Introduction to Research Seminar

While most investigators focus on their signal, and seek to eliminate any noise, studies of fluctuation phenomena can reveal important information concerning defect kinetics and conduction mechanisms not easily available through conventional transport measurement techniques. In this talk I will describe studies of current noise in thin film hydrogenated amorphous silicon (a-Si:H) that displays a spectral density that varies as the inverse of the frequency (termed 1/f noise). The conductance noise in a-Si:H is non-Gaussian, where the magnitude and spectral slope of the noise power varying in time. Fourier analysis of the noise power fluctuations yields a “second spectrum” which itself has an 1/f frequency dependence. That is, in amorphous silicon, the 1/f noise has 1/f noise! We observe striking random telegraph switching noise in these materials that is interpreted as indicating the presence of inhomogeneous current filaments whose connectivity and conductivity vary with time. These studies have been extended to other complex systems whereby current microchannels fluctuate in time. We have studied voltage fluctuations recorded from awake, behaving rats and applied the noise analysis techniques developed to investigate non-Gaussian phenomena in amorphous semiconductors. We have developed a simple yet powerful technique for identifying coherent oscillations in neurological signals that we have then been able to correlate for particular actions taken by the animal. The implications of these studies for our understanding of Parkinson’s disease will be discussed.