You are all invited to attend Nathan's PhD defense.

Date: Monday, November 23, 2009
Time: 10:00 am
Location: PHYS 401

TITLE:
Application of satellite laser altimetry data to studies of sea ice properties and processes

ABSTRACT:
Sea ice plays an important role in the global climate system by impacting the energy balance of the Earth as well as affecting the oceanic and atmospheric circulations. Recently, large changes have been observed in the Earth's areal coverage of sea ice. However, little is currently known about sea ice thickness particularly at the scales needed for climate research. Spaceborne remote sensing provides the necessary global scale of coverage, but the retrieval of sea ice thickness from space has not been possible until recently with the launch of satellite altimeters of high accuracy and precision. The Ice, Cloud, and land Elevation Satellite (ICESat) is one such laser altimeter with the potential to retrieve sea ice freeboard, which, when combined with snow depth retrievals and the assumption of hydrostatic balance allows for the determination of sea ice thickness. The goal of this study is to use data from ICESat to provide sea ice thickness values at the global scale and high spatial resolution needed for climate studies. The work presented in this thesis includes the validation and improvement of ICESat data products, development and validation of sea ice freeboard retrieval algorithms using the ICESat data products, and the development of a method to combine ICESat freeboard retrievals with a snow depth data set to determine sea ice thickness at the 70 m spatial resolution of ICESat. The ICESat data set is used to study sea ice thickness, heat exchange, and ice production in the Arctic Ocean for the 2003-2008 time period. Despite the thinning of the Arctic sea ice cover over the 2003-2008 time period, mean ice growth rates for consecutive fall and winter measurement periods remained relatively constant. An increased ice growth rate which may be expected from a thinner ice cover appeared to be balanced by warmer temperatures. An increased ocean-atmosphere heat flux is also observed due to the thinning of the sea ice cover.

Nestor successfully defended his masters thesis on November 13, 2009

TITLE:
Broad band terahertz time domain spectroscopy on polymers and organic electro-optic polymers

ABSTRACT:
Several polymers and two organic polymer composites were studied using terahertz time domain spectroscopy and analyzed using Duvillaret’s method and a dynamic range analysis to determine their credible bandwidth. Terahertz time domain spectroscopy is a technique that allows us to determine the real index of refraction and the absorption of nonconductive materials in the terahertz band. These polymers are used as hosts to build organic composites for terahertz generation through optical rectification and detection via electro-optic (EO) sampling. Knowledge of their optical parameters is important when considering them as hosts for emitters and detectors. Also, the knowledge of these parameters over a wide bandwidth is important in the determination of the degree of phase matching that these materials can have, for a given center wavelength of an optical pump pulse. Broad bandwidth and a clear spectrum were achieved with an air-plasma emitter and an organic EO polymer sensor. In this thesis a bandwidth that goes from 0.7 to 9 THz for the real index of refraction and for the absorption coefficient for the majority of the polymers, is reported.

Hui successfully defended his PhD proposal on September 3, 2009

TITLE:
The high-order quantum coherence of thermal light

ABSTRACT:
Fifty years ago, Hanbury Brown and Twiss (HBT) discovered a nontrivial intensity‐intensity correlation that the thermal light has a twice chance of being measured by two individual photo‐detectors within its coherence volume. This HBT effect was finally interpreted as intensity fluctuation. However, with careful theoretical and experimental studies, we found that intensity fluctuation faces difficulty. Recently, our theoretical and experimental works have provided some clear evidences. Moreover, we propose a serial of further works, in order to explicitly demonstrate that the HBT effect has to be described quantum mechanically as two‐photon interference.

John successfully defended his masters thesis on August 25, 2009

TITLE:
Atomic Layer Deposition of TiO₂ on Si and GaAs Substrates Using TDMATi and H₂O Precursors

ABSTRACT:
Atomic Layer Deposition (ALD) has emerged as an effective method for depositing high-quality, conformal thin films with thickness control on the monolayer level. With a homemade hot-wall, flowtube ALD reactor, TiO₂ films were deposited on Si and GaAs substrates using TDMATi and H₂O precursors. Spectroscopic ellipsometry (SE) measurements show an optimal growth rate at a furnace temperature of 200°C. SE was also used to measure the index of refraction of the films. XPS analysis indicates that the films have very little bulk contamination and are slightly over-oxidized. FTIR and XRD were used to examine film crystallization. RBS measurements of the coverage of Ti atoms were conducted over a comprehensive range of film thicknesses. AFM produced topographical images of the film surfaces that indicate RMS values of 3-4% of the film thickness.

Interfacial oxide layers are an undesired consequence of many metal-oxide/semiconductor stacks. Analysis of the films deposited on GaAs substrates focused on the interfacial native oxide layer. Films that were grown on top of a 25Å native oxide layer consumed the oxide during deposition almost completely. This “self-cleaning” effect has been attributed to methylamino ligands of the TDMATi precursor molecules.

Ross successfully defended his masters thesis on July 29, 2009.

TITLE:
Forcing Mechanisms For Heavy Precipitation in the Extratropical Transition of Atlantic Hurricanes

ABSTRACT:
Freshwater flooding is the number one inland killer associated with hurricanes that make landfall in the Mid-Atlantic region. Although great improvements in hurricane track forecasting have been made over the past decade, forecasting hurricane intensity change and rainfall has remained problematic. This challenge becomes even more difficult after the storm makes landfall. Over land, storms typically weaken; however, strong nonlinear interactions with mid-latitude systems or forcing from terrain can reintensify the storm or trigger extreme precipitation events. The goal of the work presented here is to better understand the physical processes that lead to heavy precipitation and storm reintensification during the extratropical transition of hurricanes in the Mid-Atlantic region. We use the North American Regional Reanalysis to analyze in detail two landfalling storms: Hurricane Gaston (2004) and Hurricane Ernesto (2006). Both storms presented forecast challenges and both resulted in heavy precipitation, although through different mechanisms. Gaston was shown to create its own baroclinic zone, which led to heavy rainfall and latent heat release which allowed the storm to briefly rejuvenate over land. Ernesto interacted strongly with an upper level trough and jet, which created a secondary circulation that fueled the storm with moisture from the Atlantic. A potential vorticity analysis shows evidence for a case of stolen identity and possible stratosphere-troposphere exchange (STE). Diabatic forcing in the mesoscale proved to be most important in the transition of Gaston, whereas synoptic scale interactions were crucial to the evolution of Ernesto, which also occluded very quickly. The various spatial scales and rapid transitions of both these storms provide insight into the forecasting challenges during these transition events.

Shelly successfully defended her masters thesis on July 20, 2009.

TITLE:
A study of Surface Plasmon-Coupled Emission from Rhodamine 6G using picosecond pulses

ABSTRACT:
Fluorescence measurements are used in life sciences to provide important information
about biomolecules (fluorophores) such as structure, mobility, and conformational
changes by detecting the target molecules on surfaces. Currently, fluorescence
measurements are performed using free-space (FS) detection, which are mostly isotropic,
resulting in detection of approximately 1% of the total emission. The emission process
may be limited by the background fluorescence due to its isotropic nature and,
photochemical destruction of the fluorophores.

Surface Plasmon-Coupled Emission (SPCE) is a fluorescence technique that has been
recently introduced that increases the fluorescence yield. SPCE is based on the
interaction of excited-state fluorophores with a nearby metal surface. The fluorophores
above the metal surface can couple with the plasmon resonances in the metal, resulting in
directional and wavelength-resolved emission. The coupled emission is characterized by
a dependence of the emission wavelength on the emission angle. In addition, the
emission is horizontally (p) polarized. An advantage of the SPCE over FS signal is the
reduction of the background fluorescence signal, since only fluorophores close to the
metal surface will couple to the surface plasmons.

Picosecond pulses were used to study the SPCE properties of Rhodamine 6G fluorophore
on a thin silver film. It is expected that using pulsed laser sources can greatly enhance
the SPCE signal over the FS signal. The SPCE signal is 3 times higher that the isotropic
FS signal. Thus, SPCE technique under pulsed excitation promises to be an effective tool
for fluorescence measurements in investigating the optical properties of biomolecules.

Chris successfully defended his thesis proposal on June 12, 2009.

TITLE:
A Remote Sensing Study of Boundary Layer Venting during Dynamic Events with the Atmospheric Emitted Radiance Interferometer (AERI)

ABSTRACT:
The study of atmospheric processes in the planetary boundary layer (PBL) is a very complex and interesting field. By definition, the PBL is the region of the atmosphere with turbulent motions resulting from the no-slip boundary condition with the surface, and its depth can range from 30 meters in conditions of large static stability to up to 3 kilometers in highly convective regimes. This project will quantify mixing of trace gases including CO, O₃, and H₂O into and out of the boundary layer. Our focus will be on days when either Horizontal Convective Rolls (HCR) or Low Level Jets (LLJ) occur in the boundary layer. New remote sensing techniques to retrieve information about the trace gases will be further developed using the Atmospheric Emitted Radiance Interferometer (AERI). Specifically, we will update the current CO retrieval algorithm which retrieves one mixing ratio value for the entire troposphere. The improvements will be to obtain values for CO in the boundary layer and in the free troposphere. CO’s 1-2 month lifetime makes it an excellent passive tracer of atmospheric motions; thus, monitoring it will quantify mixing from the boundary layer to the free troposphere. To validate the CO retrieval, we will utilize the 3+ years (2006-2009) of aircraft CO profiles obtained at the United States Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program Southern Great Plains (SGP) site near Lamont Oklahoma. A comparison of work already done on the new retrieval compared to the old retrieval will be shown. Also, a presentation of case study days of LLJ and HCR will highlight the need to improve the retrieval.

Andy successfully defended his masters thesis on June 11, 2009

TITLE:
Neural Networks and Atmospheric Scattering Calculations

ABSTRACT:
For the majority of the particles in the atmosphere, calculations of scattering energy loss are increasingly accurate in proportion to the computing time afforded them. Accurate radiative transfer calculations, even with the most efficient numerical methods, are computationally expensive. This becomes a serious problem for multi-decadal climate simulations for which an accurate representation of the radiative impact of atmospheric constituents is crucial. This thesis presents one method for reducing the computational expense radiative transfer calculations of aerosol scattering properties, which are used in chemical models. The goal of this research is to develop a fast scattering code using a neural network that is trained on input and output data derived from an accurate T-Matrix scattering algorithm. The input space to the neural net consists of scattering parameters that describe the atmospheric scattering conditions such as wavelength of incoming light, effective particle radius, and index of refraction. The output space consists of the coefficients of a Legendre polynomial expansion of the phase function. The neural net finds the nonlinear mapping between the input and output spaces for a training set and can subsequently be used to generate the phase function for arbitrary wavelength, particle radius and index of refraction. In this research, a neural network applicable to both Lorenz and Mie scattering is developed and tested for both accuracy and speed. The accuracy of the neural net is found to be excellent, with errors well below 10%, and runtime testing shows that the neural net is approximately 5 times faster than a lookup table.

Congratulations to (L to R) Drs. Jianning Zeng, Antonia Gambacorta, Timothy Bole and (not pictured) Mengsteab Weldegaber who graduated on May 20th, 2009. Their thesis topics ranged from the effects of electromigration on structures at the nanoscale, to feedback processes and boundary-layer phenomena in the atmosphere, to the study of emission on the scale of thousands of light-years in nearby galaxies.

Congratulations also to Eric Hughes, who was awarded an M.S. at the ceremony.

The following students have earned the following departmental awards:
    Joseph Dulny III - Outstanding Graduating Senior in Physics
    Sheng Liu - Joseph F. Mulligan Memorial Lectureship
    Aaron B. Pearlman - Donald N. Langenberg Undergraduate Research Award.
The awardees were recognized at the 4th Annual CNMS Student Recognition Day on May 8, 2009.

The following Physics students have been inducted into Sigma Pi Sigma, the National Physics Honor Society: John Carrico, Joseph Dulney III,Derek Fertig, Rory Holderness, Joseph Jancasz, and Shauna Marquess.

The UMBC chapter of Sigma Pi Sigma was established in 1980. It exists to honor outstanding scholarship in Physics; to encourage interest in Physics; to promote an attitude of service of its members towards their fellow students, colleagues and the public; and to provide a fellowship of persons who have excelled in Physics. Undergraduate candidates shall have attained at least a 3.25 grade point average on 4.0 system for Physics courses and at least a 3.0 grade point average for cumulative course grades in all courses. The inductees were recognized at the 4th Annual CNMS Student Recognition Day on May 8, 2009.

Eric successfully defended his masters thesis on May 1, 2009.

TITLE:
Using Horizontal Transport Characteristics to Infer an Emission Height Timeseries of Volcanic SO2

ABSTRACT:
Characterizing the emission height of sulfur dioxide (SO2) from volcanic eruptions yields information about the strength of volcanic activity, and is crucial for the assessment of possible climate impacts and for validation of satellite retrievals of SO2. Sensors such as the Ozone Monitoring Instrument (OMI) on the polar-orbiting Aura satellite provides accurate maps of the spatial distribution of volcanic SO2, but provide limited information on its vertical distribution. The goal of the work presented here is to explore the possibility of using a trajectory model to reconstruct both the temporal activity and injection altitude of a volcanic source from OMI column measurements of SO2 observed far from the volcano. Statistical analyses based on the distance of closest approach to the volcano of back trajectories initialized at the measurements are compared to an optimal reconstruction based on forward trajectories. The inferred altitude of the SO2 cloud is compared to the altitude of derived sulfate aerosols detected in aerosol backscatter vertical profiles form the CALIOP instrument aboard CALIPSO. The trajectory modeling analyses also provides details about the horizontal transport that are not clearly apparent from satellite measurements alone; revealing an interesting transport mechanism occurring in the subtropical jet stream.

Mengs successfully defended his dissertation on April 28, 2009.

TITLE:
Investigation of Stable and Unstable Boundary Layer Phenomena Using Observations and a Numerical Weather Prediction Model

ABSTRACT:
Despite significant advances in the simulation of synoptic scale weather events, current numerical weather prediction models show poor skill in their capability to accurately simulate sub-grid scale features, such as cloud-precipitation processes and planetary boundary layer (PBL) evolution, because too many semi-empirical parameterizations are involved. The goal of the work presented here is to evaluate the next-generation mesoscale Weather Research and Forecasting (WRF) model in simulating mesoscale weather phenomena under different PBL stratifications. The work presented in this thesis investigates the performance of the state-of-the-art mesoscale WRF model in simulating the structure and development of a daytime convective boundary layer phenomenon, (the dryline over the Southern Great Plains), and a nocturnal stable boundary layer phenomenon, (the Low-Level-Jet (LLJ) over the Mid-Atlantic region). The dryline and LLJ are two examples of boundary layer phenomena that occur under very different conditions and thus together they provide a good test of the PBL dynamics in the model. Extensive, high spatial and temporal resolution data collected during these case studies is used to evaluate the numerical results. For the unstable boundary layer, a detailed observational analysis of a non-convective dryline investigates an incorrect forecast. For the stable boundary layer, the accuracy of the timing and spatial characteristics of the LLJ for different PBL parameterizations is investigated and discussed in terms of the LLJ forcing mechanisms.

Jianning successfully defended her dissertation on April 22, 2009.

TITLE:
Extended Emission Surrounding Nearby Seyfert Galaxies

ABSTRACT:
We present the results from a search for and survey of any extended X- ray emission surrounding a class of Active Galactic Nuclei (AGN) known as “Seyfert-2” galaxies using data collected using Chandra X-ray observatory (CXO). The mirrors of this work was therefore to determine whether CXO observations help constrain current theories for AGN by probing the smallest spatial scales (> 100 pc) possible. Our sample consists of all the CXO observations of Seyfert-2 galaxies performed using the ACIS-S3 detector during the first 8 years of operation (28 objects). We find extended X-ray emission in all our Seyfert-2 sample of galaxies with a range of luminosities (10³⁸ ∼ 10⁴¹ erg s⁻¹ ). For 18 objects, the morphology is predominately bi-conical centered on the nucleus and typically extending out to a few kpc. Only a single cone is seen in 8 of the remaining ob jects, which may be indicative of intrinsically anisotropic emission. Where data is available, the X-ray cones do appear to occupy the same solid angle as the extended [OIII] emission line gas previously detected in these objects.

Our data suggest that the luminosity of the extended emission is typically a few percent of that of the nuclear source. Our findings are therefore broadly consist with current theories of AGN, but the low signal to noise for many of the observations combined with obscuration and possible contamination prevent any definitive tests of “Unified Schemes” being performed. Unfortunately this is likely to be the case for the foreseeable future.

Tim successfully defended his dissertation on February 5, 2009.

TITLE:
A Study of the Effects of Electromigration on Structures at the Nanoscale

ABSTRACT:
This thesis summarizes a study of the effects of electromigration, or diffusion influenced by applied electric fields, on nanoscale metallic structures. We have studied the impact of electromigration on two types of nanoscale systems, and as such the thesis naturally divides into two portions.

In the first portion, consisting of Chapters 2-4, we investigate the effects of electromigration on fluctuating step edges. When there is no electromigration present, a step undergoing motion by diffusion of atoms along its edge demonstrates power-law scaling in temporal correlation functions. This is verified by approximating the step as a continuum and using Langevin analysis; this approach is then extended to include electromigration forces. Under electromigration conditions, specifically for electromigration forces directed into or away from the step, we find theoretical deviations from the power-law scaling in the correlation function. We demonstrate this in two ways: through Monte Carlo simulation of step edges under electromigration conditions and through analysis of experimental measurements of current-stressed steps at the surface of silver films. We found good qualitative agreement with the theoretical expectations in both simulation and experiment, as well as good quantitative agreement in the results of the simulations.

The second portion of the thesis, consisting of Chapters 5 and 6, details an investigation of the effects of electromigration on the Rayleigh-Plateau instability in solid nanowires. We begin by deriving an equation of motion for a continuous cylinder and including an electromigration force along the symmetry axis of the cylinder. This is equivalent to a model of a nanowire carrying current, where the electromigration force is modeled as a constant.

We find power-law scaling in the pinching process with and without electromigration, though the effects of electromigration are to extend the life of the nanowire relative to those without electromigration. This is confirmed by conducting kinetic Monte Carlo simulations of aluminum nanowires under electromigration conditions. We find good agreement with the continuum model for the exponent in the power-law scaling as well as the effect of electromigration on the time at which pinching occurs. We also find evidence of self-similar behavior in the continuum model as well as in the simulations.

Junlin successfully defended her thesis proposal on January 28, 2009.

TITLE:
Entangled Photon Holes

ABSTRACT:
The concept of quantum entanglement has been identified as a key practical resource for quantum information processing. Over the past 30 years, experiments on entanglement have mostly involved studying correlations of the physical properties (such as polarization or momentum) of two distant photons. Recently, a new form of entanglement called “entangled photon holes” has been discovered. Roughly speaking, the entanglement is due to the absence of the photon pair rather than some physical property of the pairs. Although a recent experiment has provided some initial evidence of the existence of photon-hole states, the entangled nature of the state has not yet been experimentally observed. Here we propose an experimental test of Bell’s inequalities using photon-hole states. If successful, the results of this experiment would explicitly demonstrate the entangled properties of photon-hole states, which would represent a major advance in quantum optics and quantum information science.

Dr. L. Larrabee Strow, Research Professor, is a member of the science team for the satellite IBUKI launched from Japan on January 23rd. IBUKI (also known as the Greenhouse Gases Observing Satellite, GOSAT) is a Japanese mission designed to map the abundance of greenhouse gases in the atmosphere. During its five-year mission it will identify and monitor sources of CO₂ in support compliance with international treaties and agreements such as Kyoto. So far, the number of ground-based CO₂ observation points has been limited, and they have been distributed unequally throughout the world. IBUKI will enable the precise monitoring of the density of carbon dioxide by combining global observation data sent from space with data obtained on land, and with simulations. “Synergy between IBUKI/GOSAT and my recent work on global CO₂ trends using NASA's AIRS satellite instrument”, said Dr. Strow, “should improve both instruments unique view of global greenhouse gases. The very international nature of the IBUKI/GOSAT Science Team has already provided me with new collaborations in this politically relevant field of science." More information on IBUKI can be found at http://www.jaxa.jp/projects/sat/gosat/index_e.html.

Antonia successfully defended her dissertation on November 20, 2008.

TITLE:
Temperature Change And Water Vapor Feedback In The Atmosphere. A Comprehensive Assessment Using The Atmospheric Infrared Sounder Instrument On NASA Aqua Satellite

ABSTRACT:
Global surface temperature has increased ~0.2 degree Celsius per decade in the past 30 years. Observational data recorded from 1850 to 2007 indicate that the warmest 11 years have occurred between 1995 and 2006. The 2007 report of the Intergovernmental Panel on Climate Change concluded that there is a "very high confidence - 95% confidence - that the global average net effect of human activities since 1750 has been one of warming" and that "most of the observed increase in global average temperatures since the mid-20th century is very likely - 90% confidence - due to the observed increase in anthropogenic greenhouse gas concentrations".

Processes in the climate system that can either amplify or dampen the climate response to an external forcing such as an increase in anthropogenic greenhouse gas concentrations, and directly or indirectly affect the Earth's radiation budget at the top of the atmosphere are normally referred to as "climate feedbacks". Among all trace gases, water vapor is the most sensitive to temperature variations. In fact, water vapor absorbs strongly in the vibration-rotation and pure rotation bands at wavelengths in which a large portion of infrared emission occurs at temperature characteristic of the Earth's surface and atmosphere.

In the present study, we exploit the uniform spatial coverage and high vertical resolution of the Atmospheric InfraRed Sounder database of temperature and water vapor profiles to perform a detailed investigation of the covariance between temperature and water vapor. Differently from the previous studies, who only analyzed the overall tropically averaged water vapor and temperature relationship, we make a more comprehensive analysis by investigating this relationship on a local basis. By doing so, we explore the horizontal gradient of this relationship in the tropics, in order to better confine its range of variability and the interplay of the physical processes underneath it. An overall conclusion on the sign and magnitude of the tropical sensitivity to surface temperature variations by mean of water vapor feedback will be assessed.

Jeff successfully defended his dissertation on November 19, 2008.

TITLE:
Displacement Damage-Induced Electrical and Structural Effects in Gallium Arsenide Solar Cells Following Ion Irradiation

ABSTRACT:
For nearly two decades, deviations between experimental data and the nonionizing energy loss (NIEL) have been observed for GaAs devices. In particular, previous data has suggested that electrical parameters associated with GaAs solar cells can follow different energy dependences with NIEL but only at the higher proton energies. In this paper, displacement damage-induced electrical and structural effects in GaAs solar cells were monitored before and after irradiation with various ions. The radiation-induced defects responsible for causing electrical changes were characterized using illuminated current-voltage, deep level transient spectroscopy (DLTS), and electron beam induced current (EBIC) while the structural changes were monitored using transmission electron microscopy (TEM). The EBIC images showed the existence of radiation-induced active recombination volumes or defect clusters after irradiation with high energy protons (E ≥ 10 MeV) and 22 MeV silicon ions, which were not produced by lower energy protons. The TEM images revealed strain related defects that correspond to the same irradiation conditions for which the defect clusters were observed, and therefore, the defects in the TEM images are associated with those observed in the EBIC images. These defects were not observed prior to irradiation so the lattice strain in the material is definitely associated with irradiation-induced lattice defects. HRTEM imaging has shown that the disordered regions are not amorphous but probably most likely a cluster of vacancies and a surrounding region rich in interstitials, which is produced when a large number of neighboring atoms are displaced in collision cascades known as the displacement spike. The formation of the U-band defect as determined by DLTS seems to evolve under the same irradiation conditions as the defects in the images. This very broad U-band peak is consistent with what would be expected from defect clusters. From analyses of the recoil spectra, high energy recoils appear to be responsible for the formation of these disordered regions and these regions are independent of the total displacement damage energy deposited. This study has shown that NIEL scaling is only violated for incident ion energies when the defect clusters are observed.

Andrew successfully defended his dissertation on November 18, 2008.

TITLE:
Step Dynamics and the Morphological Evolution of Nanostructures

ABSTRACT:
Surface diffusion of atoms plays a significant role in the evolution of the shape of a material in the nanoscale regime because it becomes the dominant mechanism for mass transport as the surface area to volume ratio increases. In this dissertation, I present a theoretical study of the shape evolution of a particular nanostructure: the nanowire. At non-zero temperatures, atomic steps are always present on the surface of a nanostructure and their growth and motion causes a change of shape and can cause the wire to break.

I have studied the morphological evolution of nanowires before and after a break develops, the resulting segments of a broken nanowire whose tips are nanoneedles. My approach is to develop and compare a step motion model and atomistic simulations and test them against available experimental data and classical continuum theory. My approach also allowed me to derive the scaling relations and exponents describing the morphological evolution of nanowires and study the microscopic nature of the instability that causes them to break.

Hao successfully defended his thesis proposal on November 14, 2008.

TITLE:
Theoretical Comparison of Optical Approaches to Quantum Logic Gates

ABSTRACT:
Quantum computing has been of intense interest over the last 10 years because of its promising ability to do high-speed factoring and its potential for the efficient simulation of quantum dynamics. It could be implemented in many different ways using optical techniques. A better understanding of the advantages and disadvantages of these approaches would allow the experimental groups working in this area to optimize their choice of experiment and to concentrate on the approaches that are most likely to succeed. We propose to systematically analyze a number of promising optical implementations for quantum logic gates using standard density matrix theory. Basic issues of theoretical comparison of optical approaches to quantum logic gate will be presented here.

Mike successfully defended his masters thesis on October 30, 2008.

TITLE:
Improved Technologies for a Single Photon Source

ABSTRACT:
One of the key requirements for an optical approach to quantum computing is a reliable source of single photons. The efforts of this research have been directed towards improving both the heralding efficiency and heralding rates of a high performance fiber-coupled single photon source based on an ultrafast pulsed beam-like Type-II parametric down conversion (PDC) source. Entangled photons generated from PDC are inherently broadband (many frequencies) and exit the nonlinear crystal at varying angles (different directions). This makes coupling the photons into single-mode fibers, a desirable feature for quantum computing, difficult. In response to these difficulties we have explored applying multi-layered thin film broadband anti-reflection coatings onto the ends of single-mode fibers using the technique of RF Planar Magnetron Sputtering in an effort to increase the coupling efficiency of the beam-like down converted photons. In addition, we have explored theoretically the broadband nature of novel phase matching geometries to increase heralding rates and minimize photon losses. With the ability to tailor coupling fibers to various down conversion sources we hope to increase both the heralding efficiency and heralding rate to levels needed for a broad range of future experiments.

Vincenzo successfully defended his thesis proposal on October 3, 2008.

TITLE:
Gauss Sums Factorization with liquid crystals and optical interference.

ABSTRACT:
The factorization of a large number N is a quite complicated problem, that has a great impact on the computing field and, in particular, in public-key encryption. A more recent approach to factorization, proposed by Schleich, exploits the periodic properties of the Gauss sums. We propose a different implementation of Gauss sums factorization, using liquid crystals and optical interferometry. This scheme allows us to find the factors of any large number N in only one run, exploiting the spectrum of the incoming light. This apparatus is also able, in principle, to reproduce generalized exponential sums of order p. This allows, at the same time, a reduction of the number of resources to the order of 4pp N and to get a better suppression of the so called ghost factors. A future development of this work will consist of a quantum approach to factorization, exploiting the periodicity of the Gauss sums with the use of intanglement. In fact the quantum entanglement has a key role in reducing the number of resources to an order polynomial in logN, which is not achievable classically.

Congratulations go to Physics graduate students Steven Buczkowski and Kimberly Wall for winning the 2007-08 Outstanding Graduate Teaching Assistant of the Year Award! This award acknowledges and recognizes outstanding graduate teaching assistants for their contributions to the teaching mission of the Physics department at UMBC.

Steve and Kim were presented with a plaque and a check for $500 at the Physics Colloquium on September 3, 2008.

Third year Physics graduate student Steven Buczkowski has been selected to receive a NASA Earth and Space Sciences Fellowship. Steven's proposal entitled "Rainbow and Cloud Side Remote Sensing: A Novel Look at Cloud-Aerosol Interaction and Its Effect on Cloud Evolution" was one of 50 proposals accepted, out of 200 received.

A member of the UMBC Atmospheric Physics PhD program, Steven will work with his advisor, Dr. Vanderlei Martins, to characterize and develop retrieval algorithms for a novel suite of visible and infra-red cameras developed by Dr. Martins and his collaborators here and at NASA Goddard Space Flight Center.

Clouds on Earth require some airborne aerosol in order to form but regional enhancements in aerosol load (e.g. from biomass burning, etc) can have a profound effect on their evolution. These effects can range from shifting precipitation patterns to changes in planetary albedo which could influence global climate. Steven's work with Dr. Martins will seek to better understand the influence of aerosol amount and type on cloud development.

Chris successfully defended his masters thesis on August 27, 2008.

TITLE:
Laser System for the Fabrication of Toroidal Microcavities

ABSTRACT:
Toroidal micro-cavities have been shown to be one of the leading types of cavities for use in strong atom-cavity coupling. This property makes these cavities ideal for a range of applications from cavity quantum electrodynamics studies, to development of single photon sources, and quantum information technologies. The purpose of this project was to setup and test a laser facility for the final step in fabricating toroidal micro-cavities. The facility will later be used for production of these cavities for use in ongoing experiments within the UMBC Quantum Information Group.

Justin successfully defended his dissertation on August 25, 2008.

TITLE:
Initial HfO2 Growth on Si(100) and GaAs(100) Substrates using TEMAH+H2O and TDMAH+H2O ALD Processes

ABSTRACT:
Atomic layer deposition (ALD) is a cyclic growth process that is distinguished by a self-limiting, two-step surface reaction that results in precise growth control and high quality, conformal thin films. Due to the continuous downscaling of MOSFET devices, a large interest has recently developed in the ALD of high-κ dielectric materials as gate oxide layers on Si and III-V substrates. The ALD of HfO2 is an established process; however, there is still controversy over the initial growth mechanisms on differently prepared Si surfaces. This motivated a comparison of the nucleation stage of HfO2 films grown on OH- (Si-OH) and H-terminated (Si-H) Si(100) surfaces. Two different ALD chemistries are investigated, including tetrakis[ethylmethylamino]hafnium (Hf[N(CH3)(C2H5)]4), abbreviated as TEMAH, and tetrakis[dimethylamino]hafnium (Hf[N(CH3)2]4, abbreviated as TDMAH. H2O is used as the oxidizing precursor. Deposition temperatures of 250-275°C result in a linear growth per cycle of 1 Å/cycle. Techniques including Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), and transmission electron microscopy are used to examine the film interface and initial film growth. HfO2 films are also subjected to post-deposition anneals, and the film morphology is examined with X-ray diffraction, Fourier transform infrared spectroscopy and atomic force microscopy.

GaAs MOSFET devices have long proven elusive due to the lack of a stable native oxide. Recent research into high-κ dielectric materials for use in Si-based devices has presented many new options for insulating layers on GaAs. HfO2 growth on GaAs(100) from a TDMAH+H2O ALD process is studied here. Three different GaAs surface treatments are examined, including buffered oxide etch (BOE), NH4OH, and a simple acetone/methanol wash (to retain the native oxide surface). Initial HfO2 growth on these surfaces is characterized with RBS and SE. The interfacial composition is examined with XPS both before and after HfO2 deposition. Also, an interesting native oxide ‘consumption’ mechanism is investigated, which involves the dissolution of the GaAs native oxide during the ALD process. This project presents the first detailed study of HfO2 growth on GaAs with the TDMAH/H2O ALD chemistry, providing XPS, RBS and SE characterization of early film growth.

Jason Simon, a 4th year PhD student, was selected to receive the Northrop Grumman Graduate Fellowship in Quantum Optics in August.

The Northrop Grumman Fellowship provides an outstanding opportunity for a talented UMBC Physics student to work with a global leader in defense technology while earning his/her PhD. Fellowship support totals $35,000, which includes an annual stipend, tuition and health care benefits, and some travel for one year.

Dr. Ray Hoff, professor of physics and director of the collaborative NASA-UMBC research centers JCET and GEST, was recently named a Fellow of the American Meteorological Society. Hoff’s expertise on air pollution, climate and the atmosphere has been reflected in a prestigious track record of collaborations with and honors from NASA, the Environmental Protection Agency, Environment Canada, the European Economic Community and other earth science organizations. “I'm pleased and honored to have received a society fellowship at the same time as my colleagues,” said Hoff. “UMBC has clearly reached a point where awards and honors are becoming a larger part of the life of the campus. The story of UMBC as a prestigious place to do cutting-edge research is becoming more obvious to our peers and I hope that recognition spreads statewide.”

Robert C. Reno, Associate Professor and Associate Chair of Physics, has made remarkable contributions to the education of UMBC undergraduate and graduate students. During his 33-year teaching career at UMBC, Reno has taught a total number of 160 courses and developed seven original courses, many serving as the foundation of UMBC’s physics program. He redesigned two undergraduate laboratory courses, incorporating computerized data acquisition. In spring 2007, Reno debuted a new honors course that introduces students to advanced experiments using radioactive materials and x-ray generators. His work in the area of peer instruction was one of the first implementations of group learning on campus and the first in the physics department. A recipient of numerous awards, Reno has received two UMBC DRIF/SRIS awards and a U.S. Army Summer Research Fellowship. Reno earned a B.S. in physics from Manhattan College. He also earned his M.A. and Ph.D. in physics from Brandeis University. Dr. Reno was honored at the UMBC Presidential Faculty & Staff Awards Ceremony on April 11, 2007.

UMBC senior physics major Philip Graff will follow the path of science greats Isaac Newton and Stephen Hawking to Cambridge University as the second UMBC student in the past two years to win the Gate Cambridge Scholarship, one of the world’s most selective academic awards.

Graff, who will pursue a Ph.D. in physics, was one of just 45 U.S. winners chosen from more than 600 applicants and 119 finalists. Graff is UMBC’s second consecutive Gates Cambridge Scholar, following alumnus Ian Ralby ‘02, who won in 2007.
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