Patternable Process-Induced Strain in 2D Monolayers and Heterobilayers.

Strain engineering in two-dimensional (2D) materials is a powerful but difficult to control approach to tailor material properties. Across applications, there is a need for device-compatible techniques to design strain within 2D materials. This work explores how process-induced strain engineering, commonly used by the semiconductor industry to enhance transistor performance, can be used to pattern complex strain profiles in monolayer MoS2 and 2D heterostructures. A traction-separation model is identified to predict strain profiles and extract the interfacial traction coefficient of 1.3 ± 0.7 MPa/µm and the damage initiation threshold of 16 ± 5 nm. This work demonstrates the utility to (1) spatially pattern the optical band gap with a tuning rate of 91 ± 1 meV/% strain and (2) induce interlayer heterostrain in MoS2-WSe2 heterobilayers. These results provide a CMOS-compatible approach to design complex strain patterns in 2D materials with important applications in 2D heterogeneous integration into CMOS technologies, moiré engineering, and confining quantum systems.

Uniaxial Strain-Induced Stacking Order Change in Trilayer Graphene.

The layer stacking order in two-dimensional heterostructures, like graphene, affects their physical properties and potential applications. Trilayer graphene, specifically ABC-trilayer graphene, has captured significant interest due to its potential for correlated electronic states. However, achieving a stable ABC arrangement is challenging due to its lower thermodynamic stability compared to the more stable ABA stacking. Despite recent advancements in obtaining ABC graphene through external perturbations, such as strain, the stacking transition mechanism remains insufficiently explored. In this study, we unveil a universal mechanism to achieve ABC stacking, applicable for understanding ABA to ABC stacking changes induced by any mechanical perturbations. Our approach is based on a novel strain engineering technique that induces interlayer slippage and results in the formation of stable ABC domains. We investigate the underlying interfacial mechanisms of this stacking change through computational simulations and experiments. Our findings demonstrate a highly anisotropic and significant transformation of ABA stacking to large and stable ABC domains facilitated by interlayer slippage. Through atomistic simulations and local energy analysis, we systematically demonstrate the mechanism for this stacking transition, that is dependent on specific loading orientation. Understanding such a mechanism allows this material system to be engineered by design compatible with industrial techniques on a device-by-device level. We conduct Raman studies to validate and characterize the formed ABC stacking, highlighting its distinct features compared to the ABA region. Our results contribute to a clearer understanding of the stacking change mechanism and provide a robust and controllable method for achieving stable ABC domains, facilitating their use in developing advanced optoelectronic devices.

An Atomistic Insight into Moiré Reconstruction in Twisted Bilayer Graphene beyond the Magic Angle.

Twisted bilayer graphene exhibits electronic properties strongly correlated with the size and arrangement of moiré patterns. While rigid rotation of the two graphene layers results in a moiré interference pattern, local rearrangements of atoms due to interlayer van der Waals interactions result in atomic reconstruction within the moiré cells. Manipulating these patterns by controlling the twist angle and externally applied strain provides a promising route to tuning their properties. Atomic reconstruction has been extensively studied for angles close to or smaller than the magic angle (θ m = 1.1°). However, this effect has not been explored for applied strain and is believed to be negligible for high twist angles. Using interpretive and fundamental physical measurements, we use theoretical and numerical analyses to resolve atomic reconstruction in angles above θ m . In addition, we propose a method to identify local regions within moiré cells and track their evolution with strain for a range of representative high twist angles. Our results show that atomic reconstruction is actively present beyond the magic angle, and its contribution to the moiré cell evolution is significant. Our theoretical method to correlate local and global phonon behavior further validates the role of reconstruction at higher angles. Our findings provide a better understanding of moiré reconstruction in large twist angles and the evolution of moiré cells under the application of strain, which might be potentially crucial for twistronics-based applications.

Graphene and Beyond: Recent Advances in Two-Dimensional Materials Synthesis, Properties, and Devices.

Since the isolation of graphene in 2004, two-dimensional (2D) materials research has rapidly evolved into an entire subdiscipline in the physical sciences with a wide range of emergent applications. The unique 2D structure offers an open canvas to tailor and functionalize 2D materials through layer number, defects, morphology, moiré pattern, strain, and other control knobs. Through this review, we aim to highlight the most recent discoveries in the following topics: theory-guided synthesis for enhanced control of 2D morphologies, quality, yield, as well as insights toward novel 2D materials; defect engineering to control and understand the role of various defects, including in situ and ex situ methods; and properties and applications that are related to moiré engineering, strain engineering, and artificial intelligence. Finally, we also provide our perspective on the challenges and opportunities in this fascinating field.

Strain-based room-temperature non-volatile MoTe2 ferroelectric phase change transistor.

The primary mechanism of operation of almost all transistors today relies on the electric-field effect in a semiconducting channel to tune its conductivity from the conducting 'on' state to a non-conducting 'off' state. As transistors continue to scale down to increase computational performance, physical limitations from nanoscale field-effect operation begin to cause undesirable current leakage, which is detrimental to the continued advancement of computing1,2. Using a fundamentally different mechanism of operation, we show that through nanoscale strain engineering with thin films and ferroelectrics the transition metal dichalcogenide MoTe2 can be reversibly switched with electric-field-induced strain between the 1T'-MoTe2 (semimetallic) phase to a semiconducting MoTe2 phase in a field-effect transistor geometry. This alternative mechanism for transistor switching sidesteps all the static and dynamic power consumption problems in conventional field-effect transistors3,4. Using strain, we achieve large non-volatile changes in channel conductivity (Gon/Goff ≈ 107 versus Gon/Goff ≈ 0.04 in the control device) at room temperature. Ferroelectric devices offer the potential to reach sub-nanosecond non-volatile strain switching at the attojoule/bit level5-7, with immediate applications in ultrafast low-power non-volatile logic and memory8 while also transforming the landscape of computational architectures because conventional power, speed and volatility considerations for microelectronics may no longer exist.

Antiferromagnetic Spin Seebeck Effect.

We report on the observation of the spin Seebeck effect in antiferromagnetic MnF_{2}. A device scale on-chip heater is deposited on a bilayer of MnF_{2} (110) (30 nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF_{2} (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF_{2} through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9 T) are applied parallel to the easy axis of the MnF_{2} thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

Paramagnetic spin seebeck effect.

We report the observation of the longitudinal spin Seebeck effect in paramagnetic insulators. By using a microscale on-chip local heater, we generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. Using this technique at low temperatures (<20 K), we resolve the paramagnetic spin Seebeck effect in the insulating paramagnets Gd3Ga5O12 (gadolinium gallium garnet) and DyScO3 (DSO), using either W or Pt as the spin detector layer. By taking advantage of the strong magnetocrystalline anisotropy of DSO, we eliminate contributions from the Nernst effect in W or Pt, which produces a phenomenologically similar signal.

A randomized trial of 2 prescription strategies for opioid treatment of chronic nonmalignant pain.

UNLABELLED: The use of opioid medications for treating chronic noncancer pain is growing; however, there is a lack of good evidence regarding their long-term effectiveness, association with substance abuse, and proper prescribing guidelines. The current study directly compares for the first time in a randomized trial the effectiveness of a conservative, hold the line (Stable Dose) prescribing strategy for opioid medications with a more liberal dose escalation (Escalating Dose) approach. This 2-arm, parallel, randomized pragmatic clinical trial followed 135 patients referred to a specialty pain clinic at a Veterans Affairs Hospital for 12 months (94% male and 74% with musculoskeletal pain). Primary outcomes included monthly or quarterly evaluations of pain severity, pain relief from medications, pain-related functional disability, and opioid misuse behaviors. All subjects received identical pain treatment except for the application of treatment group specific strategies for opioid prescriptions. No group differences were found for primary outcomes of usual pain or functional disability although the Escalating Dose group did show a small but significantly larger increase in self-rated pain relief from medications. About 27% of patients were discharged over the course of the study due to opioid misuse/noncompliance, but there were no group differences in rate of opioid misuse. PERSPECTIVE: The results of this study demonstrate that even in carefully selected patients there is a significant risk of problematic opioid misuse. Although in general there were no statistically significant differences in the primary outcomes between groups, the escalating dose strategy did lead to small improvements in self-reported acute relief from medications without an increase in opioid misuse, compared to the stable dose strategy.

Very large scale integration of nanopatterned YBa2Cu3O7-delta Josephson junctions in a two-dimensional array.

Very large scale integration of Josephson junctions in a two-dimensional series-parallel array has been achieved by ion irradiating a YBa(2)Cu(3)O(7-delta) film through slits in a nanofabricated mask created with electron beam lithography and reactive ion etching. The mask consisted of 15820 high aspect ratio (20:1), 35 nm wide slits that restricted the irradiation in the film below to form Josephson junctions. Characterizing each parallel segment k, containing 28 junctions, with a single critical current I(ck) we found a standard deviation in I(ck) of about 16%.

Introduction of a self-report version of the Prescription Drug Use Questionnaire and relationship to medication agreement noncompliance.

The Prescription Drug Use Questionnaire (PDUQ) is one of several published tools developed to help clinicians better identify the presence of opioid abuse or dependence in patients with chronic pain. This paper introduces a patient version of the PDUQ (PDUQp), a 31-item questionnaire derived from the items of the original tool designed for self-administration, and describes evidence for its validity and reliability in a sample of patients with chronic nonmalignant pain and on opioid therapy. Further, this study examines instances of discontinuation from opioid medication treatment related to violation of the medication agreement in this population, and the relationship of these with problematic opioid misuse behaviors, PDUQ and PDUQp scores. A sample of 135 consecutive patients with chronic nonmalignant pain was recruited from a multidisciplinary Veterans Affairs chronic pain clinic, and prospectively followed over one year of opioid therapy. Using the PDUQ as a criterion measure, moderate to good concurrent and predictive validity data for the PDUQp are presented, as well as item-by-item comparison of the two formats. Reliability data indicate moderate test stability over time. Of those patients whose opioid treatment was discontinued due to medication agreement violation-related discontinuation (MAVRD) (n=38 or 28% of sample), 40% of these (n=11) were due to specific problematic opioid misuse behaviors. Based upon specificity and sensitivity analyses, a suggested cutoff PDUQp score for predicting MAVRD is provided. This study supports the PDUQp as a useful tool for assessing and predicting problematic opioid medication use in a chronic pain patient sample.

The addiction behaviors checklist: validation of a new clinician-based measure of inappropriate opioid use in chronic pain.

This study introduces the Addiction Behaviors Checklist (ABC), which is a brief (20-item) instrument designed to track behaviors characteristic of addiction related to prescription opioid medications in chronic pain populations. Items are focused on observable behaviors noted both during and between clinic visits. One hundred thirty-six consecutive veterans in a multidisciplinary Veterans Affairs Chronic Pain Clinic who were receiving long-term opioid medication treatment were included in this study. This study represents one of the first to follow a sample of chronic pain patients on opioid therapy over time, using a structured assessment tool to evaluate and track behaviors suggestive of addiction. Interrater reliability and concurrent validity data are presented, as well as a cut-off score for use in determining inappropriate medication use. The psychometric findings support the ABC as a viable assessment tool that can increase a provider's confidence in determinations of appropriate vs. inappropriate opioid use.

Clinical considerations in the treatment of chronic pain with opiates.

This article considers assessment and treatment issues for mental health practitioners working with patients using opiate medications to treat chronic pain with a particular emphasis on their potential relationship to substance abuse. We review general opiate medications, including a discussion of medications with increased addiction potential. Practice guidance is offered regarding long-term opiate treatment, including definitions of addiction, initial assessments, ongoing substance misuse monitoring, use of psychological assessment instruments, and managing medication misuse problems. Additionally, we examine the role of the mental health professional within this area and examine the incorporation of psychological interventions for patients using opiates. A case illustration includes several of these complicated issues of managing chronic pain with opiate medications.