Congratulations to Dr. Dmitry Kislitsyn!

Yesterday, Dmitry Kislitsyn successfully defended his dissertation, “Spectroscopic Studies of Nanomaterials with a Liquid-Helium-Free High-Stability Cryogenic Scanning Tunneling Microscope.” Dr. Kislitsyn has been instrumental in building and developing the Nazin Lab, and he will most certainly be missed. We wish him the best of luck as he goes to New York to begin his new position at Global Foundries!

Molecular Nanohoop Quantum Corrals: A Novel Approach to Modifying Surface Electronic Structure

Table of Contents Figure 8CPP_v13-01Quantum confinement of two-dimensional surface electronic states is a possible avenue for the controllable modification of metal surface electronic structure. The Nazin Lab used scanning tunneling microscopy and spectroscopy (STM/STS) to study the electron confinement within individual ring-shaped cycloparaphenylene (CPP) molecules, prepared by Evan Darzi and Ramesh Jasti, that formed self-assembled films on Ag(111) and Au(111) surfaces. STM imaging and STS mapping revealed the presence of electronic states localized in the interiors of CPP rings, inconsistent with the expected localization of molecular electronic orbitals. Electronic energies of these states showed considerable variations correlated with the molecular shape. These observations are explained by the presence of localized states formed due to confinement of surface electrons by the CPP skeletal framework, which thus acts as a molecular electronic “corral”. These experiments suggest an approach to robust, large-area modification of the surface electronic structure via quantum confinement within molecules forming self-assembled layers.

Benjamen N. Taber, Christian F. Gervasi, Jon M. Mills, Dmitry A. Kislitsyn, Evan R. Darzi, William G. Crowley, Ramesh Jasti, and George V. Nazin published their results, “Quantum Confinement of Surface Electrons by Molecular Nanohoop Corrals”,  in the Journal of Physical Chemistry Letters. The letter was published online on July 26, 2016, and is available at: http://pubs.acs.org/doi/abs/10.1021/acs.jpclett.6b01279.

Investigation of Dangling Bond Defects on Silicon Nanocrystals

Figure 3 from the main text.

Spatial mapping of the local density of states of a silicon nanocrystal after the creation of a dangling bond defect. From Fig. 3 of the main text.

The Nazin Lab recently published an investigation of silicon nanocrystal (SiNC) dangling bond (DB) defects, “Visualization and spectroscopy of defects induced by dehydrogenation in individual silicon nanocrystals,” in the Journal of Chemical Physics. In this communication, we use scanning tunneling spectroscopy (STS) to study the impact of dehydrogenation on the electronic structures of hydrogen-passivated silicon nanocrystals supported on the Au(111)surface. Gradual dehydrogenation results, initially, in reduction of the electronic bandgap, and eventually produces midgap electronic states. We also use theoretical calculations to show that the STS spectra of midgap states are consistent with the presence of silicon dangling bonds, which are found in different charge states. Our calculations also suggest that the observed initial reduction of the electronic bandgap is attributable to the SiNC surface reconstruction induced by conversion of surface dihydrides to monohydrides due to hydrogen desorption. Our results thus provide the first visualization of the SiNC electronic structure evolution induced by dehydrogenation and provide direct evidence for the existence of diverse dangling bond states on the SiNC surfaces. The article was published online June 28, 2016, and is available at: http://dx.doi.org/10.1063/1.4954833

Article Published in JCP

_Bent DDQT ToC_v6-01

The Nazin Lab’s article, “Real-Space Visualization of Conformation-Independent Oligothiophene Electronic Structure,” was published online in The Journal of Chemical Physics on May 17, 2016. In this article, we presented scanning tunneling microscopy and spectroscopy (STM/STS) investigations of the electronic structures of different alkyl-substituted oligothiophenes on the Au(111) surface, showing that on Au(111) oligothiophenes adopt distinct straight and bent conformations. We combined STS maps with STM images to visualize, in real space, particle-in-a-box-like oligothiophene molecular orbitals. We demonstrated that different planar conformers with significant geometrical distortions of oligothiophene backbones surprisingly exhibit very similar electronic structures, indicating a low degree of conformation-induced electronic disorder. The agreement of these results with gas-phase density functional theory calculations implies that the oligothiophene interaction with the Au(111) surface is generally insensitive to molecular conformation.

The article is available online at: http://dx.doi.org/10.1063/1.4949765.