Functional nanocomposites and organic thin films tailored on the nanoscale via vapor phase deposition

by Prof. Dr. Franz Faupel, Chair for Multicomponent Materials, Faculty of Engineering, Kiel University March 18, 2021, 10:00 a.m. EDT and 3:00 p.m. CET.

Abstract: Highly filled particulate metal-dielectric nanocomposites films have unique functional properties with hosts of applications. To explore collective interactions between the particles, we control the particle separation on the nm scale by employing vapor phase deposition, which is a scalable approach permitting, inter alia, excellent control of the filling factor. For polymer films, we have recently used initiated chemical vapor deposition (iCVD) to avoid decomposition of the functional groups, e.g. in highly stable electrets for electret microphones and magnetoelectric sensors,1 3D superhydrophobic coatings,2 and nanoscale gradient copolymers.3 The nanoparticles can form during co-deposition via self-organization or by means of high-rate gas aggregation cluster sources, which provide independent control of filling factor and size. Formation of plasmonic nanoparticles can be monitored in situ via UV-vis spectroscopy. We also demonstrated in situ control of the composition of alloy nanoparticles and the ability to fabricate multiple core-shell particles.

Recent examples of nanocomposites range from plasmonic meta-materials through photoswitchable devices to memristors and memsensors for neuromorphic electronics.4,5 We also developed a new process for photocatalytic growth of needle-like metallic nanostructures.6 Research on layered magnetoelectric sensors will be touched only briefly.7

[1]       M. Mintken, M. Schweichel, S. Schröder, S. Kaps, J. Carstensen, Y. K. Mishra, T. Strunskus, F. Faupel, R. Adelung. Nanogenerator and piezotronic inspired concepts for energy efficient magnetic field sensors. Nano Energy 2019, 56:420.

[2]       O.C. Aktas, S. Schröder, S. Veziroglu, M.Z. Ghori, A. Haidar, O. Polonskyi, T. Strunskus, K. Gleason, F. Faupel. Superhydrophobic Surfaces: Superhydrophobic 3D Porous PTFE/TiO2 Hybrid Structures. Adv. Mater. Interfaces 2019, 6:1970029.

[3]       S. Schröder, O. Polonskyi, T. Strunskus, Franz Faupel. Nanoscale gradient copolymer films via single-step deposition from the vapor phase. Materials Today 2020, 37:35.

[4]       M.H. Burk, S Schröder, W Moormann, D Langbehn, T. Strunskus, S. Rehders, R. Herges, F. Faupel. Fabrication of Diazocine-Based Photochromic Organic Thin Films via Initiated Chemical Vapor Deposition. Macromolecules 2020, 53:1164.

[5]       A. Vahl, N. Carstens, T. Strunskus, F. Faupel, A. Hassanien. Diffusive Memristive Switching on the Nanoscale, from Individual Nanoparticles towards Scalable Nanocomposite Devices. Sci. Rep. 2020, 9:1.

[6]       S. Veziroglu, A.L. Obermann, M. Ullrich, M. Hussain, M. Kamp, L. Kienle, T. Leißner, H.-G. Rubahn, O. Polonskyi, T. Strunskus, J. Fiutowski, M. Es-Souni, J. Adam, F. Faupel, O.C. Aktas. Photodeposition of Au Nanoclusters for Enhanced Photocatalytic Dye Degradation over TiO2 Thin Film, ACS Appl. Mater. Interfaces 2020, 12:14983.

[7]       B. Spetzler, C. Kirchhof, E. Quandt, J. McCord, F. Faupel. Magnetic Sensitivity of Bending-Mode Delta-E-Effect Sensors. Phys. Rev. Applied 2019, 12:064036.

Energy Harvesting from Ambient Vibrations and Magnetic Fields

by Dr. Ram Sri Ramdas, Assistant Research Professor of Materials Science and Engineering, Penn State January 28, 2021

Abstract: The low-power requirements of contemporary sensing technology attract research on alternate power sources that can replace batteries. Energy harvesters function as power sources for sensors and other low-power devices by transducing the ambient energy into usable electrical form. Piezoelectric harvesters have been demonstrating the preeminence in converting the mechanical energy in ambient vibrations and magnetic fields into electrical energy. Improving the performance of these harvesters is pivotal as the energy in the ambiance is innately low. In this talk I will focus on the design for effective transfer of energy from a source to harvesters, different methods of enhancing the performance of piezoelectric energy harvesters – multilayer and multistep, hybrid piezoelectric and electrodynamic configurations, and the key techniques for transducing stray magnetic fields into electricity using magnetoelectric composites.

Optimal absorption of energy from a vibration source entails the determination of absorber parameters that are obtained by minimizing the total energy absorbed by the system. The parameters are then used to design the energy harvesters that absorb ambient vibrations. Enhancing the performance of piezoelectric energy harvesters through a multilayer and, in particular, a multistep configuration that generates twice as much power from the same volume of the piezoelectric material will be discussed. The hybrid piezoelectric and electrodynamic energy harvesters achieving overall enhancement in power and their equivalent circuit representation for optimal power will be articulated. Although the power dependence on material, size, end-mass is discretely known, a method to delineate the contribution of each element to the power generated by the harvester could be valuable to optimally design the piezoelectric harvesters. I will discuss a scaling analysis performed on a piezoelectric unimorph harvester, which can easily be extended to any type of harvester, to identify the key factors. The stray magnetic fields around current-carrying wires and the high voltage power lines are the potential energy sources to generate electricity. The use of magnetoelectric (ME) composite consisting of piezoelectric and magnetostrictive layers coupled with magnetic tip mass can be a key technique to generate high power from low magnetic fields. Performance enhancement through flux concentration and distributed forcing architectures are also possible. The compact and optimized design of energy harvesters will accelerate the deployment of internet of things sensors and systems powered by ambient vibrations and magnetic fields.

Sensors to Sensor Systems

by Dr. Gerhard Schmidt, Faculty of Engineering, Kiel University December 14, 2020

Abstract: When measuring small magnetic fields as they appear in medical or biological applications, both, very small and very large signal amplitudes are observed at the same time. Small amplitudes stem, e.g., from human sources such as the human heart (magnetocardiography) or brain (magnetoencephalography). Low frequency signals (0.5 to 40 Hz) can be measured here with peak amplitudes of about 100 pT (heart) or even less than 1 pT (brain). Superposed to these small signals are usually large signal components that stem either from artificial sources, such as excitation signals utilized for modulation techniques, or from natural sources such as the magnetic field of the earth. Creating digital signals that can be used for detailed (medical) analyses is an interesting challenge for both, material scientists and engineers. Methods for improving the signal quality (mainly in terms of signal-to-noise ratio) can be grouped into analog and digital approaches, indicating whether they are performed prior or after the analog-to-digital (AD) conversion.

If sensors with a limited dynamical range are used in unshielded environments, additional coils can be used for creating a so-called anti field that cancels the magnetic field of the earth or other disturbing components. The driving (analog) currents of such coils can be generated adaptively using (digital) hardware. In the same manner, operation points can be stabilized. Furthermore, voltage adders can be used to cancel typical power supply distortions (50 or 60 Hz) or excitation signals that are required for modulation-based sensor read-out principles.

After the AD conversion so-called reference sensors can be used for recording signals that show a strong correlation with the disturbing but not with the desired signal component. Again, adaptive filtering techniques can be used to enhance the signal quality. However, such approaches are only successful if the analog amplifier followed by the AD converter are not saturated. Furthermore, often magnetoelectic sensors can be read out in a multitude of modes. This allows for adaptive combination of the individual signals, leading to improved robustness and better signal-to-noise ratio. In addition, several sensors can be combined and postprocessing such as digital noise suppression can be applied finally.

As a consequence, more “ingredients” than just the sensor are required for an entire sensor system. This leads to very interesting multidisciplinary research approaches. From sensors to sensor systems: it’s a rocky road.

First-Principles Discovery of Materials for Energy Conversion and Storage

by Dr. Ismaila Dabo, Associate Professor of Materials Science and Engineering at Penn State, November 25, 2020

Abstract: Materials innovations require considerable time and resources. This presentation will discuss the use of first-principles modeling for narrowing down the choice of candidate materials for target applications. The focus will be on producing hydrogen fuels photocatalytically by cleaving water molecules under solar illumination. An overview of the state of the art in electronic-structure calculations will be given and progress in overcoming the accuracy limits of these techniques will be discussed.

Strain and magnetic field sensing by magnetostrictive thin film sensors

by Dr. Dirk Meyners, Institute for Materials Science, Kiel University, October 28, 2020

Abstract: Magnetostrictive thin films transduce magnetic energy into mechanical energy or vice versa. Exploiting this property opens up new device concepts and applications. A prerequisite for the technical implementation, e.g. in highly sensitive sensors, is the compatibility of the different materials, often also the possibility of microsystem fabrication and the transfer of known concepts for magnetic thin-film systems into layer systems in the micrometer thickness range.

As a first example tunnel magnetoresistance junctions are considered. The targeted utilization of inverse magnetostriction enables highly sensitive strain gauges with gauge factors exceeding GF = 2000 [1]. They have application potential as miniaturized pressure sensors or deflection sensors in atomic force microscopes [2].

A second interesting example are magnetoelectric (ME) composites consisting of an amorphous magnetostrictive phase and a piezoelectric phase. Based on the strain-mediated ME coupling, magnetic field sensors can be realized which typically reach a detection limit ranging from 1 pT to several 100 pT [3]. Depending on the ME sensor concept, specific magnetic multi-layer systems are discussed in the view of magnetic noise suppression [4] and control of sensor operating point [5].

Halide Perovskite Crystal and Applied Physics for Photovoltaics

by Dr. Kai Wang, Assistant Research Professor at Penn State, September 29, 2020

Abstract: Halide perovskite emerges as promising photoactive candidates towards next-generation photovoltaic (PV) applications. This is closely related to the benign optoelectronic property and easy-processing of the material, and a high power conversion efficiency of the PV device. The talk will cover the general overview of this field, the challenges and thrusts for the transition towards industrialization, as well as the strategies to potentially address those current issues.

Controlling Cells by Structural and Mechanical Material Cues

by Prof. Dr. Christine Selhuber-Unkel, Heidelberg University Institute for Molecular Systems Engineering, August 27, 2020

Abstract: Cells are dynamic active systems that interact with their environments. Chemical, structural and mechanical properties of the extracellular matrix can control cell fate. Mimicking these properties of the extracellular matrix in responsive and bioinspired interfaces provides the opportunity to direct cellular properties by external cues. 3D microstructured hydrogel matrices can serve as bioinspired environments for controlling cells and particular their migration at several levels of complexity. This is not only relevant for generating 3D environments for cell growth in tissue engineering, but also for capturing pathogenic unicellular organisms.

Aeromaterials: Structuring Thin Films into 3D — from capacitors to cell templates

by Dr. Rainer Adelung, Professor of Materials Science and Engineering at Christian-Albrechts-University Kiel, July 30, 2020

Abstract: Thin film technology has pushed fascinating break through applications like microchip fabrication, medical technology or anti-reflection coatings. The presentation seeks to introduce the idea to bring the 2D thin film technology into 3D: Rolling up a thin film of nanoscopic thickness into a tube with a few micrometers in diameter, that is in space interconnected after a few tens of micrometers with other tubes pointing in different directions, will give you a relatively robust 3D tube network but with a weight in the scale of the ambient air and unusual physical properties. The talk will show that a simple sacrificial template approach can be used to realize these “aero structures”. Properties of this class of materials will be illustrated but not limited to aero carbon structures from graphene or carbon nanotubes [1], for applications like conductive silicone, energy materials  and cell templates as well as the fabrication of aero hexagonal boron nitride [2] that can be employed in optics as “artificial solid fog”.

[1] Nature Communications 8, 1215 (2017)

[2] Nature Communications 11, 1437 (2020)

Computation-Guided Discovery of Transparent Crystals with Ultrahigh Piezoelectricity

by Dr. Long-Qing Chen, Professor of Materials Science and Engineering and Professor of Engineering Science and Mechanics, Penn State, April 9, 2020

Piezoelectric crystals can generate electrical charge under an applied mechanical force and change shape under an applied electrical field. They have many applications in electromechanical devices such as ultrasonic transducers for medical imaging, actuators, etc. The piezoelectricity of a crystal is measured by the amount of strain that a crystal exhibits under an applied electric field or the amount of charge that a crystal generates under a stress. It has been a long-standing challenge to simultaneously achieve high piezoelectricity and light transparency in a crystal since the highest performance piezoelectric crystals are ferroelectrics containing high-density light-scattering domain walls within their domain structures. This presentation will discuss our recent computation-guided, rather surprising, discovery of simultaneous near-perfect light transparency and ultrahigh piezoelectricity in Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) crystals by understanding the ferroelectric domain evolution mechanisms under alternative current (AC) electric field poling using phase-field simulations. The newly discovered transparent ferroelectric crystals are expected to open up a range of electro-optical-mechanically coupled devices from high-throughput photoacoustic imaging to transparent actuators for haptic applications.

Thin Films for Piezoelectric Microelectromechanical Systems

by Dr. Susan Trolier-McKinstry, Professor of Materials Science and Engineering and Electrical Engineering, Penn State, February 17, 2020

Piezoelectric materials couple electrical and mechanical energies, and as such, offer an interesting platform to study numerous functional properties. Piezoelectric thin films are ubiquitous in filters and duplexers for cell phones and are of increasing interest in low voltage microelectromechanical systems (MEMS) for sensing, actuation, and energy harvesting. This talk will discuss how materials are optimized for these applications, as well as examples of the use of piezoelectric films over a wide range of length scales. The key figures of merit for resonators, actuators, and energy harvesting will be discussed, with emphasis on how to achieve these on practical substrates. Recent work on doped AlN for cell phone resonators will be reviewed. In addition, the roles of crystallographic orientation and domain state will be described for low voltage actuators and mechanical harvesters in thin films with the perovskite structure. Examples of integration into MEMS structures will also be discussed, including adaptive optics for X-ray telescopes, low frequency and non-resonant piezoelectric energy harvesting devices, inkjet printers, and ultrasound transducers for miniaturized medical diagnostics.

Thin Film Synthesis Activities in the Maria Group at Penn State

 by Dr. Jon-Paul Maria, Penn State, January 27, 2020

This presentation summarizes the research activities in the Maria group that involve thin film synthesis. The major categories include high mobility conducting oxides for IR plasmonic applications, reactive nanoaminates for chemical energy storage and propulsion, entropy stabilized oxides, high entropy transition metal carbines, and thin film explorations to find new functional materials. In all cases, research in the group endeavors to advance the science and understanding of synthesis in parallel to property engineering.