Search

Transition metal oxides are a class of functional materials widely used in optoelectronics, spintronics, and memory technology. The oxygen stoichiometry of these oxides plays a vital role in determining their electronic, optical, and thermal properties. Post-growth annealing in ozone has shown to be effective in modifying these properties. Here, we choose NiO, an antiferromagnetic Mott insulator in perfect stoichiometry, as an example to show that its stoichiometry can be tuned continuously in a broad range by the control of the oxidation power during growth or a post-growth topotactic reduction process. The bandgap of the as-processed NiOx films was modulated in accordance with their resistivity, lattice constant, and Ni chemical valence. This method can be readily applied to other transition metal oxides for the optimization of their properties. [ABSTRACT FROM AUTHOR]

Proton beams with energies beyond 100 MeV are essential for a wide range of applications, including modern cancer therapies. The generation of high-energetic protons beyond 100 MeV in experiments using PW-level laser pulses normally requires laser energies of 10–200 J. We propose an efficient hybrid scheme using tabletop (tens of TW) dual-laser pulses with laser energy of a few Joules with tandem solid density and near-critical density targets. The results of a 2D particle-in-cell simulation show that the combination acceleration scheme of the radiation pressure acceleration (RPA), laser wakefield acceleration (LWFA), and target normal sheath acceleration (TNSA) with the dual-pulses can considerably enhance the maximum proton energy to ∼220 MeV, which is nearly three times of the proton energy achieved by the RPA or the RPA-LWFA-TNSA using a single laser pulse. [ABSTRACT FROM AUTHOR]

To be suitable for integrated optical devices, (Pb,La)(Zr,Ti)O3 (PLZT) ferroelectric thin films require high crystalline quality, low surface roughness, high optical index, and high transparency. In this paper, PLZT thin films have been grown in situ on indium tin oxide (ITO) coated quartz substrates by rf magnetron sputtering. X-ray diffraction, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate the structural properties of these PLZT films. The results show that the ferroelectric films exhibit satisfying crystallization with the highly (110)-oriented growth from 550 °C, and the surface roughness value (∼3.1 nm) in studied films is within the optimum range so that a low optical loss can be obtained. High quality PLZT ferroelectric thin films were further investigated by electrical measurements, showing that the remnant polarization Pr and coercive field Ec are approximately 11.3 μC/cm2 and 56.2 kV/cm, respectively. Spectroscopic ellipsometry (SE) was employed to characterize the depth profiles, the microstructural inhomogeneities (void and surface roughness), refractive index n, and extinction coefficient k of the PLZT film. In the analysis of the measured SE spectra, a three-layer Lorentz model with four oscillators was adopted to represent the optical properties of the PLZT film. In this model, the film was assumed to consist of two layers (a bottom bulk PLZT and a surface layer composed of bulk PLZT as well as void). Good agreement was obtained between the measured spectra and the model calculations. The film thickness measured from SEM is consistent with that obtained by SE, while the root mean square roughness determined by AFM is also close to our fitted effective surface layer thickness obtained by SE. The PLZT thin film on ITO-coated quartz substrate is highly transparent in the visible near infrared wavelength region, and the band gap energy Eg is estimated to be 3.54 eV. The experimental results above tend to demonstrate the suitability of the PLZT films in situ grown on ITO/quartz substrates for optical applications. [ABSTRACT FROM AUTHOR]

Ferroelectric (Pb0.92La0.08)(Zr0.65Ti0.35)O3 (PLZT) film with good surface morphology and perovskite structure was grown in situ on quartz substrate by radio-frequency magnetron sputtering at 650 °C. The fundamental optical constants (the band gap energy, linear refractive index, and absorption coefficient) of the film are obtained by optical transmittance measurement. The third-order nonlinear optical properties of the films were investigated by the Z-scan technique. The magnitude and sign of the nonlinear refractive index n2 were determined, as was the negative sign, which indicated a self-defocusing optical nonlinearity. A large nonlinear refractive index as high as 1.21×10-6 esu is displayed in the film. All results show that PLZT ferroelectric thin film has potential applications in nonlinear optical devices. [ABSTRACT FROM AUTHOR]

(Pb,La)(Zr,Ti)O3 (PLZT) thin films were grown on Pt/Ti/SiO2/Si and fused quartz substrates by radio-frequency magnetron sputtering at 650 °C. X-ray diffraction analysis shows that the PLZT films are polycrystalline with (100)-preferential orientation. The Al/PLZT/Pt capacitors have been fabricated and show good ferroelectric properties with the remanent polarization of 24.3 μC/cm2 and coercive field of 142 kV/cm. The leakage current density is only about 0.86×10-7 A/cm2 at 200 kV/cm. The energy gap Eg of the films is estimated to be about 3.54 eV by optical transmittance measurements. Their fundamental optical constants are obtained by a Filmetrics F20 reflectance spectrometer (F20). These results show that the PLZT ferroelectric thin films are promising materials for optoelectronic devices. [ABSTRACT FROM AUTHOR]

We propose a method to generate a Bessel beam using cross-phase modulation based on the thermal nonlinear optical effect. The thermal nonlinear medium is shown to have the ability to vary a Gaussian beam (probe beam) into a hollow beam when the medium is illuminated with a counter-propagating Gaussian beam (pump beam). It is demonstrated that this method has no restriction to the probe beam wavelength. Moreover, the generated Bessel beam exhibits superior non-diffraction properties during propagation and self-healing after encountering an obstruction on the beam path. The parameters of the beam can be easily adjusted by both the pump beam power and the sample concentration. The merits of variable parameters, no requirement for input beam wavelengths, simple setup, and low-cost would make this method significant in a variety of applications, especially in those areas where the parameters of the Bessel beam need to be easily adjusted without changing the setup. [ABSTRACT FROM AUTHOR]

The power conversion efficiencies of organic solar cells fabricated with Ag and Ti nanoparticle arrays using nanosphere lithography are studied. The Ag nanoparticle array exhibits a broad absorption spectrum peaked at 420 nm, which spectrally overlaps with the absorption band of the organic absorbing layer centered at 520 nm, while no peak presented for the Ti nanoparticle array. Power conversion efficiencies by the solar cells with Ag and Ti nanoparticle arrays are 2.42% and 1.68%, respectively. This efficiency improvement is proposed to originate from the strong surface plasmon resonant scattering of visible light by Ag nanoparticle arrays. [ABSTRACT FROM AUTHOR]

An approach is presented to backward project an acoustic harmonic wavefield to the vibrating cylindrical source of the field. The approach is based on expanding the known pressure field on a cylindrical surface of the fluid into a series of circumferential modes with axially varying coefficients. After Fourier transforming the coefficients, each mode can be back projected to the source via the use of a backward propagator in the transform domain. As a result of the use of FFT methods the modal characteristics of the backward projected acoustic nearfield and/or the radial surface velocity of a finite cylindrical vibrator with a general velocity can be readily investigated. Numerical results are presented to illustrate the types of numerical problems and the resolution which can be obtained via the use of the method. [ABSTRACT FROM AUTHOR]

A numerical approach is presented to evaluate the surface intensity and radiation loading on a finite cylindrical surface with a known harmonic radial velocity distribution. The approach is based on a combined FFT and Green's function method [P. Stepanishen and H. W. Chen, J. Acoust. Soc. Am. Suppl. 1 73, S22 (1983)]. Surface pressure, intensity, and radiation loading are rapidly obtained via the use of standard FFT methods. The spatial fluctuations of the surface pressure and intensity for a known velocity distribution can thus be readily investigated. Numerical results are presented to illustrate the spatial variation of surface pressure and intensity as a function of axial mode shape, circumferential mode number, and frequency. Negative intensity regions and edge effects are clearly observed in the results at low frequencies. [ABSTRACT FROM AUTHOR]

This paper presents an extension of earlier works in investigating the acoustic nearfield of planar harmonic vibrators via the use of FFT methods [P. Stepanishen and K. Benjamin, J. Acoust. Soc. Am. 71, 803-812 (1982)]. In the present paper, a numerical approach is presented to evaluate the acoustic nearfield of baffled cylindrical vibrators with specified harmonic radial velocity distributions. The approach is based on the use of a combined Green's function and FFT method. The acoustic field is first represented in terms of a Fourier transform of the specified radial velocity and the resulting spectral representation is then rapidly evaluated via the use of FFT methods to obtain the spatial characteristics of the acoustic field. Extensive numerical results are presented to illustrate the spatial characteristics of the acoustic fields of finite length vibrators with axisymmetric and nonaxisymmetric distributions. [ABSTRACT FROM AUTHOR]