Explore the vast range of titles available.

Unique identification of optical devices is important for anti-counterfeiting. Physical unclonable functions (PUFs), which use random physical characteristics for authentication, are advantageous over existing optical solutions, such as holograms, due to the inherent asymmetry in their fabrication and reproduction complexity. However, whilst unique, PUFs are potentially vulnerable to replication and simulation. Here we introduce an additional benefit of a small modification to an established model of nanoparticle PUFs by using a second measurement parameter to verify their authenticity. A randomly deposited array of quantum dots is encapsulated in a transparent polymer, forming a tag. Photoluminescence is measured as a function of excitation power to assess uniqueness as well as the intrinsic nonlinear response of the quantum material. This captures a fingerprint, which is non-trivial to clone or simulate. To demonstrate this concept practically, we show that these tags can be read using an unmodified smartphone, with its built-in flash for excitation. This development over constellation-style optical PUFs paves the way for more secure, facile authentication of devices without requiring complex fabrication or characterisation techniques.

It is challenging for conventional top-down lithography to fabricate reproducible devices very close to atomic dimensions, whereas identical molecules and very similar nanoparticles can be made bottom-up in large quantities, and can be self-assembled on surfaces. The challenge is to fabricate electrical contacts to many such small objects at the same time, so that nanocrystals and molecules can be incorporated into conventional integrated circuits. Here, we report a scalable method for contacting a self-assembled monolayer of nanoparticles with a single layer of graphene. This produces single-electron effects, in the form of a Coulomb staircase, with a yield of 87 ± 13% in device areas ranging from < 800 nm 2 to 16  μ m 2 , containing up to 650,000 nanoparticles. Our technique offers scalable assembly of ultra-high densities of functional particles or molecules that could be used in electronic integrated circuits, as memories, switches, sensors or thermoelectric generators. The integration of nano-molecules into microelectronic circuitry is challenging. Here, the authors provide a scalable method for contacting a self-assembled monolayer of nanoparticles with a single layer of graphene that produces single-electron effects, in the form of a Coulomb staircase, with a yield of at least 70%.

Thin films comprising synthetically robust, scalable molecules have been shown to have major potential for thermoelectric energy harvesting. Previous studies of molecular thin-films have tended to focus on massively parallel arrays of discrete but identical conjugated molecular wires assembled as a monolayer perpendicular to the electrode surface and anchored via a covalent bond, know as self-assembled monolayers. In these studies, to optimise the thermoelectric properties of the thin-film there has been a trade-off between synthetic complexity of the molecular components and the film performance, limiting the opportunities for materials integration into practical thermoelectric devices. In this work, we demonstrate an alternative strategy for enhancing the thermoelectric performance of molecular thin-films. We have built up a series of films, of controlled thickness, where the basic units—here zinc tetraphenylporphyrin—lie parallel to the electrodes and are linked via π – π stacking. We have compared three commonly used fabrications routes and characterised the resulting films with scanning probe and computational techniques. Using a Langmuir-Blodgett fabrication technique, we successfully enhanced the thermopower perpendicular to the plane of the ZnTPP multilayer film by a factor of 10, relative to the monolayer, achieving a Seebeck coefficient of −65 μ V K −1 . Furthermore, the electronic transport of the system, perpendicular to the plane of the films, was observed to follow the tunnelling regime for multi-layered films, and the transport efficiency was comparable with most conjugated systems. Furthermore, scanning thermal microscopy characterisation shows a factor of 7 decrease in thermal conductance with increasing film thickness from monolayer to multilayer, indicating enhanced thermoelectric performance in a π – π stacked junction.

We report the self-catalysed growth of InAs nanowires (NWs) on graphite thin films using molecular beam epitaxy via a droplet-assisted technique. Through optimising metal droplets, we obtained vertically aligned InAs NWs with highly uniform diameter along their entire length. In comparison with conventional InAs NWs grown on Si (111), the graphite surface led to significant effects on the NWs geometry grown on it, i.e. larger diameter, shorter length with lower number density, which were ascribed to the absence of dangling bonds on the graphite surface. The axial growth rate of the NWs has a strong dependence on growth time, which increases quickly in the beginning then slows down after the NWs reach a length of approximately 0.8 μm. This is attributed to the combined axial growth contributions from the surface impingement and sidewall impingement together with the desorption of adatoms during the diffusion. The growth of InAs NWs on graphite was proposed following a vapour-solid mechanism. High-resolution transmission electron microscopy reveals that the NW has a mixture of pure zinc-blende and wurtzite insertions.

We report on the single-molecule electronic and thermoelectric properties of strategically chosen anthracene-based molecules with anchor groups capable of binding to noble metal substrates, such as gold and platinum. Specifically, we study the effect of different anchor groups, as well as quantum interference, on the electric conductance and the thermopower of gold/single-molecule/gold junctions and generally find good agreement between theory and experiment. All molecular junctions display transport characteristics consistent with coherent transport and a Fermi alignment approximately in the middle of the HOMO/LUMO gap. Single-molecule results are in agreement with previously reported thin-film data, further supporting the notion that molecular design considerations may be translated from the single- to the many-molecule devices. For combinations of anchor groups where one binds significantly more strongly to the electrodes than the other, the stronger anchor group appears to dominate the thermoelectric behaviour of the molecular junction. For other combinations, the choice of electrode material can determine the sign and magnitude of the thermopower. This finding has important implications for the design of thermoelectric generator devices, where both n- and p-type conductor are required for thermoelectric current generation.

Graphene (GR) remarkable mechanical and electrical properties - such as its Young's modulus, low mass per unit area, natural atomic flatness and electrical conductance - would make it an ideal material for micro and nanoelectromechanical systems (MEMS and NEMS). However, the difficulty of attaching GR to supports coupled with naturally occurring internal defects in a few-layer GR can significantly adversely affect the performance of such devices. Here, we have used a combined contact resonance atomic force microscopy (CR-AFM) and ultrasonic force microscopy (UFM) approach to characterise and map with nanoscale spatial resolution GR membrane properties inaccessible to most conventional scanning probe characterisation techniques. Using a multi-layer GR plate (membrane) suspended over a round hole we show that this combined approach allows access to the mechanical properties, internal structure and attachment geometry of the membrane providing information about both the supported and suspended regions of the system. We show that UFM allows the precise geometrical position of the supported membrane-substrate contact to be located and provides indication of the local variation of its quality in the contact areas. At the same time, we show that by mapping the position sensitive frequency and phase response of CR-AFM response, one can reliably quantify the membrane stiffness, and image the defects in the suspended area of the membrane. The phase and amplitude of experimental CR-AFM measurements show excellent agreement with an analytical model accounting for the resonance of the combined CR-AFM probe-membrane system. The combination of UFM and CR-AFM provide a beneficial combination for investigation of few-layer NEMS systems based on two dimensional materials.

Although it was demonstrated that discrete molecular levels determine the sign and magnitude of the thermoelectric effect in single-molecule junctions, full electrostatic control of these levels has not been achieved to date. Here, we show that graphene nanogaps combined with gold microheaters serve as a testbed for studying single-molecule thermoelectricity. Reduced screening of the gate electric field compared to conventional metal electrodes allows control of the position of the dominant transport orbital by hundreds of meV. We find that the power factor of graphene-fullerene junctions can be tuned over several orders of magnitude to a value close to the theoretical limit of an isolated Breit-Wigner resonance. Furthermore, our data suggest that the power factor of an isolated level is only given by the tunnel coupling to the leads and temperature. These results open up new avenues for exploring thermoelectricity and charge transport in individual molecules and highlight the importance of level alignment and coupling to the electrodes for optimum energy conversion in organic thermoelectric materials.

Originally, EIFS was designed as a perfect barrier system; that is, one which provides waterproofing protection at the exterior face of the cladding. The idea of barrier cladding assemblies is to create a face-sealed façade that repels moisture to keep the building dry. Unfortunately, barrier systems are rarely perfect. Any number of deficiencies can lead to EIFS failure. The major culprits are poor workmanship, damp climate, impact damage, building movement, and incompatible or unsound substrate.

This course provides step-by-step prescriptive advice to architects, engineers, and contractors on when it makes sense to repair or rehabilitate existing windows, and when they should advise their building owner clients to consider replacement.