Solvent-free confinement of ordered microparticle monolayers: effect of host substrate and pattern symmetry.

The self-organisation of individual suspended colloids into ordered structures that can be mediated by confinement has garnered interest recently. Despite the push for solvent reduction for sustainability reasons, the comprehension and development of solvent-free assembly methods remain largely unaddressed. In this study, we explore the effect of confinement without rigid geometrical constraints, , wall-less confinement on the assembly of monodisperse PMMA powder microspheres (diameters of 3 μm and 10 μm) on fluorocarbon-patterned heterogeneous substrates using a solvent-free rubbing assembly approach.

Molecular switching by proton-coupled electron transport drives giant negative differential resistance.

To develop new types of dynamic molecular devices with atomic-scale control over electronic function, new types of molecular switches are needed with time-dependent switching probabilities. We report such a molecular switch based on proton-coupled electron transfer (PCET) reaction with giant hysteric negative differential resistance (NDR) with peak-to-valley ratios of 120 ± 6.6 and memory on/off ratios of (2.

Navigating the Landscape of Dry Assembling Ordered Particle Structures: Can Solvents Become Obsolete?

A spur on miniaturized devices led scientists to unravel the fundamental aspects of micro- and nanoparticle assembly to engineer large structures. Primarily, attention is given to wet assembly methods, whereas assembly approaches in which solvents are avoided are scarce. The "dry assembly" strategies can overcome the intrinsic disadvantages that are associated with wet assembly, e.

Toward the Assembly of 2D Tunable Crystal Patterns of Spherical Colloids on a Wafer-Scale.

Entering an era of miniaturization prompted scientists to explore strategies to assemble colloidal crystals for numerous applications, including photonics. However, wet methods are intrinsically less versatile than dry methods, whereas the manual rubbing method of dry powders has been demonstrated only on sticky elastomeric layers, hindering particle transfer in printing applications and applicability in analytical screening. To address this clear impetus of broad applicability, we explore here the assembly on nonelastomeric, rigid substrates by utilizing the manual rubbing method to rapidly (≈20 s) attain monolayers comprising hexagonal closely packed (HCP) crystals of monodisperse dry powder spherical particles with a diameter ranging from 500 nm to 10 μm using a PDMS stamp.

Probing surface properties of organic molecular layers by scanning tunneling microscopy.

In view of the relevance of organic thin layers in many fields, the fundamentals, growth mechanisms, and dynamics of thin organic layers, in particular thiol-based self-assembled monolayers (SAMs) on Au(111) are systematically elaborated. From both theoretical and practical perspectives, dynamical and structural features of the SAMs are of great intrigue. Scanning tunneling microscopy (STM) is a remarkably powerful technique employed in the characterization of SAMs.

Influence of Wettability and Geometry on Contact Electrification between Nonionic Insulators.

Contact electrification is an interfacial process in which two surfaces exchange electrical charges when they are in contact with one another. Consequently, the surfaces may gain opposite polarity, inducing an electrostatic attraction. Therefore, this principle can be exploited to generate electricity, which has been precisely done in triboelectric nanogenerators (TENGs) over the last decades.

High-Strain-Induced Local Modification of the Electronic Properties of VO Thin Films.

Vanadium dioxide (VO) is a popular candidate for electronic and optical switching applications due to its well-known semiconductor-metal transition. Its study is notoriously challenging due to the interplay of long- and short-range elastic distortions, as well as the symmetry change and the electronic structure changes. The inherent coupling of lattice and electronic degrees of freedom opens the avenue toward mechanical actuation of single domains.

Triboelectric Charging of Particles, an Ongoing Matter: From the Early Onset of Planet Formation to Assembling Crystals.

Triboelectrification is the spontaneous charging of two bodies when released from contact. Even though its manifestation is commonplace, in for instance triboelectric nanogenerators, scientists find the tribocharging mechanism a mystery. The primary aim of this mini-review is to provide an overview of different tribocharging concepts that have been applied to study and realize the formation of ordered stable structures using different objects on various length scales.

Self-Assembled Decanethiolate Monolayers on Au(001): Expanding the Family of Known Phases.

We have studied decanethiolate self-assembled monolayers on the Au(001) surface. Planar and striped phases, as well as disordered regions, have formed after exposing the Au surface to a decanethiol solution. The planar phases that we observe have a hexagonal symmetry and have not been previously reported for thiols on the Au(001) surface and have lower coverage compared to that of the other known thiol planar phases such as the square α phase.

Interlayer electron modulation in van der Waals heterostructures assembled by stacking monolayer MoS onto monolayer graphene with different electron transfer ability.

Achieving tunable optoelectronic properties and clarifying interlayer interactions are key challenges in the development of 2D heterostructures. Herein, we report the feasible modulation of the optoelectronic properties of monolayer MoS (1L-MoS) on three different graphene monolayers with varying ability in extracting electrons. Monolayer oxygen-functionalized graphene (1L-oxo-G, a high amount of oxygen of 60%) with a work function (WF) of 5.

Energy-Level Alignment at Interfaces between Transition-Metal Dichalcogenide Monolayers and Metal Electrodes Studied with Kelvin Probe Force Microscopy.

We studied the energy-level alignment at interfaces between various transition-metal dichalcogenide (TMD) monolayers, MoS, MoSe, WS, and WSe, and metal electrodes with different work functions (WFs). TMDs were deposited on SiO/silicon wafers by chemical vapor deposition and transferred to Al and Au substrates, with significantly different WFs to identify the metal-semiconductor junction behavior: oxide-terminated Al (natural oxidation) and Au (UV-ozone oxidation) with a WF difference of 0.8 eV.

Long-range ordering of two-dimensional wide bandgap tantalum oxide nanosheets in printed films.

Two-dimensional oxide materials are a well-studied, interesting class of materials, enabled by the fact that their bulk layered metal oxides, such as titanates and niobates, can be easily exfoliated within minutes into 2D nanosheets. However, some promising oxide materials, such tantalum oxide, are much more difficult to delaminate, taking several weeks, due to the higher charge density resulting in stronger Coulombic interactions between the layers. This intrinsic constraint has limited detailed studies for exploiting the promising properties of tantalum oxide 2D nanosheets towards enhanced catalysis and energy storage.

Free energy of domain walls and order-disorder transition in a triangular lattice with anisotropic nearest-neighbor interactions.

We have derived exact expressions for the domain wall free energy along the three high-symmetry directions of a triangular lattice with anisotropic nearest-neighbor interactions. The triangular lattice undergoes an order-disorder phase transition at a temperature T_{c} given by e^{-(ε_{1}+ε_{2})/2kT_{c}}+e^{-(ε_{2}+ε_{3})/2kT_{c}}+e^{-(ε_{3}+ε_{1})/2kT_{c}}=1, where ε_{1}, ε_{2}, ε_{3} are the nearest-neighbor interaction energies, and ε_{1}+ε_{2}>0, ε_{2}+ε_{3}>0, ε_{3}+ε_{1}>0. Finally, we have derived expressions for the thermally induced meandering of the domain walls at temperatures below the phase transition temperature.

Nanoscale Work Function Contrast Induced by Decanethiol Self-Assembled Monolayers on Au(111).

In this paper, we obtain maps of the spatial tunnel barrier variations in self-assembled monolayers of organosulfurs on Au(111). Maps down to the sub-nanometer scale are obtained by combining topographic scanning tunneling microscopy images with d/d spectroscopy. The square root of the tunnel barrier height is directly proportional to the local work function and the d/d signal.

Spatial Segregation of Microspheres by Rubbing-Induced Triboelectrification on Patterned Surfaces.

Particle (monolayer) assembly is essential to various scientific and industrial applications, such as the fabrication of photonic crystals, optical sensors, and surface coatings. Several methods, including rubbing, have been developed for this purpose. Here, we report on the serendipitous observation that microparticles preferentially partition onto the fluorocarbon-coated parts of patterned silicon and borosilicate glass wafers when rubbed with poly(dimethylsiloxane) slabs.

An Arylazopyrazole-Based N-Heterocyclic Carbene as a Photoswitch on Gold Surfaces: Light-Switchable Wettability, Work Function, and Conductance.

A novel photoresponsive and fully conjugated N-heterocyclic carbene (NHC) has been synthesized that combines the excellent photophysical properties of arylazopyrazoles (AAPs) with an NHC that acts as a robust surface anchor (AAP-BIMe). The formation of self-assembled monolayers (SAMs) on gold was proven by ToF-SIMS and XPS, and the organic film displayed a very high stability at elevated temperatures. This stability was also reflected in a high desorption energy, which was determined by temperature-programmed SIMS measurements.

Universal Fermi-Level Pinning in Transition-Metal Dichalcogenides.

Understanding the electron transport through transition-metal dichalcogenide (TMDC)-based semiconductor/metal junctions is vital for the realization of future TMDC-based (opto-)electronic devices. Despite the bonding in TMDCs being largely constrained within the layers, strong Fermi-level pinning (FLP) was observed in TMDC-based devices, reducing the tunability of the Schottky barrier height. We present evidence that metal-induced gap states (MIGS) are the origin for the large FLP similar to conventional semiconductors.

Ordering of Air-Oxidized Decanethiols on Au(111).

Self-assembled monolayers (SAMs) of alkanethiols on gold are a commonly used platform for nanotechnology owing to their ease of preparation and high surface coverage. Unfortunately, the gold-sulfur bond is oxidized at ambient conditions which alters the stability and structure of the monolayer. We show using scanning tunneling microscopy and X-ray photoelectron spectroscopy that decanethiolate molecules oxidize into decanesulfonates that organize into a hitherto unknown striped phase.

Local Conduction in Mo WSe: The Role of Stacking Faults, Defects, and Alloying.

Here, we report on the surface conductivity of WSe and Mo WSe (0 ≤ x ≤ 1) crystals investigated with conductive atomic force microscopy. We found that stacking faults, defects, and chemical heterogeneities form distinct two-dimensional and one-dimensional conduction paths on the transition metal dichalcogenide surface. In the case of WSe, in addition to step edges, we find a significant amount of stacking faults (formed during the cleaving process) that strongly influence the surface conductivity.

Pressure-Induced Melting of Confined Ice.

The classic regelation experiment of Thomson in the 1850s deals with cutting an ice cube, followed by refreezing. The cutting was attributed to pressure-induced melting but has been challenged continuously, and only lately consensus emerged by understanding that compression shortens the O:H nonbond and lengthens the H-O bond simultaneously. This H-O elongation leads to energy loss and lowers the melting point.

Chemical vapor deposition growth of bilayer graphene in between molybdenum disulfide sheets.

Direct growth of flat micrometer-sized bilayer graphene islands in between molybdenum disulfide sheets is achieved by chemical vapor deposition of ethylene at about 800°C. The temperature assisted decomposition of ethylene takes place mainly at molybdenum disulfide step edges. The carbon atoms intercalate at this high temperature, and during the deposition process, through defects of the molybdenum disulfide surface such as steps and wrinkles.

Defect Dominated Charge Transport and Fermi Level Pinning in MoS/Metal Contacts.

Understanding the electronic contact between molybdenum disulfide (MoS) and metal electrodes is vital for the realization of future MoS-based electronic devices. Natural MoS has the drawback of a high density of both metal and sulfur defects and impurities. We present evidence that subsurface metal-like defects with a density of ∼10 cm induce negative ionization of the outermost S atom complex.