Nanotechnology VIII

The "internet of everything" envisions trillions of connected objects loaded with high-bandwidth sensors requiring massive amounts of local signal processing, fusion, pattern extraction and classification. From the computational viewpoint, the challenge is formidable and can be addressed only by pushing computing fabrics toward massive parallelism and brain-like energy efficiency levels. CMOS technology can still take us a long way toward this goal, but technology scaling is losing steam. Energy efficiency improvement will increasingly hinge on architecture, circuits, design techniques such as heterogeneous 3D integration, mixed-signal preprocessing, event-based approximate computing and non-Von-Neumann architectures for scalable acceleration.

Synthesis routes and optical investigations of highly fluorescent metal halide perovskite nano-platelets with controllable thickness down to one monolayer are reported [1-3]. Quantum size effects lead to drastic blue-shifts of the photoluminescence (PL) and of the excitonic onset for absorption. Exciton binding energies up to 300 meV are found which depend on the number of monolayers present in the respective nano-platelets. The radiative emission rates of these two-dimensional colloidal semiconductors are found to depend on thickness and temperature in a similar way as known for III-V quantum wells.

One of the building blocks in nanomaterials are nanowires. In this talk, we present two kind of morphologies based on them. The common feature of both morphologies is an oxide nanowire, with either modulated diameter or with nanocrystallites attached to the axis. Zn2GeO4 and Ga2O3 nanowires are the main axis. We study the shape evolution of the nanostructures by the suitable modification of the growth parameters. Structural and chemical characterization were performed by electron microscopy techniques and Raman spectroscopy. The results shed light on the understanding of the driving mechanisms that lead to the formation of complex oxide nanostructures.

Cavity structures supporting Whispering Gallery Modes (WGMs), such as nanodisk, nano-ring and –tube, has been suggested and used to fabricate low threshold micro and nanolaser. We used Displacement Talbot Lithography and inductively coupled plasma dry-etching to fabricate highly uniform arrays of InGaN/GaN nanotube LED structures on sapphire. The nature of the resonances observed in single nanotubes is compared with Finite different time domain modelling and ascribed to a combination of Whispering Gallery and Fabry-Perot modes. An in-depth, comprehensive study on the design and the fabrication of nanotube structures for WGMs based laser will be presented.

AlxGa1-xN nanowires grown by molecular beam epitaxy on Si (111) substrate, were implanted with Eu ions (fluence of 1×1014 Eu/cm2) at room temperature with a tilt of 45°. The as-implanted samples containing Al, were further submitted to rapid thermal annealing treatments in nitrogen for 30 seconds, at two temperatures 1000°C and 1200 °C, while the GaN samples were only annealed at 1000 °C. The Eu3+ luminescence was observed in all samples with the most intense emission assigned to the 5D0 - 7F2 transition, indicating that such implantation and annealing conditions successfully activated the Eu ions and efficiently recovered the crystal.

Implementation of templated polystyrene (PS) nanoparticles as an etching mask to produce silicon nanowires (SiNWs) are described. Lithographically prepared thin microstructures were then realized to define nanofabrication area. With PSS/PDDA/PSS layer, ~82% of the substrate was covered by long-range ordered PS nanoparticles. Furthermore, the spin coating parameters in relation to the hexagonal close-packed (hcp) percentage of nanoparticles were investigated. Depending on O2 plasma parameter, precise control of particle diameter and roughness can be determined. As a result, high-density SiNWs (~107/cm²) with diameter down to 146 ± 7 nm were realized by cryogenic dry etching.

The growing demand for faster communications technologies and the inherent limitations of electronic integrated circuits stimulated the research of nanophotonic components accompanied by the urgent need for nanoscale light sources. The demonstration of laser emission from single semiconductor nanowires makes them interesting to accomplish these demands in generating highly localized intense monochromatic light as they mark the lower size limit of photonic laser systems. High quality II-VI semiconductor nanowires consisting of zinc oxide (ZnO) emit in the ultraviolet spectral range acting as Fabry-Pérot laser resonators with the capability of achieving modulation speeds in the single ps regime due to ultrafast carrier thermalization and gain recovery [Nat. Phys. 10, 870 (2014)]. However, the fundamentally coupled angular emission and light-matter interaction of the nanowire device depend on the operating transverse laser mode, thus several optical measurement techniques and a combined FDTD and semiconductor Bloch equation approach [Phys. Rev. B 91, 159903 (2015)] are required for the investigation. The laser output originating out of the end facet of a single nanowire is detected “head-on”, while a double pump technique is applied to measure the laser dynamics. This measurements combined with the optical simulations prove mode switching from single transverse mode operation of the HE11 in thin ZnO NWs to an admixture of several transverse modes in thicker NWs at approximately 180 nm diameter. We furthermore predict that tapered nanowires starting with a diameter well in the multimode regime and ending in the single-mode regime show mode filtering with superior emission properties.

LEDs based on an architecture where a nanorod is embedded with a quantum well (QW) layer (a core-shell structure) provide multiple advantages over the planar devices found in most modern LED bulbs. It is critical for device performance that this layer is grown homogenously. This paper presents a study of the cathodoluminescence (CL) emitted from GaN-based structures where growth conditions during inclusion of an InGaN QW layer were varied. Spatially- and spectrally-resolved CL data allows for characterisation of emissions across a nanorod, in doing so demonstrating the ability to control InN incorporation in QWs grown on semi-polar and non-polar facets.

This project is devoted to the study of new hybrid organic/inorganic materials with suitable properties for immediate application in the actual lighting devices (LED and CFL in particular). The inorganic core is formed by Silica nanosized particles surrounded by triazine based compounds. Structurally, the organic shell will differ each other mainly for the termination group of the triazine core; the optical properties will change and can be tuned for different lighting application. The inorganic core are templated on silica nanoparticles, with different size and porous morphology to obtain a rigid and controllable structure. Optical characterization is presented on pristine organic compound and in the hybrid compounds. The phosphors have been be then inserted in commercial LED devices by drop casting and spin coating and specific degradation tests as a function of temperature and time are performed.

The application of the scanning electron microscopy techniques of electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and cathodoluminescence (CL) to the understanding of the structural and luminescence properties of a number of micropatterned and nanopatterned nitride structures will be described. ECCI and EBSD have been used to investigate the type, density and distribution of defects and the distribution of strain in patterned polar and semipolar GaN and in polar AlGaN illustrating the influence of defects and strain on luminescence properties. Our results illustrate that optimisation of patterning can be used to significantly reduce defect densities.

We proposed a new type of the methanol concentration sensor that may be integrated directly to the GaP nanostructured photocathode. Necessary attribute for this design is the possibility to make it compatible with p-type of semiconductor. This condition follows from the fact that photocathodes for the CO2 splitting are exclusively prepared from p-type of semiconductors. On the GaP substrate is deposited thin Pt supporting layer (100-200 nm thick).This layer is covered by 300 nm thick Nafion membrane that serves as proton filter. On the top of Nafion layer is deposited top Pt contact layer covered by thin nanostructured Pt layer.

This work will present the development of nanosensor systems comprised of electrode arrays with finger-widths closely related to the diameter (<100 nm) of gas sensitive structures based on Pt nanoparticle-functionalised tungsten oxide nanowires (NWs) synthesised in a single-step process via aerosol-assisted chemical vapour deposition (AACVD). Additionally, the results obtained from the test towards ethanol detection will be discussed.

Our group has developed volcano-structured double-gated field emitter arrays (FEAs), which can electrostatically focus electron beam. One of the good applications is a radiation tolerant compact image sensor which can be used in the Fukushima Daiich nuclear power plant. The image sensor using FEAs and a CdTe-based photoconductor has radiation tolerance beyond 1MGy. In the presentation, I will talk about the emission and focusing characteristics of the volcano-structured double-gated FEAs, and a radiation tolerant compact image sensor using FEAs and a CdTe-based photoconductor.

Si field emission (FE) cathodes are promising candidates for novel electron sources. We have fabricated a single ring-shaped Si ridge with a height of 15 µm and a radius of about 20 nm. The emitter was coated with a thin layer of diamond-like carbon (DLC) to lower the work function of the emitter and to improve the FE characteristics. The FE properties showed an emission current of 0.6 µA at 1 kV and a stable emission behavior with less current fluctuations and a long lifetime. The FE characteristics of samples with several concentrically ring-shaped ridges with or without DLC coating will be presented at the conference.

Li-Ion Batteries are used and built into different devices, which are operated at a variety of conditions like high temperatures, fast charging conditions or with high power. For a reliable anode, these conditions have to be tested. High temperatures reduce the capacity of a high performance silicon microwire anode drastically, but upon modifying the thermal capacity of the wires, the cycling capacity is re-established. Fast charging and discharging rates do not limit the capacity of these microwire anodes – they perform exceptionally good at high capacities independently of the C-rate. This is achieved by conditioning the SEI layer.

Segregation-enhanced self-assembling of metallic particles in the Kirkendall hollows of the SnO2 layer will be reported. A plasmonic-related optical sensing effect will then be presented for the selective detection of gases at 200-400 °C. Red- and blue-shifts of the plasmon-resonance peak due to the silver nanoparticles are monitored for different conditions of SnO2+Ag layer formation and gas exposure. The concept of plasmonic-based SnO2 sensors will be discussed in terms of the ability of metallic nanoparticles to hold plasmonic resonances and the possibility of space-limited heating of nanoparticles after relaxation of plasmonic excitations.

Investigating long-term corrosion of turquoise lead-potassium historic glass, we have detected micro and nano crystallites of orthorhombic KSbOSiO4 (KSS) in glass. We conclude that clusters of KSS precipitates give rise to internal glass corrosion: potassium as a dopant and antimony as an opacifier form KSS crystallites in the glass matrix; strain gives rise to glass cracking and formation of heterogeneous grains. The strain-induced diffusion of impurities, resembling internal gettering in the Si technology, explains changes in the glass color. The study may be important for predicting long-term stability of technical glasses as well as for synthesis of nano-KSS/glass composites.

NFFA-­Europe is a European open-­access resource for experimental & theoretical nanoscience that carries out comprehensive projects for multidisciplinary research at the nanoscale ranging from synthesis to nanocharacterization, to theory and numerical simulation. Advanced infrastructures specialized on growth, nano-­lithography, nano-­ characterization, theory and simulation and fine-­analysis with Synchrotron, FEL and Neutron radiation sources are integrated into a multi-­site combination to develop frontier research on methods for reproducible nanoscience research thus enabling European and international researchers from diverse disciplines to carry out advanced proposals impacting on science and innovation. NFFA-­Europe coordinates access to infrastructures on different aspects of nanoscience research that are not currently available at single specialized sites without duplicating specific scopes. Internationally peer-­reviewed approved user projects have access to the best suited instruments, competences and technical support for performing research, including access to analytical large scale facilities, theory and simulation and high-­ performance computing facilities. Access is offered free of charge to European users. Two researchers per user group are entitled to receive partial financial contribution towards the travel and subsistence costs incurred. The user access scheme includes at least two “installations” and is coordinated via a single entry point portal that activates an advanced user-­infrastructure dialogue to build up a personalized access programme with an increasing return on science and innovation production. NFFA-­Europe’s own research activity addresses key bottlenecks of nanoscience research: i.e. nanostructure traceability, protocol reproducibility, in-­operando nano-­manipulation and analysis, open data. (www.nffa.eu)

After decades of research and more than ten years of successful production in very high volumes Silicon MEMS microphones are mature and unbeatable in form factor and robustness. Audio applications such as video, noise cancellation and speech recognition are key differentiators in smart phones. Microphones with low self-noise enable those functions. Backplate-free microphones enter the signal to noise ratios above 70dB(A). This talk will describe state of the art MEMS technology of Infineon Technologies. An outlook on future technologies such as the comb sensor microphone will be given.

We describe the pioneering methods to create highly transparent CNT sheets by dry lamination from vertically alligned CVD forests of MWCNTs. Transparency can be further increased by converting CNT aerogels into locally collapsed meshs with micron scale oppenings by spraying Ag nanowires, which lowers sheet resistance to values of Rsh< 40 ohm/sq. such AgNW@CNT transparent sheets are deal interlayers in three terminal tandems of perovskite PV with polymeric OPV and/or inorganic solar cells. Examples of perovskite solar cell with transparent CNT and AgNW@CNT charge collectors will demonstrated the 3 D charge collection in the single junction perovskite calls, as both top laminated and bottom electrodes as well as interconnects in monolithic tandems of perovskite PV with other dissimilar materials PVs particularly with OPV and inorganic GaAs based PV. Our recent experimental results on study of photophysical processes in hybrid perovskites are briefly discussed: the fast spectroscopy of excitons, magnetic field effect on generation of correlated (e-h) pairs. Also Hall effect results, that allows to evaluate intrinsic charge carrier transport and direct measurements of mobility in these materials performed for the first time in steady-state dc transport regime. From these measurements, we have obtained the electron-hole recombination coefficient, the carrier diffusion length and lifetime. Hall carrier mobility reachs up to 60 cm2V-1s-1 in perovskite single crystals, carrier lifetimes of up to 3 ms , and carrier diffusion lengths as long as 650 microns (huge if compared to organic and even best inorganic materials). Our results demonstrate that photocarrier recombination in these disordered solution-processed perovskites is as weak as in the best direct-band inorganic semiconductors, microscopically justifying high efficiency of perovskite PV. We show that nanoimprinting can further improve the performance of perovskite photodetectors and optoelectronic devices due to higher crystallinity, better morphology and nanograting photonic crystal effects.

ZnS thin films prepared on quartz substrates by the chemical bath deposition (CBD) method with three type temperature profile processes have been investigated by XRD, SEM, EDX, and light transmission. One is a 1-step growth process, and the other is 2-step growth and self-catalyst growth processes. The surface morphology of CBD-ZnS thin films prepared by the CBD method with the self-catalyst growth process is flat and smooth compared with that prepared by the 1-step and 2-step growth processes. The self-catalyst growth process in order to prepare the particles of ZnS as initial nucleus layer was useful for improvement in crystallinity of ZnS thin films prepared by CBD.

Ge/Si(001) granular films with grain sizes of several nanometers form during MBE at 300K. Short-term annealings at 600°C form Ge/Si(001) heterostructures consisting of WL and Ge drops; pyramids and domes do not appear; c(4×2)+p(2×2) WL reconstruction typical to low-temperature MBE forms. Long-term annealing removes Ge drops: the cluster sizes increase, their density drops. WL reconstruction changes to c(4×2) typical to high-temperature MBE. Platinum silicide resistivity becomes important as film thickness reaches units of nanometers. Pt3Si resistivity is the lowest among Pt silicides. We present formation of Pt3Si/Pt2Si films at 300K on poly-Si using Pt magnetron sputtering and wet etching.

Fluorescence microscopy devices and components require stability high stability and repeatability. We present materials, microfabrication, and metrology methods for a calibration tool, which serves as a reference with excellent homogeneity. The reference is a polymer and fluorophore formulation, which was spin coated on standard silicon and glass substrates. The materials presented comprise poly(methyl methacrylate) with embedded fluorescent surface modified core-shell quantum dots. The results, evaluated through thickness distribution and fluorescence response measurements, show film thickness variation <5% and homogeneous fluorescence response. No evidence of agglomerations was seen on SEM analysis of the composite films, even when fabricated without dispersion promoters.

Complex nano-features are patterned in resist via multiple exposures and lateral displacement using Displacement Talbot Lithography. Results shows bowtie and dashes were obtained. Sub 100nm patterning of complex structures and lift-off process will be demonstrated.

We report on fabrication of GaN multilayer porous structures by means of electrochemical etching and demonstrate the feasibility of Bragg reflectors based on these structures. The multilayer porous structures have been investigated by micro-reflectivity measurements to assess their suitability for distributed Bragg reflector applications. The experimentally measured reflectance spectra were calculated by using a Transfer Matrix technique with three fitting parameters, namely the volume fraction of GaN in the porous layer, the porous GaN layer thickness, and the GaN buffer layer thickness. The deduced parameters were compared to those found from scanning electron microscopy and capacitance-voltage carrier concentration profiling.

Fast solidification of SiGe alloy layers leads to constitutional supercooling in the melt near the front of crystallization which then results in faceting of the liquid-solid interface followed by formation of nano-cellular structure. Faceting of the interface depends strongly on SiGe alloy composition and on the velocity of melt-solid interface (solidification rate). The following issues are shortly reviewed: Segregation of Ge to nanometer-scale cellular network and islands: effect of SiGe composition and crystallization velocity; Pulsed laser modification of Ge and GeSn nanodots; Laser-induced melting and recrystallization of polycrystalline Ge layer.

Irradiation of high resistivity p-like CdTe crystals pre-coated with an In dopant film from the CdTe side by nanosecond laser pulses with wavelength that is not absorbed by the semiconductor made it possible to directly affect the CdTe-In interface because radiation was strongly absorbed by a thin layer of the In film adjoining to the CdTe crystal. The doping mechanism was associated with the action of laser-induced stress wave which was generated under extreme conditions in the confined area at the CdTe-In interface under laser irradiation. The developed technique allowed avoiding evaporation of In dopant and resulted in the formation of the In-doped CdTe region and thus, creation of a built-in p-n junction. The temperature distribution inside the three layer CdTe-In-Water structure was calculated and correlations between the characteristics of the fabricated In/CdTe/Au diodes and laser processing conditions were obtained.

Connecting metals reliable with different corrosion potential is a well-known challenge. An extreme example are copper aluminum contacts. Galvanic corrosion occurs if the two different metals are in contact with each other and an electrolyte. The recently described process of nanoscale sculpturing [1] offers an alternative. The nanoscale sculpturing approach is carving out the most stable grains and planes by chemical or electrochemical treatment. Aluminium sample surfaces including alloys like AA575 exhibit afterwards single crystalline surface facets covered with nanoscale stable oxide films. Galvanically deposited copper forms extremely reliable interlocked connections on top, even enabling soldering on top.

Optical properties of two-electron prism-shaped quantum dash have been considered. The dependence of ground-state energy and Coulomb electron-electron interaction energy correction on the QD size is studied. The ground-state energy value estimations using the Heisenberg uncertainty relationship have been done by the minimization of the energy expression for two electrons. The correlation function approach is used to obtain ground state two-electron wave function. The two-electron optical absorption has been studied. The state exchange time control in quantum dash taking into account the spins of the electrons in the Russell-Saunders approximation is researched.

A selective and sensitive electrochemical biosensor was developed for Cp detection using a Cp-specific recognition aptamer. The proposed nanoaptasensor was based on a glassy carbon electrode modified with diazonium-functional multiwall carbon nanotubes. The aptamer was linked onto the electrode surface, via electrochemical approach, followed by chemical immobilization of aminated-aptamer. Each fabrication steps was accompanied by changes to the electrochemical parameters. The binding of Cp to aptamer was monitored using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The calibration curve for Cp concentration was linear at 2.0×10-2 to 80.0 ng mL-1 with detection limit of 1.7 pg mL-1. The fabricated aptasensor can serve as a powerful sensor for rapid diagnosis of Cp in human serum sample.

The resonant tunneling transport in ZnBeSe/ZnSe/ZnBeSe symmetric and asymmetric double-barriers resonant tunneling diodes (RTD) is investigated numerically. It is shown that the characteristics of the transport are sensitive to the potential barrier height and width. It is found that the peak-to-valley ratio (PVR) of symmetric RTD structure is 4.16 @ 0.21-0.22 V at 150 K, and could be optimized by employing asymmetric ZnBeSe quantum barriers with different heights. It is found that the ZnSe/Zn0.85Be0.15Se/ZnSe/ Zn0.8Be0.2Se/ZnSe asymmetric RTD structure has an extraordinarily high PVR ratio of 7.82 @ 0.17-0.175 V, which is of significant advantage for highest-frequencies, including terahertz ranges.

In this report we describe our recent results in ultrafast (femtoseconds and picoseconds) pulsed laser patterning of carbon nanomaterials (single layer graphene, graphene oxide (GO) film, carbon nanotubes). We investigated such effects of nonlinear optical interaction like selective laser ablation of graphene, laser reduction of graphene and local functionalization (oxidation) of graphene based on multiphoton absorption for microelectrode patterning.

Due to their magnetic properties, low equilibrium temperature and biocompatibility, Fe-Cr-Nb-B-particles could have potential applications in magnetic hyperthermia. To this end, magnetic particles were prepared by high energy ball milling in sodium oleate of amorphous ribbons using a Retsch200 planetary ball mill. A ferrofluid based on Fe67.2Cr12.5Nb0.3B20 particles with low Curie temperature was prepared by dispersing the obtained particles, which have dimensions under 100 nm, in a calcium gluconate solution. By applying an alternating magnetic field of 41 mT with a frequency of 185 kHz, the temperature of the ferrofluid increases up to 47°C which makes it suitable for magnetic hyperthermia.

In this work has presented a novel strategy to carry out direct and sensitive determination of Tecfidera in complex matrices based on the L-cysteine/Nano chitosan modified GCE. This structure was characterized by AFM, TEM and FT-IR spectrometry. EIS of Ferri/Ferro cyanide was used as a marker to probe the interface and as a redox probe to determine Tecfidera. The fabricated electrochemical sensor showed good electrochemical response towards Tecfidera. Under the optimized conditions, the calibration curve was linear from 0.002 to 7.00 nM with the D.L. of 0.841 pM. The practical analytical performance of the sensor was examined by evaluating the selective detection of Tecfidera in biological fluids and pharmaceutical samples.

The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN) semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN.

Silver nanoparticles were synthesized by a direct method using aqueous silver nitrate and two different leaf extracts (Ocimum gratissimum and Vernonia amygdalina). The structure and morphology of the resulting nanoparticles were studied using UV-Vis, DLS, XRD, TEM and AFM.. While the conventional method gave nanoparticles whose sizes and shapes were dependent on the concentration of the precursor materials used, the faster electrodeposition method produced nanostructures whose sizes and shapes were more uniform and dependent on the leaf extract used as well as the deposition conditions controlling the rate of silver growth on the substrate used.

Diatoms (Bacillariophyceae) are the most species-rich group of algae, they are single-celled (2-200 micrometers) characterized by a silicified cell wall called a frustule that consists of two parts called thecae. The shapes of diatoms are diverse and have a wide variety of morphological features like striae and areolae. Diatoms are a promising system for the green synthesis of nanomaterials like metallic nanoparticles (NPs). In this work, we examined the formation of silver NPs (AgNPs) by the diatom P. tricornutum cultivated under ambient conditions in the presence of silver ions.

Quantum technology field is urging for efficient light sources at telecom wavelengths suitable to deliver entangled photons. Quantum dots based on InAs/InP hold the promise to deliver such photons at 1550 nm. However, available growth techniques cannot achieve small exciton fine structure splittings and incorporation in high quality optical microcavities. We show that quantum dots grown by droplet epitaxy can address both these issues due to the strain independent growth process, and are readily suitable for the generation of entangled photons at telecom wavelengths and future application in quantum networks based on existing fibre optics infrastructure.

Establishing a reliable bidirectional communication interface between the nervous system and electronic devices is crucial for exploiting the full potential of neural prostheses. Despite recent advancements, current microelectrode technologies evidence important shortcomings, e.g. challenging high density integration, low signal-to-noise ratio, poor long-term stability, etc. Thus, efforts to explore novel materials are essential for the development of next-generation neural prostheses. Graphene and graphene-based materials possess a rather exclusive set of physicochemical properties holding great potential for biomedical applications, in particular neural prostheses. In this presentation, I will provide an overview on fundamentals and applications of several graphene-based technologies and devices aiming at developing an efficient bidirectional communication with electrogenic cells and nerve tissue. The main goal of this talk is to discuss pros and cons of graphene technologies for bioelectronics and neuroprosthetics, and at the same time to identify the main challenges ahead.