Two-dimensional micromechanical bimorph arrays for detection of thermal radiation

We demonstrate that two-dimensional arrays of micromechanical bimorphs can be used as thermal sensors to image infrared (IR) radiation. A density of 100 pixels per mm2 is achieved by coiling a bimorph beam into the shape of a flat spiral. Temperature variations of a given spiral are converted to modulations of visible light by illuminating the spiral array with a visible source. The optical properties of the spiral resemble a Fresnel zone plate when light reflected off neighboring rings of the spiral is focused. When a spiral is heated through the absorption of IR radiation, thermally induced bending of the bimorph degrades the focusing efficiency by distorting the spiral. This reduces the optical intensity at the focal point. Arrays of spirals can be monitored with a commercial CCD camera. At 40 Hz, the temperature resolution and noise equivalent power of a 75 μm diam spiral are 50 μK/√Hz and 20 nW/√Hz, respectively, and the thermal response time is 270 μs. © 1997 American Institute of Physics

Atomic force microscope lithography using amorphous silicon as a resist and advances in parallel operation

Lithography on (100) single-crystal silicon and amorphous silicon is performed by electric-field-enhanced local oxidation of silicon using an atomic force microscope (AFM). Amorphous silicon is used as a negative resist to pattern silicon oxide, silicon nitride, and selected metals. Amorphous silicon is used in conjunction with chromium to create a robust etch mask, and with titanium to create a positive AFM resist. All lithographies presented here were patterned in parallel by arrays of two piezoresistive silicon or two silicon-nitride cantilevers. Parallel arrays of five piezoresistive cantilevers were fabricated and used in imaging and lithographic applications. A 400 μm × 100 μm parallel image is obtained in the time it would normally take to obtain a 100 μm × 100 μm image. In our method of parallel operation, it is only possible to image and lithograph in modes that do not require feedback. In imaging, this limits the possible applications of the parallel AFM. During parallel lithography, discrepancies are seen between the tip in the feedback loop and those that are not. To overcome these differences it will be necessary to devise a system where each of the tips in the array are controlled by individual feedback loops

High-speed atomic force microscopy using an integrated actuator and optical lever detection

A new procedure for high-speed imaging with the atomic force microscope that combines an integrated ZnO piezoelectric actuator with an optical lever sensor has yielded an imaging bandwidth of 33 kHz. This bandwidth is primarily limited by a mechanical resonance of 77 kHz when the cantilever is placed in contact with a surface. Images scanned with a tip velocity of 1 cm/s have been obtained in the constant force mode by using the optical lever to measure the cantilever stress. This is accomplished by subtracting an unwanted deflection produced by the actuator from the net deflection measured by the photodiode using a linear correction circuit. We have verified that the tip/sample force is constant by monitoring the cantilever stress with an implanted piezoresistor. © 1996 American Institute of Physics

High-speed tapping mode imaging with active Q control for atomic force microscopy

The speed of tapping mode imaging with the atomic force microscope (AFM) has been increased by over an order of magnitude. The enhanced operation is achieved by (1) increasing the instrument's mechanical bandwidth and (2) actively controlling the cantilever's dynamics. The instrument's mechanical bandwidth is increased by an order of magnitude by replacing the piezotube z-axis actuator with an integrated zinc oxide (ZnO) piezoelectric cantilever. The cantilever's dynamics are optimized for high-speed operation by actively damping the quality factor (Q) of the cantilever. Active damping allows the amplitude of the oscillating cantilever to respond to topography changes more quickly. With these two advancements, 80μm×80 μm high-speed tapping mode images have been obtained with a scan frequency of 15 Hz. This corresponds to a tip velocity of 2.4 mm/s. © 2000 American Institute of Physics

High-bandwidth intermittent-contact mode scanning probe microscopy using electrostatically-actuated microcantilevers

A critical issue in scanning probe microscopy (SPM) in the intermittent-contact (IC) mode is the achievable bandwidth, which is limited because of the high quality factor of the cantilevers. Cantilevers for IC-mode SPM must have high stiffness for stable operation, which necessitates high quality factors for high force sensitivity, and thus results in a slow response time. Here we present an IC SPM method that achieves high bandwidth by using electrostatically-actuated cantilevers with low stiffness and low quality factor. Reliable IC operation is achieved by shaping the input signal applied to the cantilever for electrostatic actuation. By keeping the oscillation amplitude small, high-frequency operation is possible and the tipsample interaction force is reduced, which in turn prolongs the lifetime of tip and sample. For high-bandwidth imaging, the cantilever deflection signal is sampled directly at each oscillation cycle using input-based triggering. Our experimental results demonstrate the efficacy of the proposed scheme. In particular, in long-term scanning experiments, the tip diameter was maintained over a remarkable 140 m of tip travel. Moreover, as no demodulation electronics are needed, compact SPM devices using this method could be developed, including devices that employ large arrays of cantilevers in parallel operation for high throughput