Blog

3
Jul

New Publication (Co-authorship): “Effects of processing parameters on 3D structural ordering and optical properties of inverse opal photonic crystals produced by atomic layer deposition” in International Journal of Ceramic Engineering & Science

A joined publication  “Effects of processing parameters on 3D structural ordering and optical properties of inverse opal photonic crystals produced by atomic layer deposition” led by Dr. Janßen and his reseach team within the framework of the SFB986  is accepted and now in an early-view-stage at International Journal of Ceramic Engineering & Science.

Abstract: Vertical convective self‐assembly has been extensively used for the preparation of direct photonic crystals, which can be later infiltrated with a more stable material, such as oxide ceramics, by atomic layer deposition. However, the relationship between the self‐assembly parameters of the direct photonic crystals and the optical properties of the inverse opal photonic crystals remains elusive. In this work, the effect of different experimental parameters on the 3D structure and defects density of polystyrene direct photonic crystals produced by vertical convective self‐assembly was assessed. Self‐assembly was investigated using deionized water as media with polymer particles’ concentrations up to 2 mg/mL, temperatures of 40, 50 and 80°C and relative humidity of 45, 70 and 90%. The 3D structure of the resultant direct photonic materials was characterized by the combination of scanning electron microscopy and image analysis, and their optical properties was assessed by reflectance measurements. These results were correlated with the performance of oxide‐based inverse opal photonic crystals produced by the controlled infiltration of the former direct photonic crystals by atomic layer deposition (ALD). It was found that the thickness increased with the concentration of polystyrene particles, while the photonic structure ordering is dependent on the synergy between humidity and temperature. Results also showed higher defects population with increasing evaporation temperature and decreasing relative humidity.

2
Jul

Nano-Bio-Electronics Seminar 02.07.2019 1:15 pm

25
Jun

New Publication: “Microwave-induced capacitance resonances and anomalous magnetoresistance in double quantum wells” in Journal of Applied Physics

Our new publication “Microwave-induced capacitance resonances and anomalous magnetoresistance in double quantum wells” has been published today in Journal of Applied Physics.

Abstract:

Magnetotransport measurements on electron bilayer systems under low frequency continuous microwave irradiation reveal an anomalous magnetoresistance behavior. At low total imbalanced carrier densities, pronounced features in the longitudinal and Hall resistance emerge that show a surprisingly strong sensitivity to frequency, microwave power, and density. We suggest its origin to be related to resonantly induced capacitance oscillations of the two-layer system.
29
May

Update – Cover Published – for Publication: Microscaffolds by Direct Laser Writing for Neurite Guidance Leading to Tailor-Made Neuronal Networks

Our paper “Microscaffolds by Direct Laser Writing for Neurite Guidance Leading to Tailor-Made Neuronal Networks” in Advanced Biosystems is now published including a cover image. 

Abstract: While modern day integrated electronic circuits are essentially designed in a 2D fashion, the brain can be regarded as a 3D circuit. The thus enhanced connectivity enables much more complex signal processing as compared to conventional 2D circuits. Recent technological advances in the development of nano/microscale 3D structuring have led to the development of artificial neuron culturing platforms, which surpass the possibilities of classical 2D cultures. In this work, in vitro culturing of neuronal networks is demonstrated by determining predefined pathways through topological and chemical neurite guiding. Tailor‐made culturing substrates of microtowers and freestanding microtubes are fabricated using direct laser writing by two‐photon polymerization. The first scaffold design that allows for site‐specific cell attachment and directed outgrowth of single neurites along defined paths that can be arranged freely in all dimensions, to build neuronal networks with low cell density, is presented. The neurons cultured in the scaffolds show characteristic electrophysiological properties of vital cells after 10 d in vitro. The introduced scaffold design offers a promising concept for future complex neuronal network studies on defined neuronal circuits with tailor‐made design specific neurite connections beyond 2D.

28
May

Nano-Bio-Electronics Seminar 04.06.2019 1:15 pm

28
May

New Publication (Co-authorship): “Time-Resolved Analysis of the Structural Dynamics of Assembling Gold Nanoparticles” in ACS Nano

A joined publication  “Time-Resolved Analysis of the Structural Dynamics of Assembling Gold Nanoparticles” led by Prof. Martin Trebbin’s group  is accepted and now in an early-view-stage at ACS Nano.

Abstract: The hydrophobic collapse is a structural transition of grafted polymer chains in a poor solvent. Although such a transition seems an intrinsic event during clustering of polymer-stabilized nanoparticles in the liquid phase, it has not been resolved in real time. In this work, we implemented a microfluidic 3D-flow-focusing mixing reactor equipped with real-time analytics, small-angle X-ray scattering (SAXS), and UV–vis–NIR spectroscopy to study the early stage of cluster formation for polystyrene-stabilized gold nanoparticles. The polymer shell dynamics obtained by in situ SAXS analysis and numerical simulation of the solvent composition allowed us to map the interaction energy between the particles at early state of solvent mixing, 30 ms behind the crossing point. We found that the rate of hydrophobic collapse depends on water concentration, ranging between 100 and 500 nm/s. Importantly, we confirmed that the polymer shell collapses prior to the commencement of clustering.

28
May

Nature Nanotechnolgy Highlighted our Graphene Paper (Phys. Rev. Lett. 122, 046403)

Our recent paper “Resonance Microwave Measurements of an Intrinsic Spin-Orbit Coupling Gap in Graphene: A Possible Indication of a Topological State” by J. Sichau, M. Prada, T. Anlauf, T. J. Lyon, B. Bosnjak, L. Tiemann, and R. H. Blick published in Physical Review Letters has been highlighted by Nature Nanotechnology (https://doi.org/10.1038/s41565-019-0409-y).

Abstract: In 2005, Kane and Mele [Phys. Rev. Lett. 95, 226801 (2005)] predicted that at sufficiently low energy, graphene exhibits a topological state of matter with an energy gap generated by the atomic spin-orbit interaction. However, this intrinsic gap has not been measured to this date. In this Letter, we exploit the chirality of the low-energy states to resolve this gap. We probe the spin states experimentally by employing low temperature microwave excitation in a resistively detected electron-spin resonance on graphene. The structure of the topological bands is reflected in our transport experiments, where our numerical models allow us to identify the resonance signatures. We determine the intrinsic spin-orbit bulk gap to be exactly 42.2μeV. Electron-spin resonance experiments can reveal the competition between the intrinsic spin-orbit coupling and classical Zeeman energy that arises at low magnetic fields and demonstrate that graphene remains to be a material with surprising properties.

24
May

Nano-Bio-Electronics Seminar 21.05.2019 1:15 pm

2
May

New Publication: “Resonant Tunneling Induced Enhancement of Electron Field Emission by Ultra-Thin Coatings” in Scientific Reports

Our new publication “Resonant Tunneling Induced Enhancement of Electron Field Emission by Ultra-Thin Coatings” has been published today in Scientific Reports.

Abstract: The emission of electrons from the surface of a material into vacuum depends strongly on the material’s work function, temperature, and the intensity of electric field. The combined effects of these give rise to a multitude of related phenomena, including Fowler-Nordheim tunneling and Schottky emission, which, in turn, enable several families of devices, ranging from vacuum tubes, to Schottky diodes, and thermionic energy converters. More recently, nanomembrane-based detectors have found applications in high-resolution mass spectrometry measurements in proteomics. Progress in all the aforementioned applications critically depends on discovering materials with effective low surface work functions. We show that a few atomic layer deposition (ALD) cycles of zinc oxide onto suspended diamond nanomembranes, strongly reduces the threshold voltage for the onset of electron field emission which is captured by resonant tunneling from the ZnO layer. Solving the Schroedinger equation, we obtain an electrical field- and thickness-dependent population of the lowest few subbands in the thin ZnO layer, which results in a minimum in the threshold voltage at a thickness of 1.08 nm being in agreement with the experimentally determined value. We conclude that resonant tunneling enables cost-effective ALD coatings that lower the effective work function and enhance field emission from the device.

20
Apr

Successful Participtaion at BMBF Call “ForLab”

Together with Prof. Hoc Khiem Trieu (TUHH)  and Prof. Wolfgang Hansen (CHyN, UHH) we successfully participated at the BMBF Call “Forschungslabore Mikroelektronik Deutschland (ForLab)”.

The delivery of two E-Beam Raith Voyager-AddOns and a new EVG wafer bonder are already scheduled for May. Our new III-V-ICP-RIE by SENTECH is going to be installed before summer.