J. D. Adams

Automated parallel high-speed atomic force microscopy

An expandable system has been developed to operate multiple probes for the atomic force microscope in parallel at high speeds. The combined improvements from parallelism and enhanced tip speed in this system represent an increase in throughput by over two orders of magnitude. A modular cantilever design has been replicated to produce an array of 50 cantilevers with a 200 μm pitch. This design contains a dedicated integrated sensor and integrated actuator where the cells can be repeated indefinitely. Electrical shielding within the array virtually eliminates coupling between the actuators and sensors. The reduced coupling simplifies the control electronics, facilitating the design of a computer system to automate the parallel high-speed arrays. This automated system has been applied to four cantilevers within the array of 50 cantilevers, with a 20 kHz bandwidth and a noise level of less than 50 A. For typical samples, this bandwidth allows us to scan the probes at 4 mm/s.

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.

Centimeter scale atomic force microscope imaging and lithography

We present a 4 mm2 image taken with a parallel array of 10 cantilevers, an image spanning 6.4 mm taken with 32 cantilevers, and lithography over a 100 mm2 area using an array of 50 cantilevers. All of these results represent scan areas that are orders of magnitude larger than that of a typical atomic force microscope (0.01 mm2). Previously, the serial nature and limited scan size of the atomic force microscope prevented large scale imaging. Our design addresses these issues by using a modular micromachined parallel atomic force microscope array in conjunction with large displacement scanners. High-resolution microscopy and lithography over large areas are important for many applications, but especially in microelectronics, where integrated circuit chips typically have nanometer scale features distributed over square centimeter areas.

High-speed atomic force microscopy in liquid

High-speed constant force imaging with the atomic force microscope (AFM) has been achieved in liquid. By using a standard optical lever AFM, and a cantilever with an integrated zinc oxide (ZnO) piezoelectric actuator, an imaging bandwidth of 38 kHz has been achieved; nearly 100 times faster than conventional AFMs. For typical samples, this bandwidth corresponds to tip velocities in excess of 3 mm/s. High-speed AFM imaging in liquid will (1) permit chemical and biological AFM observations to occur at speeds previously inaccessible, and (2) significantly decrease measurement times in standard AFM liquid operation.

Dual integrated actuators for extended range high speed atomic force microscopy

A flexible system for increasing the throughput of the atomic force microscope without sacrificing imaging range is presented. The system is based on a nested feedback loop which controls a micromachined cantilever that contains both an integrated piezoelectric actuator and an integrated thermal actuator. This combination enables high speed imaging (2 mm/s) over an extended range by utilizing the piezoelectric actuator’s high bandwidth (15 kHz) and thermal actuator’s large response (300 nm/V). A constant force image, where the sample topography exceeds the range of the piezoelectric actuator alone, is presented. It has also been demonstrated that the deflection response of the thermal actuator can be linearized and controlled with an integrated diode.

Thin film characterization by atomic force microscopy at ultrasonic frequencies

We present a technique in which atomic force microscopy at ultrasonic frequencies is used to determine the thickness of thin films. In this technique, the resonance frequency of a flexural mode of an atomic force microscope cantilever is used to determine the tip-sample contact stiffness. This allows the film thickness to be determined, provided that the tip and sample elastic moduli and radii of curvature are known. We report experimental results for thin metal and polymer films deposited on silicon substrates and compare them with the predictions of a theoretical model.

Integration of through-wafer interconnects with a two-dimensional cantilever array

High-density through-wafer interconnects are incorporated in a two-dimensional (2D) micromachined cantilever array. The design addresses alignment and density issues associated with 2D arrays. Each cantilever has piezoresistive deflection sensors and high-aspect ratio silicon tips. The fabrication process and array operation are described. The integration of cantilevers, tips, and interconnects enables operation of a high-density 2D scanning probe array over large areas.

Methylphenidate, cognition, and epilepsy: A double-blind, placebo-controlled, single-dose study

Objective: To evaluate the potential efficacy of immediate-release methylphenidate (MPH) for treating cognitive deficits in epilepsy. Methods: This was a double-blind, randomized, single-dose, 3-period crossover study in patients with epilepsy and chronic cognitive complaints comparing the effects of placebo and MPH 10 and 20 mg given 1 week apart. Cognitive outcome was evaluated on the basis of an omnibus z score calculated from performance on the Conners Continuous Performance Test 3 (ability to discriminate between target and nontarget stimuli [d] and hit reaction time standard deviation), Symbol-Digit Modalities Test, and Medical College of Georgia Paragraph Memory Test. Adverse events and seizure frequency were monitored. An open-label follow-up is reported elsewhere. Results: Thirty-five adult patients with epilepsy participated, of whom 31 finished. Demographics included the following: mean age = 35.3 years (range 20–62 years), 13 men and 18 women, and baseline seizure frequency of 2.8 per month. Epilepsy types were focal (n = 24), generalized (n = 6), or unclassified (n = 1). Mean epilepsy duration was 12.5 years. A statistically significant performance benefit was present at both 10-mg (p = 0.030) and 20-mg (p = 0.034) MPH doses. No seizures were associated with either MPH dose. Adverse effects leading to withdrawal included cognitive “fogginess” (n = 1 on 20 mg), anxiety/agitation (n = 1 on 10 mg), and tachycardia (n = 1). One participant was lost to follow-up after one 20-mg dose without side effect. Conclusions: This single-dose study suggests that MPH may be effective in ameliorating some cognitive deficits in patients with epilepsy. Additional studies are required. ClinicalTrials.gov identifier: NCT02178995. Classification of evidence: This study provides Class II evidence that single doses of MPH improve cognitive performance on some measures of attention and processing speed in patients with epilepsy and cognitive complaints.

Nondestructive film thickness measurement using atomic force microscopy at ultrasonic frequencies

We present a technique in which atomic force microscopy (AFM) at ultrasonic frequencies is used to measure the contact stiffness between an AFM tip and thin films on silicon substrates. In this method, the resonance frequencies of the cantilever flexural modes are used to determine the tip-sample contact stiffness. We present experimental results, showing that the contact stiffness is highly sensitive to the thickness of thin metal and polymer films. These results are compared with those from out theoretical model, which we call the Contact Stiffness Algorithm (CSA), that may be used to calculate the contact stiffness between an AFM tip and an arbitrarily layered sample. Unlike transmission electron microscopy (TEM) or scanning electron microscopy (SEM) on a cross-section of the sample, this film thickness measurement technique is non- destructive. It is also capable of high lateral spatial resolution, provided that a sharp AFM tip is used. We present images of a photoresist film on silicon with contrast resulting from the elastic properties of the sample.

Methylphenidate, cognition, and epilepsy: A 1‐month open‐label trial

Cognitive difficulties are common in epilepsy. Beyond reducing seizures and adjusting antiepileptic medications, no well‐validated treatment exists in adults. Methylphenidate is used effectively in children with epilepsy and attention‐deficit/hyperactivity disorder, but its effects in adults have not been systematically evaluated. We hypothesized that methylphenidate can safely improve cognition in adults with epilepsy. We detail here the open‐label follow‐up to a double‐blind, placebo‐controlled, single‐dose study.