Ultrafast response of Ge₂Sb₂Te₅ nanoparticles:The benefits of low energy amorphization switching with the same read/write speed of bulk memories

We investigate the ultrafast response of crystalline Ge2Sb2Te5 nanoparticles (NPs) below the phase transformation threshold fluence. The observed rapid change of the optical response and the presence of coherent optical phonons are consistent with the relaxation dynamics in bulk Ge2Sb2Te5 films and, more importantly, occur within the same ultrafast timescales. We conclude that the benefit of the lower energy consumption of memories based on Ge-Sb-Te (GST) NPs aggregates, demonstrated by Casarin et al. (2018), occurs with no disadvantage, as the read/write speed can be as fast as in bulk GSTs.</p

Interband characterization and electronic transport control of nanoscaled GeTe/Sb2_2Te3_3 superlattices

The extraordinary electronic and optical properties of the crystal-to-amorphous transition in phase-change materials led to important developments in memory applications. A promising outlook is offered by nanoscaling such phase-change structures. Following this research line, we study the interband optical transmission spectra of nanoscaled GeTe/Sb$_2$Te$_3$ chalcogenide superlattice films. We determine, for films with varying stacking sequence and growth methods, the density and scattering time of the free electrons, and the characteristics of the valence-to-conduction transition. It is found that the free electron density decreases with increasing GeTe content, for sub-layer thickness below $\sim$3 nm. A simple band model analysis suggests that GeTe and Sb$_2$Te$_3$ layers mix, forming a standard GeSbTe alloy buffer layer. We show that it is possible to control the electronic transport properties of the films by properly choosing the deposition layer thickness and we derive a model for arbitrary film stacks

Ultrafast magnetodynamics with free-electron lasers

The study of ultrafast magnetodynamics has entered a new era thanks to the groundbreaking technological advances in free-electron laser (FEL) light sources. The advent of these light sources has made possible unprecedented experimental schemes for time-resolved x-ray magneto-optic spectroscopies, which are now paving the road for exploring the ultimate limits of out-of-equilibrium magnetic phenomena. In particular, these studies will provide insights into elementary mechanisms governing spin and orbital dynamics, therefore contributing to the development of ultrafast devices for relevant magnetic technologies. This topical review focuses on recent advancement in the study of non-equilibrium magnetic phenomena from the perspective of time-resolved extreme ultra violet (EUV) and soft x-ray spectroscopies at FELs with highlights of some important experimental results

Self assembling monolayers of dialkynyl bridged Pd(II) thiols obtained by thermally induced multilayer desorption: Thermal and chemical stability investigated by SR-XPS

Self assembling monolayers (SAMs) of organometallic thiols trans-[HS-Pd(PBu3)(2)-SH], trans-[HS-Pd (PBu3)(2)(-C, C-C6H5)] and trans, trans-[HS-Pd(PBu3)(2)(-C, C-C6H4-C6H4-C, C-Pd(PBu3)(2)-SH] on gold were obtained from the corresponding multilayers through thermally induced desorption. Temperature-dependent synchrotron radiation-induced X-ray photoelectron spectroscopy (SR-XPS) measurements were carried out on the heated multilayers during the annealing process, in order to investigate the thermal and chemical stability of the systems. SAMs of the same organometallic thiols were also obtained by rinsing the thick films with appropriate solvents. SR-XPS was used to ascertain that the molecular and electronic structure of the two series of SAMs are not influenced by the rinsing or thermal desorption process, i.e. both strategies allow for obtaining well ordered monolayers of organometallic thiols. (C) 2012 Elsevier B. V. All rights reserved

Ultralow-fluence single-shot optical crystalline-to-amorphous phase transition in Ge-Sb-Te nanoparticles

Here we demonstrate that the 0-dimensional confinement of Ge2Sb2Te5 results in a drastic reduction of the minimum critical fluence required for optical-induced amorphization when compared to the thin-film cases. We show that by using single-shot laser pulses, the investigated nanoparticles display a crystalline-to-amorphous transition, satisfying a mandatory requirement of a bit-memory element. These unprecedented results open a viable route to boost energy efficient phase-change processes

Gold Nanoparticle Dyads Stabilized with Binuclear Pt(II) Dithiol Bridges

The synthesis and characterization of gold nanoparticles (AuNPs-1) stabilized by a novel bifunctional thiolate organometallic complex containing Pt(II) centers, that is, trans,trans-[(CH(3)COS) (PBu(3))(2)Pt-C equivalent to C-C(6)H(4)-C(6)H(4)-C equivalent to C Pt(PBu(3))(2)(SCOCH(3))] (complex 1), has been carried out. As a comparison, gold nanoparticles stabilized with an organic thiol, allylmercaptane, that is, AuNPs-2, and self-assembled monolayers (SAMs) of both thiols were also prepared and investigated. The AuNPs-1 show a direct link between Pt(II) and Au nanoparticles through a single S bridge and are candidates for the achievement of 2D or 3D networks. The size control of the Au nanoparticles was achieved by careful control of synthesis parameters, and the hybrids were characterized by means of high-resolution transmission electron microscopy (HR-TEM) and synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS). SR-XPS measurements allowed the assessment of the anchoring of the organic or organometallic thiols onto gold substrates as well as onto gold nanoparticles. AuNPs-2 with diameters in the range from 1.6 to 3.9 nm were obtained. AuNPs-1 with an average diameter in the range of 4.5-3.6 nm were obtained, and linkage between the nanoparticles can be envisaged with the formation of dyads supported by SR-XPS measurements. In fact, S2p core-level data indicate that both sulfur atoms of the organometallic thiol chemically interact with gold grafting vicinal natioparticles

Direct observation of spin-orbit-induced 3d hybridization via resonant inelastic extreme ultraviolet scattering on an edge-sharing cuprate

Using high resolution resonant inelastic x-ray scattering measurements, we have observed that the orbital excitations of the quasi-1D spin chain compound CuGeO3 has nontrivial and noticeable orbital mixing effects from 3d valence spin-orbit coupling. In particular, the SOC leads to a significant correction of d(z2) state, which has a direct interplay with the low energy physics of cuprates. Guided by atomic multiplet based modeling, our results strongly support a 3d spin-orbit mixing scenario and explore in detail the nature of these excitations