Effects of hydrogen atoms on surface conductivity of diamond film

To investigate the effects of surface chemisorbed hydrogen atoms and hydrogen atoms in the subsurface region of diamond on surface conductivity, models of hydrogen atoms chemisorbed on diamond with (100) orientation and various concentrations of hydrogen atoms in the subsurface layer of the diamond were built. By using the first-principles method based on density functional theory, the equilibrium geometries and densities of states of the models were studied. The results showed that the surface chemisorbed hydrogen alone could not induce high surface conductivity. In addition, isolated hydrogen atoms in the subsurface layer of the diamond prefer to exist at the bond centre site of the C-C bond. However, such a structure would induce deep localized states, which could not improve the surface conductivity. When the hydrogen concentration increases, the C-H-C-H structure and C-3Hbc-C structure in the subsurface region are more stable than other configurations. The former is not beneficial to the increase of the surface conductivity. However, the latter would induce strong surface states near the Fermi level, which would give rise to high surface conductivity. Thus, a high concentration of subsurface hydrogen atoms in diamond would make significant contributions to surface conductivity

Operation Capability Analysis and Experiments of Underactuated Compliant Multi-Fingered Hands

In this paper, operation capabilities of underactuated compliant robot hands have been investigated based on the shape stability analysis of underactuated compliant fingers and operation modes analysis of human hands. It is shown that the operation modes of robot hands can be classified into two major classes, namely, enveloping grasp mode and pinch mode. For the two operation modes, two principles are respectively presented with regard to the mechanical design issues of the underactuated robot hands. According to the principles presented in this paper, a robot hand prototype with four underactuated compliant fingers has been fabricated. On the robot hand prototype, enveloping grasp capability of underactuated compliant robot hands has been verified by many experiments. For precision operations, a proposition is presented and it is shown that the prototype should be further improved

A Stepwise Optimal Design of a Dynamic Vibration Absorber with Tunable Resonant Frequency

A new kind of dynamic vibration absorber (DVA) with tunable resonant frequency is presented. The kinematics differential equation about it is built and the stepwise optimization is performed. Firstly, four main system parameters involving the ratios of mass m, natural frequency f, vibration frequency g and damping z are solved by small-step-search method to obtain optimal steady state amplitude. Secondly, the sizing optimization of the dynamic vibration absorber is proceeded to search an optimal damping effect based on the optimal parameters (g, m, z, f). And such the damping effect is simulated in a flat structure, and the results show that the working frequency band and damping effect of the DVA after optimization won 20 % of the effect of ascension compared with that before optimization

Continuous contact force model with an arbitrary damping term exponent: Model and discussion

More than twenty continuous contact force models have been presented for modeling contact-impact problems; however, there was no uniformity regarding the value of the damping term exponent in these models. A new type of continuous contact force model is proposed in this research, in which the value of the damping term exponent can be arbitrary. Then, the effect of the value of the damping term exponent on the model accuracy is investigated by comparing the simulation and experimental results. As it is almost impossible to obtain an analytical solution based on the system dynamic equation, according to the rule of energy equivalence, an approximate dynamic equation is developed by introducing an equivalent indentation and equivalent velocity. Based on the system dynamic equation and the approximate dynamic equation, a primary formula for the hysteresis damping factor of the model can be obtained. Through nondimensional analysis, new models for different values of the damping term exponent are established by modifying the primary formula. The comparison between the simulation results and published experimental data demonstrates the validities of the new models and reveals that the influence of the value of the damping term exponent on the model accuracy can be considered to be negligible. (c) 2021 Elsevier Ltd. All rights reserved