摘要:

This article describes noncontact scanning force microscopes that make use of a new type of direct‐oscillating unimorph piezoelectric microcantilever. Since the scanning force microscope system using the piezoelectric cantilever requires no external deflection detector, it is very simple, compact, and is easy to operate in comparison with the conventional system using the optical sensors. In the noncontact operation mode, the piezoelectric cantilever is more preferred to other deflection detectable cantilevers, because it can be directly oscillated by applying voltage to itself. The methods used to detect the resonance shift due to force gradients acting the tip are slope detection and frequency modulation detection. In the slope detection technique, the resonance shift is detected by measuring the change of the amplitude or phase of the induced piezoelectric current. In frequency modulation detection, the resonance shift is detected by direct measurement of the resonance frequency of the current. The piezoelectric microcantilever serves as a resonator in this technique. The constructed noncontact scanning force microscope has been used to obtain the slope detection image of the Au film surface with grains of about 50 nm diam. The measured characteristics data of the fabricated cantilevers allow us to study the dependence of minimum detectable force gradients on the lever dimensions. We have discussed the design of the cantilever for noncontact operations.

ISSN:0734-211X    

DOI:10.1116/1.589193

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

We have designed and constructed a combined surface plasmon resonance‐scanning force microscope instrument capable of providing simultaneousinsituinformation on the dynamic behavior of the refractive index and spatial characteristics of surfaces. These data show considerable potential for revealing new insights into interfacial phenomena. In this article, we describe the instrument in detail and provide a brief example of the results obtained when studying the hydrolytic degradation of a bioerodable polymer film [poly(orthoester)] exposed to an acidic environment. Analyses of the plasmon resonance and force microscopy data reveals the kinetics of the polymer degradation process and the heterogeneities in polymer distribution and degradation, respectively.

ISSN:0734-211X    

DOI:10.1116/1.589194

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

We report the first chemical identification of a cluster of atoms from identifiable sites on an extended crystal surface. The instrument used combines the functions of a scanning tunneling microscope (STM) with a time‐of‐flight (TOF) atom probe. Atoms are transferred from regions of interest identified in STM images to the tip, from which they are ejected into a TOF spectrometer. Preliminary results are shown in which a cluster of silicon atoms taken from the Si(111) 7×7 surface is identified by TOF spectra. Applications of these ‘‘atomic tweezers’’ for microanalysis are discussed.

ISSN:0734-211X    

DOI:10.1116/1.589195

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The (210) surface of ammonium perchlorate has been studied with an atomic force microscope. Unexpected surface ripples with shallow amplitudes (typically less than 3 nm) and giant wavelengths (typically between 0.5 and 1.3 μm) have been discovered. The dominant type shows a wave vector along the [001] direction, and a second type forms a pattern in which two wave vectors make an angle of ∼60° with each other. The amplitude and wavelength of the ripples are clearly correlated. Their size depends on the local surface structure, but their direction is usually keyed to the main crystalline directions. Unfortunately we have also discovered a new artifact that can produce similar images. We discuss the evidence we have gathered thus far to support the existence of the ripples in addition to that of the artifact.

ISSN:0734-211X    

DOI:10.1116/1.589196

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

We have used the tip of an ultrahigh vacuum scanning tunneling microscope to induce displacements of C60molecules on the Si(111)‐7×7 surface at room temperature. The manipulation is achieved by using a sweeping procedure we have developed which moves the tip closer to the surface and sweeps it across in a predetermined direction. Feedback control of the tunnel current is maintained throughout and the tip‐surface separation is adjusted by changing the sample bias and tunnel current. For a 0.007 monolayer (ML) coverage of C60, a sweeping area of 60 Å×60 Å was used to move individual C60molecules, while for higher coverages (0.05–0.2 ML) a sweeping area of 216 Å×216 Å was used to move large groups of C60molecules. We show an example at 0.2 ML coverage where we have removed C60over an area 110 Å×370 Å resulting in the formation of a line of C60molecules 20–30 Å in width.

ISSN:0734-211X    

DOI:10.1116/1.589197

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Cross‐sectional scanning tunneling spectroscopy experiments were performed under air‐ambient conditions on cleaved Si‐based metal–oxide–semiconductor (MOS) junctions. With the scanning tunneling microscope tip in the vicinity of the oxide–semiconductor interface, the electric field‐induced depletion region was found to pinch‐off the tunneling current similar to the effect in a MOS field‐effect transistor (MOSFET) where increasing gate bias reduces the channel current. In this study, the experimentally observed dependence of the tip‐semiconductor I‐V characteristics on the gate bias was interpreted within a transfer‐Hamiltonian tunneling model representing the tip‐semiconductor junction and including both tip‐induced band‐bending and gate bias effects.

ISSN:0734-211X    

DOI:10.1116/1.589199

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Thermal and near ultraviolet‐light induced graft copolymerization of pristine, argon‐plasma, oxygen‐plasma, and ozone‐pretreated thermoplastic [high‐density polyethylene, poly(tetrafluoro‐ ethylene), and poly(ethylene terephthalate)], partial thermoset (polyimide), and thermoset (cross‐linked polyaniline) films with hydrophilic monomers, such as acrylamide, acrylic acid, and sodium salt of styrene sulfonic acid, were carried out. The microstructures and compositions of the modified surfaces were studied by angle‐resolved x‐ray photoelectron spectroscopy and atomic force microscopy. In most cases, the density of surface grafting is enhanced by the pretreatment processes. In the case of thermoplastic films, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer which is richer in substrate chains to form a stratified surface structure. In the case of partial thermoset films, the grafted chains form either a surface layer uniformly intermixed with the substrate, or a graft‐rich surface layer in a migration that is sterically hindered due to the presence of the grafted chains. In the case of thermoset films, the hydrophilic graft remains predominantly at the outermost surface of the substrate. The surface microstructures are further supported by dynamic water contact angle measurements. The differences in the surface structure and morphology of the pristine, pretreated, and graft copolymerized surfaces are also revealed by atomic force microscopy images.

ISSN:0734-211X    

DOI:10.1116/1.589200

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Forinsituobservation in a 1 MeV TEM Co–Ge liquid alloy ion sources (LAISs) were mounted to a special specimen holder revealing the formation of the field‐stabilized Co–Ge liquid alloy cone, the change in the tip shape as a function of the ion emission current, spatial shifts of the liquid alloy cone, and microdroplet emission from Co–Ge LAISs. This has facilitated the better understanding of the ion and microdroplet emission process from Co–Ge LAISs in a large range of ion current. Below the onset voltage the shape of the tip covered with the liquid Co–Ge alloy is spherical. At the onset voltage the Taylor cone is formed. A jetlike protrusion at the cone vertex may or may not exist. At higher ion emission currents there is a jetlike protrusion at the Taylor cone vertex. The cone half‐angle α decreases and the jet lengthlincreases with increasing emission currentIe. Linear dependences of α andlonIeare found. Emission of microdroplets is observed at the shanks behind the Taylor cone. The radius of microdroplets varied between 0.035 and 10 μm. These microdroplets are emitted in time intervals of about 0.1 s and more.

ISSN:0734-211X    

DOI:10.1116/1.589201

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

We applied a time‐resolved scanning electron microscope to the analysis of the movement of micromechanical structures. A detector signal modulation method is used in our experiment. The major advantage of this method is that no hardware modifications are required to a commercially available scanning electron microscope. The test devices are simple cantilever beams fabricated from silicon dioxide with and without an aluminum coating. These cantilever beams are electrostatically excited at resonance under several conditions. Both time‐resolved images and precise resonant frequency measurements of these microcantilever beams are obtained. We found that electrically floating silicon dioxide beams without an aluminum coating can also be excited stably by an ac driving voltage at resonance under scanning electron microscopy observation. Accumulated charge on the cantilever beam caused by the electron beam irradiation is found to be positive and this charge results in a driving force between the cantilever beam and the driving electrode. A time‐resolved scanning electron microscopy method is proved to be a useful technique to determine the resonant frequencies and resonant mode shapes of micromechanical systems.

ISSN:0734-211X    

DOI:10.1116/1.589202

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Focused ion beam columns with liquid metal ion sources should be optimized to give the highest possible current in a probe of given dimension. A procedure for this optimization is presented, which includes the influence of Coulomb interactions between the particles in the beam. The column is first optimized without including the Coulomb effects and it is found that the optimized magnification and aperture size are independent of the gun brightness. The magnification approaches a constant value in the high current domain, where the gun lens aberrations seriously influence the probe size. The Coulomb effects can be characterized by pointing out a domain in the probe current‐probe size plane which is inaccessible, no matter how high the brightness of the gun may be. The approximate position of this inaccessible area can be found with a relatively small number of calculations. It is then demonstrated how the beam current as a new function of probe size can be reoptimized by the choice of magnification and aperture size. Coulomb effects turn out to be dominating the probe size except for very small probes and for very large probes.

ISSN:0734-211X    

DOI:10.1116/1.589203

出版商:American Vacuum Society    

年代:1996

数据来源: AIP