摘要:

Evidence regarding the high temperature coefficient of resistance (35&percent; per °C) in vanadium oxide multiple thin film diodes has been obtained, indicating that the source is a vanadium oxide substance formed between multiple layers of deposited vanadium. Effects of top contacts are detailed. The devices also show high sensitivity to mechanical pressure. ©1997 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1147640

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The photothermal deflection technique is applied in transverse configuration to measure the thermal diffusivity of semiconductor wafers. The large size of these samples inhibits the possibility to make the probe beam skim the sample at a small height which is required for a direct thermal diffusivity measurement. To overcome this problem, three new experimental schemes are proposed, each one based on a different geometry of the heat diffusion (one-, two-, or three-dimensional scheme). In particular for the 3D experimental scheme, a new mirage setup is described which uses two crystalline prisms 6 mm apart from each other to let the probe beam skim 50±3 &mgr;m high over the sample surface, with a spot size of 22 &mgr;m. The main advantages of this setup, here discussed, are the obtained low probe beam height which is, moreover, independent of the sample dimensions, and the cheap technology to produce the necessary high-quality prisms. The performances of the new schemes have been tested by comparing, for well-known semiconductor wafers (InSb, InAs, InP, GaAs, GaP, Ge, and Si), the experimentally measured thermal diffusivity with the values reported in the literature. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147589

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe the design and construction of a single-coil, two-channel probe for the detection of low-field magnetic resonance using dynamic nuclear polarization (DNP). The high-frequency channel of the probe, which is used to saturate the electron spins, is tuned to the electron Larmor frequency, 75 MHz at 2.7 mT, and matched to 50 &OHgr;. Low-field,1H nuclear magnetic resonance (NMR) is detected through the second, low-frequency channel at frequencies <1 MHz. The performance of the probe was tested by measuring the DNP of protons in a manganese (II) chloride solution at 2.7 mT. At the proton NMR frequency of 120 kHz, the signal amplitude was enhanced over the value without DNP by a factor of about 200. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147641

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The design and performance of miniature ac susceptometers are described that are small enough to fit inside clamp type pressure cells. The susceptometers are comprised of a primary and a balanced pair of secondaries with numbers of turns as high as 1000 to optimize the coupling to the sample and hence measurement sensitivity. Two methods of balancing the vacuum signal of the secondaries are presented, making susceptibility measurements even in clamp cells generating large stray signals possible. With the technique presented here a comprehensive series of measurements was carried out into the pressure induced magnetic quantum phase transition of MnSi. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147642

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report a shear wave reflection technique which allows time- and temperature-dependent measurements of the complex dynamic shear modulus(G*=G′+iG′′)or the dynamic shear viscosity(&eegr;s′)in the ultrasonic frequency range (3–40 MHz). The shear wave reflection method developed by Mason &etal; [Phys. Rev.75, 936 (1949)] was adapted to the possibilities of the high-frequency digital technique. A conventional single-frequency pulse-burst system and a broadband pulsed ultrasonic spectroscopic system using Fourier analysis for detection of phase and amplitude changes of the reflected signals are described alternatively. Due to digital analysis of the received signal it was possible to achieve a simplification of the experimental setup and to extend the limits of the shear wave reflection technique to about one Gigapascal (100 &mgr;m film thickness) or to minimum film thickness of about 10 &mgr;m (G′<10 MPa). Furthermore, it is possible to monitor time-dependent isothermal processes or reactions with the setup. The basic features of the two different techniques are presented together with brief experimental results on film formation from aqueous polychloroprene dispersions and of the crystallization kinetics in the films. Furthermore, temperature-dependent studies of melting and crystallization on semicrystalline polychloroprene and of the glass transition behavior of amorphous butyl acrylate/styrene copolymer films are reported. The importance of the method is discussed for both investigations of fundamental questions (e.g., film formation, reaction kinetics, or phase transitions) and technological assessment (glues, paints, etc.). ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147643

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Techniques for measurement of low-level dielectric polarization noise spectra over a broad dynamic range are described. The method provides a powerful probe of 1/fnoise and near-equilibrium dynamics in nonconducting materials of interest such as glass formers, liquid crystals, polymers, or ferroelectrics. Dielectric polarization noise was measured via voltage fluctuations in a capacitance cell filled with sample material. Measurements were carried out in the temperature range 80–400 K on glycerol and poly-vinyl-chloride near their respective glass transitions. To maximize the dynamic range and sensitivity and limit effects of stray capacitance an ultralow-noise junction field-effect transistor based preamplifier was operated adjacent to the sample in vacuum within the low-temperature cryostat. The technique offers potentially greater accuracy than susceptibility measurements in low-loss regimes, and may be useful in single-electron-transistor applications. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147940

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A pneumatically powered mechanical translator–rotator system has been designed and constructed for use in the direct laser vaporization (DLV) of materials. This translator–rotator was initially developed for the reproducible DLV production of refractory metal atoms to be reacted with small molecules and characterized in matrix isolation experiments, but has applications wherever a reproducible DLV stream of a material is required, such as matrix assisted laser desorption ionization. Key features of the new translator–rotator design are the employment of an inexpensive air ratchet to provide power for the translator–rotator mechanism, the elimination of magnetic relays and electrical limit switches through the use of an all mechanical gear and slot mechanism, and a triple O-ring gland capable of maintaining high vacuum, 10−7Torr, while the translator–rotator is in operation. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147939

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

For the investigation of particle failure in abrasive processes a single particle crusher has been developed. Basically the apparatus consists of two approaching diamond anvils between which a particle is positioned. Both the force and displacement can be either measured or controlled during an experiment. The force is determined by the current through the voice coil with a resolution of0.5 mN. The vertical displacement of the lower anvil is measured by three inductive displacement transducers, each with a resolution of0.1 &mgr;m. Single abrasive particles in the size range10–500 &mgr;mcan be used. The crushing process can be monitored through the upper anvil by a long distance microscope and recorded video. Preliminary experiments show that three different failure mechanisms can be distinguished: chipping, breaking, and fragmentation. By far the most dominant failure mechanism is chipping. The data of the crushing experiments are represented in a Weibull plot. The generally low value for the Weibull modulus indicates a large variability in strengths of the abrasive particles. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147644

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The possibility of mathematical modeling of ultrasonic beam, the most influencing factor in the ultrasonic methods in quality control of materials and constructions, is considered. We have focused attention on the distribution of acoustic energy in inspected material, since a reliable estimate of the reflector size is possible only if the former is known. In the experimental part we used an ultrasonic pulse-echo method and piezoelectric probes, as well as two basic types of reflectors that cross the ultrasonic beam and the reflectors that are within the beam, as representative for the flaw in inspected materials. In the modeling we have included realin situconditions and factors influencing the results, and the results were selected using the proposed optimal criteria. ©1997 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1147953

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Chemical vapor deposition (CVD) has for long been the mainstay for the deposition of critical device layers in integrated circuit technology. For the development of fast, high density, low voltage operated integrated circuits, materials with dielectric constant(K)less than that of the conventionally used SiO2(K=3.8)are required, due to their ability to reduce signal propagation delays, power dissipation, and cross talk when used as inter level dielectrics. The copolymeric Teflon amorphous fluoropolymer (AF) is a new lowKmaterial withK=1.9. A direct liquid injection system for the CVD of Teflon AF for interlevel dielectric applications in an ultraviolet (UV) light enhanced rapid isothermal processor is reported for the first time, to the best of our knowledge. Computer interfaced electronics were designed to permit atomizing and desolvating the liquid precursor at any desired instant and interval of time. A closed loop control system monitored and regulated the substrate temperature. The films were processed with and without the UV light source. An improvement in film properties was observed when the UV source was used during processing. Our technique offers considerable advantages over other reported methods for the processing of Teflon AF. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147926

出版商:AIP    

年代:1997

数据来源: AIP