Using Monte Carlo simulation methods in the canonical and grand canonical ensembles, we discuss the melting and the formation of ordered structures of mixed Ar-Xe submonolayer films on graphite. The calculations have been performed using two- as well as three-dimensional models of the systems studied. It is demonstrated that out-of plane motion does not affect the properties of the adsorbed films as long as the total density is not close to the monolayer completion. On the other hand, close to the monolayer completion, the promotion of particles to the second layer considerably affects the properties of mixed films. It has been shown that the mixture exhibits complete mixing in the liquid phase and freezes into solid phases of the structure depending upon the film composition. For submonolayer densities, the melting temperature exhibits non-monotonous changes with the film composition. In particular, the melting temperature initially increases when the xenon concentration increases up to about 20%, then it decreases and reaches minimum for the xenon concentration of about 40%. For still higher xenon concentrations, the melting point gradually increases to the temperature corresponding to pure xenon film. It has been also demonstrated that the topology of phase diagrams of mixed films is sensitive to the composition of adsorbed layers.
Commensurate-Incommensurate Transition in Submonolayer $^3$He on Graphite
University of Hyogo（兵库大学）；National Institute of Advanced Industrial Science and Technology (AIST)（产业技术综合研究所）；The University of Osaka（大阪大学）；The University of Tokyo（东京大学）
A few atomic layers of helium adsorbed on graphite have been attracting much attention as one of the ideal quantum systems in two dimension. Although previous reports on neutron diffraction have shown fundamental structural information in these systems, there still remain many open questions. Here, we propose surface crystal truncation rod (CTR) scatterings using synchrotron radiation X-rays as a promising method to reveal surface and interface structures of helium films on graphite at temperatures below 2 K, based on the preliminary experimental results on a monolayer of He-4 on a thin graphi…
We have measured surface morphology and gas adsorption characteristics of uncompressed pyrolytic graphite sheet (uPGS) which is a candidate substrate for AC and DC superflow experiments on monolayers of 4He below T = 1 K. The PGS is a mass-produced thin graphite sheet with various thicknesses between 10 and 100 μm. We employed a variety of measuring techniques such as imagings with optical microscope, SEM and STM, Raman spectroscopy, and adsorption isotherm. PGS has smooth and atomically-flat external surfaces with high crystallinity. Although the specific surface area (<0.1 m$^2$/g) is rather…
Initial stages of thin film growth in the presence of island-edge barriers
研究了一种亚单层薄膜生长模型，在该模型中原子与岛边缘的附着受到能垒的阻碍。预测了岛密度N_s作为通量F和温度T的函数的新行为。例如，N_s与F^X成比例，其中X= 2 i ^*/（i^*+3），其中i^* 是临界岛尺寸，与标准结果X=i^*/（i^*+2）形成对比。该理论适用于表面活性剂介导的生长和化学气相沉积。它解释了最近的实验，这些实验与标准理论不一致。
We report on the controlled growth of h-BN/graphite by means of molecular beam epitaxy (MBE). X-ray photoelectron spectroscopy (XPS) suggests an interface without any reaction or intermixing, while the angle resolved photoemission spectroscopy (ARPES) measurements show that the h-BN layers are epitaxially aligned with graphite. A well-defined band structure is revealed by ARPES measurement, reflecting the high quality of the h-BN films. The measured valence band maximum (VBM) located at 2.8 eV below the Fermi level reveals the presence of undoped h-BN films (band gap ~ 6 eV). These results dem…
The growth of up to 10 monolayer-thick Fe films on a Au(001) surface was investigated during deposition at room temperature and during annealing using low-energy electron diffraction and x-ray photoemission spectroscopy as well as locally with low-energy electron microscopy and photoemission electron microscopy. The growth proceeds with a submonolayer of Au segregating to the surface of Fe, which is in agreement with previous studies. Annealing was found to be critical for the presence of Au on the Fe surface. Our findings show that Au segregation proceeds by the formation of cracks in the Fe …
In this present work, friction and wear behavior of UNCD thin film has been studied against three different sliding counterbodies i.e. Al2O3, SiC and steel balls. UNCD/steel sliding pair showed high friction coefficient in the beginning of the sliding process which decreased to the lower value after longer sliding passes. This behavior might be explained by oxidation mechanism. However, high friction value was observed in the case of UNCD/SiC and this was attributed to strong adhesive force acting across the sliding interfaces. Stable and low friction value was measured in UNCD/Al2O3 sliding c…
Simulations of the Chain Length Dependence of the Melting Mechanism in Short-Chained n-alkane Monolayers on Graphite
用分子动力学模拟研究了一系列短链正烷烃、正辛烷（n-C8 H 18）、正癸烷（n-C10 H 22）和正十二烷（n-C12 H 26）在石墨基底表面上的固体单分子膜的熔融转变。利用以前的实验观察这些单分子膜的固相行为，本研究调查的温度依赖性的阶段和相变在这三个单分子膜在固-流相变，并比较所观察到的熔化行为，以前的研究己烷和丁烷单分子膜。特别是，这项研究似乎表明，随着链长的增加，在烷基链中形成的笨拙缺陷的熔融转变的依赖性更大。根据先前提出的足迹减少机制和其中从能量上否定了笨拙缺陷的形成的变化，模拟似乎表明癸烷和十二烷单层通常同样依赖于笨拙缺陷的形成以发生熔融转变，而辛烷单层似乎具有较少的依赖性，但遵循在丁烷和己烷单层中熔化的先前研究中建立的趋势。此外，与最近对己烷单层的研究相比，发现从固体人字形相到取向有序中间相的相变表现出一些差异，这可以解释为源于笨拙缺陷的更大影响。比较实验熔化温度提供在可能的情况下，和应用程序涉及薄膜操纵和润滑进行了讨论。
We demonstrate the extensive study on how film density and crystallinity of molybdenum carbide ($MoC_{x}$) can be tailored during plasma-enhanced ALD (PEALD) by controlling either the plasma exposure time or the ion energy. We investigated $MoC_{x}$ films grown using $Mo(^tBuN)_2(NMe_2)_2$ as the precursor and $H_2/Ar$ plasma as the co-reactant at temperatures between 150°C and 300°C. We discover a threshold for graphitic layer formation at high mean ion energies during the PEALD cycle. The supplied high energy dose allows for hybridised $sp^{2}$ carbon bonds formation, similar to high tempera…
We present a newly developed facility, comprised of a combinatorial laser molecular beam epitaxy system and an in-situ scanning tunneling microscopy (STM). This facility aims at accelerating the materials research in a highly efficient way, by advanced high-throughput film synthesis techniques and subsequent fast characterization of surface morphology and electronic states. Compared with uniform films deposited by conventional methods, the so-called combinatorial thin films will be beneficial to determining the accurate phase diagrams of different materials due to the improved control of param…
