Type Of Atomic Force Microscope Research Articles

The nano-scale viscoelasticity using atomic force microscopy in liquid environment

We measured viscoelasticity of two nanoscale systems, single protein molecules and molecular layers of water confined between solid walls. In order to quantify the viscoelastic response of these nanoscale systems in liquid environment, the measurements are performed using two types of atomic force microscopes (AFMs), which employ different detection schemes to measure the cantilever response. We used a deflection detection scheme, available in commercial AFMs, that measures cantilever bending and a fibre-interferometer based detection which measures cantilever displacement. The hydrodynamics of the cantilever is modelled using Euler–Bernoulli equation with appropriate boundary conditions which accommodate both detection schemes. In a direct contradiction with many reports in the literature, the dissipation coefficient of a single octomer of titin I278 is found to be immeasurably low. The upper bound on the dissipation coefficient is 5 × 10−7 kg s−1, which is much lower than the reported values. The entropic stiffness of single unfolded domains of protein measured using both methods is in the range of 10 mN m−1. We show that in a conventional deflection detection measurement, the phase of the bending signal can be a primary source of artefacts in the dissipation estimates. It is recognized that the measurement of cantilever displacement, which has negligibly small phase lag due to hydrodynamics of the cantilever at low excitation frequencies, is better suited for ensuring artefact-free measurement of viscoelasticity compared to the measurement of the cantilever bending. Further, it was possible to measure dissipation in molecular layers of water confined between the tip and the substrate using fibre interferometer based AFM with similar experimental parameters. It confirms that the dissipation coefficient of a single I278 is below the detection limit of AFM. The results shed light on the discrepancy observed in the measured diffusional dynamics of protein collapse measured using Force spectroscopic techniques and single-molecule optical techniques.

Method for lateral force calibration in atomic force microscope using MEMS microforce sensor

In this paper we present a simple and direct method for the lateral force calibration constant determination. Our procedure does not require any knowledge about material or geometrical parameters of an investigated cantilever. We apply a commercially available microforce sensor with advanced electronics for direct measurement of the friction force applied by the cantilever's tip to a flat surface of the microforce sensor measuring beam. Due to the third law of dynamics, the friction force of the equal value tilts the AFM cantilever. Therefore, torsional (lateral force) signal is compared with the signal from the microforce sensor and the lateral force calibration constant is determined. The method is easy to perform and could be widely used for the lateral force calibration constant determination in many types of atomic force microscopes.

Measurement of nano particle adhesion by atomic force microscopy using probability theory based analysis

We present a method to detect adhesive forces of nano particles by analysis of the distribution of measured lateral forces. The measurement protocol is suitable for all types of atomic force microscopes with a lateral force channel. Lateral forces are measured, in constant normal force contact mode, by scanning of substrates decorated with nano beads. By using probability theory, geometry based measurement errors are compensated and the real adhesion force is determined within a given confidence interval. The theoretical model can be adapted for particles with arbitrary shape and distribution of adhesion forces. It is applied to the adhesion problem of spherical particles with a Gaussian distribution of adhesion forces. We analyze the measured force distribution qualitatively and quantitatively. The theory predicts a systematic underestimation of the mean value of any particle adhesion measurement done by lateral pushing. Real measurement data of 50 nm diameter silica nano beads on silicon substrate is used to test the theoretical model for plausibility by means of information theory.

An optimized nano-positioning stage for Bristol’s Transverse Dynamic Force Microscope

Abstract: This paper presents the design process for the optimisation of a nano-precision actuation stage for a Transverse Dynamic Force Microscope (TDFM). A TDFM is an advanced type of Atomic Force microscope (AFM) that does not contact the specimen and therefore has potential for increased accuracy and decreased damage to the specimen. The nano-precision stage actuates in a horizontal plane within a region of 1 μm×1μm and with a resolution of 0.3 nm. The non-contact TDFM has been developed at Bristol University for the precise topographical mapping of biological and non-biological specimens in ambient conditions. The design objective was to maximise positional accuracy during high speed actuation. This is achieved by minimising vibrations and distortion of the stage during actuation. Optimal performance was achieved through maximising out-of-plane stiffness through shape and material selection, as well optimisation of the anchoring system. The design was subject to constraints including an in-plane stiffness constraint, space constraints and design features relating to the laser interferometry position sensing system and subsequent controller design.

A Novel Atomic Force Microscope with Multi-Mode Scanner

A new type of atomic force microscope (AFM) with multi-mode scanner is proposed. The AFM system provides more than four scanning modes using a specially designed scanner with three tube piezoelectric ceramics and three stack piezoelectric ceramics. Sample scanning of small range with high resolution can be realized by using tube piezos, meanwhile, large range scanning can be achieved by stack piezos. Furthermore, the combination with tube piezos and stack piezos not only realizes high-resolution scanning of small samples with large- scale fluctuation structure, but also achieves small range area-selecting scanning. Corresponding experiments are carried out in terms of four different scanning modes showing that the AFM is of reliable stability, high resolution and can be widely applied in the fields of micro/nano-technology.

Low-voltage and high-performance buzzer-scanner based streamlined atomic force microscope system

In this paper we present a novel scanner design in a quad-rod actuation structure, actuated by piezoelectric disk buzzers, and a new type of atomic force microscope (AFM), which uses this buzzer-scanner and a compact disk/digital-versatile-disk astigmatic optical pickup unit (OPU) for the detection of cantilever movements. Commercially available piezoelectric disk buzzers have a low capacitance and can be driven by low-voltage signal sources, such as analog outputs from a data acquisition card, without additional voltage or current amplifiers. Various scanning ranges can be realized through changing the dimensions of the actuation structure and/or the choice of disk buzzer. We constructed a buzzer-scanner and evaluated its performance. The scanner had a scanning range of 15 μm in the X and Y directions and an actuation range of 3.5 μm on the Z axis, with nonlinearity of 2.11%, 2.73%, and 2.19% for the X,Y and Z axes, respectively. The scanner had a resonance frequency of approximately 360 Hz on the X and Y axes, and 4.12 kHz on the Z axis. An OPU-AFM with this buzzer-scanner can resolve single atomic steps of a graphite substrate with a noise level of 0.06 nm. The obtained topographic images exhibit much less distortion than those obtained with an AFM using a piezoelectric tube scanner.

A new type of atomic force microscope based on chaotic motions

Local flow variation (LFV) method of non-linear time series analysis is applied to develop a chaotic motion-based atomic force microscope (AFM). The method is validated by analyzing time series from a simple numerical model of a tapping mode AFM. For both calibration and measurement procedures the simulated motions of the AFM are nominally chaotic. However, the distance between a tip of the AFM and a sample surface is still measured accurately. The LFV approach is independent of any particular model of the system and is expected to be applicable to other micro-electro-mechanical system sensors where chaotic motions are observed or can be introduced.

Line edge roughness metrology using atomic force microscopes

Line edge roughness (LER) measurements using two types of atomic force microscopes and three types of tips are compared. Measurements were made on specially prepared samples with inscribed edge roughness of different amplitudes and wavelengths. The spatial wavelengths and amplitudes each instrument was able to measure are compared. Techniques on checking the noise level of LER measuring instruments are highlighted.

In-situ monitoring of electron beam induced deposition by atomic force microscopy in a scanning electron microscope

A new type of atomic force microscope is proposed for atomic force microscopic analysis inside a scanning electron microscope. We attached a piezoresisitive atomic force microscopic cantilever to a micro manipulator to achieve a compact and guidable setup, so that the tip can be positioned under observation of the scanning electron microscopy (SEM) system. Another manipulator and a glass drain tube serve as a precise local gas injection system for organometallic vapour. Electron beam induced deposition of tungstenhexacarbonyl is carried out at a global chamber pressure of 2·10 −5 mbar or less. Characterization of the directly patterned tungsten carbide structures according to deposition rate and dotsize or linewidth is done by combination of atomic force microscopy and SEM analysis for different electron energies, exposure doses and stepsize of pattern generator. A deposition rate of 1550 nm/(nC/dot) and 10 900 nm/(nC/nm) for dot and line deposition, respectively, and a dotsize and linewidth in the range of 20 to 25 nm have been obtained.

Covalent bond force profile and cleavage in a single polymer chain

We present here the measurement of the single-polymer entropic elasticity and the single covalent bond force profile, probed with two types of atomic force microscopes (AFM) on a synthetic polymer molecule: polymethacrylic acid in water. The conventional AFM allowed us to distinguish two types of interactions present in this system when doing force spectroscopic measurements: the first interaction is associated with adsorption sites of the polymer chains onto a bare gold surface, the second interaction is directly correlated to the rupture process of a single covalent bond. All these bridging interactions allowed us to stretch the single polymer chain and to determine the various factors playing a role in the elasticity of these molecules. To obtain a closer insight into the bond rupture process, we moved to a force sensor stable in position when measuring attractive forces. By optimizing the polymer length so as to fulfill the elastic stability conditions, we were able for the first time to map out the entire force profile associated with the cleavage of a single covalent bond. Experimental data coupled with molecular quantum mechanical calculations strongly suggest that the breaking bond is located at one end of the polymer chain.

Contact and non-contact atomic-force microscopy of type I collagen

Introduction. Type I collagen was examined using two types of atomic force microscopes (AFM) in a continuing effort to refine the process of obtaining molecular information from biological materials using scanning probe microscopy. Operating in air, a contact mode (Nanoscope II) and a non-contact mode AFM (Nanoscope III) were used to image collagen fibrils polymerized from pepsin-extracted type I bovine skin collagen adsorbed onto mica substrates. AFM is a practical method for high resolution examination of extracellular matrix material without the time consuming preparative techniques required for electron microscopy.Methods. For fibrillar collagen samples, Vitrogen 100 (Collagen Corporation, Palo Alto, CA) was prepared according to a modification of the procedure provided by Collagen Corp. for neutralized isotonic collagen gels. Monomeric collagen samples were prepared by diluting the vitrogen in 0.012M HCl.Images captured with the Nanoscope II AFM (Digital Instruments, Santa Barbara, CA) used a “J” scanner (horizontal range of 120 um).

角変位検出型ＡＦＭの研究

A new type of atomic force microscope (AFM) is described, in which an optical angular sensor detects the deflected angle of a cantilever instead of the deflected displacement, and the cantilever is able to be driven by a piezo actuator directly in accordance with the profile of surface. The developed AFM has advantages that it is sensitive, compact in size, and well suited for roughness measurement of big workpieces with high scanning speed, large scanning area and small interference among three axes. It has a vertical resolution of better than 1 nm and has been successfully used to obtain several stable images of machined surfaces. The results by our AFM are compared with those by SEM and STM, and the importance of making comparisons between results by different measuring principles has been confirmed.