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Synthetic routes for the formation of opal assemblies as templates for the inverted opal vanadium oxide electrodes are presented. A method for the formation of monolayer opal templates on gold substrates is discussed and the formation of multilayer opal templates on conductive substrates by electrophoretic deposition is also described, with order defined by angle resolved light scattering measurements. Inverted opals are formed from a diluted solution of IPA and vanadium alkoxide precursor, infiltrated into the templates by several methods. The effect of different heat treatments and method of polymer template removal on the resulting inverse opal morphology and structure is investigated., EA and MO acknowledge the support of the Irish Research Council under awards RS/2010/2920 and RS/2010/2170. WK and CMST acknowledge support from the Spanish National I+D Plan projects TAPHOR (MAT-2012-31392) and CONSOLIDER nanoTHERM (CSD2010-00044). The authors thank Prof. J. D. Holmes for access to the Electron Microscopy Analytical Facility at Tyndall National Institute. COD acknowledges support from Science Foundation Ireland under award no. 07/SK/B1232a-STTF11, the UCC Strategic Research Fund, and from an Irish Research Council New Foundations Award.

The urgent need for non-toxic and abundant thermoelectric materials has become a significant motivation to improve the figures of merit of metal oxides in order to remove the barrier towards their widespread use for thermoelectric applications. Here we show the influence of a Cr layer in boosting the thermoelectric properties of vanadium pentoxide (V2O5) thin films, deposited by thermal evaporation and annealed at 500 °C. The Cr to V2O5 thickness ratio controls the morphological and thermoelectric properties of the thin films produced. The optimized Seebeck coefficient and power factor values at room temperature are +50 μV K−1 and 7.9 × 10−4 W m−1 K−2, respectively. The nanograin structure of the films is responsible for an improvement in the electrical conductivity up to 3 × 105 (Ω m)−1 with a typical thermal conductivity of 1.5 W m−1 K−1. These results combine to yield promising p-type thermoeletric CrV2O5 thin films with a ZT of 0.16 at room temperature., This work was partially supported by the Portuguese Science and Technology Foundation (FCT), Ministry for Education and Science (MEC), under PEst-C/CTM/LA0025/2011 (Strategic Project – LA 25 – 2011–2012), the Spanish Plan Nacional I + D project TAPHOR (MAT-2012-31392), the Spanish Consolider project nanoTHERM (CDS2010-00044) and mainly by the NANOTEG project: ENIAC/002/2010.

Unique bimodal distributions of single crystal epitaxially grown In2O3 nanodots on silicon are shown to have excellent IR transparency greater than 87% at 4 μm without sacrificing transparency in the visible region. These broadband antireflective nanodot dispersions are grown using a two-step metal deposition and oxidation by molecular beam epitaxy, and backscattered diffraction confirms a dominant (111) surface orientation. We detail the growth of a bimodal size distribution that facilitates good surface coverage (80%) while allowing a significant reduction in In2O3 refractive index. The (111) surface orientation of the nanodots, when fully ripened, allows minimum lattice mismatch strain between the In2O3 and the Si surface. This helps to circumvent potential interfacial weakening caused by volume contraction due to electrochemical reduction to lithium, or expansion during lithiation. Cycling under potentiodynamic conditions shows that the transparent anode of nanodots reversibly alloys lithium with good Coulombic efficiency, buffered by co-insertion into the silicon substrate. These properties could potentially lead to further development of similarly controlled dispersions of a range of other active materials to give transparent battery electrodes or materials capable of non-destructive in-situ spectroscopic characterization during charging and discharging.

We introduce a formal definition of a non local functional and show that the non local exchange-correlation potential functional, derived within Density-Functional Theory, is non local in the space of electronic densities. A previously developed non local exchange-correlation potential term, is introduced to approach the exact density-functional potential. With this approach, the electronic structure of the graphene surface and the tyrosine amino acid are calculated.

The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ∼pm V, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies., C.M.S.-T. acknowledges the financial support from the Spanish Severo Ochoa Excellence program (Grant SEV-2013-0295), the MINECO project PHENTOM (FIS2015-70682-P) and the EU project NANO-RF (Grant Agreement 318352).

This chapter reviews phonon research in ultrathin free-standing silicon membranes made of silicon-on-insulator (SOI) wafers. The membranes are stress-free and some are intentionally stressed. Their fabrication is described in both cases. Calculations and experimental work on confined acoustic phonons, dispersion relations, phonon lifetimes, and transport mechanisms in different phonon propagation regimes are gathered to provide a comprehensive view of the underlying physics.

Template-directed formation of titanium structures on block copolymer templates has been recently reported [1]. Here, the incorporation of titanium in a thin film template is studied. We show that the surface free energy contrast in microphase-separated polystyrene-block-polyethylene oxide templates is not limited to the template film surface, but directs the assembly of titanium atoms in the template thin film. The details of the self-assembly of titanium particles on the block copolymer nanostructured surface and inside the 3D film structure are studied with selected amounts of titanium. Evaporated titanium preferentially wets the polystyrene block of the block copolymer film and diffuses inside the film, conserving the block copolymer nanostructure. Increasing deposition leads to the formation of a mesoporous titanium layer on the block copolymer film, which reproduces that of the underlying template, in this particular case with a thickness of 12 nm and a periodic pore-to-pore distance of 35 nm. The formation of a mesoporous titanium layer prevents from further titanium diffusion inside the block copolymer film. The combination of the X-ray scattering techniques presented here provides sufficient sensitivity to follow the titanium formation in the three dimensional network of the block copolymer films., The authors acknowledge the financial support from the European Commission FP7 for the Integrated Infrastructure Initiative N. 262348 European Soft Matter (ESMI) and projects LAMAND (GA No. 245565), QUANTIHEAT (GA No. 604668) and MERGING (GA No. 309150). The Spanish MINECO project TAPHOR (MAT2012–31392) and the Deutsche Forschungsgemeinschaft (Grant No. KR 4522/1-1) are also acknowledged. The work at ICN2 is partially supported by the Spanish MINECO Severo Ochoa Centres of Excellence (SEV-2013-0295).

The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder., The authors acknowledge financial support from the EU FP7 project MERGING (Grant 309150), NANO-RF (Grant 318352), and QUANTIHEAT (Grant 604668); the Spanish MICINN projects nanoTHERM (Grant CSD2010-0044) and PHENTOM (FIS2015-70862-P); and the Severo Ochoa Program (MINECO, Grant SEV-2013-0295). M.R.W. acknowledges the postdoctoral Marie Curie Fellowship (IEF) HeatProNano (Grant 628197).

et al., Understanding and controlling vibrations in condensed matter is emerging as an essential necessity both at fundamental level and for the development of a broad variety of technological applications. Intelligent design of the band structure and transport properties of phonons at the nanoscale and of their interactions with electrons and photons impact the efficiency of nanoelectronic systems and thermoelectric materials, permit the exploration of quantum phenomena with micro- and nanoscale resonators, and provide new tools for spectroscopy and imaging. In this colloquium we assess the state of the art of nanophononics, describing the recent achievements and the open challenges in nanoscale heat transport, coherent phonon generation and exploitation, and in nano- and optomechanics. We also underline the links among the diverse communities involved in the study of nanoscale phonons, pointing out the common goals and opportunities., The authors acknowledge financial support by the European Commission FP7 FET Open project EUPHONON, grant agreement No. 612086.

Optical forces can set tiny objects in states of mechanical self-sustained oscillation, spontaneously generating periodic signals by extracting power from steady sources. Miniaturized self-sustained coherent phonon sources are interesting for applications such as mass-force sensing, intra-chip metrology and intra-chip time-keeping among others. In this paper, we review several mechanisms and techniques that can drive a mechanical mode into the lasing regime by exploiting the radiation pressure force in optomechanical cavities, namely stimulated emission, dynamical back-action, forward stimulated Brillouin scattering and self-pulsing., This work was supported by the European Comission project TAILPHOX (ICT-FP7-233883), the Spanish Severo Ochoa Excellence program and the MINECO project PHENTOM (FIS2015-70862-P). DNU and MFC gratefully acknowledge the support of a Ramón y Cajal postdoctoral fellowship and a Severo Ochoa studentship, respectivelyn.

In this work, the authors present and demonstrate a simple method to fabricate and mass replicate re-entrant structures. The method consists of the direct imprinting of polymer mushroomlike microstructures produced by a combination of photolithography and nickel up-plating process. In particular, they have studied the conditions to generate highly robust mushroomlike topographies and their topographical impact on the replication process. They discuss all the imprinting conditions suitable to replicate such topographies using both ultraviolet light assisted nanoimprint lithography (UV-NIL) and thermal NIL methods in two polymer films, poly(methyl methacrylate) and polypropylene, and a hybrid (organic–inorganic) UV light curable photoresist, namely, Ormocomp. Re-entrant topographies have been widely studied for liquid/oil repelling and dry adhesive properties, whereas in their experiments, they have proved evidence for their amphiphobic potential., The ICN2 is funded by the CERCA program/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa program of the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant No. SEV-2013-0295) and the EU H2020 project NMBP-PILOT-2016-721062 (FLEXPOL).

5 páginas, 5 figuras.-- et al., A novel all-inorganic electroluminescent device is demonstrated based on highly luminescent CdTe nanocrystals intercalated within a laminar hydrotalcite-like structure. The laminar scaffold acts to both support and distribute the CdTe nanocrystals. The device is synthesized using simple wet chemical processes at room temperature in ambient conditions. It has high thermal stability, operating continuously up to 90 °C, and a maximum efficiency at J = 0.12 A cm−2. The device is targeted at the automotive industry., The authors acknowledge funding from the EU FP6 project “Stabilight” (Grant No. 017328).

A series of hybrid heterostructured nanocomposites of ZnO with V2O5 nanotubes (VOx-NTs) in different mixing ratios were synthesized, with the aim of reducing the recombination of photoinduced charge carriers and to optimize the absorption of visible light. The study was focused on the use of heterostructured semiconductors that can extend light absorption to the visible range and enhance the photocatalytic performance of ZnO in the degradation of methylene blue as a model pollutant. The addition of VOx-NTs in the synthesis mixture led to a remarkable performance in the degradation of the model dye, with hybrid ZnO (stearic acid)/VOx-NTs at a ratio of 1:0.06 possessing the highest photocatalytic activity, about seven times faster than pristine zinc oxide. Diffuse reflectance spectroscopic measurements and experiments in the presence of different trapping elements allowed us to draw conclusions regarding the band positions and photocatalytic degradation mechanism. The photocatalytic activity measured in three subsequent cycles showed good reusability as no significant loss in efficiency of dye degradation was observed., Work supported by UTEM, UCh, FONDECYT 1151189; Basal Financing Program CONICYT, FB0807 (CEDENNA). CMST acknowledges the support from the Spanish MINECO projects PHENTOM (FIS2015-70862-P), Severo Ochoa (SEV-2013-0295) and from the CERCA Programme/Generalitat de Catalunya.

Complexes of Europium(III) and Terbium(III) with 2,2-bipyridine and 1,10-phenanthroline were inserted into Na-bentonite by ion exchange reactions at room temperature. The products display interlaminar distances and stoichiometries in agreement with the ion exchange capacity and the interlayer space available in the clay. The optical properties of the intercalates, being qualitatively similar to those of the free complexes, are additionally improved with respect to exchange processes with the medium, especially in a moist environment. The protection again hydrolysis, together with the intensity of the optical transition 5D0–5F2 observed in the nanocomposite, makes these products promising for the development of novel optical materials.

A scalable method for site‐selective, directed self‐assembly of colloidal opals on topologically patterned substrates is presented. Here, such substrate contains optical waveguides which couple to the colloidal crystal. The site‐selectivity is achieved by a capillary network, whereas the self‐assembly process is based on controlled solvent evaporation. In the deposition process, a suspension of colloidal microspheres is dispensed on the substrate and driven into the desired crystallization sites by capillary flow. The method has been applied to realize colloidal crystals from monodisperse dielectric spheres with diameters ranging from 290 to 890 nm. The method can be implemented in an industrial wafer‐scale process.

Sub-wavelength diffraction optical metrology has been tested in a new optical arrangement with collinear incident and scattered light through microscope optics as a demonstration of its suitability for inline lithographic process monitoring. Measured diffraction efficiencies agree with simulations performed using the finite difference time domain method, demonstrating sensitivity to features of 50nm width. It was possible to distinguish well-imprinted gratings from those containing defects (missing 50 and 100nm lines) produced during the nanoimprinting process.

This work is devoted to the quantitative evaluation of the lattice ordering of opal films. Assembling colloidal crystals in a moving meniscus under random noise agitation produced opal films with generically the same lattice but different disorders. The lattice ordering is quantified by the magnitudes of harmonics in the Fourier transforms of (i) the scanning electron microscopy images to address the in-plane lattice ordering and (ii) rotation diagrams of the optical transmission to address the regularity of crystal planes. In prepared opals, the strong deviation of the lattice from the face-centered cubic symmetry is demonstrated. We find uneven lattice responses to changing the growth conditions, e.g., the 30% improvement of the hexagonal lattice ordering in the (111) growth plane accompanied by a ten-time better ordering of (220) planes as a result of noise agitation. The suggested approach to characterize crystalline quality of the lattice is a general methodology that can be applied to the analysis of other three-dimensional photonic crystals.

Both low-dimensional bar-coded metal oxide layers, which exhibit molecular hinging, and free-standing organic nanostructures can be obtained from unique nanofibers of vanadium oxide (VO(x)). The nanofibers are successfully synthesized by a simple chemical route using an ethanolic solution of vanadium pentoxide xerogel and dodecanethiol resulting in a double bilayered laminar turbostratic structure. The formation of vanadium oxide nanofibers is observed after hydrothermal treatment of the thiol-intercalated xerogel, resulting in typical lengths in the range 2-6 microm and widths of about 50-500 nm. We observe concomitant hinging of the flexible nanofiber lamina at periodic hinge points in the final product on both the nanoscale and molecular level. Bar-coded nanofibers comprise alternating segments of organic-inorganic (thiols-VO(x)) material and are amenable to segmented, localized metal nanoparticle docking. Under certain conditions free-standing bilayered organic nanostructures are realized.

A refined coarse-grain method for simultaneous calculation of the resist viscous flow in nanoimprint lithography and the stamp/substrate deformation is presented. The method has been realized in an effective simulation tool for the verification of stamp structures on standard personal computers, by using the GDS data of the stamp design. From the presented comparison of calculated and experimental results, it can be concluded that the coarse-grain modeling allows predicting the residual layer thickness with accuracy better than 10%.

The intercalation of [Eu(2,2 bipyridine)2 ]3+ and [Eu(1,10 phenantroline)2]3+ into bentonite results in new nanocomposites which preserve the emission properties of the lanthanide. The exchange of sodium by lanthanide in the bentonite correlates with the host cation exchange capacity as well as with the guest molecular size and the interlaminar volume available in the clay. The intercalated complexes exhibit luminescence indicating an efficient protecting role of the matrix. This in turn points to lanthanide-clay nanocomposite as novel optical materials.

The intercalation of long-chain primary amines into the laminar matrices of MoS 2 or V 2 O 5 -gel leads to well ordered, lamellar organic-inorganic nanocomposites. Powder X-ray diffraction analysis, stoichiometry determined by chemical analysis, and considerations on the molecular volume of the guest and surface available indicate the guest is oriented in the interlaminar space with their molecular axis perpendicular to the matrix plane. The hydrothermal treatment of these products leads to the formation of multiwall nonotubes with the organic component intercalated between inorganic layers. The composition and the shape of the tubes indicate that the tube formation should occur by the rolling up of precursor laminae.

Optical forces can set tiny objects into states of coherent mechanical oscillation, also known as mechanical or phonon lasing. We present a novel pumping mechanism in an opto-mechanical photonic crystal that realizes mechanical lasing with relaxed requirements for the optical-mechanical modes and their inter-coupling. It derives from a spontaneously triggered thermal/free carrier self-pulsing and the anharmonic modulation of the radiation pressure force that comes as a consequence. Moreover, the feedback of the mechanics on the self-pulsing frequency-entrains both oscillators, creating a self-stabilized indecomposable system. A manifold of frequency-entrained regions with two different mechanical modes (at 54 and 122 MHz) are observed as a result of the wide tuneability of the natural frequency of the self-pulsing. The system operates at ambient conditions of pressure and temperature in a silicon compatible platform, which enables its exploitation in sensing, intra-chip metrology or time-keeping applications., Comment: 23 pages including supplementary material

The analysis of diffracted light from periodic structures is shown to be a versatile metrology technique applicable to inline metrology for periodic nanostructures. We show that 10 nm changes in periodic structures can be traced optically by means of sub-wavelength diffraction. Polymer gratings were fabricated by electron beam lithography. The gratings have a common periodicity of 6 μm, but different line width, ranging from 370 to 550 nm in 10 nm steps. A comparison between the resulting diffraction patterns shows marked differences in intensity which are used to sense nanometre scale deviations in periodic structures.

Phonons represent collective excitation states that occur in periodic elastic arrangements of atoms or molecules. High-frequency (more than 10GHz) phonons are less sensitive to thermal decoherence than lower-frequency phonons. These high-frequency phonons, however, are outside the range of most piezoelectric actuators, and alternative means of control are therefore required. In optomechanical (OM) systems, light interacts with mechanical objects.1 Radiation pressure forces are thus commonly used to activate coherent mechanical oscillations.2 So-called phonon lasing is the regime in which mechanical oscillations are self-sustained, monochromatic, coherent, and have high amplitudes. The phonon lasing regime in OM systems is commonly achieved by means of dynamical back-action (i.e, the radiation pressure force is delayed in response to a mechanical deformation), at frequencies of up to a few gigahertz.3 To be efficient, however, these methods require high-quality factor modes and high OM coupling rates. The requirements of phonon lasing techniques are thus difficult to fulfill.Phonons play an important role in the physical properties of condensed matter (e.g., thermal or electrical conductivity), and over the past few years there has been a steady increase in the amount of research on phonons.4 The term 'phononics' has now entered the scientific vocabulary to indicate a platform where coherent phonons can be generated, harnessed, and detected. Mechanical (i.e., phonon) lasing can only be achieved if the mechanical losses of the OM system can be neutralized, no matter what pumping mechanism is used. Although dynamical back-action can be used to achieve mechanical lasing, the field-enhanced cooperativity (a figure of merit) must be at least one, and the system must be in the sideband resolved regime. We recently reported a new lasing method for phonon control. In our approach, coherent high-amplitude mechanical oscillations within a one-dimensional OM crystal are produced in response to an anharmonic modulation of the intracavity radiation pressure force.6 This modulation is a consequence of spontaneous triggering in the optical cavity of a self-pulsing limit cycle (i.e., a closed trajectory along which the system oscillates in a periodic manner). In other words, there is a stable and dynamic interplay between the thermo-optic effects and dispersion of free carriers (i.e., electrons and electron holes) in the OM crystal.7 With our self-pulsing laser mechanism we are able to achieve phonon lasing under more relaxed configurations than with conventional methods. Namely, we operate our devices deep within the unresolved regime (where the mechanical period is greater than the radiative lifetime and dynamical back-action is very inefficient) and with field-enhanced cooperativity values within the 10-2 range. We therefore use relatively low-quality factor modes (102), and single-particle OM coupling rates as low as a few tens of kilohertz, for our phonon lasing technique. We do not require extreme optimization of designs, nor top-class fabrication facilities, competencies, or techniques to achieve these performances. Instead, we fabricate our devices out of standard silicon-on-insulator wafers. In addition, the patterns for these devices are written using an electron beam and are transferred to the silicon using a reactive ion etching technique. We use wet etching in buffered hydrofluoric acid to remove the buried oxide layer and to release the beam structures (see Figure 1). The feedback produced by the coherent mechanical oscillations on the self-pulsing mechanism makes our coupled system a frequency-entrained self-stabilized oscillator. Because of this self-stabilizing feature, our device is extraordinarily robust to wavelength or power fluctuations that occur within the continuous-wave laser source (which we use as a pump). We use wide dynamical frequency tuning of the self-pulsing mechanism to produce many frequency-entrained regions that are associated with the coherent amplification of different mechanical modes (at up to hundreds of megahertz). We can obtain different dynamics by simply tuning the self-pulsing frequency, by changing the wavelength of the laser that we use to pump the optical cavity. In a set of experiments, we have demonstrated that it is straightforward to move from an isolated self-pulsing mode to stable phonon lasing--see Figure 2(b)--and then to a chaotic regime (where the trajectory is no longer a limit cycle), as shown in Figure 2(a). We have been able to successfully reproduce our experimental dynamics by numerically solving the four-dimensional coupled non-linear system. In this process, we describe the temporal evolution of the free-carrier population, the temperature difference (with respect to the surroundings), as well as the physical deformation and velocity of the OM cavity.6 Our simulated trajectories, which are associated with the stable phonon lasing regime and the chaotic counterpart, are shown in Figure 2(c) and (d). We use self-pulsing dynamics--activated in an OM crystal--to achieve phonon lasing of mechanical modes, with ordinary quality factors and single-particle OM coupling rates. Our coupled system is self-stabilized and therefore robust to fluctuations in the laser source. In addition, our mechanism can be operated at atmospheric temperatures and pressures, and therefore has several potential applications (e.g., for sensing, or intra-chip time-keeping). Our future work will be focused on engineering the self-pulsing dynamics of our system, i.e., by tailoring the characteristic thermal and free-carrier recombination lifetimes. This will allow us to scale the phonon lasing frequency, up to tens of gigahertz. Furthermore, since high-intensity sound waves can also change the electronic properties of nanostructures, our phonon lasers could be used as high-speed clocks. By synchronizing the weakly coupled OM oscillators--either in the limit cycle or the chaotic regime--we may be able to expand the applications of our devices into the realm of secure communications. We also plan to integrate our silicon-on-insulator devices with electronic and photonic systems. This will allow us to create hybrid systems with added functionalities.

Mass production of nanostructured surfaces relies on the periodic repetition of micrometre scale patterns. A unit cell with nanometre features in the micrometre size range is repeated thousands of times. The ensemble can used as a diffraction grating for visible light. The relative intensity distribution of the diffraction orders is characteristic for the grating and sensitive to nanometre scale changes. A newly designed subwavelength diffraction setup allows the measurement in real time of the diffraction pattern of an illuminated polymer grating with only one detector image. The setup records diffraction patterns of, for example, polymer gratings with intentionally low scattering contrast and line features ranging from 610 to 80 nm. Thus, sub-100 nm features can be traced. The comparison of the measured diffraction patterns with simulated patterns allows to sense nanometre scale deviations from fabrication goals.

Nanofibrillated cellulose, a polymer that can be obtained from one of the most abundant biopolymers in Nature, is being increasingly explored due to its outstanding properties for packaging and device applications. Still, open challenges in engineering its intrinsic properties remain to address. The results obtained show the precise determination of significant properties as elastic properties and interactions that are compared with similar works and, moreover, demonstrate that nanofibrillated cellulose properties can be reversibly controlled, supporting the extended potential of nanofibrillated cellulose as a robust platform for green-technology applications, in press in Carbohydrate Polymers (2015)

In this work we demonstrate that Reverse Nanoimprint Lithography is a feasible and flexible lithography technique applicable to the transfer of micro and nano polymer structures with no residual layer over areas of cm2 areas on silicon, metal and non-planar substrates. We used a flexible polydimethylsiloxane stamp with hydrophobic features. We present residual layer-free patterns imprinted using a commercial poly(methylmethacrylate) thermoplastic polymer over silicon, nickel and pre-patterned substrates. Our versatile patterning technology is adaptable to free form nano structuring and has coupling to adhesion technologies., The support of the project PLAST-4-FUTURE funded by the European Commission (FP7-2012-NMP-ICT-FoF) under Grant Agreement number 314345 (www.plast4future.eu) and of the national project MAT-2012-31392 TAPHOR are gratefully acknowledged.

ACS AuthorChoice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes., A detailed understanding of the connections of fabrication and processing to structural and thermal properties of low-dimensional nanostructures is essential to design materials and devices for phononics, nanoscale thermal management, and thermoelectric applications. Silicon provides an ideal platform to study the relations between structure and heat transport since its thermal conductivity can be tuned over 2 orders of magnitude by nanostructuring. Combining realistic atomistic modeling and experiments, we unravel the origin of the thermal conductivity reduction in ultrathin suspended silicon membranes, down to a thickness of 4 nm. Heat transport is mostly controlled by surface scattering: rough layers of native oxide at surfaces limit the mean free path of thermal phonons below 100 nm. Removing the oxide layers by chemical processing allows us to tune the thermal conductivity over 1 order of magnitude. Our results guide materials design for future phononic applications, setting the length scale at which nanostructuring affects thermal phonons most effectively., This work is partly funded by the European Commission FP7-ENERGY-FET project MERGING, NMP QUANTIHEAT and ICT NANOTHERM, with Grant Agreement Nrs: 309150, 604668 and 318117, respectively. S.N. and D.D. acknowledge financial support from MPG under the MPRG program. J.S.R., M.R.W., and C.M.S.T. acknowledge support form the Spanish MINECO projects TAPHOR (MAT-2012-31392) and nanoTHERM (CONSOLIDER CSD2010-00044). M.R.W. acknowledges support of the Marie Curie Postdoctoral Fellowship HeatProNano (Grant No. 628197). M.P. and A.S. acknowledge funding from the Academy of Finland (Grant No. 252598).

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., Knowledge of the mean-free-path distribution of heat-carrying phonons is key to understanding phonon-mediated thermal transport. We demonstrate that thermal conductivity measurements of thin membranes spanning a wide thickness range can be used to characterize how bulk thermal conductivity is distributed over phonon mean free paths. A noncontact transient thermal grating technique was used to measure the thermal conductivity of suspended Si membranes ranging from 15–1500 nm in thickness. A decrease in the thermal conductivity from 74–13% of the bulk value is observed over this thickness range, which is attributed to diffuse phonon boundary scattering. Due to the well-defined relation between the membrane thickness and phonon mean-free-path suppression, combined with the range and accuracy of the measurements, we can reconstruct the bulk thermal conductivity accumulation vs. phonon mean free path, and compare with theoretical models., We acknowledge support from “Solid State Solar-Thermal Energy Conversion Centre (S3TEC),” an Energy Frontier Research Centre funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Grant No. DE-SC0001299/DE-FG02-09ER46577, the Academy of Finland under Grant No. 252598, and the EU FP7 ENERGY FET project MERGING Grant Agreement No. 309150 and the Spanish Plan Nacional project TAPHOR (MAT-2012-31392).

The directionality of the polarised light transmission has been studied in heterogeneous photonic crystals based on double-film opal in comparison to homogeneous crystals on single-film opals. In spite of additional scattering at the photonic bandgap interface, ballistic propagation has been preserved. Changes of the polarisation anisotropy in hetero-opal compared to homogeneous opal have been assigned to specific mode matching conditions at the photonic bandgap interface.

We report on the fabrication of high-quality opaline photonic crystals from large silica spheres (diameter of 890 nm), self-assembled in hydrophilic trenches of silicon wafers by using a novel technique coined a combination of "lifting and stirring". The achievements reported here comprise a spatial selectivity of opal crystallization without special treatment of the wafer surface, a filling of the trenches up to the top, leading to a spatially uniform film thickness, particularly an absence of cracks within the size of the trenches, and finally a good 3D order of the opal lattice even in trenches with a complex confined geometry, verified using optical measurements. The opal lattice was found to match the pattern precisely in width as well as depth, providing an important step toward applications of opals in integrated optics.

Opals are three-dimensional photonic crystals, self-assembled from dielectric spherical beads into a face-centered cubic lattice. By introducing intentional defects in the crystal lattice, one modifies features such as spontaneous emission and the directionality of diffracted light. We here present a method for the artificial introduction of a lattice of such intentional defects in self-assembled poly(methyl methacrylate) (PMMA) photonic crystals by means of electron beam lithography. The inscribed defects are of the size of an individual bead, providing a broad spectral range between adjacent resonance peaks. This opens for devices with single line transmission in the photonic band gap, as well as for applications in modification and control of the diffraction properties and directionality of scattered light.

The interaction between surface plasmon resonance of the metallodielectric photonic crystal and the Bragg resonance of the opal photonic crystal has been studied. Two types of samples were investigated, differing in the topology of the metal content, metal-dielectric photonic crystals prepared using layer-by-layer deposition coating spheres with oppositely charged polyelectrolyte and Au nanoparticles and infiltrated opaline structures with Au nanoparticles. It was found that when the“red”-shift of plasmon resonance overlaps the Bragg diffraction, the latter become almost disperionless.

This paper describes ways to multilayer opaline films (opaline heterostructures) composed from functional opal layers of spheres with different lattice constants. At first various monodisperse coll...

Microwave annealing is an emerging technique for achieving ordered patterns of block copolymer films on substrates. Little is understood about the mechanisms of microphase separation during the microwave annealing process and how it promotes the microphase separation of the blocks. Here, we use controlled power microwave irradiation in the presence of tetrahydrofuran (THF) solvent, to achieve lateral microphase separation in high-χ lamellar-forming poly(styrene-b-lactic acid) PS-b-PLA. A highly ordered line pattern was formed within seconds on silicon, germanium and silicon on insulator (SOI) substrates. In-situ temperature measurement of the silicon substrate coupled to condition changes during “solvo-microwave” annealing allowed understanding of the processes to be attained. Our results suggest that the substrate has little effect on the ordering process and is essentially microwave transparent but rather, it is direct heating of the polar THF molecules that causes microphase separation. It is postulated that the rapid interaction of THF with microwaves and the resultant temperature increase to 55 °C within seconds causes an increase of the vapor pressure of the solvent from 19.8 to 70 kPa. This enriched vapor environment increases the plasticity of both PS and PLA chains and leads to the fast self-assembly kinetics. Comparing the patterns formed on silicon, germanium and silicon on insulator (SOI) and also an in situ temperature measurement of silicon in the oven confirms the significance of the solvent over the role of substrate heating during “solvo-microwave” annealing. Besides the short annealing time which has technological importance, the coherence length is on a micron scale and dewetting is not observed after annealing. The etched pattern (PLA was removed by an Ar/O2 reactive ion etch) was transferred to the underlying silicon substrate fabricating sub-20 nm silicon nanowires over large areas demonstrating that the morphology is consistent both across and through the film., We gratefully acknowledge Science Foundation Ireland (SFI) CSET/CRANN and a LAMAND NMP FP7 grant for funding this project.

arXiv:1403.2250v1, Directed self-assembly of block copolymer polystyrene-b-polyethylene oxide (PS-b-PEO) thin film was achieved by a one-pot methodology of solvent vapor assisted nanoimprint lithography (SAIL). Simultaneous solvent-anneal and imprinting of a PS-b-PEO thin film on silicon without surface pre-treatments yielded a 250 nm line grating decorated with 20 nm diameter nanodots array over a large surface area of up to 4' wafer scale. The grazing-incidence small-angle x-ray scattering diffraction pattern showed the fidelity of the NIL stamp pattern replication and confirmed the periodicity of the BCP of 40 nm. The order of the hexagonally arranged nanodot lattice was quantified by SEM image analysis using the opposite partner method and compared to conventionally solvent-annealed block copolymer films. The imprint-based SAIL methodology thus demonstrated an improvement in ordering of the nanodot lattice of up to 50%, and allows significant time and cost reduction in the processing of these structures., The research leading to these results received funding from the European Union FP7 under the project LAMAND (grant agreement n° 245565), NANOFUNCTION (grant agreement no. 257375, FP7-ICT-2009-5) and by the Spanish Ministry of Economics and Competitiveness under project TAPHOR contract no. MAT2012-31392 (Plan Nacional de I + D + I (2008–2011)

We demonstrate the formation of 2D photonic crystals (opals) on gold coated silicon substrates by dip-coating at a high rate of 1 mm/min when the surfactant sodium dodecyl sulphate (SDS) is added to the solution above its critical micelle concentration. The dependence of substrate hydrophillicity is demonstrated to influence the formation of 3D templates on glass substrates using 700 nm diameter PMMA spheres. Other routes towards directing opal assembly are also discussed. Angle-resolved reflectance shows 2D and 3D light scattering characteristics from the fast-rate dip-coated monolayer 2D 3D photonic crystals grown on hydrophillized glass respectively, with a high degree of surface ordering.

A novel and simple method for producing mesoporous titanium films and supported titanium nanoparticle hexagonal arrays is presented. During evaporation on block copolymer templates, titanium self-assembles as either a mesoporous film or as a hexagonal close-packed nanodot structure. The morphology of the titanium only depends on the molecular weight of the block copolymer, which results in a remarkable fabrication technique that saves time relative to conventional methods. Analyses using scanning electron microscopy, X-ray reflectometry, and grazing-incidence small-angle X-ray scattering correlate the morphology of the titanium with the buried polymer structure. The mesoporous titanium film exhibited a pore size of approximately 16 nm, with a pore-to-pore distance of 42 nm. The average size of the hexagonally packed nanodots was 60 nm, with a center-to-center distance of 88 nm commensurate with the template features. An analysis of the chemical composition showed that the structures were titanium dioxide, which indicated that oxidation occurred during the fabrication process., The authors acknowledge financial support from the EU-FP7 Integrated Infrastructure Initiative No. 262348 from the European Soft Matter Infrastructure (ESMI), LAMAND (Grant No. 245565), MERGING (Grant No. 309150), the Spanish MINECO project TAPHOR (MAT2012−31392), and the Deutsche Forschungsgemeinschaft (Grant No. KR 4522/1-1).

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al., The interaction between phonons and photons is investigated theoretically in a phoxonic cavity inside a corrugated nanobeam waveguide presenting band gaps for both electromagnetic and elastic waves. The structure is made by drilling periodic holes on a silicon nanobeam with lateral periodic stubs and the tapered cavity is constructed by changing gradually the geometrical parameters of both the holes and stubs. We show that this kind of cavity displays localized phonons and photons inside the gaps, which can enhance their interaction and also promotes the presence of many optical confined modes with high quality factor. Using the finite-element method, we demonstrate that with appropriate design of the tapering construction, one can control the cavity modes frequency without altering significantly the quality factor of the photonic modes. By changing the tapering rates over the lattice constants, we establish the possibility of shifting the phononic cavity modes frequency to place them inside the desired gap, which enhances their confinement and increases the mechanical quality factor while keeping the strength of the optomechanic coupling high. In our calculations, we take account of both mechanisms that contribute to the acousto-optic interaction, namely photoelastic and interface motion effects. We show that in our case, these two effects can contribute additively to give high coupling strength between phononic and photonic cavity modes. The calculations of the coupling coefficient which gives the phonon-photon coupling strength give values as high as 2 MHz while photonic cavity modes display quality factor of 105 and even values up to 3.4 MHz but with smaller photonic quality factors., The authors acknowledge the support of the European Commission Seventh Framework Programs (FP7) under the FET-Open project TAILPHOX N 233883.

The effect of graphene oxidative grades upon the conductivity and hydrophobicity and consequently the influence on an enzymatic biosensing response is presented. The electrochemical responses of reduced graphene oxide (rGO) have been compared with the responses obtained from the oxide form (oGO) and their performances have been accordingly discussed with various evidences obtained by optical techniques. We used tyrosinase enzyme as a proof of concept receptor with interest for phenolic compounds detection through its direct adsorption onto a screen-printed carbon electrode previously modified with oGO or rGO with a carbon-oxygen ratio of 1.07 or 1.53 respectively. Different levels of oGO directly affect the (bio)conjugation properties of the biosensor due to changes at enzyme/graphene oxide interface coming from the various electrostatic or hydrophobic interactions with biomolecules. The developed biosensor was capable of reaching a limit of detection of 0.01. nM catechol. This tuning capability of the biosensor response can be of interest for building several other biosensors, including immunosensors and DNA sensors for various applications. © 2014 Elsevier B.V., MEC (Spain) for MAT2011-25870 grant is acknowledged.

This chapter discusses the cooling of a platform, which requires the electronic coolers to extract heat by coupling to phonons within the platform material. Major results obtained within the nanofunction NoE on the development of nanomodulated magnetic materials and the investigation of their main properties are also presented. The cooling power of the devices becomes paramount, as opposed to the base temperature that could be reached, and must exceed heat leaks into the platform from the surroundings. This indirect cooling is desirable for systems where electrical isolation from the refrigeration elements is required, such as in quantum information applications or superconducting transition edge sensors (TESs). Thick porous Si layers on the Si wafer constitute alternative structures that could replace the rather fragile silicon nitride membranes for use as thermal isolation platforms. The structure and morphology of porous Si determines its electrical and thermal conductivity.

Surfactant induced ordering of 2D and 3D colloidal crystal photonic crystals is possible on metallic substrates by dip-coating at fast rates (≈1 mm/min). Ordered monolayer opals on conductive gold-coated silicon substrates behave as a 2D diffraction grating. The method allows high throughput, ordered colloidal crystal formation useful as nanomaterials templates for energy storage or functional materials., EA and MO acknowledge the support of the Irish Research Council under awards RS/2010/2920 and RS/2010/2170. WK and CMST acknowledge support from the Spanish National I+D Plan projects TAPHOR (MAT-2012–31392) and CONSOLIDER nanoTHERM (CSD2010–00044). COD acknowledges support from Science Foundation Ireland under award no. 07/SK/B1232a-STTF11, the UCC Strategic Research Fund, and from the Irish Research Council New Foundations Award.

Photoluminescence of dye molecules embedded in PMMA opaline photonic crystals and their SnS 2 replicas has been studied. The stop-band in the emission spectrum has been demonstrated. The role of a low dielectric contrast photonic crystal is to filter the emission from embedded light sources in accord with its transmission spectrum. In contrast, inverted opaline films of a higher dielectric contrast provide stronger radiation-to-emitter interaction, which feedback results in an amplification of a spontaneous emission of dye molecules at stop-band edges. The directionality diagram of the emission has been observed in both type photonic crystals. This, so-called, self-focusing effect has been tentatively assigned to the ultra-refraction of the emitted radiation at the sample boundary, which is dictated by the configuration of dispersion surfaces in the vicinity of the photonic band gap. The self-focusing has been found strongly dependent upon the frequency.

We review photonic band gap related properties of a simple periodic system of thin dielectric layers. Properties associated with forbidden and allowed bands of such one-dimensional photonic crystals are presented. A revision of forbidden bands properties leads to an omnidirectional Bragg mirror design. The anisotropy of allowed bands suggests the formation of photon-focusing caustics in one-dimensional photonic crystals., Comment: 6 pages, 6 figures, to appear in Optics & Spectroscopy

Monodisperse PMMA beads of a size varying between 200 and 400 nm have been prepared by a modified emulsion polymerization technique. These beads sediment well on substrates to form 3-dimensional face-centered cubic packages. This method allows it to cover large glass substrates (area up to 10 × 10 cm) with an opalescent layer of the beads thus creating films with opaline structure, which can be used as photonic crystals. Choosing PMMA as the material of the beads brings several advantages, e.g., the PMMA photonic films can be precisely patterned by e-beam lithography with the feature resolution down to one bead in width and various fluorescent dyes can be incorporated in PMMA balls. Dye-impregnated PMMA opaline photonic films demonstrate the incomplete photonic band gap structure and related modification of dye photoluminescence spectrum.

We have studied the suitability of poly(methylmethacrylate) (PMMA) of different molecular weight for large area pattern transfer by embossing structures above the glass transition temperature (Tg) of the specific polymer. The molecular weight covers a range of one order of magnitude (Mw∼5.0×104–8.1×105). This range was chosen in order to obtain information regarding the flow properties that we expect to depend strongly on the molecular weight at a specific temperature. Large area pattern transfer were tested by applying a stamp with both densely packed and isolated features. The feature size ranged from 100 μm down to 450 nm. At a processing temperature of 90°C above Tg we found clear indications that flow is sufficient to transfer large, isolated features even into the polymer with the highest Mw. Problems of incomplete material transport can be related to local inhomogeneities of the imprint due to a lack of parallelism between the stamp and the sample. At 50°C above Tg incomplete flow effects were observed over the whole area and for all molecular weights. This was observed only with large, isolated structures whereas small, periodic features showed a well defined transfer.