Phonon fingerprints of CsPb2Br5.

CsPb2Br5 is a stable, water-resistant, material derived from CsPbBr3 perovskite and featuring two-dimensional Pb-Br framework separated by Cs layers. Both compounds can coexist at nanolength scale, which often produces conflicting optical spectroscopy results. We present a complete set of polarized Raman spectra of nonluminescent CsPb2Br5 single crystals that reveals the symmetry and frequency of nondegenerate Raman active phonons accessible from the basal (0 0 1) plane. The experimental results are in good agreement with density functional perturbation theory simulations, which suggests that the calculated frequencies of yet unobserved double degenerate Raman and infrared phonons are also reliable. Unlike CsPbBr3, the lattice dynamics of CsPb2Br5 is stable as evidenced by the calculated phonon dispersion. The sharp Raman lines and lack of a dynamic-disorder-induced central peak in the spectra at room temperature indicate that the coupling of Cs anharmonic motion to Br atoms, known to cause the dynamic disorder in CsPbBr3, is absent in CsPb2Br5.

HRTEM low dose: the unfold of the morphed graphene, from amorphous carbon to morphed graphenes.

We present experimental evidence under low-dose conditions transmission electron microscopy for the unfolding of the evolving changes in carbon soot during mechanical milling. The milled soot shows evolving changes as a function of the milling severity or time. Those changes are responsible for the transformation from amorphous carbon to graphenes, graphitic carbon, and highly ordered structures such as morphed graphenes, namely Rh6 and Rh6-II. The morphed graphenes are corrugated layers of carbon with cross-linked covalently nature and sp2- or sp3-type allotropes. Electron microscopy and numerical simulations are excellent complementary tools to identify those phases. Furthermore, the TEAM 05 microscope is an outstanding tool to resolve the microstructure and prevent any damage to the sample. Other characterization techniques such as XRD, Raman, and XPS fade to convey a true identification of those phases because the samples are usually blends or mixes of the mentioned phases.

Validation of pre- and postoperative nomograms used to predict the pathological stage and prostate cancer recurrence after radical prostatectomy: a multi-institutional study.

PURPOSE: To validate the preoperative and postoperative predictive tables of Johns Hopkins hospital, Baltimore, Maryland (JHH) and the prostate nomograms of Memorial Sloan Kettering Cancer Center, New York (MSKCC), most commonly used to predict the pathological tumor stage and postoperative freedom from recurrence, in a mixed cohort of Bulgarian prostate cancer patients. METHODS: Clinical and laboratory data of 282 prostate cancer patients, who underwent radical prostatectomy, were supplied from three different institutions in Bulgaria. Preoperative prostate specific antigen (PSA) values, clinical stage, biopsy Gleason score and the pathological features of the radical prostatectomy specimens were collected from each center and evaluated. Nomogram-predicted probabilities for the presence of unfavorable pathological parameters (extracapsular extension, seminal vesicle invasion/SVI, and lymph node involvement/LNI), and the 5-year freedom from recurrence were compared with actual patient outcomes. Areas under the receiver operating characteristic (ROC) curves (AUC) were determined for each variable to assess the predictive accuracy of the nomograms applied. RESULTS: The MSKCC prostate cancer nomograms showed superior accuracy for all parameters studied, as compared with the JHH predictive tables. AUC values for organ-confined disease (OCD), SVI and LNI were calculated as 0.763, 0.750, 0.756 and 0.868, 0.787, 0.874 for JHH and MSKCC nomograms, respectively. The AUC values for 5-year freedom from recurrent disease were 0.751, 0.812, 0.813 and 0.894 for pre- and postoperative JHH and MSKCC nomograms, respectively. CONCLUSION: Despite the potential for heterogeneity in patient selection and management, most predictions demonstrated high concordance with actual observations. All studied nomograms showed reasonable predictive values for the fi nal pathological features, like OCD, SVI and LNI, and for the 5-year freedom from recurrent disease. This multi-institutional study showed that each of the predictive tools studied could be used in Bulgarian patients with comparable accuracy. Compared with the JHH tables, the MSKCC prostate cancer nomograms showed higher predictive accuracy and should therefore be preferred.

Parallel and orthogonal E-field alignment of single-walled carbon nanotubes by ac dielectrophoresis.

We designed planar electrodes, for dielectrophoretic manipulation of single-walled carbon nanotubes (SWNTs), built as metal-oxide-semiconductor nanogap capacitors with common substrate and oxide thicknesses of 17 and 150 nm. Such design generates high electric fields (10(9) V m(-1)) and also the fringing field is curved due to the conducting substrate, unlike fields generated by conventionally used planar electrodes. Scanning electron microscopy images showed SWNTs aligned parallel and perpendicular to the electrodes. Raman spectroscopic mapping was used to produce separate images of the metallic (m-SWNT) and semiconducting (s-SWNT) nanotube density distributions. As expected, parallel alignment of the m-SWNTs with the E-field was found; however, also a perpendicular alignment of s-SWNTs was observed. Such orthogonal alignment of s-SWNTs is a rare observation and has not been experimentally reported before in detail with Raman images. Due to the unique electrode design, we were able to obtain substantial separation of m-SWNTs and s-SWNTs. Numerical modeling of the electric field factor of the dielectrophoresis force was done, and it matched perfectly with the experimental results. The orthogonal alignment of s-SWNTs results from comparable values of parallel and perpendicular polarizability to the nanotube axis.

Thermal mismatch strains in sidewall functionalized carbon nanotube/polystyrene nanocomposites.

We present an unusual temperature dependence of thermal strains in 4-(10-hydroxy)decyl benzoate (HDB) modified SWNTPS (SWNT-single wall carbon nanotube, PS-polystyrene) nanocomposites. The strain transfer from the matrix to nanotubes in these nanocomposites, inferred from the frequency change of the Raman active tangential modes of the nanotubes, is enhanced strongly below 300 K, whereas it is vanishingly small at higher temperatures. The increased strain transfer is suggestive of reinforcement of the HDB-SWNTPS nanocomposites at low temperatures. On the other hand, the pristine SWNTs couple weakly to the PS matrix over the entire temperature range of 4.5-410 K. We argue that the strain transfer in HDB-SWNTPS is determined by the thermomechanical properties of the interface region composed of polystyrene plasticized by the tethered alkanelike modifier.