表面粗糙度对薄膜面向热导率的影响研究

通过求解声子辐射输运方程(EPRT)计算得到了薄膜的面向晶格热导率.在薄膜界面采用与声子波长相关的镜反射率模型,考虑了薄膜的厚度、温度和表面粗糙度等对其热导率的影响.结果表明,界面粗糙度对薄膜热导率的影响很大.减小界面粗糙度,会使得薄膜热导率大大增加.另外,薄膜厚度减小使得热导率峰值对应的温度增加.     

The formation of sub-10 nm nanohole array on block copolymer thin films on gold surface using surface neutralization based on O2 plasma treatment and self-assembled monolayer

Blockcopolymer (BCP) lithography is an emerging nanolithography technique for fabrications of various nanoscale devices and materials. In this study, self-assembled BCP thin films having cylindrical nanoholes were prepared on gold by surface neutralization using self-assembled monolayer (SAM). Oxygen plasma treatment was investigated as a way to enhance the functionality of Au surface toward SAM formation. After surface neutralization, well-ordered nanoholes with 9 to 20 nm diameters were formed inside BCP thin films on Au surfaces through microphase separation. The effects of oxygen plasma treatment on the formation of BCP nanopattern were investigated using surface analysis techniques including X-ray photoelectron spectroscopy (XPS) and water contact angle measurement. Au nanodot arrays were fabricated on gold film by utilizing the BCP nanotemplate and investigated by atomic force microscopy (AFM).     

Anomalous scaling in surface roughness evaluation of electrodeposited nanocrystalline Pt thin films

Atomic force microscopy (AFM) is used to measure the surface roughness of crystalline Pt thin films as a function of film thickness and growth rate. Our films were electrodeposited on Au/Cr/glass substrates, under galvanostatic control (constant current density), from a single electrolyte containing Pt⁴⁺ ions. Crystalline structure of the films was confirmed by X-ray diffraction (XRD) technique. The effect of growth rate (deposition current density) and film thickness (deposition time) on the kinetic roughening of the films were studied using AFM and roughness calculation. The data is consistent with a rather complex behaviour known as “anomalous scaling” where both local and large scale roughnesses show power law dependence on the film thickness.     

The role of surface roughness in total internal reflection ellipsometry of hybrid systems

Total internal reflection ellipsometry (TIRE) technique was used to investigate the role of surface roughness in the hybrid system composed of octadecanethiole layer on Au thin film. The samples with Au films of different microstructure were explored. The experimental results were interpreted in the model, which took into account the surface roughness of Au film in the hybrid system. It was shown that optical parameters of octadecanethiole were in correspondence for samples of different microstructure in the case of adequate models used for interpretation of TIRE data.     

Studies of the mechanism of enhanced Raman scattering in ultrahigh vacuum

We show that enhanced Raman scattering observed from CO adsorbed on silver is dependent on surface roughness inherent in the evaporated film. Many of the proposed mechanisms of enhanced Raman scattering are not in accordance with this. We have also studied the wavelength dependence of the enhancement for this system and for CO adsorbed on gold films and show that this dependence is more complex than previously reported.     

Low temperature deposition of transparent conducting ITO/Au/ITO films by reactive magnetron sputtering

Transparent conducting indium tin oxide/Au/indium tin oxide (ITO) multilayered films were deposited on unheated polycarbonate substrates by magnetron sputtering. The thickness of the Au intermediated film varied from 5 to 20 nm. Changes in the microstructure, surface roughness and optoelectrical properties of the ITO/Au/ITO films were investigated with respect to the thickness of the Au intermediated layer. X-ray diffraction measurements of ITO single layer films did not show characteristic diffraction peaks, while ITO/Au/ITO films showed an In₂O₃ (2 2 2) characteristic diffraction peak. The optoelectrical properties of the films were also dependent on the presence and thickness of the Au thin film. The ITO 50 nm/Au 10 nm/ITO 40 nm films had a sheet resistance of 5.6 Ω/□ and an average optical transmittance of 72% in the visible wavelength range of 400-700 nm. Consequently, the crystallinity, which affects the optoelectrical properties of ITO films, can be enhanced with Au intermediated films.     

Surface roughness analysis and magnetic property studies of nickel thin films electrodeposited onto rotating disc electrodes

Ni films were electrodeposited onto polycrystalline gold substrates mounted on a rotating disc electrode. The effects of rotation speed, film thickness and current density on the kinetic roughening and magnetic properties of the films were investigated. The film surface roughness was imaged using an atomic force microscope (AFM). The results indicate that the film roughness increases as the film thickness or deposition current density increases. We found that the electrodeposited Ni films exhibit anomalous scaling since both local and large-scale roughnesses show a power-law dependence on the film thickness. The effect of electrode rotation speed on the film surface roughness was also investigated. Scanning electron microscopy studies (SEM) had a good agreement with the AFM results. The average crystalline size of the film surfaces is also calculated from X-ray line broadening using (220) peak and Debye–Scherrer formula. The obtained results agree with that of AFM and SEM. The Ni thin films which are grown at different deposition current densities and rotation speeds exhibit in-plane magnetization with coercivities less than 110 Oe.     

Dispersion and thermal resistivity in silicon nanofilms by molecular dynamics

On nanoscale, thermal conduction is affected by system size. The reasons are increased phonon scattering and changes in phonon group velocity. In this paper, the in-plane thermal resistivity of nanoscale silicon thin films is analyzed by molecular dynamics (MD) techniques. Modifications to the dispersion relation are calculated directly with MD methods at high temperature. The results indicate that the dispersion relation starts to change for very thin films, at around two nanometers. The reasons are band folding and phonon confinement. Thermal resistivity is analyzed by the direct non-equilibrium method, and the results are compared to kinetic theory with modified dispersion relations. Thermal resistivity is affected by both surface scattering and dispersion. Moreover, in thin films, the characteristic vibrational frequency decreases, which in standard anharmonic scattering models indicates a longer relaxation time and affects the resistivity. The results indicate that in very thin films, the resistivity becomes highly anisotropic due to differences in surface scattering. In two cases, surface scattering was found to be the most important mechanism for increasing thermal resistivity, while in one case, phonon confinement was found to increase resistivity more than surface scattering.     

Enhanced visible-light coloration and its mechanism of MoO3 thin films by Au nanoparticles

A new kind of MoO₃/Au film was prepared by depositing Au nanoparticles on the surface of MoO₃ thin film through spin-on coating technique. After cathodic polarization, the MoO₃/Au thin film was found to show enhanced visible-light coloration compared with MoO₃ thin films. The formation of Schottky barrier at the MoO₃/Au interface, and the visible-light coloration mechanism of the MoO₃/Au film are elucidated by the energy band theory based on surface photovoltaic spectroscopy measurements.     

Optimization of Gas Sensing Performance of Nanocrystalline SnO_2 Thin Films Synthesized by Magnetron Sputtering

Tin oxide(SnO_2) is one of the most promising transparent conducting oxide materials,which is widely used in thin film gas sensors.We investigate the dependence of the deposition time on structural,morphological and hydrogen gas sensing properties of SnO_2 thin films synthesized by dc magnetron sputtering.The deposited samples are characterized by XRD,SEM,AFM,surface area measurements and surface profiler.Also the H_2 gas sensing properties of SnO_2 deposited samples are performed against a wide range of operating temperature.The XRD analysis demonstrates that the degree of crystallinity of the deposited SnO_2 films strongly depends on the deposition time.SEM and AFM analyses reveal that the size of nanoparticles or agglomerates,and both average and rms surface roughness is enhanced with the increasing deposition time.Also gas sensors based on these SnO_2 nanolayers show an acceptable response to hydrogen at various operating temperatures.     

Coherent phonon generation and detection in ultrathin SrTiO3 grown directly on silicon

Time‐resolved two color pump‐probe polarization spectroscopy was performed at room temperature on SrTiO₃ films grown directly on Si with film thickness varying from 2 nm to 7.8 nm. An E‐symmetry mode with a characteristic frequency of 0.2 THz is impulsively generated and measured in these coherently strained tetragonal phase SrTiO₃ thin films. A superimposed exponentially decaying signal observed indicates the possible relaxational hopping of Ti ion between double potential wells. The dependence of the coherent phonon signal on pump and probe laser polarization helps to identify the symmetry of the phonon modes.     

Surface plasmon resonance characterization of thermally evaporated thin gold films

The heterogeneous character of thin gold films prepared by thermal evaporation and the dependence of this heterogeneity on the rate of their deposition must be considered when exploiting their optical properties for biosensor purposes. For instance, the performance of thin gold films for surface plasmon resonance (SPR) biosensors may drastically be degraded if care is not taken to prepare a film with a high fraction of gold (>95%). We use three different models to interpret the SPR response of gold films prepared by thermal evaporation. We show that the interpretation of the SPR curves requires considering both a global heterogeneity of the gold films and a surface roughness. Our conclusions are further corroborated by scanning surface plasmon microscope (SSPM) images of these thin gold films.     

Impurity effect on weak antilocalization in the topological insulator Bi2Te3

We study the weak antilocalization (WAL) effect in topological insulator Bi(2)Te(3) thin films at low temperatures. The two-dimensional WAL effect associated with surface carriers is revealed in the tilted magnetic field dependence of magnetoconductance. Our data demonstrate that the observed WAL is robust against deposition of nonmagnetic Au impurities on the surface of the thin films, but it is quenched by the deposition of magnetic Fe impurities which destroy the π Berry phase of the topological surface states. The magnetoconductance data of a 5 nm Bi(2)Te(3) film suggests that a crossover from symplectic to unitary classes is observed with the deposition of Fe impurities.     

Electrical conductivity dependence of thin metallic films of Au and Pd as a top electrode in capacitor applications

Electrical conductivity dependence of thin metallic films of Au and Pd over the different perovskites was investigated. It is found from electrical properties that crystallographic growth orientation of Au and Pd thin layers attained from X-ray diffraction results indicate the slop of current (I)-voltage (V) plots. Besides, surface morphology and topography was considered using Field Emission Scanning Electron Microscopy and Atomic Force Microscopy, respectively. Obtained results showed the Stranski-Krastanov growth of the Pd and Au. Indeed, diminishing of the root-mean-square roughness of Pd/BiMnO₃/SrTiO₃ following by Au deposition should be concerned due to growth of Au onto the crack-like parts of the substrate. These crack-like parts appeared due to parasitic phases of the Bi-Mn-O system mainly Mn₃O₄ (l 0 l) and Mn₃O₄ (0 0 4 l).The different response in the electrical properties of heterostructures suggests that electrical conductance of the Au and Pd thin metallic films have the crystallographic orientation dependence. Furthermore, polycrystallinity of the thin metallic films are desired in electrode applications due to increase the conductivity of the metallic layers.     

Determination of surface roughness from light scattering measurements

We have measured the angular dependence of the p- and s-pollarized light scattered on films, which are supported by fine polished Suprasil substrates. To study the roughness of the surface we have varied the evaporation process and the thickness of the silver film. We quantitatively determine the roughness structure by using a non scalar scattering theory. The roughness structure is found in good agreement with measurements on the same films using ATR-techniques.     

单晶硅薄膜法向热导率分子动力学研究

采用非平衡分子动力学方法（NEMD）研究了平均温度为 500K、厚度为 2～32nm的单晶硅薄膜的法向热导率。模拟结果表明,薄膜热导率显著低于对应温度下的体硅单晶的实验值,并随膜厚度减小以接近线性的规律减小。用声子气动力论模型的分析结果与NEMD模拟相一致,表明纳米单晶硅薄膜中声子平均自由程显著减小。     

Au cluster growth on ZnO thin films by pulsed laser deposition

Nanostructures formed by Au nanoparticles on ZnO thin film surface are of interest for applications which include medical implants, gas-sensors, and catalytic systems. A frequency tripled Nd:YAG laser (λ = 355 nm, τ_FWHM ∼ 10 ns) was used for the successive irradiation of the Zn and Au targets. The ZnO films were synthesized in 20 Pa oxygen pressure while the subsequent Au coverage was grown in vacuum. The obtained structures surface morphology, crystalline quality, and chemical composition depth profile were investigated by acoustic (dynamic) mode atomic force microscopy, X-ray diffraction, and wavelength dispersive X-ray spectroscopy. The surface is characterized by a granular morphology, with average grain diameters of a few tens of nanometers. The surface roughness decreases with the increase of the number of laser pulses applied for the irradiation of the Au target. The Au coverage reveals a predominant (1 1 1) texture, whereas the underlying ZnO films are c-axis oriented. A linear dependence was established between the thickness of the Au coverage and the number of laser pulses applied for the irradiation of the Au target.     

ITO/Au/ITO multilayer thin films for transparent conducting electrode applications

Transparent and conducting ITO/Au/ITO multilayered films were deposited without intentional substrate heating on polycarbonate (PC) substrate using a magnetron sputtering process. The thickness of ITO, Au and ITO metal films in the multilayered structure was constant at 50, 10 and 40 nm, respectively.Although the substrate temperature was kept constant at 70 °C, ITO/Au/ITO films were polycrystalline with an (1 1 0) X-ray diffraction peak, while single ITO films were amorphous. Surface roughness analysis indicated ITO films had a higher average roughness of 1.76 nm, than the ITO/Au/ITO film roughness of 0.51 nm. The optoelectrical properties of the ITO/Au/ITO films were dependent on the Au thin film, which affected the ITO film crystallinity. ITO/Au/ITO films on PC substrates were developed with a resistivity as low as 5.6 × 10⁻⁵ Ω cm and a high optical transmittance of 71.7%.     

Comparative studies on p-type CuI grown on glass and copper substrate by SILAR method

Depending upon the method of synthesis and the nature of substrate surface, there is variation in the physico-chemical properties of the material. Cuprous iodide films are deposited at room temperature on the glass and copper substrates by a simple SILAR method and the obtained results are compared. The p-type material with optical band gap 2.88 eV is found to be possessing face-centered cubic crystal structure with lattice parameter 6.134 Å. We observed irregular particles for the CuI film on the glass substrate while patterned arrays of micro-rods with cabbage like tips on copper substrate, for the same preparative conditions. Also, the material deposited on copper is showing superhydrophobic nature (contact angle ∼156°) while that on glass it is hydrophilic (contact angle ∼88°). We have characterized the thin films by X-ray diffraction, scanning electron microscopy, surface roughness and contact angle measurement, thermoelectric power measurement and optical studies. This hydrophobic, p-type material with wide band gap will be helpful in the development of optoelectronic devices.     

样品表面银膜的粗糙度对钛酸钡微球成像性能的影响

研究了样品表面镀有不同表面粗糙度的银膜对钛酸钡（BaTiO₃ glass,BTG）微球成像效果的影响,发现当银膜表面的粗糙度（RMS）从3.23 nm增大到6.80 nm时,用直径为15 μm的BTG微球观察直径为250和580 nm的微球阵列,样品的成像范围增大.另外,BTG微球还可以清晰分辨原本不可分辨的直径为200 nm的微球阵列.结果表明,粗糙银膜引起的散射作用和表面等离激元波的局域场增强效应,使得更多物体的高频信息耦合进微球,提高了微球成像的分辨率和成像范围.