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Electric double layer (EDL) gating can induce large capacitance densities (∼1−10 μF/cm^2) in two-dimensional (2D) semiconductors; however, several properties of the electrolyte limit performance. One property is the electrochemical activity which limits the gate voltage (VG) that can be applied and therefore the maximum extent to which carriers can be modulated. A second property is electrolyte thickness, which sets the response speed of the EDL gate, and therefore the timescale over which the channel can be doped. Typical thicknesses are on the order of microns, but thinner electrolytes (nanometers) are needed for very-large-scale-integration (VLSI) both in terms of physical thickness and the speed that accompanies scaling. In this study, finite element modeling of an EDL-gated field-effect transistor (FET) is used to self-consistently couple ion transport in the electrolyte to carrier transport in the semiconductor, in which density of states, and therefore, quantum capacitance is included. The model reveals that 50 to 65% of the applied potential drops across the semiconductor, leaving 35 to 50% to drop across the two EDLs. Accounting for the potential drop in the channel suggests that higher carrier densities can be achieved at larger applied VG without concern for inducing electrochemical reactions. This insight is tested experimentally via Hall measurements of graphene FETs for which VG is extended from ±3 to ±6 V. Doubling the gate voltage increases the sheet carrier density by an additional 2.3×10^13 cm^−2 for electrons and 1.4×10^13 cm^−2 for holes without inducing electrochemistry. To address the need for thickness scaling, the thickness of the solid polymer electrolyte, polyethylene oxide (PEO):CsClO_4, is decreased from 1 μm to 10 nm and used to EDL- gate graphene FETs. Sheet carrier density measurements on graphene Hall bars prove that the carrier densities remain constant throughout the measured thickness range (10 nm−1 μm). The results indicate promise for overcoming the physical and electrical limitations to VLSI while taking advantage of the ultrahigh carrier densities induced by EDL gating.

A drug delivery system for the paranasal sinuses consisting of a freeze-dried thermoresponsive hydrogel with degradable microspheres, called FD-TEMPS (Freeze Dried—Thermogel, Extended-release Microsphere-based delivery to the Paranasal Sinuses), was developed. Glass transition temperatures (Tg′) of the maximally freeze concentrated solutions consisting of poly(N-isopropylacrylamide) (pNIPAAm) and polyethylene glycol (PEG) were determined by differential scanning calorimetry, which informed optimization of the thermogel formulation. By replacing low molecular weight (MW) PEG (200 Da) with a higher MW PEG (2000 Da), the resulting freeze-dried gel exhibited a brittle texture, porous structure, and low residual moisture (

Stepper-based batch fabrication of top-gated field-effect transistors (FETs) is demonstrated on few-layer WSe2-on-sapphire grown by chemical vapor deposition. This article reports the electrical characterization of 94 transistors with three different transistor structures. ON-/ OFF-current ratios exceeding 105 at room temperature with noise-floor-limited gate current and contact-limited ON-current density of 15 nA/ $\mu \text{m}$ was achieved for FETs using a structure in which the gate overlaps the source and drain contacts. Two transistors with open channel access regions are used to allow ion doping through polyethylene oxide: cesium perchlorate (PEO: CsClO4) to induce electron and hole conductivity and allow characterization of the intrinsic FET characteristics. In these geometries, the ON-current increased by four orders of magnitude with ON-/ OFF-current ratio greater than 106 at ${V}_{\text {DS}} = -0.05$ V, compared to gate overlapped FETs. An analytic 2-D FET model was used to model the full current-voltage characteristics. This allowed the field-effect mobility to be extracted revealing the gate and drain field dependence for the first time. The fit of the measured characteristics from subthreshold to saturation is made with only four fitting parameters, revealing a field-dependent electron mobility ranging from 1 to 2.6 cm2/Vs.

Controlling the mobile ion content of ion-containing polymers is critical for advanced organic electronic applications. Here, we report a chemical strategy for achieving “on-demand” release of ions...

A molecularly thin electrolyte is developed to demonstrate a nonvolatile, solid-state, one-transistor (1T) memory based on an electric-double-layer (EDL) gated WSe2 field-effect transistor (FET). T...

A drug delivery system for the paranasal sinuses consisting of a freeze-dried thermoresponsive hydrogel with degradable microspheres, called FD-TEMPS (Freeze Dried-Thermogel, Extended-release Microsphere-based delivery to the Paranasal Sinuses), was developed. Glass transition temperatures (T

Does an individual’s risk profile predict their social distancing and mask wearing in the U.S. during the COVID-19 pandemic? Common sense and some health behavior theories suggest that as a perceived threat increases, an individual should be more likely to take preventive measures. We explore this hypothesis using survey responses collected from 1114 U.S. adults during April and October 2020, and find that neither perceived nor actual risk predicted these preventive behaviors. Instead, being an essential worker, partisanship, and believing compliance was important were more reliable predictors. These results provide guidance for better pandemic response policies and challenge models of health behavior.

The effect of nanoparticle shape on the ionic conductivity and thermal properties of solid polymer electrolytes is reported. Poly(ethylene oxide) (PEO) and LiClO4 electrolytes with an ether oxygen to Li+ molar ratio of 10:1 are filled with TiO2 nanorods and elliptical-shaped fillers in the concentration ranges of 1–2.5 and 1–10 wt %, respectively. The filler concentration that provides the maximum improvement in the ionic conductivity scales inversely with aspect ratio (AR): 10 wt % for spherical nanoparticles (AR = 1), 5 wt % for ellipses (AR ≈ 4.4), and 1–2 wt % for nanorods (AR ≈ 6.6). The same trend is true for Fe2O3 nanofillers, suggesting that the observation is independent of the chemical identity of the metal oxide filler. While the filler concentration required to maximize the conductivity improvement is correlated to the nanofiller shape, the magnitude of the improvement is correlated to the surface-to-volume ratio of the filler. Specifically, the conductivity increases 1 order of magnitude by i...

Two-dimensional van der Waals materials offer unique advantages for the development of band-to-band tunneling devices given their lack of dangling bonds, atomically flat thickness and steep band edges. Here, we present the experimental demonstration of an electric double layer (EDL) Esaki junction in synthetic WSe2 thin films. A Si-compatible process is developed for the fabrication of nanoscale FETs utilizing molecular beam epitaxy of WSe2 performed directly on top of a high-κ dielectric at back-end-of-line-friendly temperatures (2 channel and a solid polymer electrolyte, polyethylene oxide:cesium perchlorate (PEO:CsClO4). Numerical simulations are used to determine the bias dependence of the equilibrium ion and carrier density profiles. The EDL-doped tunnel diode exhibits repeatable, gate-tunable band-to-band tunneling with negative differential resistance in the forward bias regime at temperatures up to 140 K, and strong conduction in reverse bias. A maximum peak-to-valley current ratio of 3.5 is measured at 110 K.

Electric double layer (EDL) dynamics in graphene field-effect transistors (FETs) gated with polyethylene oxide (PEO)-based electrolytes are studied by molecular dynamics (MD) simulations from picoseconds to nanoseconds and experimentally from microseconds to milliseconds. Under an applied field of approximately mV/nm, EDL formation on graphene FETs gated with PEO:CsClO4 occurs on the timescale of microseconds at room temperature and strengthens within 1 ms to a sheet carrier density of nS ~1013 cm-2. Stronger EDLs (i.e., larger ns) are induced experimentally by pulsing with applied voltages exceeding the electrochemical window of the electrolyte; electrochemistry is avoided using short pulses of a few milliseconds. Dynamics on picosecond to nanosecond timescales are accessed using MD simulations of PEO:LiClO4 between graphene electrodes with field strengths of hundreds of mV/nm - 100x larger than experiment. At 100 mV/nm, EDL formation initiates in sub-nanoseconds achieving charge densities up to 6 x 1013...

A gateless lateral p-n junction with reconfigurability is demonstrated on graphene by ion-locking using solid polymer electrolytes. Ions in the electrolytes are used to configure electric-double-layers (EDLs) that induce p- and n-type regions in graphene. These EDLs are locked in place by two different electrolytes with distinct mechanisms: (1) a polyethylene oxide (PEO)-based electrolyte, PEO:CsClO4, is locked by thermal quenching (i.e., operating temperature &lt, Tg (glass transition temperature)), and (2) a custom-synthesized, doubly-polymerizable ionic liquid (DPIL) is locked by thermally triggered polymerization that enables room temperature operation. Both approaches are gateless because only the source/drain terminals are required to create the junction, and both show two current minima in the backgated transfer measurements, which is a signature of a graphene p-n junction. The PEO:CsClO4 gated p-n junction is reconfigured to n-p by resetting the device at room temperature, reprogramming, and cooling to T &lt, Tg. These results show an alternate approach to locking EDLs on 2D devices and suggest a path forward to reconfigurable, gateless lateral p-n junctions with potential applications in polymorphic logic circuits.

Controlled, tunable, and reversible negative-differential resistance (NDR) is observed in lithographically defined, atomically thin semiconducting graphene nanoribbon (GNR)-gated Esaki diode transistors at room temperature. Sub-10 nm-wide GNRs patterned by electron-beam lithography exhibit semiconducting energy bandgaps of ~0.2 eV extracted by electrical conductance spectroscopy measurements, indicating an atomically thin realization of the electronic properties of conventional 3D narrow-bandgap semiconductors such as InSb. A p–n junction is then formed in the GNR channel by electrostatic doping using graphene side gates, boosted by ions in a solid polymer electrolyte. Transistor characteristics of this gated GNR p–n junction exhibit reproducible and reversible NDR due to interband tunneling of carriers. All essential experimentally observed features are explained by an analytical model and are corroborated by a numerical atomistic simulation. The observation of tunable NDR in GNRs is conclusive proof of the existence of a lithographically defined bandgap and the thinnest possible realization of an Esaki diode. It paves the way for the thinnest scalable manifestation of low-power tunneling field-effect transistors (TFETs).

Background Preoperative immunonutrition has been proposed to reduce the duration of hospital stay and infective complications following major elective surgery in patients with gastrointestinal malignancy. A multicentre 2 × 2 factorial RCT was conducted to determine the impact of preoperative and postoperative immunonutrition versus standard nutrition in patients with oesophageal cancer. Methods Patients were randomized before oesophagectomy to immunonutrition (IMPACT®) versus standard isocaloric/isonitrogenous nutrition, then further randomized after operation to immunonutrition versus standard nutrition. Clinical and quality-of-life outcomes were assessed at 14 and 42 days after operation on an intention-to-treat basis. The primary outcome was the occurrence of infective complications. Secondary outcomes were other complications, duration of hospital stay, mortality, nutritional and quality-of-life outcomes (EuroQol EQ-5D-3 L™, European Organisation for Research and Treatment of Cancer (EORTC) QLQ-C30 and EORTC QLQ-OES18). Patients and investigators were blinded until the completion of data analysis. Results Some 278 patients from 11 Australian sites were randomized; two were excluded and data from 276 were analysed. The incidence of infective complications was similar for all groups (37 per cent in perioperative standard nutrition group, 51 per cent in perioperative immunonutrition group, 34 per cent in preoperative immunonutrition group and 40 per cent in postoperative immunonutrition group; P = 0·187). There were no significant differences in any other clinical or quality-of-life outcomes. Conclusion Use of immunonutrition before and/or after surgery provided no benefit over standard nutrition in patients undergoing oesophagectomy. Registration number: ACTRN12611000178943 (https://www.anzctr.org.au).

Endoscopic retrograde cholangiopancreatography (ERCP) is a common procedure that, in the United States, is traditionally performed by gastroenterologists. We hypothesized that when performed by well-trained surgeons, ERCP can be performed safely and effectively. The objectives of the study were to assess the rate of successful cannulation of the duct of interest and to assess the 30-day complication and mortality rates. We retrospectively reviewed the charts of 1858 patients who underwent 2392 ERCP procedures performed by five surgeons between August 2003 and June 2016 in two centers. Demographic and historical data, indications, procedure-related data and 30-day complication and mortality data were collected and analyzed. The mean age was 53.4 (range 7–102) years and 1046 (56.3%) were female. 1430 (59.8%) of ERCP procedures involved a surgical endoscopy fellow. The most common indication was suspected or established uncomplicated common bile duct stones (n = 1470, 61.5%), followed by management of an existing biliary or pancreatic stent (n = 370, 15.5%) and acute biliary pancreatitis (n = 173, 7.2%). A therapeutic intervention was performed in 1564 (65.4%), a standard sphincterotomy in 1244 (52.0%), stent placement in 705 (29.5%) and stone removal in 638 (26.7%). When cannulation was attempted, the rate of successful cannulation was 94.1%. When cannulation was attempted during the patient’s first ERCP the cannulation rate was 92.4%. 94 complications occurred (5.4%); the most common complication was post-ERCP pancreatitis in 75 (4.2%), significant gastrointestinal bleeding in 7 (0.4%), ascending cholangitis in 11 (0.6%) and perforation in 1 (0.05%). 11 mortalities occurred (0.5%) but none of which were ERCP-related. When performed by well-trained surgical endoscopists, ERCP is associated with high success rate and acceptable complication rates consistent with previously published reports and in line with societal guidelines.

Graphene has been proposed as a high-quality contact to two-dimensional (2D) transition metal dichalcogenides (TMDs) for the development of “all 2D” devices. Here, we demonstrate the direct-growth of epitaxial graphene (EG) based lateral heterostructures where the EG acts as a directly grown contact to a molybdenum disulfide (MoS2) channel. Utilizing a “seed-free” process, the nucleation of MoS2 occurs at the lateral substrate/graphene interface, and subsequently grows outward from the edge of the graphene. Transmission electron microscopy (TEM) of the heterostructure provides the first direct observation that a pristine vertical overlap of MoS2 on graphene exists, instead of previously reported horizontal stitching, and demonstrates full preservation of the van der Waals gap in the overlap region. Electrolytic gating of the MoS2/EG heterostructures provides evidence that EG can significantly improve transport compared to the traditional metal/MoS2 junctions, reducing contact resistance by > 10x, while reducing the sheet resistance by ∼ 70%.

Evaluating and tuning the properties of two-dimensional (2D) materials is a major focus of advancing 2D science and technology. While many claim that the photonic properties of a 2D layer provide evidence that the material is “high quality”, this may not be true for electronic performance. In this work, we deconvolute the photonic and electronic response of synthetic monolayer molybdenum disulfide. We demonstrate that enhanced photoluminescence can be robustly engineered via the proper choice of substrate, where growth of MoS2 on r-plane sapphire can yield >100x enhancement in PL and carrier lifetime due to increased molybdenum-oxygen bonding compared to that of traditionally grown MoS2 on c-plane sapphire. These dramatic enhancements in optical properties are similar to those of super-acid treated MoS2, and suggest that the electronic properties of the MoS2 are also superior. However, a direct comparison of the charge transport properties indicates that the enhanced PL due to increased Mo-O bonding leads to p-type compensation doping, and is accompanied by a 2x degradation in transport properties compared to MoS2 grown on c-plane sapphire. This work provides a foundation for understanding the link between photonic and electronic performance of 2D semiconducting layers, and demonstrates that they are not always correlated.

Formation of an electric double layer (EDL) is a powerful approach for exploring the electronic properties of two-dimensional (2D) materials because of the ultrahigh capacitance and induced charge in the 2D materials. In this work, epitaxial graphene Hall bar devices are gated with an EDL using a 1 μm thick solid polymer electrolyte, poly(ethylene oxide) and LiClO4. In addition to carrier density and mobility, ion dynamics associated with the formation and dissipation of the EDL are measured as a function of temperature over a gate bias range of ±2 V. The room temperature EDL formation time (∼1–100 s) is longer than the dissipation time (∼10 ms). The EDL dissipation is modeled by a stretched exponential decay, and the temperature-dependent dissipation times are described by the Vogel–Fulcher–Tammann equation, reflecting the coupling between polymer and ion mobility. At low temperatures, approaching the glass transition temperature of the electrolyte, the dissipation times of both cations and anions exceed...

Nanoscale conductive filaments, usually associated with resistive memory or memristor technology, may also be used for chemical sensing and nanophotonic applications; however, realistic implementation of the technology requires precise knowledge of the conditions that control the formation and dissolution of filaments. Here we describe and characterize an addressable direct-write nanoelectrochemical approach to achieve repeatable formation/dissolution of Ag filaments across a ~100 nm poly(ethylene oxide) (PEO) film containing either Ag(+) alone or Ag(+) together with 50 nm Ag-nanoparticles acting as bipolar electrodes. Using a conductive AFM tip, formation occurs when the PEO film is subjected to a forward bias, and dissolution occurs under reverse bias. Formation-dissolution kinetics were studied for three film compositions: Ag∣PEO-Ag(+), Ag∣poly(ethylene glycol) monolayer-PEO-Ag(+), and Ag∣poly(ethylene glycol) monolayer-PEO-Ag(+)/Ag-nanoparticle. Statistical analysis shows that the distribution of formation times exhibits Gaussian behavior, and the fastest average initial formation time occurs for the Ag∣PEO-Ag(+) system. In contrast, formation in the presence of Ag nanoparticles likely proceeds by a noncontact bipolar electrochemical mechanism, exhibiting the slowest initial filament formation. Dissolution times are log-normal for all three systems, and repeated reformation of filaments from previously formed structures is characterized by rapid regrowth. The direct-write bipolar electrochemical deposition/dissolution strategy developed here presents an approach to reconfigurable, noncontact in situ wiring of nanoparticle arrays-thereby enabling applications where actively controlled connectivity of nanoparticle arrays is used to manipulate nanoelectronic and nanophotonic behavior. The system further allows for facile manipulation of experimental conditions while simultaneously characterizing surface conditions and filament formation/dissolution kinetics.

To avoid defects associated with inhomogeneous crystallites and uneven morphology that degrade organic device performance, the deposition of ultraflat and homogeneous crystalline organic active layers is required. The growth mode transition of organic semiconducting titanyl phthalocyanine (TiOPc) molecule from monolayer-by-monolayer to bilayer-by-bilayer can be observed on highly ordered pyrolytic graphic (HOPG), while maintaining large and molecularly flat domains. The first monolayer of TiOPc lies flat on HOPG with a ∼98% face-up orientation. However, as the thickness of the TiOPc increases to over 15 monolayers (ML), the growth mode transitions to bilayer-by-bilayer with the repeated stacking of bilayers (BL), each of which has face-to-face pairs. Density functional theory calculations reveal that the increasing of thickness induces weakening of the substrate effect on the deposited TiOPc layers, resulting in the growth mode transition to BL-by-BL. The asymmetric stacking provides the driving force to ...

Macrocyclic crown ethers (CEs) have tunable cavity sizes and site-selective binding with metal ions, making the CE-ion complex a promising candidate as a two-dimensional (2D) electrolyte. In this work, density functional theory method is used to determine the energetically stable structures of 12-crown-4 ether (CE4) and 15-crown-5 ether (CE5) complexed with four cations: Li + , Na + , Mg 2 + , Ca 2 + . In addition to the CE-ion binding energies, the diffusion barriers for ion transport through the CE cavities are calculated. Among the complexes investigated, CE5 presents the lowest energy barrier for ion diffusion. The barriers for Li + travelling through a single CE5 and moving between two CE5s are 0.29 eV and 0.16 eV, respectively. Field-controlled modulation of the diffusion barrier is also demonstrated. By applying a 0.15 V/A electric field perpendicular to the plane of the CE, the diffusion barrier of Li + through one CE5 can be reduced from 0.29 to 0.20 eV to facilitate the ion transport.

Electric double-layer (EDL) gating using a custom-synthesized polyester single-ion conductor (PE400-Li) is demonstrated on two-dimensional (2D) crystals for the first time. The electronic properties of graphene and MoTe2 field-effect transistors (FETs) gated with the single-ion conductor are directly compared to a poly(ethylene oxide) dual-ion conductor (PEO:CsClO4). The anions in the single-ion conductor are covalently bound to the backbone of the polymer, leaving only the cations free to form an EDL at the negative electrode and a corresponding cationic depletion layer at the positive electrode. Because the cations are mobile in both the single- and dual-ion conductors, a similar enhancement of the n-branch is observed in both graphene and MoTe2. Specifically, the single-ion conductor decreases the subthreshold swing in the n-branch of the bare MoTe2 FET from 5000 to 250 mV/dec and increases the current density and on/off ratio by two orders of magnitude. However, the single-ion conductor suppressed the p-branch in both the graphene and the MoTe2 FETs, and finite element modeling of ion transport shows that this result is unique to single-ion conductor gating in combination with an asymmetric gate/channel geometry. Both the experiments and modeling suggest that single-ion conductor-gated FETs can achieve sheet densities up to 1014 cm-2, which corresponds to a charge density that would theoretically be sufficient to induce several percent strain in monolayer 2D crystals and potentially induce a semiconductor-to-metal phase transition in MoTe2.

Engineering p-n junctions in two-dimensional (2D) materials, specifically transition metal dichalcogenides (TMDs), entails choosing the right combination of materials in order to form the appropriate alignment of bands. A bi-polar junction having a heterogenous combinations of materials has traditionally been used for several applications such as rectifiers, photovoltaics, etc, which require separation of charge carriers. Various researchers have studied the synthesis and properties of p-n junctions in TMD-TMD heterostructures, like MoS 2 /WSe 2 , Mos 2 /ws 2 , etc.1 In this work, we show the formation of a low resistance p-n junction between graphene and molybdenum disulfide (MOS 2 ), which harnesses the high thermal and electronic mobility of graphene, which semiconducting TMDs do not provide. Our work employs epitaxial graphene (EG) on silicon carbide substrates, which has the unique property of doping modulation using hydrogen intercalation.2,3 This has not been exploited previously to construct devices using graphene-based heterostructures.

Silver nanofilament formation dynamics are reported for an ionic liquid (IL)-filled solid polymer electrolyte prepared by a direct-write process using a conductive atomic force microscope (C-AFM). Filaments are electrochemically formed at hundreds of xy locations on a (~)40 nm thick polymer electrolyte, polyethylene glycol diacrylate (PEGDA)/[BMIM]PF(6). Although the formation time generally decreases with increasing bias from 0.7 to 3.0 V, an unexpected non-monotonic maximum is observed (~) 2.0 V. At voltages approaching this region of inverted kinetics, IL electric double layers (EDLs) becomes detectable; thus, the increased nanofilament formation time can be attributed to electric field screening which hinders silver electro-migration and deposition. Scanning electron microscopy confirms that nanofilaments formed in this inverted region have significantly more lateral and diffuse features. Time-dependent formation currents reveal two types of nanofilament growth dynamics: abrupt, where the resistance decreases sharply over as little as a few ms, and gradual where it decreases more slowly over hundreds of ms. Whether the resistance change is abrupt or gradual depends on the extent to which the EDL screens the electric field. Tuning the formation time and growth dynamics using an IL opens the range of accessible resistance states, which is useful for neuromorphic applications.

We demonstrate that the exciton energy of a monolayer of tungsten diselenide on an SiO2/Si substrate can be tuned by an applied in-plane electric field for two samples with different dielectric capping materials. The exciton energy can be either red- or blue-shifted by up to 20 meV based on the polarity of the applied electric field. We argue that a piezoelectric effect creates a large internal electric field, which is either partially aligned or partially antialigned with the external electric field. Additionally, optical hysteresis is observed on cycling of the external electric field due to trapped charges.

We report extraordinarily high capacitance density in tungsten diselenide (WSe2) field-effect transistors (FETs) capped with polyethylene oxide (PEO) and ion doped with cesium perchlorate (CsCI04). The FETs have 3–4 monolayer WSe2 channels grown by chemical vapor deposition (CVD) using W(CO) 6 and H2Se at 800 °C for 30 minutes [1]. A stepper-based process was used to fabricate the transistors and an 11 nm Al 2 O 3 atomic layer deposited (ALD) gate dielectric was formed on the WSe2 with a low temperature nucleation layer, 1 nm Ah03, deposited at 110 °C to facilitate nucleation followed by a 10 nm Ah03 deposited at 200 °C, after Kwak [2]. The n-FET achieves an ON/OFF ratio of 106 with noise-floor-limited gate current. Most prior studies of WSe2 FETs have been on exfoliated materials and to our knowledge there is only one prior report of a top-gated CVD WSe2 p-FET [3]. Following FET characterization PEO: CsCI04 was drop-cast and annealed at 90 °C for 3 minutes in Ar after Xu [4], yielding a layer thickness of 400 nm as measured by transmission electron microscopy (TEM). Ion gating using a side gate ( $6\ \mu\mathrm{m}$ from the WSe2 mesa edge) produces ambipolar transfer characteristics with approximately equal ON-currents of $2\ \mu\mathrm{A}/\mu\mathrm{m}$ attributed to the multi-work-function source/drain contacts [5]. ON/OFF current ratio exceeds 106 with field-effect electron and hole mobilities of 10 and 25 cm2/Vs respectively and subthreshold swings of 260 and 180 mY/decade respectively. Atomic force microscope images show that the WSe2 nucleates in triangles which are apparent in Fig. 1; FET characteristics after testing of the transistor are shown in Fig. 2 along with TEM.

Atomically thin transition metal dichalcogenides (TMDs) are of interest for next-generation electronics and optoelectronics. Here, we demonstrate device-ready synthetic tungsten diselenide (WSe2) via metal–organic chemical vapor deposition and provide key insights into the phenomena that control the properties of large-area, epitaxial TMDs. When epitaxy is achieved, the sapphire surface reconstructs, leading to strong 2D/3D (i.e., TMD/substrate) interactions that impact carrier transport. Furthermore, we demonstrate that substrate step edges are a major source of carrier doping and scattering. Even with 2D/3D coupling, transistors utilizing transfer-free epitaxial WSe2/sapphire exhibit ambipolar behavior with excellent on/off ratios (∼107), high current density (1–10 μA·μm–1), and good field-effect transistor mobility (∼30 cm2·V–1·s–1) at room temperature. This work establishes that realization of electronic-grade epitaxial TMDs must consider the impact of the TMD precursors, substrate, and the 2D/3D inte...

The utilization of alkali salts, such as NaCl and KI, have 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 are 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 a high density of nanoscale MoS2 particles (4/{\mu}m2). 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 ~20x and degrades transistor performance., Comment: 12 pages, 4 figures

Several proposed beyond-CMOS devices based on two-dimensional (2D) heterostructures require the deposition of thin dielectrics between 2D layers. However, the direct deposition of dielectrics on 2D materials is challenging due to their inert surface chemistry. To deposit high-quality, thin dielectrics on 2D materials, a flat lying titanyl phthalocyanine (TiOPc) monolayer, deposited via the molecular beam epitaxy, was employed to create a seed layer for atomic layer deposition (ALD) on 2D materials, and the initial stage of growth was probed using in situ STM. ALD pulses of trimethyl aluminum (TMA) and H2O resulted in the uniform deposition of AlOx on the TiOPc/HOPG. The uniformity of the dielectric is consistent with DFT calculations showing multiple reaction sites are available on the TiOPc molecule for reaction with TMA. Capacitors prepared with 50 cycles of AlOx on TiOPc/graphene display a capacitance greater than 1000 nF/cm(2), and dual-gated devices have current densities of 10(-7)A/cm(2) with 40 cycles.

15-Crown-5-ether-substituted cobalt(II) phthalocyanine (CoCrPc) is an atomically thin and flat-laying, electrically insulating molecule that can solvate ions; these properties are desirable for nanoelectronic devices. A simple, solution-phase deposition method is demonstrated to produce a monolayer of CoCrPc on highly ordered pyrolytic graphite (HOPG). A uniform and continuous CoCrPc layer is obtained on freshly cleaved HOPG by solution drop casting, followed by thermal annealing under ambient pressure in Ar in the temperature range of 150–210 °C. While the quality of the monolayer is independent of annealing time, the composition of the annealing atmosphere is critical; exposure to ambient air degrades the quality of the monolayer over the time scale of minutes. Using ultrahigh vacuum scanning tunneling microscopy, a highly ordered and flat CoCrPc layer with hexagonal symmetry and average spacing of 4.09 ± 0.2 nm is observed. The band gap of the CoCrPc, measured by scanning tunneling spectroscopy, is 1.3...

Adsorption of molecules on graphene is a promising route to achieve novel functionalizations, which can lead to new devices. Density functional theory is used to calculate stabilities, electronic structures, charge transfer, and work function for a crown-4 ether (CE) molecule and a CE–Li (or CE–Li+) complex adsorbed on graphene. For a single CE on graphene, the adsorption distance is large with small adsorption energies, regardless of the relative lateral location of the CE. Because CE interacts weakly with graphene, the charge transfer between the CE and graphene is negligibly small. When Li and Li+ are incorporated, the adsorption energies significantly increase. Simultaneously, an n-type doping of graphene is introduced by a considerable amount of charge transfer in CE–Li adsorbed system. In all of the investigated systems, the linear dispersion of the pz band in graphene at the Dirac point is well-preserved; however, the work function of graphene is effectively modulated in the range of 3.69 to 5.09 e...

We present a simple and inexpensive technique to enable 3D, high-resolution, and quantitative imaging of dissolved oxygen in aqueous media using a commercially available hydrophobic dye, [Ru(dpp)3]2+. The dye is encapsulated in nanomicelles formed by a poloxamer (a biocompatible surfactant), allowing for uniform dispersion in aqueous media without long, complex, and expensive chemical synthesis procedures. The nanomicelle probes are tested and found to remain stable for several months in water and for several hours in biological media. The probes are sufficiently large in size for vasculature retention and enable intravenous oxygen imaging in vivo. The two-photon cross-section of the [Ru(dpp)3]2+ nanomicelle probes surpass that of the well-established and widely used oxygen-sensitive probes in multiphoton microscopy. We also characterize the oxygen-sensitivity of the probes as a proof of their viability as low cost and easily prepared markers for multiphoton quantitative oxygen imaging in vivo and for other applications in aqueous media.

While planar two-dimensional field effect transistors (FETs) are being widely explored [1], there are only a few reports of MoS2 [2-4] and WS 2 [5-8] nanotube (NT) and nanoribbon (NR) FETs. A benefit of these crystalline forms is the absence of edges associated with traps, and the potential for ideal subthreshold swing with wrapped gates. Density functional theory predicts that the bandgap of MoS 2 nanotubes remains direct and decreases with diameter [9] due to strain. This makes nanotubes appealing for tunnel FETs at the scaling limit because the decrease in bandgap should provide an increase in current. Here we report the first WS2 NT and NR FETs synthesized by chemical vapor transport (CVT) [10]. Prior reports on WS 2 [5-8] are based on sulphurization of W and WO nanowhiskers.

The temperature-dependent ionic conductivity and thermal properties are characterized for a solid polymer electrolyte of poly(ethylene oxide) (PEO) and LiClO4 filled with 1 wt % γ-phase core (maghemite) and α-phase shell (hematite) Fe2O3 nanorods. Samples are solvent-cast in the absence and presence of a 0.5 T magnetic field, dried at room temperature under vacuum for 72 h, and measured under nitrogen. Vibrating sample magnetometry indicates that the magnetic treatment aligns the nanorods to some extent in the desired orientation normal to the electrode surface. For samples with an ether oxygen to lithium ratio (EO/Li) of 10:1, the nanorods induce sample-to-sample variability in the ionic conductivity. The magnetic treatment eliminates this variability, and differential scanning calorimetry data support the observation that the magnetic treatment increases the structural homogeneity of the electrolyte. For samples with an EO/Li of 3:1, the ionic conductivity is 3 orders of magnitude larger for samples con...

The structure of a hydrated poly(N-isopropylacrylamide) brush loaded with 5 vol % Isoniazid is studied as a function of temperature using neutron reflectometry (NR) and atomic force microscopy (AFM). NR measurements show that Isoniazid increases the thickness of the brush before, during and after the polymer collapse, and it is retained inside the brush at all measured temperatures. The Isoniazid concentration in the expanded brush is ~14% higher than in the bulk solution, and the concentration nearly doubles in the collapsed polymer, suggesting stronger binding between Isoniazid and the polymer compared to water, even at temperatures below the lower critical solution temperature (LCST) where the polymer is hydrophilic. Typically, additives that bind strongly to the polymer backbone and increase the hydrophilicity of the polymer will delay the onset of the LCST, which is suggested by AFM and NR measurements. The extent of small-molecule loading and distribution throughout a thermo-responsive polymer brush, such as pNIPAAm, will have important consequences for applications such as drug delivery and gating.

To deposit an ultrathin dielectric onto WSe2, monolayer titanyl phthalocyanine (TiOPc) is deposited by molecular beam epitaxy as a seed layer for atomic layer deposition (ALD) of Al2O3 on WSe2. TiOPc molecules are arranged in a flat monolayer with 4-fold symmetry as measured by scanning tunneling microscopy. ALD pulses of trimethyl aluminum and H2O nucleate on the TiOPc, resulting in a uniform deposition of Al2O3, as confirmed by atomic force microscopy and cross-sectional transmission electron microscopy. The field-effect transistors (FETs) formed using this process have a leakage current of 0.046 pA/μm(2) at 1 V gate bias with 3.0 nm equivalent oxide thickness, which is a lower leakage current than prior reports. The n-branch of the FET yielded a subthreshold swing of 80 mV/decade.

We demonstrate the first electric double layer p-i-n junction in the channel of a WSe 2 field-effect transistor (FET). The measured current-voltage (I-V) characteristics have a nearly constant ideality factor over approximately three orders of magnitude in current. This is better than any prior report on WSe 2 . The formation technique has wide applicability across materials systems and is of particular interest for the formation of source-channel junctions in tunnel FETs in transition metal dichalcogenides (TMDs) [1]. The most ideal TMD p-n junctions formed to date have been achieved using buried gates under WSe 2 by Ross [2], under MoS 2 by Sutar [3], by charge transfer doping in MoS 2 by Choi [4] and Li [5], and by EDL formation in MoTe 2 by Xu [6]. The junction formation described in this paper does not require fabrication of additional field plates to position the ions.

Tin Diselenide (SnSe 2 ) is a two-dimensional layered crystal commonly found in octahedral coordination (1T phase). It has been reported to have a high electron affinity of around 5.1 eV and a bandgap of 1 eV [1-2], which can form staggered band alignment with tungsten diselenide (WSe 2 ) in Thin-TFETs [3]. However, its lack of gate modulation remains a mystery [4]. In this work, we investigate the Fermi level tunability of SnSe 2 by counter doping using a polymer electrolyte, PEO:CsClO 4 . This counter doping technique increases the on/off ratio of SnSe 2 field effect transistor (FET) from 2 times to 50 times, a record high value. Meanwhile, a device model of SnSe 2 FET with ion doping and subgap density of states (DOS) has been proposed to fit the experimental data. The extracted effective number of acceptor-like subgap states is as high as 4.16 × 1019 cm−3 (in comparison with near 5 × 1017 cm−3 extracted for amorphous thin-film transistors [5]). This can explain the weak Fermi level tunability of SnSe 2 and direct future material development towards TFETs.