摘要:

The steady‐state temperature distribution within a block ofcis‐polybutadiene has been mapped using quantitative magnetic resonance imaging. The experiment described makes use of the temperature dependence of the nuclear magnetic longitudinal relaxation time (T1) of the polymer protons. Hot and cold water flowed through two axially mounted pipes in a cylindrical sample, creating a dipolar temperature distribution. A fast inversion recovery imaging sequence was used to mapT1values in the sample with a spatial resolution of 0.3 mm and random error of ±5% for individual pixels in the 128×128 image. TheT1values thus obtained were converted into temperatures using an empirical calibration curve, leading to a temperature resolution of ±2 K for each pixel. Using a median filter (which reduces the image resolution by a variable factor of up to 3), the data are rendered smooth enough to obtain a clear contour plot. This is compared with a finite element solution of Laplace’s equation over the same domain, demonstrating that the MRI technique is reliable. A number of experimental problems limiting both the exact comparison between theory and experiment and the long‐term utility of the technique are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144732

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In this paper we describe the design of a high resolution near‐infrared photoacoustic spectrometer of the gas‐microphone type intended to be used for measuring impurity absorption spectra of semiconductors. Particular attention has been paid to the design of the photoacoustic cell to find the most suitable one, and as a result, several cells differing in geometry and materials have been investigated. We present results for the PA amplitude dependence on the modulating frequency for carbon black powder and some widely used semiconductors. The sensitivity of the spectrometer and its effectiveness in resolving active defect states existing in the subgap absorption spectra of semiconductors are demonstrated in both optically opaque and transparent thick and thin samples.

ISSN:0034-6748    

DOI:10.1063/1.1144733

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Software‐supported switching between the deep‐level transient spectroscopy (DLTS) and feedback charge method (FCM) operation modes of a versatile time‐domain spectrometer, while using identical circuitry, is demonstrated. No additional correction of the output signal for integrated leakage current is needed. The timing scheme design is discussed in more detail with reference to a practical example. The interval of achievable rate windows is not affected by the switching between the DLTS and FCM modes of the instrument. A few illustrative examples of DLTS andC‐Vplots are included.

ISSN:0034-6748    

DOI:10.1063/1.1144734

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Colloidal gold particles are used as hard, spherical imaging targets to assist in the three‐dimensional reconstruction of the atomic force probe apex. Probe reconstructions are shown to be accurate to 1 nm resolution and dynamically change as the sample is scanned, emphasizing the utility of colloidal gold particles asinsitucalibration standards for image reconstruction of a coadsorbed specimen.

ISSN:0034-6748    

DOI:10.1063/1.1144735

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The extremely high resolution of a scanning tunneling microscope (STM) or atomic force microscope allows the examination of local material faults like dislocations, grain boundaries, and cracks on an atomic scale. However, the visual field of a scanning probe microscope is small and, especially in UHV, it is difficult to position a probe tip directly above such faults since they are not very frequent on a specimen surface. Therefore, a STM for the quantitative examination of large areas in UHV was developed. A new three‐dimensional micropositioner based on inertial slip‐stick motion was built, where the vertical motion is achieved with a special seesaw‐like construction. This device is very compact and allows positioning of the piezoscanner with steps down to 20 nm length. The microspositioner is designed with low weight drives and special materials for the bearings (ruby on sapphire) to avoid sticking in UHV. First applications of a STM built with this micropositioner are shown where atomic resolution is reached.

ISSN:0034-6748    

DOI:10.1063/1.1144736

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A miniature capacitive force sensor which fits in the sample position of an atomic force microscope (AFM) has been used to calibrate the force applied by the scanning tip during nanohardness measurements. The sensor is simple, physically robust, and easily fabricated from readily available materials. It can be operated with commonly available electronic instrumentation. The device described here is optimized for tip‐sample forces between 10−4and 10−2N, a range useful for micrometer‐scale mechanical modification of surfaces. With minor design changes, sensors of this general type should be capable of much greater sensitivity. The sensor is calibrated outside the AFM by the application of free weights. Calculated estimates of AFM cantilever force constants are difficult for all but the simplest geometries and may rely on uncertain values for certain critical dimensions and material properties. These estimates can thereby be replaced by a simple and direct measurement.

ISSN:0034-6748    

DOI:10.1063/1.1144737

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A capacitance microscope has been used for imaging conducting surfaces. It differs from earlier designs in three major respects: the principle of capacitance detection, the coaxial probe employed, and the operating frequency. The impedance of the probe with respect to a conducting backplane is sensed, which allows the instrument to resolve the components of the complex capacitance. The probe and input stage design reduces the parasitic capacitances to approximately 4×10−14F. The lateral resolution achieved is approximately 10 nm.

ISSN:0034-6748    

DOI:10.1063/1.1144738

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Planar thermocouples designed for investigation of heat transfer in scanning tunneling microscopy and scanning thermal microscopy are described. The limit of sensitivity to local thermal power can be as small as 10 nW. The devices are based on two different thin films formed as a cross on a thin glass substrate. Heat fluxes in the cross point can be detected by measuring the thermoelectric signal from two ends of the cross. As described elsewhere planar thermocouples of this type have been successfully used to detect the energy which is deposited by tunneling electrons and to measure the heat which is coupled across a submicron vacuum gap between two metals by the fluctuating fields of electromagnetic surface modes.

ISSN:0034-6748    

DOI:10.1063/1.1145225

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have developed an apparatus that produces an ionized beam of mass selected clusters of controllable energy. It uses a pulse of second‐harmonic light from a Nd:YAG laser to vaporize atoms from a target disk. The clustering rate of the atoms in this expanding plume is controlled with the pressure of a He pulse injected from a fast pulsed valve. A Wiley–McLaren type time‐of‐flight mass spectrometer with a shield lens is used to monitor the cluster distribution and to optimize the control parameters of the system. The shield lens doubles the resolution and the signal‐to‐noise ratio of the spectrometer. A 4000 amu rf quadrupole with 1.2 amu resolution is used to select the mass of charged clusters. An electrostatic quadrupole is used to separate the charged clusters from the neutral clusters and the He gas. The ionized clusters are then focused onto a suitably prepared substrate by using electrostatic lenses. Time averaged deposition current densities on the order of 100 pA cm−2have been measured when the vaporization laser is fired at 10 Hz. The deposition energy of the clusters is controlled by applying a bias voltage to the substrate. A mobile vacuum chamber is used to transfer samples to various diagnostic systems.

ISSN:0034-6748    

DOI:10.1063/1.1144675

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A Cs liquid metal ion source (LMIS) and focused ion beam system for microarea secondary ion mass spectrometry (SIMS) have been developed. Because of the chemical activity, low surface tension, and high vapor pressure of Cs, few successful Cs LMISs have heretofore been reported, as opposed to the many successful applications of Ga in LMIS. A new Cs‐LMIS design had to be developed to supply Cs to the emitter/reservoir under UHV to prevent oxidation, to prevent liquid Cs from dripping off the emitter substrate, and to minimize the surface area exposed so as to minimize thermal evaporation. The last consideration is very important since the evaporation rate of Cs is many orders of magnitude higher than, e.g., Ga at the melting point. A focused Cs beam was obtained with a newly designed SIMS system, which is about 0.1 &mgr;m beam size and a beam current density on the specimen of 0.8 A/cm2. An operating time of more than 600 h has been achieved at a total emission current of 1 &mgr;A without resupplying the source material at room temperature.

ISSN:0034-6748    

DOI:10.1063/1.1144676

出版商:AIP    

年代:1994

数据来源: AIP