A5084424624- Ion-surface interactions and analysis
- Physics of Superconductivity and Magnetism
- Semiconductor materials and interfaces
- Photonic and Optical Devices
- Integrated Circuits and Semiconductor Failure Analysis
- Silicon and Solar Cell Technologies
- Semiconductor Lasers and Optical Devices
- Advanced Condensed Matter Physics
- Magnetic properties of thin films
- Semiconductor materials and devices
- Optical Network Technologies
- Advanced Fiber Optic Sensors
- Silicon Nanostructures and Photoluminescence
- Advanced Photonic Communication Systems
- Quantum and electron transport phenomena
- 3D Printing in Biomedical Research
- Surface and Thin Film Phenomena
- Advanced Fiber Laser Technologies
- Magnetic and transport properties of perovskites and related materials
- Nonlinear Optical Materials Studies
- Neuroscience and Neural Engineering
- Force Microscopy Techniques and Applications
- Copper Interconnects and Reliability
- Diamond and Carbon-based Materials Research
- Tissue Engineering and Regenerative Medicine
Boston University
2017-2024
Massachusetts Institute of Technology
2024
Hampton University
2023
Boston Medical Center
2021
Materials Science & Engineering
2019
State Innovation Exchange
2019
Public Health Department
2016
Nokia (United States)
1989-2010
Alcatel Lucent (Germany)
1987-2008
BAE Systems (United States)
2006
We have studied the effect of isotopic substitution on superconducting ${T}_{c}$ in 90-K superconductors ${\mathrm{Ba}}_{2}$Y${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and ${\mathrm{Ba}}_{2}$Eu${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ by replacing $^{16}\mathrm{O}$ with heavier isotope $^{18}\mathrm{O}$. Samples approximately 75% replaced $^{18}\mathrm{O}$ were prepared gas-phase ion exchange. In these samples phonon frequencies, measured Raman spectroscopy, are reduced expected \ensuremath{\sim}4%....
Small voids are formed in Si by MeV He implantation and annealing. We measure the equilibrium shape of these hence extract surface energy curve \ensuremath{\gamma}(\ensuremath{\theta}) for Si. \ensuremath{\gamma}(111) is global minimum, with \ensuremath{\gamma}(100)\ensuremath{\approxeq}1.1\ensuremath{\gamma}(111) all other cusps on being relatively small. The experimental compared theoretical predictions earlier experiments. Step energies obtained from...
Buried single-crystal CoSi2 layers in silicon have been formed by high dose implantation of cobalt followed annealing. These grow both the (100) and (111) orientations—those better crystallinity, but those are higher electrical quality. Electrical transport measurements on give values for resistance ratios superconducting critical temperatures that than best films grown conventional techniques comparable to bulk CoSi2.
The effect on the superconducting transition temperature of exchanging $^{18}\mathrm{O}$ for $^{16}\mathrm{O}$ in ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ has been studied. concentration two isotopes determined by Rutherford backscattering spectroscopy and Raman confirmed mass-related phonon frequency shift. substitution is found to be same O sites. Magnetic measurements reveal a nonzero isotope (\ensuremath{\alpha}=0.16\ifmmode\pm\else\textpm\fi{}0.02). exponent...
We have performed systematic tunneling measurements on two-dimensional quench-condensed films of Sn and Pb to investigate the destruction superconductivity by localization effects. With increasing sheet resistance films, energy gaps ${T}_{c}$'s decrease only slightly, but gap edges broaden until width becomes comparable gap. Associated with this broadening are low-temperature finite-resistance tails in resistive transitions.
We present a fully tunable multistage narrowband optical pole-zero notch filter that is fabricated in silicon complementary metal oxide semiconductor (CMOS) foundry. The allows for the reconfigurable and independent tuning of center frequency, null depth, bandwidth one or more notches simultaneously. It constructed using Mach-Zehnder interferometer (MZI) with cascaded all-pass (APF) ring resonators its arms. Measured nulling response exhibits ultranarrow 3 dB BW 0.6350 GHz, depth 33 dB. This...
Biomimetic on-chip tissue models serve as a powerful tool for studying human physiology and developing therapeutics; however, their modeling power is hindered by our inability to develop highly ordered functional structures in small length scales. Here, we demonstrate how high-precision fabrication can enable scaled-down of organ-level cardiac mechanical function. We use two-photon direct laser writing (TPDLW) fabricate nanoscale-resolution metamaterial scaffold with fine-tuned properties...
Diamond films and islands grown by chemical vapor deposition were implanted with boron, sodium, carbon ions at doses of 1014–1015/cm2. This structural modification the subsurface resulted in a significant reduction electric field required for electron emission. The threshold producing current density 10 mA/cm2 can be as low 42 V/μm as-implanted diamond compared to 164 high quality p-type diamond. When ion-implanted samples annealed temperatures order anneal out implantation-induced defects,...
A transmission phase grating was used to write a 94% reflectivity in-fibre index in photosensitive optical fibre with single UV laser beam at 242 nm. This method offers the possibility of high-volume production gratings.
We have studied the temperature-dependent resistivity and Hall coefficient of epitaxial $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films as a function ion-beam-induced damage. At low ion fluences behave like typical metals above superconducting transition. higher fluences, material goes continuously through metal-insulator transition with that varies $\mathrm{exp}({T}^{\ensuremath{-}\frac{1}{2}})$ but changes very little. This implies is...
The optical components industry stands at the threshold of a major expansion that will restructure its business processes and sustain profitability for next three decades. This growth establish cost effective platform partitioning electronic photonic functionality to extend processing power integrated circuits. BAE Systems, Lucent Technologies, Massachusetts Institute Technology, Applied Wave Research are participating in high payoff research development program Microsystems Technology...
Highly oriented, epitaxial Y1Ba2Cu3O7−x thin films were prepared on MgO(100) by molecular beam epitaxy at a substrate temperature of 550–600 °C. The in situ growth was achieved incorporating reactive oxygen species produced remote microwave plasma flow-tube reactor. (001) orientation is demonstrated x-ray diffraction and ion channeling. In reflection high-energy electron showed that layer-by-layer has well-ordered, atomically smooth surface the as-grown tetragonal phase an stoichiometry...
We have performed tunneling measurements on ultrathin, homogeneous, strong-coupled superconducting Pb films in the regime where ${T}_{c}$ varies with sheet resistance. The energy gap $\ensuremath{\Delta}$ and strong-coupling corrections to density of states been measured as functions resistance ${R}_{\ensuremath{\square}}$. conclude that standard picture enhanced Coulomb repulsion increasing is too naive that, presence disorder, an analysis more sophisticated than Eliashberg theory necessary.
We have measured the pinning force due to twin boundaries by measuring magnetic torque produced when a field is applied perpendicular c axis and rotated with respect ab axes. At 76 K, increases roughly fourfold, within 2° of parallel boundaries. This peak absent at 27 K. Irradiation 5×1016 cm−2 3.5 MeV protons overall critical current eliminates peaks observed
The critical currents in high quality thin films of the Tc superconductor, YBa2Cu3O7−δ, can be controllably reduced by orders magnitude using ion irradiation. This reduction current occurs without substantial decrease or increase room-temperature resistivity. Using this technique, we have fabricated weak links that exhibit an ac Josephson effect at 77 K.
We have explored the effects of ion beam irradiation on electrical and structural properties superconducting thin films ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. Damage created by nuclear-energy loss processes degrades transitions. Data from resistance measurements as well Rutherford backscattering channeling suggest that bombardment is not changing volume fraction material substantially. Instead, it appears islands good...
We demonstrate a compact fully tunable narrowband fourth-order pole-zero optical filter that is fabricated in silicon complementary-metal-oxide-semiconductor foundry. The implemented using on oxide channel waveguides and consists of Mach-Zehnder interferometer with two ring resonator all-pass filters (APFs) each arm. architecture based the sum difference APFs responses. resonators introduce nonlinear phase response arm allows carving narrow frequency bands out broad spectrum. In this paper,...
Irradiation with 3.5 MeV protons creates defects in Ba2YCu3O7−δ, which can act as strong pinning sites, comparable to those produced by neutron irradiation. Indeed well neutrons undergo momentum-transferring collisions that result atomic displacements; the additional electronic proton-solid interaction does not appear yield contribute pinning. Under optimized conditions we have obtained Jc(T→0, H=1 T)∼2×107 A/cm2 single crystals. At 77 K value is still Jc∼1.7×105 A/cm2, decreasing only...
An RF-photonic filter and down-converter system based on a compact fully tunable silicon optical has been demonstrated analyzed. Its frequency down-conversion was implemented using heterodyne detection with an injection locked laser. This filters 1.25 GHz-wide signal > 20 dB rejection very broad GHz center tuning range. The process is operated in low-IF mode to avoid laser low noises. Measured Spurious-Free Dynamic Range (SFDR) of 94.3 dB*Hz <sup...
Objective. Most preparations for making neural recordings degrade over time and eventually fail due to insertion trauma reactive tissue response. The magnitudes of these responses are thought be related the electrode size (specifically, cross-sectional area), relative stiffness electrode, degree tolerance material. Flexible carbon fiber ultra-microelectrodes have a much smaller cross-section than traditional electrodes low reactivity, thus may enable improved longevity in central peripheral...
Objective. The vision of bioelectronic medicine is to treat disease by modulating the signaling visceral nerves near various end organs. In small animal models, interest can have diameters and limited surgical access. New high-resolution methods for building nerve interfaces are desirable. this study, we present a novel interface demonstrate its use stimulation recording in nerves. Approach. We design fabricate micro-scale electrode-laden nanoclips capable interfacing with as 50 µm diameter....
Abstract Direct laser writing (DLW) is an advanced fabrication technique that allows users to create complex 3D microstructures from polymer precursors. These can be integrated with micro‐electromechanical systems (MEMS) actuators. MEMS actuators provide a convenient platform for interacting the intricate microstructures, either characterize their mechanical properties or cause them deform. Structures are fabricated directly onto electrostatic comb drives and chevron thermal produced using...