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- ItemPhotoluminescence lineshape of ZnO(New York, NY : American Inst. of Physics, 2014) Ullrich, B.; Singh, A.K.; Bhowmick, M.; Barik, P.; Ariza-Flores, D.; Xi, H.; Tomm, J.W.The merger of the absorption coefficient dispersion, retrieved from transmission by the modified Urbach rule introduced by Ullrich and Bouchenaki [Jpn. J. Appl. Phys. 30, L1285, 1991], with the extended Roosbroeck-Shockley relation reveals that the optical absorption in ZnO distinctively determines the photoluminescence lineshape. Additionally, the ab initio principles employed enable the accurate determination of the carrier lifetime without further specific probing techniques.
- ItemGraphene-Like ZnO: A Mini Review(Basel : MDPI, 2016) Ta, Huy Q.; Zhao, Liang; Pohl, Darius; Pang, Jinbo; Trzebicka, Barbara; Rellinghaus, Bernd; Pribat, Didier; Gemming, Thomas; Liu, Zhongfan; Bachmatiuk, Alicja; Rümmeli, Mark H.The isolation of a single layer of graphite, known today as graphene, not only demonstrated amazing new properties but also paved the way for a new class of materials often referred to as two-dimensional (2D) materials. Beyond graphene, other 2D materials include h-BN, transition metal dichalcogenides (TMDs), silicene, and germanene, to name a few. All tend to have exciting physical and chemical properties which appear due to dimensionality effects and modulation of their band structure. A more recent member of the 2D family is graphene-like zinc oxide (g-ZnO) which also holds great promise as a future functional material. This review examines current progress in the synthesis and characterization of g-ZnO. In addition, an overview of works dealing with the properties of g-ZnO both in its pristine form and modified forms (e.g., nano-ribbon, doped material, etc.) is presented. Finally, discussions/studies on the potential applications of g-ZnO are reviewed and discussed.
- ItemStraightforward Approach for Preparing Durable Antibacterial ZnO Nanoparticle Coatings on Flexible Substrates(Basel : MDPI, 2022) Šutka, Andris; Mežule, Linda; Denisova, Viktorija; Meier-Haack, Jochen; Kulkarni, Akshay; Bitina, Sanda; Smits, Krisjanis; Vihodceva, SvetlanaFlexible antibacterial materials have gained utmost importance in protection from the distribution of bacteria and viruses due to the exceptional variety of applications. Herein, we demonstrate a readily scalable and rapid single-step approach for producing durable ZnO nanoparticle antibacterial coating on flexible polymer substrates at room temperature. Substrates used are polystyrene, poly(ethylene-co-vinyl acetate) copolymer, poly(methyl methacrylate), polypropylene, high density polyethylene and a commercial acrylate type adhesive tape. The deposition was achieved by a spin-coating process using a slurry of ZnO nanoparticles in toluene. A stable modification layer was obtained when toluene was a solvent for the polymer substrates, namely polystyrene and poly(ethylene-co-vinyl acetate). These coatings show high antibacterial efficiency causing >5 log decrease in the viable counts of Gram-negative bacteria Escherichia. coli and Gram-positive bacteria Staphylococcus aureus in 120 min. Even after tapping these coated surfaces 500 times, the antibacterial properties remained unchanged, showing that the coating obtained by the presented method is very robust. In contrast to the above findings, the coatings are unstable when toluene is not a solvent for the substrate.
- ItemDefect-Induced Magnetism in Nonmagnetic Oxides: Basic Principles, Experimental Evidence, and Possible Devices with ZnO and TiO2(Weinheim : Wiley-VCH, 2020) Esquinazi, Pablo David; Hergert, Wolfram; Stiller, Markus; Botsch, Lukas; Ohldag, Hendrik; Spemann, Daniel; Hoffmann, Martin; Adeagbo, Waheed A.; Chassé, Angelika; Nayak, Sanjeev K.; Ben Hamed, HichemThe magnetic moment and the magnetic order induced by localized defects, like vacancies, interstitials, and/or nonmagnetic (NM) ions, in a NM oxide atomic lattice are discussed. When the defect concentration is of the order of or larger than ≈3 at%, magnetic order at room temperature can appear. Herein, the theoretical basic principles needed to understand and compute this new magnetic phenomenon in solids are developed in detail. In particular, the main results of density functional theory (DFT) calculations are used to estimate the magnetization and X-ray magnetic circular dichroism (XMCD) values. The main experimental evidences on this phenomenon are reviewed, especially magnetization, the element-specific XMCD, and transport properties in two selected oxides, ZnO and TiO2. Emphasis is given on the simplicity and efficiency ion irradiation methods have to trigger magnetic order in these oxides as well as a very sensitive method to characterize magnetic impurities. Two possible applications of this phenomenon are discussed, namely spin filtering at magnetic/NM interfaces in ZnO and perpendicular magnetic anisotropy triggered in TiO2 anatase microstructures. The existing literature on defect-induced magnetism in oxides is shortly reviewed, which provides further evidence on the robustness of this phenomenon in solids.
- ItemUncovering the (un-)occupied electronic structure of a buried hybrid interface(Bristol : IOP Publ., 2019) Vempati, S.; Deinert, J.-C.; Gierster, L.; Bogner, L.; Richter, C.; Mutz, N.; Blumstengel, S.; Zykov, A.; Kowarik, S.; Garmshausen, Y.; Hildebrandt, J.; Hecht, S.; Stahler, J.The energy level alignment at organic/inorganic (o/i) semiconductor interfaces is crucial for any light-emitting or -harvesting functionality. Essential is the access to both occupied and unoccupied electronic states directly at the interface, which is often deeply buried underneath thick organic films and challenging to characterize. We use several complementary experimental techniques to determine the electronic structure of p-quinquephenyl pyridine (5P-Py) adsorbed on ZnO(1 0 -1 0). The parent anchoring group, pyridine, significantly lowers the work function by up to 2.9 eV and causes an occupied in-gap state (IGS) directly below the Fermi level E F . Adsorption of upright-standing 5P-Py also leads to a strong work function reduction of up to 2.1 eV and to a similar IGS. The latter is then used as an initial state for the transient population of three normally unoccupied molecular levels through optical excitation and, due to its localization right at the o/i interface, provides interfacial sensitivity, even for thick 5P-Py films. We observe two final states above the vacuum level and one bound state at around 2 eV above E F , which we attribute to the 5P-Py LUMO. By the separate study of anchoring group and organic dye combined with the exploitation of the occupied IGS for selective interfacial photoexcitation, this work provides a new pathway for characterizing the electronic structure at buried o/i interfaces. © 2019 IOP Publishing Ltd.
- ItemA Holistic Solution to Icing by Acoustic Waves: De-Icing, Active Anti-Icing, Sensing with Piezoelectric Crystals, and Synergy with Thin Film Passive Anti-Icing Solutions(Weinheim : Wiley-VCH, 2023) del Moral, Jaime; Montes, Laura; Rico‐Gavira, Victor Joaquin; López‐Santos, Carmen; Jacob, Stefan; Oliva‐Ramirez, Manuel; Gil‐Rostra, Jorge; Fakhfouri, Armaghan; Pandey, Shilpi; Gonzalez del Val, Miguel; Mora, Julio; García‐Gallego, Paloma; Ibáñez‐Ibáñez, Pablo Francisco; Rodríguez‐Valverde, Miguel Angel; Winkler, Andreas; Borrás, Ana; González‐Elipe, Agustin RodriguezIcing has become a hot topic both in academia and in the industry given its implications in transport, wind turbines, photovoltaics, and telecommunications. Recently proposed de-icing solutions involving the propagation of acoustic waves (AWs) at suitable substrates may open the path for a sustainable alternative to standard de-icing or anti-icing procedures. Herein, the fundamental interactions are unraveled that contribute to the de-icing and/or hinder the icing on AW-activated substrates. The response toward icing of a reliable model system consisting of a piezoelectric plate activated by extended electrodes is characterized at a laboratory scale and in an icing wind tunnel under realistic conditions. Experiments show that surface modification with anti-icing functionalities provides a synergistic response when activated with AWs. A thoughtful analysis of the resonance frequency dependence on experimental variables such as temperature, ice formation, or wind velocity demonstrates the application of AW devices for real-time monitoring of icing processes.