Publications

DAMDID/RCDL 2016, 706, 248-262 (2017)
Metadata for Experiments in Nanoscience Foundries
Metadata is a key aspect of data management. This paper describes the work of NFFA-EUROPE project on the design of a metadata standard for nanoscience, with a focus on data lifecycle and the needs of data practitioners who manage data resulted from nanoscience experiments. The methodology and the resulting high-level metadata model are presented. The paper explains and illustrates the principles of metadata design for data-intensive research. This is value to data management practitioners in all branches of research and technology that imply a so-called “visitor science” model where multiple researchers apply for a share of a certain resource on large facilities (instruments).
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Acta Biomaterialia 51, 21–52 (2017)
Controlling the morphology and outgrowth of nerve and neuroglial cells: The effect of surface topography
Unlike other tissue types, like epithelial tissue, which consist of cells with a much more homogeneous structure and function, the nervous tissue spans in a complex multilayer environment whose topographical features display a large spectrum of morphologies and size scales. Traditional cell cultures, which are based on two-dimensional cell-adhesive culture dishes or coverslips, are lacking topographical cues and mainly simulate the biochemical microenvironment of the cells. With the emergence of micro- and nano-fabrication techniques new types of cell culture platforms are developed, where the effect of various topographical cues on cellular morphology, proliferation and differentiation can be studied. Different approaches (regarding the material, fabrication technique, topographical characteristics, etc.) have been implemented. The present review paper aims at reviewing the existing body of literature on the use of artificial micro- and nano-topographical features to control neuronal and neuroglial cells’ morphology, outgrowth and neural network topology. The cell responses–from phenomenology to investigation of the underlying mechanisms- on the different topographies, including both deterministic and random ones, are summarized.
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Microelectron. Eng. 176, 75 (2017)
Fabrication of diamond diffraction gratings for experiments with intense hard x-rays
The demands on optical components to tolerate high radiation dose and manipulate hard x-ray beams that can fit the experiment requirements, are constantly increasing due to the advancements in the available x-ray sources. Here we have successfully fabricated the transmission type gratings using diamond, with structure sizes ranging from few tens of nanometres up to micrometres, and aspect ratio of up to 20. The efficiencies of the gratings were measured over a wide range of photon energies and their radiation tolerance was confirmed using the most intense x-ray source in the world. The fidelity of these grating structures was confirmed by the quality of the measured experimental results.
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Microelectron. Eng. 177, 25 (2017)
Systematic efficiency study of line-doubled zone plates
Line-doubled Fresnel zone plates provide nanoscale, high aspect ratio structures required for efficient high resolution imaging in the multi-keV x-ray range. For the fabrication of such optics a high aspect ratio HSQ resist template is produced by electron-beam lithography and then covered with Ir by atomic layer deposition (ALD). The diffraction efficiency of a line-doubled zone plate depends on the width of the HSQ resist structures as well as on the thickness of the deposited Ir layer. It is very difficult to measure these dimensions by inspection in a scanning electron microscope (SEM) without performing laborious and destructive cross-sections by focus ion beams (FIB). On the other hand, a systematic measurement of the diffraction efficiencies using synchrotron radiation in order to optimize the fabrication parameters is not realistic, as access to synchrotron radiation is sparse. We present a fast and reliable method to study the diffraction efficiency using filtered radiation from an x-ray tube with a copper anode, providing an effective spectrum centered around 8 keV. A large number of Fresnel zone plates with varying dimensions of the resist structures and the ALD coating were measured in an iterative manner. Our results show an excellent match with model calculations. Moreover, this systematic study enables us to identify the optimum fabrication parameters, resulting in a significant increase in diffraction efficiency compared to Fresnel zone plates fabricated earlier without having feedback from a systematic efficiency measurement.
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Nanoscale , 8 , 16197 (2016)
Spatial non-uniformity in exfoliated WS 2 single layers
Monolayers of transition metal dichalcogenides (TMDs) are atomically thin two-dimensional crystals with attractive optoelectronic properties, which are promising for emerging applications in nanophotonics. Here, we report on the extraordinary spatial non-uniformity of the photoluminescence (PL) and strain properties of exfoliated WS2 monolayers. Specifically, it is shown that the edges of such monolayers exhibit remarkably enhanced PL intensity compared to their respective central area. A comprehensive analysis of the recombination channels involved in the PL process demonstrates a spatial non-uniformity across the monolayer’s surface and reflects on the non-uniformity of the intrinsic electron density across the monolayer. Auger electron imaging and spectroscopy studies complemented with PL measurements in different environments indicate that oxygen chemisorption and physisorption are the two fundamental mechanisms responsible for the observed non-uniformity. At the same time Raman spectroscopy analysis shows remarkable strain variations among the different locations of an individual monolayer, however such variations cannot be strictly correlated with the non-uniform PL emission. Our results shed light on the role of the chemical bonding in the competition between exciton complexes in monolayer WS2, providing a method of engineering new nanophotonic functions using WS2 monolayers. It is therefore envisaged that our findings could find diverse applications towards the development of TMD-based optoelectronic devices.
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J. Vac. Sci. Technol. B 34, 06K702 (2016)
Comparative study of resists and lithographic tools using the Lumped Parameter Model
A comparison of the performance of high resolution lithographic tools is presented here. The authors use extreme ultraviolet interference lithography, electron beam lithography, and He ion beam lithography tools on two different resists that are processed under the same conditions. The dose-to-clear and the lithographic contrast are determined experimentally and are used to compare the relative efficiency of each tool. The results are compared to previous studies and interpreted in the light of each tool-specific secondary electron yield. In addition, the patterning performance is studied by exposing dense lines/spaces patterns, and the relation between critical dimension and exposure dose is discussed. Finally, the lumped parameter model is employed in order to quantitatively estimate the critical dimension of lines/spaces, using each tool specific aerial image. Our implementation is then validated by fitting the model to the experimental data from interference lithography exposures and extracting the resist contrast.
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Appl. Surf. Sci. 385, 145 (2016)
Patterning of diamond like carbon films for sensor applications using silicon containing thermoplastic resist (SiPol) as a hard mask
Patterning of diamond-like carbon (DLC) and DLC:metal nanocomposites is of interest for an increasing number of applications. We demonstrate a nanoimprint lithography process based on silicon containing thermoplastic resist combined with plasma etching for straightforward patterning of such films. A variety of different structures with few hundred nanometer feature size and moderate aspect ratios were successfully realized. The quality of produced patterns was directly investigated by the means of optical and scanning electron microscopy (SEM). Such structures were further assessed by employing them in the development of gratings for guided mode resonance (GMR) effect. Optical characterization of such leaky waveguide was compared with numerical simulations based on rigorous coupled wave analysis method with good agreement. The use of such structures as refractive index variation sensors is demonstrated with sensitivity up to 319 nm/RIU, achieving an improvement close to 450% in sensitivity compared to previously reported similar sensors. This pronounced GMR signal fully validates the employed DLC material, the technology to pattern it and the possibility to develop DLC based gratings as corrosion and wear resistant refractometry sensors that are able to operate under harsh conditions providing great value and versatility.
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