Valentina Paneta

Bio: Valentina Paneta is an academic researcher from Uppsala University. The author has contributed to research in topics: Tin & Sputter deposition. The author has an hindex of 10, co-authored 25 publications receiving 239 citations.

Mechanical properties and thermal stability of reactively sputtered multi-principal-metal Hf-Ta-Ti-V-Zr nitrides

Abstract: Crystalline (Hf,Ta,Ti,V,Zr)N nitride thin films, with a high-entropy metal-sublattice, were synthesized at 440 °C by reactive magnetron sputtering using an equimolar Hf-Ta-Ti-V-Zr-compound target. The coatings are single-phase fcc structured mono-nitrides for N2/(Ar + N2) flow-rate-ratios (fN2) between 30 and 45%. For higher fN2 a small fraction of a second phase (next to the fcc matrix) can be detected by X-ray diffraction (XRD) and selected area electron diffraction (SAED). All coatings studied (prepared with fN2 between 30 and 60%) show similar chemical compositions and hardness (H) values between 30.0 and 34.0 GPa with indentation moduli of ~460 GPa. Atom probe tomography (APT) indicates a homogenous distribution of all elements within our fcc-(Hf,Ta,Ti,V,Zr)N even after vacuum-annealing at 1300 °C. While H decreased from 32.5 to 28.1 GPa by this annealing treatment, the coating is still single-phase fcc structured with a defect density (expressed by XRD and SAED features, transmission electron microscopy contrast, and grain sizes) comparable to the as-deposited state. Only after vacuum-annealing at 1500 °C, XRD and APT reveal the formation of hexagonal structured (Ta,V)2N. The onset of nitrogen-loss – detected by thermogravimetric analysis – is ~1350 °C. Based on our results we can conclude that the sluggish diffusion within our fcc-(Hf,Ta,Ti,V,Zr)N warrants the single-phase fcc structure up to 1300 °C, although ab initio based calculations would suggest the lower-entropy products [fcc-(Hf,Zr)N, fcc-(Ta,V)N, and fcc-TiN] and [fcc-(Hf,Zr)N and fcc-(Ta,Ti,V)N] to be energetically more stable up to 1302 K.

Non-reactively sputtered ultra-high temperature Hf-C and Ta-C coatings

Abstract: Transition metal carbides are known for their exceptional thermal stability and mechanical properties, notably governed by the carbon content and the prevalent vacancies on the non-metallic sublattice. However, when using reactive deposition techniques, the formation of amorphous C-containing phases is often observed. Here, we show that non-reactive magnetron sputtering of HfC 0.89 or TaC 0.97 targets lead to fully crystalline coatings. Their C content depends on the target-to-substrate alignment and globally increases from HfC 0.66 to HfC 0.76 and from TaC 0.69 to TaC 0.75 with increasing bias potential from floating to − 100 V, respectively, when using a substrate temperature T sub of 500 °C. Increasing T sub to 700 °C leads to variations from TaC 0.71 to TaC 0.81 . All HfC y films are single-phase face-centered cubic, whereas the TaC y films also contain small fractions of the hexagonal Ta 2 C phase. The highest hardness and indentation modulus among all coatings studied is obtained for TaC 0.75 with H = 41.9 ± 0.3 GPa and E = 466.8 ± 15 GPa. Ab initio calculations predict an easy formation of vacancies on the C-sublattice, especially in the Ta-C system, and a temperature driven stabilization of defected structures at high temperatures, with fewer vacancies on the C sublattice for Hf-C than for Ta-C. The predicted phase stability is proven up to 2400 °C for both systems by annealing experiments in vacuum.

Electronic Stopping of Slow Protons in Oxides: Scaling Properties

Abstract: Financial support of this work by the FWF (FWF-Project No. P22587-N20 and FWF-Project No. P25704-N20) is gratefully acknowledged. M. A. and J. I. J. acknowledge financial support by the Gobierno Vasco-UPV/EHU Project No. IT756-13, and the Spanish Ministerio de Economia y Competitividad (Grants No. FIS2013-48286-C02-02-P and FIS2016-76471-P). Fabrication and characterization of VO2 films at Vanderbilt University (CMG and RFH) was supported by a grant from the National Science Foundation (DMR-1207507). A research infrastructure fellowship of the Swedish Foundation for Strategic Research (SSF) under Contract No. RIF14-0053 supporting accelerator operation is acknowledged.

Metal-Organic Framework-Based Enzyme Biocomposites.

Abstract: Because of their efficiency, selectivity, and environmental sustainability, there are significant opportunities for enzymes in chemical synthesis and biotechnology. However, as the three-dimensional active structure of enzymes is predominantly maintained by weaker noncovalent interactions, thermal, pH, and chemical stressors can modify or eliminate activity. Metal-organic frameworks (MOFs), which are extended porous network materials assembled by a bottom-up building block approach from metal-based nodes and organic linkers, can be used to afford protection to enzymes. The self-assembled structures of MOFs can be used to encase an enzyme in a process called encapsulation when the MOF is synthesized in the presence of the biomolecule. Alternatively, enzymes can be infiltrated into mesoporous MOF structures or surface bound via covalent or noncovalent processes. Integration of MOF materials and enzymes in this way affords protection and allows the enzyme to maintain activity in challenge conditions (e.g., denaturing agents, elevated temperature, non-native pH, and organic solvents). In addition to forming simple enzyme/MOF biocomposites, other materials can be introduced to the composites to improve recovery or facilitate advanced applications in sensing and fuel cell technology. This review canvasses enzyme protection via encapsulation, pore infiltration, and surface adsorption and summarizes strategies to form multicomponent composites. Also, given that enzyme/MOF biocomposites straddle materials chemistry and enzymology, this review provides an assessment of the characterization methodologies used for MOF-immobilized enzymes and identifies some key parameters to facilitate development of the field.

Mixed-Ligand Metal-Organic Frameworks and Heteroleptic Coordination Cages as Multifunctional Scaffolds-A Comparison.

Abstract: ConspectusPorous nanostructures and materials based on metal-mediated self-assembly have developed into a vibrantly studied subdiscipline of supramolecular chemistry during the past decades. In principle, two branches of such coordination compounds can be distinguished: Metal–organic frameworks (MOFs) on the one side represent infinite porous networks of metals or metal clusters that are connected via organic ligands to give solid-state materials. On the other hand, metal–organic cages (MOCs) are discrete and soluble systems with only a limited number of pores. Formation of a particular structure type is achieved by carefully balancing the donor site angles within the ligands as well as the nature and coordination geometry of the metal component. Years of research on MOFs and MOCs has yielded numerous types of well-defined porous crystals and complex supramolecular architectures. Since various synthetic routes and postsynthetic modification methods have been established, the focus of recent developments h...

The chemistry of multi-component and hierarchical framework compounds

Abstract: Multi-component hierarchically porous materials are an emerging class of materials with tailored compositions, tunable distribution and sophisticated applications. An increasing demand for multifunctionalities and hierarchical structures has resulted in extensive studies on multi-component hierarchical metal–organic frameworks and other open framework compounds. This review article focuses on recent advances in multi-component and hierarchical framework materials, covering the design and synthetic strategies of these architectures, their characterization, and the latest applications. Multivariate MOFs prepared under various synthetic conditions (one-pot or post-synthetic) and their building block distributions are introduced and summarized. This is followed by a short review of characterization techniques including solid-state NMR and photothermal induced resonance, and their potential applications in gas storage, separation, heterogeneous catalysis, guest delivery, and luminescence. Furthermore, guided by the same design principles, the synthesis and applications of multi-component hierarchical covalent-organic frameworks, metal–organic cages and porous organic cages are introduced and discussed. Together, this review is expected to provide a library of multi-component hierarchically porous compounds, which could also guide the state-of-the-art design and discovery of future porous materials with unprecedented tunability, synergism and precision.

High-entropy ceramics: Review of principles, production and applications

Abstract: High-entropy ceramics with five or more cations have recently attracted significant attention due to their superior properties for various structural and functional applications. Although the multi-component ceramics have been of interest for several decades, the concept of high-entropy ceramics was defined in 2004 by producing the first high-entropy nitride films. Following the introduction of the entropy stabilization concept, significant efforts were started to increase the entropy, minimize the Gibbs free energy and achieve stable single-phase high-entropy ceramics. High-entropy oxides, nitrides, carbides, borides and hydrides are currently the most popular high-entropy ceramics due to their potential for various applications, while the study of other ceramics, such as silicides, sulfides, fluorides, phosphides, phosphates, oxynitrides, carbonitrides and borocarbonitrides, is also growing fast. In this paper, the progress regarding high-entropy ceramics is reviewed from both experimental and theoretical points of view. Different aspects including the history, principles, compositions, crystal structure, theoretical/empirical design (via density functional theory, molecular dynamics simulation, machine learning, CALPHAD and descriptors), production methods and properties are thoroughly reviewed. The paper specifically attempts to answer how these materials with remarkable structures and properties can be used in future applications.

A structure zone diagram including plasma based deposition and ion etching - eScholarship

Abstract: An extended structure zone diagram is proposed that includes energetic deposition, characterized by a large flux of ions typical for deposition by filtered cathodic arcs and high power impulse magnetron sputtering. The axes are comprised of a generalized homologous temperature, the normalized kinetic energy flux, and the net film thickness, which can be negative due to ion etching. It is stressed that the number of primary physical parameters affecting growth by far exceeds the number of available axes in such a diagram and therefore it can only provide an approximate and simplified illustration of the growth condition?structure relationships.