There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Publisher Summary This chapter describes the mixed mode cracking in layered materials. There is ample experimental evidence that cracks in brittle, isotropic, homogeneous materials propagate such that pure mode I conditions are maintained at the crack tip. An unloaded crack subsequently subject to a combination of modes I and II will initiate growth by kinking in such a direction that the advancing tip is in mode I. The chapter also elaborates some of the basic results on the characterization of crack tip fields and on the specification of interface toughness. The competition between crack advance within the interface and kinking out of the interface depends on the relative toughness of the interface to that of the adjoining material. The interface stress intensity factors play precisely the same role as their counterparts in elastic fracture mechanics for homogeneous, isotropic solids. When an interface between a bimaterial system is actually a very thin layer of a third phase, the details of the cracking morphology in the thin interface layer can also play a role in determining the mixed mode toughness. The elasticity solutions for cracks in multilayers are also elaborated.

Mixed mode cracking in layered materials

This article reviews the progress of atomic force microscopy in ultrahigh vacuum, starting with its invention and covering most of the recent developments. Today, dynamic force microscopy allows us to image surfaces of conductors and insulators in vacuum with atomic resolution. The most widely used technique for atomic-resolution force microscopy in vacuum is frequency-modulation atomic force microscopy (FM-AFM). This technique, as well as other dynamic methods, is explained in detail in this article. In the last few years many groups have expanded the empirical knowledge and deepened our theoretical understanding of frequency-modulation atomic force microscopy. Consequently spatial resolution and ease of use have been increased dramatically. Vacuum atomic force microscopy opens up new classes of experiments, ranging from imaging of insulators with true atomic resolution to the measurement of forces between individual atoms.

https://hep.physics.utoronto.ca/WilliamTrischuk/courses/phy189/AFM_revmodphys.pdf

Advances in atomic force microscopy

A method to bond silicon wafers directly at room temperature was developed. In this method, surfaces of two silicon samples are activated by argon atom beam etching and brought into contact in a vacuum. By the infrared microscope and KOH etching method, no void at the bonded interface was detected in all the specimens tested. In the tensile test, fracture occurred not at the interface but mainly in the bulk of silicon. From these results, it is concluded that the method realizes strong and tight bonding at room temperature and is promising to assemble small parts made by the silicon wafer process.

Surface activated bonding of silicon wafers at room temperature

Thin copper (Cu) films of 80 nm thickness deposited on a diffusion barrier layered 8 in. silicon wafers were directly bonded at room temperature using the surface activated bonding method. A low energy Ar ion beam of 40–100 eV was used to activate the Cu surface prior to bonding. Contacting two surface-activated wafers enables successful Cu–Cu direct bonding. The bonding process was carried out under an ultrahigh vacuum condition. No thermal annealing was required to increase the bonding strength since the bonded interface was strong enough at room temperature. The chemical constitution of the Cu surface was examined by Auger electron spectroscope. It was observed that carbon-based contaminations and native oxides on copper surface were effectively removed by Ar ion beam irradiation for 60 s without any wet cleaning processes. An atomic force microscope study shows that the Ar ion beam process causes no surface roughness degradation. Tensile test results show that high bonding strength equivalent to bulk ...

/pdf/room-temperature-cu-cu-direct-bonding-using-surface-3wah88y3nl.pdf

Room temperature Cu-Cu direct bonding using surface activated bonding method

In a multi-layer interconnection structure, the wiring length is to be reduced, and the interconnection is to be straightened, at the same time as measures need to be taken against radiation noise. To this end, there is disclosed a semiconductor device in which plural semiconductor substrates, each carrying semiconductor elements, are bonded together. On each semiconductor substrate is deposited an insulating layer through which is formed a connection wiring passed through the insulating layer so as to be connected to the interconnection layer of the semiconductor element. On a junction surface of at least one of the semiconductor substrates is formed an electrically conductive layer of an electrically conductive material in which an opening is bored in association with the connection wiring. The semiconductor substrates are bonded together by the solid state bonding technique to interconnect the connection wirings formed on each semiconductor substrate.

Interconnect structure for stacked semiconductor device

Using Ar beam etching in vacuum, strong bonding of Si wafers is attained at room temperature. With appropriate etching time, the bonding occurs spontaneously without any load to force two wafers together. However, surface roughness of the wafers increases during Ar beam etching. Because surface roughness has a strong influence on wafer bonding, long etching time degrades the bonding strength. Using atomic force microscope, we measured surface roughness enhancement caused by Ar beam etching, and investigated the relationship between surface roughness and bonding properties such as strength and interfacial voids. The results agree well with theoretical predictions using elastic theory and energy gain by bond formation. A guideline for successful room-temperature bonding is proposed from these results.

Effect of Surface Roughness on Room-Temperature Wafer Bonding by Ar Beam Surface Activation

Al Al joints and Al Si3N4 joints were manufactured at room temperature by means of the surface activation method. In this procedure, the surfaces to be bonded are sputter-cleaned and activated by argon fast-atom-beam (FAB) irradiation and then brought into contact with each other under a slight pressure. The primary concept of the method is based on the idea that clean metal surfaces are inherently active and react with other elements such as oxygen, nitrogen and carbon, and thus form a strong bonding with ceramics even at room temperature. Therefore it was expected that the method will be effective only in an ultra high vacuum so that the sputtered surfaces remain clean until joining. It was found, however, that such a clean environment is not necessary for joining. Surfaces activated in a vacuum containing some residual gas can be bonded very strongly and do not lose the capacity of adhering even after exposure to the residual gases after sputt-cleaning. It is found by transmission electron microscopy that the interface structure depends remarkably upon the vacuum condition in which the surfaces to be bonded are sputter-cleaned. An intermediate layer consisting of a partially amorphous phase was found in Al Al joints bonded under a vacuum pressure of 10−5Pa, while an Al Al joint without an intermediate layer was formed by ultra high vacuum bonding. It is assumed that oxygen or water in the residual gas of the vacuum was absorbed on the Al surface and dissolved into metal by the argon irradiation. Thus, an amorphous Al O solid solution or a kind of aluminium oxide is formed. Al Si3N4 joints manufactured in a high vacuum from surface activated materials showed also an intermediate layer which was, however, entirely amorphous over the whole interface and was considered to have been formed predominantly on the Si3N4 surface.

Tadatomo Suga

Papers

Surface activated bonding of silicon wafers at room temperature

Room temperature Cu-Cu direct bonding using surface activated bonding method

Interconnect structure for stacked semiconductor device

Effect of Surface Roughness on Room-Temperature Wafer Bonding by Ar Beam Surface Activation

Structure of AlAl and AlSi3N4 interfaces bonded at room temperature by means of the surface activation method