Phase-change materials are some of the most promising materials for data-storage applications. They are already used in rewriteable optical data storage and offer great potential as an emerging non-volatile electronic memory. This review looks at the unique property combination that characterizes phase-change materials. The crystalline state often shows an octahedral-like atomic arrangement, frequently accompanied by pronounced lattice distortions and huge vacancy concentrations. This can be attributed to the chemical bonding in phase-change alloys, which is promoted by p-orbitals. From this insight, phase-change alloys with desired properties can be designed. This is demonstrated for the optical properties of phase-change alloys, in particular the contrast between the amorphous and crystalline states. The origin of the fast crystallization kinetics is also discussed.

Phase-change materials for rewriteable data storage

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

The first part of this two-part review focused on the fundamental and diagnostics aspects of laser-induced plasmas, only touching briefly upon concepts such as sensitivity and detection limits and largely omitting any discussion of the vast panorama of the practical applications of the technique. Clearly a true LIBS community has emerged, which promises to quicken the pace of LIBS developments, applications, and implementations. With this second part, a more applied flavor is taken, and its intended goal is summarizing the current state-of-the-art of analytical LIBS, providing a contemporary snapshot of LIBS applications, and highlighting new directions in laser-induced breakdown spectroscopy, such as novel approaches, instrumental developments, and advanced use of chemometric tools. More specifically, we discuss instrumental and analytical approaches (e.g., double- and multi-pulse LIBS to improve the sensitivity), calibration-free approaches, hyphenated approaches in which techniques such as Raman and fluorescence are coupled with LIBS to increase sensitivity and information power, resonantly enhanced LIBS approaches, signal processing and optimization (e.g., signal-to-noise analysis), and finally applications. An attempt is made to provide an updated view of the role played by LIBS in the various fields, with emphasis on applications considered to be unique. We finally try to assess where LIBS is going as an analytical field, where in our opinion it should go, and what should still be done for consolidating the technique as a mature method of chemical analysis.

https://journals.sagepub.com/doi/pdf/10.1366/11-06574

Laser-induced breakdown spectroscopy (LIBS), part II: review of instrumental and methodological approaches to material analysis and applications to different fields.

Study of flexible nanodielectric materials (FNDMs) with high permittivity is one of the most active academic research areas in advanced functional materials. FNDMs with excellent dielectric properties are demonstrated to show great promise as energy-storage dielectric layers in high-performance capacitors. These materials, in common, consist of nanoscale particles dispersed into a flexible polymer matrix so that both the physical/chemical characteristics of the nanoparticles and the interaction between the nanoparticles and the polymers have crucial effects on the microstructures and final properties. This review first outlines the crucial issues in the nanodielectric field and then focuses on recent remarkable research developments in the fabrication of FNDMs with special constitutents, molecular structures, and microstructures. Possible reasons for several persistent issues are analyzed and the general strategies to realize FNDMs with excellent integral properties are summarized. The review further highlights some exciting examples of these FNDMs for power-energy-storage applications.

Flexible Nanodielectric Materials with High Permittivity for Power Energy Storage

Recent years have seen a growing interest in using metal nanostructures to control temperature on the nanoscale. Under illumination at its plasmonic resonance, a metal nanoparticle features enhanced light absorption, turning it into an ideal nano-source of heat, remotely controllable using light. Such a powerful and flexible photothermal scheme is the basis of thermo-plasmonics. Here, the recent progress of this emerging and fast-growing field is reviewed. First, the physics of heat generation in metal nanoparticles is described, under both continuous and pulsed illumination. The second part is dedicated to numerical and experimental methods that have been developed to further understand and engineer plasmonic-assisted heating processes on the nanoscale. Finally, some of the most recent applications based on the heat generated by gold nanoparticles are surveyed, namely photothermal cancer therapy, nano-surgery, drug delivery, photothermal imaging, protein tracking, photoacoustic imaging, nano-chemistry and optofluidics.

http://www.guillaume.baffou.com/publications/020-Baffou-LPR.pdf

Thermo‐plasmonics: using metallic nanostructures as nano‐sources of heat

The phase transformation dynamics induced in Ge2Sb2Te5 films by picosecond laser pulses were studied using real-time reflectivity measurements with subnanosecond resolution Evidence was found that the thermal diffusivity of the substrate plays a crucial role in determining the ability of the films to crystallize and amorphize A film/substrate configuration with optimized heat flow conditions for ultrafast phase cycling with picosecond laser pulses was designed and produced In this system, we achieved reversible phase transformations with large optical contrast (>20%) using single laser pulses with a duration of 30 ps within well-defined fluence windows The amorphization (writing) process is completed within less than 1 ns, whereas crystallization (erasing) needs approximately 13 ns to be completed

/pdf/rewritable-phase-change-optical-recording-in-ge2sb2te5-films-4z5cg22z6b.pdf

Rewritable phase-change optical recording in Ge2Sb2Te5 films induced by picosecond laser pulses

The existence of nonthermal, ultrafast phase transitions after strong femtosecond laser excitation has been demonstrated in several materials such as silicon [1 ‐ 3], gallium arsenide [3 ‐6], indium antimonide [7], and carbon [8]. It is accepted that such transitions are induced by a softening of the lattice structure due to the generation of a very high density electron-hole plasma, as first proposed by Van Vechten [9]. Most of the experimental and theoretical work [10‐13] has concentrated on the solid-to-liquid phase transformation of the above mentioned materials. Some authors [2,11] have also claimed the existence of an ultrafast solid-to-solid phase transition preceding nonthermal melting, although there is experimental evidence [3,7] refusing this hypothesis. In this Letter we present a time resolved study on the dynamics of femtosecond laser induced structural transformations in amorphous GeSb. We describe experimental evidence for the subpicosecond formation of a transient phase of the material and interpret our results as first indication for an ultrafast, nonthermal amorphousto-crystalline phase transition. Sb-rich amorphous GeSb films can be crystallized upon irradiation with ultrashort laser pulses [14] and show a large optical contrast upon transformation [15]. This effect makes GeSb a promising material for the development of rewritable optical memories driven by ultrashort laser pulses [16]. Recently, it has been demonstrated [17] that the energy fluence necessary to induce crystallization in this material decreases significantly for pulses shorter than a picosecond, suggesting the relevance of electronic processes in the amorphousto-crystalline transition. Amorphous Ge0.06Sb0.94, 50-nm-thick films were grown on glass substrates at room temperature in a multitarget dc magnetron sputtering system from pure (99.999%) Ge and Sb targets. The films were irradiated with 100 fs laser pulses at 620 nm delivered by a 10-Hz amplified colliding-pulse mode-locked (rhodamine 6GyDODCI) dye laser. The evolution of the reflectivity of the irradiated surface was monitored with both femtosecond time and micrometer spatial resolution by means of ultrafast time-resolved microscopy [18]. A first laser pulse excites the sample. A second time-delayed probe pulse replaces the standard illumination of an optical microscope and provides snapshot pictures of the excited surface with 100 fs time resolution. The optical micrographs are recorded with the help of a charged coupled device detector in conjunction with a computer controlled frame-grabber. Since a single laser pulse induces permanent structural changes of the irradiated area the sample is moved between two consecutive exposures. A series of pictures, covering the entire period from the initial deposition of the laser energy (pump fluence 45 mJycm 2 ) to the appearance of the final structural modifications, is shown in Fig. 1. The contrast of the images has been enhanced for reproduction purposes and

/pdf/dynamics-of-ultrafast-phase-changes-in-amorphous-gesb-films-43toqfape2.pdf

Dynamics of Ultrafast Phase Changes in Amorphous GeSb Films

We present a study of the magnetic properties of oxidized Co nanoparticles with an average grain size of 3nm, embedded in an amorphous Al2O3 matrix. These nanoparticles can be considered as imperfect Co-core CoO-shell systems. Magnetization measurements after magnetic field cooling show a vertical shift of the hysteresis loop, while no exchange bias is observed. With a simple model, we show that there is a critical grain size for hybrid ferromagnetic-antiferromagnetic particles, below which exchange bias is absent for any ratio of ferromagnetic and antiferromagnetic constituents. The reason is that the interfacial exchange energy dominates over other energies in the system due to a large surface-to-volume ratio in the nanoparticles.

/pdf/critical-size-for-exchange-bias-in-ferromagnetic-23q7eagwh6.pdf

Critical size for exchange bias in ferromagnetic-antiferromagnetic particles

Nanocomposite films comprising metal Cu nanocrystals embedded in an Al2O3 matrix were deposited by alternating pulsed laser ablation from metallic Cu and ceramic Al2O3 targets. The films were grown in vacuum on glass substrates held at room temperature. The as-grown films contain 4 nm Cu nanocrystals in an amorphous Al2O3 matrix, with a total thickness of 190 nm. The films show a substantial third-order susceptibility with an electronic nonlinear refractive index of (2.93±1.08)⋅10−10 cm2 W−1 and a nonlinear saturation of −(2.34±0.18)⋅10−5 cm W−1.

/pdf/pulsed-laser-deposition-of-cu-al2o3-nanocrystal-thin-films-o0boqzufa0.pdf

Pulsed laser deposition of Cu:Al2O3 nanocrystal thin films with high third-order optical susceptibility

Silver colloids have been formed by ion implantation in float glass. Subsequent annealing methods alter the size distribution and optical reflectivity of the colloids. Furnace anneals and rapid flame heating convert large colloids into smaller units but excimer laser annealing appears to cause a dissolution of silver into the glass network.

/pdf/annealing-of-ion-implanted-silver-colloids-in-glass-38lsgf321n.pdf

Carmen N. Afonso

Papers

Rewritable phase-change optical recording in Ge2Sb2Te5 films induced by picosecond laser pulses

Dynamics of Ultrafast Phase Changes in Amorphous GeSb Films

Critical size for exchange bias in ferromagnetic-antiferromagnetic particles

Pulsed laser deposition of Cu:Al2O3 nanocrystal thin films with high third-order optical susceptibility

Annealing of ion implanted silver colloids in glass