Projection of holograms from photorefractive OASLMs

Liquid crystals doped with fullerenes and carbon nanotubes (CNTs) act as good optical nonlinear materials. We have used these materials to build optically-addressed spatial light modulators (OASLMs). The devices comprise a single layer of doped liquid crystal acting as an active layer. Undoped LC devices with surfaces coated with fullerenes are also studied. Such OASLMs allow recording of phase holograms, and we record by imaging pre-calculated pre-recorded holograms. Writing is performed at normal incidence and reading at 45° oblique incidence. Both transmission and reflection modes of operation are used. Experimental results as well as comparison with commercially available OASLMs are presented

X-ray generation using carbon nanotubes

Since the discovery of X-rays over a century ago the techniques applied to the engineering of X-ray sources have remained relatively unchanged. From the inception of thermionic electron sources, which, due to simplicity of fabrication, remain central to almost all X-ray applications, there have been few fundamental technological advances. However, with the emergence of ever more demanding medical and inspection techniques, including computed tomography and tomosynthesis, security inspection, high throughput manufacturing and radiotherapy, has resulted in a considerable level of interest in the development of new fabrication methods. The use of conventional thermionic sources is limited by their slow temporal response and large physical size. In response, field electron emission has emerged as a promising alternative means of deriving a highly controllable electron beam of a well-defined distribution. When coupled to the burgeoning field of nanomaterials, and in particular, carbon nanotubes, such systems present a unique technological opportunity. This review provides a summary of the current state-of-the-art in carbon nanotube-based field emission X-ray sources. We detail the various fabrication techniques and functional advantages associated with their use, including the ability to produce ever smaller electron beam assembles, shaped cathodes, enhanced temporal stability and emergent fast-switching pulsed sources. We conclude with an overview of some of the commercial progress made towards the realisation of an innovative and disruptive technology.Clare Collins is studying for the MRes in Ultra Precision, funded by the EPSRC, at the University of Cambridge.This is the final published version. It first appeared at http://www.nanoconvergencejournal.com/content/2/1/1

Horizontal carbon nanotube alignment.

The production of horizontally aligned carbon nanotubes offers a rapid means of realizing a myriad of self-assembled near-atom-scale technologies - from novel photonic crystals to nanoscale transistors. The ability to reproducibly align anisotropic nanostructures has huge technological value. Here we review the present state-of-the-art in horizontal carbon nanotube alignment. For both in and ex situ approaches, we quantitatively assess the reported linear packing densities alongside the degree of alignment possible for each of these core methodologies.Isaac Newton Trust, Oppenheimer Trust, Engineering and Physical Sciences Research Council (Graphene Doctoral Training Centre and Impact Acceleration grant), Royal Society (International Exchange grant

Auditory artificial grammar learning in macaque and marmoset monkeys.

Artificial grammars (AG) are designed to emulate aspects of the structure of language, and AG learning (AGL) paradigms can be used to study the extent of nonhuman animals' structure-learning capabilities. However, different AG structures have been used with nonhuman animals and are difficult to compare across studies and species. We developed a simple quantitative parameter space, which we used to summarize previous nonhuman animal AGL results. This was used to highlight an under-studied AG with a forward-branching structure, designed to model certain aspects of the nondeterministic nature of word transitions in natural language and animal song. We tested whether two monkey species could learn aspects of this auditory AG. After habituating the monkeys to the AG, analysis of video recordings showed that common marmosets (New World monkeys) differentiated between well formed, correct testing sequences and those violating the AG structure based primarily on simple learning strategies. By comparison, Rhesus macaques (Old World monkeys) showed evidence for deeper levels of AGL. A novel eye-tracking approach confirmed this result in the macaques and demonstrated evidence for more complex AGL. This study provides evidence for a previously unknown level of AGL complexity in Old World monkeys that seems less evident in New World monkeys, which are more distant evolutionary relatives to humans. The findings allow for the development of both marmosets and macaques as neurobiological model systems to study different aspects of AGL at the neuronal level

Bulk Molybdenum Spindt Field Emission Arrays

This is the final version of the article. It first appeared from One Central Press via http://www.onecentralpress.com/bulk-molybdenum-spindt-field-emission-arrays/.This paper reports on a simple approach for fabricating modest aspect ratio field emission arrays (FEAs) directly from bulk molybdenum substrates via the use of fluorine inductive-coupled-plasma (ICP) etching. Compared to traditional Spindt array fabrication, through our outlined fabrication process all thin film interfaces have been eliminated reducing tip delamination during operation. The as-fabricated devices exhibited low turn-on electric fields (I = 100nA) of 1.21 V/μm. Arrays of more than 10$^6$ tips, with controlled inter-tip-pitches of 10 μm, have produced maximum currents of up to 140 μA (5.48 V/μm). Spatially uniform emission, that can be white light optically modulated, has been observed making our Mo-FEAs promising for use in long-term, high beam current continuous emission applications.Oppenheimer Trus

Mechanical Robustness of Graphene on Flexible Transparent Substrates.

This study reports on a facile and widely applicable method of transferring chemical vapor deposited (CVD) graphene uniformly onto optically transparent and mechanically flexible substrates using commercially available, low-cost ultraviolet adhesive (UVA) and hot-press lamination (HPL). We report on the adhesion potential between the graphene and the substrate, and we compare these findings with those of the more commonly used cast polymer handler transfer processes. Graphene transferred with the two proposed methods showed lower surface energy and displayed a higher degree of adhesion (UVA: 4.40 ± 1.09 N/m, HPL: 0.60 ± 0.26 N/m) compared to equivalent CVD-graphene transferred using conventional poly(methyl methacrylate) (PMMA: 0.44 ± 0.06 N/m). The mechanical robustness of the transferred graphene was investigated by measuring the differential resistance as a function of bend angle and repeated bend-relax cycles across a range of bend radii. At a bend angle of 100° and a 2.5 mm bend radius, for both transfer techniques, the normalized resistance of graphene transferred on polyethylene terephthalate (PET) was around 80 times less than that of indium-tin oxide on PET. After 10(4) bend cycles, the resistance of the transferred graphene on PET using UVA and HPL was found to be, on average, around 25.5 and 8.1% higher than that of PMMA-transferred graphene, indicating that UVA- and HPL-transferred graphene are more strongly adhered compared to PMMA-transferred graphene. The robustness, in terms of maintained electrical performance upon mechanical fatigue, of the transferred graphene was around 60 times improved over ITO/PET upon many thousands of repeated bending stress cycles. On the basis of present production methods, the development of the next-generation of highly conformal, diverse form factor electronics, exploiting the emerging family of two-dimensional materials, necessitates the development of simple, low-cost, and mechanically robust transfer processes; the developed UVA and HPL approaches show significant potential and allow for large-area-compatible, near-room temperature transfer of graphene onto a diverse range of polymeric supports.Oppenheimer Research Fellowship, Royal Society, Engineering and Physical Sciences Research Council (Impact Acceleration Account grant), Innovate UK (Advanced Materials Feasibility Study award

Mechanical Robustness of Graphene on Flexible Transparent Substrates

This study reports on a facile and widely applicable method of transferring chemical vapor deposited (CVD) graphene uniformly onto optically transparent and mechanically flexible substrates using commercially available, low-cost ultraviolet adhesive (UVA) and hot-press lamination (HPL). We report on the adhesion potential between the graphene and the substrate, and we compare these findings with those of the more commonly used cast polymer handler transfer processes. Graphene transferred with the two proposed methods showed lower surface energy and displayed a higher degree of adhesion (UVA: 4.40 ± 1.09 N/m, HPL: 0.60 ± 0.26 N/m) compared to equivalent CVD-graphene transferred using conventional poly(methyl methacrylate) (PMMA: 0.44 ± 0.06 N/m). The mechanical robustness of the transferred graphene was investigated by measuring the differential resistance as a function of bend angle and repeated bend–relax cycles across a range of bend radii. At a bend angle of 100° and a 2.5 mm bend radius, for both transfer techniques, the normalized resistance of graphene transferred on polyethylene terephthalate (PET) was around 80 times less than that of indium–tin oxide on PET. After 104 bend cycles, the resistance of the transferred graphene on PET using UVA and HPL was found to be, on average, around 25.5 and 8.1% higher than that of PMMA-transferred graphene, indicating that UVA- and HPL-transferred graphene are more strongly adhered compared to PMMA-transferred graphene. The robustness, in terms of maintained electrical performance upon mechanical fatigue, of the transferred graphene was around 60 times improved over ITO/PET upon many thousands of repeated bending stress cycles. On the basis of present production methods, the development of the next-generation of highly conformal, diverse form factor electronics, exploiting the emerging family of two-dimensional materials, necessitates the development of simple, low-cost, and mechanically robust transfer processes; the developed UVA and HPL approaches show significant potential and allow for large-area-compatible, near-room temperature transfer of graphene onto a diverse range of polymeric supports

Gravimetric and biological sensors based on SAW and FBAR technologies

This presentation will describe the development of Gravimetric and Biological Sensors based on SAW and FBAR Technologies. The SAW devices were fabricated on polycrystalline ZnO thin films deposited using both standard R.F. sputtering techniques and a novel High Target Utilisation Sputtering System (HiTUS). This system ensures that we can produce the low stress films at the high deposition rates necessary for such structures to operate efficiently. However in order to further improve the sensitivity of our sensors we have also investigated the use of Thin Film Bulk Acoustic Resonators (FBARs) . We will describe standard gravimetric sensors based on such material and also gravimetric sensors for use in liquid environments through the use of inclined c-axis ZnO material. The talk will conclude with a discussion of dual mode thin film FBARs for parallel sensing of both mass loading and temperature

Towards graphane field emitters.

We report on the improved field emission performance of graphene foam (GF) following transient exposure to hydrogen plasma. The enhanced field emission mechanism associated with hydrogenation has been investigated using Fourier transform infrared spectroscopy, plasma spectrophotometry, Raman spectroscopy, and scanning electron microscopy. The observed enhanced electron emissionhas been attributed to an increase in the areal density of lattice defects and the formation of a partially hydrogenated, graphane-like material. The treated GF emitter demonstrated a much reduced macroscopic turn-on field (2.5 V μm-1), with an increased maximum current density from 0.21 mA cm-2 (pristine) to 8.27 mA cm-2 (treated). The treated GFs vertically orientated protrusions, after plasma etching, effectively increased the local electric field resulting in a 2.2-fold reduction in the turn-on electric field. The observed enhancement is further attributed to hydrogenation and the subsequent formation of a partially hydrogenated structured 2D material, which advantageously shifts the emitter work function. Alongside augmentation of the nominal crystallite size of the graphitic superstructure, surface bound species are believed to play a key role in the enhanced emission. The hydrogen plasma treatment was also noted to increase the emission spatial uniformity, with an approximate four times reduction in the per unit area variation in emission current density. Our findings suggest that plasma treatments, and particularly hydrogen and hydrogen-containing precursors, may provide an efficient, simple, and low cost means of realizing enhanced nanocarbon-based field emission devices via the engineered degradation of the nascent lattice, and adjustment of the surface work function.For assistance in ATR FTIR and EDXRF measurements we thank Dr Bob Keighley and Dr Ralph Vokes of Shimadzu Corp; and for plasma optical spectrophotometry analysis, Dr Thomas Schűtte of PLASUS GmbH. This work is supported by National Key Basic Research Program 973(2010CB327705), National Natural Science Foundation Project (51120125001, 51002031, 61101023, 51202028), Foundation of Doctoral Program of Ministry of Education (20100092110015), an EPSRC Impact Acceleration grant, and the Research Fund for International Young Scientists from NSFC (510501101 42, 51350110232). MT Cole thanks the Oppenheimer Trust for their generous financial support.This is the author accepted manuscript. The final version is available from the Royal Society of Chemistry via http://dx.doi.org/10.1039/C5RA20771

Structural and electrical characterization of SiO2 gate dielectrics deposited from solutions at moderate temperatures in air

Silicon dioxide (SiO2) is the most widely used dielectric for electronic applications. It is usually produced by thermal oxidation of silicon or by using a wide range of vacuum-based techniques. By default, the growth of SiO2 by thermal oxidation of silicon, requires the use of Si substrates whereas the other deposition techniques either produce low quality or poor interface material and mostly require high deposition or annealing temperatures. Recent investigations therefore have focused on the development of alternative deposition paradigms based on solutions. Here, we report the deposition of SiO2 thin film dielectrics deposited by spray pyrolysis in air at moderate temperatures of 350 oC from pentane-2,4-dione solutions of SiCl4. SiO2 dielectrics were investigated by means of UV–Vis absorption spectroscopy, spectroscopic ellipsometry, XPS, XRD, UFM/AFM, admittance spectroscopy, and field-effect measurements. Data analysis reveals smooth (RRMS<1 nm) amorphous films with a dielectric constant of about 3.8, an optical band gap of ≈8.1 eV, leakage current densities in the order of ≈10-7 A/cm2 at 1 MV/cm and high dielectric strength in excess of 5 MV/cm. XPS measurements confirm the SiO2 stoichiometry and FTIR spectra reveal features related to SiO2 only. Thin film transistors implementing spray coated SiO2 gate dielectrics and C60 and pentacene semiconducting channels exhibit excellent transport characteristics i.e. negligible hysteresis, low leakage currents, high on/off current modulation ratio in the order of 106 and high carrier mobility