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- Title
- SCANNING FABRY-PEROT SPECTROMETER FOR TERAHERTZ AND GIGAHERTZ SPECTROSCOPY USING DIELECTRIC BRAGG MIRRORS.
- Creator
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Cleary, Justin, Peale, Robert, University of Central Florida
- Abstract / Description
-
A scanning Fabry-Perot transmission filter composed of a pair of dielectric mirrors has been demonstrated at millimeter and sub-millimeter wavelengths. The mirrors are formed by alternating quarter-wave optical thicknesses of silicon and air in the usual Bragg configuration. Detailed theoretical considerations are presented for determining the optimum design including factors that affect achievable finesse. Fundamental loss by lattice and free carrier absorption are considered. High...
Show moreA scanning Fabry-Perot transmission filter composed of a pair of dielectric mirrors has been demonstrated at millimeter and sub-millimeter wavelengths. The mirrors are formed by alternating quarter-wave optical thicknesses of silicon and air in the usual Bragg configuration. Detailed theoretical considerations are presented for determining the optimum design including factors that affect achievable finesse. Fundamental loss by lattice and free carrier absorption are considered. High resistivity in the silicon layers was found important for achieving high transmittance and finesse, especially at the longer wavelengths. Also considered are technological factors such as surface roughness, bowing, and misalignment for various proposed manufacturing schemes. Characterization was performed at sub-mm wavelengths using a gas laser together with a Golay cell detector and at millimeter wavelengths using a backward wave oscillator and microwave power meter. A finesse value of 422 for a scanning Fabry-Perot cavity composed of three-period Bragg mirrors was experimentally demonstrated. Finesse values of several thousand are considered to be within reach. This suggests the possibility of a compact terahertz Fabry-Perot spectrometer that can operate in low resonance order to realize high free spectral range while simultaneously achieving a high spectral resolution. Such a device is directly suitable for airborne/satellite and man-portable sensing instrumentation.
Show less - Date Issued
- 2007
- Identifier
- CFE0001563, ucf:47128
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001563
- Title
- NOISE CHARACERIZATION FOR PROPOSED UCF PHYISCAL SCIENCE BUILDING SITES.
- Creator
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Martinez, Jorge, Peale, Robert, University of Central Florida
- Abstract / Description
-
Today's Advance Technology Facilities require low noise levels and increased noise monitoring. Ambient noise can interfere with the accuracy and precision of experiments and manufacturing processes. Therefore preconstruction site surveys are needed to develop strategies for mitigating noise. Vibration and low frequency electromagnetic fields are particularly detrimental for sensitive instruments, and they are also difficult to mitigate. However a large part of these costs can be avoided...
Show moreToday's Advance Technology Facilities require low noise levels and increased noise monitoring. Ambient noise can interfere with the accuracy and precision of experiments and manufacturing processes. Therefore preconstruction site surveys are needed to develop strategies for mitigating noise. Vibration and low frequency electromagnetic fields are particularly detrimental for sensitive instruments, and they are also difficult to mitigate. However a large part of these costs can be avoided or minimized if a quiet building site is selected in the first place. Accelerometers and gauss meters combined with a computer for acquisition and analysis provide a low cost method of evaluating noise levels at proposed building sites. This work examines low frequency vibration and electromagnetic fields at two proposed sites for the planned Physical Science Building at the University of Central Florida.
Show less - Date Issued
- 2006
- Identifier
- CFE0001507, ucf:47156
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001507
- Title
- MONTE CARLO SIMULATION OF HOLE TRANSPORT AND TERAHERTZ AMPLIFICATION IN MULTILAYER DELTA DOPED SEMICONDUCTOR STRUCTURES.
- Creator
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Dolguikh, Maxim, Peale, Robert, University of Central Florida
- Abstract / Description
-
Monte Carlo method for the simulation of hole dynamics in degenerate valence subbands of cubic semiconductors is developed. All possible intra- and inter-subband scattering rates are theoretically calculated for Ge, Si, and GaAs. A far-infrared laser concept based on intersubband transitions of holes in p-type periodically delta-doped semiconductor films is studied using numerical Monte-Carlo simulation of hot hole dynamics. The considered device consists of monocrystalline pure Ge layers...
Show moreMonte Carlo method for the simulation of hole dynamics in degenerate valence subbands of cubic semiconductors is developed. All possible intra- and inter-subband scattering rates are theoretically calculated for Ge, Si, and GaAs. A far-infrared laser concept based on intersubband transitions of holes in p-type periodically delta-doped semiconductor films is studied using numerical Monte-Carlo simulation of hot hole dynamics. The considered device consists of monocrystalline pure Ge layers periodically interleaved with delta-doped layers and operates with vertical or in-plane hole transport in the presence of a perpendicular in-plane magnetic field. Inversion population on intersubband transitions arises due to light hole accumulation in E B fields, as in the bulk p-Ge laser. However, the considered structure achieves spatial separation of hole accumulation regions from the doped layers, which reduces ionized-impurity and carrier-carrier scattering for the majority of light holes. This allows remarkable increase of the gain in comparison with bulk p-Ge lasers. Population inversion and gain sufficient for laser operation are expected up to 77 K. Test structures grown by chemical vapor deposition demonstrate feasibility of producing the device with sufficient active thickness to allow quasioptical electrodynamic cavity solutions. The same device structure is considered in GaAs. The case of Si is much more complicated due to strong anisotropy of the valence band. The primary new result for Si is the first consideration of the anisotropy of optical phonon scattering for hot holes.
Show less - Date Issued
- 2005
- Identifier
- CFE0000863, ucf:46672
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000863
- Title
- GRATING COUPLER FOR SURFACE WAVES BASED ON ELECTRICAL DISPLACEMENT CURRENTS.
- Creator
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Brescia, Jonathan R, Peale, Robert, University of Central Florida
- Abstract / Description
-
Bound electromagnetic surface waves can be excited by free-space waves on a corrugated conduction surface. These electromagnetic surface waves, called surface plasmon polaritons (SPPs), are coupled to a plasma of free charges, which travel together with the wave. We investigated the effect of separating metal corrugations from the smooth metal ground plane with a thin dielectric layer and show that SPPs can be excited via displacement currents. However, the SPP excitation resonances broaden...
Show moreBound electromagnetic surface waves can be excited by free-space waves on a corrugated conduction surface. These electromagnetic surface waves, called surface plasmon polaritons (SPPs), are coupled to a plasma of free charges, which travel together with the wave. We investigated the effect of separating metal corrugations from the smooth metal ground plane with a thin dielectric layer and show that SPPs can be excited via displacement currents. However, the SPP excitation resonances broaden and disappear as the dielectric thickness approaches 1% of the wavelength.
Show less - Date Issued
- 2019
- Identifier
- CFH2000457, ucf:45898
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000457
- Title
- METAL BLACKS AS SCATTERING CENTERS TO INCREASE THE EFFICIENCY OF THIN FILM SOLAR CELLS.
- Creator
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Panjwani, Deep, Peale, Robert, University of Central Florida
- Abstract / Description
-
Metal nano particles are investigated as scattering centers on front surface of thin-film solar cells to improve efficiency. The principle is that scattering, which is enhanced near the plasmon resonance frequency of the particle and depends on particle size, increases the effective optical path length of incident light, leading to more light absorption in active layer of thin film solar cell. The particular types of particles investigated here are known as "metal-black", well known as an IR...
Show moreMetal nano particles are investigated as scattering centers on front surface of thin-film solar cells to improve efficiency. The principle is that scattering, which is enhanced near the plasmon resonance frequency of the particle and depends on particle size, increases the effective optical path length of incident light, leading to more light absorption in active layer of thin film solar cell. The particular types of particles investigated here are known as "metal-black", well known as an IR absorber for bolometric infrared detectors. Gold-black was deposited on commercial thin-film solar cells using a thermal evaporator in a nitrogen ambient at pressures of ~1 Torr. We suggest that the broad range of length scales for gold black particles, as quantified by scanning electron microscopy, gives rise to efficient scattering over a broad range of wavelengths across the solar spectrum. The solar cell efficiency was determined both as a function of wavelength and for a solar spectrum produced by a Xe lamp and appropriate filters. Up to 20% increase in short-circuit photocurrent, and a 7% increase in efficiency at the maximum power point, were observed.
Show less - Date Issued
- 2011
- Identifier
- CFE0004047, ucf:49153
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004047
- Title
- TUNABLE TERAHERTZ DETECTORS BASED ON PLASMON EXCIATION IN TWO DIMENSIONAL ELECTRON GASES IN INGAAS/INP AND ALGAN/GAN HEMT.
- Creator
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Saxena, Himanshu, Peale, Robert, University of Central Florida
- Abstract / Description
-
The observation of voltage-tunable plasmon resonances in the terahertz range in two dimensional electron gas (2-deg) of a high electron mobility transistor (HEMT) fabricated from the InGaAs/InP and AlGaN/GaN materials systems is reported. The devices were fabricated from a commercial HEMT wafer by depositing source and drain contacts using standard photolithography process and a semi-transparent gate contact that consisted of a 0.5 µm period transmission grating formed by electron-beam...
Show moreThe observation of voltage-tunable plasmon resonances in the terahertz range in two dimensional electron gas (2-deg) of a high electron mobility transistor (HEMT) fabricated from the InGaAs/InP and AlGaN/GaN materials systems is reported. The devices were fabricated from a commercial HEMT wafer by depositing source and drain contacts using standard photolithography process and a semi-transparent gate contact that consisted of a 0.5 µm period transmission grating formed by electron-beam lithography. Narrow-band resonant absorption of THz radiation was observed in transmission in the frequency range 10–100 cm-1. The resonance frequency depends on the gate voltage-tuned sheet-charge density of the 2deg. The fundamental and higher resonant harmonics were observed to shift towards lower frequencies with the implementation of negative gate bias. The theory of interaction of sub millimeter waves with 2deg through corrugated structure on top has been applied to calculate and understand the phenomena of resonant plasmon excitations. The observed separation of resonance fundamental from its harmonics and their shift with gate bias follows theory, although the absolute frequencies are lower by about a factor of 2-3 in InGaAs/InP system. However, calculated values match much better with AlGaN/GaN system.
Show less - Date Issued
- 2009
- Identifier
- CFE0002912, ucf:47994
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002912
- Title
- SURFACE PLASMON HOSTS FOR INFRARED WAVEGUIDES AND BIOSENSORS, AND PLASMONS IN GOLD-BLACK NANO-STRUCTURED FILMS.
- Creator
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Cleary, Justin, Peale, Robert, University of Central Florida
- Abstract / Description
-
Applications of surface plasmon polaritons (SPPs) have thus far emphasized visible and near-infrared wavelengths. Extension into the long-wave infrared (LWIR) has numerous potential advantages for biosensors and waveguides, which are explored in this work. A surface plasmon resonance (SPR) biosensor that operates deep into the infrared (3-11 µm wavelengths) is potentially capable of biomolecule recognition based on both selective binding and characteristic...
Show moreApplications of surface plasmon polaritons (SPPs) have thus far emphasized visible and near-infrared wavelengths. Extension into the long-wave infrared (LWIR) has numerous potential advantages for biosensors and waveguides, which are explored in this work. A surface plasmon resonance (SPR) biosensor that operates deep into the infrared (3-11 µm wavelengths) is potentially capable of biomolecule recognition based on both selective binding and characteristic vibrational modes. The goal is to operate such sensors at wavelengths where biological analytes are strongly differentiated by their IR absorption spectra and where the refractive index is increased by dispersion, which will provide enhanced selectivity and sensitivity. Potentially useful IR surface plasmon resonances are investigated on lamellar gratings formed from various materials with plasma frequencies in the IR wavelength range including doped semiconductors, semimetals, and conducting polymers. One outcome of this work has been the demonstration of a simple analytic formula for calculating the SPP absorption resonances in the angular reflectance spectra of gratings. It is demonstrated for Ag lamellar gratings in the 6-11 µm wavelength range. The recipe is semi-empirical, requiring knowledge of a surface-impedance modulation amplitude, which is found here by comparison to experiment as a function of the grating groove depth and the wavelength. The optimum groove depth for photon-to-SPP energy conversion was found by experiment and calculation to be ~10-15% of the wavelength. Hemicylindrical prism couplers formed from Si or Ge were investigated as IR surface plasmon couplers for the biosensor application. Strong Fabry-Perot oscillations in the angular reflectance spectra for these high index materials suggest that grating couplers will be more effective for this application in the LWIR. A variety of materials having IR plasma frequencies were investigated due to the tighter SPP mode confinement anticipated in the IR than for traditional noble metals. First doped-Si and metal silicides (Ni, Pd, Pt and Ti) were investigated due to their inherent CMOS compatibility. Rutherford backscattering spectroscopy, x-ray diffraction, scanning electron microscopy, secondary ion mass spectrometry and four point probe measurements complemented the optical characterization by ellipsometry. Calculation of propagation length and mode confinement from measured permittivities demonstrated the suitability for these materials for LWIR SPP applications. Semimetals were also investigated since their plasma frequencies are intermediate between those of doped silicon and metal silicides. The semimetal antimony, with a plasma frequency ~80 times less than that of gold was characterized. Relevant IR surface plasmon properties, including the propagation length and penetration depths for SPP fields, were determined from optical constants measured in the LWIR. Distinct resonances due to SPP generation were observed in angular reflection spectra of Sb lamellar gratings in the wavelength range of 6 to 11 µm. Though the real part of the permittivity is positive in this range, which violates the usual condition for the existence of bound SPP modes, calculations based on experimental permittivity showed that there is little to distinguish bound from unbound SPP modes for this material. The SPP mode decays exponentially away from the surface on both sides of the permittivity sign change. Water is found to broaden the IR plasmon resonances significantly at 9.25 micron wavelength where aqueous extinction is large. Much sharper resonances for water based IR SPR biosensor can be achieved in the 3.5 to 5.5 µm range. Nano-structured Au films (Au-black) were investigated as IR absorbers and possible solar cell enhancers based on surface plasmon resonance. The characteristic length scales of the structured films vary considerably as a function of deposition parameters, but the absorbance is found to be only weakly correlated with these distributions. Structured Au-black with a broad range of cluster length scales appear to be able to support multiple SPP modes with incident light coupling to the corrugated surface as seen by photoelectron emission microscopy (PEEM) and SPR experiments, supporting the hypothesis that Au-black may be a suitable material for plasmon-resonance enhancement solar-cell efficiency over the broad solar spectrum.
Show less - Date Issued
- 2010
- Identifier
- CFE0003231, ucf:48547
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003231
- Title
- INFRARED EMISSION SPECTROSCOPY OF HOT CARBON MONOXIDE.
- Creator
-
KHALILZADEH REZAIE, FARNOOD, PEALE, ROBERT, University of Central Florida
- Abstract / Description
-
Gas giant exoplanets known as hot Jupiters orbit close to their parent stars and are heated to high temperatures. Their infrared spectra, measured by photometry during secondary eclipses, are dominated by carbon monoxide and methane, the principle reservoirs of carbon on these planets. The relative CO and CH4 abundances inform us about temperature and pressure conditions and also about mixing by global winds driven by intense but asymmetric heating for these tidally locked bodies. Emission...
Show moreGas giant exoplanets known as hot Jupiters orbit close to their parent stars and are heated to high temperatures. Their infrared spectra, measured by photometry during secondary eclipses, are dominated by carbon monoxide and methane, the principle reservoirs of carbon on these planets. The relative CO and CH4 abundances inform us about temperature and pressure conditions and also about mixing by global winds driven by intense but asymmetric heating for these tidally locked bodies. Emission spectra collected during secondary eclipses, as the hot Jupiter passes behind its parent star, in principle allows a determination of the CO:CH4 concentration ratio. Since hot Jupiters exist at temperatures of order 700 K, accurate model atmospheres require high temperature line lists for relevant molecules, for which existing data bases are apparently incomplete. Since the outer atmospheres of hot Jupiters are bombarded by intense ultraviolet radiation and energetic particles, there may even be a significant degree of ionization and non-equilibrium populations among the various molecular levels. Here we present high temperature emission spectra of CO obtained from a microwave discharge plasma, where the source of CO was carbon dioxide that dissociates under microwave heating. The spectrum was measured in the range 1800-2400 cm-1 at a resolution of 0.1 cm-1. Vibrational transitions originating in up to the 13th vibrational level of the X 1S+ ground electronic term were observed. From the J values for maximum intensity lines within the rotational fine structure, we obtain a temperature estimate of ~700 K, which is comparable to the atmospheric conditions of hot-Jupiters.
Show less - Date Issued
- 2011
- Identifier
- CFE0003981, ucf:48664
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003981
- Title
- Nanoscale Functional Imaging by Tailoring Light-matter Interaction to Explore Organic and Biological Systems.
- Creator
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Otrooshi, Negar, Tetard, Laurene, Tatulian, Suren, Peale, Robert, Santra, Swadeshmukul, University of Central Florida
- Abstract / Description
-
ABSTRACTProbing molecular systems with light has been critical to deepen our understanding of life sciences. However, conventional analytical methods fail to resolve small quantities of molecules or the heterogeneity in molecules assembled into complex systems. This bottleneck is mostly attributed to light diffraction limit. In recent years, the successful implementation of new approaches to achieve sub-wavelength chemical speciation with an Atomic Force Microscope (AFM) has paved the way to...
Show moreABSTRACTProbing molecular systems with light has been critical to deepen our understanding of life sciences. However, conventional analytical methods fail to resolve small quantities of molecules or the heterogeneity in molecules assembled into complex systems. This bottleneck is mostly attributed to light diffraction limit. In recent years, the successful implementation of new approaches to achieve sub-wavelength chemical speciation with an Atomic Force Microscope (AFM) has paved the way to a deeper understanding of the effect of local composition and structure on the functional properties of a larger scale system. The combination of infrared light, to excite the vibrational modes of a sample, and AFM detection to monitor the resulting local photothermal expansion has emerged as a powerful approach. In this work, we explore new applications of AFM-infrared (IR) to further the understanding of proteins and bacterial cells. We first consider the vibrational modes and secondary structure of proteins. We show that beyond the localized IR fingerprint of the system, light polarization could affect the response of the protein. To investigate this further, we combine the AFM-IR measurements with plasmonic substrates to tune the electromagnetic field. Using plasmonic structures, we map the electromagnetic field confinement using nanomechanical infrared spectroscopy. We detect and quantify, in the near field, the energy transferred to the lattice in the form of thermal expansion resulting from the heat generated. We compare the photothermal expansion patterns in the structures under linearly and circular polarized illumination. The results suggest the formation of hot spots, of great interest for biomolecules detection. Using a model system, poly-L-lysine, we show that the IR spectrum and the vibrational circular dichroism fingerprint of a chiral biological system can be probed at the nanoscale, far beyond the conventional limits of detection. The second part of the study focuses on utilizing the capabilities of AFM-IR to investigate bacterial cells and their responses to nanoparticle-based treatments. We highlight the potential of these new capabilities to further dive into the fundamental molecular mechanism of antibacterial activity and of development of drug resistance. We conclude this work by providing a perspective on the impact nanoscale functional imaging and spectroscopy can have on life sciences and beyond.
Show less - Date Issued
- 2019
- Identifier
- CFE0007897, ucf:52750
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007897
- Title
- Dynamically Tunable Plasmonic Structural Color.
- Creator
-
Franklin, Daniel, Chanda, Debashis, Peale, Robert, Leuenberger, Michael, Wu, Shintson, University of Central Florida
- Abstract / Description
-
Functional surfaces which can control light across the electromagnetic spectrum are highly desirable. With the aid of advanced modeling and fabrication techniques, researchers have demonstrated surfaces with near arbitrary tailoring of reflected/transmitted amplitude, phase and polarization - the applications for which are diverse as light itself. These systems often comprise of structured metals and dielectrics that, when combined, manifest resonances dependent on structural dimensions. This...
Show moreFunctional surfaces which can control light across the electromagnetic spectrum are highly desirable. With the aid of advanced modeling and fabrication techniques, researchers have demonstrated surfaces with near arbitrary tailoring of reflected/transmitted amplitude, phase and polarization - the applications for which are diverse as light itself. These systems often comprise of structured metals and dielectrics that, when combined, manifest resonances dependent on structural dimensions. This attribute provides a convenient and direct path to arbitrarily engineer the surface's optical characteristics across many electromagnetic regimes. But while many of these plasmonic systems struggle to compete with the efficiency of pre-existing technologies, the ability to tune plamsonic structures post-fabrication is a distinct advantage which may lead to novel devices. In this work, I will summarize fundamental and applied aspects of tunable plasmonic systems as applied to the visible and infrared regimes. I will demonstrate how liquid crystal may be used to dynamically and reversibly tune the plasmonic resonances of metallic surfaces on a millisecond time scale. For the visible, this results in dynamic color-changing surfaces capable of covering the entire RGB color space and which is compatible with active addressing schemes. I will then show the application of these concepts to infrared absorbers through the use of liquid crystal and phase change materials. The later of these devices can find use in infrared data/image encoding, thermal management and camouflage. Together, these works explore the limits of tunable plasmonic systems and the novel devices they might lead to.
Show less - Date Issued
- 2018
- Identifier
- CFE0007001, ucf:52052
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007001
- Title
- Terahertz Emission from the Intrinsic Josephson Junctions of High-Symmetry Thermally-Managed Bi2Sr2CaCu2O8+d Annular Microstrip Antennas.
- Creator
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Bonnough, Sheila, Klemm, Richard, Peale, Robert, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
-
The intrinsic Josephson junctions in the high transition temperature superconductor Bi2Sr2CaCu2O8+? (BSCCO) have shown great potential for oscillators emitting in the terahertz frequency. The radiation frequency satisfies the conditions for both the ac Josephson effect and for a mesa cavity resonance mode. The observed angular dependence of the emissions from some mesa imply that the ac Josephson effect plays the primary role in a dual source radiation mechanism. But the integrated emission...
Show moreThe intrinsic Josephson junctions in the high transition temperature superconductor Bi2Sr2CaCu2O8+? (BSCCO) have shown great potential for oscillators emitting in the terahertz frequency. The radiation frequency satisfies the conditions for both the ac Josephson effect and for a mesa cavity resonance mode. The observed angular dependence of the emissions from some mesa imply that the ac Josephson effect plays the primary role in a dual source radiation mechanism. But the integrated emission power had generally been significantly below the 1 mW level suitable for many applications. This output power can be enhanced by a suitable design of an array of suitably shaped mesas that are all within a wavelength of each other so that their combined output is coherent. One such tightly packed array consists of concentric annuli. Here we calculate the angularly independent modes of thin annular microstrip antennas, with the ratio of the inner to the outer radii varying from 0.1 to 0.9. We then calculate the angular distribution of the emission power arising from the annular cavity modes and from the uniform ac Josephson current source at the frequencies of the cavity modes. We also calculate the five leading wavefunctions with the lowest order angular dependence for those annuli.
Show less - Date Issued
- 2018
- Identifier
- CFE0007314, ucf:52137
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007314
- Title
- Far-infrared bands in plasmonic metal-insulator-metal absorbers optimized for long wave infrared.
- Creator
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Evans, Rachel, Peale, Robert, Ishigami, Masahiro, Lyakh, Arkadiy, University of Central Florida
- Abstract / Description
-
Metal(-)insulator(-)metal (MIM) resonant absorbers comprise a conducting ground plane, a thin dielectric, and thin separated metal top-surface structures. Long-wave infrared (LWIR) fundamental absorptions are experimentally shown to be optimized for a ratio of dielectric thickness to top-structure dimension t/l (>) 0.08. The fundamental resonance wavelength is predicted by different analytic standing-wave theories to be ~2nl, where n is the dielectric refractive index. Thus, for the...
Show moreMetal(-)insulator(-)metal (MIM) resonant absorbers comprise a conducting ground plane, a thin dielectric, and thin separated metal top-surface structures. Long-wave infrared (LWIR) fundamental absorptions are experimentally shown to be optimized for a ratio of dielectric thickness to top-structure dimension t/l (>) 0.08. The fundamental resonance wavelength is predicted by different analytic standing-wave theories to be ~2nl, where n is the dielectric refractive index. Thus, for the dielectrics SiO2, AlN, and TiO2, l values of a few microns give fundamentals in the 8-12 micron LWIR wavelength region. Agreement of observed fundamental resonance wavelength with theory is better for t/l (>) ~0.2. Harmonics at shorter wavelengths are always observed, but we show that there are additional resonances in the far-infrared 20-50 micron wavelength range, well beyond the predicted fundamental. These appear to be due to dispersion. They may impact selectivity in spectral sensing applications.
Show less - Date Issued
- 2018
- Identifier
- CFE0007176, ucf:52267
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007176
- Title
- Broadband Mid-infrared Frequency Combs Generated via Frequency Division.
- Creator
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Ru, Qitian, Vodopyanov, Konstantin, Fathpour, Sasan, Wu, Shintson, Peale, Robert, University of Central Florida
- Abstract / Description
-
Frequency combs have revolutionized metrology and demonstrated numerous applications in science and technology. Combs operating in the mid-infrared region could be beneficial for molecular spectroscopy for several reasons. First, numerous molecules have their spectroscopic signatures in this region. Furthermore, the atmospheric window (3-5(&)#181;m and 8-14(&)#181;m) is located here. Additionally, a mid-infrared frequency comb could be employed as a diagnostic tool for the many components of...
Show moreFrequency combs have revolutionized metrology and demonstrated numerous applications in science and technology. Combs operating in the mid-infrared region could be beneficial for molecular spectroscopy for several reasons. First, numerous molecules have their spectroscopic signatures in this region. Furthermore, the atmospheric window (3-5(&)#181;m and 8-14(&)#181;m) is located here. Additionally, a mid-infrared frequency comb could be employed as a diagnostic tool for the many components of human breath, as well as for detection of harmful gases and contaminants in the atmosphere. In this thesis, I used synchronously pumped subharmonic optical parametric oscillators (OPOs) operating at degeneracy to produce ultra-broadband outputs near half of the pump laser frequency. One attractive property of the subharmonic OPOs is that the signal/idler waves of the OPO are frequency- and phase-locked to the pump frequency comb. We explored three new nonlinear materials in the subharmonic OPO and demonstrated a broadband spectrum for mid-infrared frequency comb generation. (1) Orientation-patterned (OP) gallium arsenide (GaAs) was selected as the first material because it has high nonlinearity. We found that the OP-GaAs based OPO yielded an approximately two-octave wide spectrum (2.8(-)11(&)#181;m). (2) Gallium phosphide (GaP) has near zero group velocity dispersion (GVD) at 4.7 (&)#181;m and a large bandgap. The OP-GaP OPO yielded a spectrum of more than two octaves (3(-)12.5(&)#181;m). Also, because of the large bandgap, GaP is suitable for telecom 1.56-(&)#181;m pumping, having the advantage of much smaller GVD than in periodically-poled-lithium-niobite (PPLN). The telecom laser (1.56(&)#181;m) pumped OP-GaP OPO was demonstrated with more than one octave wide spectrum. (3) Finally, we explored the phenomenon of random phase matching in the zinc selenide (ZnSe) polycrystalline material. The first random phase matched OPO was demonstrated with more than one octave spectrum (3.1(-) 9(&)#181;m), which is also the first OPO based on ZnSe.
Show less - Date Issued
- 2019
- Identifier
- CFE0007718, ucf:52430
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007718
- Title
- Impact of Ionizing Radiation and Electron Injection on Carrier Transport Properties in Narrow and Wide Bandgap Semiconductors.
- Creator
-
Lee, Jonathan, Flitsiyan, Elena, Chernyak, Leonid, Peale, Robert, Orlovskaya, Nina, University of Central Florida
- Abstract / Description
-
This study investigated the minority carrier properties of wide and narrow bandgap semiconductors. Included specifically are wide bandgap materials GaN and ?-Ga2O3, and narrow bandgap InAs/GaSb type-II strain-layer superlattice. The importance of minority carrier behavior in bipolar device performance is utmost because it is the limiting component in current conduction. The techniques used to determine minority carrier properties include electron beam induced current (EBIC) and...
Show moreThis study investigated the minority carrier properties of wide and narrow bandgap semiconductors. Included specifically are wide bandgap materials GaN and ?-Ga2O3, and narrow bandgap InAs/GaSb type-II strain-layer superlattice. The importance of minority carrier behavior in bipolar device performance is utmost because it is the limiting component in current conduction. The techniques used to determine minority carrier properties include electron beam induced current (EBIC) and cathodoluminescence (CL) spectroscopy. The CL spectroscopy is complemented with time-resolved CL (TRCL) for direct measurement of carrier radiative recombination lifetime. The minority carrier properties and effect of high energy radiation is explored. The GaN TRCL results suggested an activation energy effecting carrier lifetime of about 90 meV which is related to nitrogen vacancies. The effects of 60Co gamma radiation are demonstrated and related to the effects of electron injection in GaN-based devices. The effects of various high energy radiations upon Si-doped ?-Ga2O3 minority carrier diffusion length and radiative lifetime are measured. The non-irradiated sample thermal activation energies found for minority carrier diffusion length were 40.9 meV, related to shallow Si-donors in the material. The CL results demonstrate that the bandgap of 4.9 eV is slightly indirect. The thermal activation energy decreased on 1.5 MeV electron irradiation but increased for 10 MeV proton irradiation. The increase in energy was related to higher order defects and their complexes, and influenced recombination lifetime significantly. Finally, the diffusion length is reported for narrow bandgap InAs/GaSb superlattice structure and the effect of 60Co gamma radiation is demonstrated.In general, the defects introduced by high energy radiations decreased minority carrier diffusion length, except for 60Co gamma on AlGaN/GaN HEMT devices and high-temperature proton irradiated ?-Ga2O3.
Show less - Date Issued
- 2018
- Identifier
- CFE0007217, ucf:52239
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007217
- Title
- INFRARED SURFACE PLASMON POLARITONS ON SEMICONDUCTOR, SEMIMETAL AND CONDUCTING POLYMER.
- Creator
-
Shahzad, Monas, Peale, Robert, Heinrich, Helge, Coffey, Kevin, Diaz, Diego, University of Central Florida
- Abstract / Description
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Conductors with IR (infrared) plasma frequencies are potentially useful hosts of surface plasmon polaritons (SPPs) with subwavelength mode confinement for sensing applications. The underlying aim of this work is to identify such conductors that also have sharp SPP excitation resonances for biosensor applications at infrared (3-11 ?m) wavelengths, where biological analytes are strongly differentiated by their IR absorption spectra. In this work, various materials were investigated such as a...
Show moreConductors with IR (infrared) plasma frequencies are potentially useful hosts of surface plasmon polaritons (SPPs) with subwavelength mode confinement for sensing applications. The underlying aim of this work is to identify such conductors that also have sharp SPP excitation resonances for biosensor applications at infrared (3-11 ?m) wavelengths, where biological analytes are strongly differentiated by their IR absorption spectra. In this work, various materials were investigated such as a heavily doped semiconductor, a semimetal, a conducting polymer and its composite.Heavily doped silicon was investigated by tuning its plasma frequency to the infrared region by heavily doping. The measured complex permittivity spectra for p-type silicon with a carrier concentration of 6 (&)#215; 1019 and 6 (&)#215; 1020 cm-3 show that these materials support SPPs beyond 11 and 6 ?m wavelengths, respectively. SPP generation was observed in angular reflection spectra of doped-silicon gratings. Photon-to-plasmon coupling resonances, a necessary condition for sensing, were demonstrated near 10 ?m wavelength for the heaviest doped, and the observed resonances were confirmed theoretically using analytic calculations. The permittivity spectra were also used to calculate SPP mode heights above the silicon surface and SPP propagation lengths. Reasonable merit criteria applied to these quantities suggest that only the heaviest doped material has sensor potential, and then mainly within the wavelength range of 6 to 10 ?m. The semimetal bismuth (Bi) has an infrared plasmon frequency less than the infrared plasma frequency of noble metals such as gold and silver, which is one order of magnitude lower than their plasma frequencies. The excitation of IR surface plasmons on Bi lamellar gratings in the wavelength range of 3.4 (&)#181;m to 10.6 (&)#181;m was observed. Distinct SPP resonances were observed although the usual condition for bound SPP is not satisfied in this wavelength range because the real part of the permittivity is positive. The excitation of these resonances agrees theoretically with the electromagnetic surface waves called surface polaritons (SPs). The measured permittivity spectra were used to calculate the SP mode heights above the bismuth surface and SP propagation length, which satisfied our criteria for sensors.A conducting polymer and its composite with graphite were also investigated since their plasma frequency may lie in the infrared region. Polyaniline was chemically synthesized and doped with various acids to prepare its salt form. A composite material of polyaniline with colloidal and nano-graphite was also prepared. Optical constants were measured in the long wave infrared region (LWIR) and were used to calculate SPP propagation length and penetration depth. SPP resonance spectra were calculated and suggested that polyaniline and its composite can be used as a host with sufficient mode confinement for IR sensor application.
Show less - Date Issued
- 2012
- Identifier
- CFE0004598, ucf:49215
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004598
- Title
- Intracavity Laser Absorption Spectroscopy using Quantum Cascade Laser and Fabry-Perot Interferometer.
- Creator
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Medhi, Gautam, Peale, Robert, Ishigami, Marsahir, Chernyak, Leonid, Delfyett, Peter, University of Central Florida
- Abstract / Description
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Intracavity Laser Absorption Spectroscopy (ICLAS) at IR wavelengths offers an opportunity for spectral sensing of low vapor pressure compounds. We report here an ICLAS system design based on a quantum cascade laser (QCL) at THz (69.9 ?m) and IR wavelengths (9.38 and 8.1 ?m) with an open external cavity. The sensitivity of such a system is potentially very high due to extraordinarily long effective optical paths that can be achieved in an active cavity. Sensitivity estimation by numerical...
Show moreIntracavity Laser Absorption Spectroscopy (ICLAS) at IR wavelengths offers an opportunity for spectral sensing of low vapor pressure compounds. We report here an ICLAS system design based on a quantum cascade laser (QCL) at THz (69.9 ?m) and IR wavelengths (9.38 and 8.1 ?m) with an open external cavity. The sensitivity of such a system is potentially very high due to extraordinarily long effective optical paths that can be achieved in an active cavity. Sensitivity estimation by numerical solution of the laser rate equations for the THz QCL ICLAS system is determined. Experimental development of the external cavity QCL is demonstrated for the two IR wavelengths, as supported by appearance of fine mode structure in the laser spectrum. The 8.1 ?m wavelength exhibits a dramatic change in the output spectrum caused by the weak intracavity absorption of acetone. Numerical solution of the laser rate equations yields a sensitivity estimation of acetone partial pressure of 165 mTorr corresponding to ~ 200 ppm. The system is also found sensitive to the humidity in the laboratory air with an absorption coefficient of just 3 x 10-7 cm-1 indicating a sensitivity of 111 ppm. Reported also is the design of a compact integrated data acquisition and control system. Potential applications include military and commercial sensing for threat compounds such as explosives, chemical gases, biological aerosols, drugs, banned or invasive organisms, bio-medical breath analysis, and terrestrial or planetary atmospheric science.
Show less - Date Issued
- 2011
- Identifier
- CFE0004137, ucf:49040
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004137
- Title
- Radiation Effects on Wide Band Gap Semiconductor Transport Properties.
- Creator
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Schwarz, Casey, Flitsiyan, Elena, Chernyak, Leonid, Peale, Robert, Schoenfeld, Winston, University of Central Florida
- Abstract / Description
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In this research, the transport properties of ZnO were studied through the use of electron and neutron beam irradiation. Acceptor states are known to form deep in the bandgap of doped ZnO material. By subjecting doped ZnO materials to electron and neutron beams we are able to probe, identify and modify transport characteristics relating to these deep accepter states. The impact of irradiation and temperature on minority carrier diffusion length and lifetime were monitored through the use of...
Show moreIn this research, the transport properties of ZnO were studied through the use of electron and neutron beam irradiation. Acceptor states are known to form deep in the bandgap of doped ZnO material. By subjecting doped ZnO materials to electron and neutron beams we are able to probe, identify and modify transport characteristics relating to these deep accepter states. The impact of irradiation and temperature on minority carrier diffusion length and lifetime were monitored through the use of the Electron Beam Induced Current (EBIC) method and Cathodoluminescence (CL) spectroscopy. The minority carrier diffusion length, L, was shown to increase as it was subjected to increasing temperature as well as continuous electron irradiation. The near-band-edge (NBE) intensity in CL measurements was found to decay as a function of temperature and electron irradiation due to an increase in carrier lifetime. Electron injection through application of a forward bias also resulted in a similar increase of minority carrier diffusion length.Thermal and electron irradiation dependences were used to determine activation energies for the irradiation induced effects. This helps to further our understanding of the electron injection mechanism as well as to identify possible defects responsible for the observed effects. Thermal activation energies likely represent carrier delocalization energy and are related to the increase of diffusion length due to the reduction in recombination efficiency. The effect of electron irradiation on the minority carrier diffusion length and lifetime can be attributed to the trapping of non-equilibrium electrons on neutral acceptor levels. The effect of neutron irradiation on CL intensity can be attributed to an increase in shallow donor concentration. Thermal activation energies resulting from an increase in L or decay of CL intensity monitored through EBIC and CL measurements for p-type Sb doped ZnO were found to be the range of Ea = 112 to 145 meV. P-type Sb doped ZnO nanowires under the influence of temperature and electron injection either through continuous beam impacting or through forward bias, displayed an increase in L and corresponding decay of CL intensity when observed by EBIC or CL measurements. These measurements led to activation energies for the effect ranging from Ea = 217 to 233 meV. These values indicate the possible involvement of a SbZn-2VZn acceptor complex. For N-type unintentionally doped ZnO, CL measurements under the influence of temperature and electron irradiation by continuous beam impacting led to a decrease in CL intensity which resulted in an electron irradiation activation energy of approximately Ea = 259 meV. This value came close to the defect energy level of the zinc interstitial. CL measurements of neutron irradiated ZnO nanostructures revealed that intensity is redistributed in favor of the NBE transition indicating an increase of shallow donor concentration. With annealing contributing to the improvement of crystallinity, a decrease can be seen in the CL intensity due to the increase in majority carrier lifetime. Low energy emission seen from CL spectra can be due to oxygen vacancies and as an indicator of radiation defects.
Show less - Date Issued
- 2012
- Identifier
- CFE0004234, ucf:49018
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004234
- Title
- Observations, Thermochemical Calculations, and Modeling of Exoplanetary Atmospheres.
- Creator
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Blecic, Jasmina, Harrington, Joseph, Britt, Daniel, Peale, Robert, Fortney, Jonathan, University of Central Florida
- Abstract / Description
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This dissertation as a whole aims to provide the means to better understand hot-Jupiter planets through observing, performing thermochemical calculations, and modeling their atmospheres. We used Spitzer multi-wavelength secondary-eclipse observations to characterize planetary atmospheres. We chose targets with high signal-to-noise ratios, as their deep eclipses allow us to detect signatures of spectral features and assess planetary atmospheric structure and composition with greater certainty....
Show moreThis dissertation as a whole aims to provide the means to better understand hot-Jupiter planets through observing, performing thermochemical calculations, and modeling their atmospheres. We used Spitzer multi-wavelength secondary-eclipse observations to characterize planetary atmospheres. We chose targets with high signal-to-noise ratios, as their deep eclipses allow us to detect signatures of spectral features and assess planetary atmospheric structure and composition with greater certainty. Chapter 1 gives a short introduction. Chapter 2 presents the Spitzer secondary-eclipse analysis and atmospheric characterization of WASP-14b. The decrease in flux when a planet passes behind its host star reveals the planet dayside thermal emission, which, in turn, tells us about the atmospheric temperature and pressure profiles and molecular abundances. WASP-14b is a highly irradiated, transiting hot Jupiter. By applying a Bayesian approach in the atmospheric analysis, we found an absence of thermal inversion contrary to theoretical predictions. Chapter 3 describes the infrared observations of WASP-43b's Spitzer secondary eclipses, data analysis, and atmospheric characterization. WASP-43b is one of the closest-orbiting hot Jupiters, orbiting one of the coolest stars with a hot Jupiter. This configuration provided one of the strongest signal-to-noise ratios. The atmospheric analysis ruled out a strong thermal inversion in the dayside atmosphere of WASP-43b and put a nominal upper limit on the day-night energy redistribution. Chapter 4 presents an open-source Thermochemical Equilibrium Abundances (TEA) code and its application to several hot-Jupiter temperature and pressure models. TEA calculates the abundances of gaseous molecular species using the Gibbs free-energy minimization method within an iterative Lagrangian optimization scheme. The thermochemical equilibrium abundances obtained with TEA can be used to initialize atmospheric models of any planetary atmosphere. The code is written in Python, in a modular fashion, and it is available to the community via http://github.com/dzesmin/TEA. Chapter 5 presents my contributions to an open-source Bayesian Atmospheric Radiative Transfer (BART) code, and its application to WASP-43b. BART characterizes planetary atmospheres based on the observed spectroscopic information. It initializes a planetary atmospheric model, performs radiative-transfer calculations to produce models of planetary spectra, and using a statistical module compares models with observations. We describe the implementation of the initialization routines, the atmospheric profile generator, the eclipse module, the best-fit routines, and the contribution function module. We also present a comprehensive atmospheric analysis of all WASP-43b secondary-eclipse data obtained from the space- and ground-based observations using BART.
Show less - Date Issued
- 2015
- Identifier
- CFE0005926, ucf:50841
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005926
- Title
- Synchrotron based infrared microspectroscopy of carbonaceous chondrites.
- Creator
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Yesiltas, Mehmet, Peale, Robert, Fernandez, Yan, Britt, Daniel, Reach, William, University of Central Florida
- Abstract / Description
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Relationships between organic molecules and inorganic minerals are investigated in five carbonaceous chondrites, Northwest Africa 852 (CR2), Tagish Lake (C2-ungroupped), Orgueil (CI1), Sutter's Mill (CM), and Murchison (CM2), with micron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for various constituents are determined using statistical correlation analysis. Silicate band is found to be positively correlated with...
Show moreRelationships between organic molecules and inorganic minerals are investigated in five carbonaceous chondrites, Northwest Africa 852 (CR2), Tagish Lake (C2-ungroupped), Orgueil (CI1), Sutter's Mill (CM), and Murchison (CM2), with micron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for various constituents are determined using statistical correlation analysis. Silicate band is found to be positively correlated with stretching modes of aliphatic hydrocarbons in NWA 852 and Tagish Lake. The former is highly correlated with the hydration band in all meteorites. Negative correlation is observed between water+organics and carbonate bands in all meteorites. Two dimensional infrared maps for NWA 852 and Orgueil show that carbonates are spatially separated from water+organic combination, silicates, OH, and CH distributions. Overlapping of the latter three in NWA 852 and Tagish Lake suggests a possible catalytic role of phyllosilicates in the formation of organics. Additionally, spectroscopic analyses on Sutter's Mill meteorite fragments present multiple distinct mineralogies. Spatial and spectral evidences on this regolith breccia suggest mixing of multiple parent bodies. Ratios of asymmetric CH2 and CH3 band strengths for NWA 852, Tagish Lake, and Sutter's Mill are similar to the average ratio of interplanetary dust particles and Wild 2 cometary dust particles, however significantly exceeds that of interstellar medium objects and several aqueously altered carbonaceous chondrites such as Orgueil. This suggests distinct formation regions and/or parent body processing of organics for these meteorites. Our infrared spectro-microtomography measurements on Murchison meteorite, representing the first such measurement on any kind of meteorite, comprise of three-dimensional reconstructions of specific molecular functional groups for understanding the spatial distributions of these groups.
Show less - Date Issued
- 2015
- Identifier
- CFE0006061, ucf:50966
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006061
- Title
- Experiments in Graphene and Plasmonics.
- Creator
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Smith, Christian, Ishigami, Masa, Peale, Robert, Mucciolo, Eduardo, Chanda, Debashis, University of Central Florida
- Abstract / Description
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Graphene nanoribbons, graphene based optical sensors, and grating based plasmonics are explored experimentally. Graphene nanoribbons exhibit highly insulating states that may allow for graphene based digital applications. We investigate the sensitivity of these states to local charged impurities in ultra high vacuum. We look into the possibility of isolating two-dimensional films of H-BN and BSCCO, and test for any interesting phenomena. We also assess graphene's applicability for optical...
Show moreGraphene nanoribbons, graphene based optical sensors, and grating based plasmonics are explored experimentally. Graphene nanoribbons exhibit highly insulating states that may allow for graphene based digital applications. We investigate the sensitivity of these states to local charged impurities in ultra high vacuum. We look into the possibility of isolating two-dimensional films of H-BN and BSCCO, and test for any interesting phenomena. We also assess graphene's applicability for optical sensing by implementing a new style of spectral detector. Utilizing surface plasmon excitations nearby a graphene field-effect transistor we are able to produce a detector with wavelength sensitivity and selectivity in the visible range. Finally, we study another plasmonic phenomenon, and observe the resonant enhancement of diffraction into a symmetry-prohibited order in silver gratings.
Show less - Date Issued
- 2014
- Identifier
- CFE0005887, ucf:50874
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005887
