PennerGroup research

We study the properties of nanoscopic wires, particles, and films prepared by electrodeposition. Our objective is to understand how these nanomaterials behave in devices such as chemical sensors, biosensors, thermocouples, thermoelectric generators, photodetectors, and transistors. Our research is funded by the following agencies and entities:

Projects of current interest are the following:

Single crystalline nanowires from polycrystalline nanowires. Making nanowires is a central focus of our research group, and metal nanowires are important for many of the projects described below. Can we control the resistivity of these nanowires? Often, the metal nanowires we electrodeposit are nanocrystalline with a mean grain diameter of 10-100 nm. The inelastic scattering of electrons from grain boundaries (not surface scattering) provides the largest single contribution to the total resistance of this nanowire. We are studying processes for increasing the grain diameter, including laser annealing (which provides a highly local thermal annealing effect) and rapid whole-wire thermal annealing.
Project Leaders: Jungyun Kim and Crystal Yang.

Energy storage. The high surface area : volume ratio of nanowires makes them attractive candidates for electrodes in batteries and supercapacitors. The key fundamental question is: What limits the performance of these materials? We are focusing attention on MnO₂ which is a hybrid energy storage material that is capable of storing charge capacitively and Faradaically, as a change in the redox state of the Mn centers. The challenge is to prepare MnO₂ nanomaterials that charge and discharge rapidly while also producing the highest possible energy density.
Project Leader: Wenbo Yan.

Solar Energy. The problem with solar energy is the sun - it's intermittant. A method for storing the energy produced by the sun is therefore needed. A Holy Grail is the development of a water splitting system that is efficient, cheap, and durable. We are exploring the development of semiconductor nanowires that are engineered to meet these design objectives. Fundamental aspects of carrier transport in polycrystalline semiconductor nanowires is necessarily a focus of this project.

We're also studying the properties of nanowires for generating electrical power from solar-generated temperature gradients using the principles of thermoelectrics.
Project Leaders: Xiaowei Li and Rajen Dutta.

Photodetectors. A sensitive, fast photodetector based upon a photoconductive semiconductor nanowire remains an elusive goal. You can have one or the other: A fast device (盜 range) that is insensitive (Gain < 1.0), or a slow device (>1s range) that is ultrasensitive (Gain > 10⁴). We need to understand more about carrier transport through grain boundaries in polycrystalline nanowires, about electrical contacts, and other issues before we will know whether this connundrum has a fundamental science solution.
Project Leaders: Wendong Xing and Talin Ayvazian.

Chemical Sensing. Metal nanowires can function as chemical sensors that are fast, sensitive, rugged, cheap, and super power efficient. These are the conclusions of our recent work on sensors for ammonia and hydrogen gas. The key attribute of nanowires in this application is their tremendous surface area: volume ratio. One surprise is that the chemisorption of gas molecules to the metal surface is sufficient to generate a significant, measurable change in the wire resistance, enabling the detection of some gases at concentrations in the ppm range.
Project Leader: Wendong Xing.

Biosensors. Regrettably, overall cancer mortality has hardly changed in thirty years. We are collaborating with the research group of Professor Greg Weiss to detect cancer much earlier, before metastasis occurs, in the hopes of impacting this problem. Together with the Weiss Group, we have been developing a new type of disposable biosensor that we hope will permit the detection of cancer markers in urine and blood. It can be disposable because the bioaffinity reagents and the transducer are both inexpensive. One outcome of the work so far is the development of an innovative bioaffinity medium, consisting of a conductive polymer and engineered virus particles, that can be electroplated in a single step, requiring a minute or two.
Project Leaders: Keith Donavan and Crystin Eggers.

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