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Applied Physics Letters

Alok Ghanekar, Matthew Ricci, Yanpei Tian, Otto Gregory, Yi Zheng
In this theoretical study, we present a near-field thermal modulator that exhibits change in radiative heat transfer when subjected to mechanical stress/strain. The device has two terminals at different temperatures separated by vacuum: one fixed and one stretchable. The stretchable side contains one-dimensional grating. When subjected to mechanical strain, the effective optical properties of the stretchable side are affected upon deformation of the grating. This results in modulation of surface waves across the interfaces influencing near-field radiative heat transfer...
June 11, 2018: Applied Physics Letters
Eitan Edrei, Giuliano Scarcelli
Brillouin spectroscopy is a powerful optical technique for non-contact viscoelastic characterizations which has recently found applications in three-dimensional mapping of biological samples. Brillouin spectroscopy performances are rapidly degraded by optical aberrations and have therefore been limited to homogenous transparent samples. In this work, we developed an adaptive optics (AO) configuration designed for Brillouin scattering spectroscopy to engineer the incident wavefront and correct for aberrations...
April 16, 2018: Applied Physics Letters
Jordan S Lum, David M Stobbe, Mark A Borden, Todd W Murray
Phospholipid-coated microbubbles are being developed for several biomedical applications, but little is known about the effect of temperature on the viscoelastic properties of the shell. Here, we report on the use of a photoacoustic technique to study the shell properties of individual microbubbles as a function of temperature. The microbubbles were driven into small-amplitude oscillations by ultrasound waves generated from the absorption of an intensity-modulated infrared laser, and these oscillations were detected by forward-light scattering of a second blue laser...
March 12, 2018: Applied Physics Letters
Shuaa Alotaibi, Joshua Samba, Sabin Pokharel, Yucheng Lan, Kelechi Uradu, Ayodeji Afolabi, Ilyas Unlu, Gobind Basnet, Kadir Aslan, Bret N Flanders, Abdellah Lisfi, Birol Ozturk
AC electric fields were utilized in the growth of individual high-aspect ratio cobalt nanowires from simple salt solutions using the Directed Electrochemical Nanowire Assembly method. Nanowire diameters were tuned from the submicron scale to 40 nm by adjusting the AC voltage frequency and the growth solution concentration. The structural properties of the nanowires, including shape and crystallinity, were identified using electron microscopy. Hysteresis loops obtained along different directions of an individual nanowire using vibrating sample magnetometry showed that the magnetocrystalline anisotropy energy has the same order of magnitude as the shape anisotropy energy...
February 26, 2018: Applied Physics Letters
Brennan Mace, Zach Harrell, Chonglin Chen, Erik Enriquez, Aiping Chen, Quanxi Jia
The role of temperature and the oxygen content in the structural transformation and electrical conductivity of epitaxial double perovskite LaBaCo2 O5+δ (0≤ δ ≤ 1) thin films was systematically investigated. Reciprocal space mapping and ω-2θ x-ray diffraction performed at different temperatures in vacuum indicate that oxygen vacancies in the films become ordered at high temperature in a reducing environment. The changes of the oxygen content and the degree of oxygen vacancy ordering in the films result in a strong in-plane anisotropic lattice deformation and a large thermal expansion coefficient along the c-axis direction...
February 12, 2018: Applied Physics Letters
Fan Xiao, Ximiao Wen, Xing Haw Marvin Tan, Pei-Yu Chiou
A plasmonic micropillar platform with self-organized gold nanospheres is reported for the precision cell traction force measurement across a large field-of-view (FOV). Gold nanospheres were implanted into the tips of polymer micropillars by annealing gold microdisks with nanosecond laser pulses. Each gold nanosphere is physically anchored in the center of a pillar tip and serves as a strong, point-source-like light scattering center for each micropillar. This allows a micropillar to be clearly observed and precisely tracked even under a low magnification objective lens for the concurrent and precision measurement across a large FOV...
January 15, 2018: Applied Physics Letters
Zachary A Steelman, Andrew C Weems, Andrew J Traverso, Jason M Szafron, Duncan J Maitland, Vladislav V Yakovlev
Emerging medical devices which employ shape memory polymers (SMPs) require precise measurements of the glass transition temperature (Tg ) to ensure highly controlled shape recovery kinetics. Conventional techniques like differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) have limitations that prevent utilization for certain devices, including limited accuracy and the need for sacrificial samples. In this report, we employ an approach based on Brillouin spectroscopy to probe the glass transition of SMPs rapidly, remotely, and nondestructively...
December 11, 2017: Applied Physics Letters
Emilio A Nanni, Sudheer Jawla, Samantha M Lewis, Michael A Shapiro, Richard J Temkin
We report the amplification of 250 GHz pulses as short as 260 ps without observation of pulse broadening using a photonic-band-gap circuit gyrotron traveling-wave-amplifier. The gyrotron amplifier operates with a device gain of 38 dB and an instantaneous bandwidth of 8 GHz. The operational bandwidth of the amplifier can be tuned over 16 GHz by adjusting the operating voltage of the electron beam and the magnetic field. The amplifier uses a 30 cm long photonic-band-gap interaction circuit to confine the desired TE03 -like operating mode while suppressing lower order modes which can result in undesired oscillations...
December 4, 2017: Applied Physics Letters
B Dober, D T Becker, D A Bennett, S A Bryan, S M Duff, J D Gard, J P Hays-Wehle, G C Hilton, J Hubmayr, J A B Mates, C D Reintsema, L R Vale, J N Ullom
Key performance characteristics are demonstrated for the microwave SQUID multiplexer (µmux) coupled to transition edge sensor (TES) bolometers that have been optimized for cosmic microwave background (CMB) observations. In a 64-channel demonstration, we show that the µmux produces a white, input referred current noise level of [Formula: see text] at -77 dB microwave probe tone power, which is well below expected fundamental detector and photon noise sources for a ground-based CMB-optimized bolometer. Operated with negligible photon loading, we measure [Formula: see text] in the TES-coupled channels biased at 65% of the sensor normal resistance...
December 2017: Applied Physics Letters
Ashton S Hemphill, Yuecheng Shen, Yan Liu, Lihong V Wang
In biological applications, optical focusing is limited by the diffusion of light, which prevents focusing at depths greater than ∼1 mm in soft tissue. Wavefront shaping extends the depth by compensating for phase distortions induced by scattering and thus allows for focusing light through biological tissue beyond the optical diffusion limit by using constructive interference. However, due to physiological motion, light scattering in tissue is deterministic only within a brief speckle correlation time. In in vivo tissue, this speckle correlation time is on the order of milliseconds, and so the wavefront must be optimized within this brief period...
November 27, 2017: Applied Physics Letters
Jiamiao Yang, Yuecheng Shen, Yan Liu, Ashton S Hemphill, Lihong V Wang
Optical scattering prevents light from being focused through thick biological tissue at depths greater than ∼1 mm. To break this optical diffusion limit, digital optical phase conjugation (DOPC) based wavefront shaping techniques are being actively developed. Previous DOPC systems employed spatial light modulators that modulated either the phase or the amplitude of the conjugate light field. Here, we achieve optical focusing through scattering media by using polarization modulation based generalized DOPC...
November 13, 2017: Applied Physics Letters
Jiang Zhu, Buyun Zhang, Li Qi, Ling Wang, Qiang Yang, Zhuqing Zhu, Tiancheng Huo, Zhongping Chen
Incorporating different data processing methods, optical coherence tomography (OCT) has the ability for high-resolution angiography and quantitative flow velocity measurements. However, OCT angiography cannot provide quantitative information of flow velocities, and the velocity measurement based on Doppler OCT requires the determination of Doppler angles, which is a challenge in a complex vascular network. In this study, we report on a relative standard deviation OCT (RSD-OCT) method which provides both vascular network mapping and quantitative information for flow velocities within a wide range of Doppler angles...
October 30, 2017: Applied Physics Letters
Lawrence H Friedman, Wen-Li Wu, Wei-En Fu, Yunsan Chien
Features sizes in integrated circuits (ICs) are often at the scale of 10 nm and are ever shrinking. ICs appearing in today's computers and hand held devices are perhaps the most prominent examples. These smaller feature sizes demand equivalent advances in fast and accurate dimensional metrology for both development and manufacturing. Techniques in use and continuing to be developed include X-ray based techniques, optical scattering and of course the electron and scanning probe microscopy techniques. Each of these techniques have their advantages and limitations...
September 2017: Applied Physics Letters
Sushruta Surappa, Sarp Satir, F Levent Degertekin
A capacitive ultrasonic transducer based on a parametric resonator structure is described and experimentally demonstrated. The transducer structure, which we call capacitive parametric ultrasonic transducer (CPUT), uses a parallel plate capacitor with a movable membrane as part of a degenerate parametric series RLC resonator circuit with a resonance frequency of fo. When the capacitor plate is driven with an incident harmonic ultrasonic wave at the pump frequency of 2fo with sufficient amplitude, the RLC circuit becomes unstable and ultrasonic energy can be efficiently converted to an electrical signal at fo frequency in the RLC circuit...
July 24, 2017: Applied Physics Letters
Abul K Azad, Anatoly V Efimov, Shuprio Ghosh, John Singleton, Antoinette J Taylor, Hou-Tong Chen
We demonstrate a metasurface-based ultrathin flat lens operating at microwave frequencies. A series of subwavelength metallic split-ring resonators, which are sandwiched between two cross-polarized metallic gratings, are defined to obtain a radially symmetric parabolic phase distribution, covering relative phase differences ranging from 0 to 2.5π radians to create a lens. The tri-layer lens exhibits focusing/collimating of broadband microwaves from 7.0 to 10.0 GHz, with a gain enhancement of 17 dBi at a central wavelength 9...
May 29, 2017: Applied Physics Letters
Francisco J Pedraza, Chris Rightsell, G A Kumar, Jason Giuliani, Carlos Monton, Dhiraj K Sardar
The growing need for biomedical contrast agents has led to the current development of multi-functional materials such as lanthanide-based nanoparticles (NPs). The optical and magnetic properties these nanoparticles (NPs) possess are important to enhance current biomedical imaging techniques. To increase the optical emissions of the nanoparticles, neodymium (Nd3+ ) and ytterbium (Yb3+ ) were introduced into a magnetic host of NaGdF4 . The energy transfer between Nd3+ and the Yb3+ was then investigated at multiple concentrations to determine the optimal dopant levels...
May 29, 2017: Applied Physics Letters
Taesoo Kim, Elenita Palmiano, Ru-Ze Liang, Hanlin Hu, Banavoth Murali, Ahmad R Kirmani, Yuliar Firdaus, Yangqin Gao, Arif Sheikh, Mingjian Yuan, Omar F Mohammed, Sjoerd Hoogland, Pierre M Beaujuge, Edward H Sargent, Aram Amassian
Monolithically integrated hybrid tandem solar cells that effectively combine solution-processed colloidal quantum dot (CQD) and organic bulk heterojunction subcells to achieve tandem performance that surpasses the individual subcell efficiencies have not been demonstrated to date. In this work, we demonstrate hybrid tandem cells with a low bandgap PbS CQD subcell harvesting the visible and near-infrared photons and a polymer:fullerene-poly (diketopyrrolopyrrole-terthiophene) (PDPP3T):[6,6]-phenyl-C60 -butyric acid methyl ester (PC61 BM)-top cell absorbing effectively the red and near-infrared photons of the solar spectrum in a complementary fashion...
May 29, 2017: Applied Physics Letters
Radhika K Poduval, Sacha Noimark, Richard J Colchester, Thomas J Macdonald, Ivan P Parkin, Adrien E Desjardins, Ioannis Papakonstantinou
All-optical ultrasound transducers are promising for imaging applications in minimally invasive surgery. In these devices, ultrasound is transmitted and received through laser modulation, and they can be readily miniaturized using optical fibers for light delivery. Here, we report optical ultrasound transmitters fabricated by electrospinning an absorbing polymer composite directly onto the end-face of optical fibers. The composite coating consisting of an aqueous dispersion of multi-walled carbon nanotubes (MWCNTs) in polyvinyl alcohol was directly electrospun onto the cleaved surface of a multimode optical fiber and subsequently dip-coated with polydimethylsiloxane (PDMS)...
May 29, 2017: Applied Physics Letters
David Cooper, Nicolas Bernier, Jean-Luc Rouvière, Yun-Yu Wang, Weihao Weng, Anita Madan, Shogo Mochizuki, Hemanth Jagannathan
Precession electron diffraction has been used to systematically measure the deformation in Si/SiGe blanket films and patterned finFET test structures grown on silicon-on-insulator type wafers. Deformation maps have been obtained with a spatial resolution of 2.0 nm and a precision of ±0.025%. The measured deformation by precession diffraction for the blanket films has been validated by comparison to energy dispersive x-ray spectrometry, X-Ray diffraction, and finite element simulations. We show that although the blanket films remain biaxially strained, the patterned fin structures are fully relaxed in the crystallographic planes that have been investigated...
May 29, 2017: Applied Physics Letters
Nanxi Li, Zhan Su, Purnawirman, E Salih Magden, Christopher V Poulton, Alfonso Ruocco, Neetesh Singh, Matthew J Byrd, Jonathan D B Bradley, Gerald Leake, Michael R Watts
In an optical interconnect circuit, microring resonators (MRRs) are commonly used in wavelength division multiplexing systems. To make the MRR and laser synchronized, the resonance wavelength of the MRR needs to be thermally controlled, and the power consumption becomes significant with a high-channel count. Here, we demonstrate an athermally synchronized rare-earth-doped laser and MRR. The laser comprises a Si3N4 based cavity covered with erbium-doped Al2O3 to provide gain. The low thermo-optic coefficient of Al2O3 and Si3N4 and the comparable thermal shift of the effective index in the laser and microring cross-sections enable lasing and resonance wavelength synchronization over a wide range of temperatures...
May 22, 2017: Applied Physics Letters
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