Calibration Grating Research Articles

Investigation of the metrological characteristics of a scanning probe measuring microscope using TGZ type calibration gratings

The structure and operating principle of the NanoSkan-3Di scanning probe microscope are briefly described. An investigation of the metrological characteristics of this measuring system using linear TGZ-type gratings demonstrated the high level of reproducibility of the measurements and showed that the results agree with the data obtained in a calibration at the PTB (Germany).

Spectrophotometric method for measuring the groove depth of calibration reflection gratings

A method for measuring the groove depth of calibration gratings is proposed which is based on measuring the spectral dependence of the the zero-order reflection diffraction efficiency. The errors of the method are determined by three main factors: the shift of the maxima of the spectrum due to the wall slope of the grating grooves, the error in setting the wavelength of the spectrophotometer, and the divergence of the light beam in the setup. It is shown theoretically that the measurement error is in the range of 0.25–1%, depending on the fabrication technology of the grating and measuring equipment. The method was tested experimentally using commercial calibration gratings. The range of applicability of the method is discussed in terms of the geometrical parameters of the microstructure of reflection gratings and the characteristics of the spectrophotometer used.

High-Accuracy Atomic-Force-Microscope Head For Dimensional Metrology

We present the design and experimental results of a high-accuracy atomic force microscope head (HAFM) to be used for dimensional metrology. HAFM uses monolithic flexures which are designed for minimum error motion. A piezoelectric stack drives the head over a range of 20 /m. HAFM uses a self-sensing AFM probe, which is operated in constant-amplitude self-resonance, for frequency-measuring microscopy. A discrete-time surface-tracking controller is implemented on a real-time FPGA board. The controller tracks the surface by maintaining a constant self-resonance period. To avoid spurious mixing, the controller's sampling is made synchronous to the self-resonance oscillations. Three capacitive displacement sensors directly measure the surface tracking motion. We have experimentally demonstrated surface tracking control with 100 Hz unity-crossover frequency, 70 degrees phase margin, and 0.12 nm RMS noise in a 100 Hz measurement bandwidth. We have also used the HAFM to measure calibration gratings and the surface of freshly cleaved sanded Mica sample.

Cleaning AFM colloidal probes by mechanically scrubbing with supersharp “brushes”

Contamination control of atomic force microscope (AFM) tips (including standard but supersharp imaging tips and particle/colloidal probes) is very important for reliable AFM imaging and surface/interface force measurements. Traditional cleaning methods such as plasma, UV–ozone and solvent treatments have their shortcomings. Here, we demonstrate that calibration gratings with supersharp spikes can be employed to scrub away contaminants accumulated on a colloidal sphere probe by scanning the probe against the spikes at high load at constant-force mode. The present method is superior to traditional cleaning methods in several aspects. First, accumulated lump-like organic/inorganic material can be removed; second, removal is non-destructive and highly efficient based on a “targeted removal” strategy; third, removal and probe shape/morphology study can be completed in a single step (we report, to our best knowledge, the first evidence of the wear of the colloidal sphere during force measurements); and fourth, both colloidal/particle probes and standard but supersharp AFM imaging tips can be treated.

“Invisible” Silver Tracks Produced by Combining Hot‐Embossing and Inkjet Printing

AbstractHot‐embossed features are prepared by pushing customized and standard silicon calibration gratings, known as masters, into either polystyrene or polycarbonate, which are kept above their glass transition temperatures. droplet of a silver nanoparticle ink is then dispensed over one of these as‐formed grooves using an inkjet printer. The ink fills the grooves as a consequence of capillary forces and is observed to form tracks with a uniform width. The tracks are described as ‘invisible’ on account of having widths ranging from 5 to 15 µm. Wider tracks can be produced by dispensing more droplets and tracks with different morphologies can be produced by using different masters. Several as‐prepared features are thermally treated to produce conductive silver tracks. The conductivity of the tracks is found to be ∼20% that of bulk silver.

Microcantilever actuation via periodic internal heating

This paper reports electrothermal actuation of silicon microcantilevers having integrated resistive heaters. Periodic electrical excitation induced periodic resistive heating in the cantilever, while the cantilever deflection was monitored with a photodetector. Excitation was either at the cantilever resonant frequency, f(0), f(0)/2, or f(0)/3. When the time averaged maximum cantilever temperature was 174 degrees C, the cantilever out-of-plane actuation amplitude was 484 nm near the cantilever resonance frequency of 24.9 kHz. This actuation was sufficiently large to operate the cantilever in intermittent contact mode and scan a calibration grating of height of 20 nm.

Design and Modeling of a High-Speed AFM-Scanner

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A new mechanical scanner design for a high-speed atomic force microscope (AFM) is presented and discussed in terms of modeling and control. The positioning range of this scanner is 13 <formula formulatype="inline"><tex>$\mu$</tex> </formula>m in the <formula formulatype="inline"><tex>$X$</tex></formula>- and <formula formulatype="inline"><tex>$Y$</tex></formula>-directions and 4.3 <formula formulatype="inline"><tex>$\mu$</tex></formula>m in the vertical direction. The lowest resonance frequency of this scanner is above 22 kHz. This paper is focused on the vertical direction of the scanner, being the crucial axis of motion with the highest precision and bandwidth requirements for gentle imaging with the AFM. A second- and a fourth–order mathematical model of the scanner are derived that allow new insights into important design parameters. Proportional–integral (PI)-feedback control of the high-speed scanner is discussed and the performance of the new AFM is demonstrated by imaging a calibration grating and a biological sample at 8 frames/s. </para>

Polymeric nanofeatures of 100 nm using injection moulding for replication

The filling efficiency of replicated nanofeatures made with polymers using injection moulding with various moulding factors was investigated. Two simple calibration gratings with nanofeatures of 105 nm and 130 nm, respectively, were used as mould inserts to replicate nanofeatures by means of a custom-made injection machine. Nanofeatures made with polypropylene (PP), polystyrene (PS), polycarbonate (PC) and polymethylmethacrylate (PMMA) were tested because of differing viscosities and shrinkages in polymers. The results show that the surface configuration of the polymeric nanofeatures with low melt viscosity could be moulded well, while nanofeatures with high melt viscosity exhibited higher tolerance in depth. However, the moulding depth of nanofeatures could be effectively improved when mould temperature and forming pressure were higher. It was found that the reproducibility of the nanofeatures in large numbers could be replicated well after melt and mould temperatures became stable during moulding.

Topography imaging with a heated atomic force microscope cantilever in tapping mode

This article describes tapping mode atomic force microscopy (AFM) using a heated AFM cantilever. The electrical and thermal responses of the cantilever were investigated while the cantilever oscillated in free space or was in intermittent contact with a surface. The cantilever oscillates at its mechanical resonant frequency, 70.36 kHz, which is much faster than its thermal time constant of 300 micros, and so the cantilever operates in thermal steady state. The thermal impedance between the cantilever heater and the sample was measured through the cantilever temperature signal. Topographical imaging was performed on silicon calibration gratings of height 20 and 100 nm. The obtained topography sensitivity is as high as 200 microVnm and the resolution is as good as 0.5 nmHz(1/2), depending on the cantilever power. The cantilever heating power ranges 0-7 mW, which corresponds to a temperature range of 25-700 degrees C. The imaging was performed entirely using the cantilever thermal signal and no laser or other optics was required. As in conventional AFM, the tapping mode operation demonstrated here can suppress imaging artifacts and enable imaging of soft samples.

Reinforcement of polymeric nanofibers by ferritin nanoparticles

Poly(vinyl alcohol) (PVA) nanofibers containing bimolecular ferritin nanoparticles exhibited the enhancement of elastic modulus as compared to pure PVA nanofibers due to chemical interactions between the ferritin and the PVA matrix. The elastic modulus of the nanofibers was measured using a three-point bending test employing an atomic force microscope (AFM). To improve the reliability of the AFM measurements, uniform nanofibers were oriented linearly on an AFM calibration grating by introducing parallel subelectrodes in an electrospinning system. The length to diameter ratio of the measured nanofibers was &amp;gt;16. The PVA nanofibers reinforced by ferritin are applicable as artificial muscles and actuators.

A new method for characterizing nonlinearity in scanning probe microscopes using digitalimage correlation

It is essential to characterize the nonlinearity in scanning probe microscopes (SPMs) inorder to acquire spatial measurements with high levels of accuracy. In this paper, anew characterization method is presented that combines a high-resolution imageprocessing technique used by the experimental mechanics community known as DigitalImage Correlation (DIC) with digital images from a standard type of SPM knownas an atomic force microscope (AFM). The characterization results using thisnew method match those from the conventional method using micromachinedcalibration gratings. However, the new method uses the texture of a specimen surfaceand not a precisely micromachined calibration grating. As a consequence, thenew characterization technique is a more direct method for measuring scanningerrors that can be conducted in situ when imaging a specimen surface at any scalewithin the scanning range of the SPM. It also has the advantage of reconstructingthe position error curve more continuously with less noise than the conventionalmethod.

An improved wedge calibration method for lateral force in atomic force microscopy

An improved wedge calibration method for quantitative lateral force measurement in atomic force microscopy is presented. The improved method differs from the original one in several aspects. It utilizes a much simpler, commercially available, calibration grating and can be performed at any single specified applied load. It enables calibration of all types of probes, both integrated with sharp tips, and colloidal with any radius of curvature up to 2 μm. The improved method also simplifies considerably the calculation of the calibration factor by using flat facets on the calibration grating to cancel out system errors. A scheme for the data processing for on-line calibration of the lateral force is also presented.

Crosstalk problems in scanning-by-probe atomic force microscopy

Crosstalk problems in fixed optics scanning-by-probe atomic force microscopy are demonstrated by scanning a commercially available calibration grating. It is found that this scanning-by-probe scheme significantly distorts contact response detection, and may even indicate false cantilever deformation when the scanning unit grossly displaces an undeformed cantilever. A compensating electronic circuit that can successfully correct this distortion is presented.

Colloid Probe Characterization: Radius and Roughness Determination

In the last 10 years the atomic force microscope (AFM) has routinely been applied to the direct measurement of surface forces. A particle is often attached to the tip of the force-sensing cantilever in order to control the chemistry and the geometry of the interaction. Usually a spherical particle (colloid probe) is employed, and the measured interaction force is normalized by the radius, enabling comparisons to be made with both theory and other techniques. Here we report a simple method for characterizing the radius, surface roughness, and regularity of colloid probe particles. The colloid probe is “reverse imaged” by employing a surface with very sharp features. A standard calibration grating is suitable. No further equipment is required. The method is straightforward and will be of value to researchers employing the AFM for force measurement.

STM studies: spatial resolution limits to fit observations in nanotechnology

Atomically resolved Scanning Tunneling Microscopy (STM) images are nowadays currently obtained on flat surfaces without any special STM tip preparation. On the contrary, imaging of three-dimensional nanometer-scale objects exhibiting very much inclined facets, requires the use of STM tips with an appropriate geometry. The tip shape has to be controlled over the whole length that corresponds to the height of the object to be imaged. The cone angle of the tip has to be smaller than the tilt angle of the imaged facets. These criteria are also required when STM tips are used for patterning of nanometer-scale dots. In this paper, we will present the spatial resolution limits determined for these tips on different calibration gratings as well as first results obtained on nanometer scale patterning.

High-speed force sensor for force microscopy and profilometry utilizing a quartz tuning fork

Force sensors are key elements of atomic force microscopes and surface profilometers. Sensors with an integrated deflection meter are particularly desirable. Here, quartz tuning forks as used in watches are utilized as force sensors. A novel technique is employed which simplifies the interpretation of the data and increases the imaging speed by at least one order of magnitude compared to previous implementations. The variation of the imaging signal with distance fits well to a Hertzian contact model. Images of compact discs and calibration gratings, which have been obtained with scanning speeds up to 230 μm/s, are presented.

Scanning scattering microscope for surface microtopography and defect imaging

A recently developed optical-scatter instrument, the scanning scattering microscope (SSM) produces two-dimensional images of very small surface features and of variations in surface topography. In its present configuration, the lateral resolution is better than 10 μm and its sensitivity to surface roughness is in the angstrom (rms) range. The performance of the SSM has been demonstrated using calibration gratings, Si(100) surfaces, and Ge thin films grown on silicon; intercomparison also was made with atomic force microscope measurements. These results indicate that this scanned optical technique is a very useful noncontact method for evaluating surface microtopography.

A laser diffraction system with improved sensitivity for long-time measurements of sarcomere dynamics in isolated cardiac myocytes.

To measure the mechanical activity of enzymatically isolated mammalian myocytes the principle of laser light diffraction was used. Since the viability of isolated cardiac myocytes showed a marked dependence on the laser power used, an opto-electronic system with improved light sensitivity and low susceptibility to optical noise was developed. The high sensitivity was achieved by a novel approach in the detection of diffraction patterns, that provides a significant reduction of the amount of laser power required. This improvement rendered possible the application of laser diffraction during extended experiments including pharmacological interventions. The static performance of the system, as assessed by means of calibration gratings, showed a resolution in the order of 5 nm for small changes in sarcomere length in the range from 1.2 microns to 2.0 microns. Examples of measurements on resting and contracting cells are presented, and the limitations of the application of the system to biological specimens are discussed.