Silver (Ag) island films have been prepared by pulsed laser ablation in vacuum using a XeCl excimer laser. The effects
of the number of ablation pulses, the temperature and time of post-annealing on morphology and surface plasmons
properties of the prepared Ag island films were investigated by extinction spectra and scanning electron microscopy. It is
found that the films deposited with the ablation pulses of 60 or less are isolated Ag nanoparticles and the mean size of
the nanoparticles increases monotonically with increasing the number of ablation pulses. Further increase of the number
of ablation pulses up to 240, quasi-percolated Ag films are obtained, and for 600 pulses or more, continuous films will be
formed. Extinction spectra results show that localized surface plasmons (LSPs) are supported by the Ag island films,
while propagating surface plasmons are supported by the continuous Ag films. The LSPs of Ag island films consist of inplane
and out-of-plane modes. By changing the ablation pulse numbers and annealing conditions, the longitudinal and
transverse dimensions of Ag islands could be adjusted, and then the peak positions and peak widths of in-plane and outof-
plane LSPs resonance modes could be effectively controlled.
We report the photoluminescence enhancement of nc-SiC films by coating nanostructure Ag films and study the
influences of surface plasmon on photoluminescence properties by varying spacer thickness. PL curves of the samples
deposited with different thickness of α-SiNx present two PL peaks which are contributed to the interference in the films
and surface plasmon resonance, respectively. The PL intensity of the sample coated with Ag film is quenched due to
combination of Forster nonradiative process and coherent photonic mode reduction in nc-SiC films, while the PL
intensity of the samples with inserted spacer α-SiNx is enhanced because of the surface plasmon resonance.
The Si-rich SiNx:H films have been prepared by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique. Parts of the samples have been post-annealed at 800 °C in the H2, FG (10%H2 in N2), and N2 ambient, respectively. Fourier transform infrared spectroscopy (FTIR) and the optical absorption spectroscopy have been used to investigate the influence of different annealing environment on the structural and optical properties of the films. After the thermal annealing process, there is a significant increase of Si-N bonding density. Meanwhile, the band related to hydrogen (N-H and Si-H) decreased which indicates that the hydrogen is effused out of the films during the annealing treatment. The Si-sH stretching vibrations can be divided into three components by Gaussian distribution; the Si-H absorption band at different wave numbers corresponds to different configurations. The changes of the three peaks contributions decreased indicate that the configurations of the Si-H stretching vibrations band occurs restructuring in the different annealing environments. Furthermore, the investigation of the optical absorption spectroscopy suggests that the band gap Eg decreased after the thermal annealing process. The decreased optical gap should be related to the loss of hydrogen and the slightly increase in the mean size of silicon nanoparticles, which is in good agreement with that of the hydrogen bonding structure.
Protocrystalline silicon/amorphous SiC multilayer films were fabricated by helicon wave plasma enhanced chemical vapour deposition (HW-PECVD). Atom force microscopy, Raman scattering and optical absorption measurements were used to analyze the microstructure and optical properties of the multilayer films. Experiment analyses reveal that through inserting transient a-SiC layer into film depositing process, well-controlled pc-Si:H films have been obtained in the growth condition of the μc-Si:H. The optical gap is observed being tuned from 2.15 to 2.43 eV by varying single pc-Si:H layer thickness. Such multilayer structure should have potential application in constructing high efficiency and stable Si-based solar cells.
Hydrogenated nanocrystalline SiC films have been deposited by using helicon wave plasma enhanced chemical vapor deposition (HW-PECVD) in H2, SiH4 and CH4 gas mixtures at different RF powers. Their structural and optical properties have been investigated by Fourier transform infrared absorption (FTIR), atomic force microscopy (AFM) and ultraviolet-visible (UV-VIS) transmission spectra. The results indicate that RF power has an important influence on properties of the deposited films. It is found that in a 300 °C low substrate temperature, only amorphous SiC can be deposited at the radio frequency (RF) power of lower than 400 W, while nanocrystalline SiC can be grown at the RF power of equal to or higher than 400 W. The analyses show that the high plasma density of helicon wave plasma source and the high hydrogen dilution condition are two key factors for depositing nanocrystalline SiC films at a low temperature.
Nanocrystalline silicon carbide (nc-SiC) thin films were deposited by helicon wave plasma enhanced chemical vapor
deposition (HW-PECVD) technique at different hydrogen dilution ratio (RH). The PL peak energy and intensity were
systemically analyzed using photoluminescent (PL) and photoluminescent excitation (PLE) methods. As a whole, the PL
intensity shows an increasing trend and the PL peak energy presents continuous blue shifts with increasing hydrogen
dilution ratio. In addition, it is found that the spectra band of samples deposited at low RH are composed of two
components, the high energy band comes from quantum confinement effect and the low energy band is related to
radiation of surface defect. The low energy band has a decreasing trend with increasing hydrogen dilution ratio and even
disappears finally at high RH. We explain dependence of PL properties in terms of the variation of film microstructure
induced by hydrogen dilution during film deposition. The increasing of PL intensity and the decreasing of the low energy
band can both be accounted by the microstructure improvement. The decrease of PL peak energy is related to the size
decrease of SiC nanocrystals.
Structural and optical properties of the B doped, P doped and B-P codoped silicon nanocrystals have been investigated
using first-principles calculations. It was found that the codoped system tends to reduce structure distortion around B/P
impurities compared with B/P single doped systems and shows a decreased energy band gap compared with undoped
system due to there being electronic compensating effect. In addition, the spatial behaviors of density of states indicated
that codoping possesses a tendency of confining the electrons and holes around the B/P impurities, which suggests the
possibility of increasing electron emission transition rates between donor and acceptor. Moreover, the dielectric
functions calculation demonstrated that the optical absorption of codoped silicon nanocrystals have the characteristic of
the energy band gap being redshifted with respect to the undoped case together with peak appearing at lower energy side.
Thermal annealing of amorphous SiC films deposited by pulsed laser ablation is performed at different temperature of 900-1050°C in vacuum condition. The structural and optical properties of the obtained films have been investigated by Micro-Raman scattering, UV- VIS transmission, and atomic force microscopy (AFM). It has been observed that the Raman bands related to SiC TO and LO modes appear and gradually shift to higher energy with increasing the annealing
temperature, indicating that the crystallization of SiC occurs in the post-annealed films and their crystallinity increases. AFM results show that the post-annealed film is composed of compact nanoparticles and presents a rougher surface with respect to the as-deposited film. Optical band gaps deduced from UV-VIS transmission spectra are continuously increased from 1.90 eV for as deposited films to 2.45 eV of the annealed films at temperature of 1050°C. The formation of SiC nanocrystallines and the improvement of crystallinity can account for this blue-shift effect of the optical band gap.
Silicon carbide thin films are prepared by helicon wave plasma enhanced chemical vapor deposition (HW-PECVD) using a gas mixture of silane, methane, and hydrogen at a constant gas flow ratio under varying negative DC bias voltage. The structural and optical properties of the deposited films are investigated using Fourier transform infrared spectra (FTIR), ultraviolet-visible (UV-VIS) transmission spectra, and scanning electron microscopy (SEM). It is found that by applying the moderate bias on the substrates to accelerate the energetic ions, nanocrystalline silicon carbide can be deposited at lower onset temperature than without bias, and the crystalline grain size of the films is smaller and more uniform. The mechanism about the enhancing effect of the bias is discussed on the performance of positive ions in the plasma.
Hydrogenated amorphous silicon nitride (a-SiNx:H) thin films are deposited by helicon wave plasma chemical vapor deposition technique. The structural and photoluminescence properties of these films have been characterized by X-ray photoelectron spectroscopy (XPS), Photoluminescence (PL) and ultraviolet-visible (UV-VIS) spectroscopy. It is shown that the silicon atom bonds exist in the Si-Si and Si-N configurations and the amorphous silicon regions appear separately in the Si-rich a-SiNx films. All the PL spectra of the deposited films manifest itself as several interference peaks superposed on an energy-dependent Gaussian distributed band. The PL and absorption results of the deposited films with different nitrogen content support that the luminescence of the Si-rich a-SiNx:H films is related to the photo-excited carriers radiation process in the separated amorphous silicon potential well region, while the blue shift of PL main peaks and the enlargement of PL intensity with increase nitrogen content are ascribed to the size reduction of amorphous silicon separated regions and the enhancement of confinement effect.
Nanocrystalline cubic silicon carbide thin films have been fabricated by helicon wave plasma enhanced chemical vapor deposition (HWP-CVD) on Si and Corning 7059 glass substrates using the mix plasma of SiH4, CH4, and H2. The effect of negative radio-frequency (rf) bias voltage on the optical and structural of the deposited hydrogenated nanocrystalline SiC (NC-SiC:H) films has been investigated by Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UVVIS)
transmittance spectroscopy, and photoluminescence (PL) spectroscopy. It is found that with increasing the negative rf substrate bias, the NC-SiC:H thin films become denser and have fewer defects. The PL measurement indicates that all the deposited film present a strong light emission at the room temperature under an excitation of the 370 nm line of a Xe lamp. The blue-green PL peak can be ascribed to quantum confine effect of small size SiC nanocrystal in the film.
Silicon carbide thin films have been deposited by helicon wave plasma enhanced chemical vapor deposition (HW-PECVD) technique under the conditions of variant deposition temperatures from 300 to 600°C. Silane, methane and hydrogen are used as reactive gas. The structural properties of the deposited films are characterized using Fourier transform infrared (FTIR), scan electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates that the onset of growing nanocrystalline SiC films at low substrate temperature is closed related with the high plasma ionization rate of helicon wave plasma and the condition of low working gas pressure and strong hydrogen dilution in experiment. The SEM and TEM measurements confirm that the structure of the deposited films is nanocrystalline SiC grains embedded in amorphous matrix and the size of the crystalline gains increases with substrate temperature.
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