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The characterization of Cu/diamond interface thermal conductance (hc) along with an improved understanding of factors affecting it are becoming increasingly important, as Cu-diamond composites are being considered for electronic packaging applications. In this study, ∼90 nm thick Cu layers were deposited on synthetic and natural single crystal diamond substrates. In several specimens, a Ti-interface layer of thickness ⩽3.5 nm was sputtered between the diamond substrate and the Cu top layer. The hc across Cu/diamond interfaces for specimens with and without a Tiinterface layer was determined using time-domain thermoreflectance. The hc is ∼2× higher for similar interfacial layers on synthetic versus natural diamond substrate. The nitrogen concentration of synthetic diamond substrate is four orders of magnitude lower than natural diamond. The difference in nitrogen concentration can lead to variations in disorder state, with a higher nitrogen content resulting in a higher level of disorder. This difference in disorder state potentially can explain the variations in hc. Furthermore, hc was observed to increase with an increase of Ti-interface layer thickness. This was attributed to an increased adhesion of Cu top layer with increasing Ti-interface layer thickness, as observed qualitatively in the current study. [ABSTRACT FROM AUTHOR]

The optical constants of tantalum pentoxide (Ta2O5) are determined in a broad spectral region from the visible to the far infrared. Ta2O5 films of various thicknesses from approximately 170 to 1600 nm are deposited using reactive magnetron sputtering on Si substrates. X-ray diffraction shows that the as-deposited films are amorphous, and annealing in air at 800 °C results in the formation of nanocrystalline Ta2O5. Ellipsometry is used to obtain the dispersion in the visible and near-infrared. Two Fourier-transform infrared spectrometers are used to measure the transmittance and reflectance at wavelengths from 1 to 1000 μm. The surface topography and microstructure of the samples are examined using atomic force microscopy, confocal microscopy, and scanning electron microscopy. Classical Lorentz oscillators are employed to model the absorption bands due to phonons and impurities. A simple model is introduced to account for light scattering in the annealed films, which contain micro-cracks. For the unannealed samples, an effective-medium approximation is used to take into account the adsorbed moisture in the film and a Drude free-electron term is also added to model the broad background absorption. [ABSTRACT FROM AUTHOR]

Influenza results in tens of thousands of deaths annually in the USA and hundreds of thousands worldwide. COVID-19, caused by the SARS-Cov-2 virus, is even more devastating in terms of patient mortality. At the time of this writing, the nanoscopic SARS-Cov-2 virus has paralyzed the world economy and resulted in what are likely permanent changes in our expectations of society and daily life. New technology is needed to reduce the economic and social impacts of diseases such as COVID-19 and prevent additional negative consequences resulting from subsequent pandemics. As viruses such as Influenza A and SARS-Cov-2 are transmitted from person to person by exposure to infected secretions, inexpensive at-home or workplace tests for the analysis of the virus content within those secretions, such as saliva or mucus from the nasopharynx (as in a swab-based test) or oropharynx (as in a saliva-based test), will be critical for a safe return to work, school, and cultural activities. The most reliable approaches for viral sensing are polymerase chain reaction and protein detection via enzyme-linked immunosorbent assay; however, these approaches require extensive sample handling, laboratory infrastructure, and long sample-to-result time. Advances are leading to increased point-of-care capability for these testing methods, but even this effort is insufficient for curbing the impact of the current pandemic. There are many options for alternative virus (or antigen) detection currently in development. These novel approaches are more amenable for testing in home or workplace without specialized equipment and training and include measurements of mass changes, heat of adsorption, electrochemical changes, changes in optical properties, and changes in electronic properties. Of these transduction mechanisms, electronic property measurements of materials as they interact with virus-containing secretions offer the greatest potential for simplicity, selectivity, and sensitivity needed to revolutionize traditional laboratory assays for at-home pathogen detection. We have, therefore, focused this review on the operation and architecture of electronic antigen sensors, specifically those demonstrating a change in electrical conductivity when interacting with a specific antigen, with hopes that a brief summary of over five decades of research in this area will be beneficial to those developing alternative, user-friendly routes for detection of viruses at this or any time. A key element in electronic virus sensing with useful sensitivity is the use of nanomaterials with ultrahigh surface-to-volume ratios, maximizing the change in charge carrier density upon adsorption events. So-called "low-dimensional materials" are materials characterized by nanoscopic length scales in at least one dimension. One-dimensional nanomaterials such as nanowires and nanotubes are well-established as effective sensing materials with potential for high sensitivity; however, their realization on a large scale has been challenging. Two-dimensional materials are planar materials with thicknesses of one or a few molecular layers and represent the ultimate limit of the surface-to-volume ratio with promising demonstrations of large-scale production and sensitive, selective virus sensing with many options for functionalization. All aspects of 2D sensor fabrication, functionalization, and use are addressed. [ABSTRACT FROM AUTHOR]

An approach for printing micron-scale electronic devices built from two-dimensional materials is presented. Experimental phage display techniques and computational atomistic simulation approaches were used to identify a peptide molecule that effectively anchors the basal plane surface of two-dimensional (2D) MoS2 to SiO2 surfaces. This peptide was suspended in water to develop an ink suitable for aerosol jet printing. The printed substrates were then dip coated with a suspension of liquid phase exfoliated 2D MoS2 particles. Strong adhesion of physically continuous lines of these particles was observed only on regions of the substrate patterned with the peptide-based ink, thereby enabling aerosol jet printing as a template for devices based on 2D materials. Graphene was also bound to SiO2 via a similar approach, but with a different peptide known from prior work to selectively adhere to the basal plane of graphene. Fundamental peptide-surface interactions for MoS2, graphene, and SiO2 were explored via simulation and experiment. This printing method is proposed as a route towards large-scale, low temperature patterning of 2D materials and devices. The electrical properties of continuous lines of MoS2 particles printed in a single pass of peptide ink printing were measured via transmission line measurements. The results indicate that this molecular attachment approach to printing possesses several advantages such as overcoming nozzle clogging due to nanomaterial aggregation, decoupling of particle size from any dimensions associated with the printer, and single-pass printing of electrically continuous films. [ABSTRACT FROM AUTHOR]

Recent computational studies predict mechanical strain–induced changes in thermal transport, which is yet to be validated by experimental data. In this article, we present experimental evidence of an increase in thermal conductivity of nominally 200-nm-thick freestanding amorphous silicon thin films under externally applied tensile loading. Using a combination of nanomechanical testing and infrared microscopy, we show that 2.5% tensile strain can increase thermal conductivity from 1 to 2.4 W/m-K. We propose that such an increase in thermal conductivity might be due to strain-induced changes in microstructure and/or carrier density. Microstructural and optical reflectivity characterization through Raman and infrared spectroscopy are presented to investigate this hypothesis. [ABSTRACT FROM AUTHOR]

Uniform growth of pristine two dimensional (2D) materials over large areas at lower temperatures without sacrifice of their unique physical properties is a critical pre-requisite for seamless integration of next-generation van der Waals heterostructures into functional devices. This Letter describes a vapor phase growth technique for precisely controlled synthesis of continuous, uniform molecular layers of MoS2 on silicon dioxide and highly oriented pyrolitic graphite substrates of over several square centimeters at 350°C. Synthesis of few-layer MoS2 in this ultra-high vacuum physical vapor deposition process yields materials with key optical and electronic properties identical to exfoliated layers. The films are composed of nano-scale domains with strong chemical binding between domain boundaries, allowing lift-off from the substrate and electronic transport measurements from contacts with separation on the order of centimeters. [ABSTRACT FROM AUTHOR]