Search

A major application of the inversion methods is imaging all types of structural, physical, chemical and biological features of matter. The term vortex beam refers to a beam of electromagnetic radiation, electrons, photons or otherwise - whose phase changes in corkscrew-like manner along the direction of propagation. The paper is devoted to the use of scalar Bessel beams of integer and fractional modes for the reconstruction of scattering potential. In practical applications one naturally deals with Bessel beams truncated in the radial direction. The inversion formula for truncated Bessel beams is also obtained. Instead of the conventional Fourier diffraction theorem (Kak in Principles of computerized tomographic imaging, SIAM, New York, 2001), the relations connecting the scattering field and the scattering potential in the Fourier space are obtained in the explicit form.

We report on the electrical gating of the charge-density-wave phases and current in h-BN-capped three-terminal 1T-TaS2heterostructure devices. It is demonstrated that the application of a gate bias can shift the source–drain current–voltage hysteresis associated with the transition between the nearly commensurate and incommensurate charge-density-wave phases. The evolution of the hysteresis and the presence of abrupt spikes in the current while sweeping the gate voltage suggest that the effect is electrical rather than self-heating. We attribute the gating to an electric-field effect on the commensurate charge-density-wave domains in the atomic planes near the gate dielectric. The transition between the nearly commensurate and incommensurate charge-density-wave phases can be induced by both the source–drain current and the electrostatic gate. Since the charge-density-wave phases are persistent in 1T-TaS2at room temperature, one can envision memory applications of such devices when scaled down to the dimensions of individual commensurate domains and few-atomic plane thicknesses.

The goal of this study is to determine how bulk vibrational properties and interfacial structure affect thermal transport at interfaces in wide band gap semiconductor systems. Time-domain thermoreflectance measurements of thermal conductance Gare reported for interfaces between nitride metals and group IV (diamond, SiC, Si, and Ge) and group III–V (AlN, GaN, and cubic BN) materials. Group IV and group III–V semiconductors have systematic differences in vibrational properties. Similarly, HfN and TiN are also vibrationally distinct from each other. Therefore, comparing Gof interfaces formed from these materials provides a systematic test of how vibrational similarity between two materials affects interfacial transport. For HfN interfaces, we observe conductances between 140 and 300 MW m–2K–1, whereas conductances between 200 and 800 MW m–2K–1are observed for TiN interfaces. TiN forms exceptionally conductive interfaces with GaN, AlN, and diamond, that is, G> 400 MW m–2K–1. Surprisingly, interfaces formed between vibrationally similar and dissimilar materials are similarly conductive. Thus, vibrational similarity between two materials is not a necessary requirement for high G. Instead, the time-domain thermoreflectance experiment (TDTR) data, an analysis of bulk vibrational properties, and transmission electron microscopy (TEM) suggest that Gdepends on two other material properties, namely, the bulk phonon properties of the vibrationally softer of the two materials and the interfacial structure. To determine how Gdepends on interfacial structure, TDTR and TEM measurements were conducted on a series of TiN/AlN samples prepared in different ways. Interfacial disorder at a TiN/AlN interface adds a thermal resistance equivalent to ∼1 nm of amorphous material. Our findings improve fundamental understanding of what material properties are most important for thermally conductive interfaces. They also provide benchmarks for the thermal conductance of interfaces with wide band gap semiconductors.

Hydrogen bonds are fundamental to the structure and function of biological macromolecules and have been explored in detail. The chains of hydrogen bonds (CHBs) and low-barrier hydrogen bonds (LBHBs) were proposed to play essential roles in enzyme catalysis and proton transport. However, high-resolution structural data from CHBs and LBHBs is limited. The challenge is that their ‘visualization’ requires ultrahigh-resolution structures of the ground and functionally important intermediate states to identify proton translocation events and perform their structural assignment. Our true-atomic-resolution structures of the light-driven proton pump bacteriorhodopsin, a model in studies of proton transport, show that CHBs and LBHBs not only serve as proton pathways, but also are indispensable for long-range communications, signaling and proton storage in proteins. The complete picture of CHBs and LBHBs discloses their multifunctional roles in providing protein functions and presents a consistent picture of proton transport and storage resolving long-standing debates and controversies.

We report on the preparation of inks containing fillers derived from quasi-two-dimensional charge-density-wave materials, their application for inkjet printing, and the evaluation of their electronic properties in printed thin-film form. The inks were prepared by liquid-phase exfoliation of CVT-grown 1T-TaS2crystals to produce fillers with nm-scale thickness and μm-scale lateral dimensions. Exfoliated 1T-TaS2was dispersed in a mixture of isopropyl alcohol and ethylene glycol to allow fine-tuning of filler particles thermophysical properties for inkjet printing. The temperature-dependent electrical and current fluctuation measurements of printed thin films demonstrated that the charge-density-wave properties of 1T-TaS2are preserved after processing. The functionality of the printed thin-film devices can be defined by the nearly commensurate to the commensurate charge-density-wave phase transition of individual exfoliated 1T-TaS2filler particles rather than by electron-hopping transport between them. The obtained results are important for the development of printed electronics with diverse functionality achieved by the incorporation of quasi-two-dimensional van der Waals quantum materials.

Older adults are at an increased risk of experiencing gambling harm, which may be due to their use of high‐intensity gambling products such as electronic gambling machines (EGMs). However, little research has explored the motivations behind older adults’ engagement with EGMs, their understanding of the structural characteristics of EGMs, or their perceptions of risk associated with EGM gambling. This paper aims to address this gap in the literature. Focus groups were conducted in Melbourne, Australia with n = 126 adults aged 55+, who had attended a club or pub in the last 12 months. Topics included EGM attitudes and behaviours, structural characteristics of EGMs, and the potential risks associated with EGM gambling. Thematic analysis was used to interpret the data. For most participants, EGM gambling was secondary to their participation in other activities available within venues. Participants identified structural characteristics of EGMs; however, there were some misconceptions about how EGMs operated, including how or why machines paid out. Most participants perceived that they were not at risk of gambling harm because they engaged in “responsible” gambling practices such as setting limits. Older adults often engaged in EGM gambling because of its availability in community‐based venues. Older adults’ perception that they are implementing responsible gambling practices may be increasing their susceptibility to harm. There is a need to reduce the availability and accessibility of EGMs in community settings and develop public education programs that are tailored to the needs of older adults.

Social environments can be challenging for people with intellectual disability. These challenges impact a person’s social inclusion and participation in their communities. Social skills development requires training and practice, but training is often time-limited, costly, and hard to access. However, games on smart speakers provide interesting opportunities to improve training access, motivate self-directed learning, and focus on speech. The authors developed an interactive narrative-based social skills training game for smart-speakers. The game facilitates exploration of the social consequences of making various choices in different social situations and uses natural language inputs. Having tested the game with ten adults with intellectual disability, the authors offer designers insights into participant engagement and the game’s audio-only, natural language interface usability. The authors also propose four design considerations to help designers design applications that help people with intellectual disability participate in social activities.

We report on the investigation of thermal transport in noncured silicone composites with graphene fillers of different lateral dimensions. Graphene fillers are comprised of few-layer graphene flakes with lateral sizes in the range from 400 to 1200 nm and the number of atomic planes from 1 to ∼100. The distribution of the lateral dimensions and thicknesses of graphene fillers has been determined via atomic force microscopy statistics. It was found that in the examined range of the lateral dimensions, the thermal conductivity of the composites increases with increasing size of the graphene fillers. The observed difference in thermal properties can be related to the average grayphonon mean free path in graphene, which has been estimated to be around ∼800 nm at room temperature. The thermal contact resistance of composites with graphene fillers of 1200 nm lateral dimensions was also smaller than that of composites with graphene fillers of 400 nm lateral dimensions. The effects of the filler loading fraction and the filler size on the thermal conductivity of the composites were rationalized within the Kanari model. The obtained results are important for the optimization of graphene fillers for applications in thermal interface materials for heat removal from high-power-density electronics.

We report on the chemical vapor deposition (CVD) growth of quasi-one-dimensional zirconium tritelluride (ZrTe3) at temperatures below 600 °C and process times under an hour, which results in a material on a SiO2/Si wafer substrate that offers electrical conductivity comparable to the bulk. This study combines tailored CVD processing using a tube-in-a-tube technique with characterization by optical microscopy, Raman spectroscopy, and scanning electron microscopy. Transmission electron microscopy validates the composition and offers atomic contrast. Electrical transport measurements employ an yttrium-gold stack to achieve good adhesion and low contact resistance. A positive temperature coefficient is observed, as expected for a metallic material. The obtained results are important for the proposed applications of quasi-one-dimensional van der Waals materials in the next-generation electronic devices.

We report on the fabrication and characterization of electronic devices printed with inks of quasi-one-dimensional (1D) van der Waals materials. The quasi-1D van der Waals materials are characterized by 1D motifs in their crystal structure, which allow for their exfoliation into bundles of atomic chains. The ink was prepared by the liquid-phase exfoliation of crystals of TiS3into quasi-1D nanoribbons dispersed in a mixture of ethanol and ethylene glycol. The temperature-dependent electrical measurements indicate that the electron transport in the printed devices is dominated by the electron hopping mechanisms. The low-frequency electronic noise in the printed devices is of 1/fγ-type with γ ∼ 1 near-room temperature (fis the frequency). The abrupt changes in the temperature dependence of the noise spectral density and γ parameter can be indicative of the phase transition in individual TiS3nanoribbons as well as modifications in the hopping transport regime. The obtained results attest to the potential of quasi-1D van der Waals materials for applications in printed electronics.

We report on the preparation of flexible polymer composite films with aligned metallic fillers composed of atomic chain bundles of quasi-one-dimensional (1D) van der Waals material, tantalum triselenide (TaSe3). The material functionality, embedded at the nanoscale level, is achieved by mimicking the design of an electromagnetic aperture grid antenna. The processed composites employ chemically exfoliated TaSe3nanowires as the grid building blocks incorporated within the thin film. Filler alignment is achieved using the “blade coating” method. Measurements conducted in the X-band frequency range demonstrate that the electromagnetic transmission through such films can be varied significantly by changing the relative orientations of the quasi-1D fillers and the polarization of the electromagnetic wave. We argue that such polarization-sensitive polymer films with unique quasi-1D metallic fillers are applicable to advanced electromagnetic interference shielding in future communication systems.

Recent years have witnessed a much broader use of Brillouin inelastic light-scattering spectroscopy for the investigation of phonons and magnons in novel materials, nanostructures and devices. Driven by the developments in instrumentation and the strong need for accurate knowledge on the energies of elemental excitations, Brillouin–Mandelstam spectroscopy is rapidly becoming an essential technique that is complementary to Raman inelastic light-scattering spectroscopy. We provide an overview of recent progress in the Brillouin light-scattering technique, focusing on the use of this photonic method for the investigation of confined acoustic phonons, phononic metamaterials and magnon propagation and scattering. This Review emphasizes the emerging applications of Brillouin–Mandelstam spectroscopy for phonon-engineered structures and spintronic devices, and concludes with a perspective on future directions.

Background: This study examined the health literacy demands of My Health Record (MyHR) in the context of preparing for a government-announced opt-out system by repeating two studies of health information and usability conducted in 2016.Objective: To examine whether Australia’s MyHR meets the information and usability needs of people at risk of low health literacy and changes since 2016.Method: Content analysis: Informed by the 2016 methods and findings, measures of information quality, themes and target audiences were recorded and reported for each online consumer-facing health information resource. Heuristic evaluation: An evaluation of the MyHR and supporting information website was conducted using a predetermined checklist of usability criteria. A list of usability violations for both websites was identified.Results: Total number of resources grew from 80 in 2016 to 233 in 2018. There was little change since 2016 to average readability levels, target audiences, presentation style, links between resources and usability of MyHR. Compared to 2016, this study demonstrated increases in resources from non-government organisations; video resources; translated resources; and resources with themes of privacy, security and post-registration use.Conclusion: This study identified some improvements in information quality since 2016, but gaps remain in information quality and usability which may negatively impact the ability for people with low health literacy to access and use MyHR.Implications: This study provides a framework for ongoing monitoring and evaluation of the suitability of MyHR for people at risk of low health literacy.

The controlled tunability of superconductivity in low-dimensional materials may enable new quantum devices. Particularly in triplet or topological superconductors, tunneling devices such as Josephson junctions, etc., can demonstrate exotic functionalities. The tunnel barrier, an insulating or normal material layer separating two superconductors, is a key component for the junctions. Thin layers of NbSe2have been shown as a superconductor with strong spin orbit coupling, which can give rise to topological superconductivity if driven by a large magnetic exchange field. Here we demonstrate the superconductor–insulator transitions in epitaxially grown few-layer NbSe2with wafer-scale uniformity on insulating substrates. We provide the electrical transport, Raman spectroscopy, cross-sectional transmission electron microscopy, and X-ray diffraction characterizations of the insulating phase. We show that the superconductor–insulator transition is driven by strain, which also causes characteristic energy shifts of the Raman modes. Our observation paves the way for high-quality heterojunction tunnel barriers to be seamlessly built into epitaxial NbSe2itself, thereby enabling highly scalable tunneling devices for superconductor-based quantum electronics.

We report on the synthesis of the epoxy-based composites with graphene fillers and test their electromagnetic shielding efficiency by the quasi-optic free-space method in the extremely high-frequency (EHF) band (220–325 GHz). The curing adhesive composites were produced by a scalable technique with a mixture of single-layer and few-layer graphene layers of few-micrometer lateral dimensions. It was found that the electromagnetic transmission, T, is low even at small concentrations of graphene fillers: T<1% at a frequency of 300 GHz for a composite with only ϕ = 1 wt% graphene. The main shielding mechanism in composites with the low graphene loading is absorption. The composites of 1 mm in thickness and a graphene loading of 8 wt% provide an excellent electromagnetic shielding of 70 dB in the sub-terahertz EHF frequency band with negligible energy reflection to the environment. The developed lightweight adhesive composites with graphene fillers can be used as electromagnetic absorbers in the high-frequency microwave radio relays, microwave remote sensors, millimeter wave scanners, and wireless local area networks.

The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created.

In this Perspective, I present a concise account concerning the emergence of the research field investigating the phononic and thermal properties of graphene and related materials, covering the refinement of our understanding of phonon transport in two-dimensional material systems. The initial interest in graphene originated from its unique linear energy dispersion for electrons, revealed in exceptionally high electron mobility, and other exotic electronic and optical properties. Electrons are not the only elemental excitations influenced by a reduction in dimensionality. Phonons—quanta of crystal lattice vibrations—also demonstrate an extreme sensitivity to the number of atomic planes in the few-layer graphene, resulting in unusual heat conduction properties. I outline recent theoretical and experimental developments in the field and discuss how the prospects for the mainstream electronic application of graphene, enabled by its high electron mobility, gradually gave way to emerging real-life products based on few-layer graphene, which utilize its unique heat conduction rather than its electrical conduction properties.

We report results of investigation of the phonon and thermal properties of the exfoliated films of layered single crystals of antiferromagnetic FePS3and MnPS3semiconductors. Raman spectroscopy was conducted using three different excitation lasers with wavelengths of 325 nm (UV), 488 nm (blue), and 633 nm (red). UV–Raman spectroscopy reveals spectral features which are not detectable viavisible Raman light scattering. The thermal conductivity of FePS3and MnPS3thin films was measured by two different techniques: the steady-state Raman optothermal and transient time-resolved magneto-optical Kerr effect. The Raman optothermal measurements provided the orientation-average thermal conductivity of FePS3to be 1.35 ± 0.32 W m–1K–1at room temperature. The transient measurements revealed that the through-plane and in-plane thermal conductivity of FePS3are 0.85 ± 0.15 and 2.7 ± 0.3 W m–1K–1, respectively. The films of MnPS3have higher thermal conductivity of 1.1 ± 0.2 W m–1K–1through-plane and 6.3 ± 1.7 W m–1K–1in-plane. The data obtained by the two techniques are in agreement and reveal strong thermal anisotropy of the films and the dominance of phonon contribution to heat conduction. The obtained results are important for the interpretation of electric switching experiments with antiferromagnetic materials as well as for the proposed applications of the antiferromagnetic semiconductors in spintronic devices.

The magnetic properties in two-dimensional van der Waals materials depend sensitively on structure. CrI3, as an example, has been recently demonstrated to exhibit distinct magnetic properties depending on the layer thickness and stacking order. Bulk CrI3is ferromagnetic (FM) with a Curie temperature of 61 K and a rhombohedral layer stacking, whereas few-layer CrI3has a layered antiferromagnetic (AFM) phase with a lower ordering temperature of 45 K and a monoclinic stacking. In this work, we use cryogenic magnetic force microscopy to investigate CrI3flakes in the intermediate thickness range (25–200 nm) and find that the two types of magnetic orders, hence the stacking orders, can coexist in the same flake with a layer of ∼13 nm at each surface being in the layered AFM phase similar to few-layer CrI3and the rest in the bulk FM phase. The switching of the bulk moment proceeds through a remnant state with nearly compensated magnetic moment along the c-axis, indicating formation of c-axis domains allowed by a weak interlayer coupling strength in the rhombohedral phase. Our results provide a comprehensive picture on the magnetism in CrI3and point to the possibility of engineering magnetic heterostructures within the same material.

The paper is devoted to reachable sets of linear time-varying continuous systems under uncertain initial states and disturbances with a bounded uncertainty measure. The uncertainty measure is the sum of a quadratic form of the initial state and the integral over the finite-time interval from a quadratic form of the disturbance. It is shown that the reachable set of the system under this assumption is an evolving ellipsoid with a matrix being a solution to the linear matrix differential equation. This result is used to synthesize the optimal observer providing the minimal ellipsoidal set as the estimate of the system state, as well as optimal controllers steering the system state into a final target ellipsoidal set or keeping the entire system trajectory in a prescribed ellipsoidal tube under all admissible initial states and disturbances. The relationship between the optimal ellipsoidal observer and the Kalman filter are established. Numerical modeling with the Mathieu equation for parametric vibrations of a linear oscillator illustrates the results.

We use transient Rayleigh scattering to study the thermalization of hot photoexcited carriers in single GaAs0.7Sb0.3/InP nanowire heterostructures. By comparing the energy loss rate in single core-only GaAs0.7Sb0.3nanowires which do not show substantial hot carrier effects with the core–shell nanowires, we show that the presence of an InP shell substantially suppresses the longitudinal optical phonon emission rate at low temperatures which then leads to strong hot carrier effects.

We report on switching among three charge-density-wave phases, commensurate, nearly commensurate, incommensurate, and the high-temperature normal metallic phase in thin-film 1T-TaS2devices induced by application of an in-plane bias voltage. The switching among all phases has been achieved over a wide temperature range, from 77 to 400 K. The low-frequency electronic noise spectroscopy has been used as an effective tool for monitoring the transitions, particularly the switching from the incommensurate charge-density-wave phase to the normal metal phase. The noise spectral density exhibits sharp increases at the phase transition points, which correspond to the step-like changes in resistivity. Assignment of the phases is consistent with low-field resistivity measurements over the temperature range from 77 to 600 K. Analysis of the experimental data and calculations of heat dissipation indicate that Joule heating plays a dominant role in the voltage induced transitions in the 1T-TaS2devices on Si/SiO2substrates, contrary to some recent claims. The possibility of the bias-voltage switching among four different phases of 1T-TaS2is a promising step toward nanoscale device applications. The results also demonstrate the potential of noise spectroscopy for investigating and identifying phase transitions in the materials.

Micron-scale single-crystal nanowires of metallic TaSe3, a material that forms −Ta–Se3–Ta–Se3– stacks separated from one another by a tubular van der Waals (vdW) gap, have been synthesized using chemical vapor deposition (CVD) on a SiO2/Si substrate, in a process compatible with semiconductor industry requirements. Their electrical resistivity was found unaffected by downscaling from the bulk to as little as 7 nm in nanowire width and height, in striking contrast to the resistivity of copper for the same dimensions. While the bulk resistivity of TaSe3is substantially higher than that of bulk copper, at the nanometer scale the TaSe3wires become competitive to similar-sized copper ones. Moreover, we find that the vdW TaSe3nanowires sustain current densities in excess of 108A/cm2and feature an electromigration energy barrier twice that of copper. The results highlight the promise of quasi-one-dimensional transition metal trichalcogenides for electronic interconnect applications and the potential of van der Waals materials for downscaled electronics.

We investigated low-frequency current fluctuations, i.e., electronic noise, in FePS3van der Waals layered antiferromagnetic semiconductor. The noise measurements have been used as noise spectroscopyfor advanced materials characterization of the charge carrier dynamics affected by spin ordering and trapping states. Owing to the high resistivity of the material, we conducted measurements on vertical device configuration. The measured noise spectra reveal pronounced Lorentzian peaks of two different origins. One peak is observed only near the Néel temperature, and it is attributed to the corresponding magnetic phase transition. The second Lorentzian peak, visible in the entire measured temperature range, has characteristics of the trap-assisted generation–recombination processes similar to those in conventional semiconductors but shows a clear effect of the spin order reconfiguration near the Néel temperature. The obtained results contribute to understanding the electron and spin dynamics in this type of antiferromagnetic semiconductors and demonstrate the potential of electronic noise spectroscopy for advanced materials characterization.