The effect of a vacancy on the STM image of graphite

Theoretical studies have been done on graphite with a vacancy using the extended Huckel tight-binding (EHTB) method. The results of the singly- and doubly-layered samples show that there is an unexpected distance dependence of the charge density directly over the vacancy. Furthermore, the vacancy acts as a perturbation to distinguish two sublattices which exist in pristine graphite and it creates a charge enhancement in the atoms directly surrounding it.     

STM imaging of metal-coated cell plugs of the archaeobacterium Methanospirillum hungatei GP1

Scanning tunnelling microscopy (STM) images of Pt/Ir- and Pt/Ir/C-coated cell plugs of Methanospirillum hungatei showed paracrystalline structures with P6 symmetry and an 18-nm lattice constant, in agreement with electron microscopy studies. The three-dimensional STM images unambiguously distinguished the two morphologically different proteinaceous plug assemblies and led to an improved understanding of the natural internal organization of whole plugs. Tip convolution effects and the grain size of the metal coating complicated interpretation of finer structures. We discuss possible imaging mechanisms to explain observations in which part of the film was removed but the remaining part of the structure was still imaged reproducibly.     

Nucleation and growth of Cu and Ag on Si(111)7×7

By using scanning tunnelling microscopy and spectroscopy we have studied condensation of Cu and Ag on Si(111)7×7 between room temperature and 130°C in the submonolayer and monolayer range. For submonolayer coverage, both metals develop regular clusters on top of the inner adatoms of 7×7 unit cell halves, which we assign to the initial nuclei of metal condensation. The metal film growth continues by adding further metal atoms to these clusters until one half of the 7×7 unit cell is covered completely with a triangular 2-D metal island. For a coverage of three monolayers neither Cu nor Ag grows in a layer-by-layer mode. Characteristic differences observed for both metals may be explained by the more reactive nature of Cu.     

Investigation of mercury adsorption on gold films by STM

Scanning tunnelling microscopy, combined with complementary electrical and analytical measurements, provides a powerful method for examining the behaviour of mercury on gold-film sensors under actual sensor operating conditions. The films exhibit a linear increase in resistance upon adsorption of mercury, and this resistive change is accompanied by a decrease in measured barrier height at submonolayer coverages of mercury. STM studies of changes in the effective barrier height upon mercury adsorption provide evidence that mercury migrates to grain boundaries for films exposed at submonolayer coverages. Coverages in excess of a monolayer result in a nearly constant, reduced effective barrier height across the entire surface, which is indicative of a more uniform distribution of mercury over the surface. This behaviour is interpreted in terms of the adsorption of mercury onto defective, contaminated gold surfaces.     

帐篷型小型电波暗室的探讨

文章对有屏蔽特性并使用短碳纤维和电波吸收体的帐篷型小电波暗室进行了探讨。依据所使用的短碳纤维的屏蔽和吸收特性及测试结果并结合帐篷内的配置得知它有50dB屏蔽效果,帐篷内电磁环境稳定和优良,故本帐篷可实现小型电波暗室功能。     

基于隧道电流检测方式的原子力显微镜纳米检测系统设计

原子力显微镜（AFM）是当前进行材料表面微观形貌观察及分析的强有力工具之一。本文主要介绍一种隧道显微镜（STM）检测方式的原子力显微镜纳米检测系统（AFM.IPC-208B）,该AFM系统设计是在STM.IPC-205B系统设计的基础上,采用隧道电流工作方式,将STM与AFM功能组合兼容。文章详细阐述了AFM.IPC-208B系统的设计原理、镜体、扫描控制以及数据采集。新设计的AFM.IPC-208B系统仍具有0.1nm的分辨率,检测范围为0～2mm×2mm,系统操作简易,工作效率高,与原STM.IPC-205B系统兼容,工作性能稳定可靠。     

盾构法隧道施工引起地表变形分析

采用有限元软件ANSYS对盾构隧道动态开挖过程进行数值模拟,将硐周节点应力逐级释放来模拟开挖施工过程,在模拟过程中考虑了土体的分层特性、土体材料的本构非线性以及注浆施工对土体变形的影响。并采用明德林解考虑了盾壳和土体之间纵向摩擦力对土体变形的影响。分析中提出了考虑衬砌与土体共同作用的硐周结点荷载释放系数法。通过对工程实例分析验证了该方法的可行性。     

An application of three-dimensional analysis around a tunnel portal under construction

Deformation of a tunnel portal during tunnel excavation is very complex, and it can affect adjacent portal structures. During the construction of the Seoul Metro Line 7, a temporary vertical shaft was constructed by cut and cover method to take out a shield machine and to excavate subsequent tunnel by New Austrian Tunneling Method. Due to the complex structure of tunnel portals, the temporary support system of the vertical shaft was expected to be subjected to an additional load during the tunnel excavation. Thus, three-dimensional analysis of the vertical shaft, including tunnel excavation process, was performed in order to ensure the safety of overall system. This paper presents behavior of the vertical shaft based on the three-dimensional numerical analysis results during the construction sequence.     

Evaluation of the load on shield tunnel lining in gravel

It is important to evaluate accurately the load acting on a shield tunnel lining to facilitate its economical and rational design. In Japan, the load calculated by Terzaghi's formula, or overburden load, is generally adopted for the design of tunnel segments. However, some previous field measurements have shown that the actual load acting on the shield tunnel lining could be much smaller than that adopted for the design in the case of good ground conditions. In this study, field measurements at two shield tunnel construction sites in gravel were carried out, and the load acting on the shield tunnel lining was evaluated by analyzing the field data to establish the rational design of the shield tunnel segments. The method of treating the dead load of segments in the design was also investigated.