摘要:

We present a quantitative discussion of the acoustic transmission line theory pertaining to experimental results from a resonant photoacoustic cell excited in its first longitudinal mode. Window absorption is optimally suppressed by buffer volumes and tunable air columns. The acoustic behavior of an ultrasensitive one inch condenser microphone is quantitatively described. A small and sensitive photoacoustic cell has been developed for intracavity use in a CO2waveguide laser permitting measurements of ethylene down to 6 pptv (long term stability 20 pptv) with a time response of 2 s at a trace gas flow of 6 1/h. To demonstrate the fast time response within a biological application the instant ethylene release of a single tomato is measured. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147072

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have designed and demonstrated two simple and versatile reflection mode near‐field scanning optical microscopes (NSOMs). In one scanner far‐field collection is coaxial with the NSOM tip, and in the other scanner, the far‐field collection is at a 45° angle to the NSOM tip. We quantitatively compare images obtained with the two scanners. While off‐axis collection offers a significantly higher signal‐to‐noise ratio, it also introduces tip shadowing in samples with topographic features larger than approximately 40 nm. The additional contrast from the shadowing further complicates image interpretation and must be considered when performing NSOM in reflection with off‐axis collection. In addition, we discuss some general issues that should be considered when designing a reflection NSOM. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147073

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Imaging ellipsometry is presented as a technique for quantification and visualization of the lateral thickness distribution of thin (0–30 nm) transparent layers on solid substrates. The main advantage of imaging ellipsometry is that every point on a surface is measured at the same time with a high lateral resolution. The method is based on the use of combined null and off‐null ellipsometry at an incident angle close to the pseudo‐Brewster angle of a high index substrate such as silicon. In the present experimental setup, a xenon lamp, a collimator, and a wavelength‐selective filter provide an expanded collimated probe beam with a diameter of 25 mm. Other major components in the system are a polarizer, a compensator, and an analyzer. In this way, a 15×30 mm2image of a sample surface can be focused onto a charge‐coupled‐device video camera and transferred to a computer for further evaluation by image processing. Thickness measurements are performed for calibration purposes with ordinary null ellipsometry. The imaging ellipsometer has an accuracy of better than 0.5 nm at a lateral resolution of 5 &mgr;m in the present configuration, but improvements of at least a factor of 5 can be foreseen. Several aspects of the ellipsometric imaging system are illustrated in selected applications including continuous protein thickness distributions, stepped silicon dioxide thickness distributions, and visualization of protein patterning of surfaces. The latter can be used in a biosensor system as illustrated here by antigen–antibody binding studies. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147074

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A simple Kerr microscope designed forinsituinvestigation of magnetic ultrathin films in ultrahigh vacuum environment is described. The system permits quick visualization of domain patterns with 10 &mgr;m lateral resolution. Simultaneous optical magnetometry is also possible. The performance of the system is illustrated with domain images in a few layers thick Fe films on Cu(001) and W(110). ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147075

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This article will demonstrate the production and application of ‘‘mixed’’ beams for a magnetically focused nuclear microprobe. A ‘‘mixed’’ beam is defined as any two beams of ions of different species, or energy, or both that can be quickly and easily made to have the same magnetic rigidity (Rm) so that they transport, focus, and scan the same in a magnetic nuclear microprobe. Two techniques for the production of such beams will be presented. These methods include the extraction of different ions from the same source and scanning the terminal potential to produce the sameRm, and the use of a postacceleration stripper to change the charge state of one ion species to give it the sameRmas another ion species. The application of mixed beams to ion beam induced charge, scanning transmission ion microscopy, and ion microlithography will also be presented. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147076

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe the experimental work necessary on a scanning tunneling microscopy (STM) system to obtain some important feedback parameters—to have stability and good imaging conditions—such as the mechanical resonance frequency &ohgr;0, the delay time &tgr;, and the damping factor &zgr;. We study and analyze each one of the main components involved on the STM such as the feedback system, the piezoelectric elements, the rigidity of the mechanical structure (the mechanical resonance), and its relation with the scanning rate for imaging. We conclude that it is necessary to obtain these parameters with the STM in tunnel conditions, in order to consider the effects of the tip, surface contamination, and tip sample interaction. We also conclude that tripod based STM can be better than STM based on piezo tubes scanners. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147077

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A rigid scanning tunneling microscope design with an easily implemented two‐dimensional approach is presented. Also described is a simple current–voltage converter optimized for low‐current (pA) applications. Capabilities of the microscope include atomic resolution on Au(111) and molecular resolution of poorly conducting self‐assembled monolayers. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147078

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We built a scanning force microscope working in ultrahigh vacuum. The lever deflection is measured by a fiber‐optic interferometer. To detect large lever deflections the distance between the fiber end and the cantilever backside is controllable by a piezoelectric device. With this technique force–distance curves can be acquired even over large distances. We implemented a stepper motor with gear reduction system for coarse approach in our microscope. First measurements of thin gold films grown on mica obtainedinsituat 10−8Pa are presented. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147079

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The design of a low‐temperature scanning tunneling microscope is described. The microscope can be operated in ultrahigh vacuum in the temperature range between 15 and 300 K. The main features are a scanner which is based on the Besocke ‘‘beetle’’ design principle combined with a spring suspension of the microscope and complete surrounding of the whole microscope by a 4 K radiation shield. The microscope can be extended to work as a force microscope using the optical lever detection technique for force measurement. It is demonstrated that this comparatively small and reliable setup is well suited to study the adsorption of single atoms and molecules at low temperatures. Moreover, examples of lateral and vertical manipulation of atoms and molecules are shown to demonstrate the performance of the system. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147080

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The technique of high‐temperature cheap thermal resistor fabrication, based on polycrystal and fast neutron irradiated silicon carbide single crystals, is presented. The operating temperature range is 20–600 °C for polycrystal devices and 200–800 °C for single crystal devices and coefficientBin the expressionR=R0 exp(B/T) is equal to 4500 and 10 000, respectively. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147081

出版商:AIP    

年代:1996

数据来源: AIP