Nitric oxide (NO)-releasing coatings have promising potential for biomedical applications notably in implant safety and wound dressing by promoting healing and reducing bacterial growth. Yet, the production of NO-films remains difficult through classic approaches. In this study, plasma polymerized NO-coatings are produced using a helium-isopentyl nitrite mixture under two power settings and deposited on aluminum samples. Analyses of the plasma phase by mass spectroscopy reveal the presence of nitrosoxy groups (O-NO) in monomer and quasi-monomer at low power, and a higher fragmentation rate at high power. Static and no-static samples are made and analyzed by X-ray photoelectron spectroscopy showing the presence of these group for both power conditions, with a better retention on the sample's center for the latest. This study investigates the production of nitric oxide-films through atmospheric-pressure plasma jet using a helium-isopentyl nitrite mixture, on both static and nonstatic samples. Experimental parameters, including input power and nozzle-sample distances are confronted to compare their influence on the deposited films to optimize the retention of nitrosoxy groups (O-NO) on the sample's surface. image

While blood-contacting materials are widely deployed in medicine in vascular stents, catheters, and cannulas, devices fail in situ because of thrombosis and restenosis. Furthermore, microbial attachment and biofilm formation is not an uncommon problem for medical devices. Even incremental improvements in hemocompatible materials can provide significant benefits for patients in terms of safety and patency as well as substantial cost savings. Herein, a novel but simple strategy is described for coating a range of medical materials, that can be applied to objects of complex geometry, involving plasma-grafting of an ultrathin hyperbranched polyglycerol coating (HPG). Plasma activation creates highly reactive surface oxygen moieties that readily react with glycidol. Irrespective of the substrate, coatings are uniform and pinhole free, comprising O─C─O repeats, with HPG chains packing in a fashion that holds reversibly binding proteins at the coating surface. In vitro assays with planar test samples show that HPG prevents platelet adhesion and activation, as well as reducing (>3 log) bacterial attachment and preventing biofilm formation. Ex vivo and preclinical studies show that HPG-coated nitinol stents do not elicit thrombosis or restenosis, nor complement or neutrophil activation. Subcutaneous implantation of HPG coated disks under the skin of mice shows no evidence of toxicity nor inflammation.

Whilst blood‐contacting materials are widely deployed in medicine in vascular stents, catheters and cannulas, devices fail in‐situ because of thrombosis and restenosis. Furthermore, microbial attachment and biofilm formation is not an uncommon problem for medical devices. Even incremental improvements in hemocompatible materials could provide significant benefits for patients in terms of safety and patency as well as substantial cost savings.Herein, we describe a novel but simple strategy for coating a range of medical materials, that can be applied to objects of complex geometry, involving plasma‐grafting of an ultra‐thin hyperbranched polyglycerol coating (HPG). Plasma activation creates highly reactive surface oxygen moieties that readily react with glycidol. Irrespective of the substrate, coatings are uniform and pinhole free, comprising O‐C‐O repeats, with HPG chains packing in a fashion that holds reversibly binding proteins at the coating surface.In vitro assays with planar test samples show that HPG prevents platelet adhesion and activation, as well as reducing (>3log) bacterial attachment and preventing biofilm formation. Ex vivo and preclinical studies show that HPG‐coated nitinol stents do not elicit thrombosis or restenosis, nor complement or neutrophil activation. Subcutaneous implantation of HPG coated disks under the skin of mice showed no evidence of toxicity nor inflammation. This article is protected by copyright. All rights reserved

Molecular radicals such as nitric oxide (NO) play a role in numerous important biological processes. NO, however, is inherently unstable, and there is considerable interest in stable radicals with analogous behaviour, such as (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), and their potential as biologically active surface coatings. Here we show that it is possible to grow stable TEMPO monolayers with an ordered arrangement and specific orientation of the nitroxide group. A combination of high-resolution atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations reveal that strong dipole-dipole interactions between neighbouring TEMPO molecules determine their orientation, resulting in an anti-parallel arrangement with upwards and downwards facing nitroxide groups. Surface coating is made possible using plasma polymerisation, a surface molecular engineering technique suitable for growing functional coatings of highly stable organic molecules. Typically, plasma polymerisation is considered a surface-independent process, with the plasma power and pressure dominating the deposited film's properties. We therefore test this assumption and its impact on TEMPO layers by studying initial stage growth on multiple material surfaces. We show that whilst plasma polymer growth creates ordered layers on gold and graphite surfaces, there is substantial substrate-dependence with less ordered growth on other materials up to a film thickness of 30 nm, suggesting variation in molecular packing and retention. Beyond that thickness, films convergence to a flat, uniform, surface-agnostic structure. These findings establish the utility of plasma polymerisation as a method for ordered growth and demonstrate the ability to direct the orientation of TEMPO molecules and NO free radicals within a thin film.

Melanins are a class of conjugated biopolymers with varying compositions and functions, which have a variety of potential medical and technical applications. Here, this work examines the conjugated polymers derived from a variety of phenolic monomers (catechol (CAT), levodopa (DOPA), and homogentisic acid (HGA)), using a selection of different analytical chemistry techniques to compare their properties with a view to understanding structure–function relations. The polymers display measurable conductivity, with electronic properties tuned by the functional groups pendant on the polymer backbones (which served as dopants) suggesting their potential for application in electronic devices.

Melanins are a class of biopolymers that are widespread in nature, with diverse origins, compositions, and functions, and their chemical and optoelectronic properties render them potentially useful for application in materials science for various biotechnological applications. For patients with alkaptonuria, the accumulation of homogentisic acid (HGA) in their bodies is associated with the concomitant deposition of pyomelanin, which is a pigment that contains significant amounts of polymerized HGA (polyHGA) in the bodily tissues of the patients. The polymerization of HGA under various different conditions in vitro is investigated using a selection of different analytical chemistry techniques to understand if there may be a correlation between the conditions and pigment deposition in vivo, and their potential for application as green/sustainable and components of electronic devices.

Managing thermal transport in nanostructures became a major challenge in the development of active microelectronic, optoelectronic and thermoelectric devices, stalling the famous Moore's law of clock speed increase of microprocessors for more than a decade. To find the solution to this and linked problems, one needs to quantify the ability of these nanostructures to conduct heat with adequate precision, nanoscale resolution, and, essentially, for the internal layers buried in the 3D structure of modern semiconductor devices. Existing thermoreflectance measurements and "hot wire" 3ω methods cannot be effectively used at lateral dimensions of a layer below a micrometre; moreover, they are sensitive mainly to the surface layers of a relatively high thickness of above 100 nm. Scanning thermal microscopy (SThM), while providing the required lateral resolution, provides mainly qualitative data of the layer conductance due to undefined tip-surface and interlayer contact resistances. In this study, we used cross-sectional SThM (xSThM), a new method combining scanning probe microscopy compatible Ar-ion beam exit nano-cross-sectioning (BEXP) and SThM, to quantify thermal conductance in complex multilayer nanostructures and to measure local thermal conductivity of oxide and semiconductor materials, such as SiO2, SiGex and GeSny. By using the new method that provides 10 nm thickness and few tens of nm lateral resolution, we pinpoint crystalline defects in SiGe/GeSn optoelectronic materials by measuring nanoscale thermal transport and quantifying thermal conductivity and interfacial thermal resistance in thin spin-on materials used in extreme ultraviolet lithography (eUV) fabrication processing. The new capability of xSThM demonstrated here for the first time is poised to provide vital insights into thermal transport in advanced nanoscale materials and devices.

We explore how to configure an argon atmospheric-pressure plasma jet for enhancing its production of hydrogen peroxide (H2O2) in deionised water (DIW). The plasma jet consists of a quartz tube of 1.5 mm inner diameter and 3 mm outer diameter, with an upstream internal needle electrode (within the tube) and a downstream external cylindrical electrode (surrounding the tube). The plasma is operated by purging argon through the glass tube and applying a sinusoidal AC voltage to the internal needle electrode at 10 kV (peak–peak) with a frequency of 23.5 kHz. We study how the following operational parameters influence the production rate of H2O2 in water: tube length, inter-electrode separation distance, distance of the ground electrode from the tube orifice, distance between tube orifice and the DIW, argon flow rate and treatment time. By examining the electrical and optical properties of the plasma jet, we determine how the above operational parameters influence the major plasma processes that promote H2O2 generation through electron-induced dissociation reactions and UV photolysis within the plasma core and in the plasma afterglow; but with a caveat being that these processes are highly dependent on the water vapour content from the argon gas supply and ambient environment. We then demonstrate how the synergistic action between H2O2 and other plasma generated molecules at a plasma induced low pH in the DIW is highly effective at decontaminating common wound pathogens Gram-positive Staphylococus aureus and Gram-negative Pseudomonas aeruginosa. The information presented in this study is relevant in the design of medical plasma devices where production of plasma reactive species such as H2O2 at physiologically useful concentrations is needed to help realise the full clinical potential of the technology.

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.

We report on the structural, mechanical, and thermal analysis of 40 nm thick polystyrene-block-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) films coated with evaporated chromium layers of different thicknesses (1, 2, and 5 nm). Solvent annealing processes allow the structural control of the BCP films morphology by rearranging the position of the PEO cylinders parallel to the substrate plane. High-vacuum scanning thermal microscopy and ultrasonic force microscopy measurements performed in ambient pressure revealed that coated ultrathin metal layers strongly influence the heat dissipation in the BCP films and the local surface stiffness of the individual BCP domains, respectively. The measured tip sample effective thermal resistance decreases from 6.1 x 10(7) to 2.5 x 10(7) K W-1 with increasing Cr film thickness. In addition, scanning probe microscopy measurements allow the thermal and mechanical mapping of the two segregated polymer domains (PEO PS) of sub-50 nm characteristic sizes, with sub-10 nm thermal spatial resolution. The results revealed the effect of the surface morphology of the BCP and the incorporation of the metal film on the nanoscale thermal properties and volume self-assembly on the mechanical properties. The findings from this study provide insight into the formation of high aspect ratio BCP metal structures with the more established applications in lithography. In addition, knowledge of the thermal and mechanical properties at the nanoscale is required in emergent applications, where BCPs, or polymers in general, are part of the structure or device. The performance of such devices is commonly related to the requirement of increased heat dissipation while maintaining mechanical flexibility.

Michael J. Barnes Department of Electrical Engineering and Electronics, University of Liverpool, Brownlow Hill, L69 3GJ, Liverpool, UK Alexander J. Robson Department of Chemistry/Material Science Institute, University of Lancaster, Bailrigg, LA1 4YW, Lancaster, UK Javad Naderi Department of Chemistry/Material Science Institute, University of Lancaster, Bailrigg, LA1 4YW, Lancaster, UK Robert D. Short Department of Chemistry/Material Science Institute, University of Lancaster, Bailrigg, LA1 4YW, Lancaster, UK James W. Bradley a) Department of Electrical Engineering and Electronics, University of Liverpool, Brownlow Hill, L69 3GJ, Liverpool, UK

Plasma polymerization of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) yields thin films containing stable nitroxide radicals that have properties analogous to that of nitric oxide (NO) without short lifetimes. This property gives TEMPO films a wide variety of potential applications. Typically, control of the final film chemistry is difficult and the plasma discharge conditions must be tailored to in order to maximize the retention of these nitroxide groups during the polymerization and deposition process. In this study, plasma diagnostics and surface analysis of the deposited films were carried out to determine the optimal plasma conditions for the retention of nitroxide groups. These techniques included energy-resolved mass spectrometry, heated planar probe ion current measurements, deposition rate measurements, and x-ray photoelectron spectroscopy (XPS). Results show that operating the plasma with a combination of low input powers and high pressures produces a collisional discharge in which fragmentation of the TEMPO molecule is suppressed, leading to good retention of nitroxide groups. Ion energy distribution functions and quartz crystal microbalance measurements support the soft landing theory of ion deposition on the substrate within this γ-mode, in which the flux of low energy, soft landed ions form the primary contribution to film growth. XPS analysis of deposited polymers shows 75.7% retention of N-O groups in the polymer films deposited in a 25 Pa 5 W discharge.

Scanning spreading resistance microscopy (SSRM) is a powerful technique for quantitative two-and three-dimensional carrier profiling of semiconductor devices with sub-nm spatial resolution. However, considering the sub-10 nm dimensions of advanced devices and the introduction of three-dimensional architectures like fin field effect transistor (FinFET) and nanowires, the measured spreading resistance is easily impacted by parasitic series resistances present in the system. The limited amount of material, the presence of multiple interfaces, and confined current paths may increase the total resistance measured by SSRM beyond the expected spreading resistance, which can ultimately lead to an inaccurate carrier quantification. Here, we report a simulation assisted experimental study to identify the different parameters affecting the SSRM measurements in confined volumes. Experimentally, the two-dimensional current confinement is obtained by progressively thinning down uniformly doped blanket silicon on insulator wafers using scalpel SSRM. The concomitant SSRM provides detailed electrical information as a function of depth up to oxide interface. We show that the resistance is most affected by the interface traps in case of a heterogeneous sample, followed by the intrinsic resistance of the current carrying paths. Furthermore, we show that accurate carrier quantification is ensured for typical back contact distances of 1 μm if the region of interest is at least nine times larger than the probe radius.

We report the controllable growth of GaAs quantum complexes in droplet molecular-beam epitaxy, and the optical properties of self-assembled AlxGa1-xAs quantum rings embedded in a superlattice. We found that Ga droplets on a GaAs substrate can retain their geometry up to a maximum temperature of 490 degrees C during post-growth annealing, with an optimal temperature of 320 degrees C for creating uniform and symmetric droplets. Through controlling only the crystallisation temperature under As-4 in the range of 450 degrees C to 580 degrees C, we can reliably control diffusion, adsorption and etching rates to produce various GaAs quantum complexes such as quantum dots, dot pairs and nanoholes. AlxGa1-xAs quantum rings are also realised within these temperatures via the adjustment of As beam equivalent pressure. We found that crystallisation using As-2 molecules in the place of As-4 creates smaller diameter quantum rings at higher density. The photoluminescence of As-2 grown AlxGa1-xAs quantum rings embedded in a superlattice shows a dominant emission from the quantum rings at elevated temperatures. This observation reveals the properties of the quantum ring carrier confinement and their potential application as efficient photon emitters.

Advances in material design and device miniaturization lead to physical properties that may significantly differ from the bulk ones. In particular, thermal transport is strongly affected when the device dimensions approach the mean free path of heat carriers. Scanning Thermal Microscopy (SThM) is arguably the best approach for probing nanoscale thermal properties with few tens of nm lateral resolution. Typical SThM probes based on microfabricated Pd resistive probes (PdRP) using a spatially distributed heater and a nanoscale tip in contact with the sample provide high sensitivity and operation in ambient, vacuum, and liquid environments. Although some aspects of the response of this sensor have been studied, both for static and dynamic measurements, here we build an analytical model of the PdRP sensor taking into account finite dimensions of the heater that improves the precision and stability of the quantitative measurements. In particular, we analyse the probe response for heat flowing through a tip to the sample and due to probe self-heating and theoretically and experimentally demonstrate that they can differ by more than 50%, hence introducing significant correction in the SThM measurements. Furthermore, we analyzed the effect of environmental parameters such as sample and microscope stage temperatures and laser illumination, which allowed reducing the experimental scatter by a factor of 10. Finally, varying these parameters, we measured absolute values of heat resistances and compared these to the model for both ambient and vacuum SThM operations, providing a comprehensive pathway improving the precision of the nanothermal measurements in SThM.

With the advent of heat-assisted magnetic recording (HAMR) [1] the thermal transport properties of magnetic recording media have become a key performance characteristic. In this study we explore the potential of scanning thermal microscopy (SThM) [2] to resolve thermal transport on the nanoscale and use a multilayered, grain segregated conventional disk with the structure reported in [3].

The ability to uniquely identify an object or device is important for authentication. Imperfections, locked into structures during fabrication, can be used to provide a fingerprint that is challenging to reproduce. In this paper, we propose a simple optical technique to read unique information from nanometer-scale defects in 2D materials. Imperfections created during crystal growth or fabrication lead to spatial variations in the bandgap of 2D materials that can be characterized through photoluminescence measurements. We show a simple setup involving an angle-adjustable transmission filter, simple optics and a CCD camera can capture spatially-dependent photoluminescence to produce complex maps of unique information from 2D monolayers. Atomic force microscopy is used to verify the origin of the optical signature measured, demonstrating that it results from nanometer-scale imperfections. This solution to optical identification with 2D materials could be employed as a robust security measure to prevent counterfeiting.

We report the results of continuous and time-resolved photoluminescence measurements on type-II GaSb quantum rings embedded within GaAs/AlxGa1−xAs quantum wells. A range of samples were grown with different well widths, compensation-doping concentrations within the wells, and number of quantum-ring layers. We find that each of these variants have no discernible effect on the radiative recombination, except for the very narrowest (5 nm) quantum well. In contrast, single-particle numerical simulations of the sample predict changes in photoluminescence energy of up to 200 meV. This remarkable difference is explained by the strong Coulomb binding of electrons to rings that are multiply charged with holes. The resilience of the emission to compensation doping indicates that multiple hole occupancy of the quantum rings is required for efficient carrier recombination, regardless of whether these holes come from doping or excitation.

We report low-temperature photoluminescence measurements on highly-uniform GaAs/AlxGa1−xAs quantum dots grown by droplet epitaxy. Recombination between confined electrons and holes bound to carbon acceptors in the dots allow us to determine the energies of the confined states in the system, as confirmed by effective mass calculations. The presence of acceptor-bound holes in the quantum dots gives rise to a striking observation of the phonon-bottleneck effect.

Multilayer structures of active semiconductor devices (1), novel memories (2) and semiconductor interconnects are becoming increasingly three-dimensional (3D) with simultaneous decrease of dimensions down to the few nanometres length scale (3). Ability to test and explore these 3D nanostructures with nanoscale resolution is vital for the optimization of their operation and improving manufacturing processes of new semiconductor devices. While electron and scanning probe microscopes (SPMs) can provide necessary lateral resolution, their ability to probe underneath the immediate surface is severely limited. Cross-sectioning of the structures via focused ion beam (FIB) to expose the subsurface areas often introduces multiple artefacts that mask the true features of the hidden structures, negating benefits of such approach. In addition, the few tens of micrometre dimension of FIB cut, make it unusable for the SPM investigation.