Indium Growth and Island Height Control on Si Submonolayer Phases
- Iowa State Univ., Ames, IA (United States)
Nanotechnology refers any technique that involves about object with nanoscale (10-9 m) or even smaller. It has become more and more important in recently years and has changed our world dramatically. Most of modern electronic devices today should thanks to the miniaturizing driven by development of nanotechnology. Recent years, more and more governments are investing huge amount of money in research related to nanotechnology. There are two major reasons that nanostructure is so fascinate. The first one is the miniaturizing. It is obvious that if we can make products smaller without losing the features, we can save the cost and increase the performance dramatically. For an example, the first computer in the world, ENIAC, which occupied several rooms, is less powerful than the cheapest calculator today. Today's chips with sizes of less than half an inch contain millions of basic units. All these should thank to the development of nanotechnology. The other reason is that when we come to nanoscale, there are many new effects due to the quantum effect which can't be found in large systems. For an example, quantum dots (QDs) are systems which sizes are below 1μm(10-6m) and restricted in three dimensions. There are many interesting quantum effects in QDs, including discrete energy levels, and interdot coupling. Due to these properties and their small sizes, QDs have varies potential applications such as quantum computing, probe, light emitting device, solar cells, and laser. To meet the requirement of the nanoelectrical applications, the QDs must be grown highly uniformly because their property is highly dependent on their sizes. The major methods to grow uniform QDs include epitaxial, and lithograph. Lithography is a process to make patterns on a thin film by selectively removing certain parts of the film. Using this method, people have good control over size, location and spacing of QDs. For an example, the Extreme ultraviolet lithography (EUVL) have a wave length of 13.4 nm so it can curve on the surface of an sample to make structure as small as the order of 10 nm. however, lithograph usually causes permanent damages to the surface and in many cases the QDs are damaged during the lithograph and therefore result in high percentage of defects. Quantum size effect has attracted more and more interests in surface science due to many of its effects. One of its effects is the height preference in film growing and the resulting possibility of uniformly sized self-assemble nanostructure. The experiment of Pb islands on In 4x1 phase shows that both the height and the width can be controlled by proper growth conditions, which expands the growth dimensions from 1 to 2. This discover leads us to study the In/Pb interface. In Ch.3, we found that the Pb islands growing on In 4x1-Si(111) surface which have uniform height due to QSE and uniform width due to the constriction of In 4x1 lattice have unexpected stability. These islands are stable in even RT, unlike usual nanostructures on Pb/Si surface which are stable only at low temperature. Since similar structures are usually grown at low temperature, this discovery makes the grown structures closer to technological applications. It also shows the unusual of In/Pb interface. Then we studied the In islands grown on Pb-α-√3x√3-Si(111) phase in Ch.4. These islands have fcc structure in the first few layers, and then convert to bct structure. The In fcc islands have sharp height preference due to QSE like Pb islands. However, the preferred height is different (7 layer for Pb on Si 7x7 and 4 layer for Pb on In 4x1), due to the difference of interface. The In islands structure prefers to be bct than fcc with coverage increase. It is quantitatively supported by first-principle calculation. Unexpectedly, the In islands grown on various of In interfaces didn't show QSE effects and phase transition from fcc and bct structures as on the Pb-α interface (Ch.6). In g(s) curve there is no clear oscillations in the g(s) curve as the In on Pb-α phase. This may be due to the extra mobility of In atoms, which causes the In bct islands to grow too fast to be observed in diffraction or STM (Ch.5). From these experiments we can see the importance of Pb-α phase in growth of In islands. It is the best interface to grow In islands in the phases we have experimented. Recent experiments show that the Existence of Pb will decrease the diffusion speed of In. In Ch.6 we have shown that In atoms diffusion is so fast that the bct spots are not visible in diffraction. But when we put some Pb onto the In surface, we can see the bct spots, although very weak. So Pb should play an role in slowing down the indium atoms diffusion. The interaction of Pb and In may play a role, but it is still not fully understood. So the general conclusion of this thesis is that In/Pb interface has extraordinary properties and may have potential in self-assembling growth.
- Research Organization:
- Ames Lab., Ames, IA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC02-07CH11358
- OSTI ID:
- 972074
- Report Number(s):
- IS-T 2663; TRN: US201005%%175
- Country of Publication:
- United States
- Language:
- English
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