Si Nano Research Articles

Mechanism of Asymmetric Temperature Distribution of Si Nano Wire with Self-Heating

Mechanism of Asymmetric Temperature Distribution of Si Nano Wire with Self-Heating

Study of Self-Heating in Si Nano Wire

Study of Self-Heating in Si Nano Wire

Optical investigation of Si nano-crystals in amorphous silicon matrix

Paper presents the comparative investigation of photoluminescence and Raman scattering spectra of pure amorphous silicon films and amorphous silicon films with different size Si nanocrystallites. Several PL bands in the IR spectral range with maxima at 0.90, 0.98, 1.14 and 1.36eV have been revealed in studied samples. The 0.90–0.98eV PL bands are attributed to the band tail luminescence in Si nano crystallites with the size of 15–20 nm. Concurrently, the 1.18 and 1.36eV PL bands are connected, apparently, with radiative transition between quantum confined levels within Si QDs (size of 5–6nm) embedded into a-Si matrix.

기계화학적 합금화된 나노 Fe-6.5Si 분말의 자기 펄스압에 의한 동적성형

Nano Fe-6.5wt%Si powders have been synthesized by mechano-chemical process (MCP) for an application of soft magnetic core. Owing to hard and brittle characteristics of Fe-6.5Si nano powders having large surface area, it is very difficult to reach high density more than 70% of theoretical density (~7.4 g/) by cold compaction. To overcome such problem a magnetic pulsed compaction (MPC), which is one of dynamic compaction techniques, was applied. The green density was achieved about 78% (~5.8 g/) by MPC at room temperature.

The Bio-Nano-Process: Making Semiconductor Devices Using Protein Supramolecules.

AbstractThe biology and semiconductor technology have progressed independently. There was a large distance between them and a substantial interdisciplinary research area was left untouched. Recently, this situation is gradually changing. Some researchers are stimulating semiconductor technology by introducing bio-molecules into the nano-fabrication process. We proposed a new process for fabricating functional nano-structure on a solid surface using protein supramolecules, which we named “Bio Nano Process” (BNP). We employed a cage-shaped protein, apoferritin and synthesized several kinds of nanoparticles (NP) in the apoferritin cavity. A two-dimensional array of them was made on the silicon wafer and this array was heat treated or UV/ozone treated. These processes produced a two-dimensional inorganic NP array on the silicon surface. The size of the NP is small enough to be used as quantum dot and the floating nanodots memory using this NP array is now under development. We also proposed another application of the BNP, making use of the obtained nanodot array as the nanometric etching mask. This was realized by employing the neutral beam etching and 7nm Si nano columns with high aspect ratio were fabricated. These experimental results demonstrate that the BNP can fabricate the inorganic nanostructure using protein supramolecules and the BNP opened up a biological path to nanoelectronics devices.

The microstructure of Er MBE doped GaN

For a few years now, it has been possible to dope GaN layers using molecular beam epitaxy (MBE) growth. This aims to use the wide band gap semiconductors as hosts to rare earth ions and exploit the sharp emission lines from atomic shell transitions. It was shown that the whole visible spectrum can be covered by addressing different exited states of various rare earth ions. It is also suspected that as in some systems like Si(nano)/SiO 2, the energy coupling could involve defects. In this work, we carry out TEM and HREM analysis on MBE doped GaN layers grown on metal organic chemical vapour deposition (MOCVD) GaN templates. Er concentrations of 1, 6, and 16 at.% were subsequently measured by wavelength dispersive X-ray (WDX) in an electron probe. We discuss the results on the spatial distribution of the rare earth atoms at a nanometer scale.

A Si nano–micro-wire array on a Si(111) substrate and field emission device applications

A large number of Si wires on Si(111) can be fabricated selectively by the vapor–liquid–solid growth method with a high aspect ratio greater than 100. The diameter of the wire can be controlled from less than a micron to a few hundred microns. We propose a novel smart field electron emission device using silicon nano-wires fabricated by this vapor–liquid–solid growth method, and demonstrate field electron emission with a quite low operation voltage from a gated silicon nano-wire. The threshold voltage is about 13 V, and the value is similar to those for gated carbon-nanotube field emitters. The emission current reaches 10 nA at 15 V gate voltage.

Characteristics of Polycrystalline Si Nano Wire Piezoresistors

This paper describes the first study on a polycrystalline Si (poly-Si) nano wire from the viewpoint of MEMS mechanical sensor application. In order to confirm an ability of the poly-Si nano wire piezoresistor as a sensing element of a mechanical sensor, current-voltage (I-V) characteristics and the piezoresistive effect were investigated. The poly-Si nano wire piezoresistor, whose thickness is 32nm and width is 53nm, was fabricated by the combination of the electron beam (EB) direct writing and RIE. A remarkable phenomenon was observed. The longitudinal piezoresistive coefficient πl of the nano wire piezoresistor increased with a decrease in the cross section area, while the transverse piezoresistive coefficient πl was approximately zero and invariant despite variation of the cross section area. The maximum value of the longitudinal piezoresistive coefficient πl of the nano wire piezoresistor was 22×10-5(1/MPa) at impurity concentration N=5×1019 (cm-3).

Time-resolved photoluminescence characterization of nm-sized silicon crystallites in SiO 2

Time-resolved photoluminescence (PL) decays have been measured for silicon nanocrystallites embedded in silicon dioxide. The nanocrystallites were formed by implanting Si ions at various doses into thermally grown SiO 2 films, followed by thermal annealing at 1100 °C. Silicon dioxide films of various thickness in the range 100–1000 Å were used. The results show that PL could be detected even for films as thin as 100 Å. The spectral and time-dependence characteristics are very similar to those of porous Si, exhibiting a clear stretched exponential behavior. The extracted parameters τ and β are, however, somewhat higher in value for the Si nanocrystallites. This may tentatively be attributed to a high degree of passivation of the Si nano crystallites in the oxide matrix. An observed spectral redshift for thinner oxides and higher implantation doses may be explained considering the excess Si concentration along the implantation profile. The stretched exponential decay suggests that carrier trapping and diffusion occurs between adjacent nanocrystallites, most likely in the form of excitons. © 1997 Elsevier Science S.A. All rights reserved.

Optical properties of passivated Si nanocrystals and SiOx nanostructures.

Thin films of Si nanoclusters passivated with oxygen or hydrogen, with an average size of a few nanometers, have been synthesized by thermal vaporization of Si in an Ar buffer gas, followed by subsequent exposure to oxygen or atomic hydrogen. High-resolution transmission electron microscopy and x-ray diffraction revealed that these nanoclusters were crystalline. However, during synthesis, if oxygen was the buffer gas, a network of amorphous Si oxide nanostructures (an-${\mathrm{SiO}}_{\mathit{x}}$) with occasional embedded Si dots was formed. All samples showed strong infrared and/or visible photoluminescence (PL) with varying decay times from nanoseconds to microseconds depending on synthesis conditions. Absorption in the Si cores for surface passivated Si nano- crystals (nc-Si), but mainly in oxygen related defect centers for an-${\mathrm{SiO}}_{\mathit{x}}$, was observed by photoluminescence excitation spectroscopy. The visible components of PL spectra were noted to blueshift and broaden as the size of the nc-Si was reduced. There were differences in PL spectra for hydrogen and oxygen passivated nc-Si. Many common PL properties between oxygen passivated nc-Si and an-${\mathrm{SiO}}_{\mathit{x}}$ were observed. Our data can be explained by a model involving absorption between quantum confined states in the Si cores and emission for which the decay times are very sensitive to surface and/or interface states. The emission could involve a simple band-to-band recombination mechanism within the Si cores. The combined evidence of all of our experimental results suggests, however, that emission between surface or interface states is a more likely mechanism. \textcopyright{} 1996 The American Physical Society.

Computer simulation of the thermocapillary convection in a non-cylindrical floating zone

The steady surface tension-driven flow (Marangoni convection) under gravity in an axisymmetric, non-cylindrical floating zone is numerically studied for two melts with different Prandtl numbers: a Si melt and NaNO 3 melt. It is shown that for small zones and moderate temperature differences, the real shape of the melt free surface can be approximated by the static meniscus of the fluid. The equations of motion and energy are solved in such a geometry by the integro-interpolating method. While the flow patterns in a non-cylindrical zone are very similar to those in a right circular cylindrical zone, the temperature fields differ. For the high Prandtl liquid, a heat transfer by convection is dominant in the interior of the zone. As it is expected, the gravity has a negligibly small effect on the convection and the temperature field in zones under consideration.