M any two-dimensional (2D) materials exist in bulk form as stacks of bonded layers with weak van der Waals interlayer attraction. Thanks to their particular structure, they can be exfoliated into atomically thin monolayers that hold promise for next-generation flexible electronics and optoelectronics. 1,2 Graphene has received much attention in the past decade, 3 due in large part to exceptional electronic properties such as its ultrahigh carrier mobility. However, the absence of a band gap has limited the progress of graphene-based technologies. For example, graphene field-effect transistors (FETs) cannot be turned off effectively, and even though small band gaps have been successfully opened in graphene, 4À7 the development of devices operating at room temperature with a low stand-by power dissipation remains a challenge. 8 On the other hand, transition-metal dichalcogenides (TMDCs) are a class of directband gap semiconductors that are emerging as strong candidates in next-generation nanoelectronic devices. 8À12 In the monolayer form, their lack of dangling bonds, structural stability, and mobility values comparable to Si make them optimal as channel materials in FETs. 1 In particular, FETs based on single layer MoS 2 , which has a direct band gap of 1.8 eV 1,13 and mobility in the range 1À50 cm 2 V À1 s À1 at room temperature, 14À17 show low power dissipation, 8 efficient control over switching 9 and reduction of shortchannel effects. 18,19 However, in order to develop logic circuits based on TMDCs, it is necessary to fabricate both n-and p-type FETs. TMDC FETs based on a Schottky device architecture can transport either electrons (n-FET) or holes (p-FET) in the conducting channel, depending on whether the Schottky barrier height (SBH) is smaller relative to the conduction or the valence band, respectively. 20 While monolayer n-FETs have been widely reported, fabrication of p-FETs has been challenging. 20 This is due to the relative difficulty in designing MoS 2 /metal contacts * Address correspondence to tiziana.musso@aalto.fi. Our analysis shows that this is possible due to the high work function of GO and the relatively weak Fermi-level pinning at the MoS 2 /GO interfaces compared to traditional MoS 2 /metal systems (common metals are Ag, Al, Au, Ir, Pd, Pt). The combination of easy-to-fabricate and inexpensive GO with MoS 2 could be promising for the development of hybrid all-2D p-type electronic and optoelectronic devices on flexible substrates.

Phosphonic acid multi-layers are used to tune the band alignment in heterojunction devices used for photoelectrochemistry and photovoltaics.

49High-pressure synthesis of denser glass has been a long-standing interest in condensed 50 matter physics and materials science because of its potentially broad industrial application. 51 Nevertheless, understanding its nature under extreme pressures has yet to be clarified due 52 to experimental and theoretical challenges. Here we revealed the novel formation of OSi 4 53 tetraclusters associated with that of SiO 7 polyhedra in SiO 2 glass under ultrahigh pressures 54 to 200 gigapascal confirmed both experimentally and theoretically. Persistent homology 55 analyses with molecular dynamics simulations found increased packing fraction of atoms 56 whose topological diagram at ultrahigh pressures is similar to pyrite-type crystalline phase, 57 although the formation of tetraclusters is prohibited in crystalline phase. This critical 58 difference would be caused by the potential structural tolerance in the glass for distortion of 59 oxygen clusters. Furthermore, expanded electronic band gap demonstrates that chemical 60 bonds survive at ultrahigh pressure. This opens up the synthesis of novel topologically 61 disordered dense oxide glasses. 62 63 I. INTRODUCTION 64 Silica (SiO 2 ) has been known as one of the most fundamental and abundant oxides in the Earth, 65 which can be usually yielded as quartz, silica sand, or silica stone in high purity condition. Due 66 to this ubiquitous availability and abundant resource around the world, SiO 2 has been 67 extensively utilized as an industrially useful material. SiO 2 glass, with high corrosion resistance, 68 high thermo-stability, and high optical transparency, is a prototype network-forming glass which 69 can be easily synthesized by various methods and it is therefore widely used and a technologically 70 important material. Polyamorphism in SiO 2 glass under pressure is one of the most fascinating 71 and puzzling topics in condensed matter physics and glass science. Several experimental and 72 theoretical studies have been conducted to clarify the details of polyamorphism 1 in SiO 2 glass 73 under high pressure. However, due to the technical hurdles, the experimental studies have been 74 limited to very low pressure conditions, which prevents from a precise understanding of the 75 pressure effect.76 Previous experimental studies on SiO 2 glass have shown anomalous behavior under lower 77 pressures up to ~10 GPa, exhibiting elastic softening 2 and permanent densification 3 . Those78 densification-related properties are closely related to a topological transformation of the 79 tetrahedral network 4 and compaction of a significant amount of interstitial cavities in the SiO 2 80 glass 5 , rather than a change in the coordination number of silicon. At higher-pressure, transitions 81 to much denser state are attributed to changes in short-and intermediate-range ordering 82 associated with the change in oxygen coordination around silicon. Although the details on the 83 coordination state and the pressure conditions under which the coordination changes occur are 84 still a matt...

Inexpensive and energy-dense Zn metal anodes is key to the promise of aqueous Zn-ion batteries, which are heralded as an exciting battery chemistry for renewable and stationary storage. Yet, Zn deposition instability under demanding cycling conditions leads to rapid dendritic cell failure, and the hydrogen evolution reaction aggravates the issue. Electrolyte additives are a scalable solution to address the problem, but a high volume fraction is typically required for a noticeable effect. Here, a benign alcohol molecule propylene glycol is presented as an electrolyte additive that enables remarkably stable Zn anode cycling of over 1000 h at a practical 2 mA-2 mA h cm −2 at a low volume concentration when the reference cell shorts only after 30 h. The dramatic performance improvement at the low additive concentration is attributed to the effective morphology regulation and inhibition of hydrogen evolution, as revealed by spectroscopic and microscopic investigations. Ab initio molecular dynamics simulations reveal unprecedented atomistic insights behind the concentration-dependent effectivity of propylene glycol as an electrolyte additive. Excellent full cell cycling with two different positive host materials, even with high loading, highlights the potential for practical development.

A strong ordering of solvent molecules in the solid−liquid interface of a typical and characteristic organic crystal (p-nitroaniline) is observed in state-of-the-art atomic force microscopy experiments. In the current work, we use both molecular dynamics (MD) simulations and experiments in different solvents to provide a detailed understanding of the nature of the solid−liquid interface. The strong ordering of solvent molecules at the surface of p-nitroaniline is confirmed in general, but the MD simulations point to several different possible surface reconstructions, offering different ordering of water on the surface. The calculated water density profiles and local surface hydration energies suggest a novel surface structure, which is in excellent agreement with the majority of experimental results and stands as a challenge for future diffraction techniques. Our joined theoretical and experimental study emphasizes the power of high-resolution techniques to probe the solid−liquid interface in 3D while demonstrating the importance of including systematic simulation approaches to confirm the details of the molecular structure and to increase our understanding of complex heterogeneous solid−liquid interfaces.

Angstrom-confined solvents in 2D laminates can travel through interlayer spacings, through gaps between adjacent sheets, and via in-plane pores. Among these, experimental access to investigate the mass transport through in-plane pores is lacking. Our experiments allow an understanding of this mass transport via the controlled variation of oxygen functionalities, size and density of in-plane pores in graphene oxide membranes. Contrary to expectations, our transport experiments show that higher in-plane pore densities may not necessarily lead to higher water permeability. We observed that membranes with a high in-plane pore density but a low amount of oxygen functionalities exhibit a complete blockage of water. However, when water− ethanol mixtures with a weaker hydrogen network are used, these membranes show an enhanced permeation. Our combined experimental and computational results suggest that the transport mechanism is governed by the attraction of the solvents toward the pores with functional groups and hindered by the strong hydrogen network of water formed under angstrom confinement.

structurally stable and largely lack dangling bonds. The production processes of TMDs are currently well established, ranging from top-down exfoliation of the bulk material using mechanical exfoliation, solution-based approaches and the bottom-up synthesis methods using chemical vapor deposition. [7,8] TMDs have gained significant importance as excellent candidates for nanoelectronic applications. [9,10] MoS 2 is one of the most commonly studied TMD in this regard, which demonstrates a high mobility (in the range 1-50 cm 2 V −1 s −1 at room temperature [11,12] ), comparable to that of silicon. In addition, field-effect transistors (FETs) based on MoS 2 show low power dissipation [1] and efficient control over switching, [2] leading to widespread research interest in this topic.While these properties are certainly encouraging, one major limitation of such FETs is that the carrier transport in the semiconductor channel is mostly electron-mediated, [13] resulting in n-type FETs (n-FETs). Despite attempts to employ high workfunction metal contacts to obtain hole-based transport, the resulting devices have instead widely shown n-character. [13] This intrinsic behavior of the unmodified MoS 2 -metal interface hinders the construction of fully integrated circuits, [7] because of the difficulty in obtaining a CMOS (complementary metal oxide semiconductor) device, where the building block of logic gates and digital circuits require both n-and p-type MOS architectures.The fabrication of p-FETs based on monolayer MoS 2 is challenging [13] because of a particular interfacial phenomenon between the TMD and the metal contact, namely Fermi level pinning. [14,15] It is commonly believed that the interfacial gap states between MoS 2 and the metal contacts are responsible for pinning the Fermi level close to the conduction band, even upon using a high work-function metal. These gap states may be surface states (Bardeen's theory), metal-induced gap states (MIGS) or defect/disorder-induced gap states. [14,15] Guo, Francois and co-workers [16,17] consider the MIGS theory the best candidate to explain the origin of the gap states. A different point of view is assumed by McDonnell et al., [18,19] wherein they attribute the difficulty in producing hole-based MoS 2 devices to the intrinsic low work-function defects present in MoS 2 , responsible for the variability of electronic properties across the samples. These native defects such as vacancies present in MoS 2 and other TMDs like WSe 2 may actually result in variations of the TMDs work function, as observed in experiments. [20] P-type transistors based on high work function transition metal dichalcogenide (TMD) monolayers such as MoS 2 are to date difficult to produce, owing to the strong Fermi level pinning at the semiconductor/contact metal interfaces. In this work, the potential of halogenated graphenes is demonstrated as a new class of efficient hole injection layers to TMDs such as MoS 2 and WSe 2 by taking fluorographene (or GF) as a model buffer layer. Using first-principles c...

The water transport along graphene-based nanochannels has gained significant interest. However, experimental access to the influence of defects and impurities on transport poses a critical knowledge gap. Here, we investigate the water transport of cation intercalated graphene oxide membranes. The cations act as water-attracting impurities on the channel walls. Via water transport experiments, we show that the slip length of the nanochannels decay exponentially with the hydrated diameter of the intercalated cations, confirming that water transport is governed by the interaction between water molecules and the impurities on the channel wall. The exponential decay of slip length approximates non-slip conditions. This offers experimental support for the use of the Hagen-Poiseuille equation in graphene-based nanochannels, which was previously only confirmed by simulations. Our study gives valuable feedback to theoretical predictions of the water transport along graphene-based channels with water-attracting impurities.