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Since their first appearance, organic-inorganic perovskite absorbers have been capturing the attention of the scientific community. While high efficiency devices highlight the importance of band level alignment, very little is known on the origin of the strong n-doping character observed in the perovskite. Here, by means of a highly accurate photoemission study, we shed light on the energy alignment in perovskite-based devices. Our results suggest that the interaction with the substrate may be the driver for the observed doping in the perovskite samples.

The aim of the current work is to improve the response time of an optical readout based humidity sensor. Therefore, we present the application of nanoimprint lithography (NIL) on thin films which are deposited by initiated chemical vapor deposition (iCVD). Hydrogels are polymeric networks with the ability to swell after certain physical conditions change, which makes them very useful as sensing layers for optical devices. In the first step we used iCVD to deposit a humidity responsive hydrogel (here: pHEMA) as a planar thin film on sapphire substrates. To increase the effective surface area, we tried for the first time NIL on our hydrogel thin films with promising results: First, characterization with a SEM showed that NIL allows the design of large homogeneous areas of nanostructures without damaging the sensitive hydrogel thin film and having a great stability at ambient conditions. Second, NIL offers the benefit to build different geometries and sizes of nanostructures based on the requested application. For our first test we selected a simple line array structure, combined with an optical detection method as sensor principle. By choosing a specific structure to wavelength ratio the imprinted nanostructures act as a diffraction grating enabling a fast response time by increasing the effective sensing area. Since in our application the hydrogel works as the sensing element, we observed a humidity dependence behavior by measuring the intensity of the first order diffraction peak. Finally, the response time was a lot faster by using optical detection methods than commercial humidity sensors.

Presently, no resist material has suitable properties to satisfy simultaneously all requirements on lateral resolution and plasma etching resistance for pattern transfer of high aspect ratio nano-structures. Herein, a recent innovative alumina spin-on material for use as both positive and negative high resolution resist for electron beam lithography (EBL) is presented. This system turns into an almost completely inorganic alumina system when exposed to the electron beam, showing exceptional selectivity (100:1), compared to even the most robust polymeric resist, when used as mask for dry etching of silicon in fluorinated plasmas, obviating the need for a hardmask layer deposition. A full characterization of the resist selective removal under different processing conditions, such as electrons acceleration voltage and post-exposure bake temperature and time, is presented. Owing to the high selectivity and high resolution, silicon nano-structures of size down to 11 nm and high aspect ratio (up to 20) have been obtained for the first time in a one-step process.

We report the nanopatterning of the methylammonium lead iodide (MAPbI3) perovskite, a polycrystalline hybrid organic-inorganic semiconductor with very promising perspectives for photovoltaic and optoelectronic applications. Nanopatterning of MAI is obtained via Pulsed-NIL technology, an ultrafast version of the thermal nanoimprint lithography (NIL) based on stamps with integrated heaters. By Pulsed-NIL we were able to replicate onto the hybrid perovskite structures with details at the sub-100nm scale, in spite of its crystalline nature. This work shows a new possibility for the exploitation of organo-metal halide perovskites in optoelectronic devices with more complex architectures than just planar films. Display Omitted Methylammonium lead iodide thin film nanoimprinting approach is proposed.V-groove nanostructures are transferred to the photoactive material via Pulsed-NIL.The technique allows to perform the step in less than 1s.The preliminary trials show the possibility to scale up the process.

A nanofabrication process for high resolution X-ray optics and X-ray lithography masks was developed. The process is based on the plasma etching of a sacrificial hard inorganic interlayer (Si, Si(3)N(4), SiO(x) or HSQ) used for pattern transfer and aspect ratio amplification. The structures are first defined on a top thin metal film by electron beam lithography and lift-off; a thin nickel layer at the bottom of the hard interlayer is used as etch stop. A base plating (Cr/Au) under the nickel serves as seed layer for the electroplating of an X-ray absorber or phase shifting material. The fabrication is completed by the stripping of the hard template by wet or dry etching. Compared to methods based on analogous process schemes, in which the aspect ratio of nanostructures is instead amplified by pattern transfer into a sacrificial polymer interlayer by oxygen plasma, the investigated method is advantageous for the higher mechanical stability of the nanostructured hard templates with respect to the polymer ones, thus enabling the realization of higher aspect ratio features. (C) 2011 Elsevier B.V. All rights reserved.

Hybrid sol-gel materials are suitable dielectric materials for a range of optical applications, due to the versatility by which their optical and mechanical properties can be adjusted and the easy patterning by various lithographic techniques. We report on the synthesis of engineered epoxy based hybrid organic-inorganic sol-gel materials and on their lithographic processing, specifically applied to the fabrication of microlens arrays. The investigated sol-gel systems exhibit enhanced transparency in the near UV region with respect to most commercial thermoplastic polymers and sol-gel materials, used in embossing and nanoimprinting technology; in addition, they offer a better shape stability and superior mechanical properties, such as higher elastic modulus and hardness, improving the perspectives of the introduction of microstructured and nanostructured surfaces in applications where resistance to environmental mechanical-chemical degradation mechanisms is highly desirable, in particular for outdoor applications.

Organic thin film transistors were fabricated by vacuum evaporation of pentacene using different growth conditions in order to tune the pentacene layer morphology. We have performed in situ transport measurements on completed samples, and ex situ morphological characterization by atomic force microscopy. Electric properties of the microscopic interface environment at the drain/pentacene and source/pentacene interfaces were probed by Kelvin force microscopy. From the observed voltage drops at the metallic contacts we have calculated contact resistances that may be decomposed into contributions due to structural defects in the channel, due to structural defects at the metal/pentacene interface, and due to charge carrier injection at the source/pentacene interface. We observe that samples fabricated by different growth conditions exhibit different contact resistances. The most important variable contribution to the contact resistance is due to the charge carrier injection at the source/pentacene interface.

Organic photovoltaic cells (OPV) are among the most promising systems for energy extraction and conversion from renewable energy sources. However, major problem to be solved before industrial production could become economically viable is represented by their still low conversion efficiency. The organic solar cell architectures are presently the result of a compromise between achieving complete light absorption using active layers that are thicker than the optical absorption length and achieving efficient charge collection at the electrodes which is favoured in thinner layers. We present a concept and its experimental demonstration that would solve efficiently the above trade-off problem by making use of a new type of light trapping elements. The simple fabrication scheme, based on a self-aligned UV exposure process, suggests its potential up-scalability to large systems, at low production cost.

Site-controlled epitaxial growth of InAs quantum dots on GaAs substrates patterned with periodic nanohole arrays relies on the deterministic nucleation of dots into the holes. In the ideal situation, each hole should be occupied exactly by one single dot, with no nucleation onto planar areas. However, the single-dot occupancy per hole is often made difficult by the fact that lithographically-defined holes are generally much larger than the dots, thus providing several nucleation sites per hole. In addition, deposition of a thin GaAs buffer before the dots tends to further widen the holes in the [110] direction. We have explored a method of native surface oxide removal by using indium beams, which effectively prevents hole elongation along [110] and greatly helps single-dot occupancy per hole. Furthermore, as compared to Ga-assisted deoxidation, In-assisted deoxidation is efficient in completely removing surface contaminants, and any excess In can be easily re-desorbed thermally, thus leaving a clean, smooth GaAs surface. Low temperature photoluminescence showed that inhomogeneous broadening is substantially reduced for QDs grown on In-deoxidized patterns, with respect to planar self-assembled dots.

We have successfully grown regular arrays of InAs/GaAs quantum dots on patterned Si substrates. Thanks to the capability of nanoimprint lithography, we were able to obtain uniform patterns extended over some cm(2) areas, with periods of 300 nm. Ex-situ and in-situ treatments of the surface allowed us to completely remove any residual oxides prior to growth without the use of hydrogen beams, at temperatures compatible with standard III-V molecular beam epitaxy. The growth protocol was optimized in order to obtain a perfect selectivity of InAs/GaAs nanostructures in the holes, without any deposition on the planar areas. (C) 2015 Elsevier B.V. All rights reserved.

The fabrication of single electron transistors and/or highly sensitive biosensors is still a challenging task on account of the tight control required to get proper shapes and size of the electrodes. The nanosized tips and the separation of a few nanometers between electrode pairs are critical features. Conventional lithography is not suited to obtain these features because of the resolution limits, so that previous alternative approaches have involved the use of electron beam lithography, focused ion beam lithography or scanning probe nanolithography. The novel approach presented in this letter is the exploitation of X-ray lithography in the Elettra synchrotron to fabricate arrays of nanocontacts spaced a few nanometers, devoted to the design of a new class of nanodevices based on nanoparticles and/or single molecules, including single electron transistors and highly sensitive biosensors. The method to fabricate such devices is illustrated and discussed. Experimental details of the fabrication process are given and preliminary results are presented through SEM and AFM images. It is worth noting that this paper presents a viable method to produce nanocontacts by using the X-ray lithography by synchrotron radiation source, that has not yet been reported together with experimental, though preliminary, data. (c) 2006 Elsevier B.V. All rights reserved.

Pyramid wavefront sensors are the key components of new multiconjugate adaptive optics systems used for wavefront correction of terrestrial telescopes. The sensor consists of a very flat four faces pyramid made in a transparent material that requires an accurate control of the quality of its turned edges, its surfaces and the size of its pyramid tip. Moreover identical copies of these optical elements are needed to fulfil the requirements of the multiconjugate adaptive optics systems. This paper presents the fabrication method of Pyramid wavefront sensors using the LIGA process. Results are described and discussed.

Display Omitted A full 4¿ wafer is nanopatterned by an ultrafast thermal NIL process in 100µs.Stamps with integrated heater enable ultrafast cycles at very high temperature.The thermal cycle is implemented with a single short very intense current pulse.A new tool for the ultrafast NIL (or pulsed-NIL) process has been developed.The process applies to a wide range of thermoplastic materials. We present here an ultrafast thermal NIL technology, which enables the patterning of full wafers on the 100µs time-scale. This technique makes use of stamps with a heating layer integrated beneath their nanostructured surfaces. Injecting a single, short (

A technological scheme for the fabrication of metallic point contacts is presented. Nanoimprint lithography (NIL) (J. Vac. Sci. Technol. B, 14(6) (1996) 4129–4133) plays a key role in the process determining the critical dimension of the point contact. The pattern obtained by imprint has been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The masking properties of the polymer film which also serves as an insulating layer in our device, separating the electrodes between which the point contact is located, have been controlled. Our study confirms that the imprint step involved in the process and the chosen thermoplastic polymer meet the requirements for fabricating nm-scale metallic point contacts.

We present a new water-vapour-assisted nanoimprint lithography (NIL) process for the patterning of the conducting poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS). The process was optimized with respect to relative humidity, applied pressure and temperature (RH, p, T). The control of environmental humidity was found to be crucial. High quality nanostructures were reproducibly obtained at high relative humidity values (RH >= 75%), with sub-100 nm resolution features attaining aspect ratios as high as similar to 6 at similar to 95% RH. The developed process of water-vapour-assisted NIL (WVA-NIL) strongly affects the electronic properties of PEDOT: PSS. By current-voltage measurements and ultraviolet photoemission spectroscopy we demonstrate that the process parameters p, T and RH are correlated with changes of PEDOT: PSS conductivity, work function and states of the valence band. In particular, an increase in the films conductivity by factors as high as 105 and a large decrease in the work function, up to 1.5 eV, upon WVA-NIL processing were observed. Employed as an anode buffer layer in P3HT: ICBA bulk heterojunction solar cells, PEDOT: PSS processing was found to affect significantly the device performance.

We describe a scheme for the fabrication of sharp blazed gratings involving two cascaded steps of X-ray lithography (XRL) with electroplating (EP) steps interposed. The adopted iterative scheme enables the amplification by two orders of magnitude of the height of high-resolution structures of an original X-ray mask produced by Electron Beam Lithography (EBL), while minimizing the loss of lateral resolution. Nickel structures of up to 200 μm in height with blazed grating profile were obtained with The described approach is suitable for the fabrication of nickel structures, to be used in particular as master tools in hot embossing processes, in a broad range of optical applications requiring non-binary microstructures.

The quest for efficient harvesting of solar radiation is one of the major areas of research in the renewable energy field. Through different photonic architectures it is possible to augment the optical absorption by trapping light within thin and ultra-thin films, the latter being desirable to decrease costs and efficiently extract the photogenerated charge carriers. Engineering the absorbing material at the nanoscale indeed leads to interferences that can significantly increase light absorption [1].

A new, unique spin-on metal-organic resist presenting a combination of worthwhile properties is described by Giovanna Brusatin and co-workers on page 6261. The resist shows good processability, typical of polymeric resists, direct patternability with various forms of radiation, mild post-exposure treatment requirements, positive or negative tone development, and a selectivity greater than 100:1 with respect to the underlying silicon in a fluorine-based continuous plasma-etching process. The use of such materials for high-resolution deep silicon etching is time- and cost-effective compared with the pattern-transfer materials that are generally used.

We demonstrate that ultrathin (thickness below 1 μm) elastomeric stamps, directly fabricated on rigid substrates can be reliably used in microcontact printing (μCP), showing enhanced mechanical properties with respect to the thicker ones commonly utilized. Macroscopic distorsion (due to thermal expansion and external stress) and microscopic effects such as the membrane relaxation in wide unsupported areas are drastically reduced. A mix and match process (optical lithography followed by μCP) performed with submicron overlay accuracy proves the reliability of the present approach and its applicability to multilevel production processes.

A versatile micro- particle imaging velocimetry ( mu- PIV) recording system is described, which allows us to make fluid velocity measurements in a wide range of flow conditions both inside microchannels and at liquid - solid interfaces by using epifluorescence and total internal reflection fluorescence excitation. This set- up has been applied to study the slippage of water over flat surfaces characterized by different degrees of hydrophobicity and the effects that a grooved surface has on the fluid flow inside a microchannel. Preliminary measurements of the slip length of water past various flat surfaces show no significant dependence on the contact angle.

In this paper we will discuss the use of the crossbeam ZEISS XB1540 applied to photonic structures and to obtain nano-imprinting templates. Some 1D Photonic Crystals (PhC) on silica based optical waveguides are shown as well as the realization of 3D optical structures curved directly on silica and used subsequently as a master for imprinting. Focused ion beam lithography (FIB) is a technique for direct writing of patterns; it means is substantially slow, but its versatility and the combination with other "faster" techniques make it an interesting method to produce prototypes and special devices. The resolution and the perturbation of the samples are perfectly compatible with the photonic applications. In fact, the contamination due to the gallium ion implantation as well as the roughness of the vertical and horizontal surface doesn't affect the performance of the devices shown in this paper.

The objective of this benchmarking is to establish a comparison of several tools and processes used in thermal NIL with Si stamps at the nanoscale among the authors' laboratories. The Si stamps have large arrays of 50 nm dense lines and were imprinted in all these laboratories in a similar to 100 nm thick mr-18010E film. Other materials, such as mr-17010E, were also tested. Good patterns were obtained and some limitations were identified. Reducing the pressure to 15 bars enables the printing of 50 nm structures without pulling them off. At higher pressures, some bending effects resulting in pattern deformation were observed. It was proven that a pressure of 1.5 bars is sufficient to imprint perfect 50 nm lines. The influence of the antiadhesive layer and mold design has been characterized by the demonstration of pulled off lines in some cases. Moreover, it has been shown that the scatterometry method is particularly useful for the characterization of 50 nm lines and that the residual layer thickness corresponds to the theoretical estimate as long as the lines are well defined. One process was demonstrated which combines high reproducibility with high throughput, achieving a cycle time of 2 min. (c) 2007 American Vacuum Society.

Microstructuring of polymer surfaces on optical spacers allows formation of reflective light traps. Such flexible reflectors can be combined with flexible polymer solar cells. We have demonstrated enhanced absorption using Lambertian and regular light reflectors, demonstrated via luminescence from fluorescent layers. Such light traps are suitable to use in combination with polymer solar cells incorporating transparent electrodes. The possibility to enhance the concentration of excited states and photogenerated charges through light trapping also helps to increase charge carrier mobility. These experimental results indicate that light confinement may be an alternative approach for boosting the efficiency of thin film conjugated polymer photovoltaics.

We present a new method that allows to fabricate structures with tightly controlled three-dimensional profiles in the 10 nm to 100 µm scale range. This consists of a sequence of lithographic steps such as Electron Beam (EB) or Focused Ion Beam (FIB) lithography, alternated with isotropic wet etching processes performed on a quartz substrate. Morphological characterization by SEM and AFM shows that 3D structures with very accurate shape control and nanometer scale surface roughness can be realized. Quartz templates have been employed as complex system of micromirrors after metal coating of the patterned surface or used as stamps in nanoimprint, hot embossing or casting processes to shape complex plastic elements. Compared to other 3D micro and nanostructuring methods, in which a hard material is directly "sculptured" by energetic beams, our technique requires a much less intensive use of expensive lithographic equipments, for comparable volumes of structured material, resulting in dramatic increase of throughput. Refractive micro-optical elements have been fabricated and characterized in transmission and reflection modes with white and monochromatic light. The elements produce a distribution of sharp focal spots and lines in the three dimensional space, opening the route for applications of image reconstruction based on refractive optics.

We present results on a lithographic approach that combines nanoimprint (NIL) and x-ray lithography (XRL) for fabricating unconventional three-dimensional (3D) polymer structures. The use of XRL for structuring a prepatterned resist by NIL gives rise to high-resolution high-aspect-ratio structures whose overall profile is enveloped by the original 3D imprinted profile. The technological potential of this method has been demonstrated by patterning several different types of structures with XRL on an hexagonal array of hemispheres previously obtained by nanoimprinting.

The aim of this paper is to demonstrate that efficient fiber-waveguide optical coupling can be achieved using a multilevel phase diffractive element (PDE) fabricated directly on the top of the fiber by means of e-beam lithography. The diffractive phase element is calculated to focus and reshape the gaussian symmetric beam exiting a single-mode fiber into a desired asymmetric intensity distribution at the waveguide input plane. Phase modulation is obtained by multilevel profiling a polymeric material coated on the top of the fiber by means of a specific fabrication process including e-beam lithography and chemical etching. Experimental results obtained for fiber-waveguide coupling with a 20-µm diameter diffractive element are also presented.

The surface of thin-film solar cells can be tailored with photonic nanostructures to allow light trapping in the absorbing medium. This in turn increases the optical thickness of the film and thus enhances their absorption. Such a coherent light trapping is generally accomplished with deterministic photonic architectures. Here, we experimentally explore the use of a different nanostructure, a disordered one, for this purpose. We show that the disorder-induced modes in the film allow improvements in the absorption over a broad range of frequencies and impinging angles. (c) 2013 Optical Society of America

We demonstrate a novel light trapping configuration based on an array of micro lenses in conjunction with a self aligned array of micro apertures located in a highly reflecting mirror. When locating the light trapping element, that displays strong directional asymmetric transmission, in front of thin film organic photovoltaic cells, an increase in cell absorption is obtained. By recycling reflected photons that otherwise would be lost, thinner films with more beneficial electrical properties can effectively be deployed. The light trapping element enhances the absorption rate of the solar cell and increases the photocurrent by as much as 25%. (C) 2008 Optical Society of America

We propose a 3D micro and nanofabrication method with potential applications to several nanotechnology-related fields. Our approach is based on the combination of lithographic steps and isotropic wet etchings performed on a quartz or glass substrate to form 3D structures with very accurate shape control and nanometer scale surface roughness. The resulting concavities at the quartz surface are converted into convex plastic elements by hot embossing or casting techniques. Complex all-polymer refractive optical elements have been realized by this method. Upon illumination, such micro-optics focus the light into predetermined 3D distributions of focal lines and spots. The general fabrication scheme explored here is illustrated through a series of examples in optics, but is expected to offer new solutions to other fields such as medicine, microfluidics and nano-optics.

Recently, there has been growing interest in sensors based on frequency shift detection of mechanical resonators, that has led to extremely sensitive diagnostic methods for medicine and biology. Here the authors propose and demonstrate a strategy capable of detecting the presence of a few macromolecules, which uses an asymmetrical cantilever structure of several microns in size, operated at room temperature, and under ordinary vacuum conditions. The idea is to detect the presence of one or more molecules by detecting the mechanical cross-talk induced by the molecular link between a short cantilever and an array of longer cantilevers facing the short one. (c) 2007 American Institute of Physics.

A new patterning process based on the microcontact printing of self-assembled monolayers on gold is presented. The method is readily adapted to processes utilising standard optical or electron beam resists, and is fully compatible with industrial semiconductor fabrication technology. The process can also be applied to surfaces which exhibit extreme nonplanarity such as sharp edges of mesas or etch grooves.