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Research

Noise Microscopy

Noise Microscopy Setup on a Graphene Device
(ACS Nano 10 10135 2016)

   Our unique equipment ¡®noise microscopy¡¯ enables nano-resolution measurement and imaging of electrical noises in electronic materials and devices. The noise microscopy is a combined system of a conducting atomic force microscopy (cAFM) and a current-noise analyzer. Using the equipment, we can approach a sharp conducting AFM probe to a specific location on an electronic channel and measure local electrical and noise properties at the location. Further, by scanning the AFM probe measuring current/noise over the channel surface, we can obtain nano-resolution ¡®noise image¡¯ showing the distribution of electrical noises on the scanned area, simultaneously with the cAFM current image on the area. Remarkably, by analyzing the noise map, we can estimate quantitative distribution of nanoscale noise sources in electronic channels and study individual characteristics of them. To date, the noise microscopy is the only way to quantitatively study distributions and characteristics of nanoscale noise sources in an electronic channel.

  Examples of interesting research results via noise microscopy are as follows.


 1) Imaging of Charge Trap Densities in Graphene


Noise Microscopy on a Graphene Device
(ACS Nano 10 10135 2016)

  Using noise microscopy, we could map activities of localized noise sources (traps) in graphene domains. The results show high activities of noise sources and large sheet resistance values at the domain boundary and edge of graphene. In addition, we found that the top layer in double-layer graphene had lower noises than single-layer graphene.


 2) Imaging of Electrical Fluctuations in Molecular Junctions


Noise Microscopy on Molecular Junctions
(Sci. Rep. 7 43411 2017)

  The noise microscopy could be utilized to analyze noises in molecular junctions. Here, different molecular wires were patterned on a gold substrate, and the current-noise map on the pattern was measured and analyzed. Importantly, by measuring molecular junctions comprising various thiol molecules on a gold substrate, we revealed that electrical noises in a molecular system can mainly generated by the random fluctuations of bonds between molecules and metal electrodes. Further, we quantitatively compared the frequencies of such bond fluctuations in different molecular junctions and identified molecular wires with lower electrical noise, which can provide critical information for designing low-noise molecular electronic devices.

3) Trap Density Imaging on Microstructures of Polymer


Noise Microscopy on Polymer Film
(Nanoscale 8 835 2016)

  We applied the noise microscopy to study the localized noise-sources and those induced by external-stimuli in polymer films. Analyzing the current/noise imaging data, resistivity and noise source density in the films could be mapped. Particularly, a larger number of noise-sources were observed in the disordered-phase-regions than in the ordered-phase-regions in polymer films, due to structural disordering. Further, increased bias-voltages on the disordered regions resulted in increased noise sources. On photo-illumination, the ordered-phase-regions exhibited a rather large increase in the conductivity and noise source density, presumably due to release of carriers from deep-traps.