**About the Editors**

**Ehrenfried Zschech** is Department Head for Microelectronic Materials and Nanoanalysis at the Fraunhofer Institute for Ceramic Technologies and Systems in Dresden, Germany, which he joined in 2009. His responsibilities include multi-scale materials characterization and reliability engineering. Ehrenfried Zschech received his Dr. rer. nat. degree from Technische Universitat¨ Dresden. After having spent four years as a project leader in the field of metal physics and reliability of microelectronic interconnects at Research Institute for Nonferrous Metals in Freiberg, he was appointed as a university teacher for ceramic materials at Freiberg University of Technology. In 1992, he joined the development department at Airbus in Bremen, where he managed the metal physics group and studied the laser-welding metallurgy of aluminum alloys. From 1997 to 2009, Ehrenfried Zschech managed the Materials Analysis Department and the Center for Complex Analysis at Advanced Micro Devices in Dresden. In this position, he was responsible for the analytical support for process control and technology development in leading-edge semiconductor manufacturing, as well as for physical failure analysis. He holds an adjunct professorship at Faculty of Chemistry of Warsaw University, Poland, as well as honorary professorships for Nanomaterials at Brandenburg University of Technology Cottbus and for Nanoanalysis at Technische Universitat Dresden. He has ¨ published three books and he has authored or co-authored more than 200 papers in peer-reviewed journals in the areas of materials science, solid-state physics and reliability engineering. Ehrenfried Zschech is a Member of the Board of Directors of the Materials Research Society (MRS), a Member of the Senate of the European Materials Research Society (E-MRS) and an Honorary Member of the Federation of the European Materials Societies (FEMS). In 2019, he was awarded the FEMS European Materials Gold Medal.

**Robert Sinclair** is the Charles M. Pigott Professor in the School of Engineering, in the Department of Materials Science and Engineering at Stanford University. He received his PhD in Materials Science from Cambridge University in 1972. He first worked as a Research Engineer at the University of California, Berkeley from 1973 to 1977, before joining the faculty of Stanford University in the Department of Materials Science and Engineering in 1977. He was the Department Chair from 2004 to 2014, and served as the Director of Stanford Nanocharacterization Laboratory from 2002 to 2013, as well as the Director of Bing Overseas Studies Program from 2010 to 2012. He is currently Charles M. Pigott Professor in the School of Engineering, and is the Director of the Wallenberg Research Link. Professor Sinclair's research interests include development and application of advanced transmission electron microscopy techniques, including aberration correction and in situ methods, studies of material and thin film reactions in energy-related materials, semiconductor processing, magnetic computer hard discs and nanomaterials for cancer detection. He was Chair of the National Research Council Committee on Smaller Facilities, the findings of which were published by the National Academy of Science in 2006 ("Mid-size Facilities: The Infrastucture of Materials Research"). Among his recent awards and honors are the Festschrift in honor of Robert Sinclair and Nestor Zaluzec, PICO 2017 Workshop (Germany); the John M. Cowley Distinguished Lecturer, at Arizona State University in 2015; the David Turnbull Lectureship of the Materials Research Society in 2012; the Distinguished Scientist Award (Physical Sciences), Microscopy Society of America in 2009.

**Rodrigo Martins**, President of the European Academy of Sciences; President of the International Union of Materials Research Societies; Full Professor at FCT-NOVA. Member of the:


Rodrigo Martins is the founder and director of the Centre of Excellence in Microelectronics and Optoelectronics Processes of Uninova; leader of the Materials, Optoelectronics and Nanotechnologies group of I3N/CENIMAT and its sub-director; member of the nomination committee of the EIT KIC Raw Materials, Editor in Chief of the journal *Discover Materials*. He is an expert in the field of advanced functional materials, nanotechnologies, microelectronics, transparent electronics (pioneer) and paper electronics (inventor), with more than 575 papers published in WoK; Member of the:

• Steering Committee of European Technology Platform for Advanced Engineering Materials and Technologies, EuMat.


Rodrigo Martins was decorated with the gold medal of merit and distinction by the Almada Municipality for his R&D achievements, in 2016. He received more than 18 international and national prizes and distinctions for his scientific work. ORCID: http://orcid.org/0000-0002-1997-7669: Webpage: https://cemop.uninova.pt/.

**Marco Sebastiani** is currently an associate professor of Materials Science at Roma Tre University, where he is also a lecturer of materials science and technology for aeronautical engineering. Currently, his major research efforts are in the fields of surface engineering, micro-device development, thin films and small-scale mechanical behaviour. The specific focus is on (a) Micro-scale residual stress analysis by a focused ion beam (FIB) approach, (b) Nano-mechanical characterization of advanced materials and devices using nanoindentation testing, (c) Nanostructured thin film modelling and production by physical vapor deposition (PVD) processes. He is one the editors of the international peer-reviewed journal *Materials & Design* (IF 6.3), reviewer for a wide range of international journals, and participant in European and national R&D projects (among which, the role of coordinator of the FP7 and H2020 large collaborative projects: iSTRESS, www.istress.eu and OYSTER, www.oyster-project.eu). Since 2014, he is actively involved in the most important European actions for promoting the access to advanced materials characterization tools for the manufacturing industry. In particular, he is a member of the Operational Management Board at the European Materials Characterization Council (EMCC, www.characterisation.eu). He is the co-author of more than 95 papers in ISI journals, with over 2300 citations and an h-index of 28 (http://orcid.org/0000-0002-9574-1578).

**Sabrina Sartori** is an associate professor at the Department of Technology Systems at University of Oslo. She studied physical chemistry at the University of Padova and graduated from University of Bologna in 2003 with a PhD degree in Materials Science and Engineering. She joined the University of Oslo in 2013, after working as a research scientist at the Institute for Energy Technology in Norway. Her research interests and expertise cover solid state physics and chemistry, including the synthesis of materials for hydrogen storage and batteries and their structure characterization via synchrotronand neutron-based methods at large-scale facilities. Sartori established and is leading the laboratory of solid-state synthesis, and the laboratory of energy storage systems at UiO, and is the responsible of the two years Master of science program "Renewable Energy Systems". She serves as an expert and leader in various committees, boards and initiatives, including at the International Energy Agency (IEA)—Hydrogen Implementing Agreement. She received several honors for her research activity in energy storage, for instance, the Feinberg Foundation visiting faculty program award. She organized several national and international events, for instance, as co-Chair of MRS Fall meeting 2020 in Boston.

*Editorial*

## **Editorial for the Special Issue "Characterization of Nanomaterials: Selected Papers from 6th Dresden Nanoanalysis Symposium"**

**Ehrenfried Zschech 1,\*, Robert Sinclair 2, Rodrigo Martins 3, Marco Sebastiani 4 and Sabrina Sartori 5**


Received: 10 October 2019; Accepted: 18 October 2019; Published: 27 October 2019

More than ever before, materials-driven product innovations in industry and shorter time-to-market introductions for new products require high advancement rates and a tight coupling between research, development and manufacturing. This approach, where scientists and engineers from industry and research institutes work together, includes sustained progress in materials science and engineering, and in materials and process characterization. Analytical techniques and respective tools, particularly to investigate nanomaterials, are considered to be fundamental drivers for innovation in industry.

This Special Issue "Characterization of Nanomaterials" collects nine selected papers presented at the 6th Dresden Nanoanalysis Symposium, held at Fraunhofer Institute for Ceramic Technologies and Systems in Dresden, Germany, on 31 August 2018. The Dresden Nanoanalysis Symposium was organized by the Dresden Fraunhofer Cluster Nanoanalysis (DFCNA), supported by the European Materials Research Society (E-MRS) and the European Materials Characterization Council (EMCC). Following the specific motto of this annual symposium "Materials challenges—Micro- and nanoscale characterization", it covered various topics of nanoscale materials characterization along the whole value and innovation chain, from fundamental research up to industrial applications. It brought about 100 scientists and engineers together from universities, research institutions, equipment manufacturers, and industrial end-users. New results in disruptive nanoanalysis techniques were reported in several talks and in the poster sessions, and novel solutions in the field of nanoscale materials characterization for process and quality control were shown.

The scope of this Special Issue is to provide an overview of the current status, recent developments and research activities in the field of nanoscale materials characterization, with a particular emphasis on future scenarios. Primarily, analytical techniques for the characterization of thin films and nanostructures [1–9] are discussed, including modeling and simulation [9]. Particular techniques for materials characterization are 3D time-of-flight secondary ion mass spectroscopy [1], in situ X-ray di ffraction [6] and electron backscatter di ffraction [8]. Several papers cover advanced nanostructured materials for future electronic devices and sensors [2,3,5,7]. In addition, degradation processes in battery electrodes [4] and the growth kinetics of intermetallic phases [8] are addressed. We anticipate this

Special Issue to be accessible to a wide audience, as it explores not only methodical aspects of nanoscale materials characterization, but also materials synthesis, fabrication of devices and applications.

The first paper describes the application of time-of-flight secondary ion mass spectroscopy (ToF-SIMS) in 3D microstructures, specifically so-called through-silicon vias, i.e., high-aspect ratio metal contacts needed for connecting 3D-stacked microchips [1]. This novel methodical approach provides several advantages compared to other frequently used techniques such as electron microscopy. The authors used data image slicing of the 3D ToF-SIMS analysis to study the uniformity of the silicon dopant concentration in atomic layer deposited (ALD) HfO2 thin films.

Barros et al. report on the role of structure and composition on the performances of p-type SnOx thin-field transistors (TFTs) with a bottom gate configuration deposited by radio frequency magnetron sputtering at room temperature, followed by a post-annealing step [2]. X-ray di ffraction (XRD) and Mössbauer spectroscopy allow the authors to identify the best phases/compositions and thicknesses (around 12 nm) to fabricate p-type TFTs. Moreover, the authors provide an overview that presents latest developments in SnO*x* TFT processing.

Studying multi-level resistive switching characteristics of a Cu2O/Al2O3 bilayer device, other authors found that an oxidation state gradient in copper oxide induced by the fabrication process plays a dominant role in defining multiple resistance states [3]. The highly conductive grain boundaries of copper oxide—an unusual property for an oxide semiconductor—are discussed for the first time regarding their role in the resistive switching mechanism.

The authors of paper [4] study materials aging in nickel manganese cobalt (NMC) oxides and related lifetime-reducing degradation processes in cathodes of lithium-ion batteries. Sieber et al. present an approach to recover NMC particles from lithium-ion battery cathodes while preserving their chemical and morphological properties, with a minimal use of chemicals. The key task was the separation of the cathode coating layer consisting of NMC, an organic binder, and carbon black, from the Al substrate foil. This can be performed in water under strong agitation to support the slow detachment process. The authors mitigate negative e ffects such as dissolving the Al substrate foil and Al(OH)3 precipitation using pH-adjusted solutions with su fficiently high bu ffer capacities.

Dobosz et al. study the oxide layer formed on the surface of the Ga–Sn–Zn eutectic alloy using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) [5]. The authors find that it is possible to obtain nanocrystalline oxide layers that contain about 90 at-% gallium with some additions of tin and zinc.

Another paper describes the synthesis of upconverter nanostructures composed of an yttrium oxide host matrix co-doped with ytterbium and europium, i.e., Y2O3:Yb<sup>3</sup>+/Eu3<sup>+</sup> [6]. These nanostructures were characterized by X-ray di ffraction (XRD), scanning transmission electron microscopy (STEM) and scanning electron microscopy (SEM). The acetic-based nanostructures result in nanosheets with a thickness of about 50 nm, while hydrochloric and nitric-based ones result in sphere-shaped nanostructures.

Carvalho et al. report about printed and flexible inorganic electrolyte-gated transistors (EGTs) on paper, with a channel layer based on interconnected zinc oxide (ZnO) nanoparticles [7]. The ZnO nanoparticles were dispersed by ethyl cellulose (EC), an eco-friendly binder. Fully printed devices on glass substrates using a composite solid polymer electrolyte as gate dielectrics exhibit a saturation mobility above 5 cm<sup>2</sup> V−<sup>1</sup> s<sup>−</sup><sup>1</sup> after annealing at 350 ◦C. The authors optimize the nanoparticle content in the ink, resulting in the formation of a ZnO channel layer at a maximum annealing temperature of 150 ◦C, which is compatible with paper substrates.

The reactivity and kinetics of intermetallic phase growth in the Ni/Al/Ni system for nickel substrates while varying size and shape of the Ni grains are studied by Kwiecien et al. [8]. The sequence of the formation of particular intermetallic phases is determined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and electron backscattered di ffraction (EBSD) as well as transmission electron microscopy (TEM).

Finally, this Special Issue features a study of the influence of nanoscale residual stress depth gradients on the nanomechanical behavior and adhesion energy of aluminum nitride (AlN) and Al/AlN thin films sputtered on a (100) silicon substrate [9]. Using a focused ion beam (FIB) incremental ring-core method, the residual stress depth gradient is assessed in the films. The adhesion energy was then quantified using a nanoindentation-based model. The authors show that an additional Al bond layer and inhomogeneous residual stresses increase the tensile stress at the coating/substrate interface and, consequently, negatively affect the adhesion of AlN to a substrate such as silicon.

The papers collected here reflect the existing widespread interest in materials characterization for materials research, development, and innovation, but also for process and quality control in industry, and provide an insight particularly into the directions in which new developments in characterization techniques are currently headed. In this Special Issue, material transitions that are necessary to improve the performance and to maintain the reliability of products for applications in microelectronics and energy storage are highlighted.

As lively discussed and consistently found during the symposium, research and development in materials characterization techniques are increasingly needed for modern materials science, for innovation in high-tech branches and to guarantee the functionality, performance and reliability of advanced products. We hope that this Special Issue will stimulate fruitful discussions and co-operation between experts in academia and industry, who are working in the field of advanced materials characterization.

**Author Contributions:** All authors contributed to the editorial.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
