Dr. Adelina UDRESCU

In this work, three methods for the synthesis of composites based on poly(ortho-toluidine) (POT) and WS2 are reported: (a) the solid-state interaction (SSI) of POT with WS2 nanoparticles (NPs); (b) the in situ chemical polymerization (ICP) of ortho-toluidine (OT); and (c) the electrochemical polymerization (ECP) of OT. The preparation of WS2 sheets was performed by the ball milling of the WS2 NPs followed by ultrasonication in the solvent N,N'-dimethyl formamide. During the synthesis of the POT/WS2 composites by SSI and ICP, an additional exfoliation of the WS2 NPs was reported. In this work, we demonstrated the following: (a) the ICP method leads to POT/WS2 composites, which contain repeating units of POT in the leucoemeraldine salt (LS) state, while (b) the ECP method leads to POT/WS2 composites, which contain repeating units of POT in the emeraldine salt (ES) state. Capacitances equal to 123.5, 465.76, and 751.6 mF cm-2 in the cases of POT-ES/WS2 composites, synthesized by SSI, ICP, and ECP, respectively, were reported.

We report large-scale synthesis of monolayer WS2 films obtained by sulfurization of oxidized magnetron sputtered monolayer W precursors. Literature routes typically require similar to 800 degrees C, well above the 400 degrees C limit imposed by back-end-of-line (BEOL) integration. Here, using an enhanced chemical vapor deposition (CVD) approach, the magnetron sputtered ultrathin W precursor (a W monolayer film, 0.27 nm thick, which in ambient air becomes a WOx monolayer) is sulfurized at the lowest possible temperature (450 degrees C) within a microreactor, which consists of a sandwich-like structure formed by the precursor and a clean Si substrate. The obtained WS2 material has a good crystallinity and uniform morphology across the entire growth substrate, as confirmed by detailed characterization. These results highlight the versatility of the method combining magnetron sputtering and microreactor-CVD, facilitating its applications to wafer-scale synthesis of monolayer WS2, heterogeneously integrated into electronic circuits (a major objective for next-generation electronics and optoelectronics). Additionally, we investigate in detail the properties of WS2 films synthesized from a bilayer W precursor (0.43 nm thick), under the same conditions, and we calculated the frequencies of the second-order Raman scattering modes. For electrical measurements, we fabricated WS2/few-layer-graphene heterostructures, whose atomically clean interface yields reliable, low-resistance contacts. These devices exhibit resistive switching behavior, likely governed by vacancy migration, making it a promising candidate for memristive applications. Our results demonstrate that electronics-grade monolayer WS2 can be synthesized at 450 degrees C, approaching the BEOL requirement of 400 degrees C.

Diamond traceability has been a major challenge for the gemological industry in recent decades. In this context, this paper presents new studies using UV-VIS-NIR spectroscopy to identify the traceability and geographical origin of diamonds. The aim of the work is to identify characteristic centers of fancy-color diamonds collected from Cullinan Mine, Democratic Republic of Congo (DRC), and the geographical regions with unknown origin. Depending on the origin of the diamonds, the UV-VIS-NIR spectra can be differentiated as follows: (i) the diamonds collected from Cullinan Mine show absorption bands assigned to N10, NV0, NV-, N3V0, N4V2, and N4V centers, which are accompanied by a vibronic structure localized between 415 and 394 nm (2.987-3.147 eV) and (ii) the diamonds from DRC show absorption bands attributed to N10, NV-, N3V0, N1+, and NVH centers. Using Raman spectroscopy, nitrogen concentration values of diamonds collected from the Cullinan mines and DRC between 41 and 185 ppm and 204-336 ppm, respectively, were reported. We prove that the simultaneous applicability of UV-VIS-NIR spectroscopy and Raman scattering as comparative tools for assessing diamond provenance can be a valuable strategy for an initial attribution of diamonds with unknown geographical origin, knowing the optical features of diamonds collected from Cullinan Mine and DRC.

Nanocomposites based on Fe3O4 and carbonaceous nanoparticles (CNPs), including carbon nanotubes (CNTs) and graphene derivatives (graphene oxide (GO) and reduced graphene oxide (RGO)), such as Fe3O4@GO, Fe3O4@RGO, and Fe3O4@CNT, have demonstrated considerable potential in a number of health applications, including tissue regeneration and innovative cancer treatments such as hyperthermia (HT). This is due to their ability to transport drugs and generate localized heat under the influence of an alternating magnetic field on Fe3O4. Despite the promising potential of CNTs and graphene derivatives as drug delivery systems, their use in biological applications is hindered by challenges related to dispersion in physiological media and particle agglomeration. Hence, a solid foundation has been established for the integration of various synthesis techniques for these nanocomposites, with the wet co-precipitation method being the most prevalent. Moreover, the dimensions and morphology of the composite nanoparticles are directly correlated with the value of magnetic saturation, thus influencing the efficiency of the composite in drug delivery and other significant biomedical applications. The current demand for this type of material is related to the loading of a larger quantity of drugs within the hybrid structure of the carrier, with the objective of releasing this amount into the tumor cells. A second demand refers to the biocompatibility of the drug carrier and its capacity to permeate cell membranes, as well as the processes occurring within the drug carriers. The main objective of this paper is to review the synthesis methods used to prepare hybrids based on Fe3O4 and CNPs, such as GO, RGO, and CNTs, and to examinate their role in the formation of hybrid nanoparticles and the correlation between their morphology, the dimensions, and optical/magnetic properties.

New aspects concerning the photodegradation (PD) of ampicillin are reported by photoluminescence (PL), Raman scattering and FTIR spectroscopy. The exposure of ampicillin in the absence (AM) and in the presence of the excipient (AMP) to UV light leads to an intensity diminution of the photoluminescence excitation (PLE) and photoluminescence (PL) spectra and the emergence of a new IR band at 3450 cm(-1). The photoluminescence studies demonstrate that the AM PD is amplified in the presence of excipients and an alkaline medium. In this last case, the PD process of AM involves the emergence of new compounds, whose presence is highlighted by: (i) the emergence of the isosbestic point at 300 nm in the UV-VIS spectra; (ii) a change in the ratio between the absorbance of IR bands situated in the spectral ranges 1200-1660 and 3250-3450 cm(-1); and (iii) a change in the ratio between the intensities of the Raman lines localized in the spectral ranges 1050-1800 and 2750-3100 cm(-1). A chemical mechanism of the PD processes of AM in an alkaline medium is proposed.

In this work, new results concerning the potential of mixtures based on nitrogen doped titanium dioxide (TiO2:N) and carbon nanotubes (CNTs) as possible catalyst candidates for the rhodamine B (RhB) UV photodegradation are reported. The RhB photodegradation was evaluated by UV-VIS absorption spectroscopy using samples of TiO2:N and CNTs of the type of single-walled carbon nanotubes (SWNTs), double-wall carbon nanotubes (DWNTs), multi-wall carbon nanotubes (MWNTs), and single-walled carbon nanotubes functionalized with carboxyl groups (SWNT-COOH) having various concentrations of CNTs. The best photocatalytic performance was obtained for sample containing TiO2:N and 2.5 wt.% SWNTs-COOH, when approx. 85% of dye removal was achieved after 300 min. of UV irradiation. The reaction kinetics of RhB aqueous solutions containing TiO2:N/CNT mixtures followed a complex first-order kinetic model. The TiO2:N/CNTs catalyst induced higher photodegradation efficiency of RhB than TiO2:N due to the presence of CNTs, which act as adsorbent and dispersing agent and capture the photogenerated electrons of TiO2:N hindering the electron-hole recombination.

In this work, the effect of the single-walled carbon nanotubes (SWNTs) as the mixtures of metallic and semiconducting tubes (M + S-SWNTs) as well as highly separated semiconducting (S-SWNTs) and metallic (M-SWNTs) tubes on the photoluminescence (PL) of poly(3-hexyl thiophene) (P3HT) was reported. Two methods were used to prepare such composites, that is, the chemical interaction of the two constituents and the electrochemical polymerization of the 3-hexyl thiophene onto the rough Au supports modified with carbon nanotubes (CNTs). The measurements of the anisotropic PL of these composites have highlighted a significant diminution of the angle of the binding of the P3HT films electrochemical synthetized onto Au electrodes covered with M + S-SWNTs. This change was attributed to metallic tubes, as was demonstrated using the anisotropic PL measurements carried out on the P3HT/M-SWNTs and P3HT/S-SWNTs composites. Small variations in the angle of the binding were reported in the case of the composites prepared by chemical interaction of the two constituents. The proposed mechanism to explain this behavior took into account the functionalization process of CNTs with P3HT. The experimental arguments of the functionalization process of CNTs with P3HT were shown by the UV-VIS-NIR and FTIR spectroscopy as well as surface-enhanced Raman scattering (SERS). A PL quenching process of P3HT induced both in the presence of S-SWNTs and M-SWNTs was reported, too. This process origins in the various de-excitation pathways which can be developed considering the energy levels diagram of the two constituents of each studied composite.

In this work, new evidence for the photodegradation reactions of acetaminophen (AC) is reported by photoluminescence (PL), Raman scattering and FTIR spectroscopy. Under excitation wavelength of 320 nm, AC shows a PL band in the spectral range of 340-550 nm, whose intensity decreases by exposure to UV light. The chemical interaction of AC with the NaOH solutions, having the concentration ranging between 0.001 and 0.3 M, induces a gradual enhancement of the photoluminescence excitation (PLE) and PL spectra, when the exposure time of samples at the UV light increases until 140 min, as a result of the formation of p-aminophenol and sodium acetate. This behavior is not influenced by the excipients or other active compounds in pharmaceutical products as demonstrated by PLE and PL studies. Experimental arguments for the obtaining of p-aminophenol and sodium acetate, when AC has interacted with NaOH, are shown by Raman scattering and FTIR spectroscopy.

Azathioprine (Imuran), one of the oldest immunosuppressants, having been used in transplantation since the early 1960's, is known to have only two crystal forms: an anhydrous form and a dihydrate phase. We report the crystal structure of a new anhydrous solid-state form of Azathioprine, determined directly form powder X-Ray diffraction data, employing the direct-space genetic algorithm technique for structure solution, followed by Rietveld refinement. The new anhydrous polymorph is accessible only by a solid-state dehydration process of the readily obtained monohydrate form of Azathioprine, the form for which a crystal structure has not previously been reported. The IR and Raman spectra confirmed the results obtained from X-Ray diffraction indicating the presence of all functional groups involved in intermolecular hydrogen bonding which dictates different arrangement of molecules in the structural packing. (C) 2018 Elsevier B.V. All rights reserved.

Mixtures of nitrogen-doped titanium dioxide (TiO2:N) with different concentrations of Ag and/or SiO2 particles (0.5, 1 and 2 wt.%) were prepared in solid state by mechanico-chemical interactions. Using UV-VIS spectroscopy, Raman scattering, photoluminescence (PL) and photoluminescence excitation (PLE), the influence of the particles on the host material is evaluated. UV-VIS spectroscopy studies indicate a TiO2:N band gap shift to the UV range with increasing concentrations of SiO2 and Ag particles. PL intensities decrease with increasing concentrations of Ag and/or SiO2 particles in the TiO2:N host matrix, which in turn could effectively restrict the electron and hole recombination. To explain these processes, the different de-excitation ways will be advanced, taking into account the energy levels diagram of TiO2:N/Ag, TiO2:N/SiO2 and TiO2:N/Ag/SiO2 systems. PLE spectra show a gradual decrease in their relative intensities after 165 min of continuous irradiation due to photosensitivity of TiO2:N. The plasmonic effect of Ag particles in the TiO2:N/Ag system is highlighted for the first time by PLE studies.

The influence of single-walled carbon nanotubes enriched in semiconductor (S-SWNTs) and metallic (M-SWNTs) tubes on the photoluminescence (PL) of polyaniline (PANI), electrosynthesized in the presence of the H2SO4 and HCl solutions, is reported. The emission bands peaked at 407-418 and 440-520 nm indicate that the electropolymerization of aniline (ANI) leads to the formation of short and longer macromolecular chains (MCs), respectively. We demonstrate that the reaction product consists of ANI tetramers (TT) and trimers (TR) as well as PANI-salt. Using Raman scattering and IR absorption spectroscopy, a covalent functionalization of SWNTs with shorter and longer MCs of PANI-salt is demonstrated. The presence of S-SWNTs and M-SWNTs induces a decrease in ANI TT weight in the reaction product mass consisting in S-SWNTs and M-SWNTs covalently functionalized with PANI-emeraldine salt (ES) and PANI-leucoemeraldine salt (LS), respectively. A PANI PL quenching is reported to be induced of the S-SWNTs and M-SWNTs. A de-excitation mechanism is proposed to explain PANI PL quenching.

Raman enhancement in a layered structure of Bib was studied under optical excitation near the edge of the fundamental absorption band. This phenomenon simultaneously appears at a low temperature with the generation of the excitonic photoluminescence (PL) band, unequally across the Raman spectrum, i.e. in the Stokes and anti-Stokes Raman branches, being dependent on the superposition of the excitation laser line to the excitonic emission band. Performed with the use of different resonant laser light excitations, this effect is regarded as a signature of the exciton-phonon interaction, which is interpreted in terms of a stimulated Raman scattering process (SRS), resulting from the mixing inside of the sample to two optical fields, the pump laser light and the excitonic PL light. (C) 2016 Elsevier B.V. All rights reserved.

The enhancement of the Raman scattering in Cs3Bi2I9 is evaluated by the ratio I-T/I-300K between the relative intensities of the Raman line peaked at 146cm(-1), when the spectra are recorded in the temperature range of 88-300K, as a signature of exciton-phonon interactions. In the resonant and nonresonant conditions, excitation wavelengths 476, 561, and 660nm, respectively, are used in order to overlap with great accuracy the bands disclosed by diffuse reflection, photoconductivity (PC), photoluminescence (PL), and photoluminescence excitation (PLE) spectra. Based on the experimental analyses, the strength of exciton-phonon interaction is dependent on the defects in the crystal and the type-range interaction of the excitations in an independent Bi2I93- cluster. The noticeable PL band, attributed to excitons trapped on different stacking faults, manifests some defects in crystal that diminish the movement of excitons. This effect significantly decreases the overlaps of excitons with the phonons, resulting in a reduced exciton-phonon coupling.

In this paper, the interaction of poly(vinylidene fluoride) (PVDF) with single-walled carbon nanotubes (SWNTs) highly separated in metallic (M) and semiconducting (S) tubes is studied by resonant Raman scattering and FTIR spectroscopy. In this order, the PVDF/SWNTs membranes were prepared by the evaporation of dimethylformamide (DMF) from PVDF solutions containing i) the as-prepared SWNTs samples, i.e., as mixtures of metallic (33%) and semiconducting (66%) tubes (M + S-SWNTs), ii) SWNTs highly separated in metallic tubes (98%, M-SWNTs), and iii) SWNTs highly separated in semiconducting tubes (99%, S-SWNTs). An increase in the PVDF beta phase weight, highlighted by the increase in the absorbance of IR band at 843 cm(-1), is reported to take place in the presence of M + S-SWNTs and S-SWNTs. An increase of the PVDF gamma crystalline phase weight is reported for the PVDF/M + S-SWNTs, PVDF/M-SWNTs and PVDF/S-SWNTs membranes. Using Raman scattering, a donor-acceptor interaction is invoked to take place at the interface PVDF/M + S-SWNTs and PVDF/S-SWNTs. In the case of the membranes based on PVDF and M-SWNTs, the changes reported in Raman spectra of the two constituents are explained on the base induction-interaction forces between the permanent dipole of PVDF and induced dipole of M-SWNTs. (C) 2016 Elsevier B.V. All rights reserved.

Optical properties are reported for composites based on single-walled carbon nanotubes (SWNT5) and copolymer poly(3,4-ethylenedioxythiophene-co-pyrene) (PEDOT-Py) prepared by chemical polymerization of two monomers in the presence of carbon nanotubes. A charge transfer between SWNT5 and the PEDOT-Py copolymer was demonstrated by Raman scattering. The increase in the relative intensity of the Raman lines peaked at 440-577 cm(-1), which were assigned to the ethylenedioxy ring vibrational modes, indicated a significant hindrance steric in the case of the composites based on the PEDOT-Py copolymer and metallic SWNTs. The increase in the absorbance of IR band peaked at 984 cm(-1) occurred simultaneously with the disappearance of the IR band at 1639 cm(-1). This finding was a consequence of the formation of new covalent bonds between SWNTs and the thiophene and benzene rings of the repeating units of the PEDOT-Py copolymer. The photoluminescence (PL) quenching process of the PEDOT-Py copolymer was induced by semiconducting SWNTs. The PL quenching of PEDOT-Py copolymer in the presence of SWNT5 was. demonstrated based on the energy level diagrams of the two constituents of the PEDOT-Py/SWNTs composite material. (C) 2016 Elsevier B.V. All rights reserved.

SERS studies were performed on films of two families of multi-wall carbon nanotubes (MWCNTs) under an excitation light of 514.5 nm and 647.1 nm. These included Aldrich-MWCNTs, which alternate semiconducting and metallic tubes and M-MWCNTs that contain only metallic tubes obtained by water assisted catalytic chemical vapour deposition (CCVD). The two families of MWCNTs reveal similar spectra in the Stokes branch, which feature an increasing Raman intensity when the glass substrate is replaced with an Au or Ag substrate, indicating a (surface enhanced Raman scattering) SERS mechanism. In the anti-Stokes branch, despite an enhancement of approximately 100 times compared to the predictions of the Boltzmann law, only Aldrich-MWCNTs exhibit a Raman spectrum with an intensity that increases as a result of the change in the glass substrate to Au or Ag, a fact that is revealed by the signature of the SERS process. The invariance of the Raman intensity in the anti-Stokes branch as a result of the change of the substrate is characteristic of M-MWCNTs and results from a Raman light scattering process that takes place only within the skin depth of the metallic structure.

The photoluminescent (PL) properties of composites based on single-walled carbon nanotubes (SWNTs) and poly(2,2'-bithiophene-co-pyrene) (PBTh-Py), prepared by in situ chemical polymerization of the two monomers in the presence of carbon nanotubes, are reported. We demonstrate that the functionalization of SWNTs with PBTh-Py copolymer is revealed through a gradual quenching process of PL with the increase of SWNT content (semiconducting component) in the composite mass. FTIR spectroscopy indicates the existence of several steric hindrance effects that originate in the covalent functionalization of SWNTs with PBTh-Py copolymer. The film deposition of PBTh-Py copolymer and PBTh-Py/SWNTs composite onto rough Au supports induces changes in the FTIR spectrum, which originate in an adsorption mechanism caused by the preferential orientation of molecules on the metallic support. Surface-enhanced Raman scattering (SERS) spectroscopy reveals the side-wall functionalization of SWNTs with PBTh-Py copolymer by changes in the shapes, peak position and relative intensities of different Raman lines.

Although Raman spectra reveal, as a signature of double-walled carbon nanotubes (DWCNTs), two radial breathing mode (RBM) lines associated with the inner and outer tubes, the specification of their nature as metallic or semiconducting remains a topic for debate. Investigating the spectral range of the RBM lines, we present a new procedure of the indexing of the semiconducting or metallic nature of the inner and outer shell that forms the DWCNT. The procedure exploits the difference between the intensities of recorded anti-Stokes Raman spectrum and the anti-Stokes spectrum calculated by applying the Boltzmann formulae to the recorded Stokes spectrum. The results indicate that the two spectra do not coincide with what should happen in a normal Raman process, namely, that there are RBM lines of the same intensity in both spectra, as well as RBM lines of higher intensity that are observed in the calculated spectrum. This discrepancy results from the surface-enhanced Raman scattering mechanism that operates differently on metallic or semiconducting nanotubes. In this context, the analysis of the RBM spectrum can reveal pairs of lines associated with the inner/outer shell structure of DWCNT, and when the intensities between the recorded and calculated spectra coincide, the nanotube is metallic; otherwise, the nanotube is semiconducting. Copyright (c) 2014 John Wiley & Sons, Ltd.

In this work, the architecture of ZnO particles was found to be changed from nano-whiskers to flowers via the addition of fullerenes in the reaction mixture consisting of zinc chloride, sodium hydroxide and sodium dodecyl sulfate. The change in the morphological structure of ZnO particles is accompanied by a decrease in the photoluminescence (PL) intensity and the appearance of a new Raman line at 1594 cm(-1) that indicates the formation of the compound ZnC60. The growth of the ZnO flower-like particles occurs simultaneously with an aggregation process of C-60 in highly ordered structures, as evidenced in the Raman spectrum by a line at 2934 cm I. A mechanism for the growth of the ZnO flower-like particles is proposed in this work. (C) 2015 Elsevier B.V. All rights reserved.

By performing comparative Raman studies on nanometric thin films (9.5, 39, 88 and 185 nm) of copper phthalocyanine (CuPc) deposited on glass, Au and Ag supports, we demonstrate that the mechanism of the surface-enhanced Raman scattering (SERS) generated on Au and Ag substrates differs in the Stokes and anti-Stokes Raman branches depending on whether non-resonant (515.5 nm) or resonant (647.1 nm) optical excitation is applied. The evaluation of the SERS effect via the I-aS/I-S ratio reveals that this ratio is smaller or larger than that predicted by the Boltzmann law for non-resonant or resonant optical excitation, respectively. In the former case, the enhancement of the Stokes Raman emission is similar to a stimulated Raman process resulting from the plasmon coupling associated with the incident excitation light and spontaneous Stokes Raman emission. For the latter case, the amplification of the anti-Stokes Raman emission results from a wave-mixing process reminiscent of a single-beam CARS effect.