Raman Spectra of ZrS2 and ZrSe2 from Bulk to Atomically Thin Layers

In the race towards two-dimensional electronic and optoelectronic devices, semiconducting transition metal dichalcogenides (TMDCs) from group VIB have been intensively studied in recent years due to the indirect to direct band-gap transition from bulk to the monolayer. However, new materials still need to be explored. For example, semiconducting TMDCs from group IVB have been predicted to have larger mobilities than their counterparts from group VIB in the monolayer limit. In this work we report the mechanical exfoliation of ZrX2 (X = S, Se) from bulk down to the monolayer and we study the dimensionality dependence of the Raman spectra in ambient conditions. We observe Raman signal from bulk to few layers and no shift in the peak positions is found when decreasing the dimensionality. While a Raman signal can be observed from bulk to a bilayer for ZrS2, we could only detect signal down to five layers for flakes of ZrSe2. These results show the possibility of obtaining atomically thin layers of ZrX2 by mechanical exfoliation and represent one of the first steps towards the investigation of the properties of these materials, still unexplored in the two-dimensional limit

Tunable coupled surface acoustic cavities

We demonstrate the electric tuning of the acoustic field in acoustic microcavities(MCs) defined by a periodic arrangement of metal stripes within a surface acoustic delay line on LiNbO3 substrate. Interferometric measurements show the enhancement of the acoustic field distribution within a single MC, the presence of a"bonding" and"anti-bonding" modes for two strongly coupled MCs, as well as the positive dispersion of the"mini-bands" formed by five coupled MCs. The frequency and amplitude of the resonances can be controlled by the potential applied to the metal stripes

Photoluminescence study of excitons in homoepitaxial GaN

High-resolution photoluminescence spectra have been measured in high-quality homoepitaxial GaN grown on a free-standing GaN substrate with lower residual strain than in previous work. Unusually strong and well-resolved excitonic lines were observed. Based on free- and bound exciton transitions some important GaN parameters are derived. The Arrhenius plot of the free A exciton recombination yields a binding energy of 24.7 meV. Based on this datum, an accurate value for the band-gap energy, EG(4.3 K) = 3.506 eV, can be given. From the donor bound excitons and their “two-electron” satellites, the exciton localization energy and donor ionization energy are deduced. Finally, estimates of the electron and hole masses have been obtained within the effective mass [email protected] ; [email protected]

Modulation of the electronic properties of GaN films by surface acoustic waves

We report on the interaction between photogenerated electron-hole pairs and surface acoustic waves (SAW) in GaN films grown on sapphire substrates. The spatial separation of photogenerated carriers by the piezoelectric field of the SAW is evidenced by the quenching of the photoluminescence (PL) intensity. The quenching levels in GaN are significantly smaller than those measured in GaAs under similar conditions. The latter is attributed to the lower exciton ionization efficiency and carrier separation probabilities mediated by the piezoelectric effect. The PL spectra also evidence energy shifts and broadenings of the electronic transitions, which are attributed to the band gap modulation by the SAW strain [email protected]

Polarized and resonant Raman spectroscopy on single InAs nanowires

We report polarized Raman scattering and resonant Raman scattering studies on single InAs nanowires.Polarized Raman experiments show that the highest scattering intensity is obtained when both the incident and analyzed light polarizations are perpendicular to the nanowire axis. InAs wurtzite optical modes are observed. The obtained wurtzite modes are consistent with the selection rules and also with the results of calculations using an extended rigid-ion model. Additional resonant Raman scattering experiments reveal a redshifted E1 transition for InAs nanowires compared to the bulk zinc-blende InAs transition due to the dominance of the wurtzite phase in the nanowires. Ab initio calculations of the electronic band structure for wurtzite and zinc-blende InAs phases corroborate the observed values for the E1 transitions

Antibacterial action, antioxidant activity and anticoagulant effect of pectin extracted from peels of algerian citrus sinensis

In this study, we characterised the pectin extracted from peels of Algerian Citrus sinensis and evaluated its antibacterial action, antioxidant activity and anticoagulant effect. Pectin was extracted under acidic conditions using hydrochloric acid for PCT-1 and citric acid for PCT-2 and determining their physicochemical properties using Fourier-Transform Infrared spectroscopy (FTIR), X-ray powder diffraction (PXRD), differential scanning calorimetry (DSC), yield, the degree of methylation, water content and ash content. In addition, the FTIR results showed desired banding characteristics, and their thermal properties evaluated using DSC showed that the thermal degradation was around 240 °C. XRD results show that PCT-1 and PCT-2 are amorphous and have similar characteristics to commercial pectin. On the other hand, the antibacterial action showed that PCT-1 and PCT-2 have no effect on Pseudomonas aeruginosa and E. coli bacteria, unlike Staphylococcus epidermidis, where it showed considerable antibacterial action. The antioxidant activity of PCT-1 and PCT-2 was observed using the 2,2 diphenyl-1-picrylhydrazyl (DPPH) method; the absorbance values recorded for PCT-1 and PCT-2 confirmed their antioxidant potential explained by the presence of several free hydroxyl groups in the PCT-1 and PCT-2 structure. On the other hand, our findings indicate that PCT-1 and PCT-2 do not have a marked anticoagulant effect but have acceptable potential and can be used as anticoagulants for the treatment of thrombotic diseases with fewer side effects compared to the widely used heparin. These results suggest that pectin from the peels of Algerian Citrus sinensis has potential properties as a biomaterial for several biomedical applications

Ultrathin transparent Nickel electrodes for thermoelectric applications

In this work, ultrathin nickel films are developed for application as transparent electrodes in thermoelectric devices. The quality of the films is determined systematically by electrical, optical, and morphological characterization in a series of samples with different thickness. The thermal properties of the films show a dramatic dependence of the Seebeck coefficient on the film thickness. This dependence, with values ranging from −16 to +5 V K−1 for thicknesses from 10 to 2 nm, includes a change in the behavior of the thermoelectric response from n- to p-type. It has also been demonstrated that the accurate estimation of the thermal conductivity in thin films is challenging due to substrate effects. In this situation, a differential measurement method based on scanning thermal microscopy is proposed, as in these conditions the measurements are less sensitive to the substrate effects. In further works, the dependence of the thermal properties of ultrathin nickel films can be exploited as a tuning parameter for the design of thermoelectric devices

Erratum: Polarized and resonant Raman spectroscopy on single InAs nanowires (vol 84, 085318, 2011)

We found out that the polar pattern for the zinc-blende InAs LO mode displayed in Fig. 2(b) of our original paper represents the backscattering Raman intensities from a (11¯2) top surface and not as stated in the original manuscript from a (110) top surface.In the latter the LO mode is forbidden for all configurations