The scanning tunneling microscope is proposed as a method to measure forces as small as 10 N. As one application for this concept, we The SP has much in common with the STM. The tip in the STM and the stylus in the SP are both used to scan the surface, sense the variations of the sample, and generate three-dimensional images. The stylus in the profilometer is carried by a cantilever beam and it rides on the sample surface. This means that a rough surface can be plastically deformed. " The radius of this stylus is about 1 p, m, and the loading force extends from 10 to 10 N. ' The spring in the AFM is a critical component. %e need the maximum deflection for a given force. This requires a spring that is as soft as possible. At the same time a stiff spring with high resonant frequency is necessary in order to minimize the sensitivity to vibrational noise from the building near 100 Hz. The resonant frequency, fo, of the spring system is given by f0= (I/2sr)(k/nto)', where k is the spring constant and ttto is the effective mass that loads the spring.This relation suggests a simple way out of our dilemma. As we decrease k to soften the spring we must also decrease mo to keep the ratio k/mo large. The limiting case, illustrated in Fig. 1, is but a single atom adsorbed at site A in the gap of an STM. It has its own mass and an effective k that comes from the coupling to neighboring atoms.The mass of the spring in manmade structures can be quite small but eventually microfabrication'4 will be employed to fabricate a spring with a mass less than 10 '0 kg and a resonant frequency greater than 2 kHz. Displacements of 10 A can be measured with the STM when the tunneling gap is modulated. The force

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We report the specific transduction, via surface stress changes, of DNA hybridization and receptor-ligand binding into a direct nanomechanical response of microfabricated cantilevers. Cantilevers in an array were functionalized with a selection of biomolecules. The differential deflection of the cantilevers was found to provide a true molecular recognition signal despite large nonspecific responses of individual cantilevers. Hybridization of complementary oligonucleotides shows that a single base mismatch between two 12-mer oligonucleotides is clearly detectable. Similar experiments on protein A-immunoglobulin interactions demonstrate the wide-ranging applicability of nanomechanical transduction to detect biomolecular recognition.

Thin oxide films with perovskite or related structures and with transition metal doping show a reproducible switching in the leakage current with a memory effect. Positive or negative voltage pulses can switch the resistance of the oxide films between a low- and a high-impedance state in times shorter than 100 ns. The ratio between these two states is typically about 20 but can exceed six orders of magnitude. Once a low-impedance state has been achieved it persists without a power connection for months, demonstrating the feasibility of nonvolatile memory elements. Even multiple levels can be addressed to store two bits in such a simple capacitor-like structure.

We report on the first successful tunneling experiment with an externally and reproducibly adjustable vacuum gap. The observation of vacuum tunneling is established by the exponential dependence of the tunneling resistance on the width of the gap. The experimental setup allows for simultaneous investigation and treatment of the tunnel electrode surfaces.