Article
Chemistry, Multidisciplinary
Roberto Guido, Thomas Mikolajick, Uwe Schroeder, Patrick D. Lomenzo
Summary: Aluminum scandium nitride (Al1-x Sc x N) with large remanent polarization is attractive for high-density ferroelectric random-access memories. However, its cycling endurance is lower than other ferroelectric materials. Understanding the breakdown mechanism is crucial for improving memory reliability. Filaments formed due to impulse thermal process along defective pathways are proposed to play a role in the breakdown of Al1-x Sc x N ferroelectric capacitors. Stable bipolar filamentary resistive switching has been reported for the first time.
Article
Materials Science, Multidisciplinary
Georg Schoenweger, Md Redwanul Islam, Niklas Wolff, Adrian Petraru, Lorenz Kienle, Hermann Kohlstedt, Simon Fichtner
Summary: This letter reports on room temperature switchable ultra-thin (10 nm) ferroelectric Al0.72Sc0.28N films, which are important for potential applications in neuromorphic computing and memory devices. All-epitaxial Al0.72Sc0.28N/Pt heterostructures are grown by magnetron sputtering, and the Al0.72Sc0.28N film surface is protected by in situ Pt capping to avoid oxidation. The films exhibit good epitaxy and show only moderate scaling effects in terms of relative permittivity and coercive field dependence, suggesting that the critical thickness for ferroelectricity has not yet been reached.
PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS
(2023)
Article
Nanoscience & Nanotechnology
Aravind Krishnamoorthy, Subodh C. Tiwari, Aiichiro Nakano, Rajiv K. Kalia, Priya Vashishta
Summary: Scandium-doped aluminum nitride, Al1-x Sc (x) N, is a new class of displacive ferroelectric materials with high polarization and sharp hysteresis. The transition mechanism from unswitchable to switchable ferroelectrics relies on important atomic properties such as local structure and dopant distribution. Computational synthesis and characterization of Al1-x Sc (x) N reveal the impact of inhomogeneous scandium distribution on polarization reversal mechanisms.
Article
Nanoscience & Nanotechnology
Yunpeng Cai, Yishi Su, Kan Liu, Andong Hua, Xiaozhen Wang, He Cao, Di Zhang, Qiubao Ouyang
Summary: We propose a strategy to promote strength-ductility synergy in aluminum matrix composites by utilizing the microalloying effect of Sc. The addition of 0.2 wt% Sc significantly increases the fracture elongation of SiCp/Al-Cu-MgSc composite by 126%, resulting from the refinement of intergranular θ phase and the improvement of dislocation accumulation capability caused by the formation of intragranular θ' phase. Our work provides an accessible pathway consistent of high energy ball milling and microalloying of Sc to exploit aluminum matrix composites with advanced strength-ductility balance.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2023)
Article
Chemistry, Analytical
Niklas Wolff, Md Redwanul Islam, Lutz Kirste, Simon Fichtner, Fabian Lofink, Agne Zukauskaite, Lorenz Kienle
Summary: Research on wurtzite-type aluminum scandium nitride (Al1-xScxN) thin films revealed an anomalous thermal expansion at high temperatures, attributed to the coupling contributions of intrinsic and extrinsic factors. This finding is significant for the manufacturing and operation of Al1-xScxN-based devices.
Review
Chemistry, Multidisciplinary
Dong Hyun Lee, Younghwan Lee, Yong Hyeon Cho, Hyojun Choi, Se Hyun Kim, Min Hyuk Park
Summary: Ferroelectric materials are regarded as ideal for emerging memory devices due to their unique remanent polarization. However, the slow progress of ferroelectric memories is attributed to issues like the lack of CMOS-compatible and scalable materials. In recent years, the discovery of ferroelectricity in CMOS-compatible materials like (Hf,Zr)O-2 and (Al,Sc)N has sparked increasing interest. With advancements in material fabrication, a metastable polar phase and switchable polarization can be induced in these materials. However, challenges still exist for their use in emerging memory devices, which are comprehensively reviewed in this article.
ADVANCED FUNCTIONAL MATERIALS
(2023)
Article
Physics, Applied
Masato Uehara, Ryouichi Mizutani, Shinnosuke Yasuoka, Takao Shimizu, Hiroshi Yamada, Morito Akiyama, Hiroshi Funakubo
Summary: The ferroelectricity of wurtzite ScxGa1-xN was demonstrated, with high remanent polarization and adjustable coercive field. The concentration of Sc governed the coercive field in ScxGa1-xN and ScxAl1-xN, suggesting the polarization switching started in wurtzite unit cells containing Sc.
APPLIED PHYSICS EXPRESS
(2022)
Article
Materials Science, Multidisciplinary
Peng-Lin Wang, Hui-Qing Sun, Xiao Ding, Zhi-Hui Huang, Yuan Li, Fan Xia, Xiao-Yu Xia, Miao Zhang, Jian-Cheng Ma, Xiu-Yang Tan, Liang Xu, Zhi-You Guo
Summary: The RF performance of novel Sc-Doped GaN HEMTs with asymmetric air-bridge structure was analyzed using TCAD software. By utilizing an innovative design with an asymmetrical air bridge and ScAlN layer, significant improvements in transconductance and electron velocity, as well as a reduction in electron concentration, were achieved in the device. Additionally, the combined influence of the air bridge and scandium layer structure on capacitance and other parameters provides a useful approach for enhancing the DC and RF characteristics of GaN HEMTs.
RESULTS IN PHYSICS
(2021)
Article
Materials Science, Multidisciplinary
Mei Wang, Huating Bo, Aobo Wang, Zhengwang Cheng, Shengjia Li, Wei Zou, Jing He, Xinguo Ma
Summary: To adapt to the upgrading of wireless communication system, research on thin film bulk acoustic resonator (FBAR) has gained attention. This study focuses on the core functional layer, the piezoelectric film, particularly aluminum nitride (AlN) and scandium-doped AlN films, examining their characteristics and quality changes. The results show that doping with scandium significantly improves the uniformity, roughness, and stress of AlN films, making it promising for improving the performance of FBAR filters and device yield.
Article
Chemistry, Analytical
Zichen Tang, Giovanni Esteves, Jeffrey Zheng, Roy H. Olsson
Summary: Due to their favorable electromechanical properties, Aluminum Nitride (AlN) and Aluminum Scandium Nitride (Al1-xScxN) thin films have been widely used in radio frequency (RF) acoustic devices. However, the resistance to etching at high scandium alloying has hindered the realization of devices that can fully utilize the highest electromechanical coupling coefficients. In this study, the etch rates of AlN and Al1-xScxN with different scandium concentrations were investigated. The findings provide valuable insights for structure/composition analysis and potential applications.
Article
Nanoscience & Nanotechnology
Yang Yang, Stephen A. Hackney, Paul G. Sanders
Summary: Additions of Sc and Zr in the Al matrix offer significant strengthening potential at elevated temperatures due to the formation of coarsening resistant precipitates. The high-temperature properties of a supersaturated Al-0.4Sc-0.4Zr at% alloy were found to be superior to a dilute Al-0.06Sc-0.06Zr at% alloy, primarily due to the larger amount of solute resulting from rapid solidification. The deformation mechanism at elevated temperatures was identified as dislocation climb in both alloys, and the larger threshold stress in the supersaturated alloy was attributed to its unique microstructure.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2022)
Article
Nanoscience & Nanotechnology
Roberto Guido, Patrick D. Lomenzo, Md Redwanul Islam, Niklas Wolff, Maike Gremmel, Georg Schoenweger, Hermann Kohlstedt, Lorenz Kienle, Thomas Mikolajick, Simon Fichtner, Uwe Schroeder
Summary: The discovery of ferroelectricity in aluminum scandium nitride (Al1-xScxN) shows potential for technological applications in harsh environments and space-related memory applications. The high-temperature stability of piezoelectricity in aluminum nitride enhances the viability of this material. Through a combination of electrical and in-situ X-ray diffraction measurements, as well as transmission electron microscopy and energy-dispersive X-ray spectroscopy, the ferroelectric and material properties of 100 nm-thick Al0.72Sc0.28N have been studied up to 873 K. The findings demonstrate that Al0.72Sc0.28N can achieve high switching polarization and tunable coercive fields within a temperature range of 375 K from room temperature to 673 K.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Chemistry, Physical
V. N. Chuvil'deev, M. Yu Gryaznov, S. Shotin, V. Kopylov, A. Nokhrin, C. Likhnitskii, A. A. Murashov, A. A. Bobrov, N. Yu Tabachkova, O. E. Pirozhnikova
Summary: The study investigated the effect of Sc on the plasticity of ultrafine-grained Al-0.5%Mg alloys at elevated temperatures (from 300 to 500 degrees C) and strain rates (from 10(-3) to 10(-1) s(-1)), showing that the addition of 0.4% and 0.5% Sc can achieve high elongation to failure at 500 degrees C and 1.10(-1) s(-1) strain rate.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Chemistry, Multidisciplinary
Xiwen Liu, Dixiong Wang, Kwan-Ho Kim, Keshava Katti, Jeffrey Zheng, Pariasadat Musavigharavi, Jinshui Miao, Eric A. Stach, Roy H. Olsson, Deep Jariwala
Summary: The combination of FE-AlScN and 2D MoS2 shows promising characteristics for embedded memory and memory-based computing architectures, with a high ON/OFF ratio, stable memory states, and state retention.
Article
Chemistry, Physical
Danhao Wang, Ding Wang, Peng Zhou, Mingtao Hu, Jiangnan Liu, Shubham Mondal, Tao Ma, Ping Wang, Zetian Mi
Summary: Through high-resolution X-ray photoelectron spectroscopy measurements, we discovered a thick oxide layer on ScAlN when exposed to air, which significantly affects its characterization and electronic structure evaluation. By excluding the possible impact from the surface oxide layer, the band alignment of Sc0.18Al0.82N/GaN can be accurately determined. Simulation results further demonstrate that the Sc0.18Al0.82N barrier layer offers excellent charge carrier confinement and a high density of two-dimensional electron gas (2DEG) at the heterostructure interface, crucial for high-performance GaN-based high electron mobility transistors (HEMTs).
APPLIED SURFACE SCIENCE
(2023)
Article
Materials Science, Multidisciplinary
Georg Schoenweger, Md Redwanul Islam, Niklas Wolff, Adrian Petraru, Lorenz Kienle, Hermann Kohlstedt, Simon Fichtner
Summary: This letter reports on room temperature switchable ultra-thin (10 nm) ferroelectric Al0.72Sc0.28N films, which are important for potential applications in neuromorphic computing and memory devices. All-epitaxial Al0.72Sc0.28N/Pt heterostructures are grown by magnetron sputtering, and the Al0.72Sc0.28N film surface is protected by in situ Pt capping to avoid oxidation. The films exhibit good epitaxy and show only moderate scaling effects in terms of relative permittivity and coercive field dependence, suggesting that the critical thickness for ferroelectricity has not yet been reached.
PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS
(2023)
Article
Chemistry, Multidisciplinary
Kate Reidy, Paulina Ewa Majchrzak, Benedikt Haas, Joachim Dahl Thomsen, Andrea Konecna, Eugene Park, Julian Klein, Alfred J. H. Jones, Klara Volckaert, Deepnarayan Biswas, Matthew D. Watson, Cephise Cacho, Prineha Narang, Christoph T. Koch, Soren Ulstrup, Frances M. Ross, Juan Carlos Idrobo
Summary: The integration of metallic contacts with 2D semiconductors can significantly affect the local optoelectronic properties. In this study, we analyze the local excitonic changes in a 2D semiconductor MoS2 in contact with Au. Our findings suggest that the observed changes are due to the dielectric screening of the excitonic Coulomb interaction, and increasing the van der Waals distance can optimize excitonic spectra in mixed-dimensional interfaces.
Article
Nanoscience & Nanotechnology
Thorsten Schultz, Max Kneiss, Philipp Storm, Daniel Splith, Holger von Wenckstern, Christoph T. Koch, Adnan Hammud, Marius Grundmann, Norbert Koch
Summary: In this study, it is found through simulations that the detection wavelength range of GaAs/AlxGa1-xAs quantum well infrared photodetectors (QWIPs), which are currently state-of-the-art, can be substantially improved using kappa-([Al,In](x)Ga1-x)(2)O-3, while being transparent to visible light and insensitive to photon noise due to its wide band gap. It is also demonstrated that the efficiency of QWIPs critically depends on the quantum well thickness, making precise control and determination of the thickness essential.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Chemistry, Physical
He Li, Sadegh Askari, Jihao Wang, Niklas Wolff, Malte Behrens, Lorenz Kienle, Jan Benedikt
Summary: A noble-metal-free bifunctional electrocatalyst was developed through a facile strategy for rechargeable zinc-air batteries. The nitrogen-doped NiCo2O4 nanostructures on carbon paper exhibited enhanced electrocatalytic activities for oxygen evolution and reduction reactions. The plasma treatment optimized the N doping process without changing the morphology and specific surface area of the catalyst. The resulting air cathode showed improved stability and performance compared to noble-metal catalyst counterparts.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2023)
Article
Physics, Applied
Daniel Abou-Ras, Ulrike Bloeck, Sebastian Caicedo-Davila, Alberto Eljarrat, Hannah Funk, Adnan Hammud, Sinju Thomas, Dan R. Wargulski, Thomas Lunkenbein, Christoph T. Koch
Summary: This passage presents a practical tutorial on the application of correlative microscopy in optoelectronic semiconductor materials and devices. It discusses the combination of electron microscopy, scanning probe microscopy, and light microscopy for analyzing material and device properties. The tutorial also covers specimen preparation and demonstrates the ability of electron microscopy to monitor phase segregation processes in semiconductor nanoparticles and thin films, along with the explanation of algorithms for extracting phase information.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Chemistry, Multidisciplinary
Benedikt Haas, Tara M. Boland, Christian Elsaesser, Arunima K. Singh, Katia March, Juri Barthel, Christoph T. Koch, Peter Rez
Summary: Phonon scattering at grain boundaries plays a crucial role in controlling the thermal conductivity of nanoscale devices. This study uses monochromated electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) to measure the 60 meV optic mode at grain boundaries in silicon at atomic resolution. The results show the existence of localized phonon modes and support the idea that grain boundaries can act as waveguides.
Article
Chemistry, Multidisciplinary
Niklas Wolff, Tudor Braniste, Helge Krueger, Sebastian Mangelsen, Redwanul Islam, Ulrich Schuermann, Lena M. Saure, Fabian Schuett, Sandra Hansen, Huayna Terraschke, Rainer Adelung, Ion Tiginyanu, Lorenz Kienle
Summary: This paper presents the synthesis and structural characterization of a hybrid beta-Ga2O3/ZnGa2O4 nanocomposite aero-network. Structural investigations reveal the transformation of the precursor aero-GaN(ZnO) network into hollow architectures composed of beta-Ga2O3 and ZnGa2O4 nanocrystals. The hybrid nanocomposite network demonstrates narrow band green light emission of ZnGa2O4 under UV light excitation and shows high initial capacities and exceptional rate performance for electrochemical applications.
Article
Microscopy
Christoph T. Koch
Summary: Solving crystal structures from kinematical X-ray or electron diffraction patterns of single crystals requires recording more diffracted beams than the number of atoms in the structure. This method utilizes the fact that multiple scattering encodes structure factor phases in the diffracted intensities to solve the crystallographic phase problem. The retrieval of both amplitudes and phases of electron structure factors from diffraction patterns recorded with varying angle of incidence will be demonstrated, making it potentially useful for electron crystallography of beam-sensitive complex structures.
Article
Multidisciplinary Sciences
Marcel Schloz, Johannes Mueller, Thomas C. Pekin, Wouter Van den Broek, Jacob Madsen, Toma Susi, Christoph T. Koch
Summary: We propose a method for reducing the dose required for electron ptychographic reconstruction by adaptively scanning the specimen, providing spatial information redundancy in important regions. The method is based on a deep learning model trained by reinforcement learning using prior knowledge from training data. We demonstrate that adaptive scanning in electron ptychography outperforms alternative low-dose ptychography experiments in terms of reconstruction resolution and quality.
SCIENTIFIC REPORTS
(2023)
Article
Nanoscience & Nanotechnology
Md Redwanul Islam, Georg Schoenweger, Niklas Wolff, Adrian Petraru, Hermann Kohlstedt, Simon Fichtner, Lorenz Kienle
Summary: In this study, the structural and electrical properties of Al0.72Sc0.28N thin films grown on different substrates were compared. It was found that using an epitaxial Pt electrode layer on a GaN/Al2O3 substrate significantly improved the leakage current and coercive field of the material. Furthermore, an all-epitaxial Al0.72Sc0.28N/Pt/GaN stack with a sharp interface thickness of less than 1 nm was demonstrated.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Physics, Applied
Katrin Pingen, Stefan Neuhaus, Niklas Wolff, Lorenz Kienle, Agne Zukauskaite, Elizabeth von Hauff, Alexander M. Hinz
Summary: The increasing demand for More than Moore devices requires epitaxy technology to keep up with the discovery and deployment of new semiconductors. An emerging technology for cost-effective, device-quality growth is magnetron sputter epitaxy, though detailed studies on the process itself remain scarce.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Chemistry, Multidisciplinary
Georg Schoenweger, Niklas Wolff, Md Redwanul Islam, Maike Gremmel, Adrian Petraru, Lorenz Kienle, Hermann Kohlstedt, Simon Fichtner
Summary: This study investigates the ferroelectric switching characteristics of sub-5 nm thin Al0.74Sc0.26N films grown on different substrates. Significant progress has been made compared to previous wurtzite-type ferroelectrics, including record low switching voltages of 1 V, larger coercive field to breakdown field ratio on silicon substrates, and the first demonstration of true ferroelectric domains in wurtzite-type materials on the atomic scale. These findings pave the way for achieving analog switching necessary for neuromorphic computing in highly scaled devices.
Article
Chemistry, Multidisciplinary
Xuefeng Pan, Rongying Liu, Zhilong Yu, Benedikt Haas, Zdravko Kochovski, Sijia Cao, Radwan M. Sarhan, Guosong Chen, Yan Lu
Summary: This research presents a facile and green approach for the synthesis of metal/carbon nanotube (CNT) composites using a versatile glycopeptide (GP) as a stabilizer for CNTs and a reducing agent for noble metal ions. The formed GP-CNTs exhibit excellent plasticity, enabling the availability of various forms of CNT species. The metal nanoparticles can be immobilized on the CNT surface at room temperature without additional reducing agents. The Pd/CNT composite shows promising catalytic activity for the degradation of organic pollutants, enhanced by the photothermal conversion capability of CNTs.
Article
Chemistry, Multidisciplinary
Xuefeng Pan, Rongying Liu, Zhilong Yu, Benedikt Haas, Zdravko Kochovski, Sijia Cao, Radwan M. Sarhan, Guosong Chen, Yan Lu
Summary: This study reports a facile and green approach for the fabrication of metal/CNT composites using a versatile glycopeptide (GP) as a stabilizer for CNTs in water and as a reducing agent for noble metal ions. The abundant hydrogen bonds in GP endow the formed GP-CNTs with excellent plasticity, enabling the availability of polymorphic CNT species from dispersion to viscous paste, gel, and even to dough by increasing their concentration. The GP molecules can reduce metal precursors at room temperature without additional reducing agents, enabling the in situ immobilization of metal nanoparticles (e.g. Au, Ag, Pt, and Pd) on the CNT surface. The Pd/CNT composite, which combines the excellent catalytic properties of Pd particles with the photothermal conversion capability of CNTs, shows promise as a catalyst for the fast degradation of organic pollutants.
