You-yuan Zhao

Steady-state photovoltaic and electroreflective spectra in Al/vanadyl phthalocyanine (VOPc, in phase II) /indium-tin-oxide (ITO) sandwich cell

Abstract The polycrystalline VOPc films in phase II have been fabricated on an indium–tin–oxide–glass substrate. X-ray diffraction pattern and visible absorption spectrum have been used to characterize the packing structure of VOPc molecules. The photovoltaic action spectrum of Al/vanadyl phthalocyanine (in phase II)/indium–tin–oxide (Al/ VOPc/ITO) sandwich cell under different modulation frequencies of illuminating light have been measured. The VOPc film acts as a p-type semiconductor. The photovoltage is mainly generated at the Al/VOPc interface. The charge transfer excitons and Frenkel excitons have been revealed by electric modulation reflective spectroscopic technique, both of them may play an important role in the photovoltaic process.

On the role of ion flux in nanostructuring by ion sputter erosion

The role of ion flux in Si(100) nanostructuring by normal-incidence Ar+ ion sputtering has been studied. The measured relationships of the Si lateral dot size versus ion flux, the surface roughness versus ion flux, and the surface roughness versus sample temperature with ion fluxes of 20 and 380 µA cm−2 all indicate that the value of the ion flux is decisive for the validity of the Bradley–Harper (BH) model in the nanostructuring of semiconductor single crystals. In this work, for Ar+ ion sputtering of Si(100) with ion energy of 1.5 keV, it is found that only beyond ~220 µA cm−2 is the BH model well applicable, while below that the Ehrlich–Schwoebel (ES) one tends to be involved. Our results suggest that the ES barrier effect is negligible under relatively high flux conditions, while it is substantial in the case of relatively low flux; for the BH model, the situation is just the reverse. Hence, caution should be exercised as regards the value of the ion flux when one tries to tune the semiconductor nanodot size following the BH model.

Modulation of the photoluminescence of SrTiO3(001) by means of fluorhydric acid etching combined with Ar+ ion bombardment

We report a method to modulate the photoluminescence (PL) of SrTiO3(001) at room temperature by fluorhydric (HF) acid etching and Ar+ ion bombardment. The PL of the virgin sample is in the blue/green range, which can be enhanced in intensity by a factor of 7.2 after being fully etched in HF acid with the peak shape being unchanged. Ar+ ion bombardment of SrTiO3 can blueshift the overall PL, and the peak maximum becomes centred at 403 nm. After fully etching the ion-bombarded sample in HF, the PL peak stays in the blue light range, but its intensity increases to 17.5 times that of the virgin one. Oxygen vacancies assumed to be produced on the lateral sides of SrTiO3 nanograins are responsible for the PL emissions, and their variations in number and nature are attributed to the PL modulation.

A combined approach to greatly enhancing the photoluminescence of Si nanocrystals embedded in SiO2

An approach combining back-?and front-side doping of Ce3+ in Si nanocrystals embedded in SiO2 (nc-Si:SiO2) with hydrogen passivation has been developed, which largely enhances the photoluminescence (PL) of Si nanocrystals. The sample of nc-Si:SiO2 was prepared via a phase separation process of SiO thin film at 1100??C. For the back-side doping, a SiO2 buffer layer was placed between the CeF3 layer and SiO one, thus Ce3+ doping could be accomplished without disrupting the phase separation of SiO. The front-side doping was then followed by evaporating CeF3 onto the front surface of the formed nc-Si:SiO2, followed by diffusion annealing at 500??C. The double-side doping enhanced the PL intensity of Si nanocrystals by a factor of 7.3. After hydrogenation of the double-side doped sample, a 14.6-fold increase in the PL intensity was finally achieved.

A multilayered approach of Si/SiO to promote carrier transport in electroluminescence of Si nanocrystals

The electroluminescence (EL) and photoluminescence of Si nanocrystals (Si-nc) from multilayered samples of Si/SiO are investigated. Si-nc are formed within Si and SiO layers after furnace annealing. It is found that the presence of Si interlayers creates extra carrier paths for EL emission. A comparative study is further performed on a multilayered Si/SiO sample and a single-layered one with Si and SiO homogeneously mixed. Both samples have the same ratio of Si to O and the same contents of Si and O. The multilayered sample is found to have higher EL intensity, less turn-on voltage, lower resistance, and higher current efficiency than the single-layered one. The results indicate that Si interlayers in Si/SiO may act as carrier channels, which promote carrier transport and enhance the EL emission of Si-nc.

Photoluminescence responses of Si nanocrystal to differing pumping conditions

Under a CW Ar+ laser beam excitation with wavelength of 496 nm, the relationship of photoluminescence(PL) intensity versus pumping power density was investigated for both multilayered Si nanocrystaldoped SiO2/SiO2 sample (or Si-nc:SiO2/SiO2) and single-layered Si-nc:SiO2 one. The threshold of pump power density for the transition from linear to superlinear relation of PL intensity versus pump power was ∼ 86 W cm−2 for the multilayered sample, while such a transition was not found for the single-layered one that possessed the same excess Si content within the power density range of this work. Using a pulsed Ti:sapphire laser (wavelength = 400 nm), a net optical gain coefficient was measured by means of variable slit length for the multilayered sample, which was 114 cm−1 at the pump fluence of 200 mJ cm−2, but only optical absorption was found for the single-layered sample. We attributed our results to the relatively high PL efficiency of the multilayered Si-nc:SiO2/SiO2.

Nonlinear photoinduced anisotropy and modifiable optical image display in a bacteriorhodopsin/polymer composite film

The nonlinear photoinduced anisotropy with large birefringence in a bacteriorhodopsin/polymer composite (bR/PC) film was observed. The contrast ratio, a ratio of the maximum to the minimum intensity of transmitted probe light through the bR/PC film within the linear gray scale range could reach ∼350:1. An all-optical image display in different colors was performed. The intensity of the transmitted signal could be modulated by adjusting the multibeam polarization states and intensities. Therefore, the positive image, negative image, and image erasure in display were demonstrated.

Transient photovoltaic properties in Al/tin‐phthalocyanine/indium–tin–oxide sandwich cell

The intensity dependence of the transient photovoltaic response in the nanosecond region and the spectral dependence of the continuous wave (cw) photovoltaic response in Al/α‐SnPc/ITO sandwich cell have been reported. The cw photovoltaic action spectrum is similar to the absorption spectrum. The magnitude, polarity, and response time of the transient photovoltage are found to be dependent on the intensity and wavelength of the incident light, which offers a potential application in the area of light‐controlled nonlinear optoelectronic detectors.

Spin reorientation induced by Ni atoms in Fe/Cu(001)

We determined the spin reorientation transition (SRT) in face-centered-tetragonal (fct) Fe/Cu(001) from out of plane to in plane, as induced by Ni-capping atoms, by observing the magneto-optical Kerr effect. The SRT takes place when the Ni-capping layer thickness exceeds a critical value dcNi, at which point the perpendicular anisotropy of the fct-Fe film becomes equal to the in-plane anisotropy of the Ni-capping layer. We found that dcNi decreases linearly with increasing Fe film thickness. By extrapolating to zero Ni thickness, the “true” critical thickness for the fct-Fe films is estimated to be 4.3 monolayers. This result is very close to the value obtained using Co-capping layers as reported in literature.

Optical properties of spectral hole-burning material Eu3+:Y2SiO5

In this paper, optical properties of Eu3+:Y2SiO5 have been investigated. 7FJ(J equals 0,1,2,3,4)