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Semiconductor particles in the size rage 1-100 nm have special optoelectronic properties dictated by the quantum mechanics of the potential well. These particles are known as quantum dots. Fabricating structures in this size range has been a great challenge of our time. Self-assembly has become an attractive method to fabricate quantum dots. By 1990, it was known that when Ge was deposited on Si substrate, cube on cube, the Ge film is flat up to a few monolayers, and then forms three-dimensional islands.

In service, an interconnect line carries an intense electric current. The conduction electrons impact metal atoms, and motivate the atoms to diffuse in the direction of electron flow. The process, known as electromigration, has been the most menacing and persistent threat to interconnect reliability.

Early aluminum lines had the width much larger than the thickness. They behaved like blanket films. When narrow aluminum lines were introduced, in early 1980s, with the width comparable to the thickness, voids were observed in such narrow interconnects on wafers held in ovens, or even on wafers left on shelves at room temperature. The voids may sever the interconnects.

A polycrystal, held at temperature for some time t, the average grain diameter grows. A grain grows at the expense of its neighbors: small grains disappear and big ones get bigger. Total number of atoms is conserved.

Hull and Rimmer (1959) studied grain boundary cavitation. Small voids were observed at grain boundaries, particularly those transverse to the applied tensile stress. Fracture results from the growth and coalescence of these voids.

Rayleigh (1878) examined a common experience: a thin jet of liquid is unstable and breaks into droplets. When a jet is thin enough, the effect of gravity is negligible compared to surface energy. The jet changes its shape to reduce the total surface energy. Liquid flow sets the time.

A polished polycrystal has a flat surface. At room temperature, the surface remains flat for a long time. At an elevated temperature atoms move. The surface grows grooves along triple junctions, where the surface meet grain boundaries. The grooves reveal the grain boundaries in the microscope. Atoms may move in many ways. They may diffuse in the lattice, diffuse on the surface, or evaporate into the vapor phase. Here we will only consider surface diffusion. Atoms diffuse on the surface away from the triple junction, making a dent along the junction, and piling two bumps nearby.

Some phenomena due to surface diffusion:

• Flattening a surface.
• Spherodizing.
• Rayleigh instability.
• Grain boundary grooving.
• Sintering
  Self-assembled quantum dots

Diffusion and creep involve the same atomic process: atoms must change neighbors, aided by thermal energy. We explore their relation in this lecture.

I have taught this course four times before, but have never devoted lectures on basic thermodynamics. It is a subject I’m not good at, but I have used it often in research, in a loose way. One can ride a bicycle without knowing Newton’s laws, even though bicycle-riding is governed by Newton’s law. If thermodynamics gives me so much trouble, perhaps it also gives my students a lot of trouble. I have taken lectures from many teachers on the subject. None have really made me feel comfortable with it. Now I’m trying to teach you. I hope that I can help you become comfortable with the subject. Maybe you already are. Maybe you never will. I have no evidence that I can be more effective than these other teachers, but I have the enthusiasm of an amateur.

Cavity Growth Is Caused by a Series of Tiny Effects

• A tiny fraction of lattice sites are vacant.
• The tensile stress increases the vacancy concentration at the external surface by a tiny fraction.
• The tiny nonunifomity in the vacancy concentration drives diffusion.
• A tiny fraction of vacancies change site, by an atomic distance.

A solid contains a spherical cavity, subject to a hydrostatic stress. For now, we assume that the solid is stiff so we ignore its deformation. The cavity can still change its size by a special mechanism: atoms diffuse through the solid between the cavity surface and the external surface. We will concentrate in this lecture on the question, Will the cavity shrink or enlarge? We will consider the diffusion process in some detail in the next lecture, and answer the question, How fast will the cavity change its size?

Hello everyone,

 I am not facing a problem now using ABAQUS/Explicit. The material size I used in ABAQUS is much smaller than I tested in the experiment. For example the yarn length I tested is 250mm and the yarn length in my model is only 10mm. Now I need to give the fracture energy of the yarn under impact. It would be very appreciated if you could help me to solve the problem. Many thanks.

 Sun

Hi..

I'm new  to Ansys.. I need to model a composite plate with a hole. It needs to have 5 laminated layers with different fiber orientations.

I've been through all similar queries here and have managed to understand how to model the layup (using the section -> shell method).

I have also modelled a sample plate with a hole.

I have also inputed the various material properties of each individual layer (through the Material Model editor).

BUT!! HOW DO I INTEGRATE THE LAYUP WITH THE SAMPLE PLATE ???.

I met a problem when reading "complex variable methods" of Suo. The problem is explained in the attached file.

Can anybody help me ?

thanks

 hi,

I want to learn  fluid mechanics myself,  but  i have no idea how to do and where to search the sourses fluid mechanics ?? 

Thanks in advance

lyyl

  I want to do torsional analysis in ANSYS. The beam is hollow rectangular beam and the requirement is to rotate the beam in Z-direction. Can anybody guide me how to apply the torque?? I have applied the torque in the form of force but i am not satisfies with the results. Can anybody guide me how to apply torque??

hello,

I'm a new ABAQUS user. I wander if I can get the displacements of any point just by putting the mouse arrow near by it like what is done in the SAP program.

I'm searching for that option but till now didn't find it

Thanks a lot in advance

Hello,

I'm a new user of ABAQUS. I want to be able to view the displacements on the CAE deformed shape. Like to put the mouse arrow over a certain node and it writes the exact value of the deformations. (Like what can be done easily by the SAP program)

I just want to figure out how is that possible

Thank you in advance

 I am searching this book name " Introduction to Finite and spectral element  method using Matlab" . anybody can tell any website from where i can download?

thank you

sameer

Finnally I graduated in Aeronautics Engineering!

Yoy can find a monograph I made during Aeronautics Structures III about FEM in http://www.esnips.com/web/fedebertolisBusinessFiles

By

PS: It is in Spanish, english translation will be available soon.