Prabhakar R. Bandaru

Eutectic high-entropy alloys (EHEAs), such as nano-lamellar AlCoCrFeNi₂.₁, have gained widespread attention due to their excellent mechanical properties, high hardness, wear resistance, and corrosion resistance—even at elevated temperatures (e.g., >1000 °C). In this study, we investigated the corrosion behavior of AlCoCrFeNi₂.₁ EHEAs fabricated via laser powder bed fusion (L-PBF) 3D printing, as a function of annealing temperature. These EHEAs are composed of two phases: a ductile FCC L1₂ phase and a high-strength BCC B2 phase. Due to the rapid solidification inherent to L-PBF, the as-printed microstructure is far from equilibrium, resulting in a nearly homogeneous elemental distribution across phases. Upon annealing, the system evolves toward equilibrium, leading to enrichment of Cr, Co, and Fe in the FCC phase and Al and Ni in the BCC phase. Additionally, because Cr has limited solubility in the B2 phase, Cr-rich precipitates (on the order of tens of nanometers) form and become more prominent with higher annealing temperatures. Three processing conditions were considered in this study: (1) as printed, (2) annealed at 600 °C for 5 hours, and (3) annealed at 1000 °C for 1 hour. With increasing annealing temperature, the lamellar B2 phase coarsened, Cr-rich precipitates grew, and elemental segregation became more pronounced. Samples were characterized using electron backscatter diffraction to determine crystallographic orientation and energy-dispersive spectroscopy to assess local composition. Further, in situ electrochemical Atomic Force Microscopy was deployed to investigate the relationship between microstructure and corrosion behavior. These studies revealed preferential corrosion of the B2 phase and was most pronounced in regions adjacent to Cr-rich precipitates, where the matrix is depleted in Cr. Corrosion was found to be greater in samples subject to increased annealing temperature. For instance, after 5 hours exposure in 0.05 M H 2 SO 4 , corrosion pit depths increased from ~ 10 nm in the as-printed structure to ~360 nm on the sample annealed at 1000°C, while the pitted area increased from ~2% to 12%. Additionally, electrochemical impedance spectroscopy was used to quantify the charge transfer resistance-an indicator inversely proportional to the corrosion rate- and to monitor oxide evolution. Laser confocal microscopy was used to assess corrosion over larger areas and extended time scales. We expect that such a multimodal approach will inform processing methodologies to design materials systems for high mechanical performance and robust corrosion resistance. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

• IR-PiFM maps identify growth artefacts on CVD grown monolayer MoS 2 as MoO x particles. • Sacrificial Al 2 O 3 layer cleaning process removes MoS 2 surface contaminants effectively. • Thin conformal ALD seed layer (∼1.3 nm) used for high-k gate oxide on monolayer MoS 2. • Cleaned MoS 2 FETs show 10–100 × higher on-current, lower SS and lower variability. • Process is CMOS-compatible and scalable for wafer-level applications. Obstacles towards the widespread use of two-dimensional materials, including MoS 2 , are high-quality large-scale growth of low defect density monolayers. A novel surface cleaning procedure, applicable in device technology, has been developed based on the use of an ALD sacrificial layer to eliminate growth aberrations. The imperfections on MoS 2 were identified using infrared photo-induced force microscopy (IR-PiFM) as MoO x particles deposited during CVD growth process. The utility of the procedure was tested through the fabrication of top gated field effect transistors (FETs) using a bilayer stack of low temperature ALD Al 2 O 3 (LT Al 2 O 3 ) seed layer followed by HfO 2 as the gate oxide. It was observed that the cleaning process results in 1–2 orders of magnitude improvement in the on-current, with a ∼30 % reduction in subthreshold swing, along with lower device variability.

This study presents a multistep approach to enhance the corrosion resistance of aluminum (Al) screens used in the flow fields of water electrolyzers, allowing for the higher thermal conductivity material, Al, to replace titanium (Ti) in electrolyzer gas diffusion components. The approach involves electropolishing, O 2 treatment, and nanoscale conformal atomic layer deposition of an Al 2 O 3 adhesion layer followed by a bilayer TiO x protection coating on the Al screens. It is shown that optimized coatings reduce corrosion current density by 4 orders of magnitude compared to uncoated Al, with a corrosion rate of ∼7 nm per year, ensuring protection of components with the complex geometries of the electrolyzer gas diffusion layer flow field. This work provides a viable pathway to replace expensive titanium with abundant, cost-effective aluminum.

It has been indicated that the path forward for the widespread usage of ferroelectric ( FE ) materials may be considerably facilitated through the reduction of programming voltages to on-chip logic-compatible values of <1 V. Obstacles involve issues related to the scaling of the FE s to lower thickness as well as the presence of an interfacial layer (IL) between the high-permittivity FE and the substrate- resulting in wasted voltage across the IL. Here, we show how lower operating voltages along with a higher tunneling electroresistance (TER) could be achieved through IL engineering. We use piezoresponse force microscopy and fabricated ferroelectric tunnel junctions (FTJs) to show that ultrathin FE films deposited on single-layer graphene/Si can exhibit polarization switching at reduced voltages ∼0.8 V with significant TER as compared to directly depositing on Si.

Abstract A 1D unidirectional phononic waveguide embedded within a 3D hexagonal close‐packed (HCP) phononic crystal is investigated, formed through the introduction of a screw dislocation. This approach does not rely on the non‐trivial topological characteristics of the 3D crystal. The findings reveal that the screw dislocation induces a pair of helical modes with orthogonal displacements in the x ‐ and y ‐directions, which are 90 degrees out of phase, resulting in distinctive rotational motion. These helical modes exhibit directional propagation, tightly linked to the helicity of the screw dislocation. The observed directionality and robustness are attributed to the interplay between the structural helicity and the existence of a bulk bandgap. This work provides new insights into the influence of dislocation‐induced symmetry on wave propagation in phononic systems. It also offers a pathway for designing directionally selective waveguides without relying on topological properties.

Models to describe electrical conduction in quantum dot (QD) constituted films often overlook the effects of geometric disorder. We address related issues by examining the influence of the QD packing fraction (PF) on the charge transport and transmission in QD arrays. Using transfer matrix based algorithms and Monte Carlo simulations, we quantify the transmission across disordered QD assemblies. Our results indicate a critical packing fraction (PFc) of ∼ 0.64, marking a transition from a non-conducting to a conducting state, aligning well with experimental observations and analytical predictions. This study enhances the understanding of transport in QD arrays, with implications for designing efficient electronic devices based on disordered nanoscale systems.

• Voltage reduced for Ti anodization at elevated temperature. • ALD TiO x forms an effective oxygen diffusion barrier layer hence to prevent further oxidation of titanium. • ALD TiO x coating reduces corrosion of titanium in PEM electrolyzers at low pH. • Five orders of magnitude increase in current density with ALD TiO x -coated titanium. Titanium (Ti), widely used in proton exchange membrane (PEM) based water electrolyzers, is prone to oxidation and related corrosion given the high operating voltages (>2 V) and low pH (⩽5) conditions. Here, it is shown that a thin layer of ALD (atomic layer deposition) TiO x can serve as a barrier for drastically reducing the corrosion of Ti. The robustness of the coatings was evaluated at high potentials (2.4 V vs. RHE – reversible hydrogen electrode), in low pH and at elevated temperature (80 °C). A low TiO x dissolution rate (<∼5 nm year −1 ) along with five orders of magnitude enhanced current density, was observed for the ALD TiO x coated Ti compared to uncoated Ti.

The impact of solvent choice and associated working parameters on the properties of ferroelectric (FE) polymer (PVDF-TrFE) thin films, synthesized through Langmuir–Blodgett (LB) methodology, is considered. Three different solvents, i.e., Dimethyl Sulfoxide (DMSO), Cyclopentanone (CP), and a binary solvent mixture of DMSO + Acetone (DMSO + A) were utilized for the dissolution of PVDF-TrFE polymer. The synthesized thin films were characterized using piezoresponse force microscopy (PFM), from which the FE attributes were inferred. It was observed that the FE film structure obtained using the DMSO + A system was optimal, with respect to film uniformity and roughness, and yielded enhanced FE characteristics. The influence of solvents for obtaining such optimal film properties was correlated through the Hansen solubility parameters. The results of this study yield insights into conditions related to ultra-thin-film materials synthesis for FE devices.

Atomic-scale spatial resolution was achieved in the mapping and spectroscopy of polygonal grain boundaries (GBs) on atomically flat highly oriented pyrolytic graphite using scanning tunneling microscopy (STM). These GBs are long-range ordered one-dimensional periodic structures comprising pentagon-heptagon pairs. A comprehensive study combining local electronic, valleytronic, mechanical, and topological properties is conducted on this GB which reveals the interplay between these properties. On the atoms and bonds of individual GB polygons, spatially localized conductance states were probed, in addition to edge states. The spatial extent of these states was observed on GB by bias-dependent imaging. The electron scattering angle at the GB edges was also modulated with a sample bias which exhibited valley flipping and unique quantum interference effects such as backscattering and intervalley scattering. In situ strain-induced mechanical and electronic modifications were observed through surface deformation caused by the STM tip, revealing flattened electronic energy band dispersion and shifts in carrier doping.

We report the first direct extraction of CNT MOS interface metrics normalized to CNT length or CNT surface area using statistical impedance modeling and analysis of lateral capacitors measured between 100 and 300 K. Direct <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$D_{\text{it}}$</tex> extraction from impedance is a crucial step towards high performance CNT MOSFETs and is enabled by (1) a statistical approach towards modeling of CNT impedance, (2) a capacitor architecture meeting the requirements for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$D_{\text{it}}$</tex> extraction, and (3) the extension of impedance acquisition to below 1 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{fF}$</tex>. A rigorous model treatment of surface potential fluctuations <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta\psi_{\mathrm{s}}$</tex> in depletion due to fixed charge and CNT diameter variations allows to reproduce C-V features, to elucidate the physics, and to reconcile SS obtained from I-V curves with impedance data by extending the standard SS equation. CNT midgap <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$D_{\text{it}}$</tex> normalized to CNT surface area of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\cong 7\times 10^{12}\text{cm}^{-2}\text{eV}^{-1}$</tex> and increasing towards the band edge to above <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5\times 10^{13}\text{cm}^{-2}\text{eV}^{-\mathrm{I}},\psi_{\mathrm{S}}$</tex> standard deviation <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sigma_{\mathrm{s}}\cong 2.5\text{kT}$</tex>, and a midgap capture length of 0.01 nm are extracted. Preliminary process optimizations demonstrate a positive impact on the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$D_{\text{it}}$</tex> vs <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E$</tex> curve.

Models to describe electrical conduction in quantum dot (QD) constituted films often overlook the effects of geometric disorder. We address related issues by examining the influence of the QD packing fraction (PF) on the charge transport and transmission in QD arrays. Using transfer matrix based algorithms and Monte Carlo simulations, we quantify the transmission across disordered QD assemblies. Our results indicate a critical packing fraction ($PF_c $) of $\sim$ 0.64, marking a transition from a non-conducting to a conducting state, aligning well with experimental observations and analytical predictions. This study enhances the understanding of transport in QD arrays, with implications for designing efficient electronic devices based on disordered nanoscale systems.

Titanium (Ti) is widely used as anode current collectors in proton exchange membrane (PEM)-based water electrolyzers due to its self-passivated oxide layer, which protects it from corrosion in acidic solutions. However, the cost of the material and machining process for Ti is high. A wider utilization of water electrolyzers to produce hydrogen could be favored by the use of less expensive coated aluminum (Al) substrates, which could potentially replace high-cost Ti-based components. It is shown here by depositing a pinhole-free oxygen vacancy-rich titanium oxide (TiO x ) protection layer by atomic layer deposition (ALD), the corrosion resistance of Al substrates in acidic environments at oxygen evolution potentials can be enhanced. The optimization of the oxygen vacancy concentration is accomplished by tuning the ALD parameters to achieve ideal stoichiometry and conformal coating on rough substrates. The robustness of the coatings was evaluated at high potentials (2.4 V vs NHE = normal hydrogen electrode) in low pH conditions. A low TiO x dissolution rate of the order of ∼6 nm year –1 was observed. By testing under industrially relevant conditions, i.e., high applied voltages (2.4 V) and low pH, an Al loss at around the zero ppb level was achieved using optimized ALD parameters. It is proposed that a 40 nm TiO x coating on Al may be adequate to provide 60,000 h of durability in a PEM water electrolyzer anode current collector.

This work demonstrates the first nanosheet FET built on an array of dense aligned carbon nanotubes. In this device structure, the gate surrounds an aligned array of CNTs with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\approx 300\text{CNT}/\mu \mathrm{m}$</tex>. At a channel length of 70 nm the drive current exceeds <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1 \text{mA}/\mu \mathrm{m}$</tex> at -0.5 V <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{DS}}$</tex> with sub- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\mathrm{T}}$</tex> slope of 135 mV/dec, and an IMIN of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$76 \text{nA}/\mu \mathrm{m}. \mathrm{R}_{\mathrm{C}}$</tex> of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20.5 \Omega-\mu\mathrm{m}$</tex> is extracted by transmission line method. This is record-high performance for transistors with CNT channel. However, reducing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{D}_{\mathrm{I}\mathrm{T}}$</tex> and channel variability are necessary to enable energy-efficient CMOS applications.

Enhanced electrokinetic phenomena, manifested through the observation of a large streaming potential ( V s ), were obtained in microchannels with single-layer graphene (SLG)-coated and few-layer graphene (FLG)-coated surfaces. In comparison to silicon microchannels, the V s obtained for a given pressure difference along the channel (Δ P ) was higher by 75% for the graphene-based channels, with larger values in the SLG case. Computational modeling was used to correlate the surface charge density, tuned through plasma processing, and related zeta potential to measured V s . The implications related to deploying lower dimensional material surfaces for modulating electrokinetic flows were investigated.

In this study, we investigate a one-dimensional (1D) unidirectional phononic waveguide embedded within a three-dimensional (3D) hexagonal close-packed phononic crystal, achieved by the introduction of a screw dislocation. This approach does not rely on the non-trivial topological characteristics of the 3D crystal. We discover that this dislocation induces a pair of helical modes, characterized by their orthogonal $x$- and $y$-directional displacements being out of phase by 90 degrees, which results in a distinctive rotational motion. These helical modes demonstrate directional propagation, tightly linked to the helicity of the screw dislocation. Through considerations of symmetry, we reveal that the emergence of these helical modes is governed by the symmetry of the screw dislocation itself. Our findings not only provide insights into the interplay between dislocation-induced symmetry and wave propagation in phononic systems but also open new avenues for designing directionally selective waveguides without relying on the crystal's topological properties.

The incorporation of energetic helium gaseous species into materials such as tungsten (W) imparts intrinsic surface fragility, yielding fuzzy tungsten. To enhance the robustness of the surface layers, aluminum oxide (AlO x ) was deposited by atomic layer deposition into the fuzzy W. The conformally deposited ceramic yields a new class of surface composites. Structural characterization of the fuzzy W–AlO x composites through nanoindentation testing indicated enhanced indentation modulus ( E ind ) and hardness ( H ind ) and was modeled through various rules of mixtures approaches. The distribution of AlO x in fuzzy W was explored and a systematic study of the extent of incorporation of the AlO x into the fuzzy W was carried out. The synthesized composites may be utilized for improved structural characteristics, e.g., in reducing crack initiation and fracture.

The ultimate sensitivity of field-effect-transistor (FET)-based devices for ionic species detection is of great interest, given that such devices are capable of monitoring single-electron-level modulations. It is shown here, from both theoretical and experimental perspectives, that for such ultimate limits to be approached the thermodynamic as well as kinetic characteristics of the (FET surface)-(linker)-(ion-receptor) ensemble must be considered. The sensitivity was probed in terms of optimal packing of the ensemble, through a minimal charge state/capacitance point of view and atomic force microscopy. Through the fine-tuning of the linker and receptor interaction with the sensing surface, a record limit of detection as well as specificity in the femtomolar range, orders of magnitude better than previously obtained and in excellent accord with prediction, was observed.

In this study, sub-angstrom spatial resolution is achieved in mapping and spectroscopy of atoms and bonds within polygonal grain boundaries (GBs) of graphite using Scanning Tunneling Microscopy (STM). Robust van Hove singularities (VHS) are observed in addition to edge states under ambient conditions. The bias-dependent nature of these states reveals metallic traits of GB, through the charge accumulation and dissipation of localized electronic states. Utilizing a surface elastic deformation technique induced by STM tip allows pico-pinching of the GB, providing insights into its mechanical strength as well as in-situ strain-induced modification of their unique spectroscopy, revealing a tendency toward flattening of the electronic energy band dispersion. An initial atomic-level experimental technique of probing spin-polarized magnetic states is demonstrated, suggesting different densities for spin-up and spin-down states within a spin-degenerate band structure potentially applicable in spin transport or quantum spin sensing.

Carbon nanotube (CNT) transistors demonstrate high mobility but also experience off-state leakage due to the small effective mass and band gap. The lower limit of off-current ( I MIN ) was measured in electrostatically doped CNT metal-oxide-semiconductor field-effect transistors (MOSFETs) across a range of band gaps (0.37 to 1.19 eV), supply voltages (0.5 to 0.7 V), and extension doping levels (0.2 to 0.8 carriers/nm). A nonequilibrium Green’s function (NEGF) model confirms the dependence of I MIN on CNT band gap, supply voltage, and extension doping level. A leakage current design space across CNT band gap, supply voltage, and extension doping is projected based on the validated NEGF model for long-channel CNT MOSFETs to identify the appropriate device design choices. The optimal extension doping and CNT band gap design choice for a target off-current density are identified by including on-current projection in the leakage current design space. An extension doping level >0.5 carrier/nm is required for optimized on-current.

Field-effect transistors (FETs) based on two-dimensional (2D) semiconductors must have ultrathin gate dielectrics in order to achieve low voltage operation. Here we achieve conformal HfO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gate dielectrics on monolayer MoS <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> with the aid of an AlO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> seed layer deposited by "nanofog," a low temperature process at 50 °C. We study the uniformity of the nanofog layer as a function of its deposition temperature, and we also compare FETs fabricated with nanofog AlO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> seed vs. electron-beam evaporated Al seed layers, followed by HfO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> dielectric. With the nanofog seed, we achieve subthreshold slope < 100 mV/dec at room temperature and equivalent oxide thickness (EOT) of 1.3 nm. Devices with nanofog exhibit nearly hysteresis-free behavior, unlike those with the Al seed, consistent with the subthreshold data showing fewer interface defects with nanofog seed layers. The "nanofog" process is thus established as a low-temperature, industry-compatible seed layer for high-κ dielectric deposition onto 2D semiconductors.

Porous layers emergent from the bulk tungsten (W) interface subsequent to helium (He) plasma exposure, under conditions relevant to thermonuclear experiments, were found to significantly modulate the structural attributes of the W─as deduced through nanoscale indentation measurements. Plastic deformation of nanofibers constituting the fuzzy surface layer, along with an increased yield strength with layer depth, was quantified. A power-law relationship between the indentation modulus ( E ind ) and the porosity of the fuzzy W was indicated. The surface roughness of the bulk W increases with temperature prior to fuzz formation, determined by AFM. A decrease in the E ind of the bulk W underneath the fuzzy layer with increasing sample temperature when exposed to plasma, in agreement with molecular-dynamics computations, was observed.

It is shown that the electrical transport in quantum dot (QD) constituted films, synthesized through electrochemical doping, could be described through a two-step model considering (i) the tunneling transport of electrons from an electron source, and subsequent (ii) Ohmic transport through the film governed by a temperature (T) dependent mobility (μ), varying as T−α. A transfer matrix algorithm based approach for electrical field induced tunneling and α ∼ 1, was used. The indicated modeling principles could be deployed to predict the current–voltage characteristics of QD films and assemblies coupled to metallic electrodes.

Highly oriented pyrolytic graphite (HoPG) is the only monoatomic crystal found to host naturally formed moir\'e patterns on its cleaved exfoliated surfaces, which are coherent over micrometers with fixed periodicities. The authors merge the idea of STM tip-induced deformation to probe $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ the gradual nanoscale structural changes on moir\'e patterns with strain. They show the first experimental proof that one-dimensional domain walls of moir\'e patterns can laterally split into two similar to the triangular networks of one-dimensional electronic channels in domain walls, topologically protected around AA nodes. Further, domain-wall edge states are also possibly probed with spectroscopy.

A methodology to test the interlayer bonding strength of two-dimensional (2D) surfaces and associated one (1D)- and two (2D)- dimensional surface defects using scanning tunneling microscope tip-induced deformation, is demonstrated. Surface elastic deformation characteristics of soft 2D monatomic sheets of graphene and graphite in contrast to NbSe2 indicates related association with the underlying local bonding configurations. Surface deformation of 2D graphitic moire patterns reveal the inter-layer van der Waals strength varying across its domains. These results help in the understanding of the comparable interlayer bonding strength of 1D grain boundary as well as the grains. Anomalous phenomena related to probing 2D materials at small gap distances as a function of strain is discussed.

Highly oriented pyrolytic graphite (HoPG) may be the only known monatomic crystal with the ability to host naturally formed moire patterns on its cleaved surfaces, which are coherent over micrometer scales and with discrete sets of twist angles of fixed periodicity. Such an aspect is in marked contrast to twisted bilayer graphene (TBG) and other multilayered systems, where the long range coherence of the moire is not easily maintained due to twist angle disorder. We investigate the electronic and mechanical response of coherent graphite moire patterns through inducing external strain from STM tip-induced deformation. Consequently, unique anisotropic mechanical characteristics are revealed. For example, a lateral widening of one-dimensional (1D) domain walls (DWs) bridging Bernal (ABA) and rhombohedral (ABC) stacking domains (A, B and C refer to the atomic layer positioning), was indicated. Further, in situ tunneling spectroscopy as a function of the deformation indicated a tendency towards increased electrical conductance, which may be associated with a higher density of electronic states, and the consequent flattening of the electronic energy band dispersion. Such features were probed across the DWs, with implications for strain-induced electronic modulation of the moire characteristics.

The latest advances in topological physics have yielded a toolset for highly robust wave-propagation modalities for overcoming obstacles involving beam steering and lateral diffraction in surface acoustic waves (SAWs). However, extant proposals are limited to the exploitation of spin- or valley-polarized phases and rely on nonzero Berry curvature effects. Here, we propose and experimentally demonstrate a highly robust guiding principle, which instead employs an intrinsic chirality of phase vortices and maintains a zero Berry curvature for SAWs. Based on a line defect within a true triangular phononic lattice, the guided SAW mode spans a wide bandwidth [(\ensuremath{\Delta}\ensuremath{\omega}/\ensuremath{\omega}${}_{\mathrm{center}}$) \ensuremath{\sim} 10%] and is well confined in the lateral direction with 3-dB attenuation within half of a unit cell. SAW routing around sharp bends with negligible backscatter is demonstrated. The on-chip integrated design permits unidirectional SAW modes that can enable considerable miniaturization of SAW-based devices, with applications ranging from radio-frequency devices to quantum information transduction.

An ideal biosensor material at room temperature, with an extremely large surface area per unit mass combined with the possibility of harnessing quantum mechanical attributes, would be comprised of graphene and other two-dimensional (2D) materials. The sensing of a variety of sizes and types of biomolecules involves modulation of the electrical charge density of (current through) the 2D material and manifests through specific components of the capacitance (resistance). While sensitive detection at the single-molecule level, i.e., at zeptomolar concentrations, may be achieved, specificity in a complex mixture is more demanding. Attention should be paid to the influence of inevitably present defects in the 2D materials on the sensing, as well as calibration of obtained results with acceptable standards. The consequent establishment of a roadmap for the widespread deployment of 2D material-based biosensors in point-of-care platforms has the potential to revolutionize health care.