen [Cu–O(82) 2.009(5)] and N(22) [Cu–N(22) 2.010(7)].     

Crystal structures of the cobalt(III), nickel(II), copper(II), and zinc(II) complexes of 2-thio-6-picoline N-oxide

Structures of the following compounds have been solved: tris(2-thio-6-picoline N-oxide)cobalt(III), [Co(6MOS)₃], orthorhombic, Pca2₁, a = 17.871(3), b = 14.061(2), c = 15.964(2) Å, V = 4011(1) ų, Z = 8, and = 1.193 mm^–1; bis (2-thio-6-picoline N-oxide)nickel(II), [Ni(6MOS)₂], orthorhombic, Pbca, a = 15.602(8), b = 13.606(4), c = 13.348(8) Å, V = 2833(4) ų, Z = 8, and = 1.655 mm^–1; bis(2-thio-6-picoline N-oxide)copper(II), [Cu(6MOS)₂], orthorhombic, Pbca, a = 13.914(5), b = 12.984(5), c = 15.663(6) Å, V = 2830(2) ų, Z = 8, and = 1.836 mm^–1; and bis(2-thio-6-picoline N-oxide)zinc(II), [Zn(6MOS)₂], triclinic, P – 1, a = 7.9737(8), b = 11.7786(9), c = 7.9206(8) Å, = 104.502(7), = 104.495(8), = 93.445(8)°, V = 691.3(1) ų, Z = 2, and = 2.106 mm^–1. The steric effect of the methyl group in the six-position of the N-oxide ring is considered in comparing these structures to complexes of 2-thiopyridine N-oxide.     

ZnS晶体的化学气相沉积生长

本文报道了用化学气相沉积(CVD)法生长ZnS透明多晶体的实验结果,对生长的晶体的物理化学性能进行了测试,讨论了化学气相沉积工艺中影响ZnS晶体质量的因素.结果表明:选用固体硫作原料,用化学气相沉积方法,可以沉积出透明ZnS多晶体;它的透过性能极其优异,在6.2μm处无吸收峰,在中、长波红外透过率可达70;以上.     

Thermally activated delayed fluorescence host materials based on triphenylphosphine oxide derivatives

Abstract

Novel thermally activated delayed fluorescence (TADF) host molecules for blue electrophosphorescence were developed by combining the electron donor acridine derivatives with the electron acceptor triphenylphosphine oxide unit in a single molecule based on density functional theory. We obtained the energies of the first excited singlet (S₁) and triplet (T₁) states of the TADF materials by performing procedures in accordance with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to the ground state using dependence on the charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. Using DFT and TD-DFT calculations, the significant separation between the HOMO and LUMO caused a small difference in energy (ΔE_ST) between the S₁ and T₁ states. The host molecules retained high triplet energy and showed great potential for use in blue phosphorescent organic light-emitting diodes. The results also showed that these molecules are promising TADF host materials because they demonstrate a low barrier to hole and electron injection, balanced charge transport for both holes and electrons, and small ΔE_ST.     

Influence of complex formation upon inclusion of Mn(II), Co(II), Ni(II), and Cu(II) in ZnC2O4·2H2O

The inclusion of 3d‐impurities Mn(II), Co(II), Ni(II) and Cu(II) in a crystalline precipitate of ZnC₂O₄·2H₂O is investigated. This study is a part of the systematic one deal with the mechanism of inclusion of 3d‐ions in sparingly soluble oxalate systems. The experiments are carried out in bi‐ end multi‐component systems at two different mediums – one with deficiency of oxalate ions, another with excess. The insertion of 3d‐ions upon mass crystallization of ZnC₂O₄·2H₂O does not proceed by a simple ionic substitution. The results show that the inserted amount of impurity depends on some physicochemical characteristics of the neutral monooxalato complexes [MnC₂O₄]^o, [CoC₂O₄]^o, [NiC₂O₄]^o and [CuC₂O₄]^o. Good agreement between included impurity and the concentration of its complex in the solution is established. The stability constant of monooxalato complex affects the impurity inclusion. This effect depends on the medium nature. In the deficiency of oxalate ions the factor determining the inclusion is thermodynamic one – stability of monooxalato complexes. In the excess of oxalate ions inserted amount depends on kinetic factor – the formation rate of these complexes. In the term of that the insertion of Mn(II) is definitely different in the two mediums while that of the Ni (II) does not depend on the medium. The copper shows deviation from overall dependence in the two mediums due to the Jahn‐Teller distortion. Its double decreasing insertion in the excess of oxalate ions is related with stabilization of [Cu(C₂O₄)2]^2‐. The conclusions presume that by varying the background medium and taking in view the ions present in the solution, the amount of inserted impurities can be predicted and controlled. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)