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1.
The thickness dependence of the electronic conductivity of thin (5–150 nm) single-crystal (100) films of refractory metals is investigated at different temperatures ranging from 4.2 K to room temperature. Regions of square-root, quasilinear, and quadratic dependences are observed. The quasilinear thickness dependence is explained by the influence of quantum effects on the transverse motion of electrons in the case when electron scattering by the film surfaces dominates. For macroscopic film thicknesses 30–50 nm, much greater than the Fermi wavelength of an electron, quantum corrections to the electronic conductivity reach values of the order of 50%. This is a consequence of the quantum size effect for grazing electrons, which leads to an anomaly in electron scattering by the film surfaces. The region of the quadratic thickness dependence corresponds to the quantum limit, and the square-root region corresponds to the classical limit. The effect is explained in a quasiclassical two-parameter model (the effective angle α* for small-angle electrons and the parameter γ, equal to the ratio of this angle to the diffraction angle) that takes into account the diffraction angular limits for grazing electrons. The effect occurs for parameters α*≪1 and γ∼1 and differs from the “ordinary” quantum size effect. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 11, 693–698 (10 December 1997)  相似文献   

2.
郭浩民  文龙  赵志飞  步绍姜  李新化  王玉琦 《中国物理 B》2012,21(10):108101-108101
We investigated the quantum dots-templated growth of a(0001) GaN film on a c-plane sapphire substrate.The growth was carried out in a radio-frequency molecular beam epitaxy system.The enlargement and coalescence of grains on the GaN quantum dots template was observed in the atom force microscopy images,as well as the more ideal surface morphology of the GaN epitaxial film on the quantum dots template compared with the one on the AlN buffer.The Ga polarity was confirmed by the reflected high energy electron diffraction patterns and the Raman spectra.The significant strain relaxation in the quantum dots-templated GaN film was calculated based on the Raman spectra and the X-ray rocking curves.Meanwhile,the threading dislocation density in the quantum dots-templated film was estimated to be 7.1×107cm-2,which was significantly suppressed compared with that of the AlN-buffered GaN film.The roomtemperature Hall measurement showed an electron mobility of up to 1860cm2 /V·s in the two-dimensional electron gas at the interface of the Al 0.25Ga0.75 N/GaN heterojunction.  相似文献   

3.
庞斐  梁学锦  廖昭亮  尹树力  陈东敏 《中国物理 B》2010,19(8):87201-087201
<正>Transport characteristics of single crystal bismuth films on Si(lll)-7x7 are found to be metallic or insulating at temperatures below or above T_C,respectively.The transition temperature T_C decreases as the film thickness increases. By combining thickness dependence of the films resistivity,we find the insulating behaviour results from the states inside film,while the metallic behaviour originates from the interface states.We show that quantum size effect in a Bi film,such as the semimetal-to-semiconductor transition,is only observable at a temperature higher than T_C.  相似文献   

4.
熊稳  赵铧 《物理学报》2007,56(2):1061-1065
采用有效质量近似,将耦合在一起的6×6价带本征方程分开来考虑, 取激子试探波函数为z方向和x-y平面分离的形式,用变分法计算了ZnO薄膜重空穴带激子基态能、第一激发态能、束缚能和激子的半径随薄膜厚度的变化关系,并讨论了电子波函数的量子隧穿效应对厚度d<2.0 nm薄膜的能量修正. 关键词: 激子 ZnO薄膜 纤锌矿  相似文献   

5.
The size-quantized spectrum of a film (quantum well) with a variable band gap based on Pb1?x Sn x Se compounds has been studied. It is shown that an asymmetric modulation of the band gap in the film growth direction leads to the spin splitting of the electron subbands of a uniform quantum well. The effect of the state of the film surface on spontaneous polarization of the electron gas is discussed.  相似文献   

6.
40 alternate a-Si/SiN x multilayer are incorporated as an absorber layer in a p–i–n solar cell. The device is fabricated using hot-wire chemical vapor deposition (HWCVD) technique. The structure of the multilayer film is examined by high resolution transmission electron microscopy (HR-TEM) which shows distinct formation of alternate a-Si and SiN x layers. The a-Si and SiN x layers have thickness of ~3.5 and 4 nm, respectively. The photoluminescence (PL) of multilayer film shows bandgap energy of ~2.52 eV, is larger than that of the c-Si and a-Si. Dark and illuminated current–voltage (IV) characterization of the ML films shows that these ML are photosensitive. In the present work, it is seen that the p–i–n structure with i-layer as ML quantum well (QW) structures show photovoltaic effect with relatively high open-circuit voltage (V OC). The increment of bandgap energy in PL and high V OC of the device is attributed to the quantum confinement effect (QCE).  相似文献   

7.
An attempt is made to investigate the effects of size quantization on the effective mass in ultrathin films ofn-Cd3As2. It is found that the effective mass at the Fermi level depends on the size quantum number due to the effect of crystal-field splitting, resulting in different effective masses at the Fermi level corresponding to different electric subbands. It is also observed that the different effective masses closely approach each other, for a given film thickness, with increasing electron concentration and, for a given electron concentration, with increasing film thickness.  相似文献   

8.
Three new unsymmetrical isomeric diarylethenes having a methoxyl substituent at ortho‐, meta‐, and para‐position of the terminal benzene ring, namely 1‐(2,5‐dimethyl‐3‐thienyl)‐2‐[2‐methyl‐5‐(2‐methoxylphenyl)‐3‐thienyl]perfluorocyclopentene ( 1o ), 1‐(2,5‐dimethyl‐3‐thienyl)‐2‐[2‐methyl‐5‐(3‐methoxylphenyl)‐3‐thienyl]perfluorocyclopentene ( 2o ), and 1‐(2,5‐dimethyl‐3‐ thienyl)‐2‐[2‐methyl‐5‐(4‐methoxylphenyl)‐3‐thienyl]perfluorocyclopentene ( 3o ), have been synthesized. The substituent position effect of methoxyl group on their properties, including photochromism and fluorescence both in hexane solution and in PMMA film, and their electrochemical properties, were investigated in detail. These diarylethenes showed good photochromism both in solution and in PMMA film. For the same photochromic diarylethene backbone, the electron‐ donating methoxyl substituent can effectively depress the cyclization quantum yields and increase the cycloreversion quantum yields compared to those of diarylethenes bearing chlorine atoms reported previously. Diarylethenes 1o – 3o showed clear fluorescent switches by photoirradiation both in hexane and in PMMA film. In addition, cyclic voltammetry tests showed that the electron‐donating methoxyl group at different position on the terminal benzene ring had a significant effect on the electrochemical properties of these isomeric diarylethenes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

9.
Pinning properties in 100 nm thick continuous and porous superconducting Nb films are examined by ac susceptibility and dc magnetization measurements. The Nb film was deposited on a smooth Si substrate, while the porous film, NbP, was deposited on an anodized Al oxide substrate. Pores or “antidots” 40 nm in diameter, 100 nm apart, form a triangular array. The porous film presents commensurate or matching field effects for applied magnetic fields where the magnetic flux threading each unit cell is an integer number of the flux quantum, where ac shielding capability and dc diamagnetic magnetization show an abrupt increase. The response to ac fields as a function of temperature and dc field provided a way to determine that NbP sample has higher pinning than the continuous one, and that TC suppression due to fluxoid quantization is not relevant for the investigated temperature range.  相似文献   

10.
The effect of localized spins on the quantum coherence in solids is discussed. A quantum dot with an odd number of electrons can be a model system for a localized spin. It is experimentally shown that a spin flip scattering by a quantum dot pulls the trigger of quantum decoherence. On the other hand, spin flip scattering is the basic process to construct the Kondo singlet state around a magnetic impurity. Through an interference effect of the Kondo state (the Fano–Kondo effect) in a side-coupled dot system, we show experimentally that the Kondo singlet state is quantum mechanically coherent. The analysis of the Fano–Kondo lineshape indicates the locking of the phase shift to π/2, which is in agreement with theoretical predictions. The Fano–Kondo effect is also observed in an Aharonov–Bohm ring, in which a quantum dot is embedded, and also indicates the phase shift locking to π/2.  相似文献   

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