Investigations of proximity-induced superconductivity in the topological insulator Bi2Te3 by microRaman spectroscopy

We used the topological insulator (TI) Bi2Te3 and a high-temperature superconductor (HTSC) hybrid device for investigations of proximity-induced superconductivity (PS) in the TI. Application of the superconductor YBa2Cu3O7-δ (YBCO) enabled us to access higher temperature and energy scales for this phenomenon. The HTSC in the hybrid device exhibits emergence of a pseudogap state for T > Tc that converts into a superconducting state with a reduced gap for T < Tc. The conversion process has been reflected in Raman spectra collected from the TI. Complementary charge transport experiments revealed emergence of the proximity-induced superconducting gap in the TI and the reduced superconducting gap in the HTSC, but no signature of the pseudogap. This allowed us to conclude that Raman spectroscopy reveals formation of the pseudogap state but cannot distinguish the proximity-induced superconducting state in the TI from the superconducting state in the HTSC characterised by the reduced gap. Results of our experiments have shown that Raman spectroscopy is a complementary technique to classic charge transport experiments and is a powerful tool for investigation of the proximity-induced superconductivity in the Bi2Te3.

Quantum size effect on charges and phonons ultrafast dynamics in atomically controlled nanolayers of topological insulators Bi2Te3

Heralded as one of the key elements for next generation spintronics devices, topological insulators (TIs) are now step by step envisioned as nanodevices like charge-to-spin current conversion or as Dirac fermions based nanometer Schottky diode for example. However, reduced to few nanometers, TIs layers exhibit a profound modification of the electronic structure and the consequence of this quantum size effect on the fundamental carriers and phonons ultrafast dynamics has been poorly investigated so far. Here, thanks to a complete study of a set of high quality molecular beam epitaxy grown nanolayers, we report the existence of a critical thickness of around ~6 nm, below which a spectacular reduction of the carrier relaxation time by a factor of ten is found in comparison to bulk Bi2 Te3 In addition, we also evidence an A1g optical phonon mode softening together with the appearance of a thickness dependence of the photoinduced coherent acoustic phonons signals. This drastic evolution of the carriers and phonons dynamics might be due an important electron-phonon coupling evolution due to the quantum confinement. These properties have to be taken into account for future TIs-based spintronic devices.

Unique properties of silver and copper silica-based nanocomposites as antimicrobial agents

The paper reports a new route for the fabrication and determination of physicochemical properties and biological activity, of metallic silica-based nanostructure (Ag/SiO₂, Cu/SiO₂).

Morphology and local conductance of single crystalline Bi2Te3 thin films on mica

The relation between surface morphology and local conductance was studied for single crystalline thin films of Bi2Te3 grown on mica. Atomic force microscopy and electron diffraction revealed the hexagonal order of the surface with quintuple layer steps and spiral islands. Furthermore, the experiments using contact mode AFM with conducting tip performed at room temperature revealed the high conductance of the surface, which was locally reduced due to changes in the local electronic structure at the defects (e.g. edges of the terraces). Contact current-voltage characteristics tested over the surface showed a linear behavior in every point, with the resistance significantly lower than the resistance of reference metallic samples (gold, platinum). We show that local conductivity AFM is a good technique to exploit the peculiar surface properties of topological insulators.

Abstract P6-06-30: Are synchronous and metachronous bilateral breast cancers different? An immunohistochemical analysis aimed at intrinsic tumor phenotype

Background: The biology and pathomechanism of bilateral breast cancers is not fully understood: the risk of developing second (metachronous) breast cancer is 4-6 times higher than that of first primary in general population, whereas for synchronous breast cancers the number of cases is about 100 times higher than could be expected by chance alone. We compared the morphological and immunohistochemical characteristics of primary synchronous (sBBC) vs. metachronous (mBBC) bilateral breast cancers), with special focus on intrinsic tumor phenotype.

Methods: Tumor morphology and expression of 8 immunohistochemical markers were assessed in tissue microarrays containing primary breast tumor cores from 113 mBBC and 61 sBBC. Analyzed markers included hormone receptors (estrogen receptor, progesterone receptor), HER2, Ki67, cytokeratin 5/6, E-cadherin, vimentin and epidermal growth factor receptor. Surrogate intrinsic phenotypes were determined according to St Gallen 2011 criteria.

Results: mBBChad higher incidence of ductal histology (p = 0.037), lower estrogen receptor expression (p = 0.047), and higher expression of cytokeratin 5/6 (p = 0.017) and of vimentin (p = 0.008); in multivariate analysis only vimentin retained the significance (p = 0.01). Ten (13%) and 11 (26%) of mBBCand sBBC, respectively, had luminal A phenotype, 39 (50%) and 15 (36%) were luminal B HER2-negative, 13 (17%) and 12 (28%) - luminal B HER2-positive, 3 (4%) and 2 (5%) - HER2-positive (not luminal), and 12 (16%) and 2 (5%) had triple negative phenotype (p = 0.07).

Characteristics of mBBC and sBBCFeaturemBBC (%)sBBC (%)p valueDuctal histology98 (87)47 (77)0.037Grade 346 (41)17 (28)0.09Extensive intraductal component26 (23)18 (29)0.42Strong ER expression73 (67)48 (81)0.047Strong PR expression55 (49)38 (63)0.07HER2 positivity (2+, 3+)51 (46)29 (50)0.6Ki76 ≤14%24 (22)21 (35)0.06Surrogate intrinsic phenotype   luminal A10 (13)11 (26) luminal B HER2-39 (50)15 (36) luminal B HER2+13 (17)12 (28)0.07triple negative12 (16)2 (5) HER2+ (non luminal)3 (4)2 (5) CK5/6 &gt;10%28 (26)6 (11)0.017Vimentin &gt;10%25 (23)4 (7)0.008E-cadherin (+)88 (83)49 (83)0.99EGFR (+)35 (32)11 (19)0.07

Conclusion: mBBC, compared to sBBC, are characterized by more aggressive phenotype, expressed by lower expression of estrogen receptor and stronger expression of cytokeratin /6 and vimentin; this does not, however, translate into substantial differences in the proportion of intrinsic tumor phenotypes.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-06-30.

Abstract P5-04-01: Expression of epithelial-mesenchymal transition (EMT)-related markers in primary tumors and matched lymph node metastases in breast cancer patients

Background. Malignant tumors may include multiple cancer cell populations with various metastatic potential. More aggressive subpopulations might easier be captured in lymph nodes metastases (LNM) than in primary tumors (PT). We evaluated mRNA and protein levels of master EMT regulators: TWIST1, SNAIL and SLUG, protein levels of EMT-related markers: E-cadherin, vimentin, and expression of classical breast cancer receptors: HER2, ER and PR in PT and corresponding LNM. The results were correlated with clinicopathological data and patient outcomes.

Methods. Formalin-fixed paraffin-embedded (FFPE) samples from PT and matched LNM from 42 stage II-III breast cancer patients were examined. Expression of TWIST1, SNAIL and SLUG was measured by RT-qPCR, with median as cut off for positive result. Protein expression was examined by immunohistochemistry on tissue microarrays. For TWIST1, SNAIL, SLUG, E-cadherin and vimentin &gt;10% of positively stained cells defined positive result. ER and PR were scored according to Allred system, and HER2 - according to HercepTest criteria. Results were considered concordant if PT and LNM were both positive or both negative. Concordance was measured by estimating Cohen's kappa coefficient (κ), with κ value equal 1 indicating perfect agreement. Disease-free survival (DFS) and overall survival (OS) were compared using F-Cox test. Hazard ratios (HRs) with 95% confidence intervals (95% CI) were computed using Cox regression analysis.

Results. On average, expression of TWIST1, SNAIL and SLUG was significantly higher in LNM compared to PT (P &lt; 0.00001 for all). Gene and protein levels of TWIST1, SNAIL and SLUG were highly discordant between PT and matched LNM (Tab 1). Receptor conversion, particularly loss of ER and PgR, occurred in 18% and 29% of cases, respectively. Increased expression of TWIST1 and SNAIL in LNM was associated with shorter OS (p = 0.045 and p = 0.022, respectively) and DFS (p = 0.02 and p = 0.01, respectively), whereas their expression in PT had no prognostic impact. Negative-to-positive switch of TWIST, SNAIL and vimentin correlated with shorter OS and DFS. Conversion of ER and PR had no significant impact on survival.

Conclusions. LNM are enriched in cells with more aggressive phenotype, marked by elevated levels of EMT regulators. High expression of TWIST1 and SNAIL in LNM, as well as negative-to-positive conversion of both TWIST1 and SNAIL confer worse prognosis, confirming the correlation of EMT with aggressive disease behavior.

Gasochromic switching of Ta and Pd-doped nanocrystalline TiO2 thin films

In this work TiO2:(Ta, Pd) thin films with gasochromic properties have been described. Thin films were prepared by reactive magnetron sputtering process using mosaic Ti-Ta-Pd target. The amounts of dopants were 2.54 at.% and 12.36 at.% of Ta and Pd, respectively. The results of optical measurements performed at presence of ethanol and additional heating of the sample up to 350 degrees C have shown an abrupt change of transmission level from 80% down to 10% in VIS and in IR range. The gasochromic change was very fast. Moreover, rapid cooling (down to room temperature) in an air ambient results in stable thin film coloration. The reverse effect (bleaching) was obtained after annealing at 500 degrees C in an ambient air.

Biocompatible, smooth, plasma-treated nickel-titanium surface--an adequate platform for cell growth

High nickel content is believed to reduce the number of biomedical applications of nickel-titanium alloy due to the reported toxicity of nickel. The reduction in nickel release and minimized exposure of the cell to nickel can optimize the biocompatibility of the alloy and increase its use in the application where its shape memory effects and pseudoelasticity are particularly useful, e.g., spinal implants. Many treatments have been tried to improve the biocompatibility of Ni-Ti, and results suggest that a native, smooth surface could provide sufficient tolerance, biologically. We hypothesized that the native surface of nickel-titanium supports cell differentiation and insures good biocompatibility. Three types of surface modifications were investigated: thermal oxidation, alkali treatment, and plasma sputtering, and compared with smooth, ground surface. Thermal oxidation caused a drop in surface nickel content, while negligible chemistry changes were observed for plasma-modified samples when compared with control ground samples. In contrast, alkali treatment caused significant increase in surface nickel concentration and accelerated nickel release. Nickel release was also accelerated in thermally oxidized samples at 600 °C, while in other samples it remained at low level. Both thermal oxidation and alkali treatment increased the roughness of the surface, but mean roughness R(a) was significantly greater for the alkali-treated ones. Ground and plasma-modified samples had 'smooth' surfaces with R(a)=4 nm. Deformability tests showed that the adhesion of the surface layers on samples oxidized at 600 °C and alkali treatment samples was not sufficient; the layer delaminated upon deformation. It was observed that the cell cytoskeletons on the samples with a high nickel content or release were less developed, suggesting some negative effects of nickel on cell growth. These effects were observed primarily during initial cell contact with the surface. The most favorable cell responses were observed for ground and plasma-sputtered surfaces. These studies indicated that smooth, plasma-modified surfaces provide sufficient properties for cells to grow.