Measurement of phosphorus segregation in silicon at the atomic-scale using STM

In order to fabricate precise atomic-scale devices in silicon using a combination of scanning tunnelling microscopy (STM) and molecular beam epitaxy it is necessary to minimize the segregation/diffusion of dopant atoms during silicon encapsulation. We characterize the surface segregation/diffusion of phosphorus atoms from a $\delta$-doped layer in silicon after encapsulation at 250$^{\circ}$C and room temperature using secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES), and STM. We show that the surface phosphorus density can be reduced to a few percent of the initial $\delta$-doped density if the phosphorus atoms are encapsulated with 5 or 10 monolayers of epitaxial silicon at room temperature. We highlight the limitations of SIMS and AES to determine phosphorus segregation at the atomic-scale and the advantage of using STM directly

Growth of 1T ' MoTe2 by thermally assisted conversion of electrodeposited tellurium films

Molybdenum ditelluride (MoTe2) is a transition metal dichalcogenide (TMD) which has two phases stable under ambient conditions, a semiconducting (2H) and semimetallic (1T') phase. Despite a host of interesting properties and potential applications, MoTe2 is one of the less-studied TMDs, perhaps due its relatively low abundance in nature or challenges associated with its synthesis, such as the toxicity of most precursors. In this report, we describe the fabrication of thin films of phase-pure IT' MoTe2 using predeposited molybdenum and electrodeposited tellurium layers, at the relatively low temperature of 450 C. This method allows control over film geometry and over the tellurium concentration during the conversion. The MoTe2 films are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, and electron microscopies. When applied as a catalyst for the hydrogen evolution reaction, the films display promising initial results. The MoTe2 films have a Tafel slope of below 70 mV dec(-1) and compare favorably with other MoTe2 catalysts reported in the literature, especially considering the inherently scalable fabrication method. The variation in electrocatalytic behavior with thickness and morphology of the films is also investigated

Rhenium-doped MoS2 films

Tailoring the electrical properties of transition metal dichalcogenides by doping is one of the biggest challenges for the application of 2D materials in future electronic devices. Here, we report on a straightforward approach to the n-type doping of molybdenum disulfide (MoS2) films with rhenium (Re). High-Resolution Scanning Transmission Electron Microscopy and Energy-Dispersive X-ray spectroscopy are used to identify Re in interstitial and lattice sites of the MoS2 structure. Hall-effect measurements confirm the electron donating influence of Re in MoS2, while the nominally undoped films exhibit a net p-type doping. Density functional theory (DFT) modelling indicates that Re on Mo sites is the origin of the n-type doping, whereas S-vacancies have a p-type nature, providing an explanation for the p-type behaviour of nominally undoped MoS2 films

Functionalization of graphene surfaces with downstream plasma treatments

We report on an adjustable process for the functionalization of graphene surfaces with a downstream plasma source. The parameters of oxygen plasma treatments are modified such that oxygenated functionalities can be added to the surface of graphene films prepared by chemical vapour deposition in a controlled manner. The nature of induced defects is investigated thoroughly using Raman and x-ray photoelectron spectroscopy. A massivechange in the surface properties is observed through the use of contact angle and electrochemical measurements. We propose the usage of such plasma treatments to facilitate the addition of further functional groups to the surface of graphene. The incorporation of nitrogen in to the graphene lattice by substitution of oxygenated functional groups is demonstrated outlining the validity of this approach for further functionalization

Origami-based spintronics in graphene

We show that periodically folded graphene sheets with enhanced spin-orbit interaction due to curvature effects can carry spin-polarized currents and have gaps in the electronic spectrum in the presence of weak magnetic fields. Our results indicate that such origami-like structures can be used efficiently in spintronic applications

All-printed capacitors from graphene-BN-graphene nanosheet heterostructures

This work aims to develop methodologies to print pinhole-free, vertically stacked heterostructures by sequential deposition of conductive graphene and dielectric h-BN nanosheet networks. We achieve this using a combination of inkjet printing and spray-coating to fabricate dielectric capacitors in a stacked graphene/BN/graphene arrangement. Impedance spectroscopy shows such heterostructures to act as series combinations of a capacitor and a resistor, with the expected dimensional dependence of the capacitance. The areal capacitance ranges from 0.24 to 1.1?nF/cm2 with an average series resistance of ?120?k?. The sprayed BN dielectrics are pinhole-free for thicknesses above 1.65??m. This development paves the way toward fabrication of all-printed, vertically integrated, multilayer devices

Highly sensitive, transparent, and flexible gas sensors based on gold nanoparticle decorated carbon nanotubes

We report on a high performance flexible and transparent chemical sensor based on functionalised single-walled carbon nanotubes (SWCNTs). The SWCNT films were spray-deposited on transparent and flexible plastic substrates, and subsequently decorated with Au nanoparticles (AuNPs) providing a facile and cheap fabrication route. The electrical resistance of the films changed remarkably upon exposure to ammonia (NH3), AuNP decoration enhanced sensitivity to 255 ppb (parts-per-billion), one of the lowest reported so far. The reported sensor performance is a huge improvement towards low power consumption and its room temperature operation augers well for use in mobile devices for environmental protection and air quality control