The quantum size effect in thin antimony films

Thin antimony films have been epitaxially deposited at 350K onto cleavage surfaces of mica at different residual gas pressures between 10^?5 and 10^?9 torr, and their resistivity ? measured as a function of film thicknessd≦500Å at temperaturesT=110K andT=300K. The ?(d) characteristics of films deposited at residual gas pressures of about 10^?6 torr with condensation rates of about 1Å/s showed generally decreasing slopes as film thicknesses increased, but irregularities in detail. The ?(d) characteristics of films deposited at 10^?8 torr with the same condensation rate decreasing with increasingd, too, show no such irregularities but very small regular variations of ?(d) with constant oscillation length Δd between the maxima, and decreasing amplitudes with increasingd. These variations are better recognizable in a modified ?(d) graph. We tend to interprete these variations by the quantum size effect as we found oscillation lengths and amplitudes compatibel with theory.

     

Experimental study of quantum size effects in very thin metal films

The influence of the quantum size effect (QSE) in very thin Pd and Au films (0.5<d<10 [nm]) deposited on glass tips is studied by means of field emission at various anode potentials. The thickness-dependent field emission current characteristics show short periodic variations with a period of about 0.3 nm for both Pd and Au. The measured QSE oscillations and their amplitudes differ strongly from those expected qualitatively from model calculations for the smallest thicknesses. A model for the metal film based on a modification of the uniform background model is presented, and the thickness dependence of the conductance and the field emission current density are qualitatively discussed. Possible explanations of some discrepancies between calculations and the measured field emission current characteristics are proposed.     

Studying the quantum size effect in LiF-based thin films with Ag and Cu nanoclusters

The characteristic energy of distributions of Ag and Cu nanoclusters in LiF-based thin films is estimated from the slope of the I–V characteristic, built in double logarithmic coordinates logI = f (logU). It is shown that the energy states of small clusters lie above the bottom of the conduction band and form a potential barrier, while the energy states of large clusters lie below the bottom of the conduction band and form a potential well. The change in the positions of energy levels along with nanocluster size and the effect of quantum limitations imposed on the electrical and optical properties of the system are confirmed experimentally.     

Phase size effect in thin Ge-Se polycrystalline films

The Raman spectra of thin (d = 60–170 nm) Ge-Se polycrystalline films obtained by vacuum thermal evaporation of Ge₁₀Se₉₀ glass are investigated in the spectral range 110–310 cm^?1. The coexistence of the glasslike and crystalline phases α-Se, β-Se, and β-GeSe₂ is established using the X-ray diffraction method. Analysis of diffraction patterns and the Raman spectra of polycrystalline samples of various thicknesses demonstrates a phase size effect in the transition of Se from the α-monoclinic to the β monoclinic modification (d ～ 120 nm). It is found that the crystalline phase of Se is of the nanodisperse type with an average grain size of ～30–50 nm. Crystallites of β-GeSe₂ have an average size of ～100–130 nm.     

Specific field emission properties of thin palladium films

The field emission current from thin palladium films deposited on insulating tips in UHV was measured as a function of film thickness at relatively low field strengths. The observed periodic oscillations of the field emission current can be interpreted as the quantum size effect.     

Investigation of quantum size effect in magnetite films.

Oscillations of electroconductivity with the changing of applied potential and shift of Verwey temperature in thin films of magnetite are observed and explained by the size quantization of the current carriers.     

A model for the off-on transition in thin ZnTe films

Thin ZnTe films show memory switching characteristics. The transition between the high-resistive off-state and the low-resistive on-state is explained here as a thermal instability. To describe this, an electro-thermal model differing from the existing ones is worked out for the specific case of a ZnTe-on glass structure. The numerically obtained results agree well with the measured off-on transition parameters.     

Variations in thermoelectric power of thin monocrystalline films with conductivity

Starting from the bi-dimensional model for grain boundaries in monocrystalline thin films, the difference in thermoelectric power is expressed in terms of conductivity and energy dependence of the bulk electronic mean free pathU. A new procedure is suggested for measuringU.     

Spot focus size effect in spectroscopic ellipsometry of thin films

A focused as opposed to collimated light beam is typically used as probe in order to achieve a smaller as well as more intense light interrogation area in spectroscopic ellipsometry of thin films. In this work, we performed geometric ray analysis at the illumination and recording ends of such a system. The numerical results revealed substantial changes in (i) average optical path length and (ii) optical path length differences, which varied according to wavelength despite the film thickness remaining uniform. These results were able to consistently explain the anomalies found when different focus probe beam sizes were used in experimental spectroscopic ellipsometry measurements.     

The influence of substrate material and annealing procedure on the properties of superconducting thin films

Thin layers YBa₂Cu₃O_7–x. are deposited by a laser ablation technique using a pulsed excimer laser operating at 308 nm. The influence of the substrate material and the annealing procedure on the superconducting behaviour of the 123 film and the reactions between the film and the substrate are studied by resistance, X-ray patterns and TEM measurements. The best results are obtained for deposition on (100) SrTiO₃ substrates. The resistance of the 1 m thick film shows a metallic behaviour, an onset in superconductivity at a temperature of 90 K, and has zero resistance at 86 K. The 123 material has a preferential oriented c-axis perpendicular to the surface plane.     

Quantum size effect in low energy electron diffraction of thin films

Low energy electron microscopy (LEEM) is used to study the quantum size effect (QSE) in electron reflectivity from thin films. Strong QSE interference peaks are seen below 20 eV for Cu and Ag films on the W(1 1 0) surface and Sb films on the Mo(0 0 1) surface. Simple inspection of QSE interference peaks reveals that all three metals grow atomic layer-by-atomic layer. Layer-specific I(V) spectra obtained with LEEM permit structural analysis by full dynamical multiple scattering LEED calculations for a layer-by-layer view of thin film structure.     

Be(0001)薄膜中的量子尺寸效应与吸附氢的第一性原理计算

通过基于密度泛函理论的第一性原理方法对铍自由表面的电子结构及表面原子氢的吸附能作了详细计算，给出Be(0001)薄膜的电子结构、表面能、电子功函数、层间弛豫等物理量随厚度变化关系，同时讨论了原子氢在Be(0001) 表面的吸附性质，给出了吸附能及局域电子态密度随铍薄膜层厚的变化关系，体现了铍薄膜的量子尺寸效应.     

Disorder effect on the quantum Hall effect in thin films of three-dimensional topological insulators

We numerically study the quantum Hall effect (QHE) in three-dimensional topological insulator (3DTI) thin film in the presence of the finite Zeeman energy g and the hybridization gap Δ under a strong magnetic field and disorder. For Δ = 0 but g ≠ 0, the Hall conductivity remains to be odd-integer quanti-zed σ _xy = ν(e ²/h) , where ν = 2? + 1 with ? being an integer. In the presence of disorder, the Hall plateaus can be destroyed through the float-up of extended levels toward the band center and the higher plateaus disappear first. The two central plateaus with ν = ± 1 around the band center are strongest against disorder scattering. With the increasing of the disorder strength, Hall plateaus are destroyed faster for the system with a weaker magnetic field. If g = 0 but Δ ≠ 0, there is a splitting of the central (n = 0) Landau level, yielding a new plateau with ν = 0, in addition to the original odd-integer plateaus. In the strong-disorder regime, the QHE plateaus can be destroyed due to the float-up of extended levels toward the band center. The ν = 0 plateau around the band center is strongest against disorder scattering, which eventually disappears. For both g ≠ 0 and Δ ≠ 0, the simultaneous presence of nonzero g and Δ causes the splitting of the degenerating Landau levels, so that all integer Hall plateaus ν = ? appear. The ν = 0,1 plateaus are the most stable ones. In the strong-disorder regime, all QHE states are destroyed by disorder, and the system transits into an insulating phase.     

Quantum size effect in the photoemission intensity emitted from thin metal films

Photoemission spectra are calculated for thin films of Ag on Au(111) using the method of Green's function matching. For very low photon energies (ω ≲ 10 eV) the peak intensities of the thin film states oscillate with the film thickness. These oscillations are caused by the relaxation of the k_⊥-conservation of the optical excitation in photoemission.     

Quantum size effects for the extraordinary Hall effect in thin magnetic films

A theory for the extraordinary Hall effect in thin films is derived using the Kubo formalism. We calculate the skew-scattering contribution to the Hall resistivity. Oscillations of the resistivity with the thickness of the magnetic layers are obtained similar to the diagonal resistivity, but as the Hall current is due to d-electrons, the period of these oscillations is connected with the Fermi wave vector of the d-electrons.     

一种薄膜中颗粒自动分层的新机制

一般制备固体表面上薄膜的方法是在固体表面涂抹一层含有固态胶体颗粒的液体膜,然后令液体蒸发而成。染料和墨水就是由悬浮在液体中的小颗粒构成的典型胶体。当液体蒸发时,这些颗粒融合在一起形成薄膜。研究人员从理论和实验两方面展示新的结果：如果颗粒尺寸足够大,两种不同尺寸的颗粒会在干燥过程中分层。较小颗粒形成的层位于大颗粒层的上方。这种分层方式与常规方式相反。如果制备某种胶体,能够在干燥过程中形成双层结构,则这种效应可以用来创造具有特殊性能的化妆品或者电子器件。     

The quantum magnetic size effect in cylindrical conductors

Quantum magnetic size oscillations of the electron characteristics of cylindrical conductors are associated with the Fermi surface anisotropy. The oscillations predicted may be a source of important information of the electron energy spectrum of conductors.