Search

On-surface chemistry holds the potential for ultimate miniaturization of functional devices. Porphyrins are promising building-blocks in exploring advanced nanoarchitecture concepts. More stable molecular materials of practical interest with improved charge transfer properties can be achieved by covalently interconnecting molecular units. On-surface synthesis allows to construct extended covalent nanostructures at interfaces not conventionally available. Here, we address the synthesis and properties of covalent molecular network composed of interconnected constituents derived from halogenated nickel tetraphenylporphyrin on Au(111). We report that the π-extended two-dimensional material exhibits dispersive electronic features. Concomitantly, the functional Ni cores retain the same single-active site character of their single-molecule counterparts. This opens new pathways when exploiting the high robustness of transition metal cores provided by bottom-up constructed covalent nanomeshes.

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.

Guiding of the phase separation of a block copolymer (BCP) by an electric field perpendicular to the substrate is investigated in order to obtain vertical structures that can provide a mask for subsequent etching. Because of practical aspects, the substrate is bare Si without any neutral brush and the process time is limited to 1 h. A polystyrene-block polymethylmethacrylate lamellar material is employed in the study. For a unique guiding of the lamellar phase, an ordering mechanism orthogonal to the electric field is introduced by the interaction with the stamp in a thermal nanoimprint process. The naturally low surface energy of the stamp shall induce the formation of lamellae along the sidewalls of linear cavities. In order to fully utilize these two ordering mechanisms, the stamp sidewalls and the electric field, the imprint process is conducted in such a way that no residual layer remains below the stamp structures and the whole BCP is accumulated inside the cavities which are just partly filled. The electrically-assisted imprint process is studied analytically, considering the capacitive effects due to the local electric field in the cavity and in particular in the BCP. In addition, a numerical simulation is performed for the actual experimental conditions to compute the electric vector field in the BCP. In this way, an extensive understanding of the situation is gained which is the basis for choosing optimal experimental conditions for electrically-assisted thermal nanoimprint. Furthermore, the ambiguity of the electric field in a thermal nanoimprint process with partly filled cavities is addressed. The field shall induce vertical phase separation but, due to instabilities, it also may induce capillary bridges that represent replication defects. An improvement of the vertical phase separation by applying an electric field as high as 25 V/mu m could be identified under specific experimental conditions. However, the guiding effect within the cavities and thus the long-range order of the lamellae remained limited. This may be due to a field strength too low in the BCP; in the present configuration, higher field strengths are prohibited by an electrical breakthrough. Published by the AVS.

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.

Nanoelectrode arrays (NEAs) are increasingly applied for a variety of electroanalytical applications; however, very few studies dealt with the use of NEAs as an electrochemical generator of electrogenerated chemiluminescence (ECL). In the present study, arrays of nanodisc and nanoband electrodes with different dimensions and inter-electrode distances were fabricated by e-beam lithography on a polycarbonate layer deposited on boron-doped diamond (BDD) substrates. In particular, NEAs with 16 different geometries were fabricated on the same BDD sample substrate obtaining a multiple nanoelectrode and ultramicroelectrode array platform (MNEAP). After electrochemical and morphological characterization, the MNEAP was used to capture simultaneously with a single image the characteristic behaviour of ECL emission from all the 16 arrays. Experiments were performed using Ru(bpy)(3) (2+) as the ECL luminophore and tri-n-propylamine (TPrA) as the co-reactant. With a relatively limited number of experiments, such an imaging procedure allowed to study the role that geometrical and mechanistic parameters play on ECL generation at NEAs. In particular, at high concentrations of TPrA, well-separated individual ECL spots or bands revealed an ECL signal which forms a pattern matching the nanofabricated structure. The analysis of the imaging data indicated that the thickness of the ECL-emitting zone at each nanoelectrode scales inversely with the co-reactant concentration, while significantly stronger ECL signals were detected for NEAs operating under overlap conditions. Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3566]

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.

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 (

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.

This work focuses on the development of electrochemical impedance biosensors based on capacitance readout, for the detection of biomolecules in small sample volumes. We performed electrochemical impedance spectroscopy (EIS) measurements of DNA hybridization in electrochemical cells with microfabricated gold electrodes. The time stability of the device was tested in two different configurations: two microelectrodes in a microfluidic channel; two microelectrodes plus a reference electrode in an electrochemical cell. Our results demonstrate that the three-electrode setup is more stable, more reproducible, and suitable for real-time measurements. In the last part of the work we perform a test study of DNA hybridization in real time, and we show that the three-electrode configuration can measure the process in situ and in real time. (C) 2013 Elsevier B.V. All rights reserved.

To fabricate long lifetime polymer solar cells, understanding the fundamental aspects controlling the performances, stability and degradation of the devices is essential. In this study, we compare the chemical and electrical degradation behaviors of polymer solar cells based on active layers of semi-crystalline p-type polymer poly(3hexylthiophene) (P3HT) and different fullerene derivatives as acceptors. Photodegradation study by UV-visible and Fourier transform infrared (FTIR) spectroscopy and photovoltaic performance study by current-voltage measurement were done to understand and compare air stability of P3HT blended with different fullerenes. The used acceptors are indene-C(60) bisadduct (ICBA) and phenyl-C61-butyric acid methyl ester (PCBM). The obtained results show that solar cells fabricated from PCBM as acceptor are more stable than those based on ICBA. Based on the spectroscopic and electrical measurement results, it is safe to conclude that PCBM contributes more to stability of P3HT than ICBA, and that the degradation behavior is compatible with recently proposed mechanisms. Chemical properties of ICBA such as the low electron affinity could be responsible for the relative low stability of the device. (C) 2014 Elsevier B.V. All rights reserved.

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 exposed surface area of porous materials is usually determined by measuring the mass of adsorbed gas as a function of vapour pressure. Here we report a comprehensive study of adsorption in systems with closed bottom, not interconnected pores exhibiting different degrees of disorder, produced with methods encompassing nanolithography and dry and wet etching. Detailed adsorption studies of these matrices show hysteresis loops, as found always in pores having sizes of tens to hundreds of nanometres. The observed variations in the loop shape are associated with changes in the pore morphology. In regular pores formed by vertical and smooth walls, continuous adsorption is found for the first time in agreement with thermodynamic considerations valid for ideal pores. This suggests that irregularities in the walls and pore openings are the key factors behind the hysteresis phenomenon. Interestingly, pores having rough walls but a pyramidal shape also do not show any hysteresis.

Guidance molecules, such as Sema3A or Netrin-1, can induce growth cone (GC) repulsion or attraction in the presence of a flat surface, but very little is known of the action of guidance molecules in the presence of obstacles. Therefore we combined chemical and mechanical cues by applying a steady Netrin-1 stream to the GCs of dissociated hippocampal neurons plated on polydimethylsiloxane (PDMS) surfaces patterned with lines 2 mu m wide, with 4 mu m period and with a height varying from 100 to 600 nm. GC turning experiments performed 24 hours after plating showed that filopodia crawl over these lines within minutes. These filopodia do not show staining for the adhesion marker Paxillin. GCs and neurites crawl over lines 100 nm high, but less frequently and on a longer time scale over lines higher than 300 nm; neurites never crawl over lines 600 nm high. When neurons are grown for 3 days over patterned surfaces, also neurites can cross lines 300 nm and 600 nm high, grow parallel to and on top of these lines and express Paxillin. Axons - selectively stained with SMI 312 - do not differ from dendrites in their ability to cross these lines. Our results show that highly motile structures such as filopodia climb over high obstacle in response to chemical cues, but larger neuronal structures are less prompt and require hours or days to climb similar obstacles.

In this work the fabrication and characterization of boron-doped diamond (BDD) nanoelectrode arrays are discussed. The use of boron-doped diamond electrodes is very attractive due to advantageous properties including high reproducibility, stability, and robustness under extreme conditions, where conventional electrode materials may undergo severe erosion. BDD electrodes have also proved to be very useful because they show an extremely wide potential window in aqueous solutions without oxidation of the electrode itself. This allows electrochemical detection, at tiny background currents, of a number of substances that oxidize at very positive potentials, where other electrodic materials are not suitable. BDD based NEAs were prepared using Si < 100 > substrates coated with a layer of Boron doped diamond as macroelectrode. NEAs were obtained by creating an array of nanoholes by electron beam lithography (EBL) in a thin film of polycarbonate deposited on top of the macroelectrode. This approach leads to the formation of recessed nanoelectrodes. The parameters for using polycarbonate as a novel electron beam resist have been optimized and successfully used for fabrication of NEAs. The most interesting properties of this polymer for nanofabrication purposes are the high lithographic contrast, which allows the creation of structures of dimensions less than 100 nm; chemical stability, which guarantees a long-term use in electrochemical solutions and the possibility of functionalization with biological molecules (DNA and proteins). NEAs have been characterized with cyclic voltammetry and have provided voltammetric signals controlled by pure radial diffusion. The low background current of BDD added to the properties of NEAs indicate that this system can be applied for the development of sensors with high sensitivity. Polycarbonate surface of NEAs was successfully functionalized with small ss-DNA sequence, confirming the possibility of exploiting these systems as diagnostic biosensors. (C) 2013 Elsevier B.V. All rights reserved.

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.

Embryonic stem (ES) cell differentiation in specific cell lineages is a major issue in cell biology particu- larly in regenerative medicine. Differentiation is usually achieved by using biochemical factors and it is not clear whether mechanical properties of the substrate over which cells are grown can affect proliferation and differentiation. Therefore, we produced patterns in polydimethylsiloxane (PDMS) consisting of groove and pillar arrays of sub- micrometric lateral resolution as substrates for cell cultures. We analyzed the effect of different nanostructures on dif- ferentiation of ES-derived neuronal precursors into neuro- nal lineage without adding biochemical factors. Neuronal precursors adhered on PDMS more effectively than on glass coverslips. We demonstrated that neuronal yield was en- hanced by increasing pillars height from 35 to 400 nm. On higher pillar neuronal differentiation reaches � 80% 96 h after plating and the largest differentiation enhancement of pillars over flat PDMS was observed during the first 6 h of culture. We conclude that PDMS nanopillars accelerate and increase neuronal differentiation. Biotechnol. Bioeng. 2011;108: 2736-2746. 2011 Wiley Periodicals, Inc.

We have studied the composition profiles of Stranski–Krastanov InAs/GaAs quantum dots grown on patterned nanohole arrays. Two dimensional surface chemical maps obtained by X-ray photoemission electron microscopy reveal a non-uniform composition profile similar to that of standard dots grown on planar surfaces, with an enhanced In concentration at the center of the islands, with respect to the wetting layer. A statistical analysis, however, revealed an improvement of about 50% of dot composition uniformity associated with the already reported enhancement of size uniformity. No significant size or composition variation was found by changing the period of the hole pattern from 250 to 600 nm.

Ordered arrays of nanoelectrodes for electrochemical use are prepared by electron beam lithography (EBL) using polycarbonate as a novel e-beam resist. The nanoelectrodes are fabricated by patterning arrays of holes in a thin film of polycarbonate spin-coated on a gold layer on Si/Si(3)N(4) substrate. Experimental parameters for the successful use of polycarbonate as high resolution EBL resist are optimized. The holes can be filled partially or completely by electrochemical deposition of gold. This enables the preparation of arrays of nanoelectrodes with different recession degree and geometrical characteristics. The polycarbonate is kept on-site and used as the insulator that separates the nanoelectrodes. The obtained nanoelectrode arrays (NEAs) exhibit steady state current controlled by pure radial diffusion in cyclic voltammetry for scan rates up to approximately 50 mV s( - 1). Electrochemical results showed satisfactory agreement between experimental voltammograms and suitable theoretical models. Finally, the peculiarities of NEAs versus ensembles of nanoelectrodes, obtained by membrane template synthesis, are critically evaluated.

A positive tone resist for UV and X-ray lithography synthesized starting from an organically modified silicon alkoxide, bis(triethoxysilyl)benzene, through the sol–gel method, either in basic or in acid catalysis, is presented. Being directly photo-processable, the sol–gel system combines the opportunity to avoid the use of a sacrificial layer in the fabrication process, with the possibility to fit electro-optical and structural properties of the final device material to specific requirements. In addition, the positive tone behaviour allows to preserve the organic functionality of the system after irradiation. A study of the optical and structural modifications induced on the resist by irradiation has been carried out by FT-IR spectroscopy, UV–vis spectroscopy and spectroscopic ellipsometry. An interpretation of the mechanisms leading to exposed cross-linked film development is given. Experiments have demonstrated the possibility of obtaining structures on films with lateral dimensions spanning from the micron scale up to less than a hundred nm, opening the way to a possible exploitation of such positive tone functional system in the field of miniaturized sensors.

We propose fast nanoimprinting lithography (NIL) process based on the use of stamps with integrated heater. The latter consists of heavily ion implantation n-type doped silicon layer buried below the microstructured surface of the stamp. The stamp is heated by Joule effect, by 50 mu s 25 Hz repetition rate current pulses flowing in the conductive layer. Using this approach we have reproducibly imprinted areas of similar to 2 cm(2) within 16 s with residual layers in the range of few tens of nm. This result paves the way for processes in the sub-1 s timescale over large area surfaces. (C) 2008 Elsevier B.V. All rights reserved.

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.

One of the topics of the biomedical research is to design and develop new drug delivery systems able to perform time-controlled release of medicals with target specificity. Porous silicon, characterized by macropores of 2 mu m average diameter, with a 200 nm thick nanoporous coverage, was produced and its potential applications as drug-carrier were investigated. Doxorubicin loaded porous silicon bits exhibited a time-depending drug delivery profile that is in trend with the cytotoxicity of adenocarcinoma cancer cells exposed to bits. (c) 2006 Published by Elsevier B.V.

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.