摘要:

Various statistical quantities (such as average, peak-to-valley, and root-mean-square roughness) have been applied to characterize surface topography. However, they provide only vertical information. Because spectral analysis provides both lateral and longitudinal information, it is a more informative measurement than all these commonly used statistical quantities. Unfortunately, a standard method to calculate power spectral density (PSD) is not available. For example, the dimensions of PSD are often denoted as either (length)3 or (length)4. This may lead to confusion when utilizing spectral analysis to study surface morphology. In this paper, we will first compare the definitions of PSD commonly used by various authors. Using silicon surface roughness measurements as examples, we will demonstrate the advantages of spectral methods on atomic force microscopic (AFM) image analysis. In this context, we study the effects of typical AFM imaging distortions such as image bow, drift, tip-shape effects, and acoustic noise. As a result, we will provide a procedure to obtain accurate and reproducible AFM measurements. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366489

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In order to image the magnetic source distribution inside a flawed magnetically permeable structure, the truncated generalized inverse and singular value decomposition were used. These techniques were applied to the magnetic flux leakage generated when the structure is magnetized. The leakage field from different flaw shapes was simulated by placing magnetic dipoles at the boundary surfaces, which reduces the flux density in the flawed structure. A criterion to establish the generalized inverse truncation index is proposed, by using the two-dimensional correlation coefficient between the original image and the reconstructed image. Others aspects such as the measurement signal-to-noise ratio, and density of the model source distribution are also discussed. This imaging technique was successfully applied to a number of different model flaw sources. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366490

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

With the aid of particle simulation, we discuss efficiency enhancement in a single-pass Cherenkov laser by varying the permittivity of a dielectric sheet loaded on a parallel plate waveguide. For the analysis of the problem, a two-dimensional model for the Cherenkov laser is considered which is composed of a planar relativistic electron beam and a parallel plate waveguide, one plate of which is loaded with a dielectric sheet. In order to maintain the synchronism between an electron beam and an electromagnetic wave, the permittivity of the dielectric is properly varied in accordance with the variation in the average velocity of the electron beam. The result of numerical simulation shows that the efficiency of energy transfer from the electron beam to the electromagnetic wave is greatly enhanced by properly varying the permittivity of the dielectric sheet. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366491

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We here expose theoretical and experimental results on homodyne detection using near-infrared laser sources, at 1.06, 1.32, and 1.55 &mgr;m wavelengths. The used photorefractive crystals are two large size CdZnTe:V samples. With speckled beams such as the ones scattered by diffusive objects, we reach a detection limit which, at 1.55 &mgr;m, is only 1.6 times above the one obtained with plane waves in a classical interferometer and only 2 and 2.2 times above at 1.32 and 1.06 &mgr;m, respectively. It is then demonstrated that the electron–hole competition, which varies enormously between these three wavelengths and gives a nearly zero two-wave-mixing gain at 1.32 &mgr;m, does not influence the sensitivity of the system. Moreover, we show that the frequency cutoff of the system is four times higher in the attenuation regime than in the amplification one. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366492

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The temperature dependence of the photorefractive effect in a polymer composite containing poly(9-vinycarbazole), tricresyl phosphate, buckminsterfullerene, and 4-(N,N- diethylamino)-&bgr;-nitrostyrene is presented. The photoconductive, electro-optic and photorefractive properties of the material have been studied in the temperature range of 22–61 °C. An apparent increase of electro-optic modulation with temperature and its eventual saturation is observed. This behavior is attributed to the temperature activated orientational mobility of the second-order nonlinear chromophores. The polarization anisotropy between thep- ands-polarized readouts is consistent with what would be expected on the basis of directly measured effective electro-optic coefficients. By correlating the electro-optic value with the diffraction efficiency, the temperature dependence of the space-charge field is obtained and explained by temperature dependencies of the dark conductivity and the photoconductivity of the material. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366493

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A theory of Love waves propagating in a viscoelastic surface layer deposited on a perfect elastic substrate was considered. In the case of low losses(&ohgr;&eegr;44/&mgr;B0≪1)an analytical formula relating the attenuation coefficient of the Love wave and the viscoelastic parameters of the waveguide structure was established. This makes it possible to apply the obtained analytical formula in nondestructive testing for determining the rheological parameters of viscoelastic bodies. The established theory of Love waves in viscoelastic media can also be applied in seismology and integrated optics. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366494

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Reaction processes of fluorine (F) atoms in high-density carbon–tetrafluoride(CF4)plasmas were investigated using vacuum ultraviolet absorption spectroscopy. A scaling lawnF∝(nenCF4)0.5–0.7was found experimentally, wherenFis the F atom density andneandnCF4stand for the electron and parent gas(CF4)densities, respectively. The lifetime measurement in the afterglow showed that the decay curve of the F atom density was composed of two components: a rapid decay in the initial afterglow and an exponential decrease in the late afterglow. The decay time constant in the initial afterglow&tgr;1satisfied the scaling law&tgr;1∝(nenCF4)−(0.3–0.4),which is a consistent relationship with the scaling law for the F atom density. The two scaling laws and the lifetimes ofCFxradicals suggest that the major loss process of F atoms in the initial afterglow is the reaction withCFxradicals (probably,x=3) on the wall surface. The loss process in the late afterglow was simple diffusion to the wall surface. The surface loss probability of F atoms on the chamber wall was evaluated from the decay time constant in the late afterglow, and was on the order of10−3.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366495

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two-dimensional, phase resolved magnetic probe measurements have been performed in a low pressure inductively coupled cylindrical plasma source driven with a planar coil. The rf electric field and current density distributions determined from these measurements exhibit an abnormal nonmonotonic spatial evolution. Formation of a second current layer, phase bifurcation and a reversal of the rf field phase velocity have been found and are attributed to spatial dispersion of the plasma conductivity due to collisionless electron thermal motion typical of anomalous skin effect. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366496

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A particle-in-cell/Monte Carlo numerical model has been developed to simulate a direct current discharge self-consistently with the motion and thermalization of both energetic charge-exchange neutrals and sputtered cathode atoms. In the model the charged particle motions are considered in a self-consistent electric field. A one-dimensional glow discharge in Ar has been simulated for the cases of Al and Cu cathode. The background argon gas heating has been predicted, with the temperature rise being larger for the case of Cu cathode which is characterized by a higher sputtering yield than Al. The balance of power input into the gas due to the energetic neutrals, sputtered atoms, and ions is analyzed. The dominant contribution is from energetic neutrals. Comparison of the calculated fluxes of these three species at the cathode surface shows a great contribution of the energetic neutrals into sputtering of the cathode material. The effect of applied voltage has been also investigated. Lastly, the influence of the gas heating on discharge characteristics is discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366497

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Semiempirical models of electronic energy loss and damage formation for MeV ions (B, P, As) implanted in silicon at room temperature were investigated through the comparison of measurements with Monte Carlo simulations of both impurity and damage depth distributions. Accurate prediction of dopant profiles in an amorphous target and in a low-dose implanted crystal is achieved by a proper parametrization of well known analytic stopping models. Moreover, to accurately describe the dynamic effects of damage accumulation in medium dose implants, a dependence on ion energy of the efficiency parameter used in the Kinchin–Pease (KP) model must be introduced in the simulation. Such a factor, determined by the fit of the measured integral of defect profiles, is found to decrease for P and As ions with increasing the nuclear energy released to primary recoil atoms, apparently reaching a saturation value of about 0.25. Full cascade simulations show that the increasing fraction of the primary recoils energy spent in electronic processes, not considered in the simple KP approximation, cannot explain the observed trend. While the empirical adjustment of damage efficiency leads to a good agreement between simulated and experimental dopant profiles, a systematic underestimate in the depth position of the peaks of simulated damage distributions is observed, which cannot be accounted for by simple ballistic transport effects. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366498

出版商:AIP    

年代:1997

数据来源: AIP