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1.
于洪滨  高波  盖峥  杨威生 《物理学报》1997,46(3):505-510
用扫描隧道显微镜,在小隧道阻抗的条件下(小偏压和大隧道电流),通过移动针尖,实现了在室温下对真空蒸镀在高定向石墨上的、由几万个原子组成的纳米尺度金岛的操纵.在大隧道阻抗的情形下,用同一个针尖可对操纵的结果进行观察,而不会对金岛产生扰动.这种可控的操纵是通过当钨针尖与金岛间距离很近时形成的金属间黏附力大于金岛与石墨间的摩擦力而实现的 关键词:  相似文献   

2.
于洪滨  高波  盖峥  杨威生 《物理学报》1997,46(4):679-687
用扫描隧道显微镜(STM)研究了在金针尖和金样品间施加大偏压时所发生的各种不同的现象.在缓变大偏压的作用下,观察到针尖原子会发生场致扩散,导致针尖形状发生变化,并且还观察到了场发射和共振隧穿现象.提出了针尖原子的场致扩散是偏压电场使针尖表面极化引起的这一机理,并且指出了这种场致扩散在用大脉冲偏压作表面加工中起着重要的作用 关键词:  相似文献   

3.
管东波  毛健 《物理学报》2012,61(1):17102-017102
采用基于密度泛函理论的平面波超软赝势法研究了Magnéli相亚氧化钛Ti8O15的电子结构和光学性能. 计算出的能带结构显示Ti8O15相比锐钛型TiO2禁带宽度大幅度降低. 态密度分析表明, 其原因在于Ti8O15的O原子的2p轨道以及Ti原子的3p, 3d轨道相对于TiO2的相应轨道向左产生了偏移, 同时由于O原子的缺失使得Ti原子的3d, 3p轨道多余电子在Fermi能级附近聚集形成新的电子能级. 态密度分析结果还显示, 相对于TiO2, Ti8O15 Fermi能级附近电子格局发生了如下变化: O原子的2p轨道电子贡献减少, Ti原子的3d轨道的电子对Fermi能级贡献增大. 光吸收计算图谱表明, TiO2仅在紫外光区有较高的光吸收能力, 而Ti8O15由于禁带宽度变窄引起光吸收范围红移到可见光区, 从而在紫外光区和可见光区都有较高的光吸收能力, 计算结果与实验得到的紫外-可见漫反射吸收光谱结果一致. 关键词: 第一性原理 8O15')" href="#">Magnéli相亚氧化钛Ti8O15 电子结构 光学性能  相似文献   

4.
高国强  陈波  黄整  张秀兰  孙光爱  黄华山  余聪 《物理学报》2006,55(11):6036-6041
基于密度泛函理论(DFT),采用线性缀加平面波展式结合改进的局域轨道方法(APW+lo),对具有ThMn12结构的永磁材料YFe11Ti的结构和磁性进行了计算和分析.计算了YFe12,Y2Fe17,YFe11Ti的生成能,探讨了替代元素Ti的加入使YFe12系统能够保持稳定的ThMn12结构的原因以及Ti在系统中的最佳可能占位.给出了系统的晶体磁矩和各晶位原子的磁矩以及系统的电子态密度,分析了系统磁性的来源和各晶位原子磁矩的大小与其配位数和平均近邻原子距离的关系. 关键词: 12')" href="#">ThMn12 密度泛函 生成能 磁矩  相似文献   

5.
利用第一性原理研究了Ba0.5Sr0.5TiO3的能带结构和光学性质.结果表明,导带和价带都来源于钛原子3d轨道和氧原子2p轨道的杂化.导带主要由钛原子的3d轨道贡献,价带主要由氧原子的2p轨道贡献.吸收系数为105 cm-1量级,且吸收主要集中在低能区.折射率为n(0)=2.1,结果与实验符合. 关键词: 第一性原理 能带结构 光学性质  相似文献   

6.
杨景景  杜文汉 《物理学报》2011,60(3):37301-037301
为了解半导体衬底与氧化物之间存在的相互作用,以及量子尺寸效应对不同再构体的影响,制备了1—2个原子层厚的TiSi2/Si(100)纳米岛,并使用扫描隧道显微镜(STM)表征手段详细地研究了TiSi2 /Si(100)纳米岛的电子和几何特性. 结果发现:这些纳米岛表面显示出明显的金属性;其空态STM图像具有典型的偏压依赖性:在高偏压下STM 图像由三聚物形成的单胞构成,并在低偏压下STM 图像显示为密堆积的图案,这些不同的图案反映出不同能量位的态密度有明显差异. 关键词: 2纳米岛')" href="#">TiSi2纳米岛 Sr/Si(100)表面 扫描隧道显微镜  相似文献   

7.
管东波  毛健 《物理学报》2012,61(1):397-401
采用基于密度泛函理论的平面波超软赝势法研究了Magneli相亚氧化钛Ti8O15的电子结构和光学性能.计算出的能带结构显示Ti8O15相比锐钛型TiO2禁带宽度大幅度降低.态密度分析表明,其原因在于Ti8O15的O原子的2p轨道以及Ti原子的3p,3d轨道相对于TiO2的相应轨道向左产生了偏移,同时由于O原子的缺失使得Ti原子的3d,3p轨道多余电子在Fermi能级附近聚集形成新的电子能级.态密度分析结果还显示,相对于TiO2,Ti8O15Fermi能级附近电子格局发生了如下变化:O原子的2p轨道电子贡献减少,Ti原子的3d轨道的电子对Fermi能级贡献增大.光吸收计算图谱表明,TiO2仅在紫外光区有较高的光吸收能力,而Ti8O15由于禁带宽度变窄引起光吸收范围红移到可见光区,从而在紫外光区和可见光区都有较高的光吸收能力,计算结果与实验得到的紫外-可见漫反射吸收光谱结果一致.  相似文献   

8.
王福合  杨金龙  李家明 《物理学报》1998,47(11):1827-1839
为了较清楚地阐明扫描隧道显微镜针尖在样品表面原子操纵中的具体作用,根据第一性原理的离散变分理论计算,采用“团簇模型”研究了在无外加电场下,W针尖与样品Al(111)表面Al原子的相互作用.结果表明:随着W针尖与样品表面接近到一定程度(针尖与样品表面的距离S≤10a.u.(0.53nm))时,由于针尖原子与样品表面原子的相互作用,使位于针尖正下方的表面Al原子在脱离表面时感受到一稳定的势阱,即在无外场的情况下,当W针尖与样品Al(111)表面接近到一定程度时,由于针尖的吸引作用,将使针尖正下方的Al原子自动离开样品表面而移向W针尖,实现Al(111)表面单个Al原子的操纵. 关键词:  相似文献   

9.
张召富  耿朝晖  王鹏  胡耀乔  郑宇斐  周铁戈 《物理学报》2013,62(24):246301-246301
采用基于密度泛函理论的第一性原理计算方法,研究了当氮化硼纳米管(BNNT)中的B原子和N原子被5d过渡金属原子(Lu,Hf,Ta,W,Re,Os,Ir,Pt,Au,Hg)取代时BNNT的几何结构、电子结构和磁性性质. 作为对比,给出了理想BNNT,B缺陷体系(VB)和N缺陷体系(VN)的相应结果. 研究发现:5d原子取代B(B5d)时体系的局域对称性接近于C3v,但是取代N(N5d)时体系的局域对称性偏离C3v对称性较大;利用相同的5d原子进行掺杂时,B5d的成键能比N5d的成键能大;对于B5d或者N5d,其成键能基本上随着5d原子的原子序数的增大而降低;掺杂体系中出现了明显的杂质能级,给出了态密度等结果;不同掺杂情况的磁矩不同,取代B 时体系的总磁矩呈现出较强的规律性. 利用对称性和分子轨道理论解释了5d原子取代B时杂质能级的产生和磁性的变化规律. 关键词: 第一性原理计算 5d过渡金属原子 氮化硼纳米管 密度泛函理论  相似文献   

10.
n+-Si与p-Si衬底上含纳米硅的SiO2膜电致发光   总被引:3,自引:0,他引:3       下载免费PDF全文
对于Au/富Si-SiO2/p-Si和Au/富Si-SiO2/n+-Si这两种结构,研究并比较了它们的电致发光特性.对于前者,当正向偏压大于4V时发射红光,而加反向偏压时不发光;对于后者,加正向偏压不发光,而当反向偏压大于3.5V时发射红光.着重讨论了Au/富Si-SiO2/n+-Si的电致发光机制 关键词:  相似文献   

11.
利用第一性原理的离散变分局域密度泛函方法,采用团簇模型(Si34H36-W11)来模拟STM操纵Si(111)-7×7表面顶角吸附原子的过程.通过分析在进行原子操纵过程中体系的能量与电子云密度分布来研究针尖和外电场的作用.结果表明,当针尖与样品间距离较近时,利用两者间有较强的相互作用,能有效地降低脱出能的能垒高度.外电场对体系脱出能的影响与其大小及极性有关,当样品上所加正偏压增强时,脱出能曲线高度单调下降,而外电场极性为负时,反而稍有增高.仅考虑针尖和样品之间的静态电子相互作用及静电场的作用,尚不能使被操纵原子脱离样品表面.最后讨论了在Si(111)-7×7表面上进行原子操纵的其他机理.  相似文献   

12.
对第一过渡金属酞菁化合物(Metal Phthalocyanine,MPc,M=Sc,Ti,V,Cr,Mn,Fe,Co,Ni和Cu)的电子结构和基本物理化学性质进行了第一性原理计算.理论模拟出来的STM图像表现出亚分子结构,与已有的实验观察结果相当吻合,且跟金属原子的d电子组态明显有关.在小偏压条件下,第一过渡金属首尾端ScPc,NiPc和CuPc分子的中央金属离子在STM图像表现为空洞,其他所有金属酞菁分子的中央金属离子均为亮斑.同时还研究了ScPc和NiPc分子的STM图像与偏压的关系,当针尖偏压分别 关键词: STM图像模拟 金属酞菁 电子结构  相似文献   

13.
An isomer of the methylterrylene molecule was adsorbed both on Cu(111) and on a NaCl bilayer deposited on Cu(111) and imaged by ultra high vacuum scanning tunneling microscopy at low temperature (5 K). On the bare metal surface, the STM images do not reveal any intramolecular resolution and do not depend on the applied tunnel bias. On the contrary, the images acquired at specific bias voltages for the molecule on the salt layer show a striking similarity with the spatial distribution of the electronic probability density in the highest occupied molecular orbital (HOMO) and in the lowest unoccupied molecular orbital (LUMO) of free methylterrylene. They are well reproduced by elastic scattering quantum chemistry calculations. These data provide a direct view of the hyperconjugative interaction between the methyl group and the frontier orbitals of terrylene.  相似文献   

14.
Bias-dependent features of the insulating NaCl layer grown on Cu(001) have been investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The apparent layer thickness of the NaCl film is variable at bias voltages ranging from 2.8 to 3.2 V as well as from 4.0 to 5.0 V, and the Moiré pattern induced by NaCl–Cu lattice mismatch also shows bias dependence. The z–V (dz/dV–V) curves and dI/dV mapping measurements reveal that the resonant tunneling between the image potential states (IPSs) on Cu(001) and the Fermi level of the STM tip leads to drastic variations of these features.  相似文献   

15.
We report the field-assisted H2O etching that enabled us to fabricate nano-tips from polycrystalline <1 1 0> oriented tungsten wires at room temperature. We optimized the sharpening procedure in order to obtain field emissions (FEs) with high collimation. The typical tip apex was composed of a large base and a nano-protrusion with a radius of curvature less than 3.5 Å. The narrowest opening angle (full width at half maximum) of the FE was 4.3° at 150 pA. We prepared two types of tips using two different applied bias voltages during the H2O etching. The electron microscope images and the analysis of Fowler-Nordheim (FN) plots revealed that the sizes of the individual bases depended on the fixed bias voltages during the H2O etching and affected their FE properties. In addition, we could confirm that the FE current from the nano-tip was more stable than that of the normal tip.  相似文献   

16.
17.
The focus of this work has been on the pre-breakdown phenomena and the breakdown characteristics of N2 gas in a sphere-plane gap under various impulse voltages. Both electrical and optical experimental investigation methods were used. Following parameters were considered: gas pressure range from 0.2 to 0.6 MPa, electric field utilization factor of the electrode configuration 71%, positive and negative impulse waveforms with the rise time of 500 ns, 1.2 μs and 180 μs. The observed discharge processes before the breakdown through the light emission images by the ICCD camera are in good agreement with the streamer mechanism. Under both polarity stresses, discharges are initially concentrated around the tip of the sphere and later pointing towards the earth electrode. However, negative streamers are thinner and more diffuse. As expected, the breakdown voltages for negative polarity are lower than those for positive polarity regardless of the gas pressure and shape of the applied impulse voltage. The breakdown voltage is increased with shortening the rise time of pulse waveforms. As a substitute for SF6, N2 gas under pressures above 0.3 MPa can reach the standard rated withstand voltage for 24 kV C-GIS.  相似文献   

18.
Scanning tunneling microscopy (STM) under ultra-high vacuum conditions is used to study the initial stages of adsorption of C60F18 and C60F36 fluorofullerene molecules on Si(111)-7 x 7 and Si(100)-2 x 1 surfaces. Spatially resolved STM images of individual molecules and ab initio calculations show that the fluorofullerene molecules interact with an Si surface, with the F atoms oriented toward the surface. The large electric dipole moment of the molecules induces strong polarization on the surface, but the charge transfer is weak. The presence of C60F36 isomers with different symmetry—T, C 3, and C 1—is revealed in STM images for the first time.  相似文献   

19.
The release of gold atoms from an octanethiol monolayer on Au(1 1 1) and the subsequent formation of single-layer-high gold islands have been investigated using a scanning tunnelling microscope (STM) in air. When the bias voltage between the STM tip and the sample is above the threshold for water electrolysis, reactive desorption of the thiol molecules takes place leading to the release of gold adatoms. The number of released atoms has been evaluated as a function of exposure to the tip current under both positive and negative bias voltages. Tip-induced ripening of the gold islands, and more interestingly, tip-induced disintegration of small islands are observed.  相似文献   

20.
We present a short outline of the first STM experiments with spin-polarized electrons performed in ultrahigh vacuum by using ferromagnetic CrO2 tips and a Cr(001) single crystal surface. A clear distinction can be made between topographic STM line scans obtained with a non-magnetic tungsten tip and those obtained with a ferromagnetic CrO2 tip, which are modified due to an additional contribution from spin-dependent vacuum tunneling. STM therefore has the potential to measure the local electron spin polarization of the free surface as well as the spatial distribution of spins on the atomic scale.  相似文献   

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