Publications

In this study, polystyrene composites (PS-GO(f)) with variable concentration (0.5; 1; 2; 3; 4; and 5 wt%) of GO(f) were obtained through the in-situ polymerisation of the styrene in the presence of benzoyl peroxide and graphene oxide(GO) functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane(gamma-MPTS). For determining the morphological and structural particularities of polymeric composites transmission electron microscopy (TEM) measurements were performed. The influence of functionalized GO on thermal and combustion properties of polystyrene (PS)-based composite materials was determined through several methods: Thermogravimetry (TGA); derived thermogravimetry (DTG); microscale combustion calorimetry analysis (MCC); and chemical kinetic studies through TGA and MCC determinations at similar heating rates.

Deposition of Ge nanoparticles in Si3N4 films by heating Si and quartz substrates at 500 degrees C were obtained using co-sputtering Ge, and Si3N4. Their structure and photo-electrical behaviour were investigated by transmission electron microscopy, current - voltage and spectral photo-current investigations, respectively. The spectral photoresponse were correlated with microscopy results. Depending on the measuring temperature, the current under illumination increases with about five orders of magnitude compared with the dark one. The photo-current spectra measured in photovoltaic regime and at -1 V show a single cut-off wavelength in near infrared domain at about 1362 nm.

The memory properties of a trilayer structure of ZrO2/Ge-ZrO2/ZrO2/Si-p were investigated. The trilayer was prepared by magnetron sputtering deposition followed by a rapid thermal annealing process for obtaining Ge nanocrystals embedded in ZrO2 matrix. The X-ray diffraction patterns obtained on annealed structures show that both trilayer structures are cristallized, with narrow diffraction peaks. Ge as a separated phase is not evidenced in the diffractograms, instead is possible that Ge atoms enters in ZrO2 lattice structure and form a compound of ZrO3GeO8 crystallized in the tetragonal phase. In the case of ZrO2 control structure, the diffractograms show that the ZrO2 layer is crystallized in tetragonal phase. The memory properties are evidenced by C-V characteristics with counterclockwise hysteresis loop and a memory window of Delta V=1.1V for the structure annealed at 570 degrees C and Delta V=0.8 V for the structure annealed at 650 degrees C. The influence of the interface SiO2 layer on the frequency dependence of capacitance was evidenced by C-f characteristics.

The paper presents the research results in the field of TiNiCu shape memory alloys processed by powder metallurgy techniques. The powders mixtures used to synthesize Ti50Ni30Cu20 alloys were obtained by blended constitutive elemental powders or by mechanical alloying of powder mixtures for 10 and 20 hours, respectively. Finally, a subsequent annealing process was carried out, followed by a rapid cooling in ice water. All experiments were performed under 99.9% argon atmosphere. At room temperature, the obtained materials contained monoclinic and orthorhombic martensite type. The structural and thermal investigation of these materials were discussed in view of the potential development of actuators.

Context: The work shows the alignment of virtual environment to the needs of the industrial revolution of level 4. Purpose or Goal: The work insists on the qualities that remote experiment offers for the global engineer creation and on the skills for hiring and rapid adaptation to the industry needs. Approach: In the university environment the remote experiment plays a decisive role in facilitating e-learning development for specialties that cannot exist without an experimental-applying part. Remote experiment must to satisfy both the needs of evolution in education and those from the industry (i.e. globalization, digitalization, socio-economic world). It is noted the emergence of new skills namely: "Cognitive flexibility" and "Emotional intelligence". After us, the most important trend, derived from the application of remote experiment and its use is "acceptance of failure". Until recently, the failure was penalized with bad marks. Acceptance is defined as a succession of failures by whose gradual removal, the amount of accumulated knowledge increases. It was concluded that failure is an important part of the road to innovation and creativity. Actual or Anticipated Outcomes: Technology progresses exponentially and the society linear. Over time, it can create a gap between technology and society. It was found from practice that the remote experiment is much more connected to the needs of industry than classical laboratories. Conclusions/Recommendations: Remote experiments can create skills and competencies faster than those achieved through classical learning systems for immediate necessity in industry.

This paper presents the study of the development of complex organic materials deposited by the Langmuir Blodgett technique. We have synthetized Langmuir Blodgett multilayers for the recognition of toxic chemicals in the air and / or ultraviolet radiation. The sensitive materials are based on multilayers of stearic acid metal salts combined with nanocarbon and metalloporphyrin structures. We prepared and obtained by the Langmuir Blodgett method films with nano-metric thicknesses combined in different concentrations of metal salts of fatty acids, Nano carbon structures and metalloporphyrins. Further we have characterized and tested the materials obtained for the sensitivity and selectivity of multilayers under the influence of various toxic gases and / or ultraviolet radiation obtaining high results in the field of sensors.

Phosphate-tellurite crystalline materials containing titanium and aluminum oxide as well as a tellurite crystalline material containing lithium, barium and aluminum oxide were synthesized and investigated by X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. XRD analysis shows peaks specific to the crystalline phases Al(PO3)(3) and TiP2O7. FTIR analysis revealed absorption bands specific to the bending and stretching vibration modes of the phosphate and tellurite crystalline networks.

The current increasing interest in portable biosensing platforms led to their development on flexible porous substrates, such as filter paper. As these devices rely on fluid transport under capillary action, without the use of an external force, studies of the diffusion process can provide useful data for optimizing their working capabilities. We present here the results obtained by experimentally studying the radial diffusion of various fluids. The diffusion in filter paper has been recorded for six fluids with different viscosity. For each of them, the displacement of the fluid front has been measured along eight radial directions and then we investigated the possibility of describing this diffusion process using Gillespie's model.

The development of short-wave infrared (SWIR) photonics based on GeSn alloys is of high technological interest for many application fields, such as the Internet of things or pollution monitoring. The manufacture of crystalline GeSn is a major challenge, mainly because of the low miscibility of Ge and Sn. The use of embedded GeSn nanocrystals (NCs) by magnetron sputtering is a cost-effective and efficient method to relax the growth conditions. We report on the use of GeSn/SiO2 multilayer deposition as a way to control the NC size and their insulation. The in situ prenucleation of NCs during deposition was followed by ex situ rapid thermal annealing. The nanocrystallization of 20X(11nm_Ge0.865S0.135/1.5nm_SiO2) multilayers leads to formation of GeSn NCs with similar to 16% Sn concentration and similar to 9 nm size. Formation of GeSn domes that are vertically correlated contributes to the nanocrystallization process. The absorption limit of similar to 0.4 eV in SWIR found by ellipsometry is in agreement with the spectral photosensitivity. The ITO/20x(GeSn NC/SiO2)/p-Si/Al diodes show a maximum value of the SWIR photosensitivity at a reverse voltage of 0.5 V, with extended sensitivity to wavelengths longer than 2200 nm. The multilayer diodes have higher photocurrent efficiency compared to diodes based on a thick monolayer of GeSn NCs.

Eutectic particles of B4C-TiB2 were reinforced with Ti by spark plasma sintering (SPS) or infiltration. The SPSed samples with 20, 30 and 40 wt. % Ti consisted of ceramic phases, and had a bicontinuous macrostructure formed by the Ti-rich region and the eutectic particles region, while the infiltrated sample was a complex composite comprised of a 3D Ti-rich continuous network, composite in nature, that contained Ti-metal and in which are embedded isolated ceramic (eutectic) particles. The SPSed samples are brittle with the maximum bending strength of 300 MPa for the 30 wt. % Ti, higher than for a reference sample produced by SPS from directionally solidified eutectic particles. A higher amount of added Ti results in a higher displacement in the bending test suggesting a higher fracture toughness. Simultaneous strengthening and toughening of the composite was realized. The infiltrated sample was ductile, while its bending strength (220 MPa) was comparable to the values measured for the brittle as-introduced reference sample and the sample with 20 wt. % Ti, both produced by SPS. In the SPSed and infiltrated samples at the interface between the Ti-rich region and B4C-TiB2 eutectic particles, a local 'pull-out' intergranular fracturing mechanism mainly involving Ti-B 1D-grains was observed. This local micromechanism together with a 'pull out' macromechanism of the eutectic grains from the Ti-rich component are considered important for the bridging/anchoring behavior responsible for the strengthening and toughening processes in our novel hierarchical composites.