C60单晶的汽相生长

报道使用Ｃ＿６０粉末，利用双炉装置，通过闭管汽相法生长Ｃ＿６０单晶的实验及结果。Ｃ＿６０单晶的质量很好，较大单晶的尺寸为０．５ｍｍ×０．６１ｍｍ×１．０ｍｍ。Ｘ射线衍射和电子衍射图的分析得到室温下Ｃ＿６０单晶为ｆ＿ｃｃ结构，确定了晶格常数，还进行了Ｒａｍａｎ光谱实验，实验结果表明，热、冷区温度及两者的温度差是影响大尺寸Ｃ＿６０单晶汽相生长的主要因素，对此进行了详细的讨论。     

基于激发态吸收的C60分子全光开关特性研究

用５３２．０ｎｍ的脉冲Ｎｄ：ＹＡＧ激光作为泵浦光，７４７．０ｎｍ的连续半导体激光作为探测光，在Ｃ₆₀甲苯溶液中，利用Ｃ₆₀分子的三重态－三重态非线性吸收效应，获得Ｃ₆₀分子的全光开关和全光调制特性，并用速率方程进行了动力学数值模拟，得到与实验相一致的结果。 关键词：     

低压-金属有机物汽相外延生长的Ga1-xInxAs/InP激光器中深能级的研究

应用深能级瞬态谱（ＤＬＴｓ）技术详细研究低压－金属有机物汽相外延（ＬＰ－ＭＯＶＰＥ）生长的Ｇａ_０．４７Ｉｎ_０．５３Ａｓ／Ｉｎｐ量子阱、宽接触和质子轰击条形异质结激光器中的深能级。样品的ＤＬＴＳ表明，在宽接触激光器的ｉ－Ｇａ_０．４７Ｉｎ_０．５３Ａｓ有源层里观察到Ｈ１（Ｅ_ｖ＋０．０９ｅＶ）和Ｅ１（Ｅ_ｃ－０．３５ｅＶ)陷阱，它们可能分别与样品生长过程中扩散到ｉ－Ｇａ_{０．４ 关键词：}     

C60单晶生长及特性的研究

用气相生长法生长了最大线度约为１．５ｍｍ的C₆₀单晶。单晶Ｘ射线衍射分析结果表明，该C₆₀单晶为ｆｃｃ结构，晶格常数为１．４１３ｎｍ，在２５１Ｋ附近与相变有关的电导率的尖锐跳变表明，C₆₀单晶具有很高的纯度和良好的均匀性。观察到在２７４Ｋ附近激活能的变化，这可能是另一个相变的反映。 关键词：     

铊系超导单昌的低温生长

采用蠕爬型助熔剂ＣａＯ－ＣｕＯ和蒸发型复合助熔剂ＣａＯ－ＣｕＯ－ＮａＣｌ来制备Ｔｌ－Ｂａ－Ｃａ－Ｃｕ－Ｏ超导单晶，生长炉最高温度８９０℃和８５０℃，因而实现了铊系单晶的低温生工。生长出的单晶分别是典型尺寸为２．０×１．５×０．２ｍｍ＾３，Ｔｃ在１００Ｋ与１１９Ｋ之间的Ｔｌ－２２１２相单晶和尺寸为１．２×１．０×０．１ｍｍ＾３。Ｔｃ约为１１５Ｋ的Ｔｌ－２２２３相超导单晶。     

Gd1-xCaxBa2Cu3O7-y高温超导体压力效应的研究

研究了Ｇｄ_1-xＣａ_xＢａ₂Ｃｕ₃Ｏ_7-y（０．０≤Ｘ≤０．２０）高温超导体在常压和高压下的超导电性在１－３００Ｋ温度范围内，利用Ｂｒｉｄｇｍａｎ对顶砧获得压力达９．０ＧＰａ，测量了（Ｘ＝０．１０，０．１５，０．２０）样品的ｄＴ_c／ｄｐ分别为７．６８，７．８和４．４６Ｋ／ＧＰａ。发现Ｔ_c的压力导数随着ｃａ²⁺含量的增加而下降，分析了氧含量对Ｔ_c和ｄＴ_c／ｄＰ的影响．利用常压下晶格参数精修值和阳离子与氧离子间距随压力的改变，说明ＣｕＯ₂面在超导电性上的作用，用ＣｕＯ₂面之间耦合解释Ｔ_c（Ｐ）曲线的非线性关系。 关键词：     

铊系超导单晶的低温生长

采用蠕爬型助熔剂ＣａＯ－ＣｕＯ和蒸发型复合助熔剂ＣａＯ－ＣｕＯ－ＮａＣｌ来制备Ｔｌ－Ｂａ－Ｃａ－ＣＵ－Ｏ超导单晶，生长炉最高温度分别为８９０℃和８５０℃，因而实现了铊系单晶的低温生长．生长出的单晶分别是典型尺寸为２．０×１．５×０．２ｍｍ３，Ｔｃ在１００Ｋ与１１９Ｋ之间的Ｔｌ－２２１２相单晶和尺寸为１．２×１．０×０．１ｍｍ３，Ｔｃ约为１１５Ｋ的Ｔｌ－２２２３相超导单晶．采用蠕爬型助熔剂可以降低熔点而不引进其它非组元杂质，但导致熔料蠕爬，对生长大块单晶不利．采用蒸发型复合助熔剂克服了熔料的蠕爬现象，减少了铊的损失，对生长多铜氧层的单晶有利．     

C60分子晶体中的类非晶散射研究

根据Ｘ射线衍射基本理论，计算了Ｃ₆₀分子晶体中的各种堆积方式下的Ｘ射线衍射花样，对Ｃ₆₀分子晶体中的类非晶散射产生的原因进行了探讨，指出在Ｃ₆₀分子晶体中，Ｃ₆₀分子有两种运动方式．非晶散射是Ｃ₆₀分子晶体固有结构特征所造成的 关键词：     

电子关联对C60激子极化子的影响

本文采用扩展的Ｈｕｂｂａｒｄ模型，在电子－晶格耦合的紧束缚近似下，研究了光激发下的Ｃ₆₀，分子的激子态和极化子态。我们发现，电子关联效应相当敏感地影响到单态和三态激子的束缚能。同时，Ｃ₆₀分子动力学晶格弛豫使激子极化子得以形成。光激发下的Ｃ₆₀分子，在电子相互作用Ｕ～５．０ｅＶ，Ｖ～２．０ｅＶ时，能够定性地解释荧光发射谱。 关键词：     

高Jc Tl系2223相银包套带材的磁通钉扎和耗散

测量了Ｔｌ系２２２３相银包套超导带（Ｊ_c＝１．５×１０^４Ａ·ｃｍ^-2，７７Ｋ，０Ｔ）在０－０．８Ｔ磁场下电阻转变展宽，实验结果引用热激活磁通蠕动模型加以解释。磁场平行于带面（Ｈ∥ａｂ面）和磁场垂直于带面（Ｈ⊥ａｂ面）两种情况下，激活能与磁场之间满足幂指数关系：Ｕ_0∥＝０．２１ H^-0.3(eV),Ｕ_0⊥＝０．１5 H^-0.4(eV)，其中Ｈ的单位为ｋＧ。 关键词：     

A DOUBLE-TEMPERATURE-GRADIENT TECHNIQUE FOR THE GROWTH OF PURE C60 SINGLE CRYSTALS FROM THE VAPOR PHASE

Pure C₆₀ single crystals were grown by a sublimation-condensation method in an evacuated dosed quartz tube situated in a double-temperature-gradient furnace. Large C₆₀ single crystals, up to a size of 0.6 mm×1.0 mm×2.0 mm with quite smooth and shiny faces, were obtained. X-ray diffraction, electron diffraction and X-ray morphology were carried out and showed that the quality of large C₆₀ single crystals grown by the double-temperature-gradient technique is excellent. In this paper the experimental results of the growth of large C₆₀ single crystals are reported and the morphological and structural characterizations are discussed in detail.     

Electroconductivity and pressure–temperature states of step shocked C60 fullerite

A study of electrophysical and thermodynamic properties of C₆₀ single crystals under step shock loading has been carried out. The increase and the following reduction in specific electroconductivity of C₆₀ fullerite single crystals at step shock compression up to pressure 30 GPa have been measured. The equations of state for face centred cubic (fcc) C₆₀ fullerite as well as for two-dimensional polymer C₆₀ and for three-dimensional polymer C₆₀ (3D-C₆₀) were constructed. The pressure–temperature states of C₆₀ fullerite were calculated at step shock compression up to pressure 30 GPa and temperature 550 K. The X-ray diffraction studies of shock-recovered samples reveal a mixture of fcc C₆₀ and a X-ray amorphous component of fullerite C₆₀. The start of the formation of the X-ray amorphous component occurs at a pressure P _m≈ 19.8 GPa and a temperature T _m≈ 520 K. At pressures exceeding P _m and temperatures exceeding T _m, the shock compressed fullerite consist of a two-phase mixture of fcc C₆₀ fullerite and an X-ray amorphous component presumably consisting of the nucleators of polymer 3D-C₆₀ fullerite. The decrease in electroconductivity of fullerite can be explained by the percolation effect caused by the change of pressure, size and number of polymeric phase nuclei.     

C60单晶的表面形貌与生长缺陷

用气相法生长出了毫米尺寸的具有规则晶面和金属光泽的高质量的纯C₆₀单晶.X射线衍射分析表明,C₆₀单晶在室温下具有面心立方(fcc)结构,晶格常数为α=1.4199(4)nm。用扫描电子显微镜和光学显微镜观察了C₆₀单晶的形貌,除观察到fcc结构的晶体所特有的{111}和{200}两种稳定晶面以及非常容易形成的孪晶之外,还发现了在{111}面上的树枝状、垄状和生长丘以及在{200}面上的树枝状、游泳池状和生长丘的生长缺陷。对C_{60 关键词：}     

Effect of external pressure on Tc of as‐grown and thermally treated superconducting Rbx Fe2–ySe2 single crystals

We report on the effect of external pressure on the superconducting transition temperature (T_c) of as‐grown and thermally treated single crystals of superconducting iron chalcogenide Rb_0.85Fe_1.9Se₂. The superconducting transition temperature of 27.1 K at ambient pressure for the as‐grown sample was found to increase up to 33.2 K for the sample annealed for 3 h at 215 °C in vacuum. An increase of T_c up to 28.2 K was observed for the as‐grown sample at a pressure of 0.83 GPa. For all the studied crystals, annealed in the temperature range between 215 °C and 290 °C, the external pressure seems to decrease the superconducting transition temperature and a negative pressure coefficient of T_c was observed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of electron irradiation on the paramagnetic state of La0.67Ca0.33MnO3

The effect of point defects on the magnetic properties of La_0.67Ca_0.33MnO₃ polycrystals and single crystals has been studied. The magnetic susceptibility χ _dc of the initial samples and samples irradiated by electrons to the maximum dose F = 9 × 10¹⁸ cm^?2 has been measured in the temperature region 80 K < T < 650 K. Local variations of Mn-O-Mn bond angles and lengths result in a nonmonotonic dose dependence of the Curie temperature T _C. At high doses of electron irradiation, F ≥ 5 × 10¹⁸ cm^?2, the temperature of the transition from the ferromagnetic to polaron state in a single crystal is found to increase. In the paramagnetic region close to T _C, ferromagnetically ordered polarons are observed to exist, while at T > 1.2T _C, localization of e _g electrons initiates formation of paramagnetic polarons with a higher magnetic moment. Electron irradiation stimulates persistence of magnetic polarons up to higher temperatures T > 2T _C.     

Manifestation of quantum statistics in vibrational dynamics of poly(ethylene) crystals

The temperature dependences of the transverse expansion ?_⊥(T) and the longitudinal contraction ?_‖(T) (with respect to the axes of chain molecules) in large-sized poly(ethylene) (PE) crystal grains (100×60×60 nm) are measured using x-ray diffraction in the temperature range 5–380 K. The temperature dependence of the elongation of the molecular skeleton ?_C(T) is obtained by Raman spectroscopy. It is found that the dependences ?_⊥(T), ?_‖(T), and ?_C(T) exhibit a similar specific nonlinear behavior. Analysis of these dependences indicates that the nonlinearity is associated with the quantum statistics of transverse vibrations. The energies and amplitudes of zero-point (at T=0) transverse (torsional and bending) vibrations and the relevant zero-point components ?_‖(0) and ?_C(0) are estimated. It is revealed that the zero-point components make a considerable contribution to the dynamics of the PE crystal up to the melting temperature (～400 K).     

Effect of γ irradiation on the structural and thermal properties of [N(C2H5)4]2ZnBr4 in the vicinity of a first-order phase transition

The unit cell parameters a and c of nonirradiated [N(C₂H₅)₄]₂ZnBr₄ crystals in the temperature region 90–300 K and of samples irradiated with γ rays to doses of 10⁶ and 5 × 10⁶ R in the 270-to 300-K interval were measured using x-ray diffraction. The data obtained were used to derive the thermal expansion coefficients α_a and α_c. It is shown that the parameter a increases and the parameter c decreases with increasing temperature. In the vicinity of the phase transition (PT) at T = 285 K, the temperature dependences of a(T) and c(T) reveal anomalies in the form of jumps and the α_a(T) and α_c(T) curves have a maximum and a minimum, respectively. The heat capacity of nonirradiated and irradiated [N(C₂H₅)₄]₂ZnBr₄ samples was measured by adiabatic calorimetry. A maximum was found in the C _p(T) curve at T = 285 K. Both x-ray diffraction and heat capacity measurements showed that the PT temperature decreased after γ irradiation.     

C60 growth on Si(100), GaSe(0001) and GeS(001)

C₆₀ films have been grown in ultra high vacuum on various crystalline substrates and the structure of the films has been investigated by low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS). The C₆₀ films form randomly oriented nanocrystals on Si(100), mesoscopic polycrystals on GaSe(0001) and microscopic single crystals on GeS(001). The vibrational structure of the C₆₀/substrate interfaces is analyzed in detail by HREELS carried out in the dipole and impact scattering regimes. It is shown that the epitaxy of C₆₀ on GeS(001) is induced by the weak van der Waals bonding and the peculiar corrugation of the substrate surface.     

Structural manipulation of ultrathin organic films on metal surfaces: the case of decane thiol/Au(111)

3 (CH₂)₉]SH) have been adsorbed on Au(111) single crystals both via vacuum deposition and from an ethanolic solution. The epitaxial structure of the ultrathin organic films has been identified at room temperature via low-energy electron diffraction to be c(4×2)R30° for the solution grown film and rectangular c(23×) for the vacuum deposited film. These structures correspond to molecules adsorbed on the surface with their carbon chains flat on the surface (vacuum deposited) and nearly perpendicular (solution grown). It is demonstrated that this orientation can be changed reversibly in vacuum via either annealing the films or exposing them to additional gas. Received: 7 February 1997/Accepted: 27 May 1997     

A double-temperature-gradient technique for the growth of single-crystal fullerites from the vapor phase

Fullerite single crystals were prepared by a sublimation-condensation method in a closed evacuated glass tube situated in a double-temperature-gradient furnace. Crystals of various size and up to 9 mg weight with well expressed smooth and shiny faces were obtained. X-ray analysis, interfacial angle measurements and observed morphological habits of selected crystals of C₆₀ confirm the theoretically predicted and experimentally well established fcc structure at room temperature with two types of morphological faces, namely {111} and {100}. A strong tendency to twinning was observed. In the case of C₇₀ crystals, a pure fcc structure was observed. Information on growth kinetics and on instability versus exposure to air and light were obtained from surface studies. Characteristic changes in a thin surface layer were observed when crystals were exposed to air and light. A new phase of C₆₀ stabilized by oxygen was characterized.