National Institute Of Materials Physics - Romania

In this paper, potassium based triple cation mixed-halide perovskite films were explored in order to enhance the stability and photovoltaic performance of perovskite based solar cells. It was found that adding potassium (K+) to a double cation mixed halide perovskite (FA(0.80)MA(0.20)PbI(2.8)Cl(0.2)), structural, morphological and optoelectronic properties of perovskites are improved. The perovskite films were prepared by one-step spin coating method with and without K+ and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). The results indicate that potassium incorporation reduces significantly the yellow non-perovskite delta-phase formation and improves the perovskite film quality, thus contributing to the reduction of hysteresis, improves the stability and increases the PCE up to 12.51%. Furthermore, the doped devices exhibit reduced hysteresis and provide remarkable shelf stability by retaining more than 70% of the initial efficiency with low humidity over 850 h. (C) 2020 Elsevier B.V. All rights reserved.

Cu-Fe-Sn-S films were obtained on indium tin oxide / glass substrates by a low-cost electrodeposition using an aqueous solution of CuSO4, FeSO4, SnSO4, and Na2S2O3 at room temperature followed by high-temperature sulfurization (500 degrees C) in argon flow. A range of cathodic potentials have been used for electrodeposition, those being chosen after a preliminary cyclic voltammetry study. The coatings were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray Photoelectron Spectroscopy and conventional spectroscopy (diffuse reflectance and specular transmission). The results are discussed with respect to the used applied potential.

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.

A simple dynamic method was developed to evaluate the components in the equivalent circuit of a ferroelectric capacitor. The method is based on the application of short trapezoidal voltage pulses of variable amplitude and the analysis of the resulting current by considering the ferroelectric capacitor as a parallel R-p-C-p equivalent circuit. The values of R-p and C-p components are obtained in relation to different stages of polarization switching as the amplitude of the applied pulses increases. The most important result obtained by applying the present method is the evidence of an abrupt decrease of the R-p value (about 2 orders of magnitude) at the coercive voltage, while the equivalent C-p does not present a dramatic variation during polarization switching. This is interpreted in the context of negative capacitance obtained for ferroelectrics when polarization passes through zero value. The results obtained by using the proposed dynamic characterization method that will be referred to as "dynamic dielectric characterization", are in good agreement with those obtained by classic capacitance-voltage measurements. A method to stabilize the negative capacitance for longer periods of time is also presented by adding an external resistance in series with the ferroelectric capacitor.

Phase-change memories have reached an advanced degree of maturity, although, to be able to meet the increasing storage demand, multilevel capability is needed. A GeTe memristor is obtained in an amorphous state and it is subjected to a specific thermal treatment which initiates the transition toward the crystalline state. It is found that this crystalline state initialization process is highly beneficial for subsequently obtaining a large number of intermediate resistive states between the high and low resistive states. Multiple resistance levels are achieved by operating the devices in both DC sweeps and rectangular pulse modes in the low-voltage subthreshold regime. The conduction is modeled using a space charge limited conduction model, showing three distinct conduction regions in the high resistive state which merge toward a single conduction region as the low resistive state is approached. The obtained memristors can be used as multilevel nonvolatile memories or as synapses in neuromorphic computing.

The bone remodeling field has shifted focus towards the delineation of products with two main critical attributes: internal architectures capable to promote fast cell colonization and good mechanical performance. In this paper, Luffa-fibers and graphene nanoplatelets were proposed as porogen template and mechanical reinforcing agent, respectively, in view of framing 3D products by a one-stage polymer-free process. The ceramic matrix was prepared through a reproducible technology, developed for the conversion of marble resources into calcium phosphates (CaP) powders. After the graphene incorporation (by mechanical and ultrasonication mixing) into the CaP matrix, and Luffa-fibers addition, the samples were evaluated in both as-admixed and thermally-treated form (compact/porous products) by complementary structural, morphological, and compositional techniques. The results confirmed the benefits of the two agents' addition upon the compact products' micro-porosity and the global mechanical features, inferred by compressive strength and elastic modulus determinations. For the porous products, overall optimal results were obtained at a graphene amount of <1 wt.%. Further, no influence of graphene on fibers' ability to generate at high temperatures internal interconnected-channels-arrays was depicted. Moreover, its incorporation led to a general preservation of structural composition and stability for both the as-admixed and thermally-treated products. The developed CaP-reinforced structures sustain the premises for prospective non- and load-bearing biomedical applications.

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 discovery of ferroelectricity in doped HfO2 represents an excellent opportunity to overcome the obstacles in manufacturing reliable ferroelectric field effect transistors (FeFET) for nonvolatile memory applications, considering that HfO2 is compatible with Si and Ge and it is already used in semiconductor industry. The presence of interface defects may have detrimental effects on the operation of FeFETs, so their role is systematically investigated in this study in correlation with the substrate doping. Metal-ferroelectric-semiconductor (MFS) structures are fabricated by depositing Hf0.5Zr0.5O2 (HZO) layers on n-type Ge substrate. Their electric properties are compared with those of MFS structures obtained by depositing HZO on p-type Ge, to study the influence of the doping. It is found that, although the ferroelectric properties of HZO are similar, the capacitance and impedance of the MFS structures behave differently. For n-Ge, the occupation probability of a large number of low-lying interface defect acceptor states, charges the interface negatively which adversely affects the C-V response of the MFS, albeit without harming the ferroelectric (P-V) hysteresis. Although the interface defects do not harm ferroelectricity, they could inhibit inversion in p-type Ge or accumulation in n-type Ge so they should be taken into account when designing Ge FeFET devices.

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.

Terahertz time-domain spectroscopy (THz-TDS) was employed for estimation of intrinsic dielectric loss of Zr0.8Sn0.2TiO4 (ZST) ceramics. Single-phase ZST dielectric resonators (DRs) with various synthesis parameters and, consequently, different extrinsic losses, were prepared by conventional ceramic technology. Even though the DRs exhibit a similar microstructure, their quality factor (Q is the inverse of dielectric loss tangent) measured in microwave (MW) domain at 6 GHz varies between 2500 and 8400. On the other hand, it was found that the THz dielectric loss is less sensitive to the sample preparation. The intrinsic losses (Q x f similar to 60 THz) of the ZST ceramics have been derived from THz data.