Ag Si project

The silver silicon interfaces have peculiar steps on both silicon surfaces. In the silver layer, many silicon islands were observed, which are formed by the eutectic reaction between silver and silicon.

It is likely that dissolved silicon in the eutectic melt crystallized on the silicon surface and the crystallization was so rapid that the silver islands were left along the bottom line of the crystallized silicon steps.

We can observe the morphology of the silicon crystallization on the silicon substrate by removing the silver layer with acid.

SECONDARY ION MASS SPECTROMETRY

SIMS is a characterization technique commonly employed in the semiconductor device industry for obtaining information regarding either element concentration at the surface or at various depths below the surface of a sample or thin film. There are two primary types of SIMS techniques that provide data of this sort, and they are called static SIMS and dynamic SIMS, respectively.

Dynamic SIMS:
Dynamic SIMS uses a high-energy primary ion beam and corresponding short times to erode away the material surface and obtain a depth profile of the sample.Dynamic SIMS allows for depth profiling of elemental concentration with a sensitivity in the range of parts per billion (ppb), or in the range of 10¹⁴ atoms*cm^-3. This technique is extremely powerful and currently does not have any complimentary techniques that obtain results on the same level of sensitivity. Dynamic SIMS also provides depth resolution on the level of several nanometers, which is something that no other current technique can claim.
Physical Mechanism of SIMS:
The dynamic SIMS characterization technique works by first striking a sample with a primary ion beam. This operation is performed in an ultra high vacuum environment with typical pressures of about 10-9 to 10-10 torr. Ultra high vacuum is required to prevent any interaction of the primary ion beam or emitted secondary ions with gas molecules.The primary ion beam is created by an ion source of which there are four primary types: electron, plasma, radio frequency, and liquid metal ion sources . The primary ion beam typically ranges in energy from 0.5 to 20 keV, and may consist of reactive ions such as O₂⁺, O^-, Cs⁺, or inert ions like Ar⁺, Xe⁺, or Ga⁺ depending upon the type of ion source.
In dynamic SIMS, primary ions that strike a sample may collide with target surface atoms and displace them if the primary ion energy is larger than the displacement energy (15-40 eV) of the target atoms. The primary ions may also become imbedded in the surface of the sample. Target atoms impacted by primary ions may be displaced toward the sample, and collide with more target atoms.
The target atoms that recoil back through to the surface constitute sputtered material, which gives rise to secondary ion emission. Secondary ion emission will only take place if the target atom strikes the surface with energy greater than the surface binding energy. This process of sputtering classifies SIMS as a destructive process since material is physically removed from the sample.
Ion Collection and Analysis:
The secondary ions that are ejected from the sample may be either positive or negative, and are collected in an energy analyzer, which provides enhanced resolution. From there, the ions are transferred to a mass spectrometer that analyzes the mass to charge ratio for purposes of identifying the element. Finally, the ions travel into a detector, which is similar to a Faraday cup, that allows for current to be measured and data interpreted.
Static SIMS would produce a mass spectrum as the primary result, whereas dynamic SIMS allows the user to obtain a depth profile of elements in the sample. The third type of possible output is an image of the sample by a process called imaging SIMS, but is less relevant to the problem that has been posed.

Ag Cu Au in Si

The extremely fast diffusivity of Cu and its pronounced tendency to precipitate on cooling indicate that Cu is dissovled interstitially in the Si lattice.
By contranst, extended investigations of the Au diffusion in Si strongly support the view that the majority of Au atoms are incorporated on substitutional sites.
Ag appears to be predominantly interstitial with a much lower solubility than Cu and Au.

Ref: J.Phys. D: Appl Phys 20 (1987) p1148-1155

Self Assembly

Self-assembly is a method of constructing devices and machines whose dimensions are measured in nanometers. The Self Assembling structure is formed by a competition between short-range attractive and long-range repulsive interactions that leads to stabilization of domains with characteristic feature dimensions.

two dimensional self assembly:
Most of the papers published today are dealing with films in monolayer scale. And themodynamic properties of domain structures resulting from competing interactions has been the subject of many theoretical studies. Quantitative information on the forces that drive pattern formation is lacking because it is difficult to measure forces on the length scale of self-assembly directly.

Three dimensional self assembly:
Only a few papers reported self assembling structure in 3 dimensions. Not to mention the theory studies and quantitative studies.

What're Materials?

Major Categories:

	Metals Whole periods of human civilization - such as the Bronze and Iron ages - are named for metals. These were the first materials to be "engineered," that is, people changed them to fit what they needed to do, rather than just letting their natural properties determine what they could be used for. These days, materials scientists are using metals in ways no one could have pictured even a few years ago - for example, shaping copper into tiny wires a thousand times skinnier than a strand of your hair!
	Ceramics Think about a china teapot - that's one type of ceramic. But ceramics can also be used to create bone and tooth replacements, super-strong cutting tools, or to conduct electricity. With the addition of oxygen or nitrogen, metals become ceramics, too.
	Semiconductors One of these materials - silicon - is making it possible for you to read these words right now! That's because silicon is the essential material in an electronic computer chip. "Semiconductor" means a material can conduct electricity with a bit of help in the form of added "impurities." Your CD, DVD player, and telephone - all depend on semiconductors.
	Polymers Polymers are just very big molecules made of smaller molecules linked together into long, repeating chains. You may not know it, but you're in touch with polymers every day more than any other kind of material. Rubber bands are made of polymers, so are paints and every kind of plastic. And by the way, most of the food you eat is made of natural polymers!