Department of Physics
http://hdl.handle.net/1957/13831
2015-02-19T21:09:19ZTerahertz induced transparency in single-layer graphene
http://hdl.handle.net/1957/54919
Terahertz induced transparency in single-layer graphene
Paul, Michael J.; Lee, Byounghwak; Wardini, Jenna L.; Thompson, Zachary J.; Stickel, Andrew D.; Mousavian, Ali; Choi, Hyunyong; Minot, Ethan D.; Lee, Yun-Shik
We show that the transmission of a terahertz (THz) pulse through single-layer graphene is strongly
nonlinear. As the peak electric field of the THz pulse exceeds 50 kV/cm, the graphene becomes
increasingly transparent to the THz radiation. When field strength reaches 800 kV/cm, the increased
transparency corresponds to a two-fold decrease in the time-average sheet conductivity of the graphene
(time averaged over the duration of the pulse). Time-resolved measurements reveal that the
leading portion of the pulse creates transparency for the trailing portion, with a 10-fold suppression
in sheet conductivity at the tail of the strongest THz pulse. Comparing the THz-induced transparency
phenomena in different sample geometries shows that substrate-free graphene is the best geometry
for maximizing the nonlinear transparency effect.
This is the publisher’s final pdf. The published article is copyrighted by the American Institute of Physics Publishing and can be found at: http://scitation.aip.org/content/aip/journal/apl;jsessionid=5e5u4415ethj6.x-aip-live-03.
2014-12-01T00:00:00ZApproach to approximating the pair distribution function of inhomogeneous hard-sphere fluids
http://hdl.handle.net/1957/54598
Approach to approximating the pair distribution function of inhomogeneous hard-sphere fluids
Lurie-Gregg, Paho; Schulte, Jeff B.; Roundy, David
We introduce an approximation for the pair distribution function of the inhomogeneous hard sphere fluid. Our
approximation makes use of our recently published averaged pair distribution function at contact, which has
been shown to accurately reproduce the averaged pair distribution function at contact for inhomogeneous density
distributions. This approach achieves greater computational efficiency than previous approaches by enabling the
use of exclusively fixed-kernel convolutions and thus allowing an implementation using fast Fourier transforms.
We compare results for our pair distribution approximation with two previously published works and Monte
Carlo simulation, showing favorable results.
This is the publisher’s final pdf. The published article is copyrighted by the American Physical Society and can be found at: http://journals.aps.org/pre/.
2014-10-21T00:00:00ZThe contact value approximation to the pair distribution function for an inhomogeneous hard sphere fluid
http://hdl.handle.net/1957/54549
The contact value approximation to the pair distribution function for an inhomogeneous hard sphere fluid
Lurie-Gregg, Paho
We construct the contact value approximation (CVA) for the pair distribution function,
g(²)(r₁, r₂), for an inhomogeneous hard sphere fluid. The CVA is an average of two radial
distribution functions, which each take as input the distance between the particles, |r₂ −r₁|,
and the average value of the radial distribution function at contact, gσ(r) at the locations
of each of the particles. In a recently published paper, an accurate function for gσ(r) was
developed, and it is made use of here. We then make a separable approximation to the
radial distribution function, gS(r), which we use to construct the separable contact value
approximation (CVA-S) to the pair distribution function.
We compare the CVA and CVA-S to Monte Carlo simulations that we have developed and
run as well as to two prior approximations to the pair distribution function. This comparison
is done in three main cases: When one particle is near a hard wall; when there is an external
particle the size of a sphere of the fluid; and for various integrals that illustrate typical use-cases
of the pair distribution function. We show reasonable quantitative agreement between
the CVA-S and simulation data, similar to that of the prior approximations. However, due
to its separable nature, the CVA-S can be efficiently used in density functional theory, which
is not the case of the prior approximations.
2014
2014-10-03T00:00:00ZMeasurement and Modeling of Zinc Sulfide Thin Films using Ellipsometry and Reflection Spectroscopy: A Comparison of Optical Characterization Techniques
http://hdl.handle.net/1957/53769
Measurement and Modeling of Zinc Sulfide Thin Films using Ellipsometry and Reflection Spectroscopy: A Comparison of Optical Characterization Techniques
Kratzer, Aaron
Zinc sulfide thin films on silicon wafers were analyzed for layer thickness, refractive index, and absorption using reflection spectroscopy (RS), spectroscopic ellipsometry (SE), and modeling programs. RS and refractive index values from literature were used to model film thickness based on reflection and the SCOUT modeling program was used to analyze the reflectance data and generate model RS data. SE was used to measure film thickness and complex index of refraction and a VASE32 program was used to model the layers of the thin film and generate model SE data. Goals include comparing SE and RS as possible non-destructive analysis tools and developing the most efficient SCOUT interface for analyzing available optical data.
Both RS and SE data analysis have the ability to measure the thickness d and complex refractive index n and κ of ZnS given the complex refractive index of the silicon wafer. The SCOUT optical modeling software generates a graphical user interface and can analyze RS data and can be configured to analyze SE data as well.
2014
2014-06-11T00:00:00Z