51 research outputs found
Structure and peculiarities of the (8 x n)-type Si(001) surface prepared in a molecular-beam epitaxy chamber: a scanning tunneling microscopy study
A clean Si(001) surface thermally purified in an ultrahigh vacuum
molecular-beam epitaxy chamber has been investigated by means of scanning
tunneling microscopy. The morphological peculiarities of the Si(001) surface
have been explored in detail. The classification of the surface structure
elements has been carried out, the dimensions of the elements have been
measured, and the relative heights of the surface relief have been determined.
A reconstruction of the Si(001) surface prepared in the molecular-beam epitaxy
chamber has been found to be (8 x n). A model of the Si(001)-(8 x n) surface
structure is proposed.Comment: 4 pages, 8 figures. Complete versio
STM and RHEED study of the Si(001)-c(8x8) surface
The Si(001) surface deoxidized by short annealing at T~925C in the ultrahigh
vacuum molecular beam epitaxy chamber has been in situ investigated by high
resolution scanning tunnelling microscopy (STM) and reflected high energy
electron diffraction (RHEED). RHEED patterns corresponding to (2x1) and (4x4)
structures were observed during sample treatment. The (4x4) reconstruction
arose at T<600C after annealing. The reconstruction was observed to be
reversible: the (4x4) structure turned into the (2x1) one at T>600C, the (4x4)
structure appeared again at recurring cooling. The c(8x8) reconstruction was
revealed by STM at room temperature on the same samples. A fraction of the
surface area covered by the c(8x8) structure decreased as the sample cooling
rate was reduced. The (2x1) structure was observed on the surface free of the
c(8x8) one. The c(8x8) structure has been evidenced to manifest itself as the
(4x4) one in the RHEED patterns. A model of the c(8x8) structure formation has
been built on the basis of the STM data. Origin of the high-order structure on
the Si(001) surface and its connection with the epinucleation phenomenon are
discussed.Comment: 26 pages, 12 figure
Recommended from our members
Alternative catalyst and exhaust gas sensor work at Argonne National Laboratory
Research programs at Argonne National Laboratory in the areas of automobile emissions monitoring and control are described. The mandate to improve automobile efficiency while reducing Pollution requires the development of new catalysts for exhaust emissions control that are capable of functioning efficiently under lean-burn engine operating conditions. It is also desirable that the use of expensive noble metal catalysts be avoided. NO{sub x} emissions will not be efficiently controlled by the current three-way, supported noble metal catalysts under lean-burn conditions. New catalysts are being sought that could effect the selective catalytic reduction (SCR) of NO{sub x} by exhaust hydrocarbons in the presence of oxygen. Molecular sieve zeolites of the ZSM-5 and ferrierite types, ion-exchanged with copper ions, are the best of the catalysts known to effect this chemistry, but the mechanism of the SCR is still not understood. In this project the authors will first undertake the investigation of the SCR of NO using model reactions to test postulated mechanistic pathways. Initial experiments have been devised to investigate the possible participation of metal alkyl complexes, metal oxime complexes, N-alkyl-N-nitroso-alkylaminato-metal complexes, and metal nitrile complexes in the zeolites. ANL will also develop microsensors, based on surface acoustic wave (SAW) chemical sensing techniques, and a micro mass-spectrometer (MS) for tailpipe or engine-out emission monitoring. The sensor configurations and sensing techniques of the proposed SAW and micro-MS are described
- …