Comment on "Investigation on the structure and thermoelectric properties of CuxTe binary compounds" by Shriparna Mukherjee et al., Dalton Trans., 2019, 48, 1040.

The Raman spectra of copper tellurides are nearly unknown. This is due not only to the difficulty in obtaining single-phase specimens, but also to the low inelastic light scattering efficiency of Cu2-xTe. To date, only the Raman spectrum of the vulcanite phase, CuTe, has been both measured and calculated by density functional theory. The authors of the commented work reported the Raman spectra of Cu2Te, Cu1.6Te and Cu1.25Te samples. However, the assignment of the measured modes has been defective and their Raman spectra lack some of the features usually found for copper tellurides.

Vibrational and electrical properties of Cu2-xTe films: experimental data and first principle calculations.

Vibrational and electrical properties of sputtered films of the copper telluride system are presented. Despite of its technological importance in photovoltaics, the fundamental properties of copper tellurides are poorly understood. Films were deposited at 200 °C by rf sputtering from targets containing mixtures of copper and tellurium powders at nominal concentrations of Cu1.25Te, Cu1.5Te, Cu1.75Te and Cu2Te. Remarkably for the copper telluride system, it was possible to obtain single-phase vulcanite (CuTe) from the Cu1.25Te target. Two-phase mixtures of rickardite (Cu7Te5) and weissite (Cu2-xTe) were achieved for other cases. Raman spectra were obtained using two laser lines: 633 and 488 nm. Density functional theory was employed to calculate the phonon dispersion curves and density of states for vulcanite. The Raman bands were in good correspondence with the calculated frequencies. In general, the Raman spectra consisted of high-intensity totally symmetric modes superimposed on monotonically decaying signals. These were explained in terms of three contributing phenomena: convolution of vibrational normal modes, phonon-coupled charge density fluctuations and time-varying local-field contributions to the electric susceptibility. Studies on the conductivity, mobility and carrier concentration were carried out by the Van der Pauw method. Micro/nano scale surface potential studies were performed through Kelvin probe force microscopy mapping.

Lithium Adsorption on Graphene: From Isolated Adatoms to Metallic Sheets.

We have studied Li adsorption on graphene for Li concentrations ranging from about 1% to 50% by means of density functional theory calculations. At low adsorbant densities, we observe a strong ionic interaction characterized by a substantial charge transfer from the adatoms to the substrate. In this low concentration regime, the electronic density around the Li adatoms is well localized and does not contribute to the electronic behavior in the vicinity of the Fermi level. For larger concentrations, we observe the formation of a chemically bound Li layer characterized by a stronger binding energy as well as a significant density of states above the Fermi level coming from both graphene and the two-dimensional Li sheet.