摘要:

Polarized differential absorption spectra ofCr4+-doped forsterite have been studied using a picosecond pump–probe technique. For pump beam and probe beam polarization parallel to theaaxis, an excited state absorption in the 450–800 nm region is observed and assigned to the3T2→3T1(3P)transition ofCr4+ion. The lifetime of the3T1(3F)state is estimated to be less than 15 ps. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118909

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Triatomic ionic excimers have now been observed. Alkali rare-gas triatomic ionic molecules have been produced by electron beam excitation. Emission spectra centered at ∼159 nm due toKr2+Cs radiative decay were recorded. Lifetime and binding energy of the lowest excited state are estimated; the ground state is repulsive. Two formation channels for these triatomic ions are proposed and their rate coefficients estimated. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118941

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Frequency modulation atomic force microscopy (FM-AFM) has made imaging of surfaces in ultrahigh vacuum with atomic resolution possible. Here, we demonstrate a new approach which simplifies the implementation of FM-AFM considerably and enhances force sensitivity by directly exciting the cantilever with the thermal effects involved in the deflection measurement process. This approach reduces the mechanically oscillating mass by 6 to 8 orders of magnitude as compared to conventional FM-AFM, because external actuators and oscillating cantilever mounts are not needed. Avoiding external actuators allows the use of cantilevers with very high oscillation frequencies, which results in improved force sensitivity. Further, the implementation and operation of this new technique is significantly simplified, because external actuator, bandpass filter, and phase shifter are eliminated. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118910

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The excitation of the standing plasma waves in induced-base hot-electron transistors (IBHETs) and its impact on the IBHET high-frequency operation are considered. It is shown that the plasma waves result in resonant behavior of the IBHET performance at high frequencies. The frequency dependent small-signal transconductance of the IBHET is calculated using an analytical model. The resonant frequencies and the sharpness of the resonant peaks are found as functions of structural parameters and bias voltage. The resonant frequencies can correspond to the terahertz range. The resonant transconductance can significantly exceed the steady-state transconductances of the IBHET. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118911

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Diamondlike carbon (DLC) thin films have been prepared by chemical vapor deposition assisted by electron cyclotron resonance plasma at low pressure with radio frequency (rf) power applied to the substrate. The microstructure studies by transmission electron microscopy and electron energy loss spectroscopy show the existence of nanocrystalline diamond grains in DLC films prepared at 0.35 Pa. The cluster’s size varies from 4 to 30 nm with bias voltage(Vb)varying from−200to−600 V.A phase transition from hexagonal to cubic diamond was also observed with increasingVb.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118912

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

When a Si substrate is etched in aSF6electron cyclotron resonance plasma with the sample maintained at∼−130 °C,reaction products condense preferentially at nucleation sites on the surface, and automatically form etch masks. Si pillars,∼10 nmin diameter and∼0.1 &mgr;mhigh, are then formed. When deposited Au clusters(diameter=1.5±0.7 nm)are used as condensation nuclei, fabricated pillars with an average diameter of 9 nm, standard deviation of 1.5 nm, are formed. This remarkably narrow diameter distribution confirms that the phenomenon is useful in nanostructure formation, and that the process is compatible with electron beam lithography. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118913

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Investigations of the healing of electromigration-induced open-circuit failed submicron Al(0.5&percent;Cu) interconnects were performed usingin situtransmission electron microscopy (TEM). The samples consisted of 4000 Å thick Al (0.5&percent;Cu) patterned over a TEM-transparent window into five runners in parallel, with linewidths 0.2, 0.3, 0.5, 0.8, and 1.0 &mgr;m. A novel sample design minimized any Joule heating in the runners. Our approach has allowed us to observe voids form, grow, migrate, fail a runner, and heal all with respect to the detailed local microstructure of the runners. In this letter, we focus on our time-resolved observations of the mechanisms of healing. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118914

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A complex photothermal refractive index change in host-guest liquid crystals was determined with a novel interferometric method. The complex refractive index change was proportional to the pump beam intensity. The absolute value of the real part was about ten times as large as that of the imaginary one. The absolute value of the extraordinary refractive index change was about nine times as large as that of the ordinary one. The real part of the extraordinary refractive index change was negative, while that of the ordinary one was positive, and the imaginary part of both the extraordinary and ordinary refractive index change was negative. These results can be explained by the photothermal effects in the host-guest liquid crystals and dyes. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118915

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We propose a novel method of measuring the cholesteric pitch of a liquid crystal (LC) in a circularly aligned configuration. The LC cell is made with one homogeneously rubbed surface and one circularly rubbed surface so that it produces a disclination line passing through the singularity created by the circular rubbing. This disclination line is associated with two domains with different twist orientations. In such a geometry, the relationship between the angular deviation of the disclination line and the cholesteric pitch is analytically derived. The concept of a homogeneous-circular configuration is adopted to accurately measure the cholesteric pitch of LC in a broad range from 0.5 to 500 &mgr;m. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118916

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

During the early stages of oxidation of (111) NiAl at 1100 °C, an alumina scale forms and undergoes a series of allotropic phase transformations. In the final stages of phase development, the metastable &THgr;-alumina transforms to the equilibrium &agr;-alumina phase. Images formed using the photoluminescence from traceCr3+impurities in the scale, in conjunction with scanning electron microscopy, indicate that the &agr;-alumina forms by a nucleation and growth process within the &THgr;-alumina matrix. Lateral impingement of the growing &agr;-alumina islands coincides with the reported drop in oxidation kinetics to those characteristic of long-term oxidation of NiAl. Unlike most interface-controlled transformations, the kinetics of the &thgr;–to–&agr; transformation in the lateral growth are found to be logarithmic. Possible causes of these unusual kinetics are proposed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118917

出版商:AIP    

年代:1997

数据来源: AIP