Sunday, June 13, 2010

Dual beam FIB

Microscopy is a monopoly business of the biologists, but we materials scientists live under the impression that microscopy is our business; at last we found one of them which is not meant for biologists. Its a Focused Ion Beam (FIB) with dual beam,I am talking about. I am not going into details of what all these beams mean but briefly i will touch upon the issue. In the optical microscope we use light as a medium which illuminates the surface, so thats optical beam and we use glass lenses for magnification. Then we generate electrons and we use it for different electron microscopes so we use electron beam there, here magnetic lenses are used instead of glass lenses. Ion beam was introduced around 20 years back, where usually liquid metals (primarily gallium Ga) are ionized and can be used to form a beam. The magnetic lenses doesn't work for ion beam so electrostatic lenses are used. Advantages? no its not the correct word; it is the new characterization possibility that this microscope has generated. Ion beam has momentum 400 times larger than an electron beam, so it can knock out materials from very precise location of a sample whether its metal or ceramics. The question arrives why one need to remove materials from the surface? there various reasons, but the primary beneficiaries are the semi conductor techies for whom the interfaces are really important. There are very advanced applications such as study of electrical properties of single carbon nanotube or y junction nanotube. FIB has been extensively used in pattering different contacts which can be used for measuring electrical properties in the micron scale even in the nanometer scale. The dual beam FIB has another advantage, it has an electron beam as well and thats the reason the instrument is called dual beam FIB. It had opened a spectrum of other characterization which can be carried out. The maximum use is the preparation of specimen for transmission electron microscope (TEM). Those who has prepared specimens using traditional ion milling, know how difficult it is to prepare specimen for TEM, when you have ceramics god help you! also carrying out TEM of interfaces was a big challenge. In the dual beam FIB as one thins the specimen using ion beam it is possible to monitor the thinning process using the electron beam simultaneously. The tougher part is to take out the slice out from the specimen. There is a needle called micromanupulator which enters and attaches to the specimen. Its very tricky as things move at a step of hundreds of nanometer, but the FIB has a stage which is piezo controlled hence it is possible to do things carefully. Although it requires quite good level of skills, the outcome it amazing! The other two very important characterization which is possible using dual beam is to prepare 3D crystal orientation map through Electron Backscattered Diffraction, its a reconstruction of 2D slices as the ion beam can form slices as thin as 100 nm. Again similar analysis is possible using the chemical composition (EDX analysis)
All these techniques are wonderful when you start studying grain boundaries and interfaces, but when you have ceramics, which are highly insulating, life really becomes nightmare. The ion beam bombards ion at 30Kv energy, which is huge. Damage of the surface, loss of stability, there are significant no of issues which pops up. well there are ways to avoid them and i must admit at the days end what this tool one can produce amazing results!

Wiki has a nice article on FIB, much more informative than this.

Sunday, June 06, 2010

Oil wont run out

Saw this nice video in TED talks, there is always hope...