Developments of scanning probe microscopy with stress/strain fields

An innovative stress/strain fields scanning probe microscopy in ultra high vacuum (UHV) environments is developed for the first time. This system includes scanning tunneling microscope (STM) and noncontact atomic force microscope (NC-AFM). Two piezo-resistive AFM cantilever probes and STM probes used in this system can move freely in XYZ directions. The nonoptical frequency shift detection of the AFM probe makes the system compact enough to be set in the UHV chambers. The samples can be bent by an anvil driven by a step motor to induce stress and strain on their surface. With a direct current (dc) power source, the sample can be observed at room and high temperatures. A long focus microscope and a monitor are used to observe the samples and the operation of STM and AFM. Silicon(111) surface in room temperature and silicon(001) surface in high temperature with stress were investigated to check the performance of the scanning probe microscope.     

The tetrahedral tip as a probe for scanning near-field optical microscopy at 30 nm resolution

The tetrahedral tip is introduced as a new type of a probe for scanning near-field optical microscopy (SNOM). Probe fabrication, its integration into a scheme of an inverted photon scanning tunnelling microscope and imaging at 30 nm resolution are shown. A purely optical signal is used for feedback control of the distance of the scanning tip to the sample, thus avoiding a convolution of the SNOM image with other simultaneous imaging modes such as force microscopy. The advantages of this probe seem to be a very high efficiency and its potential for SNOM at high lateral resolution below 30 nm.     

A nanopositioner for scanning probe microscopy: the KoalaDrive

We present a new type of piezoelectric nanopositioner called KoalaDrive which can have a diameter less than 2.5 mm and a length smaller than 10 mm. The new operating principle provides a smooth travel sequence and avoids shaking which is intrinsic to nanopositioners based on inertial motion with sawtooth driving signals. In scanning probe microscopy, the KoalaDrive can be used for the coarse approach of the tip or sensor towards the sample. Inserting the KoalaDrive in a piezo tube for xyz-scanning integrates a complete scanning tunneling microscope (STM) inside a 4 mm outer diameter piezo tube of <10 mm length. The use of the KoalaDrive makes the scanning probe microscopy design ultracompact and accordingly leads to a high mechanical stability. The drive is UHV, low temperature, and magnetic field compatible. The compactness of the KoalaDrive allows building a multi-tip STM as small as a single tip STM.     

扫描隧道探针的制备研究

本文概述针尖对扫描隧道显微镜的重要性,总结制备探针的各种技术,并着重介绍电化学腐蚀制备钨和铂铱合金探针的原理及电路设计。     

A fast and versatile scan unit for scanning probe microscopy

In scanning probe microscopy (SPM), the image acquisition time is usually very long because of the limited speed with which the scanning device can trace the topography of the specimen under feed-back control. This limitation is often brought about by the natural frequency of the scanner in the direction perpendicular to the sample plane that confines the usable bandwidth of the feed-back loop. In this paper, we present a piezo-ceramic scanner that provides a large scan range and at the same time allows for adjustment of the probe-to-sample distance faster by about one order of a magnitude than a conventional setup. This is achieved through the combination of a large single tube scanner that provides a high-scan range and a small piezo element for swift motion in the direction perpendicular to the sample plane. The natural frequency in this direction lies at about 275 kHz. We outline the design considerations to avoid disturbing excitation of the scanner through the fast piezo element.     

An improved dynamic model of tuning fork probe for scanning probe microscopy

This paper presents a two coupled oscillators model to describe the dynamics of a tuning fork with a probe attached. The two coupled oscillators are unbalanced only in their effective masses and the damping ratios. By applying a frequency domain system identification approach in experimental investigation of various probe attachment cases, a good accuracy of the model is demonstrated. The effectiveness of the model is further demonstrated in quantitative analysis of the noise performance and the sensitivity of force sensing with a tuning fork probe. Compared with existing models, the proposed model can more accurately characterize the dynamics of a tuning fork probe.     

Modeling electric-field-sensitive scanning probe measurements for a tip of arbitrary shape

We present a numerical method to model electric-field-sensitive scanning probe microscopy measurements which allows for a tip of arbitrary shape and invokes image charges to exactly account for a sample dielectric overlayer. The method is applied to calculate the spatial resolution of a subsurface charge accumulation imaging system, achieving reasonable agreement with experiment.     

Simulation-aided design and fabrication of nanoprobes for scanning probe microscopy

We proposed and demonstrated a flexible and effective method to design and fabricate scanning probes for atomic force microscopy applications. Computer simulations were adopted to evaluate design specifications and desired performance of atomic force microscope (AFM) probes; the fabrication processes were guided by feedback from simulation results. Through design-simulation-fabrication iterations, tipless cantilevers and tapping mode probes were successfully made with errors as low as 2% in designed resonant frequencies. For tapping mode probes, the probe tip apex achieved a 10 nm radius of curvature without additional sharpening steps; tilt-compensated probes were also fabricated for better scanning performance. This method provides AFM users improved probe quality and practical guidelines for customized probes, which can support the development of novel scanning probe microscopy (SPM) applications.     

A single gold particle as a probe for apertureless scanning near-field optical microscopy

We report on the fabrication, characterization and application of a probe consisting of a single gold nanoparticle for apertureless scanning near-field optical microscopy. Particles with diameters of 100 nm have been successfully and reproducibly mounted at the end of sharp glass fibre tips. We present the first optical images taken with such a probe. We have also recorded plasmon resonances of gold particles and discuss schemes for exploiting the wavelength dependence of their scattering cross-section for a novel form of apertureless scanning near-field optical microscopy.     

Electrochemical deposition of molecular adsorbates for in situ scanning probe microscopy

We have studied gold and graphite electrodes in an electrochemistry cell under various solutions using the scanning tunneling microscope (STM). The gold (111) surface yields quite reproducible images and cyclic voltammograms. In situ voltammograms show that, under certain conditions, nanomolar quantities of DNA fragments can suppress the adsorption of a buffer salt of millimolar concentration. When the DNA concentration is reduced below that required for a monolayer coverage, the salt adsorption is restored. We show images of bare gold, gold covered with an adsorbate produced by the buffer salt, and gold prepared with a concentration of DNA fragments close to that required for monolayer coverage added to the buffer. Under these conditions, the surface is found to be uniformly covered with a characteristic structure.     

Qualitative analysis of smear layer treated with different etidronate concentrations: A scanning electron microscopy study

The aim of this study was to examine the smear layer removal capacity of various etidronate treatments. Seventy‐eight roots were instrumented up to apical size X4 and randomly divided into five treatment groups and a positive control group (n = 13). Groups were as follows: irrigation with 5 ml of sterile saline (control) for 3 min, 5 ml of 17% ethylenediaminetetraacetic acid (EDTA) for 3 min, 5 ml of 9% A1‐hydroxyethylidene‐1,1‐bisphosphonate (HEBP) for 3 min, 5 ml of 18% HEBP for 3 min, irrigation with 5 ml of 1% sodium hypochlorite (NaOCl) + 9% HEBP for 3 min, and 5 ml of 2% NaOCl + 18% HEBP for 3 min. The roots were examined using a scanning electron microscope. The smear layer scores in the 2% NaOCl + 18% HEBP group were lower than those in the other treatment groups and the control group (p < .05). There were no significant differences among the treatment groups in the smear layer scores of the coronal and middle thirds. However, the smear layer scores in the 2% NaOCl + 18% HEBP treatment group were lower those in the 9% HEBP and 18% HEBP treatment groups in the apical third (p < .05). In the clinical setting, the recommended concentration of HEBP is 18%, and it should be used with an oxidizing agent to ensure optimum smear layer removal.     

Effect of tip shape on capacitance determination accuracy in scanning capacitance microscopy

We present an analysis of the measurement error caused by the stray field of scanning capacitance microscope probes of various shapes. Cylindrical islands and wells of varying radius and height or depth, in both conducting surfaces and structures containing dielectric films, were used as test features for modelling. The results show that high accuracy and good contrast of small details are contradictory requirements. Probes with small radius of curvature of the tip apex yield smaller errors on features with small diameter but larger ones on features with large diameter than tips with large radius of curvature. The stray electrostatic field causes large errors, which are exceptionally severe with microfabricated probes. Contrary to general belief, differential measurements, based on modulation of the probe/sample separation or of the width of depletion layer in semiconductors, do not reduce the effect of the stray field significantly. For best results, the probe should be shielded as close to the tip apex as possible. In the case of microfabricated probes, at least the side of the cantilever facing the sample should be shielded.     

Measurement of specimen charging in scanning electron microscopy with a kelvin probe

A vibrating Kelvin probe in form of a platinum wire loop is used to measure the surface potential U_s on electron-irradiated free-floating metal and insulator specimens as a function of electron energy E. This allows an accurate measurement of the critical electron energy E₂ for no charging. At energies below E₂, the positive charging increases with decreasing energy to U_s=2–5 eV at E=0.5 keV and switching off the collector bias of the Everhart-Thornley detector. A two-to threefold increase of U_s is observed when the bias is switched on. For E > E₂, the strong increase of a negative surface potential can be measured. Insulating films free-supported on a conductive substrate show a steep decrease to small positive and negative U_s when the film thickness becomes lower than the electron range at a critical energy E₃ > E₂. At insulating specimen the temporal decrease of charging can be measured when the electron beam is switched off.     

Use of scanning probe microscopy to study the evolution of nanometer sized liquid structures

The evolution of the profile of nanometer sized water drops on a mica surface has been studied through hydration scanning probe microscopy. A time range from a few seconds down to a fraction of millisecond after the formation of the drop has been explored. This high time resolution has been obtained by sampling a series of statistically equivalent drops. This approach also avoids any probe interference during the drop evolution process.     

A study of hydrogenated carbon fibers by scanning electron microscopy and confocal laser scanning microscopy

The hydrogen absorption process is studied in carbonaceous fibers produced from a mixture of methane and hydrogen. The absorption of the hydrogen was examined in two types of fibers, in “as-grown” state and after a process of desorption during an annealing to 1.473 K under vacuum. Later to its production process, the fibers withstand an oxidation in air to 973 K. The fibers were examined by means of scanning electron microscopy (SEM) and confocal microscopy by reflection. Differences in the behavior during the oxidation were observed between the fibers in as-grown state and those subjected to a further annealing. It could be verified that the fibers were really constituted by two different phases. In one of the phases, the storage of the hydrogen absorbed took place, whereas in the other phase there was no alteration. The process of annealing prior to the absorption of the hydrogen has an appreciable effect on the desorption rate of the hydrogen. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc.     

Quantitative characterization of crosstalk effects for friction force microscopy with scan-by-probe SPMs

If the photodetector and cantilever of an atomic force microscope (AFM) are not properly adjusted, crosstalk effects will appear. These effects disturb measurements of the absolute vertical and horizontal cantilever deflections, which are involved in friction force microscopy (FFM). A straightforward procedure is proposed to study quantitatively crosstalk effects observed in scan-by-probe SPMs. The advantage of this simple, fast, and accurate procedure is that no hardware change or upgrade is needed. The results indicate that crosstalk effects depend not only on the alignment of the detector but also on the cantilever properties, position, and detection conditions. The measurements may provide information on the origin of the crosstalk effect. After determination of its magnitude, simple correction formulas can be applied to correct the crosstalk effects and then the single-load wedge method, using a commercially available grating, can be employed for accurate calibration of the lateral force.     

Calibration and examination of piezoresistive Wheatstone bridge cantilevers for scanning probe microscopy

This paper describes the method of determining the force constant and displacement sensitivity of piezoresistive Wheatstone bridge cantilevers applied in scanning probe microscopy (SPM). In the procedure presented here, the force constant for beams with various geometry is determined based on resonance frequency measurement. The displacement sensitivity is measured by the deflection of the cantilever with the calibrated piezoactuator stage. Preliminary results show that our method is capable of measuring the force constant of Wheatstone bridge cantilevers with an accuracy of better than 5% and this is used as feedback for improvement of sensor micromachining process.     

Detection of human serum albumin on protein array using scanning tunneling microscopy

Electrical detection of biological binding events, such as protein–protein interaction and DNA hybridization, has emerged as an alternative method to conventional colorimetric and fluorescence based methods. In this study, we demonstrate an electrical detection technique of protein array which can be simply extended for multifunctional measurements and detection of biological binding events on micro-scale array. Micro-contact technique was used for the fabrication of protein chip. The fabricated protein array on Au substrate was characterized by fluorescence microscopy and scanning tunneling microscopy (STM). The chip was designed to investigate immunocomplexes comprised of our model protein, human serum albumin (HSA), corresponding antibody fragments, and Au nanoparticle–antibody conjugates. The peak-like pulse obtained by electrical tunneling current between these complexes and the STM tip varies on the surface density of the bound complexes. Using the electrical detection technique based on STM, 100 fg/mL of HSA could be successfully detected by STM. Importantly, the proposed concept of measurement could allow multiple analyses of analytes at nano-scale array, which is difficult to be analyzed by conventional fluorescence based method.     

A microheater with temperature stabilization for a scanning probe microscope

A microheater for conducting measurements by the scanning probe microscopy technique at various temperatures is described. The temperature stabilization accuracy is 0.05°C in a range of 20–80°C. A negligible temperature drift of 40 nm/°C (in the sample plane) and 100 nm/°C (along the normal) allows the study of temperature-dependent structural changes and phase transitions in polymer materials, biological objects, and other samples.