National Institute Of Materials Physics - Romania

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.

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.

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.

Commercial nanopowders of MgB2 were characterized from the viewpoint of granulometric distribution, structure, microstructure, and pH behavior in water. The powders are very different: a higher amount of the MgB2 phase with a lower tendency for agglomeration determines a higher rate of pH-increase. A higher rate of pH-increase usually produces a stronger antimicrobial activity against Staphylococcus aureus, Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Candida parapsilosis reference strains. The variation of the pH-increase rate suggests the possibility of temporo-spatial control of MgB2 bioactivity, although the contribution of other factors should not be neglected. Remarkably, the efficiency of the MgB2 powders is higher against biofilms than on microbes in the planktonic state. Further, our experiments confirm the antimicrobial efficiency of MgB2 in the in vitro tests against 29 methicillin resistant clinical S. aureus isolates and 33 vancomycin resistant E. faecium/faecalis strains, but in this case the biofilms are more resistant than planktonic cells. The MgB2 treatment of infected mice led to a significant decrease of E. coli colonization in liver, spleen and peritoneal liquid and it also caused changes in the intestinal microbiota. The activity of powders on HeLa and HT-29 tumor cell lines was assessed by inverted microscopy, flow cytometry, and evaluation of the cellular cycle. MgB2 inhibits tumor cell growth influencing DNA synthesis (S-phase). The obtained results indicate that the tested powders could provide promising solutions for the development of large-spectrum multifunctional antimicrobial and anti-biofilm agents, and/or for anti-cancer therapies. (C) 2021 The Authors. Published by Elsevier B.V.

Graded structures with different architectures were obtained by spark plasma sintering from (Ba1-xSrx)TiO3 (BST, x = 0.10; 0.20; 0.30) powders. The presence of the composition gradient was confirmed by structural and compositional investigations using X-ray diffraction and electron microscopy combined with energy dispersive X-ray spectroscopy. The concentration gradient was either asymmetric (3 layers, starting with x = 0.10 and ending with x = 0.30) or symmetric (5 or 6 layers, starting and ending with x = 0.10, and with a single or double x = 0.30 layer in the middle, respectively). Electrical measurements reveal a decrease of the dielectric constant with increasing the number of the layers. It was found that the symmetric graded structure with 6 layers has the best thermal stability of both, the dielectric constant (variation of only 8% between zero and 100 degrees C) and the py-roelectric coefficient (6% variation between zero and 80 degrees C). In addition, an enhancement of the pyroelectric signal for frequencies above 100 Hz is obtained in symmetric structures, an effect that is attributed to the additive contributions of the signals originated from the layers with different Sr content. (C) 2021 The Author(s). Published by Elsevier B.V.

Herein we show the terahertz (THz) time-domain ellipsometry investigation of the InSb semiconductor. At room temperature, the carriers of InSb are thermally excited to the conduction band due to its narrow bandgap. We, nevertheless, show that THz ellipsometry can detect subtle differences between carrier densities of undoped and lightly doped InSb bulk semiconductors. The advantage of THz ellipsometry over other THz time-domain spectroscopy techniques is that it does not require reference measurements through an aperture or standard mirrors.

Composites of BaTiO3 (BT) and doped-PZT (d-PZT) micro-particles randomly dispersed in a PDMS matrix were prepared by a molding process. The morpho-structural characterization, performed by SEM and XRD, showed ceramic micro-grains of cubic BT and orthorhombic d-PZT, randomly dispersed in the PDMS matrix. Polarization (P) as a function of the applied field (E) was measured for composite samples, as well as for polymer samples. Hysteresis loops typical for a dielectric material were obtained, but also atypical ones, especially for higher fraction of polymer in composite, lower fields and shorter measuring periods, as a result of the dielectric relaxation in polymer and the presence of interfacial polarization charges at the contact between polymer and ferroelectric. All these composites show very low polarizations (less than 0.2 mu C/cm(2) and 0.05 mu C/cm(2) the maximum and remnant polarization, respectively), caused by the very low dielectric constant of the polymer (less than 10), which drastically reduces, up to 100 times, the electric field effectively applied to the ferroelectric. Weak pyroelectric response was recorded on BT/PDMS, but a typical behavior of a pyroelectric detector was observed. A figure of merit of the material which exceeds 10(-4) m(2) /C was estimated.

We fabricated Sn-doped TiO2 nanotubular film via annealing of anodized TiO2 nanotubes grown on F-SnO2 (FTO) glass. Annealing was carried out at 500 degrees C in ambient air. Anatase crystal structure was achieved with no change in nanotubular morphology in respect to as-anodized amorphous TiO(2 )nanotubes. The X-ray photoelectron spectroscopy analysis revealed Sn on the surface of TiO2 film, following the thermal treatment, probably caused by the diffusion from FTO glass. Depth profile examination of the film chemical composition was conducted by elastic recoil detection analysis, which showed that in addition to the diffusion of Sn from FTO, diffusion of Ti to FTO concurrently occurred. Thus, a higher concentration of Sn was found at the bottom of the tubes, while a lower concentration was present on the tubes' surface top. This explains the improved optical response revealed by a diffuse reflectance spectroscopy. The absorption enhancement demonstrated that Sn-doped TiO2 film was efficient in the degradation of methyl orange dye under visible light.