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Over the last half century, the existence of an additional thermal transition in between the glass transition and the Curie/melting transition has been frequently observed on vinylidenefluoride-based ferro-, pyro- and piezoelectric homo- and co-polymers. The transition has also been observed recently in some of the related relaxor-ferroelectric terpolymers. Despite its well-known existence and the rich history of its treatment in the literature, the origin(s) and a more or less complete picture of the mid-temperature transition have remained elusive until now. Over the years, several authors have put forth various explanations for the so-called mid-temperature transition — some complementary and some contradictory to each other. At the 17th IEEE International Symposium on Electrets (ISE-17) in Limerick, Ireland, in September 2019, the mysterious mid-temperature transition and its possible mechanism(s) became the subject of a panel discussion a) to mark the Golden Jubilee of the discovery of piezoelectricity in polyvinylidenefluoride (PVDF) by Heiji Kawai of Kobayashi Institute of Physical Research, Japan, as well as the Centennial of the first recognition of ferroelectricity in piezoelectric Seignette's or Rochelle salt. The panel put forward a new hypothesis that the mid-temperature transition is most likely a result of several interrelated processes that take place within the respective temperature range. The relevant processes include an upper glass transition or relaxation, a relaxation related to conformational disorder, possible imperfect/time-dependent structures formed as a result of thermal processing and secondary crystallization, as well as interface polarization effects at crystalline-amorphous boundaries. The article captures the essence of the panel discussion and the perspectives obtained therefrom to elucidate the complex mid-temperature transition in vinylidenefluoride-based ferro-, pyro- and piezoelectric homo-, co- and ter-polymers.

Plasmon-enhanced photocatalysis provides opportunities for controlling chemical reaction rates, especially when the influence of the light is to enhance or alter charge transfer properties. Semiconductor photocatalysts with an inverse opal or photonic crystal structure not only provide large, open and accessible surface area, they are electrically interconnected as a porous network. This becomes a useful scaffold to dock metallic nanoparticles whose size can be tuned to absorb specific frequencies resonant with their localised surface plasmon resonance. Coupling this with the nature of the metal-semiconductor band structure (where the metal oxide is wide band gap) and exploiting certain properties of photonic crystals, more efficient photocatalysts are possible. We demonstrate semiconducting photonic crystal plasmonic photocatalysts using V2O5 and TiO2 as visible light semiconductor catalysts that showed superior performance to a conventional TiO2 support for hydrogenation of 4-nitrophenol. The approach married the photonic band gap, metal oxide semiconductor bandgap, slow photon effect and localised surface plasmon polaritons to maximum photon absorption to modulate charge transfer and electron density either in the metal nanoparticle, or the conduction band of the semiconductor to give a better photocatalyst. References [1] S. Linic, U. Aslam, C. Boerigter, M. Morabito, Nat. Mater. 14, 567 (2015) [2] S. Linic, P. Christopher, D. B. Ingram, Nat. Mater. 10, 911 (2011) [3] G. Collins, A. Lonergan, D. McNulty, C. Glynn, D. Buckley, C. Hu, and C. O’Dwyer, Adv. Mater. Interfaces. 7, 1901805 (2020). [4] E. Armstrong, C. O’Dwyer, J. Mater. Chem. C 3, 6109 (2015) [5] C. O’Dwyer, Adv. Mater. 28, 5681 (2016) [6] T. Baba, Nat. Photon. 2, 465 (2008) [7] G. Collins, E. Armstrong, D. McNulty, S. O’Hanlon, H. Geaney, C. O’Dwyer, Sci. Technol. Adv. Mater. 17, 563 (2016) [8] A. Lonergan, D. McNulty, C. O’Dwyer, J. Appl. Phys. 124, 095106 (2018) [9] G. Collins, M. Blomker, M. Osaik, J. D. Holmes, M. Bredol, C. O’Dwyer, Chem. Mater. 25, 4312 (2013) [10] J. Liu, H. Zhao, M. Wu, B. Van der Schueren, Y. Li, O. Deparis, J. H. Ye, G. A. Ozin, T. Hasan, B. L. Su, Adv. Mater. 29, 1605349 (2017) [11] S. O’Hanlon, D. McNulty, C. O’Dwyer, J. Electrochem. Soc. 164, D111 (2017) [12] D. McNulty, E. Carroll, C. O’Dwyer, Adv. Energy Mater. 7, 1602291 (2017) Figure 1. V2O5 3D macroporous inverse opal photonic crystal decorated with Au nanoparticles. Figure 1

Black phosphorus (BP) is emerging as a promising candidate for electronic, optical, and energy storage applications. However, its poor ambient stability remains a critical challenge. Evaluation of few-layer liquid-exfoliated BP during ambient exposure using X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy allows its surface chemistry to be investigated. Oxidation of liquid-exfoliated few-layer BP initially occurs through nonbridging oxide species, which convert to bridging oxide species after ambient exposure. We demonstrate the instability of these bridging oxide species, which undergo hydrolysis to form volatile phosphorus oxides and evaporate from the BP surface. FTIR spectroscopy, scanning transmission electron microscopy, and atomic force microscopy were used to confirm the formation of liquid oxides through a continuous oxidation cycle that results in the decomposition of BP. Furthermore, we show that the instability of few-layer BP originates from the formation of bridging oxide species.

Additive manufacturing and 3D printing in particular have the potential to revolutionize existing fabrication processes, where objects with complex structures and shapes can be built with multifunctional material systems. For electrochemical energy storage devices such as batteries and supercapacitors, 3D printing methods allows alternative form factors to be conceived based on the end use application need in mind at the design stage. Additively manufactured energy storage devices require active materials and composites that are printable, and this is influenced by performance requirements and the basic electrochemistry. The interplay between electrochemical response, stability, material type, object complexity and end use application are key to realising 3D printing for electrochemical energy storage. Here, we summarise recent advances and highlight the important role of methods, designs and material selection for energy storage devices made by 3D printing, which is general to the majority of methods in use currently.

Energy Autonomous Wearable Sensors (EAWS) have attracted a large interest due to their potential to provide reliable measurements and continuous bioelectric signals, which help to reduce health risk factors early on, ongoing assessment for disease prevention, and maintaining optimum, lifelong health quality. This review paper presents recent developments and state-of-the-art research related to three critical elements that enable an EAWS. The first element is wearable sensors, which monitor human body physiological signals and activities. Emphasis is given on explaining different types of transduction mechanisms presented, and emerging materials and fabrication techniques. The second element is the flexible and wearable energy storage device to drive low-power electronics and the software needed for automatic detection of unstable physiological parameters. The third is the flexible and stretchable energy harvesting module to recharge batteries for continuous operation of wearable sensors. We conclude by discussing some of the technical challenges in realizing energy-autonomous wearable sensing technologies and possible solutions for overcoming them.

Since the isolation of two-dimensional (2D) phosphorene, black phosphorus (BP) has gained popularity due to its high carrier mobility and tunable bandgap. Poor ambient stability of BP remains a key issue and impedes its use in electronic applications. Here we report a new stabilization strategy based on covalent functionalization of liquid exfoliated few-layer BP using aryl iodonium salts. Arylation of BP using iodonium salts enables covalent modification without inducing oxidation and alters the degradation chemistry of BP by inhibiting bridged oxygen formation through attachment to surface oxygen sites. In comparison, functionalization using aryl diazonium salts results in oxidation and aryl multilayer formation and does not adequately disrupt noncovalent solvent passivation. Aryl functionalization of BP using iodonium salts displays superior ambient stability compared to arylation using diazonium salts associated with greater covalent functionalization as characterized using X-ray photoelectron spectroscopy, scanning transmission electron microscopy, photoluminescence, and attenuated total reflectance infrared spectroscopy.

The nature of the surface roughness of electrolessly etched p-type Si nanowires (NWs) is examined using high resolution transmission electron microscopy and shown to comprise individual silicon nanocrystallites throughout the waviness of the roughness features. As the frequency of roughness features are believed to be sources of surface and boundary scattering, the thermal conductivity below the Casimir limit is still not fully explained. The frequency shift and development of asymmetry in the optical phonon mode in silicon was monitored by Raman scattering measurements as a function of temperature (>1000 K). We assessed the influence of Si NW roughness features on phonon scattering mechanisms including quantum confinement of phonons from roughness nanocrystals, boundary scattering, and optical phonon decay to interacting 3- and 4-phonon processes that may contribute to the cause of significant thermal conductivity suppression in rough Si nanowires. High temperature studies and detailed examination of the substrate of roughness revealed high frequency optical phonon contributions to thermal conductivity suppression.

Plasmonic photocatalysis has facilitated rapid progress in enhancing photocatalytic efficiency under visible light irradiation. Poor visible-light-responsive photocatalytic materials and low photocatalytic efficiency remain major challenges. Plasmonic metal-semiconductor heterostructures where both the metal and semiconductor are photosensitive are promising for light harvesting catalysis, as both components can absorb solar light. Efficiency of photon capture can be further improved by structuring the catalyst as a photonic crystal. Here we report the synthesis of photonic crystal plasmonic photocatalyst materials using Au nanoparticle-functionalized inverse opal (IO) photonic crystals. A catalyst prepared using a visible light responsive semiconductor (V2O5) displayed over an order of magnitude increase in reaction rate under green light excitation ($\lambda$=532 nm) compared to no illumination. The superior performance of Au-V2O5 IO was attributed to spectral overlap of the electronic band gap, localized surface plasmon resonance and incident light source. Comparing the photocatalytic performance of Au-V2O5 IO with a conventional Au-TiO2 IO catalyst, where the semiconductor band gap is in the UV, revealed that optimal photocatalytic activity is observed under different illumination conditions depending on the nature of the semiconductor. For the Au-TiO2 catalyst, despite coupling of the LSPR and excitation source at $\lambda$=532 nm, this was not as effective in enhancing photocatalytic activity compared to carrying out the reaction under broadband visible light, which is attributed to improved photon adsorption in the visible by the presence of a photonic band gap, and exploiting slow light in the photonic crystal to enhance photon absorption to create this synergistic type of photocatalyst., Comment: 19 pages, 8 figures, + Supporting information

New techniques to directly grow metal oxide nanowire networks without the need for initial nanoparticle seed deposition or postsynthesis nanowire casting will bridge the gap between bottom-up formation and top-down processing for many electronic, photonic, energy storage, and conversion technologies. Whether etched top-down, or grown from catalyst nanoparticles bottom-up, nanowire growth relies on heterogeneous material seeds. Converting surface oxide films, ubiquitous in the microelectronics industry, to nanowires and nanowire networks by the incorporation of extra species through interdiffusion can provide an alternative deposition method. It is shown that solution-processed thin films of oxides can be converted and recrystallized into nanowires and networks of nanowires by solid-state interdiffusion of ionic species from a mechanically contacted donor substrate. NaVO3 nanowire networks on smooth Si/SiO2 and granular fluorine-doped tin oxide surfaces can be formed by low-temperature annealing of a Na diffusion species-containing donor glass to a solution-processed V2 O5 thin film, where recrystallization drives nanowire growth according to the crystal habit of the new oxide phase. This technique illustrates a new method for the direct formation of complex metal oxide nanowires on technologically relevant substrates, from smooth semiconductors, to transparent conducting materials and interdigitated device structures.

New types of transparent conducting materials (TCMs) are being sought due to the increase in demand for their use in next generation electronics and photonics. Methods to improve transparency be inferred by controlling porosity (graded refractive index), or from a change in the crystal structure of some materials that are not inherently transparent at visible frequencies. Transparent materials with tunable optical properties are important in conductive and capacitive displays, tandem solar cells, organic PVs and other devices. Transparent conducting oxides (TCO) have been extensively used in various technologically important applications including solar cells, flat panel displays, antireflective coatings, (organic)light emitting diodes and many other uses as advanced optical materials. Nanoporous and nanostructured films, assemblies and arrangements are important from an applied point of view in microelectronics, photonics and optical materials. The ability to minimize reflection, control light output and use contrast and variation of the refractive index to modify photonic characteristics can provide routes to enhanced photonic crystal devices, omnidirectional reflectors, antireflection coatings and broadband absorbing or reflecting materials. Here, we detail how interdiffusion processes can be used to modify the crystallinity and phase of solution processed semiconducting oxides, to dielectric complex oxides on glass as thin films or as oxide nanowire networks. In addition, we demonstrate how electrodeposition of mobile ionic species on TCOs and SiO2/Si can allow this process to happen from a top down process, enabling patterned optically transparent coatings with in-plane semiconductor-dielectric contrast. Last, we show how these processes can allow networks of oxide nanowire to form directly from solution processed oxide thin films on a range of substrate types. Antireflective properties and the onset of broadband transparency for interdiffusion-mediated oxide conversion processes are also shown. References [1] C. M. Eliason and M. D. Shawkey, Opt. Express, 22, A642 (2014). [2] C. Glynn and C. O'Dwyer, Adv. Mater. Interfaces, 4, 1600610 (2017). [3] C. O’Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nature Nanotechology, 4, 239 (2009). [4] J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics, 1, 176 (2007). [5] C. O'Dwyer and C. M. S. Torres, Front. Physics, 1, 18 (2013). [6] C. Glynn, D. Creedon, H. Geaney, J. O'Connell, J. D. Holmes and C. O'Dwyer, ACS Appl. Mater. Interfaces, 6, 2031 (2014). [7] K. K. Banger, Y. Yamashita, K. Mori, R. L. Peterson, T. Leedham, J. Rickard and H. Sirringhaus, Nature Materials, 10, 45 (2011). [8] C. Glynn, D. Creedon, H. Geaney, T. Collins, E. Armstrong, M. A. Morris and C. O'Dwyer, Sci. Rep., 5, 11574 (2015). [9] C. Glynn, D. Aureau, G. Collins, S. O'Hanlon, A. Etcheberry and C. O'Dwyer, Nanoscale, 7, 20227 (2015). [10] C. Glynn, H. Geaney, D. McNulty, J. O'Connell, J. D. Holmes and C. O’Dwyer, J. Vac. Sci. Technol. A, 35, 020602 (2017). [11] C. Glynn, L. Balobaid, D. McNulty and C. O’Dwyer, ECS J. Solid State Sci. Technol., 6 N227 (2017).

Nanocrystalline cobalt molybdate (CoMoO4) nanoflakes were grown directly on carbon fibre cloth (CFC) via a simple hydrothermal method without any template or surfactant. A symmetric supercapacitor was fabricated using CoMoO4 nanoflakes/CFC as both negative and positive electrodes. The device has delivered the maximum specific capacitance of 8.3 F g−1 at a constant current density of 1 A g−1 in organic electrolyte. It offers the reasonable energy (2.6 Wh kg−1) and power density (748.8 W kg−1) as comparable to the carbon based symmetric supercapacitors. As a catalyst for methanol oxidation, the CoMoO4 nanoflakes showed high current density (25 mA cm−2) and low onset potential (0.38 V). The impressive bi-functional electrochemical activity of CoMoO4 on CFC is mainly attributed to its porous microstructure, where reasonable electrical conductivity resulted from binder-free and intimate metal oxide/substrate integration.

Monolayer doping (MLD) involves the functionalization of semiconductor surfaces followed by an annealing step to diffuse the dopant into the substrate. We report an alternative doping method, oxide-MLD, where ultrathin SiO

Monolayer doping (MLD) involves the functionalization of semiconductor surfaces followed by an annealing step to diffuse the dopant into the substrate. We report an alternative doping method, oxide-MLD, where ultrathin SiO2 overlayers are functionalized with phosphonic acids for doping Si. Similar peak carrier concentrations were achieved when compared with hydrosilylated surfaces (∼2 × 1020 atoms/cm3). Oxide-MLD offers several advantages over conventional MLD, such as ease of sample processing, superior ambient stability, and minimal carbon contamination. The incorporation of an oxide layer minimizes carbon contamination by facilitating attachment of carbon-free precursors or by impeding carbon diffusion. The oxide-MLD strategy allows selection of many inexpensive precursors and therefore allows application to both p- and n-doping. The phosphonic acid-functionalized SiO2 surfaces were investigated using X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy, whereas doping was assessed using electrochemical capacitance voltage and Hall measurements.

Oxide phase nanowires are important for applications ranging from optoelectronics to water splitting, but prove difficult to grow in high density with good crystalline quality and phase purity. Heterogeneous catalysts are typically required to nucleate growth. This work demonstrates that dispersions of oxide nanowires can be formed directly from solution processed oxide thin films. We also examine the effect of changes in applied pressure between a solution processed vanadium oxide thin film and a surface-contacted glass coupon on the catalyst-free formation of interconnected sodium vanadate nanowire structures by interdiffusion. Under different applied pressures, meshes of high quality crystalline oxide nanowires formed on the surface, and we examine the nature of phase conversion and nanostructure growth including larger shards composed of multiple conjoined nanowires are also examined. The optical properties of the oxides NWs formed by interdiffusion from oxide thin films show promising properties for application as antireflective coatings across a broadband spectral range. This interdiffusion technique is effective for high quality oxide nanowire growth without catalysts directly from insulating or conducting thin films by direct contact with a source of diffusing species.

Transparent thin films can now be site-selectively patterned and positioned on surface using mask-defined electrodeposition of one oxide and overcoating with a different solution-processed oxide, followed by thermal annealing. Annealing allows an interdiffusion process to create a new oxide that is entirely transparent. A primary electrodeposited oxide can be patterned and the secondary oxide coated over the entire substrate to form high color contrast coplanar thin film tertiary oxide. The authors also detail the phase formation and chemical state of the oxide and how the nature of the electrodeposited layer and the overlayer influence the optical clearing of the patterned oxide film.

Nanostructured surfaces are common in nature and exhibit properties such as antireflectivity (moth eyes), self-cleaning (lotus leaf), iridescent colors (butterfly wings), and water harvesting (desert beetles). We now understand such properties and can mimic some of these natural structures in the laboratory. However, these synthetic structures are limited since they are not easily mass produced over large areas due to the limited scalability of current technologies such as UV-lithography, the high cost of infrastructure, and the difficulty in nonplanar surfaces. Here, we report a solution process based on block copolymer (BCP) self-assembly to fabricate subwavelength structures on large areas of optical and curved surfaces with feature sizes and spacings designed to efficiently scatter visible light. Si nanopillars (SiNPs) with diameters of ∼115 ± 19 nm, periodicity of 180 ± 18 nm, and aspect ratio of 2–15 show a reduction in reflectivity by a factor of 100

The functionalization and subsequent monolayer doping of InGaAs substrates using a tin-containing molecule and a compound containing both silicon and sulfur was investigated. Epitaxial InGaAs layers were grown on semi-insulating InP wafers and functionalized with both sulfur and silicon using mercaptopropyltriethoxysilane and with tin using allyltributylstannane. The functionalized surfaces were characterized using X-ray photoelectron spectroscopy (XPS). The surfaces were capped and subjected to rapid thermal annealing to cause in-diffusion of dopant atoms. Dopant diffusion was monitored using secondary ion mass spectrometry. Raman scattering was utilized to nondestructively determine the presence of dopant atoms, prior to destructive analysis, by comparison to a blank undoped sample. Additionally, due to the As-dominant surface chemistry, the resistance of the functionalized surfaces to oxidation in ambient conditions over periods of 24 h and 1 week was elucidated using XPS by monitoring the As 3d core level for the presence of oxide components.

The Li+ insertion and extraction characteristics at n-type and p-type Si(100) electrodes with different carrier density and doping type are investigated by cyclic voltammetry and constant current measurements. The insertion and extraction potentials are demonstrated to vary with cycling and the occurrence of an activation effect is shown in n-type electrodes where the charge capacity and voltammetric currents are found to be much higher than p-type electrodes. A rate-dependent redox process influenced by the surface region electronic density, which influences the magnitude of cyclic voltammetry current is found at Si(100) surface regions during Li insertion and extraction. At p-type Si(100) surface regions, a thin, uniform film forms at lower currents, while also showing a consistently high (>70%) Coulombic efficiency for Li extraction. The p-type Si(100) surface region does not undergo crack formation after deintercalation and the amorphization was demonstrated using transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and Raman scattering demonstrate that highly doped n-type Si(100) retains Li as a silicide and converts to an amorphous phase as a two-step phase conversion process. The findings show the succinct dependence of Li insertion and extraction processes for uniformly doped Si(100) single crystals and how the doping type and its effect on the semiconductor-solution interface dominate Li insertion and extraction, composition, crystallinity changes and charge capacity.

The understanding of the mechanisms of macropore formation in p-type Si with respect to modulation of the pore diameter is still in its infancy. In the present work, macropores with significantly modulated diameters have been produced electrochemically in p-type Si. The effect of the current density and the amount of surfactant in the etching solution are shown to influence the modulation in pore diameter and morphology. Data obtained during the etching process by in situ FFT impedance spectroscopy correlate the pore diameter variation with certain time constants found in the kinetics of the dissolution process. Raman scattering and electron microscopy confirm the mesoscopic structure and roughening of the pore walls. Spectroscopic and microscopic methods confirm that the pore wall morphology is correlated with the conditions of pore modulation.

Porous semiconductors structured top-down by electrochemical means, and from bottom-up growth of arrays and arrangements of nanoscale structures, are shown to be amenable to a range of useful thermal, optical, electrical and electrochemical properties. This paper summarises recent investigations of the electrochemical, electrical, optical, thermal and structural properties of porous semiconductors such as Si, In2O3, SnO2 and ITO, and dispersions, arrays and arrangements of nanoscale structures of each of these materials. We summarize the property-inspired application of such structurally engineered arrangements and morphologies of these materials for antireflection coatings, broadband absorbers, transparent contacts to LEDs that improve transmission, electrical contact and external quantum efficiency. Additionally the possibility of thermoelectric performance through structure-mediated variation in thermal resistance and phonon scattering without a p-n junction is shown through phonon engineering in roughened nanowires. Lastly, we show that bulk crystals and nanowires of p- and n-type doped Si are promising for use as anodes in Li-ion batteries.

With advances in nanolithography and dry etching, top-down methods of nanostructuring have become a widely used tool for improving the efficiency of optoelectronics. These nano dimensions can offer various benefits to the device performance in terms of light extraction and efficiency, but often at the expense of emission color quality. Broadening of the target emission peak and unwanted yellow luminescence are characteristic defect-related effects due to the ion beam etching damage, particularly for III–N based materials. In this article we focus on GaN based nanorods, showing that through thermal annealing the surface roughness and deformities of the crystal structure can be “self-healed”. Correlative electron microscopy and atomic force microscopy show the change from spherical nanorods to faceted hexagonal structures, revealing the temperature-dependent surface morphology faceting evolution. The faceted nanorods were shown to be strain- and defect-free by cathodoluminescence hyperspectral imaging, micro-Raman, and transmission electron microscopy (TEM). In-situ TEM thermal annealing experiments allowed for real time observation of dislocation movements and surface restructuring observed in ex-situ annealing TEM sampling. This thermal annealing investigation gives new insight into the redistribution path of GaN material and dislocation movement post growth, allowing for improved understanding and in turn advances in optoelectronic device processing of compound semiconductors.

The extensive benefits of the new generation of nanostructured surfaces is very promising for enhancing light absorption efficiency in photonic devices. However, the low throughput and the high cost of available technologies such as lithography for fabrication of nanostructures has proved to be a difficult technological hurdle for advanced manufacturing. In this research we present a solution based process based on high molecular weight block copolymer (BCP) nanolithography for fabrication of periodic structures on large areas of optical surfaces. Block copolymer self- assembly technique is a solution based process that offers an alternative route to produce highly ordered photonic crystal structures. BCPs forms nanodomains (5-10 nm) due to microphase separation of incompatible constitute blocks. The size and shape of the nanostructure can be customised by the molecular weight and volume fraction of the polymer blocks. However, the major challenge is BCPs do not phase separate into their signature ordered pattern above 100 nm, whereas for nanofeatures to be used as photonic gratings, they must be greater than 100 nm (typically ¼ wavelength). This is due to significant kinetic penalty arising from higher entanglement in high molecular weight polymers. In this work we present the results of exploiting commercially available block copolymers to phase separate into periodic domains greater than 100 nm. The process do not include any blending with homopolymers, or adding colloidal particles, and to our best knowledge, has not been yet achieved or reported in the literatures. We have pattern transferred the BCP mask to silicon substrate by reactive ion etch (ICP-RIE). The final product is black silicon, consists of hexagonally packed conic Si nanofeatures with diameter above 100nm and periodicity of 200 nm. The height of the Si nanopillars varies from 100 nm to 1 micron. We have characterized the angle dependent optical reflectance properties of the black silicon. The antireflective properties of the Si nanofeatures were probed in the 400 nm – 2500 nm wavelength range and compared to an Au reflectance standard. As the subwavelength grating is made from the same material as the substrate (Si), the index matching at the substrate interfaces has lead to highly improved antireflecting performance. The reflectivity of the silicon substrate shows one order of magnitude reduction in a broad range of wavelength from NIR to UV-visible, below 1%. The simplicity of the solution based large block copolymer nanolithography and the capability of integration to existing fabrication process, makes this novel technique a very attractive alternative for manufacturing photonic crystals on large, arbitrary shaped and curved objects such as photovoltaics and IR camera lenses for medical imaging.

We have shown that SiNWs formed on (100) Si substrates by metal-assisted chemical etching can exhibit different Raman scattering processes that are dependent on the orientation of examined NWs to the incident excitation light. The SiNWs retain the single crystal orientation and doping from the original bulk substrate and form as rough and mesoporous NWs with a SiOx shell surrounding the NW. The Raman scattering spectra of vertical and horizontally lying SiNWs showed quantum confined phonon scattering processes from narrow and roughened NWs, whose spectral resolution was increased by orienting NW horizontal to the beam to maximize probe cross-section. SiOx contributions were not evident and specific substrate Raman modes were suppressed for horizontal NWs. Beam induced heating to 425 K showed pronounced red-shifting and asymmetry of the TO, 2TO and 2TA phonon modes consistent with phonon quantum confinement effects not observable when the NW were parallel to incident excitation.

New types of transparent conducting materials (TCMs) are being sought due to the increase in demand for their use in next generation electronics and photonics. Methods to improve transparency be inferred by controlling porosity (graded refractive index), or from a change in the crystal structure of some materials that are not inherently transparent at visible frequencies. Transparent materials with tunable optical properties are important in conductive and capacitive displays, tandem solar cells, organic PVs and other devices. Transparent conducting oxides (TCO) have been extensively used in various technologically important applications including solar cells, flat panel displays, antireflective coatings, (organic)light emitting diodes and many other uses as advanced optical materials. Nanoporous and nanostructured films, assemblies and arrangements are important from an applied point of view in microelectronics, photonics and optical materials. The ability to minimize reflection, control light output and use contrast and variation of the refractive index to modify photonic characteristics can provide routes to enhanced photonic crystal devices, omnidirectional reflectors, antireflection coatings and broadband absorbing or reflecting materials. Here, we detail how interdiffusion processes can be used to modify the crystallinity and phase of solution processed semiconducting oxides, to dielectric complex oxides on glass as thin films or as oxide nanowire networks. In addition, we demonstrate how electrodeposition of mobile ionic species on TCOs and SiO2/Si can allow this process to happen from a top down process, enabling patterned optically transparent coatings with in-plane semiconductor-dielectric contrast. Last, we show how these processes can allow networks of oxide nanowire to form directly from solution processed oxide thin films on a range of substrate types. Antireflective properties and the onset of broadband transparency for interdiffusion-mediated oxide conversion processes are also shown. References M. Eliason and M. D. Shawkey, Opt. Express, 22, A642 (2014). C. Glynn and C. O'Dwyer, Adv. Mater. Interfaces, 4, 1600610 (2017). C. O’Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nature Nanotechology, 4, 239 (2009). Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics, 1, 176 (2007). C. O'Dwyer and C. M. S. Torres, Front. Physics, 1, 18 (2013). C. Glynn, D. Creedon, H. Geaney, J. O'Connell, J. D. Holmes and C. O'Dwyer, ACS Appl. Mater. Interfaces, 6, 2031 (2014). K. Banger, Y. Yamashita, K. Mori, R. L. Peterson, T. Leedham, J. Rickard and H. Sirringhaus, Nature Materials, 10, 45 (2011). C. Glynn, D. Creedon, H. Geaney, T. Collins, E. Armstrong, M. A. Morris and C. O'Dwyer, Sci. Rep., 5, 11574 (2015). C. Glynn, D. Aureau, G. Collins, S. O'Hanlon, A. Etcheberry and C. O'Dwyer, Nanoscale, 7, 20227 (2015). C. Glynn, H. Geaney, D. McNulty, J. O'Connell, J. D. Holmes and C. O’Dwyer, J. Vac. Sci. Technol. A, 35, 020602 (2017). C. Glynn, L. Balobaid, D. McNulty and C. O’Dwyer, ECS J. Solid State Sci. Technol., 6 (2017).

Devices composed of transparent materials, particularly those utilizing metal oxides, are of significant interest due to increased demand from industry for higher fidelity transparent thin film transistors, photovoltaics and a myriad of other optoelectronic devices and optics that require more cost-effective and simplified processing techniques for functional oxides and coatings. Here, we report a facile solution processed technique for the formation of a transparent thin film through an inter-diffusion process involving substrate dopant species at a range of low annealing temperatures compatible with processing conditions required by many state-of-the-art devices. The inter-diffusion process facilitates the movement of Si, Na and O species from the substrate into the as-deposited vanadium oxide thin film forming a composite fully transparent V0.0352O0.547Si0.4078Na0.01. Thin film X-ray diffraction and Raman scattering spectroscopy show the crystalline component of the structure to be [small alpha]-NaVO3 within a glassy matrix. This optical coating exhibits high broadband transparency, exceeding 90-97% absolute transmission across the UV-to-NIR spectral range, while having low roughness and free of surface defects and pinholes. The production of transparent films for advanced optoelectronic devices, optical coatings, and low- or high-k oxides is important for planar or complex shaped optics or surfaces. It provides opportunities for doping metal oxides to ternary, quaternary or other mixed metal oxides on glass, encapsulants or other substrates that facilitate diffusional movement of dopant species.

Both transparent oxides and transparent conductive oxides are of particular research interest for future applications in flexible, optically transparent thin film transistors and luminescent devices. We report the formation of a transparent oxide material based on the interdiffusion of Na-O and Si-O species with dip-coated V2O5 thin films on a borosilicate glass substrate. The deposition process used a facile solution processed dip-coating technique in the high-rate draining regime. Liquid precursors of vanadium alkoxide and alkoxide-polyethylene glycol mixtures were used for thin film deposition. We examine the effect of annealing condition on the phase conversion process, morphology and optical transmittance due to the conversion of the V2O5 films to completely transparent ternary mixed metal oxide thin films. The work also examines the role of polymer-assisted deposition on the development of the V-O-Na-Si transparent thin films during different annealing conditions. Polymer-assisted V2O5 thin films on glass are shown to convert to optically clear thin films during annealing, with a transparency >95% across the visible spectrum, and a blue-shift of the absorption edge to maintain >90% transparency at 380 nm.

Solution processed metal oxide thin films are important for modern optoelectronic devices ranging from thin film transistors to photovoltaics and for functional optical coatings. Solution processed techniques such as dip-coating, allow thin films to be rapidly deposited over a large range of surfaces including curved, flexible or plastic substrates without extensive processing of comparative vapour or physical deposition methods. To increase the effectiveness and versatility of dip-coated thin films, alterations to commonly used precursors can be made that facilitate controlled thin film deposition. The effects of polymer assisted deposition and changes in solvent-alkoxide dilution on the morphology, structure, optoelectronic properties and crystallinity of vanadium pentoxide thin films was studied using a dip-coating method using a substrate withdrawal speed within the fast-rate draining regime. The formation of sub-100 nm thin films could be achieved rapidly from dilute alkoxide based precursor solutions with high optical transmission in the visible, linked to the phase and film structure. The effects of the polymer addition was shown to change the crystallized vanadium pentoxide thin films from a granular surface structure to a polycrystalline structure composed of a high density of smaller in-plane grains, resulting in a uniform surface morphology with lower thickness and roughness.

Embedding 2D layered materials into polymers can form a paint with many useful applications. In bulk form the thermoelectric material bismuth telluride (Bi2Te3) has a high figure of merit (ZT) at room temperature. When bulk Bi2Te3 is exfoliated to smaller dimensions, such as its 2D form (nanosheets), its thermoelectric effects are improved by reduction in thermal conductivity due to phonon confinement and scattering, thus increasing the ZT. The difficulty involved in incorporating nanosheets into energy harvesting systems motivated the search for a form of Bi2Te3 that retains the high ZT apparent at the nanoscale with the capability of being deposited or painted onto device infrastructures. This work highlights a method whereby solvent exfoliation of Bi2Te3 into solution-dispersible 2D nanosheets can form a practical thin film that can be distributed across a surface. Optical transmission measurements quantify the relationship between efficient and stable exfoliation and the reduction in optical density. Optimized exfoliated suspension are also shown to form smooth, uniform blends when mixed with poly ethylene glycol and other polymers to produce a paintable Bi2Te3film that can be applied to surfaces using an innovative painting technique. Atomic force microscopy, transmission electron spectroscopy, Raman spectroscopy and scanning electron spectroscopy are used to examine the structure of the 2D nanosheets and the highly reproducible Bi2Te3thin films. Electrical transport studies show that the films have conductive pathways over a range of surfaces and various structural formations, linking the conductivity to the percolating conduction through the nanosheet ensemble. The combination of the facile preparation method and the scope for diverse surface coating as a cohesive and conductive thin film offers methods for integration with heat producing devices for energy harvesting applications. Direct Seebeck coefficient and thermal diffusivity measurements examine the role of the pain conductivity on its thermoelectric response. Separately, MoS2 nanosheets are also demonstrated by solvent exfoliation of uniquely formed hexagonal single crystals. These crystals are formed under high pressure from layered MoS2 and this talk demonstrates how multi-micron scale dimension flakes of 2D and few-layer hexagonal MoS2can be formed from compressed soluble solutions of the 2D and layered material. Finally, we demonstrate a method whereby 2D layers of V2O5 can be turbostratically assembled using organic-inorganic interactions with alkylamines under hydrothermal conditions, to scroll into very high quality V2O5 nanotubes. V2O5 layered materials intercalated with 1D Pt-Pt metal complexes exhibit high directional conductivity. We also show that the method can be used to make nanotubes of 2D and layered materials, and how MoS2 sheets can also be rolled into nanotubular form.

High quality 2D and 3D inverse opals and hollow sphere arrays of vanadium oxide are grown on conductive substrates from colloidal polymer sphere templates formed by electrophoretic deposition or surfactant-assisted dip-coating. Inverse opals (IOs) are formed using variants of solution drop-casting, N2-gun assisted infiltration and high-rate (200 mm min−1) iterative dip-coating methods. Through Raman scattering, transmission electron microscopy and optical diffraction, we show how the oxide phase, crystallinity and structure are inter-related and controlled. Opal template removal steps are demonstrated to determine the morphology, crystallinity and phase of the resulting 2D and 3D IO structures. The ability to form high quality 2D IOs is also demonstrated using UV Ozone removal of PMMA spheres. Rapid hydrolysis of the alkoxide precursor allows the formation of 2D arrays of crystalline hollow spheres of V2O5 by utilizing over-filling during iterative dip-coating. The methods and crystallinity control allow 2D and 3D hierarchically structured templates and inverse opal vanadium oxides directly on conductive surfaces. This can be extended to a wide range of other functional porous materials for energy storage and batteries, electrocatalysis, sensing, solar cell materials and diffractive optical coatings.

Routes towards the formation of inverted opal vanadium oxide electrodes are presented. Different methods of template infiltration using an IPA diluted solution of vanadium triisopropoxide are discussed and the resulting morphologies investigated using scanning electron microscopy. The effect of different heat treatments and method of sphere removal on morphology and structure is also considered. Solvent template removal retains thehydrolysed amorphous V2O5 structure. Raman scattering spectroscopy identifies the degree of V2O5 crystallinity that results from the different heat treatments. For a thicker inverted opal formed using a polystyrene template as opposed to a monolayer PMMA template, under similar conditions a different phase of vanadium oxide is observed evident by variations inRaman scattering response.

This report investigates the influence of electrolyte selection and the addition of Pd nanoparticle catalysts on the morphology of discharge products for Li-O2 battery cathodes. Super P carbon cathodes (on stainless steel current collectors) were subjected to single discharges at various applied currents (50 µA, 100 µA, 250 µA) using either a sulfolane/LiTFSI or TEGDME/LITFSI electrolyte. The morphologies of the discharge product were noted to be different for each electrolyte while there was also a clear variation with respect to applied current. Finally, the impact of adding 25% (by weight) Pd nanoparticle catalysts to the cathodes was investigated. The results obtained show clearly that the nature of discharge products for Li-O2 battery cathodes are strongly dependent on applied current, electrolyte choice and the addition of a catalyst material.

Using an alkoxide-based precursor, a strategy for producing highly uniform thin films and multilayers of V2O5 is demonstrated using dip coating. Defect-free and smooth films of V2O5 on different surfaces can be deposited from liquid precursors. We show how pinholes are formed due to heterogeneous nucleation during hydrolysis as the precursor forms a nanofluid. Using knowledge of instability formation often found in composite nanofluid films and the influence of cluster formation on the stability of these films, we show how polymer-precursor mixtures provide optimum uniformity and very low surface roughness in amorphous V2O5 and also orthorhombic V2O5 after crystallization by heating. Pinhole and roughness instability formation during the liquid stage of the nanofluid on gold and ITO substrates is suppressed giving a uniform coating. Practically, understanding evolution pathways that involve dewetting processes, nucleation, decomposition, or hydrolysis in complex nanofluids provides a route for improved uniformity of thin films. The method could be extended to improve the consistency in sequential or iterative multilayer deposits of a range of liquid precursors for functional materials and coatings.

Electroactive hybrid and layered oxides and related materials where the inorganic phase is the host, offering the conductivity characteristics of semiconductors, have been used in thin film transistors and related electronic devices where the host–guest interaction offered conductivity with improved processability. We describe the synthesis and characterization of a nanocomposite that shows large conductivity anisotropy when deposited as a thin film. We prepared the material by inserting quasi 1-dimensional potassium tetracyanoplatinate metal complexes with insulating electrical properties in between stacked nanosheets of vanadium oxide xerogels. Detailed structural and compositional analysis using transmission electron microscopy and X-ray photoelectron spectroscopy confirms that the hybrid material forms from a topotactic reaction and the framework of the layered host oxide structure is maintained. The hybrid film demonstrates a ∼1000-fold conductivity change between transport parallel and perpendicular to the film at room temperature. Temperature dependent transport measurements confirm Ohmic conduction perpendicular to the stack and small polaron hopping conduction parallel to the layering direction of the film. The conductivity anisotropy and simple synthesis demonstrate that nanostructured layered hybrids can provide alternative materials for thin film complementary logic and resistive memory.

peer-reviewed By using Si(100) with different dopant type (n(++)-type (As) or p-type (B)), we show how metal-assisted chemically etched (MACE) nanowires (NWs) can form with rough outer surfaces around a solid NW core for p-type NWs, and a unique, defined mesoporous structure for highly doped n-type NWs. We used high resolution electron microscopy techniques to define the characteristic roughening and mesoporous structure within the NWs and how such structures can form due to a judicious choice of carrier concentration and dopant type. The n-type NWs have a mesoporosity that is defined by equidistant pores in all directions, and the inter-pore distance is correlated to the effective depletion region width at the reduction potential of the catalyst at the silicon surface in a HF electrolyte. Clumping in n-type MACE Si NWs is also shown to be characteristic of mesoporous NWs when etched as high density NW layers, due to low rigidity (high porosity). Electrical transport investigations show that the etched nanowires exhibit tunable conductance changes, where the largest resistance increase is found for highly mesoporous n-type Si NWs, in spite of their very high electronic carrier concentration. This understanding can be adapted to any low-dimensional semiconducting system capable of selective etching through electroless, and possibly electrochemical, means. The process points to a method of multiscale nanostructuring NWs, from surface roughening of NWs with controllable lengths to defined mesoporosity formation, and may be applicable to applications where high surface area, electrical connectivity, tunable surface structure, and internal porosity are required. (C) 2013 AIP Publishing LLC. PUBLISHED peer-reviewed

A comprehensive review of recent advances in solution processing and growth of metal-oxide thin films for electronic and photonic devices is presented, with specific focus on precise solution-based technological coatings for electronics and optics, and new concepts for oxide material growth for electrochemical, catalytic, energy storage and conversion systems, information technology, semiconductor device processing and related devices. Throughout, the nature of the soluble precursors solutions and their relationship to film formation process by various solution coating techniques are collated and compared, highlighting advantages in precursor design for creating complex oxides for devices. Because of the versatility of solution-processable oxides and functional material coating, it is important to capture the advances made in oxide deposition for plastic electronics, see-through and wearable devices, and high-fidelity thin film transistors on curved or flexible displays. Solution processing, even for oxides, allows control over composition, thickness, optical constants, porosity, doping, tunable optical absorbance/transmission, band structure engineering, 3D-substrate coating, complex composite oxide formation and multi-layered oxide systems that are more difficult to achieve using chemical vapor deposition (CVD) or atomic layer deposition (ALD) processes. We also discuss limitations of solution processing for some technologies and comment on the future of solution-based processing of metal-oxide materials for electronics, photonics and other technologies.

Many modern technologies are based on materials that are deposited on special underlying materials. Optical coatings can prevent tarnishing, give anti-reflection benefits, and in some cases filter out harmful UV rays. In consumer devices, many modern optoelectronic devices that make up a vast majority of electronic products such as active displays, touch screens etc. are based thin film transistors and transparent materials, as are parts of solar cells, smart windows, antireflection coatings for a range of devices and applications, anti-fingerprint and antifogging glass, among many other modern uses of see-through materials and coatings with well-defined characteristics in visible light. While the science and technology of controlling materials into a whole host of electronics and photonic or optical devices has advanced considerably in the last decade, industry still requires all this to be done without using critical raw materials, expensive coating methods that are often very slow, and to do so at much lower temperatures for coating on to curved or flexible displays or materials – all without sacrificing quality that current methods provide. Here, we report a facile solution processed technique for the formation of a transparent thin film through an inter-diffusion process involving substrate dopant species at a range of low annealing temperatures compatible with processing conditions required by many state-of-the-art devices. The inter-diffusion process facilitates the movement of Si, Na and O species from the substrate into the as-deposited vanadium oxide thin film forming a composite fully transparent V0.0352O0.547Si0.4078Na0.01. Thin film X-ray diffraction and Raman scattering spectroscopy show the crystalline component of the structure to be α-NaVO3 within a glassy matrix. This optical coating exhibits high broadband transparency, exceeding 90-97% absolute transmission across the UV-to-NIR spectral range, while having low roughness and free of surface defects and pinholes. The production of transparent films for advanced optoelectronic devices, optical coatings, and low- or high-k oxides is important for planar or complex shaped optics or surfaces. It provides opportunities for doping metal oxides to new ternary, quaternary or other mixed metal oxides on glass, encapsulants or other substrates that facilitate diffusional movement of dopant species. References (1) C. Glynn, D. Creedon, H. Geaney, T. Collins, E. Armstrong, M. A. Morris and C. O'Dwyer, Sci. Rep., 5, 11574 (2015). (2) C. Glynn, D. Aureau, G. Collins, S. O'Hanlon, A. Etcheberry and C. O'Dwyer, Nanoscale, 7, 20227 (2015). (3) S. O'Hanlon, C. Glynn and C. O'Dwyer, ECS J. Solid State Sci. Technol., 5, R3100 (2016). (4) K. K. Banger, Y. Yamashita, K. Mori, R. L. Peterson, T. Leedham, J. Rickard and H. Sirringhaus, Nat. Mater., 2011, 10, 45-50. (5) K. Ellmer, Nat. Photon, 2012, 6, 809-817. (6) C. G. Granqvist, Thin Solid Films, 2014, 564, 1-38. (7) H. Dotan, O. Kfir, E. Sharlin, O. Blank, M. Gross, I. Dumchin, G. Ankonina and A. Rothschild, Nat. Mater., 2013, 12, 158-164. Figure 1

The electronics industry is beginning to show interest in 2D molybdenum disulfide (2D‐MoS2) as a potential device material due to its low band gap and high mobility. However, current methods for its synthesis are not “fab” friendly and require harsh environments and processes. Here, a novel method to prepare MoS2 nanowire arrays and layered structures via self‐assembly of a block copolymer system is reported. Well‐controlled films of microphase separated line‐space nanopatterns have been achieved by solvent annealing process. The self‐assembled films are used as “templates” for the generation of nonstoichometric molybdenum oxide by in situ inclusion technique following UV/Ozone treatment. Well‐ordered array of MoS2 and a layered structure are then prepared by chemical vapor deposition using sulfur powder at lower temperature. The surface morphology, crystal structure, and phases are examined by different microscopic and spectroscopic techniques. This strategy can be extended to several other 2D materials systems and open the pathway toward better optoelectronic and nanoelectromechanical systems.

Si nanowires (NWs) are shown to develop internal mesoporosity during metal assisted chemical etching from Si wafers. The onset of internal porosity in n+-Si(100) compared to p-Si(100) is examined through a systematic investigation of etching parameters (etching time, AgNO3 concentration, HF % and temperature). Electron microscopy and Raman scattering show that specific etching conditions reduce the size of the internal Si nanocrystallites in the internal mesoporous structure to 3–5 nm. Mesoporous NWs are found to have diameters as large as 500 nm, compared to ~100 nm for p-NWs that develop surface roughness. Etching of Si (100) wafers results in (100)-oriented NWs forming a three-fold symmetrical surface texture, without internal NW mesoporosity. The vertical etching rate is shown to depend on carrier concentration and degree of internal mesoporosity formation. Raman scattering of the transverse optical phonon and photoluminescence measurements confirm quantum size effects, phonon scattering and visible intense red light emission between 685 and 720 nm in internally mesoporous NWs associated with the etching conditions. Laser power heating of NWs confirms phonon confinement and scattering, which is demonstrated to be a function of the internal mesoporosity development. We also demonstrate the limitation of mesoporosity formation in n+-Si NWs and development of porosity within p-Si NWs by controlling the etching conditions. Lastly, the data confirm that phonon confinement and scattering often reported for Si NWs is due to surface-bound and internal nanostructure, rather than simply a diameter reduction in NW materials.

Current lithium-ion battery anode research involves significant investigations of semiconducting materials, particularly Si as its theoretical specific capacity is >4000 mAh/g1. Previous theoretical studies showed that porous Si with a large pore size and high porosity can maintain its structure after Li ion induced alloying and swelling. Metal-assisted chemical (MAC) etching is shown here to form internally mesoporous nanowires in the form of a layer, etched from highly doped Si2-4. Some porous materials are well known to exhibit pseudocapacitive behaviour in aqueous electrolytes5,6. Maintaining the structure without stress-induced cracked caused by volumetric changes in material is crucial in achieving a high capacity and long cycle retention. Almost all investigations of nanoscale Si involve their deposition onto a metallic current collector electrode within the battery cell. Here, we demonstrate that pseudocapacitive behaviour can be harnessed when Si nanowires are etched to maximum mesoporosity, forming an electrically dead layer on silicon current collector electrodes. This limits insertion or alloying processes to form Li-Si phases7and charge is stored within the electric double layer, even in Li-ion containing electrolytes. Measurements using cyclic and linear voltammetry supported by Raman scattering spectroscopy and electron microscopy confirm surface charge storage mechanisms; pseudocapacitance is not observed when the same nanowires are used on stainless steel current collectors. In such cases, the rate of lithiation is shown to be related to the degree of porosity and the net surface electronic density of the porous silicon in accumulation mode during charging. References C. K. Chan, H. Peng, G. Liu, K. McIlwrath, X. F. Zhang, R. A. Huggins and Y. Cui, Nat. Nanotechnol. 3, 31 (2008). W. McSweeney, O. Lotty, N. Mogili, C. Glynn, H. Geaney, D. Tanner, J. Holmes and C. O'Dwyer, J. Appl. Phys. 114,034309 (2013). A. I. Hochbaum, D. Gargas, Y. J. Hwang, P. Yang, Nano Lett. 9, 3550 (2009). W. McSweeney, O. Lotty, J. D. Holmes and C. O'Dwyer, ECS Trans., 35, 25 (2011). P. Simon and Y. Gogotsi, Nat. Mater. 7, 845 (2008). T. Brezesinski, J. Wang, S. H. Tolbert and B. Dunn, Nat. Mater. 9, 146 (2010). W. McSweeney, O. Lotty, C. Glynn, H. Geaney, J. D. Holmes and C. O'Dwyer, Electrochim. Acta, 135, 356 (2014).

New types of transparent conducting materials (TCMs) are being sought due to the increase in demand for their use in next generation electronics and photovoltaics. Methods to improve transparency be inferred by controlling porosity (graded refractive index), or from a change in the crystal structure of some materials that are not inherently transparent at visible frequencies. Transparent materials with tunable optical properties are important in conductive and capacitive displays, tandem solar cells, organic PVs and other devices. In thin film oxide deposition, where non-uniformities and porosity are not ideal, diffusion from glass substrates into oxide thin films during thermal treatment has previously been considered detrimental and was suppressed using diffusion barriers such as thick coatings of SiO2. In this work, we show how the transparency and conductivity of a dip-coated thin film of vanadium oxide can be markedly improved by substrate diffusion during thermal treatment, resulting in a completely transparent thin film of vanadium oxide-based material with an order of magnitude increase in electrical conductivity. The phase change and stoichiometry variation during thermal annealing of the vanadium oxide dip-coated from liquid precursors is elucidated using X-Ray photoelectron spectroscopy (XPS) and Raman scattering spectroscopy. Angle-resolved transmission spectra correlated the transparency to the changes in optical properties of the thin films and electron microscopy confirms no formal structural change contributes to the change in transparency. Hall probe measurements demonstrate improved conductivity with transparency due to diffusion of cations from the substrate into the host material lattice. References: C. M. Eliason and M. D. Shawkey, Opt. Express, 22, A642 (2014). C. O’Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nature Nanotechology, 4, 239 (2009). J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics, 1, 176 (2007). C. O'Dwyer and C. M. S. Torres, Front. Physics, 1, 18 (2013). C. Glynn, D. Creedon, H. Geaney, J. O'Connell, J. D. Holmes and C. O'Dwyer, ACS Appl. Mater. Interfaces, 6, 2031 (2014). K. K. Banger, Y. Yamashita, K. Mori, R. L. Peterson, T. Leedham, J. Rickard and H. Sirringhaus, Nature Materials, 10, 45 (2011). J. Mannhart and D. G. Schlom, Science, 327, 1607 (2010). F. Nicholas, M. P. Sean, W. H. Mark and S. S. N. Bharadwaja, Journal of Physics D: Applied Physics, 42, 055408 (2009). T. Manning, I. Parkin, Polyhedron, 23, 3087 (2004).

Silicon nanostructures and methods to grow them and influence their structure and morphology has recently been demonstrated to offering a useful strategy to control thermal conductivity and light-matter interactions. The transport and scattering of phonons in Si has demonstrated effective thermoelectric performance largely due to effects caused by surface roughening and nanoscale irregularities in the crystal structure that contribute to diffuse boundary scattering mechanisms. When confinement effects are introduced in crystalline materials the electron and phonon transport can be significantly due to three discrete effects: increased boundary scattering, changes in phonon dispersion, and quantization of phonon transport. Using both room-temperature and in-situ thermal Raman scattering spectroscopy the transport of phonons within Si and its nanostructures can be probed quickly and with little sample preparation. Both ambient and high temperature characteristics of the Si are examined and phonon transport changes between the b-Si and the SiNWs can be linked to scattering effects due to the different morphologies possible using metal-assisted chemical etching to form NWs with tunable porosity and surface roughness. This work demonstrates that by increasing the number of available scattering sites in nanostructured Si within the structure (not just boundary scattering at rough surfaces), the role of four phonon processes on the phonon transport within Si can be optimised. This study is important for providing information on the phonon transport within Si and its nanostructures allowing morphologies that affect phonon transport to be exploited for engineering the thermoelectric properties of future Si devices. References J. Lim, K. Hippalgaonkar, S. C. Andrews, A. Majumdar, P. Yang, Nano Letters, 12, 2475 (2012). J. Tang, H.-T. Wang, D. H. Lee, M. Fardy, Z. Huo, T. P. Russell, P. Yang, Nano Letters, 10, 4279 (2010). A. I. Hochbaum, R. Chen, R.D. Delgado, W. Liang, E. C. Garnett, M. Najarian, A. Majumdar, P. Yang, Nature, 451, 163 (2008). A. I. Boukai, Y. Bunimovich, J. Tahir-Kheli, J. K. Yu, W. A. Goddard, J. R. Heath, Nature, 451, 168 (2008). K. Q. Peng, J. J. Hu, Y. J. Yan, Y. Wu, H. Fang, Y. Xu, S. T. Lee, J. Zhu, Advanced Functional Materials, 16, 387 (2005).

Sub-20 nm diameter Ge nanowires with narrow size distributions were grown from Ag nanoparticle seeds in a supercritical fluid (SCF) growth process. The mean Ge nanowire diameter and size distribution was shown to be dependent upon Ag nanoparticle coalescence, using both spin-coating and a block copolymer (BCP) templating method for particle deposition. The introduction of a metal assisted etching (MAE) processing step in order to "sink" the Ag seeds into the growth substrate, prior to nanowire growth, was shown to dramatically decrease the mean nanowire diameter from 27.7 to 14.4 nm and to narrow the diameter distributions from 22.2 to 6.8 nm. Hence, our BCP-MAE approach is a viable route for controlling the diameters of semiconductor nanowires whilst also ensuring a narrow size distribution. The MAE step in the process was found to have no detrimental effect on the length or crystalline quality of the Ge nanowires synthesised.

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Embedding 2D layered materials into polymers and other materials as composites has resulted in the development of ultrasensitive pressure sensors, tunable conductive stretchable polymers, and thermoelectric coatings. As a wettable paint or ink, many 2D materials may be penciled, printed, or coated onto a range of surfaces for a variety of applications. However, the intrinsic conductive properties of painted coatings using 2D and layered materials are not completely understood, and conductive polymer additives may mask underlying properties such as directional conductivity. We report a process for making a paint from solvent-exfoliated Bi2Te3 into solution-dispersible 2D and few-layer (multiple quintuple) nanosheet inks, that form smooth, uniform paint blends at several concentrations of Bi2Te3. The individual solvent-exfoliated nanosheets are edge-coated by (poly)ethylene glycol to produce a paint, stable over extended period in solution. Electrical transport is found to be sensitive to aspect ratio, and conduction along the painting direction is suppressed for longer strips so long as the aspect ratio is high (4-10× or more), but for short and wide paint strips (aspect ratio ≤1), conductance is improved by a factor of 3×. Square 2D paint regions show no clear directional preference for conductance at room temperature but are markedly affected by higher temperatures. Conductivity along a preferential conduction pathway through the nanosheet ensemble is modulated by 2D nanosheet stacking along the direction of paint application for a given aspect ratio. This paint and insights into geometrical 2D composite conduction may have implications for conductive composites, thermoelectrics, and writable circuits using 2D material paints or inks. Fil: Carroll, Elaine. University College Cork; Irlanda Fil: Buckley, Darragh. University College Cork; Irlanda Fil: Mogili V., Vishnu N.. Centro Nacional de Pesquisa em Energia e Materiais. Brazilian Nanotechnology National Laboratory; Brasil Fil: McNulty, David. University College Cork; Irlanda Fil: Moreno, Mario Sergio Jesus. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Glynn, Colm. University College Cork; Irlanda Fil: Collins, Gillian. University College Cork; Irlanda Fil: Holmes, Justin D.. University College Cork; Irlanda. Tyndall National Institute; Irlanda. Trinity College Dublin; Irlanda Fil: Razeeb, Kafil M.. Tyndall National Institute; Irlanda Fil: O'Dwyer, Colm. University College Cork; Irlanda. Tyndall National Institute; Irlanda