The aim of this article is to perform an evaluation on mechanical properties of graphene covering silicon nanofilms by using molecular dynamics calculations. The deformation process of the composite film is simulated under uniaxial tensile loading to demonstrate the structural evolution, and the structural failure mode is discussed considering various film thicknesses and temperatures. The results show that size effect of thickness on the strength is significant at the thickness less than 4 nm and thinner thickness can help improve tensile properties of the nanofim. The 1 nm thick film has significantly better mechanical properties due to its different structural failure mode, and the substrate silicon is the weakness which limits mechanical properties of the composite film under high temperatures. It is hoped that our findings will be helpful for applications of graphene in silicon-based devices and materials.The size effect of structural evolution on graphene covering silicon nanofilms is explored. We investigated the deformation process of the composite film under uniaxial tensile loading. We discussed the structural failure mode of graphene covering silicon nanofilms. We find the size effect of thickness on the strength is significant at the thickness less than 4 nm. We detect the 1 nm thick film has significantly better mechanical properties due to its different structural failure mode. It implies the findings will be helpful for applications of graphene in silicon-based devices.

The purpose of this article is to provide a systematic evaluation to examine characteristics of the thermal conductivity and thermal rectification of H-terminated graphene nanoribbons (HGNRs) with Lpristine/LH-terminated = 1. The results show that HGNR thermal conductivities increase in both directions across the entire temperature range tested. Simultaneously, thermal rectification of HGNRs at various temperatures is detected. We found that with increasing temperature the thermal rectification has a gradual decreasing tendency. Furthermore, the overlap of power spectra was calculated to elucidate the underlying mechanism of thermal rectification. This work indicates a possible route to achieve thermal rectification for 2D materials by hydrogenation engineering.

The aim of this paper is to improve the field emission properties of graphene-carbon nanotube composites by doping nitrogen atom. The electronic structure and field emission mechanism of the composite have been investigated by first principle methods. Compared to pristine graphene-carbon nanotube composite, work functions and ionization potentials with ten different doping positions decrease drastically as well as energy gap, which illustrates the enhancement of field emission properties. In this study, the most preferable doping position (doping position 2) can be inferred. Due to the doping of nitrogen atom, coupled electron states is generated, more electrons aggregate at the doping position. All results suggest that the field emission properties of graphene-carbon nanotube composite can be improved by doping nitrogen atom. The work we have done is significant for obtaining better electron sources with less energies, our investigation will provide a theoretical reference for the design and manufacture of new field emission devices.

In intelligent mechanism design, isomorphism identification of mechanism kinematic chains (IIMKC) is aimed at avoiding repeated mechanism design and is proved to be an NP-complete problem. In this paper, kinematic chains are represented by graphs. An improved hybrid immune algorithm, which integrates the clonal selection immune algorithm with genetic algorithm and the local search algorithm, is proposed to solve IIMKC problem. Moreover, the novel saving and updating operator is proposed to save the best antibodies and maintain a diverse repertoire of antibodies for improving performance of clonal selection. In addition, the pseudo-crossover operator is introduced to enhance the efficiency of genetic algorithm. Simulation results validate the high efficiency and robustness of the hybrid immune algorithm.

We investigated the thermal conductivity of bilayer graphene nanoribbons (BGNs) using nonequilibrium molecular dynamics method (NEMD). The relationships among thermal conductivity, different ways of stacking, size, interfacial temperature and edge shape were studied. Two different stacking ways for BGNs are AA-stacked type and AB-stacked type. The results show that the thermal conductivities of AA-stacked BGNs are slightly higher than those of AB-stacked BGNs under the same simulation conditions because of different crystal structures. The thermal conductivity of zigzag BGNs (ZBGNs) first increases and then decreases with increasing width. However, the thermal conductivity of armchair BGNs (ABGNs) monotonously increases with increasing width. The thermal conductivity of BGNs increases with the length of the simulation system. In addition BGNs show temperature dependence and edge-shape dependence for thermal conductivity. We have explained the simulation results by the inter-layer phonon coupling and the phonon scattering, which have been shown to significantly affect the thermal conductivity of BGNs. The systematic analysis of thermal conductivity of BGNs did not only help to obtain conclusions regarding the achievable thermal performance, but also provided the possibility to design different dimensional BGNs for different BGNs-based thermal and microelectronic components.

The aim of this article is to provide a systematic evaluation to investigate the characteristics of the field emission properties of graphene–carbon nanotube composites. A model of graphene–carbon nanotube composites is established, and the C–C bond length, binding energy, energy level, ionization potential and work function are calculated by a first principles method. The results show that the composite structure formed by a combination of graphene and carbon nanotubes has higher stability and better semiconductor properties. When an electric field is applied, the orbital energy of the composite material increases and the band gap reveals a downward trend, which has a positive effect on the improvement of the field emission properties. With an increase in the electric field, the work functions and ionization potentials descend and the Mulliken charge moves effectively, which further shows that graphene–carbon nanotube composites have excellent characteristics and potential in field emission. The local electron density distribution also shows some changes. Our study is helpful to expand the application of graphene and carbon nanotubes, as well as provide a theoretical reference for the design of new field emission devices.

We investigated the lattice constants, band structure, and optical properties of In-doped n-type ZnO under high pressure according to first principles. The results show that lattice constants a and c decrease and the bandgap increases with increasing pressure. The conduction band minimum always moves to higher energy, whereas the valence band maximum moves to lower energy with increasing pressure, so the bandgap broadens. The curve shape for optical parameters is almost unchanged with increasing pressure, but all the peaks move to higher energy (blue shift). The results provide a theoretical reference for the design of UV devices comprising In-doped ZnO.

•We proposed a systematic evaluation on thermal resistance and junction temperature of LED.•We investigated temperature distribution to understand thermal resistance and location of LED.•We detected that junction temperature change with heat source and thickness.•It implies a potential method for evaluation on thermal reliability of LED lamps.The understanding of thermal resistance and junction temperature is important in the area of designing efficient, long-lasting high-power Light Emitting Diodes (LEDs) and diode stacks. This paper developed a systematic evaluating program for investigating the effect of location and thickness on the thermal resistance and junction temperature of LED on an aluminum substrate. Structure function measurements were implemented by Thermal Transient Tester (T3ster) and Integrating Sphere on LED placed on an aluminum plate. The temperature distribution of LED was analyzed to understand the relationship between thermal resistance and location of the LED on the aluminum base. Meantime, to evaluate the validity of the test, the simulation is developed by considering structure properties. The simulation curve basically has a similarity with the experimental curve in the overall. It implies that the evaluating method can provide guidance in understanding thermal reliability of LED lamps and designing thermal management techniques.

We predict that there is a critical value of Al2O3/ZnO nano thin interface thickness based on two assumptions according to an interesting phenomenon, which the thermal conductivity (TC) trend of Al2O3/ZnO nano thin interface is consistent with that of relevant single nano thin interface when the nano thin interface thickness is > 300 nm; however, TC of Al2O3/ZnO nano thin interface is higher than that of relevant single nano thin interface when the thin films thickness is < 10 nm. This prediction may build a basis for the understanding of interface between two different oxide materials. It implies an idea for new generation of semiconductor devices manufacturing.

The models of graphene nanoribbons (GNRs) with angles 0°, 30°, 60°, 90° and 120° were constructed to investigate the thermal conduction by using the reverse non-equilibrium molecular dynamics method. A substantially negative correlation between the thermal conductivity and the bent angle shows a nonlinear decline from 0° to 90°. It also shows that there is a little increase from 90° to 120° due to the edge effect. To weaken the edge effect, the nitrogen doping method is adopted to recompose the bent GNRs. The results show that it is effective for the thermal management, and a strict monotonous relationship between the thermal conductivity and bent angle can be obtained. In the meantime, an interesting phenomenon is observed that the GNRs with edge modification by N-doping can get a much better thermal conduction than original GNRs without edge modification. We can understand the physical mechanism by phonon analysis for these GNRs. The investigation implies that we can change the thermal conductivity of GNRs by design by N-doping.

A systematic investigation of the thermal conductivity of zigzag graphene nanoribbons (ZGNRs) doped with nitrogen and containing a vacancy defect was performed using reverse nonequilibrium molecular dynamics (RNEMD). The investigation showed that the thermal conductivity of the ZGNRs was significantly reduced by nitrogen doping. The thermal conductivity dropped rapidly when the nitrogen doping concentration was low. Also, the presence of a vacancy defect was found to significantly decrease the thermal conductivity. Initially, as the vacancy moved from the heat sink to the heat source, the phonon frequency and the phonon energy increased, and the thermal conductivity decreased. When the distance between the vacancy in the ZGNR and the edge of the heat sink reached 2.214 nm, tunneling began to occur, allowing high-frequency phonons to pass through the vacancies and transfer some energy. The curve of the thermal conductivity of the ZGNRs versus the vacancy position was found to be pan-shaped, with the thermal conductivity of the ZGNRs controlled by the phonon. These findings could be useful when attempting to control heat transfer on the nanoscale using GNR-based thermal devices.

The aim of this article is to provide a systematic method to perform numerical evaluation on the cross-plane thermal conductivity of Al2O3/ZnO film interface. The Equilibrium Molecular Dynamics (EMD) simulations method is used to investigate the cross-plane thermal conductivity of Al2O3/ZnO film interface along the direction of Z axis at different equilibrium temperature and film interface thickness. The Buckingham two-body potential function and Green–Kubo linear response theory are used for modeling and calculation. The results show that the size effect is obvious. It implies the film interface thickness is 23.4–52 Å and the equilibrium temperature is 300–600 K. The cross section thermal conductivity of Al2O3/ZnO film interface increases with the increase of interface thickness, and decreases with the increase in equilibrium temperature.Keywords: Al2O3/ZnO film interface; Buckingham potential function; molecular dynamics simulations; thermal conductivity;

The aim of this article is to provide a systematic method to perform optimization design for chip placement of multi-chip module in electronic packaging. Based on the investigation of the structural and thermal characteristics of multi-chip module, the key performance indexes of multi-chip module that include the lowest internal temperature objective, thermal-transfer accuracy, chip placement are analyzed. A hybrid model is presented by using genetic algorithm and response surface methodology for optimization. Furthermore, some design processes for improving the performance are induced. Finally, an example is discussed to apply the method.

The objective of this research work is to provide a systematic method to perform molecular dynamics simulation or evaluation for meshing friction properties approach of micro/nano-gear train in MEMS. A model for meshing friction of micro/nano-gear train is proposed by using molecular dynamics based on investigation about a pair of meshing nano-teeth. The results show that the frictional characteristics in single meshing region are similar to the situation in the normal macro-gears meshing; however, the zero fictional force is not shown on the node of meshing. The maximum of the frictional force becomes larger and larger and the minimum of the frictional force becomes smaller and smaller when the number of the atomic layer in z direction increases. So the curve of the frictional force becomes steeper than the situation in normal macro-gears meshing. The maximum and the minimum of the frictional force are all invariable but the curve of the frictional force becomes steeper when the angular velocity of the powered gear increases. In the other case, there are no any changes in curve of the frictional force when the resisting torque increases.

Electronic equipment’s system is always manufactured as a superprecision system. However, it will be used in harsh environment. For example, the computer in moving vehicles will be acted by vibrations. The objective of this paper is to provide a systematic investigation to test and computer-aided design of the vibration isolator for protection of electronic equipment’s system in harsh vibration environment. A micro-oil damping vibration isolator is designed and manufactured through coupling the oil and spring by ingenious tactics. The structure of the oil damping vibration isolator can achieve circulating oil damping function with an inner tube and an outer tube (some orifices are manufactured on upside and underside of the inner tube). The dynamics of the key model machine is systematically investigated. Based on the test, a nonlinear dynamic model for the vibration isolator is presented by analyzing the internal fluid dynamic phenomenon with respect to the vibration isolator. The model considers all the physical parameters of the structure. Comparisons with experimental data confirm the validity of the model. In the other, the model is integrated by introducing normalization measure. The normalization model shows the actual physical characteristics of the oil damping vibration isolator by considering quadratic damping, viscous damping, Coulomb damping, and nonlinear spring forces. An approximate solution is deduced by introducing harmonic transform method and Fourier transform method. Therefore, a parameter-matching optimal model for computer-aided design of the vibration isolator is build based on approximate solution. An example confirms the validity of the computer-aided design integration.

The MEMS design and modeling tools that have been developed typically rely on finite element models, or even more coarse-grained macro models. However, some of the next generation of MEMS devices will be so small that the finite element models are pushed to the atomic limit where they fail, and a new type of model becomes necessary. The aim of this research work is to provide a systematic method to perform molecular dynamics simulation or evaluation for adhesion of micro/nano-gear train during surface sliding friction in MEMS. In this paper, molecular dynamics simulations of adhesion problem in micro-gear train are proposed. Based on analysis of surface sliding friction and the transmitting characteristics of micro-gear train, a simplified model to simulate surface sliding between metals by MD is proposed because the surface property is a dominant factor for the performance of gear system. The simulation results show that adhesion tends to occur between two micro-gears after certain cycles and such adhesion accounts for the friction force and the temperature increase. The driving force also plays a significant role on adhesion of micro-gears. The simulation results are in consistence with the experimental results in the literature. The MD model presented in this paper meets a lot of the important requirements of the tribology design of micro-gears and other heterogeneous MEMS. It is meaningful to prolong the lifetime of micro-gear train by using the model to select proper parameters.

When using graph theory for kinematic structure enumeration, the isomorphism identification of graphs is an important and complicated problem. The problem is known to be an NP-complete problem. This paper presents a mixed algorithm based on a mapping property, a genetic algorithm, and a simulated annealing algorithm for the isomorphism identification problem. A validity encoding scheme was developed by considering the mapping relationship between two graphs, and some reset measures for the crossover and mutation operators were developed based on the characteristics in which the encoding cell could not be reiterated. A simulated annealing algorithm was introduced into the mixed algorithm to prevent premature convergence in resolution, and some other measures were developed for improving the efficiency, based on the parameter selection. An example shows that the mixed algorithm is a valid algorithm for the isomorphism identification of kinematic structure graphs in mechanism design. It will be a reliable isomorphism identification algorithm for intelligent computer-aided design (CAD) and manufacturing (CAM).

The aim of this article is to provide a systematic investigation to the design or optimal design of the shock absorber for the protection of a precision system as electronic packaging system in harsh vibration-impact environment. To get the dual demand of resisting violent impact and attenuating vibration in vibration-impact-safety for precision equipment or components, a novel micro fluid coupling damping shock absorber is designed and manufactured through coupling the oil, rubber ball and spring by ingenious tactics. The physical mechanism of the actual shock absorber is systematically investigated. The experimental results of the key-model machine in dynamic tests show complex nonlinear dynamic characteristics. Based on the test, the nonlinear dynamic model for the shock absorber is presented by analyzing the internal fluid dynamic phenomenon with respect to the shock absorber. Comparisons with experimental data confirm the validity of the model. The model is integrated by introducing normalization measure in progress. The approximate formulae are deduced by introducing some transformation tactics. These approximate theoretical formulae include the output response of the system, absolute acceleration transmissibility in vibration or impact, and the maximum relative displacement in impact process etc. So the optimal model for parameters matching the design is built. The parameters matching the design are discussed based on an approximate solution in progress. Finally, an example of the applied product is described.

•The new connection properties among vertices are explored.•The proposed algorithm, namely DMA, is very effective and reliable.•DMA is very fast.Kinematic chain isomorphism identification is a crucial issue in mechanism topology and an important application of Graph Isomorphism to mechanisms. In this paper, a kinematic chain is uniquely represented by a graph, and a fast deterministic algorithm called the Dividing and Matching Algorithm (DMA) is proposed. First, the vertices of each graph are divided by the degree. Then, vertex connection properties in a sub-graph and between sub-graphs are explored. Accordingly the expanded square degree and the correlation degree are proposed, based on which, the Dividing Vertex Algorithm (DVA) is developed to divide vertices into sets. Moreover, it is proved that only the vertices from the corresponding sets between two graphs are possible to be bijective or matched, which avoids exhaustive search. Eventually, a backtracking procedure is employed to match the vertices between corresponding sets by calling up DVA repeatedly. DMA detects whether the adjacency matrices of two graphs can be adjusted to be equivalent by changing the orders of vertices. Justifications for the reliability of each part of DMA are provided. The experiments and comparisons with existing algorithms show the effectiveness and efficiency of DMA.