National Institute Of Materials Physics - Romania

In this paper, we report studies on Al2O3/Ge/Al2O3 trilayer memory structures deposited by magnetron sputtering at room temperature on p-Si substrates coated with 3 nm SiO2. The changes of the structure, morphology and memory properties induced by rapid thermal annealing (RTA) in a broad temperature range 550-900 degrees C have been carefully investigated. High resolution transmission electron microscopy (HRTEM) revealed the existence of distinct RTA effects for different temperature ranges, in correlation with memory properties measured on Al/Al2O3/Ge/Al2O3/SiO2/p-Si/Al devices. Thus, at temperatures smaller than 650 degrees C, Ge diffuses into adjacent Al2O3, the layers remaining amorphous. The memory window increases from as-deposited samples to those annealed at 600 degrees C reaching the maximum of 5.4 V. After RTA at 700 degrees C, Ge nanocrystals (NCs) in intermediate Ge layer and Ge-rich amorphous nanoparticles in Al2O3 tunnel oxide are formed. Increasing RTA temperature to 800 and 900 degrees C, Ge NCs are no longer formed due to Ge strong diffusion. Instead, Ge-rich mixed GeAl oxide NCs of unknown crystalline structure are evidenced by HRTEM. The memory window continuously decreases with annealing temperature in the range 650-900 degrees C. The ON (OFF) charge loss of only 11% (9.8%) was found by extrapolation to 10 years.

Currently, there is a considerable time-lag in the industrialisation of innovative technological solutions for the functionalization of osseous implants, with ever-demanding healthcare requirements (e.g., controlled release of therapeutic ions, match of biomaterial degradation - bone growth rates, antimicrobial efficiency). As third-generation biomaterials, phosphate bio-glasses (PBGs) have demonstrated an ability to stimulate specific biological responses from tissue to molecular level, by successfully coupling bioactive and resorbable material properties. Here, radio-frequency magnetron sputtered (RF-MS) PBGs were explored as sacrificial resorbable layers for prospective biomedical implant designs. A PBG powder with a 50-P2O5, 35-CaO, 10-Na2O and 5-Fe2O3 composition (mol%) was used as source (target) material. The influence of the argon working pressure (0.2-1 Pa) - one of the most prominent RF-MS variables - on the morphology, structure, uniformity, composition, degradation rate and cytocompatibility of PBG films was investigated. The engineered modification of physical-chemical and biological features of the PBG sputtered films was multi-parametrically surveyed by AFM, EDXS, spectroscopic ellipsometry, GIXRD, FTIR spectroscopy measurements and in vitro assays. Results suggested that the film thickness, composition, density and structure were preserved over a uniformity region having a diameter of similar to 30 mm, irrespective of sputtering pressure. The network connectivity and the surface porosity of the films were found to have antagonistic roles with respect to the in vitro degradation performance. The possibility of fine tuning the composition, structure and thereby biological interaction of the PBG films by conveniently modifying the sputtering pressure was shown (i.e., permitting their complete controlled degradation, without cytotoxic effects). This work is the first to show in vitro cytocompatibility outcomes of sputtered PBG films and their cross-area uniformity, and thus, it could prove to be an important technological step in their future biomedical application and suggest implications for future industrial scale-up.

We explore higher order dynamical effects in the transport through a two-dimensional nanoscale electron system embedded in a three-dimensional far-infrared photon cavity. The nanoscale system is considered to be a short quantum wire with a single circular quantum dot defined in a GaAs heterostructure. The whole system, the external leads and the central system are placed in a constant perpendicular magnetic field. The Coulomb interaction of the electrons, the paraand diamagnetic electron-photon interactions are all treated by a numerically exact diagonalization using step-wise truncations of the appropriate many-body Fock spaces. We focus on the difference in transport properties between a description within an electric dipole approximation and a description including all higher order terms in a single photon mode model. We find small effects mostly caused by an electrical quadrupole and a magnetic dipole terms that depend strongly on the polarization of the cavity field with respect to the transport direction and the photon energy. When the polarization is aligned along the transport direction we find indications of a weak self-induction that we analyze and compare to the classical counterpart, and the self-energy contribution of high-order interaction terms to the states the electrons cascade through on their way through the system. Like expected the electron-photon interaction is well described in the dipole approximation when it is augmented by the lowest order diamagnetic part for a nanoscale system in a cavity in an external magnetic field.

For successful bone remodelling, the implantable 3D structures require suitable internal architectures which can be achieved by the use of fibres as natural templates. The ability of fibres to generate complex configurations for 3D bioceramic products was preliminary reported by sacrificial fibrous-porogen method. This study aims to demonstrate the safe-prospect of repurposing natural-fibres (i.e. luffa, hemp, wool) for embedment into a calcium phosphate (CaPs) matrix prepared through a completely reproducible route, and the beneficial influence of fibres upon structural, topographic and mechanical features of CaPs-products, since a complete assessment of the fibres-combustion-products resulted after thermal treatment was not yet disclosed. The complex investigation program based on i) thermo-gravimetric (TGA-DTG), ii) structural (XRD, FTIR-ATR), iii) morpho-compositional (SEM/EDS) and, most importantly, iv) biological cytotoxicity assays of fibres-derived chars, clearly indicated that luffa-fibres are the safest (>95% cell-survival) to be considered for bioceramic porous-orthopaedic-implants. Further, as exposed by nano-CT, the high temperature pyrolysis of luffa-fibres led to 3D interconnected channels inside the products, which allows a suitable vascularization and osteointegration. The topographic reconstruction of channels-inside-surface revealed a secondary 3D network of micro-pores. Along with the mechanical features, the novel bioceramic porous structures stand as reliable bone-repair alternatives.

The growth of electrical transportation is crucially important to mitigate rising climate change concerns regarding materials supply. Supercapacitors are high-power devices, particularly suitable for public transportation since they can easily store breaking energy due to their high-rate charging ability. Additionally, they can function with two carbon electrodes, which is an advantage due to the abundance of carbon in biomass and other waste materials (i.e., plastic waste). Newly developed supercapacitive nanocarbons display extremely narrow micropores (0.8 nm), as it increases drastically the capacitance in aqueous electrolytes. Here, we present a strategy to produce low-cost flexible microporous electrodes with extremely high power density (100 kW kg(-1)), using fourty times less activating agent than traditionnal chemically activated carbons. We also demonstrate that the affinity between the carbon and the electrolyte is of paramount importance to maintain rapid ionic diffusion in narrow micropores. Finally, this facile synthesis method shows that low-cost and bio-based free-standing electrode materials with reliable supercapacitive performances can be used in electrochemistry. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Partially-oriented MgB2 bulk discs (13 and 9 %) with the starting compositions of (MgB2)(0.99)(B4C)(0.01) and (MgB2)(0.99)(c-BN)om were fabricated by slip casting under an H-0 = 12 T magnetic field (perpendicular to the disc surface) and subsequent spark plasma sintering. The maximum critical current density and irreversibility field are for H//H-0 (H=applied field). These values are higher or similar to the randomly-oriented samples with the same composition. The maximum volume pinning force (F-p) is lower in the partially-oriented ones than in the randomly-oriented samples. The pinning-force-related parameters depend on the additive and orientation. Assessment of the major pinning mechanism within the scaling and percolation models considering these parameters shows significant limitations. A method to scale F-p is proposed; for the randomly and partially-oriented samples (that show an extra peak in F-p), the single and double Gaussian functions fit well. The results suggest an anisotropic influence of carbon substituting for boron in the MgB2.

The investigation of the effect of carbon nanomaterials and lipids on the aggregation particularities of the amyloid beta/A beta(1-42) layers is important for understanding the generation mechanism of neuronal disorder and how it can be inhibited. Additionally, amyloids are nanomaterials with a wide area of potential applications from nanotechnology to biotechnology. This paper presents a study about the preparation of A beta(1-42) layer by two different methods, Langmuir-Blodgett (L-B) and drop cast (DC), on Si and Si covered by a layer of Buckminster fullerene, C-60, and on the effect of fullerene layer or/and cholesterol (Ch) on the generation of A beta(1-42) secondary structure forms, relevant for specific applications. AFM, SEM FTIR and Raman analysis offered details about the layer surface topography, morphology and particularities of the secondary structure generated in the process of A beta(1-42) molecules aggregation. This study showed that the presence of Ch inhibited the formation of fibrils in A beta(1-42) film deposited by L-B on Si covered by C-60 The structures developed during aggregation were correlated with the topography and roughness of the films. The presence of Ch determined a decrease in roughness for L-B film and increase in roughness for DC film deposited on Si covered by C-60 layer.

A hybrid direct current magnetron sputtering/high-power impulse magnetron sputtering (DCMS/HiPIMS) technique was used to improve the structural and electrical properties of single-crystal titanium carbide (TiC) thin films. The hetero-epitaxial TiC films, similar to 60 nm thick, were grown on MgO (001) substrates at temperatures ranging from 200 degrees C to 800 degrees C, by co-sputtering of Ti and C targets powered by DCMS and HiPIMS, respectively. Films' composition and the structural, morphological, and electrical properties were comparatively investigated to those of a set of samples deposited at same temperatures by reactive-DCMS (R-DCMS) in Ar/CH4 atmosphere. The composition and the FWHM of rocking curves of the films deposited by R-DCMS varied from TiC0.84 to TiC0.94 and from 1.38 degrees to 0.64 degrees, respectively, as the growth temperature increased. TiC0.94 - TiC0.96 layers were deposited by hybrid DCMS/HiPIMS method at temperatures higher than 400 degrees C, fully strained over their full thickness, with FWHM of rocking curves of about 0.13 degrees. Electrical resistivity values measured for these films were of about 155 mu Omega cm, significantly close to those corresponding to bulk TiC0.95 single crystals. The resistivity of R-DCMS films is higher by 6% to 23% in comparison with that of the DCMS/HiPIMS grown samples, depending on the growth temperature.

We investigate topological and disorder effects in non-Hermitian systems with chiral symmetry. The system under consideration consists in a finite Su-Schrieffer-Heeger chain to which two semi-infinite leads are attached. The system lacks the parity-time and time-reversal symmetries and is appropriate for the study of quantum transport properties. The complex energy spectrum is analyzed in terms of the chain-lead coupling and chiral disorder strength, and shows substantial differences between chains with even and odd number of sites. The mid-gap edge states acquire a finite lifetime and are both of topological origin or generated by a strong coupling to the leads. The disorder induces coalescence of the topological eigenvalues, associated with exceptional points and vanishing of the eigenfunction rigidity. The electron transmission coefficient is approached in the Landauer formalism, and an analytical expression for the transmission in the range of topological states is obtained. Notably, the chiral disorder in this non-Hermitian system induces unitary conductance enhancement in the topological phase. (C) 2020 Elsevier B.V. All rights reserved.

Despite extensive studies on lanthanide (Ln) doped TiO2 nanoparticles, there is still considerable uncertainty as to whether Ln reside in the bulk (either as substitutional or interstitial dopant) or on the surface. Herein, new Ln (Eu, Sm, Nd and Er) discrete substitutional centers are identified in the anatase phase using low temperature, site selective time-gated luminescence spectroscopy. The excitation wavelength spanned UV (TiO2 host absorption) to visible excitation range into Ln f-f absorption transitions. The Ln multisite distribution is described in terms of fingerprint emission/excitation spectra and emission decays. The emission of Ln centers cover the visible (Eu, Sm) to near-infrared range (Nd, Er) and display narrow emission with full width at half maximum (FWHM) as small as 0.2 nm. The role of TiO2 host in sensitization of Ln emission is emphasized for each center. We have also found that besides discrete distribution, Ln distribute continuously on closely related anatase lattice sites. In this case, the Ln emission is significantly broader, with FWHM around 20 nm and change continuously in spectral shape and intensity with the excitation wavelength. The challenges encountered while identifying the Ln centers in TiO2 and comparison with case of CeO2 and SnO2 are also discussed. (C) 2020 Elsevier B.V. All rights reserved.