摘要:

A recently developed spin coating method has been employed to produce a homogeneous distribution of nanometer‐sized metal clusters onto a flat oxidic support. The particle size and distribution, and the total amount of material deposited has been studied by comparing the results of atomic force microscopy (AFM), Rutherford backscattering spectroscopy (RBS), and the appropriate hydrodynamic deposition equations. It is shown that the AFM is capable of producing a three‐dimensional image of the surface which enables the particle number density and particle heights to be accurately determined. However, it is clear that as a result of tip convolution effects the particle diameter cannot be accurately determined. Using a hemispherical particle model the amount of material deposited during spin coating can be calculated from the AFM images. This calculation is shown to be accurate to approximately 50% in comparison with the results obtained from RBS. In contrast, it is shown that for a copper acetate precursor the predictions of the hydrodynamic equations are accurate to 2%. In the light of these results an assessment is made of the utility of AFM in the investigation of model catalyst systems and fundamental metal cluster studies.

ISSN:0734-211X    

DOI:10.1116/1.589140

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

We have succeeded in imaging individual C60molecules that have been adsorbed onto the tunneling region of a scanning tunneling microscopy tip. The individual tip‐adsorbed molecules are imaged by scanning the fullerene‐adsorbed tip over a defect covered graphite surface. The defects are generated by low energy argon ion bombardment and protrude from the graphite surface. These nanometer‐size defects serve as a surface tip array which inverse images the molecules adsorbed to the tip when the surface is scanned.

ISSN:0734-211X    

DOI:10.1116/1.589141

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Near‐field optical microscopy generally uses a tapered optical fiber, which is metal coated, to form a sub‐wavelength sized light source. Here, a technique for the fabrication of a new type of probe is described. The new design is based on atomic force microscope probes and consists of a silicon nitride cantilever with a solid transparent conical tip. The probes are made using micromechanical techniques, which allow batch fabrication of the probes. A near‐field scanning optical microscope system was built to test the probes. This system features force detection by a beam deflection technique and subsequent force feedback together with a conventional optical microscope. A major advantage of the apparatus is the ease at which images are obtained. Results on a test sample show that an optical resolution of 300 nm can be obtained together with a simultaneous height image.

ISSN:0734-211X    

DOI:10.1116/1.589142

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

A piezoresponse technique based on scanning force microscopy (SFM) has been used for studying domain structure in ferroelectric thin films. Studies were performed on Pb(Zrx,Ti1−x)O3(PZT) thin films produced by a sol–gel method. The piezoresponse images of the PZT films were taken before and after inducing polarization in the films by applying a direct current voltage between the bottom electrode and the SFM tip. Polarization induced patterns were written with 20 V pulses and subsequently imaged by the SFM piezoresponse technique. The effect of the film structure on the imaging resolution of domains is discussed.

ISSN:0734-211X    

DOI:10.1116/1.589143

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Electron trajectories and light emitting images for the electron emission from a single starlike thin‐film field emitter and a 200‐μm‐sq field emitter array have been studied. In the early stage of electron emission from the starlike field emitters, a unique light emitting image appeared on a phosphor screen. The image consisted of an upper hornlike and a lower mountainlike pattern, their geometrical configuration roughly agreeing with the simulation results of electron trajectories using a finite integral equation method code. From the observation of the light emitting images for the starlike field emitters, we found that the images of the starlike field emitters resulted from overlapping electron beams emitted from the four apices of each field emitter. The emitted electrons had an electron emitting angle of 40° and a horizontal electron spread angle of 30°–40° at an anode voltage of 340 V. An increase in the anode voltage to 680 V reduced the vertical electron emitting angle to 30°.

ISSN:0734-211X    

DOI:10.1116/1.589144

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

A Cl2plasma generated by an electron cyclotron resonance source was used to etch field emitter arrays in Si. Compared to wet etching, emitter arrays with sharper emitter tips and higher packing density can be formed by dry etching. Mask erosion was used to control the etch profile in Si. SiO2masks with different profiles were patterned by wet and dry etching, and the effects of the initial SiO2masks slope and etch conditions on the resultant Si profile were investigated. The lateral etch rate of SiO2decreased from 363 to 150 nm/min as the SiO2slope increased from 17° to 45°. As a result, the slope of the Si etch profile increased from 52° to 78° after dry etching to a depth of 1.8 μm. The ion flux and energy, controlled through coupled microwave and rf power, were used to obtain the desired etch rate and basewidth of the emitters. By increasing the pressure during etching, the lateral etch rate of SiO2was reduced and more vertical Si profiles were developed. As pressure was increased from 0.5 to 10 mTorr, the lateral etch rate of SiO2reduced from 414 to 144 nm/min while the vertical Si etch rate did not change significantly. This caused the slope of the Si etch profile to increase from 42° to 69°. Using the above technique, arrays of sharp emitter tips in Si with 2.2 μm basewidth and 11 μm height were fabricated and packing densities up to 1×107tip/cm2were achieved.

ISSN:0734-211X    

DOI:10.1116/1.589145

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Ballistic electron emission microscopy is used to investigate the electron scattering properties of undamaged and focused ion beam implanted Au/GaAs diodes. Implanted regions show decreased ballistic electron transmission attributed to increased scattering. A quantitative model of electron transport is developed that includes quantum mechanical transmission at the interface, scattering effects from optical phonons and implantation induced defects in the semiconductor, and scattering in the metal layer. Model predictions of scattering in undamaged regions show good agreement with the data. However, we conclude additional scattering effects must be included to describe the implanted structures.

ISSN:0734-211X    

DOI:10.1116/1.589146

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The atomic structure and atomic scale roughness of GaAs(001)2×4 surfaces fabricated by molecular beam epitaxy was examined by scanning tunneling and atomic force microscopy. In particular, the size and spatial distribution of atomic steps at the surface was quantitatively determined as a function of annealing time and annealing temperature. Two different parameters are required to fully describe the surface roughness. In general, we found that prolonged annealing under vacuum of surfaces produced by thermal desorption of As cap layers is sufficient to reduce the surface roughness to that typical of as‐grown surfaces.

ISSN:0734-211X    

DOI:10.1116/1.589147

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Phase‐sensitive photoreflectance (PR) has been used here to study undoped AlGaAs/GaAs single and multiple quantum well structures. The PR features of these structures exhibited a phase detection angle dependence as a function of spectral energy at the output of the lock‐in amplifier, which was attributed to the differences in temporal behavior of the PR features from different layers within these structures.

ISSN:0734-211X    

DOI:10.1116/1.589148

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Nonlinear characteristics induced by accumulation of photogenerated carriers in a cap layer on a GaAs/GaAlAs multi‐quantum well (MQW) structure can be observed at 300 K under weak photoexcitation (2.5 mW/cm2). Photoinduced currents (PIC) are measured for various structures of cap layer. Negative differential properties are observed in the relations between PIC and forward bias voltage for the MQW structures with a cap layer including InAs/GaAs short period superlattice. The phenomenon is reduced in the case of a cap layer including an InGaAs alloy and disappears in the case of that composed of only GaAs. These experimental results are explained reasonably considering the capability of the cap layer to accumulate photogenerated carriers.

ISSN:0734-211X    

DOI:10.1116/1.589149

出版商:American Vacuum Society    

年代:1996

数据来源: AIP