Guangsheng Fu

Influence of pulse repetition rate on the average size of silicon nanoparticles deposited by laser ablation

To investigate the influence of pulse repetition rate on the average size of the nanoparticles, nanocrystalline Si films were prepared by pulsed laser ablation in high-purity Ar gas with a pressure of 10 Pa at room temperature, under the pulse repetition rates between 1 and 40 Hz, using a nanosecond laser. Raman, X-ray diffraction spectra, and scanning electron microscopy images show that with increasing pulse repetition rate, the average size of the nanoparticles in the film first decreases and reach its minimum at 20 Hz, and then increases, which may be attributed to the nonlinear dynamics of the laser-ablative deposition. In our experiment conditions, the duration of the ambient restoration, a characteristic parameter being used to distinguish nonlinear or linear region, is about a few seconds from the order of magnitude, which is consistent with the previous experimental observation. More detailed model to explain quantitively the observed effect is under investigation.

Square pattern formation in a gas discharge system

The square pattern is observed in dielectric barrier discharge in argon for the first time. The hexagon pattern and the mixture of hexagon and square structure are also observed. The square pattern can remain stable for several tens of minutes. The spatio-temporal dynamics of square pattern formation is investigated by optical method. The measurement results show that the square pattern is an interleaving of two square patterns, which is the reason of the stability of square pattern.

Effect of gas pressure on the synthesis of carbon nitride films during plasma-enhanced chemical vapor deposition

Carbon nitride thin films have been synthesized on Si(100) substrate by d.c.-glow discharge plasma enhanced hot filament chemical vapor deposition. The effect of gas pressure on the properties of the deposited films was investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The influence of gas pressure on the growth mechanism of carbon nitride films has been discussed and it was concluded that higher pressure is favorable to the synthesis of crystalline carbon nitride.

Bipolar resistive switching behavior of La0.5Sr0.5CoO3−σ films for nonvolatile memory applications

Polycrystalline La0.5Sr0.5CoO3 (LSCO) film is prepared on Pt/Ti/SiO2/Si substrates by pulsed laser deposition in order to explore the resistive switching behavior of the Ag/LSCO/Pt structure. It is found that the oxygen stoichiometric LSCO (LSCO-2) structure does not possess distinct rectifying behavior, while the oxygen deficient La0.5Sr0.5CoO3−σ (LSCO-1) structure exhibits very stable bipolar resistive switching behavior, which is attributed to the oxygen vacancies in the LSCO film. The resistance ratio between high resistance state and low resistance state is about 100, which can be maintained up to 200 cycles and 25 h with no observable degradation, indicating that the Ag/LSCO-1/Pt device possesses very good endurance and retention characteristics. Moreover, the current-voltage characteristic of Ag/LSCO-1/Pt heterostructure can be well explained by the space-charge-limited conduction mechanism. The present results provide essential evidence for the analysis of the switching mechanism and evaluation of...

Textured diamond films growth on (100) silicon via electron-assisted hot filament chemical vapor deposition

Textured (100) diamond films are successfully grown on single-crystalline (100) silicon substrate by electron assisted hot filament chemical vapor deposition from a gas mixture of methane and hydrogen. The effects of various parameters have been studied. The optimal growth conditions are obtained and the oriental growth character is discussed.

Dissociation process of CH4/H2 gas mixture during EACVD

The dissociation process of CH4/H2 gas mixture during EACVD has been investigated using Monte Carlo simulation for the first time. The electron velocity distribution and H2 dissociation were obtained over a wide range: 100<E/N<2000 Td. The variation of CH4 dissociation with CH4 concentration in the filling gas has been simulated. The electron velocity profile is asymmetric for the component parallel to the field. Most electrons possess non-zero velocity parallel to the substrate. The number of atomic H is a function of E/N. There are two peaks at E/N=177 Td and 460 Td. The appropriate E/N is suggested to be 500–800 Td for low temperature deposition. The main diamond growth precursor is proposed to be CH3 and CH3+.

Investigation of Pt/Pb(Zr0.2Ti0.8)O3/Ti-Al-O/Si heterostructure as metal/ferroelectric/insulator/semiconductor

Pt/Pb(Zr0.2Ti0.8)O3(PZT)/Ti-Al-O(TAO)/Si heterostructure has been fabricated as the metal/ferroelectric/insulator/semiconductor structure. It is found that PZT film is polycrystalline, and TAO film is amorphous. Moreover, the memory windows are 3.4u2009V, 5.9u2009V, 8.6u2009V, and 11.2u2009V corresponding, respectively, to the voltages of 10u2009V, 12u2009V, 14u2009V, and 16u2009V, indicating that the memory window increases linearly with the increase of applied voltage, which can be attributed to the increase of the polarization and coercive voltage of the Pb(Zr0.2Ti0.8)O3 film. The leakage current density of the device, measured at 15u2009V, is 3.54u2009×u200910−6 A/cm2, is favorable for the device application.

Angular distribution of damping coefficient of ablated particle in pure He, Ne, and Ar gases

To investigate the angular distribution of damping coefficient of ablated particle under various ambient gases, nanocrystalline silicon films are systemically deposited on a circular substrate by pulse laser ablation in pure He, Ne, and Ar gases, respectively. Scanning electron microscopy images and Raman and X-ray diffraction spectra indicate that the average size of Si nanoparticles decreases with the increase of the departure angle between the film and the plume, and Ne gas induces the smallest and most uniform Si nanoparticles in size among all the three gases. Further theoretical simulation demonstrates the bigger the departure angle, the smaller the damping coefficient of ablated particle, and the damping coefficient in Ne gas is largest for the same angle, implying the most effective energy transfer between Si and ambient atoms.

Dependence of the photoluminescence from silicon nanostructures on the size of silicon nanoparticles

The size dependence of photoluminescence (PL) from nanostructure semiconductors is examined. Considering the dependence of PL on both the silicon nanoparticles (Si NPs) sizes and their dispersion, we incorporated quantum confinement effects along with the effects of localized surface states to obtain an analytical expression for the PL spectra of silicon nanostructures. In order to obtain an insight into the effects of various parameters influencing the PL spectral profile in silicon nanostructures, we computed the PL spectra using relevant numbers in the expression. The computer-simulated results show (i) a marked deviation of PL spectrum from the normal distribution at higher energies due to the increase in oscillator strength with the decreasing mean Si NP size, (ii) The peak position redshifts and the peak intensity reduces with an increase in the standard deviation, and (iii) the luminescence peak blueshifts as the mean Si NP size decreases. To test our model, the Si NPs embedded in silicon nitride films were prepared by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique using the H2 diluted SiH4 and N2 as reactant gas sources. The simulated PL spectra fit the experimental one rather nicely. And our results can explain the reported experimental observations on the luminescence from Si NPs.

The dynamic characteristics of sulfur sensitization centers in T-grain AgBrI microcrystals

The microwave absorption dielectric-spectrum technique was used to study the decay kinetics of the free photoelectrons and shallow-trapped electrons in the sulfur-sensitized T-grain AgBrI crystals prepared under different sensitization times. It was found that, from the dependence of the kinetic behavior of photoelectrons in the sensitized T-grain AgBrI emulsions, the optimal sensitization time was 45min. With an increase of the sensitization time, the trap effect of the sulfur sensitization centers varies from the hole trap to shallow electron trap, and to deep electron trap, corresponding to the sulfur sensitization centers in the forms of a monomer, dimmer, and cluster of Ag2S, respectively. The range of the shallow electron trap depth traps was determined to be 0.26–0.27eV.