Magnetic and electrical transport properties of delta-doped amorphous Ge:Mn magnetic semiconductors

We report on the growth and characterization of delta-doped amorphous Ge:Mn diluted magnetic semiconductor thin films on GaAs (0 0 1) substrates. The fabricated samples exhibit different magnetic behaviors, depending on the Mn doping concentration. The Curie temperature was found to be dependent on both the Mn doping concentration and spacing between the doping layers. A sharp drop in magnetization and rise in resistivity are observed at low temperature in samples with high Mn doping concentrations, which is also accompanied by a negative thermal remanent magnetization (TRM) in the higher temperature range. The temperature at which the magnetization starts to drop and the negative TRM appears show a correlation with the Mn doping concentration. The experimental results are discussed based on the formation of ferromagnetic regions at high temperature and antiferromagnetic coupling between these regions at low temperature.     

Structural,elastic, electronic,andoptical properties of layered TiNX (X = F,Cl, Br,I) compounds: a density functional theory study

ABSTRACT

Titanium nitride halides, TiNX (X = F, Cl, Br, I) in the α-phase (orthorhombic) are exciting quasi two-dimensional (2D) electronic systems exhibiting a fascinating series of electronic ground states. Pristine TiNX are semiconductors with varying energy gaps and possess attractive properties for potential applications in optoelectronics, photovoltaics, and thermoelectrics. Alkali metal intercalated TiNCl becomes superconducting at reasonably high temperature. We have revisited the electronic band structure of TiNX using density functional theory (DFT) based calculations. The atomic orbital resolved partial electronic energy densities of states are calculated together with the total density of states (TDOS). The structural and elastic properties have been investigated in details for the first time. The elastic anisotropy has been explored. The optical properties of TiNX are studied for the first time. The Debye temperatures have been calculated and the related thermal and phonon parameters are discussed. The calculated physical parameters are compared with existing theoretical and experimental results and showed fair agreement. TiNX are found to reflect electromagnetic radiation strongly in the mid ultraviolet region. The elastic properties show high degree of anisotropy. The effect of halogen atoms on various structural, elastic, electronic, and thermal properties in TiNX are also discussed in detail.     

非线形CS2 分子单重态和三重态的密度泛函理论

应用密度泛函理论 (DFT)的B3LYP和B3PW91两种方法 ,在 6 3 11+G 和aug cc pVTZ基组水平上 ,分别优化了CS2 可能存在的非线形单重态和三重态构型 ,在全局势能面上共发现 3个单重态 (电子态 1 A1 )和 5个三重态 (电子态分别为 3A2 、3B2 和 3B2 )的非线形CS2 异构体 ,正则振动频率分析证明所得到构型均是位能面上的极小 .计算所得CS2 异构体的相对能量顺序为 4t3B2 相似文献   

Sin－1N和Sin－2N2（n=3~9）团簇结构与光振动能谱

用密度泛函理论(DensityFunctionalTheory,DFT)的B3LYP/6-311G(d)方法,对Sin－1N和Sin－2N2(n=3~9)团簇的几何构型、总能量、光振动能谱等性质进行了理论研究.通过对基态结构的几何参量分析发现,对Sin－2N2(n=3~9)团簇,只有在SiN2和Si2N2结构中N-N成键;n＞4团簇结构,N-N不成键.对团簇能量讨论的结果表明;对于Sin－1N(n=3~9)团簇,总原子数是偶数的团簇比奇数的稳定;对于Sin－2N2(n=3~9)团簇,总原子数是奇数的团簇比偶数的稳定.     

丙烯腈双自由基终止过程态密度变化的研究

本文采用密度泛函理论对丙烯腈单体自由基(CH3)2(CN)C-CH2-(CN)CH两种终止反应过程中各原子态密度变化进行研究.用B3LYP/6-31G(d)基组对反应物、偶合中间体、过渡态和产物的结构进行优化,计算了各物种的红外频率和各原子的态密度.研究结果表明,偶合中间体a和歧化产物P的化学稳定性较好,丙烯腈单体自由基R和过渡态TS的化学稳定性比较差;各驻点物种的HOMO、LUMO轨道基本是相同原子贡献,且C、N原子贡献程度基本在95%左右;丙烯腈单体自由基R、过渡态TS的HOMO、LUMO相对比较独立,与前线轨道附近的其他能级（HOMO-2、HOMO-1、LUMO+1、LUMO+2）的能量差比较大.     

Si(001)-(2*2*1):H表面O2吸附的密度泛函理论研究

建立了一种计算Si(001)-(2×2×1):H表面O2吸附的理论模型．在周期性边界条件下,采用基于密度泛函理论广义梯度近似的超软赝势法对Si(001)-(2×2×1):H表面O2吸附进行了第一性研究．通过占位能的计算,得到了Si(001)-(2×2×1):H表面O2的最佳吸附位置．计算结果表明吸附后的反应产物应为Si=O和H2O,从理论上支持了D．Kovalev等人提出反应机制．     

丙烯腈双自由基终止过程态密度变化的研究

本文采用密度泛函理论对丙烯腈单体自由基(CH3)2(CN)C-CH2-(CN)CH两种终止反应过程中各原子态密度变化进行研究.用B3LYP/6-31G(d)基组对反应物、偶合中间体、过渡态和产物的结构进行优化,计算了各物种的红外频率和各原子的态密度.研究结果表明,偶合中间体a和歧化产物P的化学稳定性较好,丙烯腈单体自由基R和过渡态TS的化学稳定性比较差;各驻点物种的HOMO、LUMO轨道基本是相同原子贡献,且C、N原子贡献程度基本在95%左右;丙烯腈单体自由基R、过渡态TS的HOMO、LUMO相对比较独立,与前线轨道附近的其他能级（HOMO-2、HOMO-1、LUMO+1、LUMO+2）的能量差比较大.     

运用表面增强拉曼散射(SERS)和密度泛函数理论(DFT)模拟计算研究对硝基苯胺在金纳米颗粒表面吸附行为

在沉积金纳米颗粒的干燥滤纸上进行对硝基苯胺的表面增强拉曼散射(SERS)光谱研究,并与对硝基苯胺在金胶水溶液中的表面增强拉曼散射(SERS)光谱相比,分子拉曼光谱发生了很大变化。同时利用DFT理论计算对硝基苯胺在金胶颗粒上的吸附行为的拉曼光谱。DFT理论模拟计算和FI-Raman实验分析都表明这种变化源于对硝基苯胺的不同吸附方式。SERS和DFT结合研究分子的吸附是一种有效的技术。     

缺陷碳纳米管限域金属Ti原子的理论研究

基于密度泛函第一性原理研究了金属原子Ti在原始、单空位缺陷(SV)、Stone-Wales(SW)缺陷碳纳米管内外的吸附情况.我们的计算结果表明金属Ti原子在缺陷碳纳米管内外结合能的排列顺序为:SVSW-zSW-xpristine(外吸附),SVSW-xSW-zpristine(内吸附).同时,我们通过吸附结构、电子密度和态密度等分析了Ti原子与碳纳米管的作用机制.其中,SV缺陷碳纳米管由于失去一个碳原子而形成了的三个悬键具有很强的结合能力,金属原子Ti在SV缺陷碳纳米管内外的吸附能力都是最强的.对于SW缺陷的碳纳米管,由于缺陷的位置不同,对于金属原子Ti内外吸附的能力也是不同的.因此,缺陷的存在能调节碳纳米管载体对Ti原子的吸附性能.     

静水压力对Al14Mn2P16磁光性质影响的密度泛函理论研究

采用第一性原理,研究不同静水压力(0~20 GPa)下Al14Mn2P16的弹性与磁光性质.计算得到基态是铁磁态.弹性稳定性判据表明该体系是稳定的.研究发现磁矩随静水压力的增加而减小.静水压力低于5 GPa时,居里温度达到184 K,随着静水压力的增加略有下降;有趣的是,当静水压力高于5 GPa时,随着静水压力的增加,居里温度急剧下降,在18 GPa时消失.同时还发现随静水压力的增加可见光范围的吸收峰有明显的蓝移,当静水压力达到20 GPa时,可见光范围的吸收峰消失.     

2-巯基-5-甲基苯并咪唑振动光谱的密度泛函理论研究

本文选用密度泛函理论中的B3LYP杂化泛函,在B3LYP/6-311++G(d, p)水平下,优化了2-巯基-5-甲基苯并咪唑分子(MMBI)的结构,优化结果表明,2-巯基-5-甲苯并咪唑分子是一个近平面结构.通过频率计算,获得了2-巯基-5-甲基苯并咪唑分子(MMBI)的拉曼光谱,并和实验获得的拉曼光谱图进行了对比,实验和理论计算获得的拉曼光谱图基本上是一致的,表明本文选取的DFT理论计算方法是可靠的.结合VEDA4软件对2-巯基-5-甲基苯并咪唑分子的拉曼谱带简正振动模式进行了指认.此外,分析并讨论了2-巯基-5-甲基苯并咪唑分子(MMBI)前线轨道,HOMO和LUMO轨道能级差为4.51 eV,电子有从HOMO跃迁到LUMO的趋势.采用含时密度泛函理论(time dependent density functional theory, TDDFT)对2-巯基-5-甲基苯并咪唑分子(MMBI)的激发态进行了计算分析,计算结果表明乙醇溶剂中2-巯基-5-甲基苯并咪唑分子(MMBI)理论计算的吸收波长为226 nm, 288 nm.对研究2-巯基-5-甲基苯并咪唑分子的性质,提供了理论...     

Magnetic properties of the semifluorinated and semihydrogenated 2D sheets of group-IV and III-V binary compounds

By performing first-principles calculations, the intriguing electronic and magnetic properties of the semidecorated sheets of group-IV and III-V binary compounds are investigated. Our results indicate that the semifluorinated and semihydrogenated ab (ab = SiC, GeC, SnC, BN, AlN, and GaN) sheets exhibit diverse electronic and magnetic properties. Accordingly, the electronic and magnetic properties of the semidecorated sheets can be precisely modulated by controlling the adsorbed atoms on the a sites. Further, the preference of ferromagnetic or antiferromagnetic coupling can be attributed to the combined effects of both through-bond spin polarization and p-p direct interaction for the semidecorated ab sheets.     

DFT and TD-DFT approach for the analysis of NLO and OLED applications of 9-anthraldehyde

The geometric parameters characterization and ground state energies for 9-anthraldehyde have been calculated using density functional theory (DFT). NBO analysis has been done on the same level to investigate the hyper conjugative interaction. HF/6-31G (d) method is adopted to calculate the first order hyperpolarizability (β). Frontier molecular orbital analysis has also been done in support of β. The excited state energies, as well as absorption wavelengths, are computed using time dependent-density functional theory (TD-DFT). For the emission wavelength the excited state geometry optimization has been carried out using configuration interaction singlets (CIS). The emission wavelength has been calculated in TD-DFT approach. The theoretical data so obtained is analyzed for the applications of NLO and OLED. One of the important conclusions from our study is that this material is suitable for both the applications. The macroscopic second harmonic generation (SHG) efficiency has also been identified through Kurtz–Perry powder technique.     

Adsorption of NO and N2O on Fe-BEA and H-BEA zeolites

FT-IR (Fourier-transform infrared) spectroscopy and density function theory (DFT) methods have been applied to the investigation of the interaction of NO and N₂O with Fe³⁺ species in a beta zeolite (BEA). The geometries for H-BEA and Fe-BEA represented as 10T cluster, and NO and N₂O adsorption on them in η¹-O and η¹-N modes have been completely optimized. The results show that NOx could be adsorbed on Fe³⁺ species and Brønsted acid sites in two modes, but NOx is mainly bonded by N to H or Fe atom and the iron site is preferred. NOx adsorbed on Fe³⁺ species is more stable than on Brønsted acid sites. Adsorption energies for N₂O and NO follow the order of NO > N₂O, predicating that the affinity of NO molecule on BEA zeolite is much stronger than N₂O molecule on BEA zeolite.     

四种耐热含能化合物电子结构的第一性原理研究

本文模拟计算了2,2’,4,4’,6,6’-六硝基联苯(HNBP)、2,2’,4,4’,6,6’-六硝基二苯乙烯(HNS)、2,5-二苦基-1,3,4-噁二唑(DPO)和5,5''-双(2,4,6-三硝基苯基)-2,2''-双(1,3,4-噁二唑)(TKX-55)四种耐热含能化合物的分子结构、Mulliken电荷布居、分子静电势(MEP)和Hirshfeld表面, 通过研究其分子特性、电子特性以及分子间相互作用, 以了解高耐热性含能化合物的耐热机理. 结果表明, 桥连接结构的复杂性以及分子间强氢键相互作用会增强含能化合物的稳定性. 此外, 本研究还发现中间基团的加入会对四种含能化合物分子两侧芳香环上碳原子的电荷分布以及分子表面正负静电势区域面积产生一定的影响.     

扑尔敏分子的密度泛函理论研究

马来酸氯苯那敏（chlorpheniramine maleate,CPM）,化学名为2-[对-氯-α-（二甲氨基）乙基丁苯基], 又名扑尔敏,分子式C20H23ClN2O4,本文采用密度泛函理论（density functional theory,DFT）,在M06-2X/6-311+g(d,p)水平上对扑尔敏分子的两种可能的结构进行了优化,优化结果显示分子基态结构具有C1对称性,分子由50个原子组成,共有144个简正自由度,所有的简正振动模式均具有拉曼活性。计算结果表明,吡啶环和苯环所在平面的二面角是92.1°,丁烯二酸和苯环所在平面的二面角是-174.5°。O40-H41和H41-N25键长分别为0.103nm、0.162nm,O40-H41-N25键角为175.29°,采用多功能波函数Multiwfn软件处理结果表明用于表征氢键强度的CVB指数（CVB指数越负,通常氢键越强。）为-0.2268,结果表明O40-H41-N25原子之间存在氢键,马来酸通过羧基上的氢原子和氯苯那敏吡啶环上的N原子通过氢键作用相结合;通过频率计算,获得了扑尔敏分子的拉曼光谱,并利用势能函数分布（PED）对拉曼光谱进行了指认,对谱图信息比较丰富的200-1800cm-1波段进行了分析归属;此外分析并讨论了扑尔敏分子的前线轨道,扑尔敏分子的最高占据轨道HOMO和最低未占据分子轨道LUMO轨道能量分别为-7.95ev、-1.05ev,能级差为6.90ev。为扑尔敏分子的光谱测定和电子结构分析提供了理论基础。     

Cd、Sr掺杂Mg2Ge电子结构和光学性质的第一性原理研究

此文用基于密度泛函理论(DFT)的第一性原理计算方法,分别研究了本征、掺Cd、掺Sr的Mg₂Ge的能带结构、电子态密度和光学性质.研究结果表明,本征Mg₂Ge是一种间接带隙半导体,带隙值为0.228eV.Sr的掺入使其变成带隙为0.591 eV的直接带隙半导体,Cd掺杂Mg₂Ge后表现出半金属性质.掺杂后的主要吸收峰减小,吸收谱范围增加.在可见光能量范围内,掺杂的Mg₂Ge有更低的反射率,对可见光的利用率增强.此外,掺杂还提高了高能区的光电导率.     

两种常用合成抗氧化剂的拉曼光谱研究

随着社会的不断进步,食品工业得到快速发展,随之食品安全问题也层出不穷。由于合成抗氧化剂价格较低且对食品有较好的防腐保鲜作用,常被一些食品生产商过量添加在食品中,严重危及人们身心健康。因而,对于食品中合成抗氧化剂的检测研究是十分必要的。丁基羟基茴香醚(BHA)和叔丁基对苯二酚(TBHQ)是两种常见的合成抗氧化剂。实验上, 利用共聚焦显微拉曼光谱仪分别对BHA和TBHQ进行拉曼光谱检测,获得样品的拉曼散射谱。理论上,应用密度泛函理论DFT(B3LYP)的三参数混合方法及6-31G(d, p)基组对其进行空间结构优化并计算其拉曼光谱,给出了光谱强度图。将理论结果与实验结果进行对比发现,在50～4 000 cm-1范围内BHA及TBHQ分子拉曼特征明显且拉曼活性较强,其振动频率在实验上和理论上显示出较好的一致性。另外,给出了BHA和TBHQ分子的红外活性、拉曼活性以及各频率谱线对应的振动模式归属。结果表明,BHA和TBHQ分子的拉曼频移表征物质的特征结构,可以作为鉴定和识别的检测依据。该研究报道了抗氧化剂BHA和TBHQ的拉曼光谱,并对其理论机制进行分析,为拉曼光谱技术应用于食品添加剂研究领域提供了理论和实验依据。