BACKGROUND:  The reduced scale of CMOS technology and the development of biological and medical technology makes the detection and characterization of single atoms and molecules critical. Conventional capacitance based defect characterization methods, such as deep level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR) cannot be applied to nanodevices and molecular study due to lack of sensitivity.

INNOVATION:  Telegraph signal microscopy (TSM) can be combined with atomic force microscopy to acquire morphology and characterize materials at the nanometer scale. When TSM and AFM are integrated, image and single atom information can be acquired simultaneously. The innovation lies in understanding the structure of the TSM probe and the integration of the entire system.

TSM uses random telegraph signals (RTS) in 1-dimensional nanodevices, such as carbon nanotubes or nanowires. A telegraph signal microscope is composed of an RTS probe, scanning stage (controlling the X-Y coordinates of the RTS probe) and optical microscope. The Fermi energy of the RTS probe is calculated. Then the probe is put close to the test surface. If the energy of a specific atom aligns with the probe Fermi energy, RTS can happen. By observing the current, the energy information of the atom can be analyzed. RTS phenomena have been observed in other devices, but to date, no other groups have experimentally demonstrated RTS in nanoscale devices.

In addition to atomic and molecular characterization, TSM can be implemented in a low temperature environment to probe spin, mapping out and manipulating single spin in conjunction with EPR and nuclear magnetic resonance. Finally, Fermi energy of the probe is sensitive to electron/hole creation by incidence of a single photon, enabling use of this technology as a photon detector as well.

DEVELOPMENT-TO-DATE:  A complete device has been assembled and tested with single wall carbon nanotubes and Indium Oxide nanowire FETs. RTS amplitudes up to 60% total current were observed, demonstrating good sensitivity and signal to noise ratio. Defect information, material damage, bandgap calculation for CNT and transition coefficients due to single defect Coulomb potential have been detected.

Reference: UCLA Case No. 2005-439

US Patent Application: 20060231754