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Articles 1 - 20 of 20
Full-Text Articles in Physics
Pressure- And Temperature-Dependent Inelastic Neutron Scattering Study Of The Phase Transition And Phonon Lattice Dynamics In Para-Terphenyl, Qingan Cai, Michael Mcintire, Luke L. Daemen, Chen Li, Eric Chronister
Pressure- And Temperature-Dependent Inelastic Neutron Scattering Study Of The Phase Transition And Phonon Lattice Dynamics In Para-Terphenyl, Qingan Cai, Michael Mcintire, Luke L. Daemen, Chen Li, Eric Chronister
Chemistry and Biochemistry Faculty Research
Inelastic neutron scattering has been performed on para-terphenyl at temperatures from 10 to 200 K and under pressures from the ambient pressure to 1.51 kbar. The temperature dependence of phonons, especially low-frequency librational bands, indicates strong anharmonic phonon dynamics. The pressure- and temperature-dependence of the phonon modes suggest a lack of phase transition in the region of 0-1.51 kbar and 10-30 K. Additionally, the overall lattice dynamics remains similar up to 200 K under the ambient pressure. The results suggest that the boundary between the ordered triclinic phase and the third solid phase, reported at lower temperatures and higher pressures, …
Lattice Thermal Conductivity Of Quartz At High Pressure And Temperature From The Boltzmann Transport Equation, Xue Xiong, Eugene J. Ragasa, Aleksandr V. Chernatynskiy, Dawei Tang, Simon R. Phillpot
Lattice Thermal Conductivity Of Quartz At High Pressure And Temperature From The Boltzmann Transport Equation, Xue Xiong, Eugene J. Ragasa, Aleksandr V. Chernatynskiy, Dawei Tang, Simon R. Phillpot
Physics Faculty Research & Creative Works
The thermal conductivities along the basal and hexagonal directions of α-quartz silica, the low-temperature form of crystalline SiO2, are predicted from the solution of the Boltzmann transport equation combined with the van Beest, Kramer, and van Santen potential for the temperature up to 900 K and the pressure as high as 4 GPa. The thermal conductivities at atmospheric pressure, which show a negative and nonlinear dependence on temperature, are in reasonable agreement with the experimental data. The influence of pressure on thermal conductivity is positive and linear. The pressure (P) and temperature (T) dependences of the thermal conductivity …
Impact Of Anharmonicity On The Vibrational Entropy And Specific Heat Of Uo₂, M. S. Bryan, J. W. L. Pang, B. C. Larson, Aleksandr V. Chernatynskiy, D. L. Abernathy, K. Gofryk, M. E. Manley, For Full List Of Authors, See Publisher's Website.
Impact Of Anharmonicity On The Vibrational Entropy And Specific Heat Of Uo₂, M. S. Bryan, J. W. L. Pang, B. C. Larson, Aleksandr V. Chernatynskiy, D. L. Abernathy, K. Gofryk, M. E. Manley, For Full List Of Authors, See Publisher's Website.
Physics Faculty Research & Creative Works
The impact of anharmonicity on the vibrational entropy and heat capacity of UO2 has been investigated from 10 to 1200 K using inelastic neutron-scattering measurements of the phonon density of states (PDOS). Small changes in the PDOS are observed from 10 to 295 K, with more noticeable changes appearing in the 750- and 1200-K data. The specific heat determined from the PDOS measurements is in agreement with macroscopic specific heat measurements, and the overall impact of nondilation anharmonicity on the specific heat has been shown to be less than 2%. An analysis of the phonon measurements shows that the softening …
Large And Realistic Models Of Amorphous Silicon, Dale Ingram, Bishal Bhattarai, Parthapratim Biswas, David A. Drabold
Large And Realistic Models Of Amorphous Silicon, Dale Ingram, Bishal Bhattarai, Parthapratim Biswas, David A. Drabold
Faculty Publications
Amorphous silicon (a-Si) models are analyzed for structural, electronic and vibrational characteristics. Several models of various sizes have been computationally fabricated for this analysis. It is shown that a recently developed structural modeling algorithm known as force-enhanced atomic refinement (FEAR) provides results in agreement with experimental neutron and X-ray diffraction data while producing a total energy below conventional schemes. We also show that a large model (∼ 500 atoms) and a complete basis is necessary to properly describe vibrational and thermal properties. We compute the density for a-Si, and compare with experimental results.
Transient Lattice Deformations Of Crystals Studied By Means Of Ultrafast Time-Resolved X-Ray And Electron Diffraction, Runze Li, Kyle Sundqvist, Jie Chen, H. E. Elsayed-Ali, Jie Zhang, Peter M. Rentzepis
Transient Lattice Deformations Of Crystals Studied By Means Of Ultrafast Time-Resolved X-Ray And Electron Diffraction, Runze Li, Kyle Sundqvist, Jie Chen, H. E. Elsayed-Ali, Jie Zhang, Peter M. Rentzepis
Electrical & Computer Engineering Faculty Publications
Ultrafast lattice deformation of tens to hundreds of nanometer thick metallic crystals, after femtosecond laser excitation, was measured directly using 8.04 keV subpicosecond x-ray and 59 keV femtosecond electron pulses. Coherent phonons were generated in both single crystal and polycrystalline films. Lattice compression was observed within the first few picoseconds after laser irradiation in single crystal aluminum, which was attributed to the generation of a blast force and the propagation of elastic waves. The different time scales of lattice heating for tens and hundreds nanometer thick films are clearly distinguished by electron and x-ray pulse diffraction. The electron and lattice …
Prospective Solid-State Photonic Cryocooler Based On The “Phonon-Deficit Effect”, Gurgen Melkonyan, Armen Gulian
Prospective Solid-State Photonic Cryocooler Based On The “Phonon-Deficit Effect”, Gurgen Melkonyan, Armen Gulian
Mathematics, Physics, and Computer Science Faculty Articles and Research
In this design microwave photons are propagating in a sapphire rod, and are being absorbed by a superconductor deposited on the surface of the rod. The frequency of the radiation is tuned to be less than the energy gap in the superconductor, so that the pair breaking is not taking place. This photon pumping redistributes the electron-hole quasiparticles: their distribution function is non-equilibrium, and the “phonon-deficit effect” takes place. There is a dielectric material deposited on top of superconductor, which serves asthe “cold finger” of the cooler. Its “acoustical density” is supposed to be smaller than that of the superconducting …
Kapitza Resistance Of Si/Sio₂ Interface, Bowen Deng, Aleksandr V. Chernatynskiy, Marat Khafizov, David H. Hurley, Simon R. Phillpot
Kapitza Resistance Of Si/Sio₂ Interface, Bowen Deng, Aleksandr V. Chernatynskiy, Marat Khafizov, David H. Hurley, Simon R. Phillpot
Physics Faculty Research & Creative Works
A phonon wave packet dynamics method is used to characterize the Kapitza resistance of a Si/SiO2 interface in a Si/SiO2/Si heterostructure. By varying the thickness of SiO2 layer sandwiched between two Si layers, we determine the Kapitza resistance for the Si/SiO 2 interface from both wave packet dynamics and a direct, non-equilibrium molecular dynamics approach. The good agreement between the two methods indicates that they have each captured the anharmonic phonon scatterings at the interface. Moreover, detailed analysis provides insights as to how individual phonon mode scatters at the interface and their contribution to the Kapitza …
Phonon Thermal Transport Through Tilt Grain Boundaries In Strontium Titanate, Zexi Zheng, Xiang Chen, Bowen Deng, Aleksandr V. Chernatynskiy, Shengfeng Yang, Jinjun Xiong, Youping Chen
Phonon Thermal Transport Through Tilt Grain Boundaries In Strontium Titanate, Zexi Zheng, Xiang Chen, Bowen Deng, Aleksandr V. Chernatynskiy, Shengfeng Yang, Jinjun Xiong, Youping Chen
Physics Faculty Research & Creative Works
In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO3. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO3 contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza …
Temperature-Dependent Photoluminescence Of Ge/Si And Ge 1-Ysn Y/Si, Indicating Possible Indirect-To-Direct Bandgap Transition At Lower Sn Content, Mee-Yi Ryu, Thomas R. Harris, Yung Kee Yeo, Richard T. Beeler, John Kouvetakis
Temperature-Dependent Photoluminescence Of Ge/Si And Ge 1-Ysn Y/Si, Indicating Possible Indirect-To-Direct Bandgap Transition At Lower Sn Content, Mee-Yi Ryu, Thomas R. Harris, Yung Kee Yeo, Richard T. Beeler, John Kouvetakis
Faculty Publications
Temperature (T)-dependent photoluminescence (PL) has been investigated for both p-Ge and n-Ge1-ySny films grown on Si substrates. For the p-Ge, strong direct bandgap (ED) along with weak indirect bandgap related (EID) PL at low temperatures (LTs) and strong ED PL at room temperature (RT) were observed. In contrast, for the n-Ge1-ySny, very strong dominant EID PL at LT and strong ED PL were observed at RT. This T-dependent PL study indicates that the indirect-to-direct bandgap transitions of Ge1-ySn …
Sum Rules And Universality In Electron-Modulated Acoustic Phonon Interaction In A Free-Standing Semiconductor Plate, Shigeyasu Uno, Darryl H. Yong, Nobuya Mori
Sum Rules And Universality In Electron-Modulated Acoustic Phonon Interaction In A Free-Standing Semiconductor Plate, Shigeyasu Uno, Darryl H. Yong, Nobuya Mori
All HMC Faculty Publications and Research
Analysis of acoustic phonons modulated due to the surfaces of a free-standing semiconductor plate and their deformation-potential interaction with electrons are presented. The form factor for electron-modulated acoustic phonon interaction is formulated and analyzed in detail. The form factor at zero in-plane phonon wave vector satisfies sum rules regardless of electron wave function. The form factor is larger than that calculated using bulk phonons, leading to a higher scattering rate and lower electron mobility. When properly normalized, the form factors lie on a universal curve regardless of plate thickness and material.
Ferroelectric Phase Transitions In Three-Component Short-Period Superlattices Studied By Ultraviolet Raman Spectroscopy, Dmitri Tenne, H. N. Lee, R. S. Katiyar, X. X. Xi
Ferroelectric Phase Transitions In Three-Component Short-Period Superlattices Studied By Ultraviolet Raman Spectroscopy, Dmitri Tenne, H. N. Lee, R. S. Katiyar, X. X. Xi
Physics Faculty Publications and Presentations
Vibrational spectra of three-component BaTiO3SrTiO3CaTiO3 short-period superlattices grown by pulsed laser deposition with atomic-layer control have been investigated by ultraviolet Raman spectroscopy. Monitoring the intensity of the first-order phonon peaks in Raman spectra as a function of temperature allowed determination of the ferroelectric phase transition temperature, Tc. Raman spectra indicate that all superlattices remain in the tetragonal ferroelectric phase with out-of-plane polarization in the entire temperature range below Tc. The dependence of Tc on the relative thicknesses of ferroelectric (BaTiO3) to non-ferroelectric materials (SrTiO3 and CaTiO3 …
The Fabrication And Characterization Of Granular Aluminium/Palladium Bilayer Microbolometers, Thomas E. Wilson
The Fabrication And Characterization Of Granular Aluminium/Palladium Bilayer Microbolometers, Thomas E. Wilson
Physics Faculty Research
Superconducting granular aluminium/palladium bilayer microbolometers with subnanosecond response can be easily fabricated using an all lift-off process with image-reversal lithography. The palladium capping layer allows for convenient and reproducible Ohmic contacts to be made to the device. We report their fabrication, resistance–current calibration, responsivity and response time. Finally, a deconvolution algorithm is used to improve the time resolution to approximately 1 ns while obtaining the incident photon and phonon fluxes in both direct photoexcitation and phonon heat pulse experiments.
Strain-Free Ge/Gesisn Quantum Cascade Lasers Based On L-Valley Intersubband Transitions, Greg Sun, H. H. Cheng, J. Menéndez, Jacob B. Khurgin, R. A. Soref
Strain-Free Ge/Gesisn Quantum Cascade Lasers Based On L-Valley Intersubband Transitions, Greg Sun, H. H. Cheng, J. Menéndez, Jacob B. Khurgin, R. A. Soref
Physics Faculty Publications
The authors propose a Ge/Ge0.76Si0.19Sn0.05 quantum cascade laser using intersubband transitions at L valleys of the conduction band which has a “clean” offset of150 meV situated below other energy valleys (Γ,X). The entire structure is strain-free because the lattice-matched Ge and Ge0.76Si0.19Sn0.05 layers are to be grown on a relaxed Ge buffer layer on a Si substrate. Longer lifetimes due to the weaker scattering of nonpolar optical phonons reduce the threshold current and potentially lead to room temperature operation.
Carrier Capture Dynamics Of Inas/Gaas Quantum Dots, T. Piwonski, I. O'Driscoll, J. Houlihan, G. Huyet, R. J. Manning, A. V. Uskov
Carrier Capture Dynamics Of Inas/Gaas Quantum Dots, T. Piwonski, I. O'Driscoll, J. Houlihan, G. Huyet, R. J. Manning, A. V. Uskov
Physical Sciences Publications
Carrier dynamics of a 1.3μm InAs∕GaAs quantum dot amplifier is studied using heterodyne pump-probe spectroscopy. Measurements of the recovery times versus injection current reveal a power law behavior predicted by a quantum dot rate equation model. These results indicate that Auger processes dominate the carrier dynamics.
Erratum: “Terahertz Studies Of The Dielectric Response And Second-Order Phonons In A Gase Crystal” [Appl. Phys. Lett.87, 182104 (2005)], B. L. Yu, F. Zeng, V. Kartazayev, R. R. Alfano, K. C. Mandal
Erratum: “Terahertz Studies Of The Dielectric Response And Second-Order Phonons In A Gase Crystal” [Appl. Phys. Lett.87, 182104 (2005)], B. L. Yu, F. Zeng, V. Kartazayev, R. R. Alfano, K. C. Mandal
Faculty Publications
No abstract provided.
Carrier Dynamics In Α‐Fe2o3 (0001) Thin Films And Single Crystals Probed By Femtosecond Transient Absorption And Reflectivity, Alan G. Joly, Joshua R. Williams, Scott A. Chambers, Gang Xiong, Wayne P. Hess, David M. Laman
Carrier Dynamics In Α‐Fe2o3 (0001) Thin Films And Single Crystals Probed By Femtosecond Transient Absorption And Reflectivity, Alan G. Joly, Joshua R. Williams, Scott A. Chambers, Gang Xiong, Wayne P. Hess, David M. Laman
All Faculty Scholarship for the College of the Sciences
Femtosecond transient reflectivity and absorption are used to measure the carrier lifetimes in α‐Fe2O3 thin films and single crystals. The results from the thin films show that initially excited hot electrons relax to the band edge within 300 fs and then recombine with holes or trap within 5 ps. The trapped electrons have a lifetime of hundreds of picoseconds. Transient reflectivity measurements from hematite (α‐Fe2O3)single crystals show similar but slightly faster dynamics leading to the conclusion that the short carrier lifetimes in these materials are due primarily to trapping to Fe d- …
Progress Towards Terahertz Acoustic Phonon Generation In Doping Superlattices, Thomas E. Wilson
Progress Towards Terahertz Acoustic Phonon Generation In Doping Superlattices, Thomas E. Wilson
Physics Faculty Research
Progress is described in experiments to generate coherent terahertz acoustic phonons in silicon doping superlattices by the resonant absorption of nanosecond-pulsed far-infrared laser radiation. Future experiments are proposed that would use the superlattice as a transducer in a terahertz cryogenic acoustic reflection microscope with sub-nanometer resolution.
Terahertz Studies Of The Dielectric Response And Second-Order Phonons In A Gase Crystal, B. L. Yu, F. Zeng, V. Kartazayev, R. R. Alfano, K. C. Mandal
Terahertz Studies Of The Dielectric Response And Second-Order Phonons In A Gase Crystal, B. L. Yu, F. Zeng, V. Kartazayev, R. R. Alfano, K. C. Mandal
Faculty Publications
No abstract provided.
Progress Towards Terahertz Acoustic Phonon Generation In Doping Superlattices, Thomas E. Wilson
Progress Towards Terahertz Acoustic Phonon Generation In Doping Superlattices, Thomas E. Wilson
Physics Faculty Research
Progress is described in experiments to generate coherent terahertz acoustic phonons in silicon doping superlattices by the resonant absorption of nanosecond-pulsed far-infrared laser radiation. Future experiments are proposed that would use the superlattice as a transducer in a terahertz cryogenic acoustic reflection microscope with sub-nanometer resolution.
Tb3+-Doped K Pb2Br5: Low-Energy Phonon Mid-Infrared Laser Crystal, U. N. Roy, R. H. Hawrami, Y. Cui, S. Morgan, A. Burger, K. C. Mandal, C. C. Noblitt, S. A. Speakman, K. Rademaker, S. A. Payne
Tb3+-Doped K Pb2Br5: Low-Energy Phonon Mid-Infrared Laser Crystal, U. N. Roy, R. H. Hawrami, Y. Cui, S. Morgan, A. Burger, K. C. Mandal, C. C. Noblitt, S. A. Speakman, K. Rademaker, S. A. Payne
Faculty Publications
No abstract provided.