摘要:

We present time‐resolved luminescence measurements fromn+n−n+‐GaAs homostructures and from an AlGaAs/GaAs heterostructure using a scanning tunneling microscope for excitation. From the transient decay of the luminescence intensity, the minority carrier lifetime in the semiconductor can be determined. The longest lifetime measured is 200 ns for a GaAs homostructure. We also demonstrate that the presented technique can be used for the study of recombination at heterointerfaces.

ISSN:0734-211X    

DOI:10.1116/1.588721

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Luminescent porous poly‐Si thin films can be obtained by electrochemical etching of phosphorus‐doped poly‐Si films deposited by low‐pressure chemical‐vapor deposition. As‐deposited poly‐Si film has no photoluminescence but all porous poly‐Si films, large area or micron‐size patterns, show comparable orange‐red photoluminescences to those obtained from crystal Si. High‐resolution atomic force microscopy and scanning electron microscopy analyses show that all porous poly‐Si films have smooth surfaces and uniform thicknesses, and are composed of Si grains (∼150 nm) with nanopores (∼20 nm) formed around the surfaces. The pores increase with anodization time, and grow preferentially along the poly‐Si grain boundaries and the Si 〈100〉 crystal directions. The evolution of the microstructure is analogous to that of the etching of a coral ball layer due to sea water.

ISSN:0734-211X    

DOI:10.1116/1.588722

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

For micropatterned or technological samples and to achieve overlap with lower magnification microscopic techniques, there is a demand for high‐resolution imaging capabilities in combination with reproducible sample translation. Degradation of the signal‐to‐noise ratio and piezo nonlinearities limit the maximum scan range, resolution and, in particular, the linearity of piezo scanners. To overcome these problems, we have designed and operated a compact three‐dimensional inertially driven translation device for scanning probe microscopy techniques. We demonstrate the operation of the device, which can access a volume of 2 cm3in three‐dimensional space and permits imaging with atomic resolution. Reproducibility of step size is analyzed in detail. The importance of selected material pairing of the sliding components is discussed for ultrahigh vacuum operation.

ISSN:0734-211X    

DOI:10.1116/1.588723

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

In macroscopic photothermal measurement techniques inhomogeneous thermal waves are used to probe thermal properties of materials on a macroscopic scale. The same principle has been adapted to a high‐resolution scanning thermal microscope. Heating the thermal probe periodically results in an amplitude and a phase signal which can be referred to the dynamical thermal behavior of the sample. This measurement mode allows the investigation of the thermal diffusivity of samples in contrast to experiments known from static scanning thermal microscopy which are related to the thermal conductivity. The photothermal scanning thermal microscope technique was used to investigate grains of thin polycrystalline diamond films. For topography measurements the thermal probes were additionally employed for scanning tunneling microscopy.

ISSN:0734-211X    

DOI:10.1116/1.588724

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Simulations of the interaction of light with tunneling electrons in a scanning tunneling microscope suggest that there is a resonance in which the tunneling current is markedly increased. If a laser operating near the resonance is amplitude modulated, then the tunneling current will have components at the frequency of modulation and its harmonics, as well as at optical frequencies and dc. It is suggested that this effect should be considered as a new mode for laser‐assisted scanning tunneling microscopy. The simulations for the examples were made by solving the one‐dimensional time‐dependent Schrödinger equation by the numerical procedure of shooting methods, using a planar–planar scanning tunneling microscope model with the exact multiple image potential.

ISSN:0734-211X    

DOI:10.1116/1.588725

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

A scanning force microscope can be used to measure a device’s internal electrical potential with high spatial and temporal resolution. We present experimental results taken with a scanning force tester constructed in our lab that offers nanometer spatial resolution and gigahertz measurement bandwidth. The results are comparable to network analyzer results.

ISSN:0734-211X    

DOI:10.1116/1.588726

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The similarity of the operating principles of the atomic force microscope and the phonograph has suggested testing of a phonograph cartridge as a force sensor for scanning force microscopy (SFM). The results were surprisingly good. A stereophonic piezoelectric cartridge showed a height resolution limit of 0.01 Å, and was used, with the original stylus, to take SFM images in both normal and lateral force modes. The device works in constant height mode on a height range of more than 106, from less than 1 Å to about 100 μm, but its high capacitance sensors also allow the feedback mode operation. A model of the lateral resolution of an exploring stylus that allows a direct comparison with the resolution of optical instruments is discussed.

ISSN:0734-211X    

DOI:10.1116/1.588727

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

A scanning shearing stress microscopy has been developed in order to investigate shearing stress effect in the surface. This microscopy is based on scanning tunneling microscopy and makes it possible to measure shearing stress. The sample is coupled on the AT‐cut quartz resonator which is oscillated at its resonance frequency, and the shift of the resonant frequency corresponding to the strength of the shearing stress in the sample can be measured. Gold thin films have been observed for the surface topography as the image of scanning tunneling microscopy and also the distribution of subsurface shearing stress is identified, simultaneously. The strong shearing stresses are generated at the hollow parts of the surface topography. These stresses are caused by the frictional force between the scanning tunneling microscope tip and the sample surface which is oscillated laterally.

ISSN:0734-211X    

DOI:10.1116/1.588728

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Active noise reduction has been accomplished in atomic force microscopy by applying a high frequency, low amplitude vibration to the cantilever while it is in contact with a surface. The applied excitation (≳200 kHz; ∼1 nm) is acoustically coupled to the tip and dampens the resonanceQfactors of the system. The applied frequency is well above the bandwidth of the acquisition system (50 kHz). We call this mode ‘‘gamble mode’’ or ‘‘resonance contact.’’

ISSN:0734-211X    

DOI:10.1116/1.588729

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

In this article a novel probe for atomic force microscopy will be introduced. It is based on a conventional micromachined silicon cantilever with an integrated electronic sensor which determines the cantilever deflection. The principle setup of this probe is described and a theoretical and an experimental investigation of the sensitivity of the probe will be presented. The probe is suitable for operation in the static as well as in the dynamic mode and was employed for imaging various materials. To enhance the sensitivity of the detection system and to obtain simultaneously a cantilever with a small spring constant, the geometry of the cantilever was modified. Finite element method calculations were performed to get the optimum sensor design. Furthermore, a different cantilever concept was designed to perform lateral force microscopy as well.

ISSN:0734-211X    

DOI:10.1116/1.589161

出版商:American Vacuum Society    

年代:1996

数据来源: AIP