Current Research
The ensuing energy crisis presents the scientific community with challenges in the development and optimization of clean energy alternatives. As the geological energy supply, in its many forms, continues to diminish, there is an essential demand for technologies that rely on the harvesting of energy from sources of high abundance, to be swiftly incorporated into main-stream use. Adding to the problem, anthropogenic interference with the climate system can only be halted through the stabilization of greenhouse-gas concentrations, resulting in a call-to-action of with unprecedented urgency (often compared to that of the Manhattan Project).
On the light-to-electricity front, crystalline silicon photovoltaic (PV) cells offer excellent efficiency (40-50%), but suffer from degradation effects over time and are still formidable in cost. There has been a recent influx of photovoltaic (PV) devices utilizing nanoscale sized semiconducting crystals (quantum dots) [Graetzel et al., 1991; Kamat et al., 2008; Aydil, et al., 2007], which are robust against degradation and cost significantly less, although their efficiencies are lower at the moment.
Fig. 1. Emerging technologies in alternative energy. All involve charge transfer at the fundamental level.
Fundamental to all PV devices is interfacial charge transfer. We seek to provide insights to the improvement and development of PV applications through investigation of the fundamental mechanisms associated with interfacial charge transfer. Our technique, ultrafast electron diffraction (UED), is a pump-probe method where femtosecond laser excitation serves as the pump and electron diffraction as the probe. This provides structural information on an ultrafast timescale. Additionally, because our probe is charged, it is sensitive to photofields in the probe volume. The result is a collective, nonhomogeneous shift in the diffraction maxima, or 'Coulomb refraction' of the diffracted beam (Fig. 2). We can effectively separate peak shifts arising from photofields with those associated with thermal expansion, and measure the photoinduced surface potential, or photovoltage [Murdick et al., 2008]. Thus, UED allows for the direct determination of the coupling of charge transfer to atomic motion - a question of great interest [Petek et al., 2007].
Fig. 2. Coulomb refraction. The laser induced field (E) at the crystal surface alters
the electon trajectory (grey - no field; red - photofield present).
Education
Ph.D. Physics Michigan State University 8 / 2009 (tentative)
M.S. Physics Oakland University 2004
B.S. Physics Oakland University 2002
Publications
(1) Ryan A. Murdick and Bradley J. Roth
Magnetoencephalogram Artifacts Caused by Electroencephalogram Electrodes
Medical and Biological Engineering and Computing 41 203 (2003) PDF (543 kB)
(2) Ryan A. Murdick and Bradley J. Roth
A Comparative Model of Two Mechanisms from which a Magnetic Field Arises in the Heart
Journal of Applied Physics 95 5116 (2004) PDF (160 kB)
(3) Bradley J. Roth, Salil G. Patel, and Ryan A. Murdick
The Effect of the Cut Surface During Electrical Stimulation of a Cardiac Wedge Preparation
IEEE Transactions on Biomedical Engineering 53 1187 (2006) PDF (942 kB)
(4) Chong-Yu Ruan, Yoshie Murooka, Ramani K. Raman, and Ryan A. Murdick
Dynamics of Size-Selected Gold Nanoparticles Studied by Ultrafast Electron Nanocrystallography
Nano Letters 7(5) 1290 (2007) PDF (616 kB)
(5) Ryan A. Murdick, Ramani K. Raman, Yoshie Murooka, and Chong-Yu Ruan
Photovoltage Dynamics of the Hydroxylated Si(111) Surface Investigated by Ultrafast Electron Diffraction
Physical Review B 77 245329 (2008) PDF (432 kB)
Poster Presentations
(1) Direct determination of transient heating in a nanoconfined environment by ultrafast electron diffraction
American Vacuum Society, Michigan Chapter of the AVS
34th Annual Spring Symposium - Ann Arbor, Michigan (2007) PDF (3.6 MB)
(2) Photovoltage dynamics of the Si/SiO2 surface investigated by ultrafast electron diffraction
Center for Nanomaterials Design and Assembly
Summer Conference on Complex and Nanostructured Materials for Energy Applications - East Lansing, Michigan (2008)
PDF (531 kB)
The ensuing energy crisis presents the scientific community with challenges in the development and optimization of clean energy alternatives. As the geological energy supply, in its many forms, continues to diminish, there is an essential demand for technologies that rely on the harvesting of energy from sources of high abundance, to be swiftly incorporated into main-stream use. Adding to the problem, anthropogenic interference with the climate system can only be halted through the stabilization of greenhouse-gas concentrations, resulting in a call-to-action of with unprecedented urgency (often compared to that of the Manhattan Project).
On the light-to-electricity front, crystalline silicon photovoltaic (PV) cells offer excellent efficiency (40-50%), but suffer from degradation effects over time and are still formidable in cost. There has been a recent influx of photovoltaic (PV) devices utilizing nanoscale sized semiconducting crystals (quantum dots) [Graetzel et al., 1991; Kamat et al., 2008; Aydil, et al., 2007], which are robust against degradation and cost significantly less, although their efficiencies are lower at the moment.
Fig. 1. Emerging technologies in alternative energy. All involve charge transfer at the fundamental level.
Fundamental to all PV devices is interfacial charge transfer. We seek to provide insights to the improvement and development of PV applications through investigation of the fundamental mechanisms associated with interfacial charge transfer. Our technique, ultrafast electron diffraction (UED), is a pump-probe method where femtosecond laser excitation serves as the pump and electron diffraction as the probe. This provides structural information on an ultrafast timescale. Additionally, because our probe is charged, it is sensitive to photofields in the probe volume. The result is a collective, nonhomogeneous shift in the diffraction maxima, or 'Coulomb refraction' of the diffracted beam (Fig. 2). We can effectively separate peak shifts arising from photofields with those associated with thermal expansion, and measure the photoinduced surface potential, or photovoltage [Murdick et al., 2008]. Thus, UED allows for the direct determination of the coupling of charge transfer to atomic motion - a question of great interest [Petek et al., 2007].
Fig. 2. Coulomb refraction. The laser induced field (E) at the crystal surface alters
the electon trajectory (grey - no field; red - photofield present).
Education
Ph.D. Physics Michigan State University 8 / 2009 (tentative)
M.S. Physics Oakland University 2004
B.S. Physics Oakland University 2002
Publications
(1) Ryan A. Murdick and Bradley J. Roth
Magnetoencephalogram Artifacts Caused by Electroencephalogram Electrodes
Medical and Biological Engineering and Computing 41 203 (2003) PDF (543 kB)
(2) Ryan A. Murdick and Bradley J. Roth
A Comparative Model of Two Mechanisms from which a Magnetic Field Arises in the Heart
Journal of Applied Physics 95 5116 (2004) PDF (160 kB)
(3) Bradley J. Roth, Salil G. Patel, and Ryan A. Murdick
The Effect of the Cut Surface During Electrical Stimulation of a Cardiac Wedge Preparation
IEEE Transactions on Biomedical Engineering 53 1187 (2006) PDF (942 kB)
(4) Chong-Yu Ruan, Yoshie Murooka, Ramani K. Raman, and Ryan A. Murdick
Dynamics of Size-Selected Gold Nanoparticles Studied by Ultrafast Electron Nanocrystallography
Nano Letters 7(5) 1290 (2007) PDF (616 kB)
(5) Ryan A. Murdick, Ramani K. Raman, Yoshie Murooka, and Chong-Yu Ruan
Photovoltage Dynamics of the Hydroxylated Si(111) Surface Investigated by Ultrafast Electron Diffraction
Physical Review B 77 245329 (2008) PDF (432 kB)
Poster Presentations
(1) Direct determination of transient heating in a nanoconfined environment by ultrafast electron diffraction
American Vacuum Society, Michigan Chapter of the AVS
34th Annual Spring Symposium - Ann Arbor, Michigan (2007) PDF (3.6 MB)
(2) Photovoltage dynamics of the Si/SiO2 surface investigated by ultrafast electron diffraction
Center for Nanomaterials Design and Assembly
Summer Conference on Complex and Nanostructured Materials for Energy Applications - East Lansing, Michigan (2008)
PDF (531 kB)