摘要:

Controllable etching of GaAs(100) has been electrochemically achieved on a nanometer scale by using a scanning tunneling microscope (STM) in acidic solutions(pH=2–3).The realized features onn-GaAs(100) surface were as small as 10 nm. We studied the dependence of the etching rate on the potentials applied to the STM tip as well as the GaAs substrate. These results indicate that the hole injection from the tip is responsible for the local etching of GaAs surfaces in electrolytes rather than local charges induced by an electric field.

ISSN:1071-1023    

DOI:10.1116/1.589553

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

For large movable parts in the microelectromechanical systems, etch holes are needed to facilitate the releasing process. These etch holes obviously weaken the structure and affect its mechanical properties. New techniques and structures have been developed to measure the mechanical properties of very thin microelectromechanical systems (MEMS) materials. A dog-bone shaped tensile specimen is imposed with a uniaxial stress field and strain is directly measured on the specimen with the interferometric strain/displacement gage. This testing approach has been used to study the effect of etch holes on the mechanical properties of polysilicon thin film. The material is phosphorus doped, low pressure chemical vapor deposited polysilicon deposited at MCNC the multi-user MEMS processes. The specimen is 3.5 μm thick and 0.6 mm wide at its narrowest point. The etch holes are about 5 μm in diameter and 30 μm apart. Compared with the mechanical properties of the specimens without etch holes, the tensile strength has dropped by 50% and the Young’s modulus decreases only about 18% due to the existence of the etch holes. Finite element modeling is applied to the specimens with etch holes and in agreement with the test results.

ISSN:1071-1023    

DOI:10.1116/1.589554

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

The effect of variedH+concentration on surface morphology of porous silicon (PS) is observed by atomic force microscopy technique. A new mechanism of PS formation concerningH+effect is proposed. The photoluminescence (PL) spectra of two typical PS samples have different responses in the short-wavelength region. Surface photovoltage spectra results imply that the short-wavelength PL band of the PS sample prepared in highH+concentration may be related to direct band-gap transition.

ISSN:1071-1023    

DOI:10.1116/1.589555

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

A strong photoluminescence (PL) with a peak position of ∼420 nm (2.95 eV) under exciting radiation of λ=300 nm, and two new luminescence peaks at ∼420 and 470 nm, under λ=633 nm excitation at room temperature are observed, evidently for Ge nanocrystallites embedded inSiO2thin films(Ge–SiO2)prepared by the ion-beam sputtering technique. The studies reveal that the nanometer-size crystalline Ge have a type of face-centered-cubic structure and characteristics of direct optical transition. It is suggested that the visible PL ofGe–SiO2thin films is not only related to the quantum size effect due to three-dimensional confinement of electrons and holes, but also closely associated with the particular microstructure of the Ge nanocrystallites.

ISSN:1071-1023    

DOI:10.1116/1.589556

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

The generalized phonon density of states for Al nanoclusters was studied theoretically using molecular dynamics. By doing this anharmonic effects could be fully considered. In order to investigate the structure of the clusters we have also calculated the structure factorS(q)(Fourier transform of the pair correlation function). The calculations were done for systems consisting of 500 atoms and at several temperatures. Stable and metastable cluster states are observed: The clusters in the metastable state show a well defined peak in the structure factorS(q)which we interpret as superstructure. The appearance of the superstructure in the metastable state is accompanied by substantial change in the phonon density of states.

ISSN:1071-1023    

DOI:10.1116/1.589557

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

We performed quadrupole mass spectrometry (QMS) of Si clusters that thermally desorbed from various surfaces in ultrahigh vacuum. To investigate the effect of substrate on cluster formation, different kinds of substrates were prepared: Si(100) wafers, Si(111) wafers, and Si-deposited Ta polycrystalline sheets. When Si wafers were heated at 900–1300 °C, QMS spectra showed that clusters up toSi6sublimed from the surfaces. Both of (100) and (111) had the same activation energy for desorption of the clusters. On the contrary, QMS spectra from Si-deposited Ta at 1500 °C showed monomeric Si only. These results agree with the thermodynamic consideration that the desorption rate of each cluster is determined by its formation energy. The relation of cluster formation with the surface structure is also discussed.

ISSN:1071-1023    

DOI:10.1116/1.589558

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Nanoparticulate titanium dioxide-stearate(TiO2-St)monolayer was directly obtained usingTiO2hydrosol as the subphase. The atomic force microscopy images of monolayer, show that the higher coverage were obtained through deposition on the hydrophilic Si(100) surface rather than the hydrophobic Si(100) surface. From the surface photovoltage spectra ofTiO2-Stmonolayer, it can be followed that the photovoltage response of then-type silicones increased by a factor of 25, and 5 times after a monolayer ofTiO2-StLangmuir–Blodgett (LB) films was transferred onto hydrophobic and hydrophilic Si surface, respectively. On the contrary, the photovoltage response value is reduced by ∼40 and 5 times by the deposition of the LB monolayer in the case of the hydrophobic and hydrophilicp-type Si surface, respectively. It is considered that the enhancement of the photovoltage response may be due to the ordered electrostatic potential orientation of the Si(100)/TiO2-St/ITOheterostructures.

ISSN:1071-1023    

DOI:10.1116/1.589559

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

The structure of theCr(001)-p-(1×1)-Nsurface was studied by use of the tensor low energy electron diffraction (LEED) current-voltage(I–V)analysis. From the LEED diffraction pattern observed in the process of cleaning of the Cr(001) surface, N was found to form a(1×1)structure on the Cr(001) surface. ExperimentalI–Vcharacteristic curves for theCr(001)-p-(1×1)-Nstructure were generated by Video LEED System and these experimental results were compared with that obtained through theoretical calculations via the TLEED program to analyze surface structure. As a result, we found that N is adsorbed in the hollow site on the Cr(001) surface. The interlayer distances ofdN1,d12,andd23are found to be 0.251, 1.814, and 1.410 Å, respectively.

ISSN:1071-1023    

DOI:10.1116/1.589560

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

We have systematically investigated, by using scanning tunneling microscopy, the adsorption and film growth ofC60on the various GaAs(001) surface phases prepared by molecular-beam epitaxy. For most phases, theC60overlayer exhibits the usual close-packed fcc(111) configuration with its lattice constant close to that of the bulkC60crystal. However, in the case ofC60on the As-rich2×4substrate, the epitaxial growth is found to be quite different and unique;C60film takes its (110) crystalline axis; theC60overlayer is highly strained with a lattice expansion of∼13%,and this structure is very stable at least up to 10 ML. We will address the underlying formation mechanism of this new structure in terms of a charge transfer from the As-dangling bonds toC60sand a site-specificC60-substrate interaction, as confirmed by molecular dynamic simulations. The present system provides a unique opportunity to study fullerene and/or noble-gas related two-dimensional phenomena, and demonstrates a potential for fabrication of novel fullerene-based devices, such as strained superlattice structures.

ISSN:1071-1023    

DOI:10.1116/1.589561

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

We developed an atomic force microscopy with the tip position was accurately controlled through the magnetic interaction between a coil and the magnet fixed behind the cantilever. By incorporating a feedback system, we could control the motion of a soft cantilever (0.68 N/m) in air and liquid, and obtain force curves without instabilities originating from the strong attractive and adhesive forces between the tip and the sample.

ISSN:1071-1023    

DOI:10.1116/1.589562

出版商:American Vacuum Society    

年代:1997

数据来源: AIP