Van Der Waals Contacts Research Articles

Origins of genuine Ohmic van der Waals contact between indium and MoS2

The achievement of ultraclean Ohmic van der Waals (vdW) contacts at metal/transition-metal dichalcogenide (TMDC) interfaces would represent a critical step for the development of high-performance electronic and optoelectronic devices based on two-dimensional (2D) semiconductors. Herein, we report the fabrication of ultraclean vdW contacts between indium (In) and molybdenum disulfide (MoS2) and the clarification of the atomistic origins of its Ohmic-like transport properties. Atomically clean In/MoS2 vdW contacts are achieved by evaporating In with a relatively low thermal energy and subsequently cooling the substrate holder down to ~100 K by liquid nitrogen. We reveal that the high-quality In/MoS2 vdW contacts are characterized by a small interfacial charge transfer and the Ohmic-like transport based on the field-emission mechanism over a wide temperature range from 2.4 to 300 K. Accordingly, the contact resistance reaches ~600 Ω μm and ~1000 Ω μm at cryogenic temperatures for the few-layer and monolayer MoS2 cases, respectively. Density functional calculations show that the formation of large in-gap states due to the hybridization between In and MoS2 conduction band edge states is the microscopic origins of the Ohmic charge injection. We suggest that seeking a mechanism to generate strong density of in-gap states while maintaining the pristine contact geometry with marginal interfacial charge transfer could be a general strategy to simultaneously avoid Fermi-level pinning and minimize contact resistance for 2D vdW materials.

Quantitative analysis of weak current rectification in molecular tunnel junctions subject to mechanical deformation reveals two different rectification mechanisms for oligophenylene thiols versus alkane thiols.

Metal-molecule-metal junctions based on alkane thiol (CnT) and oligophenylene thiol (OPTn) self-assembled monolayers (SAMs) and Au electrodes are expected to exhibit similar electrical asymmetry, as both junctions have one chemisorbed Au-S contact and one physisorbed, van der Waals contact. Asymmetry is quantified by the current rectification ratio RR apparent in the current-voltage (I-V) characteristics. Here we show that RR < 1 for CnT and RR > 1 for OPTn junctions, in contrast to expectation, and further, that RR behaves very differently for CnT and OPTn junctions under mechanical extension using the conducting probe atomic force microscopy (CP-AFM) testbed. The analysis presented in this paper, which leverages results from the previously validated single level model and ab initio quantum chemical calculations, allows us to explain the puzzling experimental findings for CnT and OPTn in terms of different current rectification mechanisms. Specifically, in CnT-based junctions the Stark effect creates the HOMO level shifting necessary for rectification, while for OPTn junctions the level shift arises from position-dependent coupling of the HOMO wavefunction with the junction electrostatic potential profile. On the basis of these mechanisms, our quantum chemical calculations allow quantitative description of the impact of mechanical deformation on the measured current rectification. Additionally, our analysis, matched to experiment, facilitates direct estimation of the impact of intramolecular electrostatic screening on the junction potential profile. Overall, our examination of current rectification in benchmark molecular tunnel junctions illuminates key physical mechanisms at play in single step tunneling through molecules, and demonstrates the quantitative agreement that can be obtained between experiment and theory in these systems.

Crystal structure of 2-hy-droxy-2-phenyl-aceto-phenone oxime.

The title compound [systematic name: 2-(N-hy-droxy-imino)-1,2-di-phenyl-ethanol], C14H13NO2, consists of hy-droxy phenyl-aceto-phenone and oxime units, in which the phenyl rings are oriented at a dihedral angle of 80.54 (7)°. In the crystal, inter-molecular O-HOxm⋯NOxm, O-HHydr⋯OHydr, O-H'Hydr⋯OHydr and O-HOxm⋯OHydr hydrogen bonds link the mol-ecules into infinite chains along the c-axis direction. π-π contacts between inversion-related of the phenyl ring adjacent to the oxime group have a centroid-centroid separation of 3.904 (3) Å and a weak C-H⋯π(ring) inter-action is also observed. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H (58.4%) and H⋯C/C⋯H (26.4%) contacts. Hydrogen bonding and van der Waals contacts are the dominant inter-actions in the crystal packing.

Synthesis of 2D semiconducting single crystalline Bi2S3 for high performance electronics.

2-Dimensional (2D) semiconducting materials are attractive candidates for future electronic device applications due to the tunable bandgap, transparency, flexibility, and downscaling to the atomic level in material size and thickness. However, 2D materials have critical issues regarding van der Waals contact, interface instability and power consumption. In particular, the development of semiconducting electronics based on 2D materials is significantly hindered by a low charge-carrier mobility. In order to improve the critical shortcoming, diverse efforts have been made in synthesis and device engineering. Here, we propose a synthesis method of single crystalline 2D Bi2S3 by chemical vapor deposition for high performance electronic device applications. The ion-gel gated field effect transistor with the as-grown Bi2S3 on the SiO2 substrate exhibits a high mobility of 100.4 cm2 V-1 S-1 and an on-off current ratio of 104 under a low gate voltage below 4 V at room temperature without chemical doping and surface engineering. The superior performance is attributed to the high crystal quality of Bi2S3 that shows low sulfur vacancies and atomic ratio close to the ideal value (2 : 3) under a rich sulfur growth process using H2S gas instead of sulfur powder. The synthesis method will provide a platform to realize high performance electronics and optoelectronics based on 2D semiconductors.

Novel mechanisms of the conformational transformations of the biologically important G·C nucleobase pairs in Watson-Crick, Hoogsteen and wobble configurations via the mutual rotations of the bases around the intermolecular H-bonds: a QM/QTAIM study.

At the MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p) level of quantum-mechanical theory, we provide for the first time a comprehensive investigation of the physico-chemical mechanisms of the 55 conformational transformations of the biologically-important G·C nucleobase pairs – Watson–Crick (WC), reverse Watson–Crick (rWC), Hoogsteen (H), reverse Hoogsteen (rH), wobble (w) and reverse wobble (rw) base pairs by the participation of the G and C bases in the canonical and rare tautomeric forms (“r” – means reverse configuration of the base pair). It was established that all these G·C nucleobase pairs can conformationally transform into each other without the changing of the tautomeric status of the G and C bases. These transitions occur through significantly non-planar transition states via the mutual rotation of the G and C bases relative to each other within the G·C nucleobase pair around the upper, middle or lower intermolecular H-bonds: WC ↔ rWC, WC ↔ rwWC, rWC ↔ WC, rWC ↔ wWC, wWC ↔ rwWC, H ↔ rH, H ↔ rwH, rH ↔ H, rH ↔ wH, wH ↔ rwH. Gibbs free energies ΔG of activation for these conformational transformations are ΔG = 2.96–19.04/3.58–13.36 kcal mol−1 (in vacuum under normal conditions (T = 298.15 K)), which means that these reactions proceed quite fast. Obtained conformational transformations are accompanied by the disruption and further formation of the intermolecular specific contacts in the G·C nucleobase pairs (H-bonds and attractive van der Waals contacts). As a result, 76 conformers of the G·C nucleobase pairs were established – 48 base pairs in WC, rWC, wWC and rwWC configurations and 28 base pairs in H, rH, wH and rwH configurations with relative Gibbs free ΔG/electronic ΔE energies in the range ΔG/ΔE = 0.00–44.73/0.00–46.99 and ΔG/ΔE = 0.00–37.52/0.00–38.54 kcal mol−1, respectively (in vacuum under normal conditions). Experimental investigation and verification of the novel G·C nucleobase pairs are promising tasks for the future research. Based on the obtained data, biologically important conclusions were made about the importance of the conformational mobility of the G·C nucleobase pairs for the understanding of the functioning of the DNA and RNA molecules and their transition from the parallel into the anti-parallel duplexes and vice versa.

Mechanism of recognition of parallel G-quadruplexes by DEAH/RHAU helicase DHX36 explored by molecular dynamics simulations

Because of high stability and slow unfolding rates of G-quadruplexes (G4), cells have evolved specialized helicases that disrupt these non-canonical DNA and RNA structures in an ATP-dependent manner. One example is DHX36, a DEAH-box helicase, which participates in gene expression and replication by recognizing and unwinding parallel G4s. Here, we studied the molecular basis for the high affinity and specificity of DHX36 for parallel-type G4s using all-atom molecular dynamics simulations. By computing binding free energies, we found that the two main G4-interacting subdomains of DHX36, DSM and OB, separately exhibit high G4 affinity but they act cooperatively to recognize two distinctive features of parallel G4s: the exposed planar face of a guanine tetrad and the unique backbone conformation of a continuous guanine tract, respectively. Our results also show that DSM-mediated interactions are the main contributor to the binding free energy and rely on making extensive van der Waals contacts between the GXXXG motifs and hydrophobic residues of DSM and a flat guanine plane. Accordingly, the sterically more accessible 5′-G-tetrad allows for more favorable van der Waals and hydrophobic interactions which leads to the preferential binding of DSM to the 5′-side. In contrast to DSM, OB binds to G4 mostly through polar interactions by flexibly adapting to the 5′-terminal guanine tract to form a number of strong hydrogen bonds with the backbone phosphate groups. We also identified a third DHX36/G4 interaction site formed by the flexible loop missing in the crystal structure.

Rational Computational Design of Fourth-Generation EGFR Inhibitors to Combat Drug-Resistant Non-Small Cell Lung Cancer.

Although the inhibitors of singly mutated epidermal growth factor receptor (EGFR) kinase are effective for the treatment of non-small cell lung cancer (NSCLC), their clinical efficacy has been limited due to the emergence of various double and triple EGFR mutants with drug resistance. It has thus become urgent to identify potent and selective inhibitors of triple mutant EGFRs resistant to first-, second-, and third-generation EGFR inhibitors. Herein, we report the discovery of potent and highly selective inhibitors of EGFR exon 19 p.E746_A750del/EGFR exon 20 p.T790M/EGFR exon 20 p.C797S (d746-750/T790M/C797S) mutant, which were derived via two-track virtual screening and de novo design. This two-track approach was performed so as to maximize and minimize the inhibitory activity against the triple mutant and the wild type, respectively. Extensive chemical modifications of the initial hit compounds led to the identification of several low-nanomolar inhibitors of the d746-750/T790M/C797S mutant. Among them, two compounds exhibited more than 104-fold selectivity in the inhibition of EGFRd746-750/T790M/C797S over the wild type. The formations of a hydrogen bond with the mutated residue Ser797 and the van der Waals contact with the mutated residue Met790 were found to be a common feature in the interactions between EGFRd746-750/T790M/C797S and the fourth-generation inhibitors. Such an exceptionally high selectivity could also be attributed to the formation of the hydrophobic contact with a Gly loop residue or the hydrogen bond with Asp855 in the activation loop. The discovery of the potent and selective EGFRd746-750/T790M/C797S inhibitors were actually made possible by virtue of the modified protein–ligand binding free energy function involving a new hydration free energy term with enhanced accuracy. The fourth-generation EGFR inhibitors found in this work are anticipated to serve as a new starting point for the discovery of anti-NSCLC medicines to overcome the problematic drug resistance.

Self-driven WSe2 photodetectors enabled with asymmetrical van der Waals contact interfaces

Self-driven photodetectors that can detect light without any external voltage bias are important for low-power applications, including future internet of things, wearable electronics, and flexible electronics. While two-dimensional (2D) materials exhibit good optoelectronic properties, the extraordinary properties have not been fully exploited to realize high-performance self-driven photodetectors. In this paper, a metal–semiconductor–metal (MSM) photodetector with graphene and Au as the two contacts have been proposed to realize the self-driven photodetector. Van der Waals contacts are formed by dry-transfer methods, which is important in constructing the asymmetrical MSM photodetector to avoid the Fermi-level pinning effect. By choosing graphene and Au as the two contact electrodes, a pronounced photovoltaic effect is obtained. Without any external bias, the self-driven photodetector exhibits a high responsivity of 7.55 A W−1 and an ultrahigh photocurrent-to-dark current ratio of ~108. The photodetector also shows gate-tunable characteristics due to the field-induced Fermi-level shift in the constituent 2D materials. What is more, the high linearity of the photodetector over almost 60 dB suggests the easy integration with processing circuits for practical applications.

Crystal structure of cephalexin monohydrate, C16H17N3O4S(H2O)

The crystal structure of cephalexin monohydrate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Cephalexin monohydrate crystallizes in space group C2 (#5) with a = 27.32290(17), b = 11.92850(4), c = 16.75355(8) Å, β = 108.8661(4)°, V = 5166.99(3) Å3, and Z = 12. Although the general arrangement of molecules is similar to that in cephalexin dihydrate, the structural differences result in very different powder patterns. The crystal structure is characterized by alternating layers of hydrogen bonds and van der Waals contacts parallel to the bc-plane. The water molecules occur in clusters. Five of the six protons in the water molecules act as donors in O–H⋯O hydrogen bonds. The sixth hydrogen atom acts as a donor to two different phenyl ring carbon atoms to form bifurcated O–H⋯C hydrogen bonds. Each cephalexin molecule is a zwitterion, containing ammonium and carboxylate groups. The ammonium ions form N–H⋯O hydrogen bonds to carboxylate groups and water molecules, as well as to carbonyl groups. The powder pattern is included in the Powder Diffraction File™ as entry 00-065-1417.

GC-MS aided In silico molecular docking studies on the anti-sickling properties of Zanthoxylum zanthoxyloides (Lam.) Zepern. &amp; Timler stem bark

Zanthoxylum zanthoxyloides is an important medicinal herb in African traditional medicine. It has been used to treat an array of pathological conditions, most notably is sickle cell anaemia, one of the most important genetic haematological conditions affecting individuals of African descent. This study identifies and evaluates Zanthoxylum zanthoxyloides bioactives with potential haemoglobin oxygen-affinity modulatory activity. Phytochemical constituents identified via gas chromatography-mass spectrometry of a 70% ethanolic stem bark extract of Zanthoxylum zanthoxyloides (Lam.) Zepern. and Timler were analyzed for their in silico anti-sickling activity. Gas chromatography-mass spectrometry aided in silico molecular docking studies identified the presence of two compounds, 7-(dimethylamino)-2,3-dihydro-1H cyclopenta[c]chromen-4-one and (8S,9S,10R,13S,14S,16R,17S)-17-acetyl-6,10,13,16-tetramethyl-8,9,11,12,14,15,16,17-octahydrocyclopenta[a]phenanthren-3-one, with a strong binding affinity for the active pocket located at the N-terminal region (valine 1) of the alpha globin subunit of haemoglobin S. Further analysis of the binding pose of the ligands demonstrated the formation of favourable interactions including hydrogen bonding, π-cation, van der Waals and hydrophobic contacts. Computational investigations on the pharmacokinetic profile of 7-(dimethylamino)-2,3-dihydro-1H cyclopenta[c]chromen-4-one and (8S,9S,10R,13S,14S,16R,17S)-17-acetyl-6,10,13,16-tetramethyl-8,9,11,12,14,15,16,17-octahydrocyclopenta[a]phenanthren-3-one reveals a favourable oral bioavailability and drug-likeness profile. The findings add to the evidence bolstering the role of Zanthoxylum zanthoxyloides in the management of sickle cell anemia.

Mimicking Natural Photosynthesis: Designing Ultrafast Photosensitized Electron Transfer into Multiheme Cytochrome Protein Nanowires.

Efficient nanomaterials for artificial photosynthesis require fast and robust unidirectional electron transfer (ET) from photosensitizers through charge-separation and accumulation units to redox-active catalytic sites. We explored the ultrafast time-scale limits of photo-induced charge transfer between a Ru(II)tris(bipyridine) derivative photosensitizer and PpcA, a 3-heme c-type cytochrome serving as a nanoscale biological wire. Four covalent attachment sites (K28C, K29C, K52C, and G53C) were engineered in PpcA enabling site-specific covalent labeling with expected donor-acceptor (DA) distances of 4–8 Å. X-ray scattering results demonstrated that mutations and chemical labeling did not disrupt the structure of the proteins. Time-resolved spectroscopy revealed three orders of magnitude difference in charge transfer rates for the systems with otherwise similar DA distances and the same number of covalent bonds separating donors and acceptors. All-atom molecular dynamics simulations provided additional insight into the structure-function requirements for ultrafast charge transfer and the requirement of van der Waals contact between aromatic atoms of photosensitizers and hemes in order to observe sub-nanosecond ET. This work demonstrates opportunities to utilize multi-heme c-cytochromes as frameworks for designing ultrafast light-driven ET into charge-accumulating biohybrid model systems, and ultimately for mimicking the photosynthetic paradigm of efficiently coupling ultrafast, light-driven electron transfer chemistry to multi-step catalysis within small, experimentally versatile photosynthetic biohybrid assemblies.

Energy Transfer across Nonpolar and Polar Contacts in Proteins: Role of Contact Fluctuations.

Molecular dynamics simulations of the villin headpiece subdomain HP36 have been carried out to examine relations between rates of vibrational energy transfer across non-covalently bonded contacts and equilibrium structural fluctuations, with focus on van der Waals contacts. Rates of energy transfer across van der Waals contacts vary inversely with the variance of the contact length, with the same constant of proportionality for all nonpolar contacts of HP36. A similar relation is observed for hydrogen bonds, but the proportionality depends on contact pairs, with hydrogen bonds stabilizing the α-helices all exhibiting the same constant of proportionality, one that is distinct from those computed for other polar contacts. Rates of energy transfer across van der Waals contacts are found to be up to 2 orders of magnitude smaller than rates of energy transfer across polar contacts.

Role of Protein Motions in Catalysis by Formate Dehydrogenase.

We have analyzed the reaction catalyzed by formate dehydrogenase using transition path sampling. This system has recently received experimental attention using infrared spectroscopy and heavy-enzyme studies. Some of the experimental results point to the possible importance of protein motions that are coupled to the chemical step. We found that the residue Val123 that lies behind the nicotinamide ring occasionally comes into van der Waals contact with the acceptor and that in all reactive trajectories, the barrier-crossing event is preceded by this contact, meaning that the motion of Val123 is part of the reaction coordinate. Experimental results have been interpreted with a two-dimensional formula for the chemical rate, which cannot capture effects such as the one we describe.

Graphene based Van der Waals contacts on MoS2 field effect transistors

Device performance of two dimensional (2D) material based field effect transistors is severely limited by the relatively high contact resistance encountered at the contact-channel interface. Metal-graphene hybrid contacts have been previously used to improve the contact resistance of devices based on thick exfoliated materials. Here we report a novel 2D FET fabrication process entailing the transfer of metal-graphene hybrid contacts on top of 3 monolayer-thick chemical vapor deposition (CVD) MoS2, enabling a lithography free contacting strategy, with respect to MoS2. Three different metal-graphene stacks consisting of Ni, Pd and Ru, have been fabricated, transferred onto MoS2 and characterized extensively using electrical and physical characterization techniques. We find strong correlation between the measured electrical characteristics and physical characterization of the contact interface. From Raman spectra measurement, maximum charge transfer of 1.7 × 1013 cm−2 is observed between graphene and Ru, leading to an improved contact resistance for MoS2 devices with Ru-Gr contacts. Ru-Gr contact shows the lowest contact resistance of 9.34 kΩ · µm among the three metal-graphene contact stacks reported in this article. This contact resistance is also the best among reported CVD grown graphene contacted MoS2 devices. Using more than 400 devices, we study the impact of the different metal-graphene contacts on other electrical parameters such as hysteresis, sub-threshold swing and threshold voltage. The metal-graphene contact stack transfer technique represents a technologically relevant contacting approach which can be further up-scaled to larger wafer areas.

Screening fermi-level pinning effect through van der waals contacts to monolayer MoS2

Nano-electronic devices incorporating Van der Waals electrical contact, particularly on two-dimensional semiconductor, offer exceptional electrical performance. However, the fabrication of Van der Waals electrical contact is still a challenge. Here, layered reduced graphene oxide (rGO) flakes are employed as buffer to construct the Van der Waals electrical contact in monolayer molybdenum disulfide (MoS2) transistors, and screen the Fermi-level pinning effect. The results show that the work function of monolayer MoS2 would increase by 0.12 eV and its electron concentration would decrease by 0.74 × 1012 cm−2, demonstrating the p-type doping role of rGO flakes. To quantitatively reveal the role of rGO buffer layer during the electrode fabrication, the MoS2 transistors w/o rGO buffer layer were fabricated on single monocrystalline MoS2 domain. Though comparatively studying the electrical properties at room/low temperature, it has been demonstrated the rGO buffer layer would contribute to forming van der Waals contacts and lead the dramatically decrease of Schottky barrier resulting in about ten times device mobility enhancement in MoS2 transistor.

Investigation of binding interaction between human serum albumin with zirconium complex of curcumin and curcumin

The current study investigates the binding process of Zr(CUR) as a novel six-coordinate complex of zirconium with curcumin ligand and curcumin (CUR); as the main pharmacologically active ingredient of turmeric to human serum albumin (HSA); using fluorescence spectroscopy, infrared spectroscopy and molecular docking techniques. The fluorimetric results revealed that Zr(CUR) and CUR could effectively quench the endogenous fluorescence of HSA, formed a 1:1 complex, with a static quenching mechanism. The distance between donor (HSA) and acceptor (Zr(CUR) and CUR) were determined to be 3.15 nm for Zr(CUR) and 2.95 nm for CUR on the basis of the Forester’s theory of non-radiative energy transfer. Results of the infrared absorption spectrum show that the secondary structure of HSA changes for both types. Molecular docking results indicated that for structure with minimum binding energy Zr(CUR) and CUR are in the position between IIA and IIIA. Also, a docking study showed that Zr(CUR) and CUR have several hydrogen bonds and Van der Waals contact with HSA. Communicated by Ramaswamy H. Sarma

Low‐Power Complementary Inverter with Negative Capacitance 2D Semiconductor Transistors

AbstractA fundamental limit for the supply voltage of conventional field‐effect transistors is the long high‐energy tail of the Boltzmann distribution of the carrier population at the source junction, which requires a gate voltage at least 60 mV to change one decade of current. Here 2D semiconductors are adopted as channel materials and hafnium zirconium oxide (HZO) as negative capacitance (NC) gate stack to realize low‐power complementary logic inverter. With HZO/Al2O3 NC gate stack, the 2D semiconductor field‐effect transistor (FET) shows an average subthreshold slope less than Boltzmann limit (as low as 18 mV dec−1) at room temperature for both forward and reverse gate voltage sweeps, which allows to reach the same ON‐state current at a lower Vdd without increasing the OFF‐state current. The drain current can be modulated by 5 × 104 within 220 mV, still exhibiting average SS below 60 mV dec−1. By constructing van der Waals contact to improve the charge injection and control the carrier type, unipolar p‐type WSe2 FET with reduced hole Schottky barrier height is achieved. The complementary inverter with MoS2 and WSe2 NCFETs shows the power consumption of 68 pW.

Some thermodynamic effects of varying nonpolar surfaces in protein-ligand interactions.

Understanding how making structural changes in small molecules affects their binding affinities for targeted proteins is central to improving strategies for rational drug design. To assess the effects of varying the nature of nonpolar groups upon binding entropies and enthalpies, we designed and prepared a set of Grb2-SH2 domain ligands, Ac-pTyr-Ac6c-Asn-(CH2)n-R, in which the size and electrostatic nature of R groups at the pTyr+3 site were varied. The complexes of these ligands with the Grb2-SH2 domain were evaluated in a series of studies in which the binding thermodynamics were determined using isothermal titration calorimetry, and binding interactions were examined in crystallographic studies of two different complexes. Notably, adding nonpolar groups to the pTyr+3 site leads to higher binding affinities, but the magnitude and energetic origins of these effects vary with the nature of the R substituent. For example, enhancements to binding affinities using aliphatic R groups are driven by more favorable changes in binding entropies, whereas aryl R groups improve binding free energies through a combination of more favorable changes in binding enthalpies and entropies. However, enthalpy/entropy compensation plays a significant role in these associations and mitigates against any significant variation in binding free energies, which vary by only 0.8kcal•mol-1, with changes in the electrostatic nature and size of the R group. Crystallographic studies show that differences in ΔG° or ΔH° correlate with buried nonpolar surface area, but they do not correlate with the total number of polar or van der Waals contacts. The relative number of ordered water molecules and relative order in the side chains at pTyr+3 correlate with differences in -TΔS°. Overall, these studies show that burial of nonpolar surface can lead to enhanced binding affinities arising from dominating entropy- or enthalpy-driven hydrophobic effects, depending upon the electrostatic nature of the apolar R group.

Hydrogen Plasma Exposure of Monolayer MoS2 Field-Effect Transistors and Prevention of Desulfurization by Monolayer Graphene.

Atomic vacancies related to structural disorder and doping variation influence carrier transport in monolayer transition-metal dichalcogenide devices. Here, we investigate the effect of hydrogen plasma exposure (HPE) on monolayer MoS2 field-effect transistors (FETs). We observe that a 1% increase in sulfur vacancy after HPE results in incremental 0.06 eV of the Schottky barrier. Short-range scattering from the sulfur vacancies reduces the carrier mobility of monolayer MoS2 by 2 orders of magnitude. Despite the defects and grain boundaries formed during the chemical vapor deposition and transferring process, the surface desulfurization induced by the proton exposure and thermally accelerated oxidation can be blocked by monolayer graphene cladding with a van der Waals contact distance of 2.5 Å. The material-level study indicates a promising route for a low-cost and robust fabrication of smart sensor circuits on a monolithic MoS2 wafer, where the bare MoS2 FETs can serve as proton sensors, with their electronic readout processed by a logic circuit of graphene-protected pristine FETs with a high on/off ratio.

Cycloalkyl Groups as Subunits of Artificial Carbohydrate Receptors: Effect of Ring Size of the Cycloalkyl Unit on the Receptor Efficiency

1,3,5‐Trisubstituted 2,4,6‐triethylbenzenes consisting of isopropyl groups as recognition units have previously been shown to have interesting binding properties towards selected carbohydrates. The design of such artificial carbohydrate receptors was inspired by the mode of action of carbohydrate‐binding proteins, namely by the participation of the isopropyl side chain of valine in the formation of van der Waals interactions with the carbohydrate substrate. This study aimed to investigate how the replacement of the isopropyl groups by other structural motifs, such as cycloalkyl groups of varying sizes (three to seven‐membered rings), influences the binding properties of the acyclic compounds towards carbohydrates. The cyclopropyl moiety represents a cyclic analog of the isopropyl group, whereas the other cycloalkyl units can be regarded as structural elements, which differ from the structure of the isopropyl group by a –(CH2)n‐bridge (n = 1–4) between the two methyl groups. Furthermore, according to the natural interactions, the cyclopentyl group should be able to participate in the formation of van der Waals contacts in a similar way as that observed for the pyrrolidine ring of proline in some protein‐carbohydrate complexes. Such systematic binding studies allow the identification of interesting structure‐activity relationships, which are very useful for the development of artificial carbohydrate receptors with predictable binding properties.