Doping is a fundamental requirement for tuning and improving the properties of conventional semiconductors. Recent doping studies including niobium (Nb) doping of molybdenum disulfide (MoS2) and ...tungsten (W) doping of molybdenum diselenide (MoSe2) have suggested that substitutional doping may provide an efficient route to tune the doping type and suppress deep trap levels of 2D materials. To date, the impact of the doping on the structural, electronic, and photonic properties of in situ‐doped monolayers remains unanswered due to challenges including strong film substrate charge transfer, and difficulty achieving doping concentrations greater than 0.3 at%. Here, in situ rhenium (Re) doping of synthetic monolayer MoS2 with ≈1 at% Re is demonstrated. To limit substrate film charge transfer, r‐plane sapphire is used. Electronic measurements demonstrate that 1 at% Re doping achieves nearly degenerate n‐type doping, which agrees with density functional theory calculations. Moreover, low‐temperature photoluminescence indicates a significant quench of the defect‐bound emission when Re is introduced, which is attributed to the MoO bond and sulfur vacancies passivation and reduction in gap states due to the presence of Re. The work presented here demonstrates that Re doping of MoS2 is a promising route toward electronic and photonic engineering of 2D materials.
This work demonstrates in situ rhenium (Re) doping of synthetic monolayer MoS2 with ≈1 at% Re on r‐plane sapphire. Electronic measurements elucidate that 1 at% Re doping achieves nearly degenerate n‐type doping, which agrees with density functional theory calculations. Low‐temperature photoluminescence measurements reveal suppression of defect emission induced by Re doping, resulting from the passivation of defects due to the presence of Re.
Atomically thin two-dimensional (2D) metals may be key ingredients in next-generation quantum and optoelectronic devices. However, 2D metals must be stabilized against environmental degradation and ...integrated into heterostructure devices at the wafer scale. The high-energy interface between silicon carbide and epitaxial graphene provides an intriguing framework for stabilizing a diverse range of 2D metals. Here we demonstrate large-area, environmentally stable, single-crystal 2D gallium, indium and tin that are stabilized at the interface of epitaxial graphene and silicon carbide. The 2D metals are covalently bonded to SiC below but present a non-bonded interface to the graphene overlayer; that is, they are 'half van der Waals' metals with strong internal gradients in bonding character. These non-centrosymmetric 2D metals offer compelling opportunities for superconducting devices, topological phenomena and advanced optoelectronic properties. For example, the reported 2D Ga is a superconductor that combines six strongly coupled Ga-derived electron pockets with a large nearly free-electron Fermi surface that closely approaches the Dirac points of the graphene overlayer.
The utilization of alkali salts, such as NaCl and KI, has enabled the successful growth of large single domain and fully coalesced polycrystalline two-dimensional (2D) transition-metal dichalcogenide ...layers. However, the impact of alkali salts on photonic and electronic properties is not fully established. In this work, we report alkali-free epitaxy of MoS2 on sapphire and benchmark the properties against alkali-assisted growth of MoS2. This study demonstrates that although NaCl can dramatically increase the domain size of monolayer MoS2 by 20 times, it can also induce strong optical and electronic heterogeneities in as-grown, large-scale films. This work elucidates that utilization of NaCl can lead to variation in growth rates, loss of epitaxy, and high density of nanoscale MoS2 particles (4 ± 0.7/μm2). Such phenomena suggest that alkali atoms play an important role in Mo and S adatom mobility and strongly influence the 2D/sapphire interface during growth. Compared to alkali-free synthesis under the same growth conditions, MoS2 growth assisted by NaCl results in >1% tensile strain in as-grown domains, which reduces photoluminescence by ∼20× and degrades transistor performance.
The rise of two-dimensional (2D) materials research took place following the isolation of graphene in 2004. These new 2D materials include transition metal dichalcogenides, mono-elemental 2D sheets, ...and several carbide- and nitride-based materials. The number of publications related to these emerging materials has been drastically increasing over the last five years. Thus, through this comprehensive review, we aim to discuss the most recent groundbreaking discoveries as well as emerging opportunities and remaining challenges. This review starts out by delving into the improved methods of producing these new 2D materials via controlled exfoliation, metal organic chemical vapor deposition, and wet chemical means. We look into recent studies of doping as well as the optical properties of 2D materials and their heterostructures. Recent advances towards applications of these materials in 2D electronics are also reviewed, and include the tunnel MOSFET and ways to reduce the contact resistance for fabricating high-quality devices. Finally, several unique and innovative applications recently explored are discussed as well as perspectives of this exciting and fast moving field.
Beyond the intrinsic properties of 2D materials, another advantage is the tunability that follows from their low dimensionality. Here, large‐area Nb‐doped MoS2 monolayer films deposited by metal ...organic chemical vapor deposition that can function as electrical contacts or chemical sensors are demonstrated. Compared to pristine MoS2, Nb‐doped MoS2 exhibits a relatively faster growth rate and quenched PL due to formation of mid‐gap energy bands. When the Nb concentration reaches 5 at%, doped MoS2 shows clear p‐type characteristics, evident by a 1.7 eV shift of the Fermi level toward the valence band maximum. Doping also impacts transport at the metal/MoS2 interface, demonstrated by Pt–Ir metallization that is Schottky‐limited when in contact with undoped MoS2 but Ohmic on Nb‐MoS2. Moreover, a 50 × improved signal‐to‐noise ratio is demonstrated in sensing triethylamine compared to undoped MoS2, with <15 parts‐per‐billion detection limit.
This article demonstrates the uniform in situ Nb doping on MoS2 in centimeter scale. Nb‐MoS2 is p‐type with ≈5.6% Nb concentration (Nb/Mo). This doping system activates the lower detection limits (15 ppb) to triethylamine. Meanwhile, p‐type MoS2 benefits the metal contact performance, evident by Ohmic like I–V curve when contacting Pt/Ir alloy.
In article number 1706950, Joshua A. Robinson and co‐workers demonstrate in‐situ Re doping of synthetic monolayer MoS2 with ≈1 at% Re on r‐plane sapphire. Electronic measurements and density ...functional theory calculations show that 1 at% Re doping achieves nearly degenerate n‐type doping. Low‐temperature photoluminescence reveals a suppression of defect emission, resulting from the passivation of defects due to the presence of Re. Picture Credit: Donna Deng.
The field of two-dimensional (2D) materials has witnessed several significant advancements in a short period of time. There have been extensive research efforts dedicated to this field and an ...expanding community of researchers built around the same. The focus of this review article is on the most recent milestones in several aspects of 2D materials with emphasis on transition metal dichalcogenides, such as improved synthesis and property engineering, approaching this from both experimental and theoretical viewpoints. There is also an attempt at highlighting some emerging material properties that are of interest and use of these 2D materials in several electronic applications.
Background Radial access for percutaneous coronary intervention (PCI) has been shown to reduce access site complications, improve patient comfort and reduce mortality. Use of a sheathless guiding ...catheter for transradial PCI has the potential reduce trauma to the radial artery and to further expand the type of cases where this approach can be utilised. We report our initial experience with the recently developed Sheathless Eaucath. Methods We retrospectively evaluated outcomes in consecutive patients who underwent PCI using the Sheathless Eaucath at our institution between February 2009 and November 2011. All procedures were performed via radial access. There were no exclusion criteria. Results The study included 120 patients. Of these 87 (72.5%) presented with acute coronary syndromes. Primary PCI was performed in nine and rescue PCI in seven patients. Interventions were performed on a total of 147 lesions. The majority of lesions were complex (68% classified as type B2 or C). Bifurcation lesions were treated in 42.5% and chronic total occlusions in 5% of patients. Adjunctive devices including rotablation, IVUS and 6 or 7 Fr thrombus aspiration catheters were used in 30% of patients. Angiographic success was achieved in 97.5%. Five patients suffered peri-procedural non-ST-elevation myocardial infarctions. There was no in-hospital target vessel revascularisation or death. Peri-procedural radial artery occlusion was infrequent (2.3%). Haematomas larger than 5 cm occurred in two patients. No other vascular complications occurred. Conclusion Use of the Sheathless Eaucath is safe and allows complex interventions to be undertaken transradially with a high success rate.
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