任何一种化学元素的用途的介绍!英文最好……

任何一种化学元素的用途的介绍!英文最好……

纭匋br/>Silicon as a material in microelectronics
Microelectronics is probably the most important achievement of our time,comparable with the invention of letterpress in the 16th,the invention of the stean engine in the 18th or the invention of the electricity in the 19th century,respectively.If nowadays one is talking about "scientific revolution",the term microelectronics is inevitable.The technologies associated with the headwords "Internet" and "data highway" wouldn't be conceivable without the invention of the transistor by Bardeen and Brattain.Although the first transitors were realized with germanium,todays microelctronics technology is dominated by exclusively one material:silicon.In fact,some materials have better properties,for instance,gallium arsenide (GaAs),but there are many reasons why silicon is the material of choice:
Silicon is the second frequent element on the earth,the accessible part of the earth consists of 27.5% of this element (predominatly as silicondioxide,SiO2)
Silicon crystal growth technology is the most evolved one regarding purity,crystal defects (i.e.dislocations) and size (the industry is now starting to develop technologies for processing 12 inch wafers,i.e.single crystals with a diameter of a long playing record)!
It is possible and easy to grow a stable passivation layer of SiO2 on the silicon surface,a very important point regarding the processes in microelectronics,like photolithography or field and barrier oxides for transistors,for instance.
On the other hand silicon is also a very intersting material for electrochemists,as we will see in the next paragraph.
Silicon as a material in electrochemistry
Bardeen and Brattain,even though for a different purpose,have probably performed the first electrochemical experiments with semiconductors.Meanwhile semiconductor electrochemistry is a well established,independent scientific reasearch area.Especially the silicon/hydrofluoric acid contact shows very interesting behaviour,which is not quite well understood:
Anodic dissolution with formation of anodic oxides (electropolishing)
Current and voltage oscillations
Anodic dissolution with porous silicon formation
The last part of this short introcution will focus on the last-mentioned material,porous silicon.
A "new material":Porous silicon
The first observation of porous silicon layers goes back 40 years and was done by Uhlir and Turner.Though,they interpretated the black/brown coloured surface as precipitation of silicon related species from solution.Today it is generally accepted,that porous silicon formation is an etching process,where Si-atoms are dissolved from the bulk material and the original crystal structure remains uneffected.
Dependent on the experimental conditions (doping density of bulk material,electrolyte concentration,current density,etchung voltage,temperature) different modifications of porous silicon can be formed,which make it necessary to introduce a classification of the different pore types.With this different pore etching techniques it is now possible to vary not only the electronical but also the mechanical properties of silicon in a scale from millimetres to nanometres.
Nanoporous silicon
One of the remarkeble features of nanoporous silicon is its unusual optical properties.The nanoporous structures have dimensions in the low nm-range.If the structure size reaches a value below,say 3 nm,quantum effects can occur and therefore nanoporous samples can exhibit strong visible photoluminescence and electroluminscence,as can be seen in the picture below.
Photoluminescence of a nanoporous silicon sample
This is why the material is very interesting for applications in optoelectronics,because then it will be possible to integrate optoelctronical devices directly on silicon substrates!
Macroporous silicon
Another very promising material is macroporous silicon,which can be obtained only on n-type bulk material.The principle of macropore etching was predicted by Föll and Lehmann,who suggested to use backside illumination for pore growth.In contrast to the commonly used front side illumination for PS formation on n-type silicon,where holes,which are essential for silicon dissolution,are generated close to the sidewalls of the pores,the backside illumination has a tremendous advantage.The holes supplied at the back side of the wafers have to reach the silicon/electrolyte interface by diffusion.Because the front side of the wafer is in the dark and therefore in depletion,the holes will preferently reach depressions or pits,where the electrical field is enhanced and promote dissolution there.With this technique it is possible to create pores (or better:trenches) with diameters in the µm range and lengths of several hundred microns up to wafer thickness!Two examples for macropores are shown in the figures below.
Examples for macropores in n-type silicon
Meanwhile this material is the first out of the different types of porous silicon that has found commercial applications in capacitor technology.In addition,some more possible and partly realized applications of commercial as well as academic interests are worth to mention:
Microsystem technology
ink jet nozzles
channel plates
three dimensional microstructuring of silicon with high aspect ratios
Photonic bandgap material
Defined model (porous) electrodes in semiconductor electrochemistry