Nanostructured silicon thin film solar cells are promising, due to the strongly enhanced light trapping, high carrier collection efficiency, and potential low cost. Ordered nanostructure arrays, with large-area controllable spacing, orientation, and size, are critical for reliable light-trapping and high-efficiency solar cells. Available top-down lithography approaches to fabricate large-area ordered nanostructure arrays are challenging due to the requirement of both high lithography resolution and high throughput. Here, a novel ordered silicon nano-conical-frustum array structure, exhibiting an impressive absorbance of 99% (upper bound) over wavelengths 400-1100 nm by a thickness of only 5 μm, is realized by our recently reported technique self-powered parallel electron lithography that has high-throughput and sub-35-nm high resolution. Moreover, high-efficiency (up to 10.8%) solar cells are demonstrated, using these ordered ultrathin silicon nano-conical-frustum arrays. These related fabrication techniques can also be transferred to low-cost substrate solar energy harvesting device applications.

We report on radio-controlled insect biobots by directing the flight of Manduca sexta through neuromuscular activation. Early metamorphosis insertion technology was used to implant metal wire probes into the insect brain and thorax tissue. Inserted probes were adopted by the developing tissue as a result of the metamorphic growth. A mechanically and electrically reliable interface with the insect tissue was realized with respect to the insect's behavioral and anatomical adoption. Helium balloons were used to increase the payload capacity and flight duration of the insect biobots enabling a large number of applications. A super-regenerative receiver with a weight of 650 mg and 750 muW of power consumption was built to control the insect flight path through remotely transmitted electrical stimulation pulses. Initiation and cessation of flight, as well as yaw actuation, were obtained on freely flying balloon-assisted moths through joystick manipulation on a conventional model airplane remote controller.

A betavoltaic cell in 4H SiC is demonstrated. A p-n diode structure was used to collect the charge from a 1mCi Ni-63 source. An open circuit voltage of 0.72V and a short circuit current density of 16.8nA∕cm2 were measured in a single p-n junction. A 6% lower bound on the power conversion efficiency was obtained. A simple photovoltaic-type model was used to explain the results. Fill factor and backscattering effects were included in the efficiency calculation. The performance of the device was limited by edge recombination.

A reciprocating cantilever utilizing emitted charges from a millicurie radioisotope thin film is presented. The actuator realizes a direct collected-charge-to-motion conversion. The reciprocation is obtained by self-timed contact between the cantilever and the radioisotope source. A static model balancing the electrostatic and mechanical forces from an equivalent circuit leads to an analytical solution useful for device characterization. Measured reciprocating periods agree with predicted values from the analytical model. A scaling analysis shows that microscale arrays of such cantilevers provide an integrated sensor and actuator platform.

The challenge for new biosensors is to achieve detection of biomolecules at low concentrations, which is useful for early-stage disease detection. Nanomechanical biosensors are promising in medical diagnostic applications. For nanomechanical biosensing at low concentrations, a suffi cient resonator device surface area is necessary for molecules to bind to. Here we present a low-concentration (500 aM sensitivity) DNA sensor, which uses a novel nanomechanical resonator with ordered vertical nanowire arrays on top of a Si / SiO 2 bilayer thin membrane. The high sensitivity is achieved by the strongly enhanced total surface area-to-volume ratio of the resonator (10 8 m − 1 ) and the state-of-the-art mass-per-area resolution (1.8 × 10 − 12 kg m − 2 ). Moreover, the nanowire array forms a photonic crystal that shows strong light trapping and absorption over broad-band optical wavelengths, enabling high-effi ciency broad-band optothermo-mechanical remote device actuation and biosensing on a chip. This method represents a mass-based platform technology that can sense molecules at low concentrations.

This article compares resonant ultrasound spectroscopy ͑RUS͒ and other resonant methods for the determination of viscoelastic properties such as damping. RUS scans from 50 to 500 kHz were conducted on cubical specimens of several materials including brass, aluminum alloys, and polymethyl ͑methacrylate͒ ͑PMMA͒, a glassy polymer. Comparison of damping over the frequency ranges for broadband viscoelastic spectroscopy ͑BVS͒ and RUS for indium tin alloy in shear modes of deformation discloses a continuation of the tan ␦ power-law trend for ultrasonic frequencies up to 300 kHz. For PMMA, resonant peaks were sufficiently broad that higher modes in RUS began to overlap. Tan ␦ via RUS and BVS for PMMA agreed well in the frequency range where the methods overlap. RUS is capable of measuring tan ␦ as high as several percent at the fundamental frequency. Since higher modes are closely spaced, it is impractical to determine tan ␦ above 0.01-0.02 at frequencies other than the fundamental.

R esearch on pervasive computing systems has focused on algorithms, system architectures, and software issues associated with systems that compute for extended time periods and that are incorporated into everyday objects. However, as the time period for system use increases, hardware reliability becomes an important design factor. A possible reliability metric for pervasive computing systems could be the degree to which the systems are immune to power loss and wide variations in operating conditions. The goal is to achieve power sources that operate over a wide temperature range and for extended time periods with high reliability. To reach this goal, researchers have investigated technologies for miniature micropower applications and developed radioisotope power generators (see the "Related Energy Sources" sidebar). Unfortunately, the former usually suffer from low energy densities, low conversion efficiencies, or unreliability, while the latter suffer from low energy conversion efficiencies, taking away from the high energy densities that radioisotope thin films offer. To help remedy this, we've created a power source employing radioactive thin films and piezoelectric unimorphs, using a nonthermal energy conversion cycle that enables much higher energy conversion efficiency.The kinetic energy of the particles emitted from radioisotopes is temperature insensitive up to fusion temperatures (radioactive thin films emit electrons as beta particles, helium nuclei as alpha particles, and photons as x-rays). This can extend a pervasive computing system's operating temperature range, possibly from milliKelvin to thousands of Kelvin, assuming the hardware is composed of the appropriate materials. Moreover, radioactive thin films emit energy over a time governed by the half-life, which can be very long. For the 63 Ni ␤-source we used, the half-life is 100.2 years. Hence, the power sources we describe could extend a system's operating life by several decades or even a century, during which time the system could gain learned behavior without worrying about the power turning off.Radioactive thin-film-based power sources also have energy density orders of magnitude higher than chemical-reaction-based energy sources. This enables submillimeter-scale power sources, which is significant given the crucial role that metrics of power and energy density play in determining pervasive computing systems' usefulness in applications limited by size.For example, although pacemakers and diabetes-monitoring equipment are already available, no system is small enough to fit inside a prostrate or brain for long-term monitoring A long-lasting radioisotope micropower generator for self-powered sensor microsystems promises to make pervasive computing systems more reliable. Its higher energy conversion efficiency enables microsystems with small amounts of radioactivity to realize sensor and basic computation operations.

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