摘要:

A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.366536

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Recent advances in atomic-force microscopy have moved beyond the original quasistatic implementation into a fully dynamic regime in which the atomic-force microscope cantilever is in contact with an insonified sample. The resulting dynamical system is complex and highly nonlinear. Simplification of this problem is often realized by modeling the cantilever as a one degree of freedom system. This type of first-mode approximation (FMA), or point-mass model, has been successful in advancing material property measurement techniques. The limits and validity of such an approximation have not, however, been fully addressed. In this article, the complete flexural beam equation is examined and compared directly with the FMA using both linear and nonlinear examples. These comparisons are made using analytical and finite difference numerical techniques. The two systems are shown to have differences in drive-point impedance and are influenced differently by the interaction damping. It is shown that the higher modes must be included for excitations above the first resonance if both the low and high frequency dynamics are to be modeled accurately. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365935

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report a new method of achieving tip–sample distance regulation in an atomic force microscope (AFM). A piezoelectric quartz tuning fork serves as both actuator and sensor of tip–sample interactions, allowing tip–sample distance regulation without the use of a diode laser or dither piezo. Such a tuning fork has a high spring constant so a dither amplitude of only 0.1 nm may be used to perform AFM measurements. Tuning-fork feedback is shown to operate at a noise level as low as that of a cantilever-based AFM. Using phase-locked-loop control to track excursions in the resonant frequency of a 32 kHz tuning fork, images are acquired at scan rates which are fast enough for routine AFM measurements. Magnetic force microscopy using tuning-fork feedback is demonstrated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365936

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The theoretical performances of a split detector and a lateral effect detector used as a position sensitive device in the optical beam deflection method are compared. It is shown that the limit to the resolution in both cases is essentially equal. The possibility of improving the resolution in angle deflection by reflecting the beam from a cylindrical mirror, as was recently proposed by A. Yarai, Y. Fukunaga, K. Sakamoto, and T. Nakanishi [Jpn. J. Appl. Phys.33, 3251 (1994)] is also explored. It is shown that using a cylindrical mirror does not result in a smaller theoretical limit to the resolution. However, it does improve the resolution in some cases and may have practical uses. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365941

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new numerical technique to compensate for the dynamical effects in experimental x-ray intensity profiles is proposed and implemented to enhance the crystal-lattice strain determination algorithm which is applicable to x-ray diffraction data collected from nearly perfect crystals. A practical procedure for the preliminary treatment of experimental data exhibiting dynamical features was tested using three sets of data representing different cases of near-surface distorted layers. It is shown that the influence of the substrate peak on the overall diffraction pattern can be removed by an iterative modification of the very vicinity of the Bragg region in experimental intensity profile. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365937

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The ordinary and extraordinary refractive indices of rutile(TiO2)have been measured as a function of temperature and wavelength within the ranges 30–160 °C and 454–1330 nm, respectively, by using a prism coupling reflectivity setup. The measurements have been done with regard to the accurately known indices of a congruentLiNbO3substrate. The index values are given with the same accuracy as that of the substrate taken as reference, i.e., ±0.001 at room temperature and ±0.003 at 160 °C. The room temperature values are coincident with those previously published by other workers. Sellmeier-like equations which include wavelength and temperature as variables within the studied ranges are given for both indices. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365938

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Quasi-phase-matched waveguides are known to degrade when generating high intensity short wavelength light. Photoinduced changes in the refractive indices can lead to reduced efficiency by broadening phase-matching curves or inducing power dependent losses. In this work a pump-probe technique was used to investigate photorefractive effects in nonlinear optical waveguides. A strong two photon photorefractive effect in single domain and Ti-poledLiNbO3was found that is considerably reduced in electric field periodically poledLiNbO3and is absent in Rb-exchangedKTiOPO4.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365939

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

LiNbO3single crystals with a composition close to stoichiometry are grown by using a double crucible Czochralski method equipped with an automatic powder supply system. The photorefractive properties are compared with those ofLiNbO3crystals grown from the congruent composition melt. Two beam coupling experiments show that both nondoped and Fe-doped stoichiometric crystals exhibit stronger photorefractive effect than the Fe-doped congruent crystals.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365863

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Proton-exchangedLiNbO3optical waveguides(HxLi1−xNbO3)exhibit very complex structural behavior which is different from that known for their powders. Seven crystallographic phases have been identified in theHxLi1−xNbO3layers. A method to determine the proton concentration in different phases has been proposed. Correlation between the crystal structure, hydrogen concentration, and the ordinary and extraordinary refractive indices has been experimentally determined allowing one to explain some optical phenomena observed and to predict the characteristics of a great variety of proton exchanged waveguides. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365864

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Three-dimensional simulations of pyrolytic laser direct writing from gas-phase precursors are presented. They are based on a fast method for the calculation of temperature distributions induced by an energy beam in deposits of arbitrary shape. Analytical approximations, fast Fourier transform, and the multigrid technique are combined in the algorithm. Temperature dependences of the absorptivities and heat conductivities of the deposit and the substrate have been taken into account. Self-consistent modeling of the growth process allows one to explain oscillations in the height and width of lines caused by the feedback between the shape of the deposit, the temperature distribution, and the growth rate. For the deposition of W from an admixture ofWCl6+H2anda-SiO2substrates, the oscillations originate from a sharp increase in the absorptivity of the deposit with temperature. With the deposition of Si fromSiH4,or C fromCH4,C2H2,andC2H4,ontoa-SiO2,the oscillations are related to the large ratio of height/width of the deposit and the increase in temperature on its upper surface. This increase also explains the transition from line-type to fiber-type growth. The hysteresis of this transition with respect to laser power and scanning velocity is explained as well. The same algorithm can be used in the modeling of pyrolytic etching and e-beam microprocessing when the feedback between the temperature distributions and changes in the processing geometry is important. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365865

出版商:AIP    

年代:1997

数据来源: AIP