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Nanoelectronic devices that are self-powered through the conversion of mechanical energy into electronic energy are of great interest for the fields of wearables and medical implants. The ability to find nanomaterials that have piezoelectric properties suitable for nanogenerators can be a challenge. Zinc oxide (ZnO) is a well-known material that has one of the highest piezoelectric tensors among tetrahedrally bonded semiconductors, due to its buckled noncentrosymmetric structure on the (0001) and (0001̅)] surfaces. However, this piezoelectric response is diminished in few-layered two-dimensional (2D) ZnO, as it loses it buckled structure and becomes graphitic. As a consequence, ultrathin 2D ZnO sheets are not suitable for nanoscale devices that rely on a piezoelectric response. In this work, we show that defects, specifically, zinc and oxygen vacancies, and adsorbed oxygen, can restore the wurtzite structure and piezoelectric response of free standing 2D ZnO sheets at specific thicknesses. Using density functional theory calculations, we show that both a 1 monolayer (ML) surface coverage of oxygen and a 25% concentration of zinc vacancies can restore the buckling in few-layer 2D ZnO nanosheets. For a 1.48 nm thick sheet with a 25% Zn vacancy concentration, an e33 value of 1.26 C/m2 can be achieved, which is 120% enhancement compared to the bulk value. These findings provide a methodology for screening piezoelectric properties of other materials and demonstrate that defects can be used to restore the wurtzite structure and dielectric properties of ultrathin 2D ZnO sheets that would allow them to be used in nanoscale piezoelectric devices. [ABSTRACT FROM AUTHOR]

The effect of atomic S on the adhesion of Fe(110) surfaces using density functional theory (DFT) within the plane-wave pseudopotential is examined. The effect of relaxation of the interfaces at equilibrium is investigated and indicates to increase the strength of the interface, while reducing the equilibrium interfacial separation.

Organic/inorganic polymer hybrid (OIPH) materials are studied. The atomistic details and mechanisms of interactions between the components of the OIPH materials at various stages of their formation are reported.

The relative stabilities and properties of different arrangements of S on Fe(110) at a 1/3 monolayer coverage is compared using density functional theory calculations. For all studied arrangements, S is absorbed in the three high-symmetry adsorption sites, 4-fold hollow, 3-fold hollow, bridge and atop sites.

The effects of adsorbed S at different coverages on the adhesion of Fe(110) surfaces in the match and mismatch is examined using density functional theory (DFT). S is adsorbed in the atop, bridge, and 4-fold hollow sites on one side of the inter face in c(2 x 2) and p(1 x 1) arrangements, corresponding to coverages of 1/2 an 1 monolayer.

Adsorption of atomic sulfur at different coverages on the Fe(110) surface is examined using density functional theory (DFT) in order to investigate the effect that adsorbate-adsorbate interactions may have on the surface properties. The bonding of S to the surface is found to change from being S-Fe dominated at the lower coverages to being S-S dominated at the higher coverages where the adjacent S atoms are closer together and interact strongly with each other.

Using tangible models to help students visualize chemical structures in three dimensions has been a mainstay of chemistry education for many years. Conventional chemistry modeling kits are, however, limited in the types and accuracy of the molecules, bonds and structures they can be used to build. The recent development of 3D printing technology has allowed a much wider variety of molecules to be created for teaching but is not simple to do. Creating the files needed to print molecular structures is often technically difficult and requires the use of multiple software programs, which are not always user-friendly. Not all educators or students have the resources or technical skill to create such files and so are put off trying to use 3D printing in the classroom. Here we demonstrate a simple method to easily generate the files needed for the 3D printing of almost any molecule using the National Institutes of Health Print Exchange server (or simple alternatives). The basic molecule structure may be created in-house or easily sourced online from databases such as UniProt or PubChem. The options for quickly and cheaply printing such structures in a range of materials using online and local stores, as well as in-house 3D printers, are explored and a simple protocol is described. The method brings 3D printing to a wider audience, thus helping to spread its use in chemical pedagogy, and may also be used in self-directed learning exercises by students themselves. [ABSTRACT FROM AUTHOR]

Manipulating the exchange bias (EB) effect using an electronic gate is a significant goal in spintronics. The emergence of van der Waals (vdW) magnetic heterostructures has provided improved means to study interlayer magnetic coupling, but to date, these heterostructures have not exhibited electrical gate-controlled EB effects. Here, we report electrically controllable EB effects in a vdW heterostructure, FePS 3 -Fe 5 GeTe 2 . By applying a solid protonic gate, the EB effects were repeatably electrically tuned. The EB field reaches up to 23% of the coercivity and the blocking temperature ranges from 30 to 60 K under various gate-voltages. The proton intercalations not only tune the average magnetic exchange coupling but also change the antiferromagnetic configurations in the FePS 3 layer. These result in a dramatic modulation of the total interface exchange coupling and the resultant EB effects. The study is a significant step toward vdW heterostructure-based magnetic logic for future low-energy electronics.

Tungsten disulfide (WS 2 ) exhibits intriguing tribological properties and has been explored as an excellent lubricious material in thin-film and solid lubricants. However, the poor dispersibility of WS 2 has been a major challenge for its utilization in liquid lubricant applications. Herein, a top-down integrated approach is presented to synthesize oxygenated WS 2 (WS 2 -O) nanosheets via strong acid-mediated oxidation and ultrasound-assisted exfoliation. The ultrathin sheets of WS 2 -O, comprising 4-7 molecular lamellae, exhibit oxygen/hydroxyl functionalities. The organosilanes having variable surface-active leaving groups (chloro and ethoxy) are covalently grafted, targeting the hydroxyl/oxygen functionalities on the surface of WS 2 -O nanosheets. The grafting of organosilanes is governed by the reactivity of chloro and ethoxy leaving groups. The DFT calculations further support the covalent interaction between the WS 2 -O nanosheets and organosilanes. The alkyl chain-functionalized WS 2 -O nanosheets displayed excellent dispersibility in mineral lube base oil. A minute dose of chemically functionalized-WS 2 (0.2 mg.mL -1 ) notably enhanced the tribological properties of mineral lube oil by reducing the friction coefficient (52%) and wear volume (79%) for a steel tribopair. Raman analysis of worn surfaces revealed WS 2 -derived lubricious thin film formation. The improved tribological properties are attributed to ultralow thickness, stable dispersion, and low shear strength of chemically functionalized WS 2 nanosheets, along with protective thin film formation over the contact interfaces of a steel tribopair. The present work opens a new avenue toward exploiting low-dimensional nanosheets for minimizing energy losses due to high friction.

Two-dimensional transition-metal dichalcogenides possess inherent structural characteristics that can be harnessed for enhancement of tribological properties by making them dispersible in lube media. Here, we present a hydrothermal approach to preparing MoS 2 nanosheets comprising 4-10 molecular lamellae. A structural-defect-mediated route for grafting of octadecylamine (ODA) on MoS 2 nanosheets is outlined. The unsaturated d orbitals of Mo at the sulfur vacancies on the MoS 2 surface are coupled with the electron-rich nitrogen center of ODA and yield ODA-functionalized MoS 2 (MoS 2 -ODA). The MoS 2 -ODA nanosheets exhibit good dispersibility in lube base oil and are used as an additive (optimized dose: 0.1 mg·mL -1 ) to mineral oil. It is shown that even at low concentration, MoS 2 -ODA nanosheets significantly reduce the friction (48%) and wear (44%). Microscopy (field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM)) and spectroscopy (Raman and elemental mapping) analyses of worn scars revealed the formation of MoS 2 -based protective thin films for lowering of friction and wear. This work, therefore, presents a pathway for low-friction lubricants by deploying functionalized low-dimensional material systems.

Chromism-based optical filters is a niche field of research, due to there being only a handful of electrochromic materials. Typically, electrochromic transition metal oxides such as MoO 3 and WO 3 are utilized in applications such as smart windows and electrochromic devices (ECD). Herein, we report MoO 3- x -based electrically activated ultraviolet (UV) filters. The MoO 3- x grown on indium tin oxide (ITO) substrate is mechanically assembled onto an electrically activated proton exchange membrane. Reversible H + injection/extraction in MoO 3- x is employed to switch the optical transmittance, enabling an electrically activated optical filter. The devices exhibit broadband transmission modulation (325-800 nm), with a peak of ∼60% in the UV-A range (350-392 nm). Comparable switching times of 8 s and a coloration efficiency of up to 116 cm 2 C -1 are achieved.

Boron nitride nanotubes (BNNTs) represent a relatively new class of materials that provides alternative electrical and thermal properties to the carbon analogue. The high chemical and thermal stability and large band gap combined with high electrical resistance make BNNTs desirable in several thin-film applications. In this study, stable BNNT and hexagonal boron nitride (hBN) particle dispersions have been developed using environmentally friendly advanced oxidation processing (AOP) that can be further modified for electrophoretic deposition (EPD) to produce thin films. The characterization of the dispersions has revealed how the hydroxyl radicals produced in AOP react with BNNT/hBN and contaminant boron nanoparticles (BNPs). While the radicals remove the carbon contaminant present on BNNT/hBN and increase dispersion stability, they also oxidize the BNPs and the boron oxide produced, which, conversely, reduces the dispersion stability. The use of high- or low-powered ultrasonication in combination with the AOP affects the rate of the competing reactions, with low-powered sonication and AOP providing the best combination for producing stable dispersions with high concentrations. BNNT/hBN dispersions were functionalized with polyethyleneimine to facilitate EPD, where films of several micrometer thickness were readily deposited onto stainless steel and glass-fiber fabrics. BNNT/hBN films produced on glass fabrics by EPD exhibited a consistent through-thickness macroporosity that was facilitated by platelet and nanotube stacking. The film macroporosity present on the coated fabrics was suitable for use as separator layers in supercapacitors and provided improved device robustness with a minimal impact on electrochemical performance.