摘要:

We demonstrate the spectroscopic capabilities of an ac scanning tunneling microscope. This ac scanning tunneling microscope has a bias voltage modulation frequency tunable over the range dc–20 GHz and is thus capable of recording images and local spectra of insulating as well as conducting substrates. In this article we detail the spectral sensitivity and the tip‐sample separation dependence of the spectra recorded by simultaneously tuning the modulation and detection frequencies. Spectra of an evaporated gold film and of self‐assembled monolayers of CH3(CH2)15SH and of CH3O2C(CH2)15SH on gold are presented.

ISSN:0734-2101    

DOI:10.1116/1.578339

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Operational aspects of a newly developed simultaneous near‐field optical and force microscope are considered. Using a glass probe, the technique is capable of monitoring the sample topography, through its force microscopy capability, as well as the sample’s optical parameters, using the light guiding properties of the tip. In addition, the force signal can be used reliably as a feedback signal, thus allowing a crash‐free detection of optical fields in the vicinity of opaque steps on the sample. Results are presented on imaging a variety of samples including biological and nonbiological objects and thin film structures. In each instance, results obtained with different modalities are compared. It is shown that the simultaneity of the images obtained with different modalities can be very useful in, and sometimes necessary for, sample identification.  

ISSN:0734-2101    

DOI:10.1116/1.578340

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

We present a novel technology for the fabrication of quantum dot structures using the deposition of ultrafine aerosol Ag particles onto the surface of GaInAs/InP quantum well structures grown by metal‐organic vapor‐phase epitaxy. The particles, ranging in size between 30 and 40 nm, are subsequently used as an etching mask. The aerosol particles are produced by homogeneous nucleation and have a diameter in the range of 2–100 nm. After size selection, the monodisperse particles with a very narrow size distribution are deposited onto the semiconductor surface at a density of about 109cm−2. Optimized CH4/H2/Ar electron cyclotron resonance plasma etching at low energy (about 100 eV) results in the formation of free‐standing columns 50–80 nm in diameter and 120–280 nm in height. Their size and stability were found to be dependent on the etching conditions (e.g., methane concentration and ion energy) and the diameter of the particles. Low‐temperature cathodoluminescence was used to evaluate the optical quality of the quantum dot structures fabricated by this technique.

ISSN:0734-2101    

DOI:10.1116/1.578341

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

We have designed a novel scanning tunneling microscope (STM) and control electronics system to investigate STM‐based nanostructure fabrication on semiconductor surfaces. Several elements of our design are unique to this application. The STM, which resides in a vacuum chamber, can be positioned anywhere on a 1 cm×1 cm sample. This is accomplished by using three piezoelectric motors (Burleigh Inchworms) and locating the tip position with a long working distance optical microscope (Questar). One piezoelectric motor is used for the coarseZapproach while the other two adjust theX,Ytip position. The tip is attached to a tube‐type piezoelectric scanner. The piezo tube’sx–yscan range is 12 μm×12 μm. The tube’s mechanical and electrical response are linear to 6 kHz and allow rapid scanning. Both tip and sample are attached to the microscope magnetically to facilitate rapid self‐aligned exchange under vacuum. A computer controlled pattern generation system allows arbitrary patterns to be drawn on the sample. The critical electromechanical issues involved in the construction and operation of such a system are discussed in detail.

ISSN:0734-2101    

DOI:10.1116/1.578342

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

We present the design and theory of operation of a new fiber‐optic detection mechanism for force microscopy. The technique comprises a differential fiber Michelson interferometer, in which most spurious signals due to environmental variations are automatically rejected. Any residual fluctuations are canceled by the action of a feedback mechanism, which also ensures operation at maximum sensitivity. This detection technique is capable of high sensitivity response to both high and low frequency tip variations, and can thus be used in the attractive and repulsive modes. A number of results are presented on the applications of a force microscope utilizing this detection mechanism. Both ac and dc modes of operation are demonstrated.

ISSN:0734-2101    

DOI:10.1116/1.578343

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

We have investigated the influence of HF concentration on the initial stages of electroless deposition for various metals (Al, Au, Cu, Sn, and Pd) onto silicon using atomic force microscopy. As the HF concentration in the plating solution increased, the rate of metal deposition correspondingly increased for Au, Cu, and Pd. In the case of Au and Cu, uniformly sized nuclei comprised the first deposited layer. However for Al and Sn, deposition occurred only at sporadic sites on the surface and was independent of HF concentration. For all of the metal ion studied, deposition initiated preferentially at flaws on the surface. The electroless process indicates a direct displacement mechanism which results in the simultaneous dissolution of Si as the metal ion is reduced at the surface. For all the metal ions deposited in this manner, metal adhesion to the Si surface was poor.

ISSN:0734-2101    

DOI:10.1116/1.578344

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

The atomic force microscope (AFM) designs described here are based on the high sensitivity of scanning tunneling microscopy (STM) technology. It utilizes short range repulsive contact forces between a small stylus and a sample surface to produce high resolution images of defects and structural features of the surface. An adjacent tunnel gap controls contact forces and provides a very sensitive feedback signal for aZ‐direction piezoelectric drive to maintain a constant force value during raster scanning. A STM may serve as an AFM by attaching an AFM adapter. The same piezoelectric drive mechanism, electronics, and recording system can be automatically employed to produce AFM images. This report contains a progression of AFM designs, based on the tunnel current control principle, construction and calibration of AFM levers, AFM applications, and high resolution AFM images.

ISSN:0734-2101    

DOI:10.1116/1.578345

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

The atomic force microscope (AFM) is capable of imaging surfaces at very high resolution. The AFM has been used to image living glial cells in culture. Typical images reveal the three‐dimensional shape of the cell and often internal cellular structures are visible. In this report, it is shown that by increasing the imaging force, cells can be removed from the surface on which they are grown. Although the forces involved in this process are complex, it is possible to compare relative adhesion of different types of living cells to a particular substrate.

ISSN:0734-2101    

DOI:10.1116/1.578346

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

In a previous paper [J. A. DeRose, T. Thundat, L. A. Nagahara, and S. M. Lindsay, Surf. Sci.256, 102 (1991)], the conditions which can be used to grow Au films epitaxially on muscovite mica to obtain large area, flat faces are reported. Since then, it has been reported that Au films grown on an amorphous substrate [J. Hwang and M. A. Dubson, J. Appl. Phys.72, 1852 (1992)] (nonepitaxy) have shown to be at least as smooth as those on mica. In this article, the results from scanning tunneling microscopy analysis of Au films grown on mica, glass cover slips, and fused silica are compared. By comparing the rms surface roughness (zdata standard deviation, SD) values for each film type, we find that the mica films show the smoothest surfaces, i.e., smallest rms surface roughness values. We then attempt to explain these results by taking into account the accepted model of film growth from the vapor (physical vapor deposition) and the surface structure of bare mica, glass (optical microscope slide cover slip), and fused silica as shown with atomic force microscopy.

ISSN:0734-2101    

DOI:10.1116/1.578347

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

We have used scanning probe microscopy and transmission electron microscopy (TEM) to investigate the molecular orientation of cobalt naphthalocyanine (CoNc) vacuum deposited onto a NaCl substrate. Atomic force microscopy observations taken on CoNc deposited at room temperature reveal mostly amorphous grains with only few regions showing columnar structure. For CoNc films deposited at 250 °C, scanning tunneling microscopy and TEM showed domains of columnar structure arranged in various orientation. The periodicity of the columnar structure was determined to be 1.5 and 0.34 nm from x‐ray and electron diffraction and indicates that the molecules are standing with their planes perpendicular to the underlying NaCl substrate surface.

ISSN:0734-2101    

DOI:10.1116/1.578348

出版商:American Vacuum Society    

年代:1993

数据来源: AIP