Robert Barrett

Atomic resolution with an atomic force microscope using piezoresistive detection

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 Arms vertical resolution in a 10 Hz–1 kHz bandwidth.

Atomic force microscopy using a piezoresistive cantilever

An atomic force microscope (AFM) is an instrument which measures the topography of a surface by bringing a cantilever beam into contact with a sample and measuring the deflection of the cantilever as it is scanned across the surface. The complexity of an AFM is predominantly governed by the detector used for measuring the deflection of the cantilever probe. The authors describe the fabrication of a silicon cantilever beam with an integrated piezoresistor for sensing its deflection. A silicon-on-insulator material is used for the fabrication. A p-type resistor is fabricated at the surface of the cantilever along a <110> direction so that the piezoresistive effect of silicon causes its resistance to vary linearly with its deflection. The cantilevers considered typically have spring constants from 1 to 10 N/m and minimum detectable deflections from 1 to 10 AA over a 10-Hz-1-kHz frequency range. The cantilevers were successfully used in an AFM, and an image of a grating was obtained with this technique.<<ETX>>

2. Design Considerations for an STM System

Publisher Summary This chapter discusses that in the early years the rate of success in the groups that pioneered the new era, with the scanning tunneling microscopy (STM), was limited by the technical difficulties associated with the new instrument. It discusses that the STM is a viable instrument for studying the conducting surfaces with atomic resolution. Since then, the field has experienced a tremendous increase in popularity. The chapter also discusses STM instrumentation. It describes the fundamental application of the STM: imaging and spectroscopy in both ultra-high vacuum (UHV) and ambient environments. The most convenient STM mode is operation in air— that is, the air-STM is often used for inert samples. The most stringent STM mode is operation in ultrahigh vacuum— that is, the UHV-STM is required for accurate and reliable studies of clean surfaces. The design concepts of the two instruments are quite similar, but the construction and operation of the air-STM is simpler by far. Acoustic coupling through the air is always present in the air-STM; however, the air-STM, with its compact and rigid form, is less sensitive to mechanical vibrations. The chapter also presents theoretical analysis of the systems for feedback control and vibration isolation as applied to STM. It is possible to design the STM without this rigorous calculation of the behavior of the feedback and isolation systems, but the analysis allows improving the performance of the STM when it is constrained to operate under specific conditions. It discusses typical problems and difficulties that are encountered in operating an STM together with possible remedies and improvements.