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The Nazin group investigates the connection between the chemical structure and properties of nanoscale materials and devices. We are particularly interested in real-space experimental approaches that provide spectroscopic information on the atomic and molecular scales. Some of the research directions are described below:

1) Nanoscale inorganic semiconductors: In collaboration with our industrial partners, we explore strategies for surface passivation and functionalization of semiconducting nanocrystals, with potential applications in optoelectronics and photovoltaics. The properties of devices based on such nanocrystals are strongly affected by localized sub-bandgap states associated with surface imperfections. To understand the nature of such surface states, a correlation between their properties and the atomic-scale structure of chemical imperfections responsible for their appearance must be established. To achieve this, we use Scanning Tunneling Spectroscopy to visualize electronic states in individual nanocrystals (Fig. 1).

Fig. 1: Spatial mapping of electronic states in individual PbS nanocrystals.

2) Organic semiconductors: Research in organic semiconductors is aimed at understanding the impacts of the molecular structure, composition and packing in molecular solids on the processes associated with energy and charge transfer, which are central to the operation of electronic and photovoltaic devices based on organic semiconductors.

Fig. 2: STM image of a pair of oligothiophene molecules.

3) Carbon nanotubes: Our group is applying advanced STM-based spectroscopic techniques to understand the fundamental properties of electronic and excitonic states in carbon nanotubes (CNTs). The unique photophysics of semiconducting single-wall carbon nanotubes is a result of a complex interplay among several factors arising from their low-dimensionality:  (a) the primary photoexcitations in CNTs are described by one-dimensional excitonic bands formed via strongly correlated electron-hole interactions;  (b) variations of the excitonic bandgap are caused by environmental inhomogeneities and CNT defects; (c) photo-generated excitons tend to diffuse along the nanotube axis and can become trapped in regions with smaller excitonic bandgaps, or on individual defects;  (d) relatively low luminescence yields are typically observed, a consequence of defect-induced quenching, and the intrinsic hierarchy of the excitonic manifold containing dark excitonic bands. Our STM-based spectroscopic approach enables direct visualization of these effects providing information inaccessible to any other measurement technique.

Fig. 3: STM image of a carbon nanotube.

Our research is at the intersection of several disciplines, including surface science, molecular spectroscopy, materials science and solid state physics. Students working in our group have the opportunity to participate in construction of novel instrumentation and learn such techniques as ultra high vacuum technology, scanning probe microscopy, nanoscale device fabrication and optical spectroscopy.

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