Dr. Stephen J. Fonash
 
Dr. Stephen J. Fonash
Bayard D. Kunkle Chair in Engineering Sciences
Director, Penn State Center for Nanotechnology Education & Utilization
Director, PA Nanofabrication Manufacturing Technology Partnership
Director, National Science Foundation Nanotechnology Advanced Technology Education Center

Dr. Stephen Fonash holds the Bayard D. Kunkle Chair in Engineering Sciences, at the Pennsylvania State University. His activities at Penn State include serving as the director of Penn State’s Center for Nanotechnology Education and Utilization (CNEU), director of the National Science Foundation Advanced Technology Education Center, and director of the Pennsylvania Nanofabrication Manufacturing Technology Partnership.

Prof. Fonash’s education contributions focus on nanotechnology post-secondary education and workforce development. His research activities encompass the processing and device physics of micro- and nanostructures including solar cells, sensors, and transistors. He has published over 300 refereed papers in the areas of education, nanotechnology, photovoltaics, microelectronics devices and processing, sensors, and thin film transistors. His book “Solar Cell Device Physics” has been termed the “bible of solar cell physics” and his solar cell computer modeling code AMPS is used by almost 800 groups around the world. Dr. Fonash holds 29 patents in his research areas, many of which are licensed to industry. He is on journal boards, serves as an advisor to university and government groups, has consulted for a variety of firms, and has co-founded two companies. Prof. Fonash received his Ph.D. from the University of Pennsylvania. He is a Fellow of the Institute of Electrical and Electronics Engineers and a Fellow of the Electrochemical Society.

Some Research Activities

(1) Nanowire sensor structures

Dr. Fonash’s research group’s activities include the development of metallic, semiconductor, and polymer electronic nanowire sensors for the detection of various chemical and bio-molecular species.  The goal is to exploit the detection phenomena available in nanowires, which are inherently fast, selective, and highly responsive due to the dimensional scale of these devices.  The group is currently working to advance this technology and to further improve on sensor fabrication methodologies.  Below are examples of a gold nanowire sensor and a polymer sensor developed in the research group.   The gold nanowire sensor structure, for example, can detect trace concentrations of elemental and ionic mercury.

Images of a gold nanowire sensor
Images of a gold nanowire sensor

Response of gold nanowire sensor to elemental and ionic mercury
Response of gold nanowire sensor to elemental and ionic mercury

Image of polyaniline nanowires for humidity detection
Image of polyaniline nanowires
for humidity detection
Response of polyaniline nanowire sensor to humidity
Response of polyaniline nanowire sensor
to humidity

(2) Nanofluidics

Dr. Fonash’s research group’s activities in nano-total analysis system (nTAS) area include exploiting a novel nanofluidic flow control and its application in a highly integrated bio-molecular detection system. Active nanofluidic flow control is accomplished by utilizing the parallel flow control (PFC) configuration and allows the primary problems of fluidic systems including interfacing, measuring, and manipulating, which have been plaguing nanofluidics, to be successfully solved. PFC uses flow in a pressure-driven micro-channel, which interfaces with the “outside world”, to set up the pressure gradient across a nano-channel. Based on the size-scale differences between these micro- and nano-channels which are arranged in parallel, micro to nano-channel flow rate ratios of and higher are easily attainable with the PFC approach thereby allowing the attainment of a broad range of fine nanofluidic flow control. Direct, real-time flow rate measurements in the nano-channel can be achieved by having an additional serpentine measurement micro-channel in series with the nano-channel. Furthermore, such PFC systems can be utilized in highly integrated bio-molecular detection, allowing, for example, a system integrating nanofluidic flow control with a nano-gap capacitor sensing structure. In this detection scheme, probe molecules are attached on electrode surface to catch and recognize the target molecules which can be detected by the electrical signal change. This novel sensing structure offers high sensitivity by minimizing noise through overlapping the electrical double layers between two electrodes due to the unique sub-50nm gap. The integrated nano-gap sensor and nano-scale fluid control structure is also very capable of selectivity. This can be realized by the immobilization of specific target and probe molecules on the electrode surface. This particular research effort has the goal of significant advances in nano-total analysis system (nTAS) and miniaturized chemical process systems.

 

 

 

(3) The “Grow-in-Place” Approach for Nanowire Growth and Positioning

The Fonash research group has also introduced a novel self-assembling “grow-in-place” technique based on the vapor-liquid-solid (VLS) nanowire growth mechanism. In this approach, a metal nanoparticle seeded in a pre-fabricated nanochannel template is used as the catalyst for silicon nanowire (SiNW) growth while the size, position, orientation and number of SiNWs are controlled by the template. Devices can be fabricated on the grown nanowires using conventional micro- or nano-fabrication techniques. This grow-in-place approach eliminates the need for any collection, positioning and assembling steps for nanowire device fabrication.

Template with metal catalyst in the middle of nanochannel
Template with metal catalyst in the middle of nanochannel

SiNW growth and extrusion out of growth-guiding nanochannel by VLS mechanism
SiNW growth and extrusion out of growth-guiding nanochannel by VLS mechanism


(4) A New Transistor Concept: the AMOSFET

A new transistor concept, the accumulation metal oxide semiconductor transistor (AMOSFET), has been proposed and demonstrated by Dr Fonash’s group. The AMOSFET uses a very simple configuration with ohmic source/drain contacts on a single (n or p) doped untra-thin semiconductor. In the ON-state, an appropriate gate voltage on the device leads to the formation of an accumulation layer underneath the gate, leading to current conduction between source and drain. In the Off-state, an appropriate gate voltage effectively depletes the entire semiconductor region covered by the gate, suppressing the off current and thereby ambipolar behavior. The AMOSFET device shows excellent device performance with on-off ratios up to and subthreshold swings of 160 mV/dec seen so-far experimentally and on-off ratio values of and subthreshold swings of 65 mV/dec predicted by numerical modeling. The AMOSFET was experimentally demonstrated using silicon nanowires (SiNW) to take advantage of their ultra-thin cross-sectional dimensions.

FESEM image of AMOSFET produced using a silicon nanowire (SiNW)
FESEM image of AMOSFET produced using a silicon nanowire (SiNW)

 

top
© 2008 Dr. Stephen J. Fonash