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

A standard baseline scenario 2,3 that assumes no policy intervention to limit greenhouse-gas emissions has 10 TW (10 ؋ 10 12 watts) of carbon-emission-free power being produced by the year 2050, equivalent to the power provided by all today's energy sources combined. Here we employ a carbon-cycle/energy model to ¶ Present address: Boeing, Saal Beach, California 90740-7644, USA.

The atomic force microscope (AFM) can be used to image the surface of both conductors and nonconductors even if they are covered with water or aqueous solutions. An AFM was used that combines microfabricated cantilevers with a previously described optical lever system to monitor deflection. Images of mica demonstrate that atomic resolution is possible on rigid materials, thus opening the possibility of atomic-scale corrosion experiments on nonconductors. Images of polyalanine, an amino acid polymer, show the potential of the AFM for revealing the structure of molecules important in biology and medicine. Finally, a series of ten images of the polymerization of fibrin, the basic component of blood clots, illustrate the potential of the AFM for revealing subtle details of biological processes as they occur in real time.

Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.

A new detection scheme for atomic force microscopy (AFM) is shown to yield atomic resolution images of conducting and nonconducting layered materials. This detection scheme uses a piezoresistive strain sensor embedded in the AFM cantilever. The cantilever is batch fabricated using standard silicon micromachining techniques. The deflection of the cantilever is measured directly from the resistance of the piezoresistive strain sensor without the need for external deflection sensing elements. Using this cantilever we achieved 0.1 Årms vertical resolution in a 10 Hz–1 kHz bandwidth.