Recent advances allow us to manipulate, control, and measure local phenomena at nanometer scales. Size dependent behavior of solids has become the hallmark of nanoscale science and nanotechnology. As systems decrease in size, the influence of surfaces and interfaces can dominate the properties. In fact, properties of surfaces and interfaces dictate the behavior of devices ranging from biosensors to solar cells to computer processors. This is particularly true as the size of the constituents decreases. This talk will present three model examples of behavior at interfaces that have dramatic consequences to system properties that also illustrate novel measurements of local properties.
First, local measurements of metal-semiconductor interfaces with diameters ranging from 1nm to 100nm are compared. The electronic transport properties of these interfaces are found to be both size and orientation dependent. The local properties are determined by tunneling into supported metal clusters with scanning tunneling microscopy and by direct contact with scanning probe based impedance probes.
Second, complex properties of interfaces between engineered proteins and electrodes are probed. The simultaneous detection of electron transport and the effect of optical absorption on dielectric polarizability in oriented peptide single molecular layers will be demonstrated. The approach enables a quantitative comparison of the change in polarization volume between the ground state and excited state in a single molecular layer in a manner that allows spatial mapping relevant to ultimate device design.
Finally, metal nanoparticle-molecule arrays are fabricated in which particles are spanned by single molecules producing percolative pathways. The molecule is designed to be optically active and the wavelength and temperature dependences of photo current are compared. It is found that the photocurrent is a consequence of the interaction of the molecules with the surface plasmons. The outcome of this interface configuration is the transduction of optical energy into electrical current in a molecular device.