Contact Mode Atomic Force Microscopy Research Articles

9.3 Scanning Local Acceleration Microscopy: SLAM

In chapter 8.2, it has been shown that local spectoscopy of samples can be performed using theScanning Local-Acceleration Microscope, abbreviated SLAM. It is a modification of contact-modeAtomic Force Microscopy (AFM) and its principle is to excite the sample at frequencies above theresonance of the tip-sample system. As the acoustic wavelength is much larger than the sample’sdimension, there is no propagation of the vibration, but a quasi-uniform displacement motion of thewhole sample, which cyclically pushes on the AFM tip (fig. 9.3.1). As the vibration frequency isabove the first contact resonance of the tip-sample system, the inertia of the tip prevents it fromcompletely following the imposed displacement, inducing a non-negligible cyclic stress and givingrise to a cyclic deformation of the sample in the region of the contact between the tip and the sample.All other parts of the sample remain undeformed.

Atomic Force Microscopy Observation of the Nanostructure of Tetradecyltrimethylammonium Bromide Films Adsorbed at the Mica/Solution Interface

An investigation was performed by atomic force microscopy (AFM) using two measuring modes on the nanostructure of adsorbed films of tetradecyltrimethylammonium bromide (C14TAB) formed at the solution/mica interface. Cylindrical micelle-like aggregates, quite similar to those reported by Manne and Gaub (Science 1995, 270, 1480−1482), were found in noncontact AFM observations based on the electrostatic repulsive force between mica substrate with adsorbed C14TAB and AFM probe. The cylindrical micelle-like structure was observed only above the critical micelle concentration (cmc) of C14TAB (3.5 mM), and the diameter of the cylinder was ca. 5−6 nm. In contrast, a hexagonal lattice-like structure with a 1.0−1.2 nm lattice spacing, which differs from that for mica substrate, was found in a wide range of surfactant concentrations covering those above and below the cmc when contact mode AFM observations were carried out in the adhesive force region. The adsorbed state of C14TAB on the mica substrate was discussed ...

Mapping of Lateral Vibration Amplitude of the Tip at a Sub-Atomic Level in Contact Mode Atomic Force Microscopy.

Mapping of Lateral Vibration Amplitude of the Tip at a Sub-Atomic Level in Contact Mode Atomic Force Microscopy.

原子間力顕微鏡のACノンコンタクトモードによる天然雲母およびSUS304鋼表面の純水濡れ形態観察

原子間力顕微鏡のACノンコンタクトモードによる天然雲母およびSUS304鋼表面の純水濡れ形態観察

Atomic force microscopy imaging of the membrane part CF0 and the subunit III complex of chloroplast ATP-synthase

ATP-synthases consist of a hydrophilic part F1 containing the nucleotide binding sites and a hydrophobic membrane integrated part F0 which is involved in proton translocation. The structure of F0 is only partly known. We isolated the membrane part F0 from Spinacia oleracea chloroplasts using a new protocol. Starting with the holoenzyme, F1 was removed by treatment with Na-thiocyanate, then F0 was purified by a sucrose density gradient centrifugation followed by native preparative electrophoresis. Due to the mild purification conditions all four F0 subunits I, II, III and IV were found in the resulting complex. Heat treatment of this complex leaves intact only the subunit III complex. Since the protein was obtained in dodecylmaltoside-lipid-micelles, 2D crystallisation was initiated by dialysis in presence of additional lipid. The subunit III complex forms two different kinds of 2D crystals, while F0 builds large 2D sheets of F0 aggregated in an unordered way. These sheets and crystals were imaged on mica surface by contact mode atomic force microscopy. The surface profiles of subunit III crystals are easily interpreted and similar to earlier data [H. Seelert (2000) Nature 405, 418-9], whereas the F0 sheets yield profiles of weak height contrast. Therefore these F0 images were processed electronically to reduce image noise. The resulting images are compared to our earlier data obtained by transmission electron microscopy after negative staining.

Ge Layer Transfer To Si For Photovoltaic Applications

ABSTRACTWe have successfully used hydrophobic direct wafer bonding along with hydrogen-induced layer splitting of germanium to transfer 700 nm thick, single-crystal germanium (100) films to silicon (100) substrates without using a metallic bonding layer. The metal-free nature of the bond makes the bonded wafers suitable for subsequent epitaxial growth of layered solar cells at high temperatures without concern about metal contamination of the device active region. Contact mode atomic force microscopy images of the transferred germanium surface generated by the formation of micro-bubbles and micro-cracks along the hydrogen-induced layer-splitting interface reveals minimum rms surface roughness of between 10 nm and 23 nm. Electrical measurements indicated ohmic I-V characteristics for germanium layers bonded to silicon substrates with ∼400 Ω cm−2 resistance at the interface. Triple-junction solar cell structures grown on these Ge/Si heterostructure templates by metal-organic chemical vapor deposition show comparable photoluminescence intensity and minority carrier lifetime to a control structure grown on bulk Ge. The use of a molecular beam epitaxy Ge buffer layer to smooth the cleaved surface of the Ge heterostructure has been shown to smooth the rms surface roughness from ∼11 nm to as low as 1.5 nm with a mesa-like morphology that has a top surface roughness of under 1.0 nm giving a promising surface for improved solar cell growth on solar cell structures.

強磁性トンネル接合のスピン依存局所伝導特性

The local electrical properties in ferromagnetic tunnel junctions was measured using contact-mode Atomic Force Microscopy (AFM). The electrical current images reflected the barrier height distribution determined by local I-V curve measurement The TMR ratio was estimated from the current histogram. The estimation closely fitted the experimental temperature dependence of TMR ratio. The TMR ratio was shown to increase with a decrease in the deviation of barrier height distribution and with an increase in average barrier height The effect of the local current channel with low barrier height on the TMR ratio is also discussed.

An Investigation of Scanning Capacitance Microscopy on Iron-Contaminated p-Type Silicon

Scanning capacitance microscopy ~SCM! is employed to examine iron-contaminated p-type Si samples. For slightly contaminated samples, a dc voltage of 20.8 V, applied between the sample and the conductive tip, induces positive trapped charges. Owing to the existence of these charges, the region containing trapped charges exhibits an obviously low dC/dV signal. According to contact-mode atomic force microscopy results, the surface morphology has little effect on the SCM signal. The experimental results indicate that SCM is capable of detecting the distribution of oxidation-related defects which cannot otherwise be easily observed by atomic force microscopy and transmission electron microscopy. © 2001 The Electrochemical Society. @DOI: 10.1149/1.1389877# All rights reserved.

Ion and molecular recognition effects on the crystallisation of bovine serum albumin–salt mixtures

The effects of various bio-medically important salts Na, K, Li, Mg, Ca, Ni, Co, Cr, Fe and Cl on the dendritic or simple crystallisation of aqueous solutions of Bovine Serum Albumin have been investigated by contact or non-contact mode Atomic Force Microscopy. Four classes of structure are observed depending on the nature of the cation; a) unstructured protein–salt aggregates, b) large scale protein–salt meso-composites, c) mixed salt–protein gels, and d) microscopically phase separated systems.

Atomic Force Microscope Image Contrast Mechanisms on Supported Lipid Bilayers

This work presents a methodology to measure and quantitatively interpret force curves on supported lipid bilayers in water. We then use this method to correlate topographic imaging contrast in atomic force microscopy (AFM) images of phase-separated Langmuir-Blodgett bilayers with imaging load. Force curves collected on pure monolayers of both distearoylphosphatidylethanolamine (DSPE) and monogalactosylethanolamine (MGDG) and dioleoylethanolamine (DOPE) deposited at similar surface pressures onto a monolayer of DSPE show an abrupt breakthrough event at a repeatable, material-dependent force. The breakthrough force for DSPE and MGDG is sizable, whereas the breakthrough force for DOPE is too small to measure accurately. Contact-mode AFM images on 1:1 mixed monolayers of DSPE/DOPE and MGDG/DOPE have a high topographic contrast at loads between the breakthrough force of each phase, and a low topographic contrast at loads above the breakthrough force of both phases. Frictional contrast is inverted and magnified at loads above the breakthrough force of both phases. These results emphasize the important role that surface forces and mechanics can play in imaging multicomponent biomembranes with AFM.

Thermal and Chemical Stability and Adhesion Strength of Pt Nanoparticle Arrays Supported on Silica Studied by Transmission Electron Microscopy and Atomic Force Microscopy

The thermal, chemical, and mechanical stability of Pt nanoparticles supported on silica has been measured with transmission electron microscopy (TEM) and atomic force microscopy (AFM). The nanoparticle arrays were fabricated using electron beam lithography, which produced uniform particle sizes (20 ± 1 nm) and uniform interparticle distances (150 ± 1 nm). TEM studies provided information about the array periodicity, particle dimensions, and crystallinity of individual particles. Before heat treatments, individual Pt nanoparticles were found to be polycrystalline with crystalline domain sizes of 4−8 nm. After heating to 1000 K in high vacuum (10-7 Torr) and 1 atm H2, the crystalline domain sizes within individual particles grew larger, without noticeable deformation of the array. A similar enlargement of crystalline domains was seen in 1 atm O2 at a lower temperature of 700 K. Using contact mode AFM, the height, periodicity, and adhesion of the particles were determined. On a newly prepared sample, Pt part...

Atomic force microscope: a tool for studying ionophores

The aim of the investigations was to show the analytical use of an atomic force microscopy (AFM) tip coated with an ion-selective membrane and to show that the ion-selective boundary potential is detectable as a force induced by ion-selective electrostatic interactions, which are more pronounced than double-layer forces. This new technique allows the area-specific ion exchange over boundaries to be displayed with a destruction-free technique by AFM in an aqueous buffer. From experiments with ISEs (ion-selective electrodes), a boundary potential for valinomycin was assumed to be established in close vicinity to a K+-releasing surface. To trace this boundary potential, an AFM tip was coated with a potassium-selective polymer film containing valinomycin as used in preparing ISEs. The K+-releasing substrate was prepared by incorporating a lipophilic potassium salt into a plasticized PVC layer. In contact with an electrolyte such as sodium chloride solution, an ion exchange takes place. Analogue experiments were performed using a sodium-selective ionophore, DD16C5, incorporated into the coating of the AFM tip, with a Na+-releasing substrate. The boundary potential was traced and investigated with the help of force vs distance curves. The resulting adhesion forces for a valinomycin-coated tip in a 150 mM NaCl solution were 9.8+/-3.275 nN using a blank PVC substrate and 330.15+/-113.0 nN using a substrate containing 10 wt % potassium tetrakis(4-chlorophenyl) borate. The selectivity of the ion-selective AFM tips was measured on sodium relative to potassium-releasing substrates and studied in different salt solutions with concentrations between 10 mmol L(-1) and 1 mol L(-1). For valinomycin, a force selectivity coefficient log Kf(K,Na) of -2.5+/-0.5 for K+ against Na+ and a selectivity coefficient log Kf(Na,K) of -4 +/- -0.5 for DD16C5 were measured. In addition, the surface of the polymer substrate was imaged by AFM in contact mode with and without lipophilic potassium salt. The modulation of the force-distance curves induced by the ion exchange was compared to the experimental change in elasticity of the blank and ion-exchanging substrate. The Young's moduli measured with strain force analysis on a potassium-containing substrate were 5 times smaller than the ones registered with nanoindentation and did not explain the modulation of the force vs distance curves.

Evaluation of Intermittent Contact Mode AFM Probes by HREM and Using Atomically Sharp CeO2 Ridges as Tip Characterizer

The imaging process of the atomic force microscope (AFM) in contact, noncontact, and intermittent contact mode is still debated after more than a decade of widespread use, in particular when imaged features are approaching atomic dimensions. Several models for the interaction between the tip and the surface have been suggested, but generally they all need an exact description of the geometry of either the tip, the surface, or both. We present here a tip characterizer with close to reproducible geometry, exactly known angles of all surfaces, and sharp features with close to atomic dimension. It has been tested on three commercial AFM probes and a laboratory-made electron-beam-deposited tip, sharpened by oxygen plasma etching. High-resolution transmission electron microscopy has been used to unambiguously verify the tip shapes down to atomic dimensions, both before and after imaging in intermittent contact mode. The effect on the recorded AFM images is shown of tip shape, tip wear, spallation, and accumulation on the tip of amorphous and crystalline debris. The imaging is shown to be a dynamic event, with a continuously changing tip and occasional catastrophic events that give abrupt changes in imaging conditions. The tips are severely worn down already after scanning a few centimeters, but accumulated amorphous material may still give it imaging capabilities in the nanometer range, even with having a tip radius exceeding 130 nm. Accumulated amorphous material seems to be more important than previously believed. Procedures for tip in situ characterization and reliable imaging are suggested.

Atomic force microscopy study of erythrocyte shape and membrane structure after treatment with a dihydropyridinic drug

The overall shape and membrane surface of human erythrocytes (RBCs) in the presence of nifedipine (a dihydropyridinic drug used in the clinical treatment of hypertension and angina pectoris) were imaged by contact-mode atomic force microscopy. Nifedipine induces in RBCs relevant morphological changes the extent of which increases as a function of drug concentration and incubation time. The modifications have been interpreted as mainly due to insertion of nifedipine into the outer layer of the RBC membrane. The potential effect of nifedipine as a hemoglobin denaturant has been ruled out by x-ray absorption near-edge structure and optical spectroscopies.

Atomic Force Microscopy of Living Cells

This paper is a review of our results of the application of atomic force microscopy (AFM) to the three-dimensional observation of living cells. First, we showed AFM images of living cultured cells in fluid. Contact mode AFM of living cells provided precise information on the shape of cellular processes (such as spike-like processes or lamellipodia) at the cellular margin. The contour of cytoskeletal elements just beneath the cell membrane was also clearly observable on the upper surface of the cells. Secondly, we showed the data on the discrepancy between the AFM images of living cells and fixed cells. These findings were useful for evaluating AFM images of living cells. Finally, we described the time-lapse AFM of living cells. A fluid chamber system enabled us to obtain AFM images of living cells for over 1 h at time intervals of 2–4 min. A series of these AFM images were useful for examining the movements of cellular processes in relation to subcellular cytoskeletal elements. Time-lapse movies produced by sequential AFM images also gave a realistic view of the cellular dynamics.

Effect of an Oxidized Gold Substrate on Alkanethiol Self-Assembly

UV-cleaned gold substrates incubated in solutions of alkanethiol show islands on the monolayer surface when imaged with noncontact atomic force microscopy (AFM). The height of the islands above the monolayer is approximately twice the height of the alkanethiol monolayer, and the diameter of the islands is 20-200 nm. These islands are easily pushed aside during contact mode AFM imaging without damaging the underlying monolayer. Islands are observed on gold substrates exposed to solutions of octadecane-, hexadecane-, and dodecanethiol and 1′-thiahexa(ethylene oxide)-1-octadecane at 0.01-1.0 mM concentrations in ethanol and hexadecane. AFM on samples with submonolayer coverage shows that the islands are not observed until the late stages of monolayer formation. Islands are not observed on freshly deposited gold substrates or on UV-cleaned gold substrates that are exposed to ethanol for longer than 10 min prior to incubation in alkanethiol solutions. We conclude that the island formation is associated with oxidation of the gold surface and that the islands are primarily composed of alkanethiol. We hypothesize that the stability of these structures may be due to the formation of multimolecular complexes of alkanethiols.

An atomic force microscopy investigation of bioadhesive polymer adsorption onto human buccal cells

Atomic force microscopy (AFM) was used to examine the buccal cell surface in order to image the presence of adsorbed bioadhesive polymers identified from previous work. Isotonic saline solution (5 ml) containing either polycarbophil (pH 7.6), chitosan (pH 4.5) or hydroxypropyl methylcellulose (pH 7.6) (0.5% w/v) was exposed to freshly collected buccal cells (ca. 48×10 4 cells/test) for 15 min at 30°C. The cells were then rinsed with a small volume of double distilled water, allowed to air-dry on a freshy cleaved mica surface and imaged using contact mode AFM. Untreated cells showed relatively smooth surface characteristics, with many small ‘crater-like’ pits and indentations spread over cell surfaces. Cells that had been treated with all the investigated polymers appeared to have lost the crater and indentation characteristic and gained a higher surface roughness. These results suggest that polymer chains had adsorbed onto the cell surfaces. Quantitative image analysis of cell topography showed significant increases ( P<0.05) in arithmetic roughness average ( R a) for all the investigated polymer treated cells surfaces with respect to untreated control specimens. The changes in surface topography indicate the presence of adsorbed polymer, confirming previous work. This study demonstrates the suitability of AFM as a powerful and sensitive technique for detecting and imaging bioadhesive polymers present on mucosal cell surfaces.

Atomic force microscopy in the surface characterization of semiconductors and superconductors

Abstract In the present paper I summarize the recent experience of my laboratory in the field of atomic force microscopy (AFM) applied to the study of the surfaces of both semiconducting and superconducting materials. I show that very useful results, both in fundamental and in applied physics, can be obtained by using simple contact-mode AFM in air, provided that particular attention is paid to the vibration isolation of the experimental set-up and to the cleavage of the samples' surface just before the measurement. Some examples are presented from the study of conventional and high-T C,. layered superconductors up to the atomic resolution, to the precise determination of the thickness of GaAs/AlAs multilayers and of the best deposition parameters for the sputtering of piezoelectric thin films.

Microfabrication of miniature aperture at the apex of SiO 2 tip on silicon cantilever for near-field scanning optical microscopy

In this paper we present a novel batch fabrication method of a miniature aperture at the apex of SiO 2 tip on a Si cantilever for near-field scanning optical microscopy (NSOM). The Si cantilever was microfabricated from Si(100) wafer, a SiO 2 pyramidal tip was formed near the end of the Si cantilever by thermal oxidation at low temperature. Due to the effect of locally compressive intrinsic stress, the thermal silicon oxide at the apex is thinner than that at the side wall of the pyramidal etch pit [R.B. Maruss, T.T. Sheng, J. Electrochem. Soc. 129 (6)(1982) 1278–1283; S. Akamine, C.F. Quate, J. Vac. Sci. Technol., B 10 (5)(1992) 2307–2310]. Thus, a tiny aperture can be created at the apex of SiO 2 tip by selective etching the SiO 2 in buffered-HF (BHF) solution. Using this etching method aperture size ranging from 150 to 500 nm have been successfully fabricated. By optimizing the SiO 2 etching time and oxidation condition, sub-100 nm size aperture or aperture array are feasible using the fabrication method. The fabricated probe was combined to an atomic force microscope (AFM) as an AFM/NSOM probe. The AFM in contact mode and corresponding NSOM images of several surfaces were simultaneously obtained. By optimizing the structure of the cantilever we expect to produce a high frequency probe for NSOM, NSOM based data storage and lithography.

AFM-induced melt growth on n-paraffin crystals

The {001} surfaces of n-C 23H 48 paraffin crystals have been investigated by ex situ alternative contact mode atomic force microscopy (AC-AFM). Although the crystals were scanned in air, without any solution present and below the melting temperature of n-C 23H 48, crystal growth or etching was revealed in all experiments, independently of the AC-AFM settings. Formation of 2D islands, growing spirals and pinning of advancing steps have been observed. It is shown that these crystal growth phenomena, which involve the nucleation and the propagation of monomolecular steps, are induced by the presence of the AFM tip. From temperature- and melting point-dependent measurements it is concluded that the observed crystal growth on n-C 23H 48 crystals is caused by a combination of local heating by the AFM laser beam and the action of capillary forces at the AFM tip, which generate a liquid paraffin bridge between tip and specimen surface. Control over the occurrence of growth versus etching was limited and is associated with the amount of paraffin stored in the liquid bridge. This type of ex situ investigations gives a good opportunity to study melt growth on a molecular scale, which would have been impossible with AFM in situ experiments, because of the extremely high requirements for temperature control needed for that case. Despite the different mechanism from that in ‘real’ melt growth experiments, the current system behaves remarkably similarly. Furthermore, the method may be suitable for surface patterning applications.