A modified embedded-atom method interatomic potential for indium

A semi-empirical interatomic potential for indium has been developed based on the MEAM (modified embedded-atom method) formalism. The potential describes various fundamental physical properties (cohesive energy, lattice parameters, elastic constants, structural energy differences, surface energy and relaxation, vacancy formation and diffusion energy, etc.) of indium in good agreement with relevant experimental data and/or first-principles calculations. The potential also describes bulk properties of non-equilibrium structures (fcc and bcc) of indium in good agreement with first-principles calculations. Because the potential formalism is exactly the same as other previously developed MEAM potentials for a wide range of elements, it can be easily extended to multi-component systems such as In–N, In–As, Ga–In and Ga–In–N.     

Structural and thermal properties of calcium using an MEAM potential

Structural and thermal properties of Ca are examined using a modified embedded-atom method (MEAM) interatomic potential. We developed an MEAM interatomic potential for calcium (Ca) using a first-principles method based on density functional theory (DFT). The material parameters, such as the cohesive energy, equilibrium atomic volume, and bulk modulus, are used to determine the MEAM potential parameters. The elastic constants and various point defect energies, such as monovacancy and interstitial defects, are also examined while developing the potential. Several structural properties of Ca, such as different surface formation energies, stacking fault energies, and thermal properties, such as coefficient of thermal expansion, specific heat and melting temperature, are investigated using the potential. We found that the present MEAM potential gives a good overall agreement with DFT calculations and experiments.     

A modified embedded atom method interatomic potential for carbon

A semi-empirical interatomic potential for carbon has been developed, based on the modified embedded atom method formalism. The potential describes the structural properties of various polytypes of carbon, elastic, defect and surface properties of diamonds as satisfactorily as the well-known Tersoff potential. Combined with the Lennard-Jones potential, it can also reproduce the physical properties of graphite and amorphous carbon reasonably well. The applicability of the present potential to atomistic approaches on carbon nanotubes and fullerenes is also shown. The potential has the same formalism as previously developed MEAM potentials for bcc, fcc and hcp elements, and can be easily extended to describe various metal–carbon alloy systems.     

Atomistic Modeling of pure Mg and Mg–Al systems

Interatomic potentials for pure Mg and the Mg–Al binary system have been developed based on the modified embedded-atom method (MEAM) potential formalism. The potentials can describe various fundamental physical properties of pure Mg (bulk, point defect, planar defect and thermal properties) and alloy behaviors (thermodynamic, structural and elastic properties) in reasonable agreement with experimental data or higher-level calculations. The applicability of the potential to atomistic investigations on the deformation behavior of pure Mg and the effect of alloying element Al on it is discussed.     

Modified embedded-atom interatomic potential for Fe-Ni,Cr-Ni and Fe-Cr-Ni systems

A semi-empirical interatomic potential formalism, the second-nearest-neighbor modified embedded-atom method (2NN MEAM), has been applied to obtaining interatomic potentials for the Fe-Ni, Cr-Ni and Fe-Cr-Ni systems using previously developed MEAM potentials of Fe and Ni and a newly revised potential of Cr. The potential parameters were determined by fitting the experimental data on the enthalpy of formation or mixing, lattice parameter and elastic constant. The present potentials generally reproduced the fundamental physical properties of the Fe-Ni and Cr-Ni alloys. The enthalpy of formation or mixing of the disordered phase at finite temperature and the enthalpy of mixing of the liquid phase are reasonable in agreements with experiment data and CALPHAD calculations. The potentials can be combined with already-developed MEAM potentials to describe Fe-Cr-Ni-based multicomponent alloys. Moreover, the average diffusivities in the unary, some binary and ternary alloys were simulated based on present potential. Good agreement is obtained in comparison with experimental data.     

A modified embedded-atom method interatomic potential for the V-H system

An interatomic potential for the vanadium-hydrogen binary system has been developed based on the second nearest-neighbor modified embedded-atom method (2NN MEAM) potential formalism, in combination with the previously developed potentials for V and H. Also, first-principles calculation has been carried out to provide data on the physical properties of this system, which are necessary for the optimization of the potential parameters. The developed potential reasonably reproduces the fundamental physical properties (thermodynamic, diffusion, elastic and volumetric properties) of V-rich bcc solid solution and some of the vanadium hydride phases. The applicability of this potential to the development of V-based alloys for hydrogen applications is discussed.     

Second nearest-neighbor modified embedded-atom method interatomic potentials for the Pt-M (M = Al,Co, Cu,Mo, Ni,Ti, V) binary systems

Interatomic potentials for Pt-M (M = Al, Co, Cu, Mo, Ni, Ti, V) binary systems have been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The parameters of pure Mo have also been newly developed to solve a problem in the previous 2NN MEAM potential in which the sigma and α-Mn structures become more stable than the bcc structure. The potentials reproduce various materials properties of alloys (structural, thermodynamic and order-disorder transition temperature) in reasonable agreements with relevant experimental data and other calculations. The applicability of the developed potentials to atomistic investigations for the shape and atomic configuration of Pt bimetallic nanoparticles is demonstrated.     

Second nearest-neighbor modified embedded-atom method interatomic potentials for the Co-M (M = Ti,V) binary systems

Interatomic potentials for the Co–Ti and Co–V binary alloy systems have been developed based on the second nearest-neighbor modified embedded-atom method (2NN MEAM) interatomic potential formalism. Newly developed potentials reproduce various structural and thermodynamic properties of the binary alloys in reasonable agreement with experiments, first-principles calculations, and CALPHAD-type thermodynamic assessments. It is emphasized that these potentials can serve as groundwork for atomistic studies on the design of highly efficient trimetallic noble metal catalysts.     

Modified embedded-atom method interatomic potentials for Mg–X (X=Y,Sn, Ca) binary systems

Interatomic potentials for pure Ca and Mg–X (X=Y, Sn, Ca) binary systems have been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The potentials can describe various fundamental physical properties of pure Ca (bulk, defect and thermal properties) and the alloy behavior (structural, thermodynamic and defect properties of solid solutions and compounds) of binary systems in reasonable agreement with experimental data or first-principles and other calculations. The applicability of the developed potentials to atomistic investigations of the deformation behavior of Mg and its alloys is discussed together with some challenging points that need further attention.     

Construction of modified embedded atom method potentials for the study of the bulk phase behaviour in binary Pt–Rh, Pt–Pd, Pd–Rh and ternary Pt–Pd–Rh alloys

A first attempt is made to simulate the solid part of the phase diagram of the ternary Pt–Pd–Rh system. To this end, Monte Carlo (MC) simulations are combined with the Modified Embedded Atom Method (MEAM) and optimised parameters entirely based on Density Functional Theory (DFT) data. This MEAM potential is first validated by calculating the heat of mixing or the demixing phase boundary for the binary subsystems Pt–Rh, Pt–Pd and Pd–Rh. For the disordered alloy systems Pt–Rh and Pt–Pd, the MC/MEAM simulation results show a slightly exothermic heat of mixing, thereby contradicting any demixing behaviour, in agreement with other theoretical results. For the Pd–Rh system the experimentally observed demixing region is very well reproduced by the MC/MEAM simulations. The extrapolation of the MEAM potentials to ternary systems is next validated by comparing DFT calculations for the energy of formation of ordered Pt–Pd–Rh compounds with the corresponding MEAM energies. Finally, the validated potential is used for the calculation of the ternary phase diagram at 600 K.     

Design and batch fabrication of probes for sub-100 nm scanningthermal microscopy

A batch fabrication process has been developed for making cantilever probes for scanning thermal microscopy (SThM) with spatial resolution in the sub-100 nm range. A heat transfer model was developed to optimize the thermal design of the probes. Low thermal conductivity silicon dioxide and silicon nitride were chosen for fabricating the probe tips and cantilevers, respectively, in order to minimize heat loss from the sample to the probe and to improve temperature measurement accuracy and spatial resolution. An etch process was developed for making silicon dioxide tips with tip radius as small as 20 nm. A thin film thermocouple junction was fabricated at the tip end with a junction height that could be controlled in the range of 100-600 nm. These thermal probes have been used extensively for thermal imaging of micro- and nano-electronic devices with a spatial resolution of 50 nm. This paper presents measurement results of the steady state and dynamic temperature responses of the thermal probes and examines the wear characteristics of the probes     

Modified embedded-atom method interatomic potentials for Mg-Nd and Mg-Pb binary systems

Interatomic potentials for the Mg-Nd and Mg-Pb binary systems have been developed within the framework of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The potentials describe a wide range of fundamental materials properties (thermodynamic, structural and elastic properties of compound and solution phases) of relevant systems in reasonable agreement with experimental data or first-principles and CALPHAD calculations. The applicability of the developed potentials to atomistic simulations on deformation behavior in Mg and its alloys is demonstrated by showing that the potentials reproduce related material properties reasonably and are transferable sufficiently.     

Fabrication of thermal microbridge actuators and characterization of their electrical and mechanical responses

This study presents thermal silicon microbridge actuators which have been made by a novel fabrication process utilizing dry processes for all critical steps. The fabrication process results in microbridges which are fully oxide covered, with excellent surface quality and dimensional control. The microbridges are made in the device layer of a silicon-on-insulator (SOI) wafer which ensures uniform doping profile and accurate thickness control. The electrical and mechanical responses of the bridges were measured upon rapid heating up to near the melting point of silicon. Up to 12 μm mechanical deflection due to thermal expansion was detected by white light interferometry (WLI) which allowed accurate measurement. Mechanical deflection has previously not been measured for silicon microlamps. Thermal conduction in the air gap between the actuator and the neighbouring solid silicon parts was analysed and shown to be more important than convection or radiation, even at very high operation temperatures.     

Microfluidic switchboards with integrated inertial pumps

Arrays of H-shaped microfluidic channels connecting two different fluidic reservoirs have been built with silicon/SU8 microfabrication technologies utilized in production of thermal inkjet printheads. The fluids are delivered to the channels via slots etched through the silicon wafer. Every H-shaped channel comprises four thermal inkjet resistors, one in each of the four legs. The resistors vaporize water and generate drive bubbles that pump the fluids from the bulk reservoirs into and out of the channels. By varying relative frequencies of the four pumps, input fluids can be routed to any part of the network in any proportion. Several fluidic operations including dilution, mixing, dynamic valving, and routing have been demonstrated. Thus, a fully integrated microfluidic switchboard that does not require external sources of mechanical power has been achieved. A matrix formalism to describe flow in complex switchboards has been developed and tested.     

A semi-empirical atomic potential for the Fe-Cr binary system

Asemi-empirical atomic potential, the second nearest-neighbor MEAM, has been applied to obtain an atomic potential for the Fe-Cr system, based on the previously developed potentials for pure Fe and Cr. The procedure for the determination of potential parameter values and the performance of the assessed alloy potential were also presented. It was shown that the potential describes the basic thermodynamic property and alloy behavior in the bcc solid solution successfully, as well as many physical properties of pure Fe and Cr. The limit in the applicability of the present potential is also discussed.     

Steady-state measurement of wafer bonding cracking resistance

A steady-state wedge-opening test has been developed in order to measure the fracture toughness of bonded silicon wafers. Comparison between non-steady-state and steady-state tests is performed. The importance of allowing the rotation of the testing stage is discussed and appears to be essential in order to have the wedge perfectly aligned with the sample. Significant influence of (1) surface treatment; (2) thermal annealing; and (3) crack velocity on the toughness is observed for Si/Si wafer bonding and related to the interface chemistry.     

Process Development for CMOS-MEMS Sensors With Robust Electrically Isolated Bulk Silicon Microstructures

This paper presents a deep reactive-ion etching (DRIE)-based post-CMOS micromachining process that provides robust electrically isolated single-crystal silicon (SCS) microstructures for integrated inertial sensors. Several process issues arise from previously reported three-axis CMOS microelectromechanical system (MEMS) accelerometers, including sidewall contaminations of SCS microstructures in plasma etch and a severe silicon undercut caused by overheating of suspended microstructures. Solutions to these issues have been found and are discussed in detail in this paper. In particular, a lumped-element model is developed to estimate the temperature rise on suspended microstructures in a silicon DRIE process. Based on the thermal modeling and experiments, a thick photoresist layer has been used as a thermal path to avoid the severe silicon undercut. The sidewall contamination problem is also eliminated using the modified CMOS-MEMS process. A three-axis accelerometer with a low-noise, low-power on-chip amplifier has been successfully fabricated using the new process. Footing effect was observed on the backside of the sensor microstructure, but it has little effect on the structural integrity and sensitivity of the sensor.     

Wafer-compatible fabrication and characteristics of nanocrystalline silicon thermally induced ultrasound emitters

Novel thermally induced ultrasound emitter without using any mechanical surface vibration systems has been developed with a high reliability. This emitter is based on a characteristic thermal property of nanocrystalline silicon (nc-Si) of which thermal conductivity and heat capacity per unit volume are extremely lowered in comparison to those of single-crystalline silicon (c-Si) due to complete carrier depletion associated with a strong quantum confinement effect. It is demonstrated here that a wafer-compatible electrochemical processing is available for the fabrication of this device by the use of appropriate masking and isolation techniques, and that more than 300 chips can be produced from a 4-inch wafer with a sufficiently high yield. The fundamental ultrasonic emission characteristics of the fabricated emitter are evaluated in terms of frequency response and the emission angle dispersion. The experimental results show that the fabricated device exhibits a flat frequency response with little distortion over a wide range as expected. Also the ultrasonic pressure is generated isotropically. This emitter is promising for applications to functional ultrasonic devices.     

Thermal characterization of surface-micromachined silicon nitridemembranes for thermal infrared detectors

The aim of this work is to provide a thorough thermal characterization of membrane structures intended for thermal infrared detector arrays. The fabrication has been conducted at temperatures below 400°C to allow future post processing onto existing CMOS readout circuitry. Our choices of membrane material and processing technique were plasma enhanced chemical vapor deposited silicon nitride (SiN) and surface micromachining, respectively. The characterization gave for the thermal conductance (G) and thermal mass between the membrane and its surroundings 1.8·10^-7 W/K and 1.7·10^-9 J/K, respectively, which are close to the best reported values elsewhere. From these results the thermal conductivity and specific heat of SiN were extracted as 4.5±0.7 W/m.K and 1500±230 J/kg.K. The contribution to G from different heat transfer mechanisms are estimated. A model describing the pressure dependence of G was developed and verified experimentally in the pressure interval [5·10^-3, 1000] mbar. Finally, the influence of the thermal properties of the membrane on infrared detector performance is discussed