Parallel nanoimaging and nanolithography using a heated microcantilever array

The atomic force microscope (AFM) is a powerful tool for the measurement of forces at the micro/nano scale when calibrated cantilevers are used. Besides many existing calibration techniques, the thermal calibration is one of the simplest and fastest methods for the dynamic characterization of an AFM cantilever. This method is efficient provided that the Brownian motion (thermal noise) is the most important source of excitation during the calibration process. Otherwise, the value of spring constant is underestimated. This paper investigates noise interference ranges in low stiffness AFM cantilevers taking into account thermal fluctuations and acoustic pressures as two main sources of noise. As a result, a preliminary knowledge about the conditions in which thermal fluctuations and acoustic pressures have closely the same effect on the AFM cantilever (noise interference) is provided with both theoretical and experimental arguments. Consequently, beyond the noise interference range, commercial low stiffness AFM cantilevers are calibrated in two ways: using the thermal noise (in a wide temperature range) and acoustic pressures generated by a loudspeaker. We then demonstrate that acoustic noises can also be used for an efficient characterization and calibration of low stiffness AFM cantilevers. The accuracy of the acoustic characterization is evaluated by comparison with results from the thermal calibration.

An atomic force microscope (AFM) cantilever based coordinate measuring probe applicable for true three dimensional measurements of microstructures is presented. The probe has a shaft glued to a commercial AFM cantilever and a probing sphere located at the free end of the shaft. A conventional optical lever method is applied to detect the bending, torsion, and the dynamic behavior of the AFM cantilever which will change dramatically when the probe sphere is in proximity to the object to be measured. The probe has advantages such as small probing force (<1μN), high probing sensitivity allowing nanometer measurement resolution, easy exchange of probing elements, and low cost. Measurements of a microgear and a fuel injection nozzle using the developed probe are demonstrated, indicating its promising application potential.

This paper reports a thermal sensor assembled by two multi-walled carbon nanotubes (MWCNTs) inside a field emission scanning electron microscope (FESEM) which constructed a probe tip in order to detect the local environment of single cell. An atomic force microscope (AFM) cantilever was used for substrate which is composed by Si3N4, and double side was covered by gold layer. Two MWCNTs were assembled to both side of AFM cantilever individually by employing a nanorobotic manipulation. Then another AFM cantilever was used as an end effector to manipulate the MWCNTs to touch, and used electron beam induced deposition (EBID) to bonding the two MWCNTs. The MWCNTs probe thermal sensor was evaluation inside a thermostated container for 30°C to 60°C. The experimental results show the positive characteristics of the temperature coefficient of resistance (TCR). We hope this result will be used rapidly in future. © 2012 IEEE.

Calibration of AFM cantilever stiffness: a microfabricated array of reflective springs

We present a systematic study of the frequency noise experienced by a charged atomic force microscope cantilever due to thermal dielectric fluctuations in a thin-film sample of poly(vinyl acetate). Here, the tip of the commercial atomic force microscope cantilever oscillates in the conventional direction, normal to the surface of the film, complementing our previous studies of dielectric fluctuations carried out using an ultrasensitive custom-fabricated cantilever oscillating parallel to the film surface. We show that frequency noise induced by mechanical vibrations can be distinguished from frequency noise resulting from thermal dielectric fluctuations by the dependence on applied voltage and tip-sample separation, allowing molecular information to be unambiguously extracted. A linear response theory for cantilever frequency noise over a molecular material correctly reproduces the observed dependences on frequency, voltage, and tip-sample separation. The technique is shown to measure primarily fluctuations in the electric field gradient over the surface, which in these measurements are generated by orientational relaxation of polar polymer segments.

This paper presents a study on the dynamic response of an atomic force microscope (AFM) cantilever with a solid state heating element in liquid and its application for measuring the temperature-dependent viscosity of liquids. A finite difference model (FDM) predicts the frequency response of a heated cantilever immersed in liquid and calibrates the liquid viscosity from the measured cantilever resonant frequency (f0) at different cantilever heater temperatures. The technique measures a wide range of liquid viscosities (0.0005–0.005 kgm−1s−1) at temperatures ranging from 20 to 55 °C with high sensitivity (7.1 × 10−7 kgm-1s-1/Hz for 50 wt% ethylene glycol/water). The measurement requires heating a liquid volume of about 10 nl, which is more than 1000X smaller than other microcantilever-based viscosity measurements.

This paper presents improved design, fabrication, and characterization of a small array of silicon microcantilever heaters with integrated piezoresistors. The fabricated microcantilever arrays are made from single crystal silicon with selective doping such that parasitic bending and electromigration can be suppressed during high temperature operation. Detailed characterization was performed to test the device electrical, thermal, and mechanical properties. The performance and crosstalk between heater and piezoresistor elements was thoroughly tested. The resistive heater can reach temperature higher than 600°C, and its temperature coefficient of electrical resistance was 2.01 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> Ω/Ω-°C. When biased at 2 V in a Wheatstone bridge, the deflection sensitivity of the piezoresistor was 4.25 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> V/V-μm and remarkably, the heater circuit had a non-negligible deflection sensitivity of 7.86 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> V/V-μm. Both the piezoresistor and the resistive heater were interfaced with a commercial atomic force microscope (AFM) to measure their sensitivities during topography sensing of a calibration grating. As expected, the sensitivity of thermal reading was at least one order of magnitude greater than that of piezoresistive reading.

This paper explores strategies for fabricating and maintaining a sharp atomic force microscope (AFM) tip suitable for AFM data storage applications. To this end, AFM cantilevers have been incorporated into micromachined sled carriers and air-bearing sliders. These supports act to limit the maximum loading force on the AFM tip and allow for improved vibration immunity for the AFM cantilever in comparison to macroscopic loading schemes. Readback from a patterned rotating disk has been demonstrated using these devices. Silicon-carbide AFM cantilevers with diamond tips have been fabricated in a process compatible with that of the sleds and sliders. Molded silicon-nitride tips defined by the intersection of three surfaces have also been fabricated for AFM cantilevers. The molds for plane-plane-concave tips are defined by two silicon {111} planes and a silicon-dioxide curved surface. By geometry, the three surfaces necessarily have a unique intersection point, which may improve the consistency in sharpness of these tips relative to conventional pyramidal tips.

This study presents the design and implementation of a prototype device that interfaces with commercial atomic force microscopy (AFM) instruments to accurately measure ex vivo, regional, passive elasticity measurements of the murine myocardium in three-dimensions (3D). The constructed prototype has a translation stage base allows fine adjustment of planar location at the micrometer level of accuracy. Four degrees of motional freedom are allowed in total, permitting fine, independent rotations of the murine heart (oriented at right-angles with respect to its normal mode of operation) at 2–5° increments, along its two axes of symmetry. Successful mounting of the constructed prototype was realized on the AFM’s base platform, with Zpositioning maintained through the instrument’s electronics. Measurements of normal epicardial tissue elasticity in one excised male C57BL/6 heart led to a mean value (over 15 epicardial locations) of 51.8 ± 5.4 kPa. A flexible, versatile, and low-cost prototype assembly was designed, implemented, and tested to conduct epicardial elasticity measurements in a semi-automatedmanner, using AFM. The epicardial elasticity values are within expected, published ranges for the normal myocardium of 10–55 kPa. Efforts are ongoing to allow 3D regional elasticity measurements at finer resolution with potential usefulness to studies of genetically altered mice.

A commercial atomic force microscope (AFM) was equipped with a hot stage for conducting thermal cycling experiments up to 398 K, as well as a vacuum and purge system to provide a protective environment during heating. Two different hot-stage configurations, one for studying features in the plane of a microelectronic device, and the other for studying features on its cross section, were developed. It is shown that the AFM retains its calibration with no significant introduction of errors at temperatures up to 398 K. Two applications of in situ hot-stage atomic force microscopy, related to microelectronic devices, have been demonstrated. First, the in-plane coefficient of thermal expansion of a low dielectric constant (low-k) thin film dielectric material used in back-end interconnect structures was measured. Second, the equipment was used to conduct in situ studies of deformation of Cu thin film interconnect lines at the back end of silicon chips, under thermo-mechanical loads simulating those imposed on chip-level interconnect structures by a microelectronic package. The design of a bimetallic thermo-mechanical loading stage, which was used for the latter experiments in conjunction with the hot stage, is also discussed.

A high velocity accessory for friction force microscopy measurements for velocities up to the mm/s range was developed for a commercial stand-alone atomic force microscope (AFM). The accessory consists of a shear piezo element, which rapidly displaces the sample in the lateral direction, perpendicular to the main axis of the AFM cantilever. Friction forces, which are acquired via conventional optical beam deflection detection, can thus be measured as a function of velocity and load in controlled environment (0–40% relative humidity and 0–40°C). Using the accessory, a broad range of velocities up to several mm/s can be accessed independent of the lateral scan size up to a maximum scan size of 1000nm. The velocity dependence of friction forces and coefficients was measured on organic [poly(methylmethacrylate)], as well as inorganic [oxidized Si(100)] samples to demonstrate the feasibility and underline the importance of high velocity nanotribology using this accessory.

Current methods to study atomic force microscope (AFM) cantilever dynamics use model simplification or are based on the non-trivial solution of the equation of motion. As an alternative method, transfer function analysis gives a more complete description of system dynamics. In this work a transfer function study of two different AFM configurations, the point force and base driven cantilever, is presented. Exact analytical expressions of the infinite dimensional transfer function are derived for cantilever deflection and slope along the cantilever. Frequency response and transfer function infinite product expansion are obtained for the case where system outputs are set at the free end of the cantilever. The frequency response reflects the full complexity of cantilever dynamics affected by the presence of an infinite number of poles and zeros. An analytical expression for all the zeros and poles of the system is obtained. From the frequency response and pole-zero investigations it is shown how cantilever actuation and output measurement affect AFM operation and cantilever dynamics modelling. Transfer function analysis of AFM cantilevers opens the possibility of model based AFM operation to increase imaging and manipulation performance.

We investigate in theory and experiment the intermittent contact interaction between an atomic force microscope (AFM) cantilever and a nanowire under ambient conditions. The nanowire is modeled as a spring reacting instantaneously to any change of the force between the wire and the cantilever. This implies that the cantilever is subject to an “effective” force-distance relation, containing not only the surface forces but also the deflection of the nanowire. Experimentally, CVD-grown tin oxide nanowires and lithographically structured silicon nanowire arrays were investigated by intermittent contact AFM. By comparison of experimental and simulated distance-dependent resonance curves it is found that the nanowires behave like “fast nanosprings” and that the adhesion force is one of the key factors determining distance-dependent resonance curves. The results are fully applicable to a scenario in which a cantilever equipped by a nanowire interacts with a surface.

Mechanical characterization of nanofibers using a nanomanipulator and atomic force microscope cantilever in a scanning electron microscope

In this study we present measurements of the hydrodynamic force exerted on a glass sphere glued to an atomic force microscopy (AFM) cantilever approaching a mica surface in water. A large sphere was used to reduce the impact of the cantilever beam on the measurement. An AFM cantilever with large stiffness was used to accurately determine the actual contact position between the sphere and the sample surface. The measured hydrodynamic force with different approach velocities is in good agreement with the Taylor force calculated in the lubrication theory with the no-slip boundary conditions, which verifies that there is no boundary slip on the glass and mica surfaces. Moreover, a detailed procedure of how to subtract the electrostatic double-layer force is presented.