480 results match your criteria Applied Physics Letters[Journal]

A laboratory-based, low-energy, multi-modal x-ray microscope with user-defined resolution.

Appl Phys Lett 2022 Jun 8;120(23):234101. Epub 2022 Jun 8.

Department of Medical Physics and Biomedical Engineering, University College London, Malet Place, Gower Street, London WC1E 6BT, United Kingdom.

We report on the development of a low-energy x-ray phase-based microscope using intensity-modulation masks for single-shot retrieval of three contrast channels: transmission, refraction, and ultra-small-angle scattering or dark field. The retrieval method is based on beam tracking, an incoherent and phase-based imaging approach. We demonstrate that the spatial resolution of this imaging system does not depend on focal spot size nor detector pixel pitch, as opposed to conventional and propagation-based x-ray imaging, and it is only dependent on the mask aperture size. Read More

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Trench field-effect transistors integrated in a microfluidic channel and design considerations for charge detection.

Appl Phys Lett 2022 May 13;120(19):192102. Epub 2022 May 13.

Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.

Field-effect transistors (FETs) combined with a microfluidic system allow for the electrical detection of charged materials moving in a microfluidic channel. Here, we demonstrate trench-shaped silicon FETs with the combination of a microfluidic channel that can be used for simultaneous electrical and optical detection of charged fluorescent beads. The n-channel silicon trench FETs have a maximum transconductance of 1. Read More

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Broadband terahertz time-domain polarimetry based on air plasma filament emissions and spinning electro-optic sampling in GaP.

Appl Phys Lett 2022 May 3;120(18):181107. Epub 2022 May 3.

Department of Biomedical Engineering, State University of New York at Stony Brook, Stony Brook, New York 11794, USA.

We report on a time-domain polarimetry (TDP) system for generating and detecting broadband terahertz (THz) waves of different polarization angles. We generate THz waves from two-color laser filaments and determine their polarization states with a detection bandwidth of up to 8 THz using a spinning gallium phosphide crystal. The polarization of THz emission can be controlled by adjusting the position and tilt angle of the β-barium borate crystal. Read More

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Interactions and non-magnetic fractional quantization in one-dimension.

S Kumar M Pepper

Appl Phys Lett 2021 Sep 15;119(11):110502. Epub 2021 Sep 15.

Department of Electronic and Electrical Engineering, UCL, Torrington Place, London WC1E 7JE, United Kingdom and London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom.

In this Perspective article, we present recent developments on interaction effects on the carrier transport properties of one-dimensional (1D) semiconductor quantum wires fabricated using the GaAs/AlGaAs system, particularly the emergence of the long predicted fractional quantization of conductance in the absence of a magnetic field. Over three decades ago, it was shown that transport through a 1D system leads to integer quantized conductance given by N·2e/h, where N is the number of allowed energy levels (N = 1, 2, 3, …). Recent experiments have shown that a weaker confinement potential and low carrier concentration provide a testbed for electrons strongly interacting. Read More

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September 2021

Strain rate induced toughening of individual collagen fibrils.

Appl Phys Lett 2022 Mar 18;120(11):114101. Epub 2022 Mar 18.

Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

The nonlinear mechanical behavior of individual nanoscale collagen fibrils is governed by molecular stretching and sliding that result in a viscous response, which is still not fully understood. Toward this goal, the mechanical behavior of individual reconstituted mammalian collagen fibrils was quantified in a broad range of strain-rates, spanning roughly six orders of magnitude, from 10 to 35 s. It is shown that the nonlinear mechanical response is strain rate sensitive with the tangent modulus in the linear deformation regime increasing monotonically from 214 ± 8 to 358 ± 11 MPa. Read More

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Distinctive ionic transport of freshly excised human epileptogenic brain tissue.

Appl Phys Lett 2021 Dec;119(25):253701

Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA.

Epileptogenic lesions have higher concentrations of sodium than does normal brain tissue. Such lesions are palpably recognized by a surgeon and then excised in order to eliminate epileptic seizures with their associated abnormal electrical behavior. Here, we study the frequency-dependent electrical conductivities of lesion-laden tissues excised from the brains of epilepsy patients. Read More

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December 2021

Synthetic aperture interference light (SAIL) microscopy for high-throughput label-free imaging.

Appl Phys Lett 2021 Dec 8;119(23):233701. Epub 2021 Dec 8.

Quantitative phase imaging (QPI) is a valuable label-free modality that has gained significant interest due to its wide potentials, from basic biology to clinical applications. Most existing QPI systems measure microscopic objects via interferometry or nonlinear iterative phase reconstructions from intensity measurements. However, all imaging systems compromise spatial resolution for the field of view and vice versa, i. Read More

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December 2021

Low-noise photon counting above 100 million counts per second with a high-efficiency reach-through single-photon avalanche diode system.

Appl Phys Lett 2021 ;118(13)

Joint Quantum Institute, National Institute of Standards and Technology and University of Maryland, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.

We demonstrate a method that allows a high-efficiency single-photon-avalanche diode (SPAD) with a thick absorption region (> 10 μm) to count single photons at rates significantly higher than previously demonstrated. We apply large (> 30 V) AC bias gates to the SPAD at 1 GHz and detect minute avalanches with a discrimination threshold of 5(1) mV by means of radio-frequency (RF) interferometry. We measure a reduction by a factor of ≈ 500 in the average charge per avalanche when compared to operation in its traditional active-quenching module, and a relative increase of >19 % in detection efficiency at 850 nm. Read More

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January 2021

X-ray-induced acoustic computed tomography (XACT) imaging with single-shot nanosecond x-ray.

Appl Phys Lett 2021 Nov 2;119(18):183702. Epub 2021 Nov 2.

The Department of Radiological Sciences, University of California, Irvine, California 92617, USA.

X-ray-induced acoustic computed tomography (XACT) has emerged as a promising imaging modality with broad applications in both biomedicine and nondestructive testing. The previous XACT imaging systems require thousands of averages to achieve reasonable images. Here, we report the experimental demonstration of single-shot XACT imaging of a metal object using a single-shot 50 ns x-ray pulse. Read More

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November 2021

Disinfection of in ice by surface dielectric barrier discharge plasma.

Appl Phys Lett 2021 Aug;119(9):090601

NHC Key Laboratory of Biosafety, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing 102206, China.

A variety of pathogens can cause people to suffer from serious diseases, and the transmission of COVID-19 through the cold chain has once again attracted people's attention to cold chain disinfection. Unfortunately, there is no mature cold chain disinfection technique yet. In this study, a low-temperature plasma disinfection technique for a cold chain is proposed. Read More

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Constant amplitude driving of a radiofrequency excited plasmonic tunnel junction.

Appl Phys Lett 2021 May 11;118(19). Epub 2021 May 11.

Institute of Physics, Czech Academy of Sciences, Cukrovarnická 10/112, CZ16200 Praha 6, Czech Republic.

Constant-amplitude bias modulation over a broad range of microwave frequencies is a prerequisite for application in high-resolution spectroscopic techniques in a tunneling junction as e.g. electron spin resonance spectroscopy or optically detected paramagnetic resonance. Read More

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Ultrafast amplitude modulation for molecular and hemodynamic ultrasound imaging.

Appl Phys Lett 2021 Jun;118(24):244102

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.

Ultrasound is playing an emerging role in molecular and cellular imaging thanks to new micro- and nanoscale contrast agents and reporter genes. Acoustic methods for the selective detection of these imaging agents are needed to maximize their impact in biology and medicine. Existing ultrasound pulse sequences use the nonlinearity in contrast agents' response to acoustic pressure to distinguish them from mostly linear tissue scattering. Read More

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Measurements of acoustic radiation force of ultrahigh frequency ultrasonic transducers using model-based approach.

Appl Phys Lett 2021 May;118(18):184102

Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA.

Even though ultrahigh frequency ultrasonic transducers over 60 MHz have been used for single-cell-level manipulation such as intracellular delivery, acoustic tweezers, and stimulation to investigate cell phenotype and cell mechanics, no techniques have been available to measure the actual acoustic radiation force (ARF) applied to target cells. Therefore, we have developed an approach to measure the ARF of ultrahigh frequency ultrasonic transducers using a theoretical model of the dynamics of a solid sphere in a gelatin phantom. To estimate ARF at the focus of a 130 MHz transducer, we matched measured maximum displacements of a solid sphere with theoretical calculations. Read More

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Optical coherence viscometry.

Appl Phys Lett 2021 Apr 20;118(16):164102. Epub 2021 Apr 20.

Department of Radiology, Mayo Clinic, Rochester, Minnesota 55905, USA.

We report a technique, named optical coherence viscometry (OCV), to measure the viscosity of Newtonian fluids in a noncontact manner. According to linear wave theory with small amplitudes, capillary waves are associated with fluid mechanical properties. To perform this measurement and avoid the overdamped effects of capillary waves in viscous fluids, transient acoustic radiation force was applied to generate capillary waves. Read More

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Ultrasound differential phase contrast using backscattering and the memory effect.

Appl Phys Lett 2021 Mar 26;118(12):124103. Epub 2021 Mar 26.

Department of Biomedical Engineering, Boston University, Boston Massachusetts 02215, USA.

We describe a simple and fast technique to perform ultrasound differential phase contrast (DPC) imaging in arbitrarily thick scattering media. Although configured in a reflection geometry, DPC is based on transmission imaging and is a direct analog of optical differential interference contrast. DPC exploits the memory effect and works in combination with standard pulse-echo imaging, with no additional hardware or data requirements, enabling complementary phase contrast (in the transverse direction) without any need for intensive numerical computation. Read More

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High-speed label-free two-photon fluorescence microscopy of metabolic transients during neuronal activity.

Appl Phys Lett 2021 Feb 23;118(8):081104. Epub 2021 Feb 23.

Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

The brain is an especially active metabolic system, requiring a large supply of energy following neuronal activation. However, direct observation of cellular metabolic dynamics associated with neuronal activation is challenging with currently available imaging tools. In this study, an optical imaging approach combining imaging of calcium transients and the metabolic co-enzyme nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) is utilized to track the metabolic dynamics in hippocampal neuron cultures. Read More

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February 2021

Ultra-compact visible light depolarizer based on dielectric metasurface.

Appl Phys Lett 2020 4;116(5):0511031-511035. Epub 2020 Feb 4.

National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University 210093, China.

With rapid development towards shrinking the size of traditional photonic systems such as cameras, spectrometers, displays and illumination systems, there is an urgent need for high performance and ultra-compact functional optical elements. The large footprint of traditional bulky optical elements, their monofunctional response and the inability for direct integration into nanophotonic devices have severely limited progress in this area. Metasurfaces, consisting of an array of subwavelength nanoscatterers with spatially varying geometries, have shown remarkable performance as ultrathin multifunctional optical elements. Read More

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February 2020

The effect of surface roughness on laser-induced stress wave propagation.

Appl Phys Lett 2020 Sep 24;117(12):121601. Epub 2020 Sep 24.

Department of Mechanical Engineering, University of Kentucky, Lexington, Kentucky 40506, USA.

We investigate laser-induced acoustic wave propagation through smooth and roughened titanium-coated glass substrates. Acoustic waves are generated in a controlled manner via the laser spallation technique. Surface displacements are measured during stress wave loading by the alignment of a Michelson-type interferometer. Read More

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September 2020

Nonlinear losses in magnon transport due to four-magnon scattering.

Appl Phys Lett 2020 ;117(4)

Institut für Ionenstrahlphysik und Materialforschung, Helmholtz-Zentrum Dresden-Rossendorf, D-01328 Dresden, Germany.

We report on the impact of nonlinear four-magnon scattering on magnon transport in microstructured CoFe waveguides with low magnetic damping. We determine the magnon propagation length with microfocused Brillouin light scattering over a broad range of excitation powers and detect a decrease of the attenuation length at high powers. This is consistent with the onset of nonlinear four-magnon scattering. Read More

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January 2020

Ultraminiature AlN diaphragm acoustic transducer.

Appl Phys Lett 2020 Oct;117(14):143504

Singular Medical USA, Irvine, California 92614, USA.

Piezoelectric acoustic transducers consisting of a circular aluminum nitride and silicon nitride unimorph diaphragm and an encapsulated air-filled back cavity are reported. Analytical and finite element analysis models are used to design the transducer to achieve low minimum detectable pressure (MDP) within chosen size restrictions. A series of transducers with varying radii are fabricated using microelectromechanical systems (MEMS) techniques. Read More

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October 2020

Enhancing sensitivity of lateral flow assay with application to SARS-CoV-2.

Appl Phys Lett 2020 Sep;117(12):120601

Texas A&M University, College Station, Texas 77843, USA.

Lateral flow assay (LFA) has long been used as a biomarker detection technique. It has advantages such as low cost, rapid readout, portability, and ease of use. However, its qualitative readout process and lack of sensitivity are limiting factors. Read More

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September 2020

A predictive model of the temperature-dependent inactivation of coronaviruses.

Appl Phys Lett 2020 Aug;117(6):060601

Department of Mechanical Engineering, Rice University, 6100 Main Street, Houston, Texas 77005, USA.

The COVID-19 pandemic has stressed healthcare systems and supply lines, forcing medical doctors to risk infection by decontaminating and reusing single-use personal protective equipment. The uncertain future of the pandemic is compounded by limited data on the ability of the responsible virus, SARS-CoV-2, to survive across various climates, preventing epidemiologists from accurately modeling its spread. However, a detailed thermodynamic analysis of experimental data on the inactivation of SARS-CoV-2 and related coronaviruses can enable a fundamental understanding of their thermal degradation that will help model the COVID-19 pandemic and mitigate future outbreaks. Read More

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Transcranial focused ultrasound generates skull-conducted shear waves: Computational model and implications for neuromodulation.

Appl Phys Lett 2020 Jul 24;117(3):033702. Epub 2020 Jul 24.

Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91125, USA.

Focused ultrasound (FUS) is an established technique for non-invasive surgery and has recently attracted considerable attention as a potential method for non-invasive neuromodulation. While the pressure waves in FUS procedures have been extensively studied in this context, the accompanying shear waves are often neglected due to the relatively high shear compliance of soft tissues. However, in bony structures such as the skull, acoustic pressure can also induce significant shear waves that could propagate outside the ultrasound focus. Read More

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Silicon carbide zipper photonic crystal optomechanical cavities.

Appl Phys Lett 2020 Jun 3;116(22):221104. Epub 2020 Jun 3.

Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York 14627, USA.

We demonstrate a silicon carbide (SiC) zipper photonic crystal optomechanical cavity. The device is on a 3C-SiC-on-silicon platform and has a compact footprint of ∼30 × 1 m. The device shows an optical quality of 2800 at telecom and a mechanical quality of 9700 at 12 MHz with an effective mass of ∼3. Read More

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Upper limit for angular compounding speckle reduction.

Appl Phys Lett 2019 May 28;114(21):211101. Epub 2019 May 28.

Angular compounding is a technique for reducing speckle noise in optical coherence tomography that is claimed to significantly improve the signal-to-noise ratio (SNR) of images without impairing their spatial resolution. Here, we examine how focal point movements caused by optical aberrations in an angular compounding system may produce unintended spatial averaging and concomitant loss of spatial resolution. Experimentally, we accounted for such aberrations by aligning our system and measuring distortions in images and found that when the distortions were corrected, the speckle reduction by angular compounding was limited. Read More

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Perspectives on high resolution microvascular imaging with contrast ultrasound.

Appl Phys Lett 2020 May;116(21):210501

The Joint Department of Biomedical Engineering, The University of North Carolina at Chapel Hill and North Carolina State University, Campus Box 7575, Chapel Hill, North Carolina 27599, USA.

Recent developments in contrast enhanced ultrasound have demonstrated a potential to visualize small blood vessels , unlike anything possible with traditional grayscale ultrasound. This Perspective article introduces microvascular imaging strategies and their underlying technology. Read More

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Changes in microbubble dynamics upon adhesion to a solid surface.

Appl Phys Lett 2020 Mar 24;116(12):123703. Epub 2020 Mar 24.

Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, USA.

The interaction between an acoustically driven microbubble and a surface is of interest for a variety of applications, such as ultrasound imaging and therapy. Prior investigations have mainly focused on acoustic effects of a rigid boundary, where it was generally observed that the wall increases inertia and reduces the microbubble resonance frequency. Here we investigate the response of a lipid-coated microbubble adherent to a rigid wall. Read More

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Super-shear evanescent waves for non-contact elastography of soft tissues.

Appl Phys Lett 2019 Aug 21;115(8):083701. Epub 2019 Aug 21.

Department of Bioengineering, University of Washington, Seattle, Washington 98195, USA.

We describe surface wave propagation in soft elastic media at speeds exceeding the bulk shear wave speed. By linking these waves to the elastodynamic Green's function, we derive a simple relationship to quantify the elasticity of a soft medium from the speed of this supershear evanescent wave (SEW). We experimentally probe SEW propagation in tissue-mimicking phantoms, human cornea , and skin using a high-speed optical coherence elastography system. Read More

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Engineering the gain-bandwidth product of phototransistor diodes.

Appl Phys Lett 2019 Jul 30;115(5):051104. Epub 2019 Jul 30.

Bio-Inspired Sensors and Optoelectronics Laboratory, Northwestern University, 2145 Sheridan Rd, Evanston, Illinois 60208, USA.

In recent years, phototransistors have considerably expanded their field of application, including for instance heterodyne detection and optical interconnects. Unlike in low-light imaging, some of these applications require fast photodetectors that can operate in relatively high light levels. Since the gain and bandwidth of phototransistors are not constant across different optical powers, the devices that have been optimized for operation in low light level cannot effectively be employed in different technological applications. Read More

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Viscoelastic second normal stress difference dominated multiple-stream particle focusing in microfluidic channels.

Appl Phys Lett 2019 Dec 24;115(26):263702. Epub 2019 Dec 24.

Center of Excellence for Biomedical Microfluidics, Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah 84112, USA.

Particle focusing in viscoelastic fluid flow is a promising approach for inducing particle separations in microfluidic devices. The results from theoretical studies indicated that multiple stream particle focusing can be realized with a large magnitude of the elastic second normal stress difference (N). For dilute polymer solutions, theoretical and experimental studies show that the magnitude of N is never large, no matter how large the polymer molecular weight nor how high the shear rate. Read More

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December 2019