A simple and efficient technique for fabricating two-dimensional arrays of silicon nanotips by using electron beam
lithography (EBL) and reactive ion etching (RIE) was reported. For the RIE processes, two kind of reactive gases, CHF3
and SF6, were used as plasma etching source for Si. The experiment results indicate that the reactive ion etching
mechanism is different: the isotropic process for SF6 and anisotropic for CHF3. It is found that the mixed O2/SF6 plasma
etching can improve the properties of profile and surface of Si nanotips. Under the condition of ratio ~15%, the 10 nm
top size of Si nanotips was obtained.
We propose an approach to achieve single layer of Si nanodots arrays on insulating layer by using KrF pulsed excimer
laser irradiation on ultra-thin hydrogenated amorphous silicon films followed by thermal annealing. Under the suitable
fabrication conditions, the area density of formed Si nanostructures can be higher than 1011cm-2 as revealed by AFM
images. The size of formed Si nanodots is 3-4 nm for sample with initial a-Si:H film thickness of 4 nm. Room
temperature visible light emission can be observed from laser irradiated a-Si:H film after thermal annealing. The results
on electron field emission properties were also presented in this paper.
The effect of hydrogen plasma annealing on the microstructural transition from disorder to order in amorphous silicon film is studied in this paper. Combined with the Fourier Transmit Infrared spectroscopy, Raman scattering and absorption spectra, it is found that there exists two steps for the reaction between atomic hydrogen and Si network. It is shown that the hydrogen plasma treatment conditions strongly influence the microstructures of the amorphous Si films.
A novel method to prepare nanomolds is reported, which is using multilayer thin-film deposition technique. A-Si/SiNx multilayer thin film is deposited on Si substrate in the conventional plasma enhanced chemical vapour deposition (PECVD) system. Then the relievo structure of alternative strips and grooves can be obtained on the cleaved cross-section of multilayer thin film by selective etching process. The strips of the etched sample have smooth and vertical sidewalls with small roughness. Due to the slow deposition rate, the thickness of the sublayer, therefore the size of the strips and grooves can be controlled on the nanometer scale by altering deposition time. The smallest width we get by now is the 20nm strips and 20nm grooves.
Light emission variated from violet-blue to red-infrared is observed from a-Si:/SiO2 multilayers during step by step annealing. The peak of photoluminescence (PL) changes in the range between 417nm and 750nm under excitation of 325nm light as a function of annealing temperature, which is strong enough to be observed by naked eyes. Combined with Fourier Transform Infrared (FTIR) measurements, the correlation of the red PL excited by 488nm Ar+ laser and the structural evolution during the step by step annealing is detailed studied. The origins of different PL bands and the role of hydrogen and oxygen in microstructures of a-Si:/SiO2 multilayers are discussed
The layer-by-layer method is employed to prepare a-SiNx:H microcavity structure in a Plasma Enhanced Chemical Vapor Deposition (PECVD) chamber. Measurements of transmittance spectrum of as-grown samples show that the transmittance resonant peak of a cavity mode at 750 nm is introduced into the band gap of one-dimensional photonic crystal distributed Bragg reflectors based on hydrogenated amorphous silicon nitride. Also the PL measurements of a-SiNx:H microcavities are performed. There is a well agreement between the transmittance spectra and the PL of microcavity samples. In order to clarify the microcavity effects on the bulk a-SiNx:H, the PL of a λ/2-thick layer of bulk a-SiNx:H obtained under the same experimental conditions is presented. By comparison, a dramatic narrowing of emission linewidth and enhancement of PL intensity is observed. The wide emission band with 208 nm is strongly narrowed to 17 nm, and the resonant enhancement of the peak PL intensity is about two orders of magnitude with respect to the emission of the λ/2-thick layer of bulk a-SiNx:H. A linewidth of Δλ=17 nm and a quality factor of Q=50 are achieved in our one-dimensional a-SiNx photonic crystal microcavities.
We report a new method of preparing patterned nano-crystalline Si (nc-Si) by pulsed laser interference crystallization of a- Si:H thin films. A KrF excimer pulsed laser with wavelength 248 nm and pulse duration 30 ns is employed as a coherent ultra-violet beam source; a one-/two-dimensional (1D/2D) silica phase-shifting grating is used to form a high-contrast laser interference pattern behind it. During the laser treatment, the a-Si:H film is placed behind near contact with the phase grating. A transient thermal 1D/2D grid is then directly formed on the sample, leading to the local crystallization of the a-Si:H films and forming of nano- crystalline Si. The crystallinity of nc-Si films is verified by Raman scattering. Atomic force microscopy clearly shows a morphology of 1D/2D regular sub-micron patterns formed by locally crystallized stripes/dots, which are composed of densely gathered crystallites with a lateral size of approximately 50 - 100 nm and a height of approximately 10 - 20 nm. The interfaces between the crystallized and the amorphous zones are abrupt. Transmission electron micropsy demonstrates a lateral size distribution of nc-Si within the crystallized zones. This new approach has a potential application in the nano-electronics and nano-optoelectronics.
The synthesis and the characterization of the quantum dot quantum well (QDQW) system are described. The chemical synthesis and substitution method are used to synthesize the three-layered structure compound CdS/CuS/CdS which consists of a core of the CdS nanocrystal and a well of monolayers of CuS capped by monolayers of CdS acting as the outermost shell. The results of inductive coupled plasma mass spectroscopy (ICP-MS) measurement and the absorption spectra confirm the formation of the three-layered system CdS/CuS/CdS.
Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were fabricated in the plasma-enhanced chemical vapor deposition system by using silane (SiH4) and two kind of carbon sources, methane (CH4) and xylene (C8H10), respectively. The optical band gap of methane-made a-Si1- xCx:H was varied from 1.9 eV to 2.6 eV while that of xylene-made a-Si1-xCx:H could be extended to 3.5 eV. Fourier transform infrared spectra demonstrated the existence of aromatic ring in xylene-made a-Si1-xCx:H, which is much different from the carbon configuration of methane-made a-Si1-xCx:H. Visible light emission at room temperature was observed from xylene-made a-Si1-xCx:H films. The photoluminescence peak shifted from 630 nm (1.97 eV) to 450 nm (2.75 eV) when the optical band gap of samples increased from 2.3 eV to 3.5 eV. KrF pulse laser with wavelength of 248 nm was used to crystallize these two kinds of films at room temperature. For both samples the conductivities can reach 10-5S/cm and are enhanced by over four orders of magnitude.
The luminescent nanocrystal Ge embedded in a-SiO2 matrix was prepared by thermal oxidation of a-Si1-xGex:H films under conventional conditions. It was found that nc-Ge were formed through the selective oxidation of Si in a-GexSi1-x:H alloys and precipitation of Ge during oxidation. The average size of nc-Ge changed from 4 nm to 6 nm with the various conditions and Ge contents. Visible photoluminescence with peak energy 2.2 eV was observed from the oxidized samples where the nc-Ge have an average size of 4 nm. In order to control the size distribution of nc-Ge, we used multilayer films of a-Si:H/a-Si1-xGex:H instead of unlayered a-Si1-xGex:H alloy films to prepare nc-Ge embedded in SiO2 matrix. We found that the size of nc-Ge in perpendicular direction can be well confined by the SiO2 sublayers simultaneously formed.
Plasma enhanced chemical vapor deposited a-Si:H/a-SINx:H superlattices on silicon wafers were annealed by KrF excimer pulsed laser. Room temperature visible electroluminescence (EL) was successfully realized from these silicon-based superlattices structures with quite low threshold biased value 3.0V. It is a promising new way, in which all procedures are compatible with current silicon ULSI technology, to the realization of opto-electronic devices different from the porous silicon. Luminescent properties of samples with different laser annealing energy densities were compared and a preferred annealing condition was given.
We have reported for the first time on visible photoluminescence (PL) in crystallized a-Si:H/aSiNx:H multilayers structure by CW Ar ion laser annealing treatments. In this paper we present new results on visible PL and electroluminescence (EL) from crystallized a:SiH and its based multilayers by using KrF excimer pulse laser irradiating treatments. Strong and stable PL and EL have been observed by naked eye in both laser irradiated a-Si:H and a-Si:H/aSiNx:H multilayers samples at room temperature. The EL peak of crystallized a-Si:H/a-SiNx:H multilayers is blue shifted from 1.79 eV to 2.00 eV with narrowing the well layer thickness from 4 nm to 2 nm which suggests the origin of the light emission should be related to the quantum size effect.
Hydrogenated amorphous silicon carbide alloys were produced by using organic carbon source, xylene, instead of generally used methane. It was found that the optical band gap of present samples is significantly increased and reaches as high as 3.1eV with increasing the xylene gas fraction to 80 percent. The film configuration was also investigated and it was shown that there exist a lot of aromatic rings in the film network. An intense blue light emission has been observed from the present samples. The luminescence wavelength is peaked in the range of 490nm to 610nm, the origin of the light emission is briefly discussed in this paper.
We report a new type of binary-phase optical beam splitters combined with a two-dimensional Dammann grating and a Fresnel zone plate as one element which has both functions of beam splitting and focussing. Amorphous silicon nitride (a-SiNx:H) thin films deposited by plasma enhanced chemical vapor deposition (PECVD) method have been used for fabricating such an optical element. We have obtained 3 X 3 arrays of equal intensity and focused beams which generated by the beam splitter based on our own design. The relative distribution error of the intensity in each beam of the array is less than 5%.
We report two kinds of method for preparing luminescent silicon films with quantum crystallites (QCs) structures: (1) Using laser annealing technique to crystallize ultrathin amorphous silicon layers which were constructed in a-Si:H/a-SiNx:H multiquantum well (MQW) structures. (2) Applying the layer-by-layer deposition technique to the growth of silicon QCs by varying the hydrogen plasma exposure time. The novel structures of these two types of QCs films were characterized by X-ray diffraction and Raman scattering spectroscopy. The room temperature visible photoluminescence (PL) from Si QCs with size of 4 nm or less has been observed in most of samples.
Ge nanocrystals embedded in a-SiNx matrix were prepared by the PECVD method with SiH4, GeH4 and NH3 mixed in H2 plasma and followed the thermal-annealing treatment, which was based on the preferential chemical bonding formation of Si-N and Ge-Ge. The samples were characterized by infrared absorption, X-ray diffraction, Raman scattering spectra and TEM micrograph. Visible photoluminescence was observed at room temperature with the PL peak at about 560 nm and the linewidth about 0.45 eV. We are temporarily using the quantum confinement model to explain the PL mechanism.
The a-Si:H based compositional periodic and quasiperiodic superlattices (SLs) have been investigated by low-angle x-ray diffraction, Auger electron spectrum (AES), and cross-section TEM micrograph experiments. We show that most of the structures have sharp and smooth interfaces to better than 6 angstrom. The results also indicate that the peculiarities of quasiperiodic a-Si:H SLs are very different from those of periodic structures. The quantum size effects in a-Si:H SLs has been verified by the wavelength differential absorption (WDA) spectrum measurements.
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