Nonergodicity of blinking nanocrystals and other Lévy-walk processes

We investigate the nonergodic properties of blinking nanocrystals modeled by a Lévy-walk stochastic process. Using a nonergodic mean field approach we calculate the distribution functions of the time averaged intensity correlation function. We show that these distributions are not delta peaked on the ensemble average correlation function values; instead they are W or U shaped. Beyond blinking nanocrystals our results describe ergodicity breaking in systems modeled by Lévy walks , for example, certain types of chaotic maps and spin dynamics to name a few.     

Fabrication and temperature-dependent photoluminescence spectra of Zn–Cu–In–S quaternary nanocrystals

A series of Zn-Cu-In-S nanocrystals （ZCIS NCs） are prepared and the optical properties of the ZCIS NCs are tuned by adjusting the reaction time. It is interesting to observe that the temperature-dependent photoluminescence （PL） spectra of the ZCIS NCs show a redshift with decreasing intensity at low temperature （50-280 K） and a blueshift at high temperature （318--403 K）. The blueshift can be explained by the thermally active phonon-assisted tunneling from the excited states of the low-energy emission band to the excited states of the high-energy emission band.     

Dielectric matrix imposed stress–strain effect on photoluminescence of Ge nanocrystals

Ge nanocrystals embedded in SiO₂ and Lu₂O₃ matrices were fabricated using the pulsed laser deposition method and investigated using high-resolution transmission electron microscopy, X-ray diffractometry and photoluminescence spectroscopy. X-ray diffractometry and Fullprof computer program clearly revealed the bond lengths of Ge nanocrystals embedded in Lu₂O₃ matrix is smaller than that in SiO₂ matrix, which can be attributed to the greater compressive stress exerted on Ge nanocrystals by the Lu₂O₃ matrix. The greater compressive stress will lead to much more defects induced at the interface of Ge nanocrystals and thus enhance the intensity of photoluminescence. The findings presented here indicate that the matrix environment of the nanocrystals plays a significant role in the photoluminescence property.     

Tuning defect-related photoluminescence of Ge nanocrystals by stress

Ge nanocrystals embedded in SiO₂ and Lu₂O₃ thin films were fabricated using a pulsed laser deposition method. Two dimensional finite element calculations and Raman spectra clearly revealed that the Ge nanocrystals certainly experienced greater compressive stress in a Lu₂O₃ thin film than in a SiO₂ thin film. This may lead to much more stress-relaxing defects at the interface of Ge nanocrystals embedded in a Lu₂O₃ thin film and thus enhances the intensity of defect-related photoluminescence. The findings presented here indicate that the matrix environment of the nanocrystals plays a significant role in the defect-related photoluminescence property.     

Frequency-stabilized semimonolithic frequency doubler with high output power

The frequency-doubled Nd:YAP laser with high out- put power is an important pumping source for quan- tum information, quantum optics, and nonlinear optics experiments[1-6]. Intracavity frequency-doubled[7-11] and external frequency-doubled lasers[12-18] are two usual methods to generate continuous second harmonic wave. For the former, the frequency-doubling nonlinear crystal and the active medium of the laser are put in the same resonant cavity, thus the process of frequency doubling possibly…     

Infrared photoluminescence from GeSi nanocrystals embedded in a germanium–silicate matrix

We investigate the structural and optical properties of GeO/SiO₂ multilayers obtained by evaporation of GeO₂ and SiO₂ powders under ultrahigh vacuum conditions on Si(001) substrates. Both Raman and infrared absorption spectroscopy measurements indicate the formation of GeSi nanocrystals after postgrowth annealing at 800°C. High-resolution transmission electron microscopy characterizations show that the average size of the nanocrystals is about 5 nm. For samples containing GeSi nanocrystals, photoluminescence is observed at 14 K in the spectral range 1500–1600 nm. The temperature dependence of the photoluminescence is studied.     

Measurement of acoustic field radiated by low frequency power ultrasonic transducer with laser-interferometer

1 IntroductionThe research of the characteristic of acoustic field radiated by ultrasonic transducer isvery important for the making of ultrasonic transducer and ultrasonic technology application.Among the research methods of the acoustic field such as mechanical, electrical and thermal,because optical method make no disturbance to the acoustic source and field as well as it can doabsolute measurement of the acoustic field parameters with the wavelength of the optic wavesit was highly regarded…     

Up conversion luminescence of Yb3+–Er3+ codoped CeO2 nanocrystals with imaging applications

The effects of Yb³⁺ doping on up conversion in Yb³⁺–Er³⁺ co-doped cerium oxide nanocrystals are reported. Green emission around 545 and 560 nm attributed to the ²H_11/2, ⁴S_3/2→⁴I_15/2 transitions and red emission around 660 and 680 nm due to ⁴F_9/2→ ⁴I_15/2 transitions under 975 nm excitation were studied at room temperature. Both green and red emission intensities increase as the Yb³⁺ concentration increases from 0%. Emission strength starts to decrease after the Yb³⁺ concentration exceeds a critical amount. The green emission strength peaks around 1% Yb³⁺ concentration while the red emission strength peaks around 4%. An explanation of competition between different decay mechanisms is presented to account for the luminescence dependence on Yb³⁺ concentration. Also, the application of up converting nanoparticles in biomedical imaging is demonstrated.     

Large-scale synthesis and photoluminescence properties of?SiC networks

By using a novel and low-cost microwave method, three-dimensional SiC networks have been synthesized in large-scale. The composition and structural features of the product were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The results show that the SiC networks consist of nanocable X-junction and Y-junction. Some nanocables are composed of 3C–SiC multicore encapsulated in single amorphous SiO₂ shell. The SiC networks emitted stable violet–blue light around 380 nm under 325-nm excitation. Compared to the emission peak of the SiC networks after etched and the reported results of 3C–SiC nanowires, the emission peak of the SiC networks shows significant blueshift. The origin of the photoluminescence for the SiC networks could be due to two possible reasons: the central crystalline SiC nanowires and amorphous SiO₂ shell. A two-step growth mechanism of the SiC networks was proposed based on the experimental characterizations. The successful synthesis of SiC networks is an important step in the development of SiC-based electronic devices and circuits.     

Vibration power flow in infinite stiffened-plate with force excitation applied on plate

1IlltroductionStthened-Plateisthetypicalunitinbuilt-upstructuressuchasships,airplanesandbuild-ings.Thereforeitisofprofoundsignificancetostudytheenergytransndssioninthemnotonlyforfurtherstudyonmorecomplicatedbuilt-upstructures,butalsofortheengineeringapplicationinthefuture.However,becauseofthecomplicatedboundaryconditionsofthesestructures,itisverydifficulttoobtainexactsolutionsofthesestructures.Goodnumericalresultsmnybegivenbythefiniteelementmethod,butitisofnouniversalsignificanceinexplainingt…     

Quantitative analysis of the self-absorption and reemission effects on the emission spectrum of photoluminescence in right-angle excitation–detection configuration

A theoretical approach based on differential radiative transport is proposed to quantitatively analyze the selfabsorption and reemission effects on the emission spectrum for right angle excitation–detection photoluminescence measurements,and the wavelength dependence of the reemission effect is taken into account.Simulations and experiments are performed using rhodamine 6G solutions in ethanol as model samples.It is shown that the self-absorption effect is the dominant effect on the detected spectrum by inducing pseudo red-shift and reducing total intensity;whereas the reemission effect partly compensates for signal decrease and also results in an apparent signal gain at the wavelengths without absorption.Both effects decrease with the decrease in the sample concentration and the propagation distance of the emission light inside the sample.We therefore suggest that diluted solutions are required for accurate photoluminescence spectrum measurements and photoluminescence-based measurements.     

Preparation and application of the 3C–SiC substrate to piezoelectric micro cantilever transducers

This study examines the fabrication process and mechanical properties of piezoelectric films with the substrate, which is made from silicon carbide. After depositing the PZT thick film on silicon carbide substrate and silicon substrate respectively, it was shown that silicon carbide substrate formed a stable interface with PZT thick film up to 950?°C, compared with silicon substrate. In addition, the dielectric constant of the PZT thick film sintered at 950?°C on a silicon carbide substrate was 843, and this value was about over 25 % improved value compared with that on a silicon substrate. A thick film piezoelectric micro transducer of a micro cantilever type was fabricated by using a multifunctional 3C–SiC substrate. The fabricated micro cantilever was a micro cantilever with multiple thin films on either silicon or silicon carbide substrate. The piezoelectric thick-film micro cantilever that was fabricated by using a SiC substrate showed excellent mechanical and thermal properties. The piezoelectric micro cantilever on the SiC substrate shows an excellent sensitivity towards the change of mass compared with the piezoelectric micro cantilever on the Si substrate.     

Surface–plasmon-coupled photoluminescence from CdS nanoparticles with Au films

The enhancement of surface–plasmon-coupled photoluminescence from CdS nanoparticles was examined for various thicknesses of sputtered Au films. The improved luminescence with thickness control of Au correlated well with the increased density of surface–plasmon states, which was modified by the plasmon-dispersion relation at the planar Au/PMMA interface. By annealing the Au films to form a rough surface morphology, the emission in the CdS nanoparticles was further enhanced by the improved excitation and coupling of the surface–plasmon modes.     

Synchrotron-radiation photoemission study of the ultrathin Ba/3C–SiC(111) interface

Electronic structure of the Ba/3C–SiC(111) interface has been detailed studied in situ in an ultrahigh vacuum using synchrotron radiation photoemission spectroscopy with photon energies in the range of 100–450 eV. The 3C–SiC(111) samples were grown by a new method of epitaxy of low-defect unstressed nanoscaled silicon carbide films on silicon substrates. Valence band photoemission and both the Si 2p, C 1s core level spectra have been investigated as a function of Ba submonolayer coverage. Under Ba adsorption two induced surface bands are found at binding energies of 2 eV and 6 eV. It is obtained that Ba/3C–SiC(111) interface can be characterized as metallic-like. Modification of both the Si 2p and C 1s surface-related components were ascertained and shown to be provided by redistribution effect of electron density between Ba adatoms and both the Si surface and C interface atoms.     

Intracavity frequency doubling of Yb-doped fiber laser with 540–550 nm tuning

The intracavity doubling of a tunable Yb-doped fiber laser is studied. The phase effects are observed, analyzed and compensated. A smooth wavelength dependence of the second harmonic is obtained in the wavelength interval 540–550 nm. The second-harmonic output is greater than 300 mW at an LD pump power of 18 W.     

Enhancement of Smith—Purcell radiation with surface-plasmon excitation

With the aid of a three-dimensional particle-in-cell code simulation,the enhancement of Smith-Purcell radiation with a surface-plasmon mode excited by a single electron bunch and by a premodulated electron beam is considered in the paper.In the simulation,the model is a grating covered by Ag film.The results demonstrate that when the surface-plasmon mode is excited by a single electron bunch,the maximum radiation occurs at an observation angle depending on the surface-plasmon frequency,and the radiation power can be enhanced more than ten times.And for pre-bunched electron beam excitation,when one of the harmonics of the bunching frequency is resonant with that of the surface-plasmon mode,the radiation power is twenty times more than that from a perfectly conducting grating excited by the same premodulated electron beam.     

Blue–green luminescent CdZnSeS nanocrystals synthesized with activated alkyl thiol

Semiconductor nanocrystals with blue–green luminescence are potentially useful in various applications, but the preparation has not been easy compared to regular semiconductor nanocrystals with emission in the orange–red range. In this research alloyed CdZnSeS nanocrystals with luminescence covering the wavelength range from 430 to 560 nm are obtained by a one-step method with the assistance of alkyl thiol compound 1-dodecanethiol, which serves both as the sulfur source and surface ligand. The luminescence of CdZnSeS nanocrystals can be tuned from blue to green by altering the Cd:Zn molar ratio. Besides, the amount of 1-dodecanethiol in the reaction mixture can influence the emission wavelength by restricting the growth of nanocrystals. The dual control of both particle composition and size has enabled the tuning of luminescence to cover the blue–green spectral window. This research presents a convenient method to synthesize nanocrystals with tunable blue–green emission; these materials can be useful in advanced technologies such as photovoltaics, lighting and display.     

Effects of annealing temperature on the electrical property and microstructure of aluminum contact on n-type 3C–SiC

The 3C-SiC thin films used herein are grown on Si substrates by chemical vapor deposition. A1 contacts with differ- ent thickness values are deposited on the 3C-SiC/Si （100） structure by the magnetron sputtering method and are annealed at different temperatures. We focus on the effects of the annealing temperature on the ohmic contact properties and mi- crostructure of A1/3C-SiC structure. The electrical properties of A1 contacts to n-type 3C-SiC are characterized by the transmission line method. The crystal structures and chemical phases of A1 contacts are examined by X-ray diffraction, Raman spectra, and transmission electron microscopy, respectively. It is found that the A1 contacts exhibit ohmic contact behaviors when the annealing temperature is below 550 ℃, and they become Schottky contacts when the annealing tem- perature is above 650 ℃. A minimum specific contact resistance of 1.8 × 10-4 Ω cm2 is obtained when the A1 contact is annealed at 250 ℃.     

Nonstationary spectroscopy of the 1–2.5 THz frequency band with the use of solid-state devices

We develop the principles of construction of a gas spectrometer based on nonstationary effects (freely decaying polarization, fast sweep, etc.) with the use of solid-state devices in the terahertz frequency band. A spectrometer based on quantum semiconductor superlattices (QSSLs), which is operated at up to 2.5 THz and meets the requirements of high and ultra-high resolution spectroscopy is implemented. As the radiation source in this spectrometer, we use a frequency synthesizer which was developed by the authors of this paper. The device is based on a phase-shift keyed Gunn oscillator and a QSSL frequency multiplier. As the receiving system, a QSSL mixer operated in harmonic mode was employed. The possibilities of harmonic generation by using the radiation of a spectrally pure Gunn oscillator and a QSSL frequency multiplier are studied with the help of the IR Fourier spectrometer “BOMEM” DA3.002 with Si-composite bolometer operated at a temperature of 4.2 K. The 45th harmonic at a frequency of about 6.5 THz was reached in the experiment. The spectral absorption lines of NH3 and CO at 2400017.632 and 1841345.506 MHz, respectively, were measured.