Ultrafast optical manipulation of atomic arrangements in chalcogenide alloy memory materials

A class of chalcogenide alloy materials that shows significant changes in optical properties upon an amorphous-to-crystalline phase transition has lead to development of large data capacities in modern optical data storage. Among chalcogenide phase-change materials, Ge2Sb2Te5 (GST) is most widely used because of its reliability. We use a pair of femtosecond light pulses to demonstrate the ultrafast optical manipulation of atomic arrangements from tetrahedral (amorphous) to octahedral (crystalline) Ge-coordination in GST superlattices. Depending on the parameters of the second pump-pulse, ultrafast nonthermal phase-change occurred within only few-cycles (~ 1 ps) of the coherent motion corresponding to a GeTe4 local vibration. Using the ultrafast switch in chalcogenide alloy memory could lead to a major paradigm shift in memory devices beyond the current generation of silicon-based flash-memory.Comment: 11 pages, 7 figures, accepted for publication in Optics Expres

Photo-induced Tellurium segregation in MoTe2\mathrm{MoTe_2}

We report on the coherent phonon spectroscopy of polymorphic $\mathrm{MoTe_2}$ single crystals using a femtosecond-pulsed laser to investigate the relationship between structural phase transitions and photo-thermal effects induced by high-density laser excitation. Even when a femtosecond pulsed laser was used, which generally induces fewer heat accumulation effects than the case for a CW laser, tellurium segregation was observed in coherent phonon spectra with increasing excitation density, while no structural phase transition among polymorphs of $\mathrm{MoTe_2}$ was observed. The use of higher photon-energy excitation, however, was found to suppress tellurium segregation.Comment: 15 pages, 4 figures, accepted for Physica Status Solidi (RRL) - Rapid Research Letter

Coherent monochromatic phonons in highly purified semiconducting single-wall carbon nanotubes

We have used a femtosecond pump-probe impulsive Raman technique to explore the polarization dependence of coherent optical phonons in highly purified and aligned semiconducting single-wall carbon nanotubes (SWCNTs). Coherent phonon spectra for the radial breathing modes (RBMs) exhibit a different monochromatic frequency between the film and solution samples, indicating the presence of differing exciton excitation processes. By varying the polarization of the incident pump beam on the aligned SWCNT film, we found that the anisotropy of the coherent RBM excitation depends on the laser wavelength, which we consider to be associated with the resonant and off-resonant behavior of RBM excitation

Mirror-symmetric Magneto-optical Kerr Rotation using Visible Light in [(GeTe)2(Sb2Te3)1]n Topological Superlattices

Interfacial phase change memory (iPCM), that has a structure of a superlattice made of alternating atomically thin GeTe and Sb2Te3 layers, has recently attracted attention not only due to its superior performance compared to the alloy of the same average composition in terms of energy consumption but also due to its strong response to an external magnetic field (giant magnetoresistance) that has been speculated to arise from switching between topological insulator (RESET) and normal insulator (SET) phases. Here we report magneto-optical Kerr rotation loops in the visible range, that have mirror symmetric resonances with respect to the magnetic field polarity at temperatures above 380 K when the material is in the SET phase that has Kramers-pairs in spin-split bands. We further found that this threshold temperature may be controlled if the sample was cooled in a magnetic field. The observed results open new possibilities for use of iPCM beyond phase-change memory applications

Measuring serum and drainage fluid interleukin-6 and tumor necrosis factor-α levels for early detection of infectious complications after minimally invasive surgery for gastric cancer

Itami T., Kurokawa Y., Yoshioka R., et al. Measuring serum and drainage fluid interleukin-6 and tumor necrosis factor-α levels for early detection of infectious complications after minimally invasive surgery for gastric cancer. European Journal of Surgical Oncology 50, 108564 (2024); https://doi.org/10.1016/j.ejso.2024.108564.Objective: Interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) are inflammatory cytokines produced in response to biological invasion or infection. Their levels are elevated in the blood and locally. We examined whether measuring IL-6 and TNF-α levels in serum or drainage fluid on postoperative day (POD) 1 could detect infectious complications after minimally invasive surgery for gastric cancer. Methods: This cohort study included 205 consecutive patients who underwent laparoscopic or robot-assisted gastrectomy for gastric cancer between November 2020 and July 2023. We measured serum and drainage fluid IL-6 and TNF-α levels on POD 1 after gastrectomy. Receiver operating characteristic (ROC) curves were created to compare the diagnostic values of each cytokine and serum C-reactive protein levels for detecting postoperative infectious complications. Results: IL-6 and TNF-α levels in the serum or drainage fluid were significantly higher in patients with an infectious complication. In addition, drainage fluid IL-6 levels were significantly different in patients with versus without intra-abdominal abscess. In the ROC curve analysis, serum and drainage fluid IL-6 had the highest AUC values for any infectious complication and intra-abdominal abscess, respectively. POD 1 serum IL-6 level above 47 pg/mL could detect any infectious complication with sensitivity of 74.1 % and specificity of 71.8 %. POD 1 drainage fluid IL-6 level above 14,750 pg/mL had 100 % sensitivity for detecting intra-abdominal abscess with specificity of 56.0 %. Conclusions: Measurement of IL-6 levels in blood and drainage fluid on POD 1 is valuable for early detection of postoperative infectious complications or intra-abdominal abscess after gastric cancer surgery