ABSTRACT The synthesis and self-assembled monolayer (SAM) formation of a calix[4]crown-5 derivati... more ABSTRACT The synthesis and self-assembled monolayer (SAM) formation of a calix[4]crown-5 derivative are reported. Several techniques, including electrochemistry, atomic force microscopy (AFM), Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and contact angle measurements have been applied to characterise the monolayer film designed for chemical sensor applications. The recognition properties of this SAM for metal cations has been investigated using impedance spectroscopy (IS) showing an electrochemical response proportional to calcium ion concentration in the range from 10(-7) M to 10(-2) M. This response is related to microscopic changes at the gold surface induced by selective binding by the immobilised calixarene.
DOI: 10.1002/aelm.201600049 circuit current at the maximum power point, which manifests as a low ... more DOI: 10.1002/aelm.201600049 circuit current at the maximum power point, which manifests as a low fi ll factor (FF) in the device characteristics. In this work, we develop a counterintuitive concept based on the use of relatively insulating nanoparticles as a route toward creating strong local fi eld enhancement at one device contact, designed to improve the overall charge conduction through structuring of the metal contact. Furthermore, we use the resulting electric fi eld screening below the insulating nanoparticle to extract currents that are closer to the short circuit conditions with respect to current density–voltage curves. In this study, solution-cast Bi 2 O 3 nanoparticles and nanoparticle clusters (≈100–200 nm in diameter) have been used as a means to produce structured back contacts due to the shadowing effect from the nanoparticles during the thermal evaporation of the electrode metal (Al). The formation of a discontinuous Al contact is shown to lead to enhanced electric fi elds adjacent to the geometric edges produced by the Bi 2 O 3 shadowing. The use of Bi 2 O 3 nanoparticles is driven by the low work function formed at the BHJ/Bi 2 O 3 contact, which maintains the built-in potential gradient of the organic diodes observed under short circuit conditions while allowing the structuring of the metal contact during the metal deposition. The relatively large particle size, combined with the low conductivity of this material system, ensures that there is no undesired charge transport through the nanoparticle allowing the active layer volume underneath the particle to be effectively under short circuit conditions under AM 1.5G illumination. We note that while we have used Bi 2 O 3 as an “interfacial” modifi er on this occasion, this material system has a number of uses as a nano-shell coating for PSCs, [ 17 ] for solid electrolytes, [ 18 ] and as an active component in X-ray detectors, [ 19,20 ] making the concepts developed here widely applicable to other technologies and device architectures. The combination of these device design concepts, with active layer restructuring and trap passivation, is a precursor to an experimentally observed overall effi ciency enhancement in excess of 30%, with further improvements possible for specifi c material combinations. Prior to fabrication of the devices, a theoretical simulation was undertaken in order to examine the potential for desirable fi eld enhancement confi gurations using a discontinuous Al contact. For this purpose, a COMSOL Multiphysics simulation was conducted depicting a non-uniform aluminum coating on an insulating particle which rests on a semiconductor surface. The resulting voltage and electric fi eld distributions are shown in Figure 1 . For the observation of localized electric fi eld enhancements, two conditions that can occur during the deposition of Al were investigated: (1) the formation of a continuous Effective extraction of charges from polymer solar cells (PSCs) is one of the principle bottlenecks hampering device effi ciency. While a number of methods have been developed, such as modifi cation of interfacial layer transport properties or addition of inorganic nanostructures such as nanotubes, signifi cant effi ciency gains are often elusive. [ 1 ] In this work, we introduce a simple processing methodology that allows the structuring of the PSC back contact, which subsequently produces a fi eld enhanced charge extraction and results in an overall effi ciency gain of 30% (from an initial power conversion effi ciency [PCE] of 5.9% to 7.6%). The fundamental interest in developing methodologies for improving PSC effi ciency stems from the advantages of lowcost manufacturability, lightweight, and form factor, as well as the printable nature of solution processed organic photovoltaic (OPV) materials utilized, on fl exible substrates. [ 1 ] These developments date back to the initial discovery of ultrafast electron transfer in the organic bulk heterojunction (BHJ) architecture. [ 2 ] Since then, there has been a signifi cant effort to improve PCEs, [ 3,4 ] with developments which include the synthesis of new narrow band gap materials, the introduction of nanoscale additives for hybrid devices and the design of novel device architectures. [ 5–8 ]
We introduce a combined process for the reduction of graphene oxide (GO) via vitamin C (ascorbic ... more We introduce a combined process for the reduction of graphene oxide (GO) via vitamin C (ascorbic acid) and thermal annealing.
Silver-functionalized reduced graphene oxide (Ag-rGO) nanosheets were prepared by single chemical... more Silver-functionalized reduced graphene oxide (Ag-rGO) nanosheets were prepared by single chemical and thermal processes, with very low concentration of silver. The resulting carbon framework consists of reduced graphene oxide (rGO) sheets or 3D networks, decorated with anchored silver nanoparticles. The Ag-rGO nanosheets were dispersed into a polymer matrix and the composites evaluated for use as biological scaffolds. The rGO material in poly(dimethylsiloxane) (PDMS) has been tested for antimicrobial activity against Gram-positiveStaphylococcus aureus(S. Aureus) bacteria, after exposure times of 24 and 120 hours, as well as in the determination of cell viability on cultures of fibroblast cells (NIH/3T3). Using 1 mL of Ag-rGO in PDMS the antibacterial effectiveness againstStaphylococcus aureuswas limited, showing an increased amount of Colony Forming Units (CFU), after 24 hours of contact. In the cell viability assay, after 48 hours of contact, the group of 1 mL of Ag-rGO with PDMS w...
A generic electromagnetic model for the working principles of triboelectric nanogenerators derive... more A generic electromagnetic model for the working principles of triboelectric nanogenerators derived using Maxwell's equations, to a universally applicable framework.
We report on the synthesis of two and three dimensional carbonaceous sponges produced directly fr... more We report on the synthesis of two and three dimensional carbonaceous sponges produced directly from graphene oxide (GO) into which functionalized iron nanoparticles can be introduced to render it magnetic. This simple, low cost procedure, wherein an iron polymeric resin precursor is introduced into the carbon framework, results in carbon-based materials with specific surface areas of the order of 93 and 66 m(2) g(-1), compared to approx. 4 m(2) g(-1) for graphite, decorated with ferromagnetic iron nanoparticles giving coercivity fields postulated to be 216 and 98 Oe, values typical for ferrite magnets, for 3.2 and 13.5 wt% Fe respectively. The strongly magnetic iron nanoparticles are robustly anchored to the GO sheets by a layer of residual graphite, on the order of 5 nm, formed during the pyrolysis of the precursor material. The applicability of the carbon sponges is demonstrated in their ability to absorb, store and subsequently elute an organic dye, Rhodamine B, from water as req...
Graphene-based carbon sponges can be used in different applications in a large number of fields i... more Graphene-based carbon sponges can be used in different applications in a large number of fields including microelectronics, energy harvesting and storage, and environmental remediation. The functionality and scope of their...
The use of polymers is becoming increasingly common in the production of biomedical devices. For ... more The use of polymers is becoming increasingly common in the production of biomedical devices. For such devices we have investigated the forming of polymer micro and nanostructures in poly(ethylene naphthalate) (PEN), using imprint techniques such as hot embossing (HE) [1] and nanoimprinting (NI) [2], and compared the performance of PEN with a commonly used polymer for imprint techniques, poly(methyl methacrylate) (PMMA). PEN is a semi-crystalline, thermoplastic polyester, available since 1948 [3], with good mechanical properties and a working temperature up to 155°C [4]. It is resistant to dilute acids and organic solvents, and has good optical clarity and UV radiation absorbance [5]. At physiological conditions PEN is stable and biocompatible. As a consequence, it already has applications in the production of food containers, in particular plastic bottles, which can withstand the temperatures required for sterilisation. Its inherent strength and dimensional stability also means PEN ...
Coatings or films are applied to a substrate for several applications, such as waterproofing, cor... more Coatings or films are applied to a substrate for several applications, such as waterproofing, corrosion resistance, adhesion performance, cosmetic effects, and optical coatings. When applying a coating to a substrate, it is vital to monitor the coating thickness during the coating process to achieve a product to the desired specification via real time production control. There are several different coating thickness measurement methods that can be used, either in-line or off-line, which can determine the coating thickness relative to the material of the coating and the substrate. In-line coating thickness measurement methods are often very difficult to design and implement due to the nature of the harsh environmental conditions of typical production processes and the speed at which the process is run. This paper addresses the current and novel coating thickness methodologies for application to chromium coatings on a ferro-magnetic steel substrate with their advantages and limitation...
Thick film (≥5 μm thick) semiconducting polymer diodes incorporating poly(triarylamine) (PTAA) ha... more Thick film (≥5 μm thick) semiconducting polymer diodes incorporating poly(triarylamine) (PTAA) have been produced and applied as direct x-ray detectors. Experiments determined that a rectifying diode behavior persists when increasing the thickness of the active layer above typical thin film thicknesses (≪1 μm), and the electrical conduction mechanism of the diodes has been identified. Direct current and photoconductivity measurements on indium tin oxide/poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)/PTAA/metal diodes confirm that carrier conduction occurs via a Poole–Frenkel mechanism. The energy band structure of diodes (having gold or aluminum top electrodes) has been elucidated and used to explain the resulting electrical characteristics. Theoretical calculations show that, upon irradiation with x-rays, the diode quantum efficiency increases with increasing polymer film thickness. The diodes produced here display characteristics similar to their thin film analogs, meanin...
ABSTRACT The synthesis and self-assembled monolayer (SAM) formation of a calix[4]crown-5 derivati... more ABSTRACT The synthesis and self-assembled monolayer (SAM) formation of a calix[4]crown-5 derivative are reported. Several techniques, including electrochemistry, atomic force microscopy (AFM), Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and contact angle measurements have been applied to characterise the monolayer film designed for chemical sensor applications. The recognition properties of this SAM for metal cations has been investigated using impedance spectroscopy (IS) showing an electrochemical response proportional to calcium ion concentration in the range from 10(-7) M to 10(-2) M. This response is related to microscopic changes at the gold surface induced by selective binding by the immobilised calixarene.
DOI: 10.1002/aelm.201600049 circuit current at the maximum power point, which manifests as a low ... more DOI: 10.1002/aelm.201600049 circuit current at the maximum power point, which manifests as a low fi ll factor (FF) in the device characteristics. In this work, we develop a counterintuitive concept based on the use of relatively insulating nanoparticles as a route toward creating strong local fi eld enhancement at one device contact, designed to improve the overall charge conduction through structuring of the metal contact. Furthermore, we use the resulting electric fi eld screening below the insulating nanoparticle to extract currents that are closer to the short circuit conditions with respect to current density–voltage curves. In this study, solution-cast Bi 2 O 3 nanoparticles and nanoparticle clusters (≈100–200 nm in diameter) have been used as a means to produce structured back contacts due to the shadowing effect from the nanoparticles during the thermal evaporation of the electrode metal (Al). The formation of a discontinuous Al contact is shown to lead to enhanced electric fi elds adjacent to the geometric edges produced by the Bi 2 O 3 shadowing. The use of Bi 2 O 3 nanoparticles is driven by the low work function formed at the BHJ/Bi 2 O 3 contact, which maintains the built-in potential gradient of the organic diodes observed under short circuit conditions while allowing the structuring of the metal contact during the metal deposition. The relatively large particle size, combined with the low conductivity of this material system, ensures that there is no undesired charge transport through the nanoparticle allowing the active layer volume underneath the particle to be effectively under short circuit conditions under AM 1.5G illumination. We note that while we have used Bi 2 O 3 as an “interfacial” modifi er on this occasion, this material system has a number of uses as a nano-shell coating for PSCs, [ 17 ] for solid electrolytes, [ 18 ] and as an active component in X-ray detectors, [ 19,20 ] making the concepts developed here widely applicable to other technologies and device architectures. The combination of these device design concepts, with active layer restructuring and trap passivation, is a precursor to an experimentally observed overall effi ciency enhancement in excess of 30%, with further improvements possible for specifi c material combinations. Prior to fabrication of the devices, a theoretical simulation was undertaken in order to examine the potential for desirable fi eld enhancement confi gurations using a discontinuous Al contact. For this purpose, a COMSOL Multiphysics simulation was conducted depicting a non-uniform aluminum coating on an insulating particle which rests on a semiconductor surface. The resulting voltage and electric fi eld distributions are shown in Figure 1 . For the observation of localized electric fi eld enhancements, two conditions that can occur during the deposition of Al were investigated: (1) the formation of a continuous Effective extraction of charges from polymer solar cells (PSCs) is one of the principle bottlenecks hampering device effi ciency. While a number of methods have been developed, such as modifi cation of interfacial layer transport properties or addition of inorganic nanostructures such as nanotubes, signifi cant effi ciency gains are often elusive. [ 1 ] In this work, we introduce a simple processing methodology that allows the structuring of the PSC back contact, which subsequently produces a fi eld enhanced charge extraction and results in an overall effi ciency gain of 30% (from an initial power conversion effi ciency [PCE] of 5.9% to 7.6%). The fundamental interest in developing methodologies for improving PSC effi ciency stems from the advantages of lowcost manufacturability, lightweight, and form factor, as well as the printable nature of solution processed organic photovoltaic (OPV) materials utilized, on fl exible substrates. [ 1 ] These developments date back to the initial discovery of ultrafast electron transfer in the organic bulk heterojunction (BHJ) architecture. [ 2 ] Since then, there has been a signifi cant effort to improve PCEs, [ 3,4 ] with developments which include the synthesis of new narrow band gap materials, the introduction of nanoscale additives for hybrid devices and the design of novel device architectures. [ 5–8 ]
We introduce a combined process for the reduction of graphene oxide (GO) via vitamin C (ascorbic ... more We introduce a combined process for the reduction of graphene oxide (GO) via vitamin C (ascorbic acid) and thermal annealing.
Silver-functionalized reduced graphene oxide (Ag-rGO) nanosheets were prepared by single chemical... more Silver-functionalized reduced graphene oxide (Ag-rGO) nanosheets were prepared by single chemical and thermal processes, with very low concentration of silver. The resulting carbon framework consists of reduced graphene oxide (rGO) sheets or 3D networks, decorated with anchored silver nanoparticles. The Ag-rGO nanosheets were dispersed into a polymer matrix and the composites evaluated for use as biological scaffolds. The rGO material in poly(dimethylsiloxane) (PDMS) has been tested for antimicrobial activity against Gram-positiveStaphylococcus aureus(S. Aureus) bacteria, after exposure times of 24 and 120 hours, as well as in the determination of cell viability on cultures of fibroblast cells (NIH/3T3). Using 1 mL of Ag-rGO in PDMS the antibacterial effectiveness againstStaphylococcus aureuswas limited, showing an increased amount of Colony Forming Units (CFU), after 24 hours of contact. In the cell viability assay, after 48 hours of contact, the group of 1 mL of Ag-rGO with PDMS w...
A generic electromagnetic model for the working principles of triboelectric nanogenerators derive... more A generic electromagnetic model for the working principles of triboelectric nanogenerators derived using Maxwell's equations, to a universally applicable framework.
We report on the synthesis of two and three dimensional carbonaceous sponges produced directly fr... more We report on the synthesis of two and three dimensional carbonaceous sponges produced directly from graphene oxide (GO) into which functionalized iron nanoparticles can be introduced to render it magnetic. This simple, low cost procedure, wherein an iron polymeric resin precursor is introduced into the carbon framework, results in carbon-based materials with specific surface areas of the order of 93 and 66 m(2) g(-1), compared to approx. 4 m(2) g(-1) for graphite, decorated with ferromagnetic iron nanoparticles giving coercivity fields postulated to be 216 and 98 Oe, values typical for ferrite magnets, for 3.2 and 13.5 wt% Fe respectively. The strongly magnetic iron nanoparticles are robustly anchored to the GO sheets by a layer of residual graphite, on the order of 5 nm, formed during the pyrolysis of the precursor material. The applicability of the carbon sponges is demonstrated in their ability to absorb, store and subsequently elute an organic dye, Rhodamine B, from water as req...
Graphene-based carbon sponges can be used in different applications in a large number of fields i... more Graphene-based carbon sponges can be used in different applications in a large number of fields including microelectronics, energy harvesting and storage, and environmental remediation. The functionality and scope of their...
The use of polymers is becoming increasingly common in the production of biomedical devices. For ... more The use of polymers is becoming increasingly common in the production of biomedical devices. For such devices we have investigated the forming of polymer micro and nanostructures in poly(ethylene naphthalate) (PEN), using imprint techniques such as hot embossing (HE) [1] and nanoimprinting (NI) [2], and compared the performance of PEN with a commonly used polymer for imprint techniques, poly(methyl methacrylate) (PMMA). PEN is a semi-crystalline, thermoplastic polyester, available since 1948 [3], with good mechanical properties and a working temperature up to 155°C [4]. It is resistant to dilute acids and organic solvents, and has good optical clarity and UV radiation absorbance [5]. At physiological conditions PEN is stable and biocompatible. As a consequence, it already has applications in the production of food containers, in particular plastic bottles, which can withstand the temperatures required for sterilisation. Its inherent strength and dimensional stability also means PEN ...
Coatings or films are applied to a substrate for several applications, such as waterproofing, cor... more Coatings or films are applied to a substrate for several applications, such as waterproofing, corrosion resistance, adhesion performance, cosmetic effects, and optical coatings. When applying a coating to a substrate, it is vital to monitor the coating thickness during the coating process to achieve a product to the desired specification via real time production control. There are several different coating thickness measurement methods that can be used, either in-line or off-line, which can determine the coating thickness relative to the material of the coating and the substrate. In-line coating thickness measurement methods are often very difficult to design and implement due to the nature of the harsh environmental conditions of typical production processes and the speed at which the process is run. This paper addresses the current and novel coating thickness methodologies for application to chromium coatings on a ferro-magnetic steel substrate with their advantages and limitation...
Thick film (≥5 μm thick) semiconducting polymer diodes incorporating poly(triarylamine) (PTAA) ha... more Thick film (≥5 μm thick) semiconducting polymer diodes incorporating poly(triarylamine) (PTAA) have been produced and applied as direct x-ray detectors. Experiments determined that a rectifying diode behavior persists when increasing the thickness of the active layer above typical thin film thicknesses (≪1 μm), and the electrical conduction mechanism of the diodes has been identified. Direct current and photoconductivity measurements on indium tin oxide/poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)/PTAA/metal diodes confirm that carrier conduction occurs via a Poole–Frenkel mechanism. The energy band structure of diodes (having gold or aluminum top electrodes) has been elucidated and used to explain the resulting electrical characteristics. Theoretical calculations show that, upon irradiation with x-rays, the diode quantum efficiency increases with increasing polymer film thickness. The diodes produced here display characteristics similar to their thin film analogs, meanin...
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Papers by Christopher A Mills