摘要:

One of the advantages of the use of optical fibers for sensing is their ability to perform distributed measurements. Several distributed sensors that measure temperature along optical fibers are already commercially available. All of them are based on Raman thermometry. However, the spatial resolution that they achieve is limited to 1 m, making them unsuitable for applications where higher spatial resolution is needed. Also, their temperature range is very dependent on the behavior of fibers at high temperature, a subject which still needs investigation. In this article, we present a distributed optical fiber sensor that addresses these two issues. On one hand, the combination of Raman thermometry with the time-correlated single-photon counting technique permits the achievement of high spatial resolutions (0.1 m). On the other hand, the use of specially coated fibers allows measurement of high temperatures. We have investigated the system temperature sensitivity and have evaluated the measurement errors introduced by the high-temperature behavior of carbon- and gold-coated fibers. We demonstrate that the system is very appropriate for high-temperature distributed measurements with high spatial resolution. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148025

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The design and construction of a 10 kg transportable flexure-strip beam balance to be used in searches of composition-dependent forces and/or tests of the weak equivalence principle is discussed. The results of the instrument performance presented herein are based upon operation of the balance under simulated experimental conditions that require our balance maintains a high level of sensitivity (i.e., resolution associated with the standard deviation of our data sample) during a continuous measurement process which alternates between two different elevations, a unique application for a beam-balance measuring device. Our results indicate that this balance is the most sensitive transportable balance used in measurement in the 10 kg load capacity range, obtaining a measurement sensitivity of about 15–20 &mgr;Gal. Also, we have established that our method of balance transport affects the sensitivity less than 15 &mgr;Gal at the 95&percent; confidence level. An increase in sensitivity of approximately 30 would be required to establish new upper limits on composition-dependent forces in the interaction range of most interest. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148026

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A simple silicon two-dimensional (2D) flow sensor for the measurement of both flow direction and speed is described. By integrating two couples of silicon spreading-resistance temperature (SRT) sensors in two perpendicular directions on the surface of a silicon chip, this sensor can detect flow speed and flow direction &fgr; in a full range of 360°. Experimental results confirm theoretical analysis that the output of the sensor increases with the square root of the flow velocity, and the outputs in the two perpendicular directions are proportional to sin &fgr; and cos &fgr;, respectively. The effects of sensor layout are also discussed. With complete oxide isolation for the SRT sensors, the flow sensor could achieve higher sensitivity by operating above the intrinsic temperature of silicon(∼150 °C), or could be used to detect fluid flow at a temperature as high as 300 °C. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148027

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We designed and built a combination of a scanning tunneling microscope (STM) and a scanning electron microscope (SEM) which is working under ultrahigh vacuum conditions (base pressure typically7⋅10−11 mbar). The SEM is ideally used for surveying the sample and to control the STM tip positioning, while the STM extends the resolution range into the atomic scale. The design concept allows moving the STM tip freely over the sample under SEM control and using both imaging techniques simultaneously. The system is equipped with an electron energy analyzer (cylindrical sector analyzer) providing Auger electron spectroscopy, scanning Auger microscopy (SAM) and x-ray photoelectron spectroscopy capabilities. In addition, low energy electron diffraction and reflection high energy electron diffraction facilities are installed. In order to use these very different imaging techniquesin situ, several special solutions had to be incorporated in the design of the system; they are described in detail. Some results are presented which demonstrate the performance of the STM/SEM system. Atomic resolution of the STM, a SEM resolution of up to 20 nm, and a SAM resolution of better than 100 nm were achieved. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148028

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A flexible electronic setup on a PC platform and the software implementation in Windows Microsoft environment, for a multipurpose head for scanning probe microscopy (SPM), has been developed. The integrated, multiapplication data acquisition system is linked to a PC-Pentium controller, through a digital I/O board, and consists of: (i) an asynchronous acquisition for real time removal of following error from SPM images; (ii) a three-axes, computer controlled micropositioning stage; (iii) software for electronic control, data acquisition, and graphics elaboration performed through subroutines of Visual Basic (Visual Basic Programming System Professional edition for Windows is a registered trademark of Microsoft Corporation, USA.), and PV-WAVE personal edition. (PV-WAVE Personal edition for Windows is a registered trademark of Visual Numerics, USA.) ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148029

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Based on the push–pull mechanism, we have developed a piezoelectric micropositioner, with a new mechanical construction. The positioner is basically composed of two piezoelectric actuators as the source of the motion and three permanent magnet feet to produce enough friction force for clamping. The movement of more than 5 mm with the steps of 150–700 nm at the speed of 50–200 steps per second can be accomplished by applying very low driving voltage to the positioner. The absence of clamping voltage in this positioner makes it well suited for use in ballistic electron emission microscope (BEEM). A BEEM operated in a gas-controlled environment based on it has been built and its performances have been tested. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148030

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a new design of a low-temperature ultrahigh-vacuum (UHV) scanning tunneling microscope setup with a combination of a solenoid and a split-pair magnet. The scanning tunneling microscope can be operated at temperatures down to 8 K and in a rotatable magnetic field of up to 1 T. Magnetic fields of up to 7 T perpendicular and 2 T parallel to the sample surface can be applied. The UHV part of the system allowsin situpreparation and low energy electron diffraction/Auger analysis of samples. First topographic and spectroscopic measurements onp-InAs(110) are presented. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148031

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The electrochemical etching technique has been widely used in the fabrication of microtips. In this article, an improved feedback control technique for the dc electrochemical fabrication of scanning tunneling microscopy microtips is presented. Distinguished from the conventional control techniques, this newly developed method directly uses the etching current as the only control signal instead of comparing it with the reference current. Therefore, the control process is more accurate. The tungsten tips with radius of curvature down to 20 nm can be produced reproducibly. By varying the cutoff time of the control circuit, tips with different radii of curvature can be fabricated. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148032

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A quasilogarithmic current–voltage converter has been built which allows currents spanning an exceptionally broad range from 10 pA to 10 mA with a bandwidth greater than 2 kHz to be measured. The converter is based on the virtual ground scheme employing semiconductor diodes as nonlinear elements in the feedback path. It is ideally suited for studying local interactions in scanning tunneling microscopy. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148005

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A heatable high pressure cell for angle dispersive neutron powder diffraction has been developed. This cell, called Kiel-Berlin Cell I, is of the piston–cylinder-type and based on a design first introduced by McWhan. High temperature conditions under high pressure are achieved by a graphite resistance heater surrounding the sample container. The cell operates up to temperatures of 700 K and pressures of 1.5 GPa, simultaneously. We report the design of the cell along with calibration data. We also give a brief and representative account of pressure-temperature-dependent studies in which the present cell was used. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148033

出版商:AIP    

年代:1997

数据来源: AIP