Femtosecond x-ray diffraction reveals a liquid–liquid phase transition in phase-change materials

6 pags., 5 figs.In phase-change memory devices, a material is cycled between glassy and crystalline states. The highly temperature-dependent kinetics of its crystallization process enables application in memory technology, but the transition has not been resolved on an atomic scale. Using femtosecond x-ray diffraction and ab initio computer simulations, we determined the time-dependent pair-correlation function of phase-change materials throughout the melt-quenching and crystallization process. We found a liquid–liquid phase transition in the phase-change materials AgInSbTe and GeSb at 660 and 610 kelvin, respectively. The transition is predominantly caused by the onset of Peierls distortions, the amplitude of which correlates with an increase of the apparent activation energy of diffusivity. This reveals a relationship between atomic structure and kinetics, enabling a systematic optimization of the memory-switching kinetics.F.Q., A.K., M.N., and K.S.T. gratefully acknowledge financial support from the German Research Council through the Collaborative Research Center SFB 1242 project 278162697 (“Non-Equilibrium Dynamics of Condensed Matter in the Time Domain”), project C01 (“Structural Dynamics in Impulsively Excited Nanostructures”), and individual grant So408/9-1, as well as the European Union (7th Framework Programme, grant no. 280555 GO FAST). M.J.S., R.M., and M.W. acknowledge financial support from the German Research Council through the Collaborative Research Center SFB 917 (“Nanoswitches”) and individual grant Ma-5339/2-1. M.J.S., I.R., and R.M. also acknowledge the computational resources granted by JARA-HPC from RWTH Aachen University under project nos. JARA0150 and JARA0183. M.T., A.M.L., and D.A.R. were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, through the Division of Materials Sciences and Engineering under contract no. DE-AC02-76SF00515. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. J.L. acknowledges support from the Swedish Research Council. J.S. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities through research grant UDiSON (TEC2017-82464-R). P.Z. gratefully acknowledges funding by the Humboldt Foundatio

Modelling and optimisation of femtosecond laser-produced K-alpha sources

The most reliable prognostic factor in colon cancer is the TNM classification. The objective of this study was to assess and compare the prognostic role of tumor-infiltrating lymphocytes (TILs) in stage II colon cancer.Immunohistochemistry was used to assess the density of TILs that were positive for cluster of differentiation 3 (CD3) (T-cell coreceptor), CD45 isoform RO (CD45RO) (protein tyrosine phosphatase), nuclear transcription factor forkhead box P3 (FOXP3), and CD25 (a type I transmembrane protein) according to tumor site (intraepithelial and stromal) in samples from 87 patients who had stage II colon cancer. These variables were evaluated for their association with histopathologic features along with overall survival (OS) and disease-free survival (DFS).Intraepithelial CD3-posititve (CD3+), CD45RO+, CD25+, and FOXP3+ TILs were associated significantly with better DFS (P = .049, P = .009, P = .013, and P = .001, respectively). The estimated 5-year OS rates for patients who had high-density CD45RO+ and FOXP3+ expression was 100% for both compared with 79.2% and 78.8% for patients who had low-density CD45RO+ and FOXP3+ expression (P = .017 and P = .040, respectively). A significant prognostic factor for both OS and DFS was high-density stromal CD45RO+ lymphocytic infiltration (OS: P = .031; relative risk [RR], 0.134; 95% confidence interval [CI], 0.015-1.164; DFS: P = .013; RR, 0.198; 95% CI, 0.055-0.710); whereas intraepithelial FOXP3+ expression was an independent prognostic factor for DFS (P = .032; RR, 0.108; 95% CI, 0.014-0.821).FOXP3+ and CD45RO+ TILs demonstrated independent prognostic significance for survival in the current investigation. These results may help to improve the prognostication of early stage colon cancer. Cancer 2010

Optimized K alpha x-ray flashes from femtosecond-laser-irradiated foils

We investigate the generation of ultrashort K alpha pulses from plasmas produced by intense femtosecond p-polarized laser pulses on Copper and Titanium targets. Particular attention is given to the interplay between the angle of incidence of the laser beam on the target and a controlled prepulse. It is observed experimentally that the K alpha yield can be optimized for correspondingly different prepulse and plasma scale-length conditions. For steep electron-density gradients, maximum yields can be achieved at larger angles. For somewhat expanded plasmas expected in the case of laser pulses with a relatively poor contrast, the K alpha yield can be enhanced by using a near-normal-incidence geometry. For a certain scale-length range (between 0.1 and 1 times a laser wavelength) the optimized yield is scale-length independent. Physically this situation arises because of the strong dependence of collisionless absorption mechanisms-in particular resonance absorption-on the angle of incidence and the plasma scale length, giving scope to optimize absorption and hence the K alpha yield. This qualitative description is supported by calculations based on the classical resonance absorption mechanism and by particle-in-cell simulations. Finally, the latter simulations also show that even for initially steep gradients, a rapid profile expansion occurs at oblique angles in which ions are pulled back toward the laser by hot electrons circulating at the front of the target. The corresponding enhancement in K alpha yield under these conditions seen in the present experiment represents strong evidence for this suprathermal shelf formation effect

Ultrafast x-ray diffraction

In the last few years the generation of femtosecond pulses in the X-ray regime has become possible. These ultrashort X-ray pulses have enabled femtosecond time-resolution to be extended to X-rays

Monitoring of the ultrafast vibrational kinetic during formation of photo-induced linkage isomers in Na 2 [Fe(CN) 5 NO] . 2H 2 O single crystal

A femtosecond visible pump-infrared probe time resolved absorption experiment makes it possible to reveal the ultrafast vibrationnal kinetic associated to formation of light-induced linkage isomers in Na 2 [Fe(CN) 5 NO]2H 2 O (SNP) single crystals. Time-resolved spectroscopy on a femtosecond scale makes it possible to observe and to record photochemical processes [1-2]. The ultrafast study of electronic, vibrational and structural changes during light-induced isomerization reveals the correlation between the changes of the electron density and the structural response of matter. Consider an electronic transition that excites a molecule from a (bonding) ground state to an (reactive) excited state that is the starting point for, e.g., the rotation of a ligand in a molecule. According to the Born-Oppenheimer approximation the direct electronic excitation in the sub-femtosecond range is followed by a slower nuclear response in the fs-ps range. The nuclear motion (e.g. rotation) of the ligand starts in a highly excited state and in the absence of luminescence will end in highly excited vibrational-rotational states of the novel geometry. The excess energy will be dissipated during the thermalization of this highly excited vibrational-rotational state towards its ground state. A typical example for such ultrafast photochemical processes is the photo-induced linkage isomerism of the nitrosyl ligand in coordination complexes [3]. Here we study the prototypic case of [Fe(CN) 5 NO] 2-anion. As shown in Figure 1 the ground state (GS) is characterized by a linear Fe-NO coordination. The irradiation with light in the blue-green spectral range (e.g. λ ~ 500 nm) induces a charge-transfer transition. Thereby the system changes symmetry from a 1 A 1 state to a 1 E doubly degenerate state. As a consequence the doubly degenerate deformational mode δ(Fe-NO) can induce a rotation of the NO ligand. The rotation of about 90° yields the side-on configuration of Fe< N O (metastable state MS2) while a rotation of 180° results in the isonitrosyl configuration Fe-ON (metastable state MS1). The transition from the excited ground state 1 E towards MS2 occurs radiationless in about 300±30 fs [3]. In the case of the NO ligand the structure of GS and the metastable states MS1 and MS2 is known from X-ray and neutron diffraction measurements at low temperatures in the static regime [4,5,6]. Moreover, the GS, MS1, and MS2 have clearly distinguished (NO) vibration frequency centered at 1961 cm-1 (5100 nm), 1831 cm-1 (5460 nm) and 1631 cm-1 (6130 nm) respectively [7]. Hence optical This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

Ultrafast laser-induced melting and ablation studied by time-resolved diffuse X-ray scattering

Time-resolved diffuse X-ray scattering with 50 fs, 9.5 keV X-ray pulses from the Linear Coherent Light Source was used to study the structural dynamics in materials undergoing rapid melting and ablation after fs laser excitation

Femtosecond x-ray diffraction reveals a liquid–liquid phase transition in phase-change materials

In phase-change memory devices, a material is cycled between glassy and crystalline states. The highly temperature-dependent kinetics of its crystallization process enables application in memory technology, but the transition has not been resolved on an atomic scale. Using femtosecond x-ray diffraction and ab initio computer simulations, we determined the time-dependent pair-correlation function of phase-change materials throughout the melt-quenching and crystallization process. We found a liquid–liquid phase transition in the phase-change materials Ag4In3Sb67Te26 and Ge15Sb85 at 660 and 610 kelvin, respectively. The transition is predominantly caused by the onset of Peierls distortions, the amplitude of which correlates with an increase of the apparent activation energy of diffusivity. This reveals a relationship between atomic structure and kinetics, enabling a systematic optimization of the memory-switching kinetics

Femtosecond x-ray diffraction reveals a liquid–liquid phase transition in phase-change materials

In phase-change memory devices, a material is cycled between glassy and crystalline states. The highly temperature-dependent kinetics of its crystallization process enables application in memory technology, but the transition has not been resolved on an atomic scale. Using femtosecond x-ray diffraction and ab initio computer simulations, we determined the time-dependent pair-correlation function of phase-change materials throughout the melt-quenching and crystallization process. We found a liquid–liquid phase transition in the phase-change materials Ag4In3Sb67Te26 and Ge15Sb85 at 660 and 610 kelvin, respectively. The transition is predominantly caused by the onset of Peierls distortions, the amplitude of which correlates with an increase of the apparent activation energy of diffusivity. This reveals a relationship between atomic structure and kinetics, enabling a systematic optimization of the memory-switching kinetics