Mark A. Wendman

Bio: Mark A. Wendman is an academic researcher from University of California. The author has contributed to research in topics: Cantilever & Non-contact atomic force microscopy. The author has an hindex of 7, co-authored 7 publications receiving 710 citations.

Short cantilevers for atomic force microscopy

Abstract: We have designed and tested a family of silicon nitride cantilevers ranging in length from 23 to 203 μm. For each, we measured the frequency spectrum of thermal motion in air and water. Spring constants derived from thermal motion data agreed fairly well with the added mass method; these and the resonant frequencies showed the expected increase with decreasing cantilever length. The effective cantilever density (calculated from the resonant frequencies) was 5.0 g/cm3, substantially affected by the mass of the reflective gold coating. In water, resonant frequencies were 2 to 5 times lower and damping was 9 to 24 times higher than in air. Thermal motion at the resonant frequency, a measure of noise in tapping mode atomic force microscopy, decreased about two orders of magnitude from the longest to the shortest cantilever. The advantages of the high resonant frequency and low noise of a short (30 μm) cantilever were demonstrated in tapping mode imaging of a protein sample in buffer. Low‐noise images were tak...

Rapid imaging of calcite crystal growth using atomic force microscopy with small cantilevers

Abstract: Using a 26 μm cantilever with a resonant frequency of 100 kHz in water, we were able to obtain sequential images of calcite crystal steps growing from a screw dislocation. The small cantilever permitted acquisition of 250 nm images at scan rates of 104 lines/s (1.2 s/image). From this sequence we directly measured critical step lengths (the length of the shortest step that can advance) of 6–21 nm. These values provided a rough estimate of (0.25±0.13 J/m2) for the step energy per unit length per unit step height on the (104) face of calcite.

Microfabrication of cantilevers using sacrificial templates

Abstract: A sacrificial cantilever is used as a template for making cantilevers of non-standard materials for use in an atomic force microscope. The desired metal is deposited onto the sacrificial cantilever, followed by removal of the sacrificial cantilever.

Atomic force microscope for small cantilevers

Abstract: We have designed and built an atomic force microscope (AFM) with optical beam deflection detection providing a focused spot size of 1.6 micrometers in diameter. This small spot size was implemented with a variable focus adjustment that allows us to re-focus on each cantilever. This design opens up the usage of a new range of small cantilevers with low-noise characteristics. We have microfabricated novel aluminum cantilevers with dimensions as small as 9 micrometers in length and 2.5 micrometers in width and have characterized them with this new AFM. The resonance frequency of the smallest cantilever was 2.5 MHz in air and 0.94 MHz in water. We demonstrated the imaging capabilities of the AFM head by imaging abalone nacre with a 10 micrometers long cantilever using the tapping mode in liquid at a drive frequency of 442 KHz.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Atomic force microscopy using small cantilevers

Abstract: We have applied a new generation of short cantilevers with high resonant frequencies to tapping mode atomic force microscopy of a process in situ. Crystal growth in the presence of protein has been imaged stably at 79 lines/s (1.6 s/image), using a 26 micrometers long cantilever with a spring constant of 0.66 N/m at a tapping frequency of 90.9 kHz. This high scan speed nearly eliminated distortion in the step edge motion and allowed imaging of finer features along the step edges. Atomic force microscopy with short cantilevers therefore allows higher resolution imaging of crystal growth in space as well as time.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Calibration of rectangular atomic force microscope cantilevers

Abstract: A method to determine the spring constant of a rectangular atomic force microscope cantilever is proposed that relies solely on the measurement of the resonant frequency and quality factor of the cantilever in fluid (typically air), and knowledge of its plan view dimensions. This method gives very good accuracy and improves upon the previous formulation by Sader et al. [Rev. Sci. Instrum. 66, 3789 (1995)] which, unlike the present method, requires knowledge of both the cantilever density and thickness.

Frequency response of cantilever beams immersed in viscous fluids with applications to the atomic force microscope

Abstract: The vibrational characteristics of a cantilever beam are well known to strongly depend on the fluid in which the beam is immersed. In this paper, we present a detailed theoretical analysis of the frequency response of a cantilever beam, that is immersed in a viscous fluid and excited by an arbitrary driving force. Due to its practical importance in application to the atomic force microscope (AFM), we consider in detail the special case of a cantilever beam that is excited by a thermal driving force. This will incorporate the presentation of explicit analytical formulae and numerical results, which will be of value to the users and designers of AFM cantilever beams.

Cantilever transducers as a platform for chemical and biological sensors

Abstract: Since the late 1980s there have been spectacular developments in micromechanical or microelectro-mechanical (MEMS) systems which have enabled the exploration of transduction modes that involve mechanical energy and are based primarily on mechanical phenomena. As a result an innovative family of chemical and biological sensors has emerged. In this article, we discuss sensors with transducers in a form of cantilevers. While MEMS represents a diverse family of designs, devices with simple cantilever configurations are especially attractive as transducers for chemical and biological sensors. The review deals with four important aspects of cantilever transducers: (i) operation principles and models; (ii) microfabrication; (iii) figures of merit; and (iv) applications of cantilever sensors. We also provide a brief analysis of historical predecessors of the modern cantilever sensors.

A high-speed atomic force microscope for studying biological macromolecules.

Abstract: The atomic force microscope (AFM) is a powerful tool for imaging individual biological molecules attached to a substrate and placed in aqueous solution. At present, however, it is limited by the speed at which it can successively record highly resolved images. We sought to increase markedly the scan speed of the AFM, so that in the future it can be used to study the dynamic behavior of biomolecules. For this purpose, we have developed a high-speed scanner, free of resonant vibrations up to 60 kHz, small cantilevers with high resonance frequencies (450–650 kHz) and small spring constants (150–280 pN/nm), an objective-lens type of deflection detection device, and several electronic devices of wide bandwidth. Integration of these various devices has produced an AFM that can capture a 100 × 100 pixel2 image within 80 ms and therefore can generate a movie consisting of many successive images (80-ms intervals) of a sample in aqueous solution. This is demonstrated by imaging myosin V molecules moving on mica (see http://www.s.kanazawa-u.ac.jp/phys/biophys/bmv_movie.htm).