Applied Physics Letters

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 in vitro mechanical behavior of individual reconstituted mammalian collagen fibrils was quantified in a broad range of strain-rates, spanning roughly six orders of magnitude, from 10-4 to 35 s-1 . 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...

Hyperspectral electroluminescence and photoluminescence imaging of photovoltaic materials and devices produces three-dimensional spatially and spectrally resolved luminescence data, which can be calibrated to an absolute scale, enabling the extraction of high resolution maps of quantities such as the local voltage (quasi-Fermi-level splitting). This extraction requires supplemental measurements of external quantum efficiency (EQE), but these do not have the same spatial resolution. Previously, assumptions have been made to overcome this limitation...

We have investigated the magnetic correlations among 7 nm iron oxide nanoparticles embedded in stretched silicone elastomers using polarized Small Angle Neutron Scattering (SANS). The magnetic nanoparticle (MNP)-elastomer composite can be stretched during experiments, and macroscopic deformations cause rearrangement of the iron oxide particles on the nanoscale. Polarized neutrons can be used to nondestructively probe the arrangement of magnetic nanoparticles before and after stretching, so that the relationship between applied stress and nanoscale magnetization can be interrogated...

Characterization of the magnetization dynamics of single-domain magnetic nanoparticles (MNPs) is important for magnetic particle imaging (MPI), magnetic resonance imaging (MRI), and emerging medical diagnostic/therapeutic technologies. Depending on particle size and temperature, nanoparticle magnetization relaxation time constants span from nanoseconds to seconds. In solution, relaxation occurs via coupled Brownian and Néel relaxation mechanisms. Even though their coexistence complicates analysis, the presence of two timescales presents opportunities for more direct control of magnetization behavior if the two processes can be understood, isolated, and tuned...

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. The low-frequency (<1000 Hz) conductivity of biological tissue primarily probes extracellular solvated sodium-cations traveling parallel to membranes within regions bounded by blockages...

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.e., suffer from a limited space bandwidth product. Current solutions to this problem involve computational phase retrieval algorithms, which are time-consuming and often suffer from convergence problems...

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. A two-stage dedicated amplification and a 128-channel parallel data acquisition configuration were introduced for XACT imaging to enable sufficient acoustic signal amplification and maintain an overall low noise level for single-shot XACT imaging...

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·2e2 /h, where N is the number of allowed energy levels (N = 1, 2, 3, …)...

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. The disinfection effect of plasma generated by surface dielectric barrier discharge on Escherichia coli in ice at cryogenic temperature is studied, and the possible disinfection mechanism is discussed...

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 in vivo 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. However, such pulse sequences typically scan the sample using focused transmissions, resulting in a limited frame rate and restricted field of view...

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. Here, we present an optical method for determining the frequency-dependent magnitude of the transfer function of a dedicated high-frequency line integrated with a scanning probe microscope. The method relies on determining the energy cutoff of the plasmonic electroluminescence spectrum, which is linked to the energies of the electrons inelastically tunneling across the junction...

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...

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. Within a very limited field-of-view using optical coherence tomography, wave motion acquired in the time domain was analyzed using Fourier methods to study the wave velocity dispersion and attenuation relationships for capillary waves, which can reduce the fluid quantity drastically into tissue culture scale...

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...

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. Results show distinct cellular components for the NAD(P)H response following neuronal activity, where notable differences in the NAD(P)H dynamics between neurons and astrocytes can be directly observed...

Geometric dispersion in integrated microresonators plays a major role in nonlinear optics applications, especially at short wavelengths, to compensate the natural material normal dispersion. Tailoring of geometric confinement allows for anomalous dispersion, which in particular enables the formation of microcombs which can be tuned into the dissipative Kerr soliton (DKS) regime. Due to processes like soliton-induced dispersive wave generation, broadband DKS combs are particularly sensitive to higher-order dispersion, which in turn is sensitive to the ring dimensions at the nanometer-level...

Transition-edge sensors (TESs) are two-dimensional superconducting films utilized as highly sensitive detectors of energy or power. These detectors are voltage biased in the superconducting-normal transition where the film resistance is both finite and a strong function of temperature. Unfortunately, the amount of electrical noise observed in TESs exceeds the predictions of existing noise theories. We describe a possible mechanism for the unexplained excess noise, which we term "mixed-down noise." The source is Johnson noise, which is mixed down to low frequencies by Josephson oscillations in devices with a nonlinear current-voltage relationship...

Cryogenic operation of complementary metal oxide semiconductor (CMOS) silicon transistors is crucial for quantum information science, but it brings deviations from standard transistor operation. Here, we report on sharp current jumps and stable hysteretic loops in the drain current as a function of gate voltage V G for both n - and p -type commercial-foundry 180-nm-process CMOS transistors when operated at voltages exceeding 1.3 V at cryogenic temperatures. The physical mechanism responsible for the device bistability is impact ionization charging of the transistor body, which leads to effective back-gating of the inversion channel...

We demonstrate the electrical detection of magnon-magnon hybrid dynamics in yttrium iron garnet/permalloy (YIG/Py) thin film bilayer devices. Direct microwave current injection through the conductive Py layer excites the hybrid dynamics consisting of the uniform mode of Py and the first standing spin wave ( n = 1) mode of YIG, which are coupled via interfacial exchange. Both the two hybrid modes, with Py or YIG dominated excitations, can be detected via the spin rectification signals from the conductive Py layer, providing phase resolution of the coupled dynamics...

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...