Sub-surface laser nanostructuring in stratified metal/dielectric media: a versatile platform towards flexible, durable and large-scale plasmonic writing

Laser nanostructuring of pure ultrathin metal layers or ceramic/metal composite thin films has emerged as a promising route for the fabrication of plasmonic patterns with applications in information storage, cryptography, and security tagging. However, the environmental sensitivity of pure Ag layers and the complexity of ceramic/metal composite film growth hinder the implementation of this technology to large-scale production, as well as its combination with flexible substrates. In the present work we investigate an alternative pathway, namely, starting from non-plasmonic multilayer metal/dielectric layers, whose growth is compatible with large scale production such as in-line sputtering and roll-to-roll deposition, which are then transformed into plasmonic templates by single-shot UV-laser annealing (LA). This entirely cold, large-scale process leads to a subsurface nanoconstruction involving plasmonic Ag nanoparticles (NPs) embedded in a hard and inert dielectric matrix on top of both rigid and flexible substrates. The subsurface encapsulation of Ag NPs provides durability and long-term stability, while the cold character of LA suits the use of sensitive flexible substrates. The morphology of the final composite film depends primarily on the nanocrystalline character of the dielectric host and its thermal conductivity. We demonstrate the emergence of a localized surface plasmon resonance, and its tunability depending on the applied fluence and environmental pressure. The results are well explained by theoretical photothermal modeling. Overall, our findings qualify the proposed process as an excellent candidate for versatile, large-scale optical encoding applications. Keywords : Ceramic materials; Composite films; Environmental technology; Film growth; Film preparation; Multilayer films; Multilayers; Nanocrystals; Optical data processing; Plasmons; Silver; Substrates; Surface plasmon resonance; Thin films; Ultrathin films, Laser annealing; Localised surface plasmon resonance; Multi-layer thin film; Nano-structuring; Plasmonics, Nanocomposite film

The heterogeneous nucleation of threading dislocations on partial dislocations in III-nitride epilayers

Abstract III-nitride compound semiconductors are breakthrough materials regarding device applications. However, their heterostructures suffer from very high threading dislocation (TD) densities that impair several aspects of their performance. The physical mechanisms leading to TD nucleation in these materials are still not fully elucidated. An overlooked but apparently important mechanism is their heterogeneous nucleation on domains of basal stacking faults (BSFs). Based on experimental observations by transmission electron microscopy, we present a concise model of this phenomenon occurring in III-nitride alloy heterostructures. Such domains comprise overlapping intrinsic I 1 BSFs with parallel translation vectors. Overlapping of two BSFs annihilates most of the local elastic strain of their delimiting partial dislocations. What remains combines to yield partial dislocations that are always of screw character. As a result, TD nucleation becomes geometrically necessary, as well as energetically favorable, due to the coexistence of crystallographically equivalent prismatic facets surrounding the BSF domain. The presented model explains all observed BSF domain morphologies, and constitutes a physical mechanism that provides insight regarding dislocation nucleation in wurtzite-structured alloy epilayers

Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy

We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content attained through temperature adjustment. At lower indium contents, strain relaxation by V-pit formation dominated, with concurrent formation of an indium-rich interfacial zone. With increasing indium content, this mechanism was gradually substituted by the introduction of a self-formed strained interfacial InGaN layer of lower indium content, as well as multiple intrinsic basal stacking faults and threading dislocations in the rest of the film. We show that this interfacial layer is not chemically abrupt and that major plastic strain relaxation through defect introduction commences upon reaching a critical indium concentration as a result of compositional pulling. Upon further increase of the indium content, this relaxation mode was again gradually succeeded by the increase in the density of misfit dislocations at the InGaN/GaN interface, leading eventually to the suppression of the strained InGaN layer and basal stacking faults

Microstructure of N-face InN grown on Si (111) by plasma-assisted MBE using a thin GaN–AlN buffer layer

The structural properties of 2 mm thick N-face InN film, grown on Si (111) by plasma source molecular beam epitaxy after the initial deposition of 20 nm AlN and 40 nm GaN, were examined by transmission electron microscopy. The lattice mismatched GaN/AlN and InN/GaN interfaces limited the propagation of threading dislocations (TDs). Dislocation annihilation interactions occurred in the first ~200 nm of the InN film and reduced the TD density. However, the density of screw and mixed type TDs was four times higher than edge type ones. This was attributed to the observed GaN/InN interfacial roughness, which was introduced by terminating TDs from the GaN/AlN buffer layer. Strain measurements showed that the InN film, as well as both buffer layers, was relaxed

Electron microscopy of InGaN nanopillars spontaneously grown on Si(111) substrates

The mopholological, structural and chemical properties of InxGa1−xN nanopillars directly grown on Si (111) substrates, by molecular beam epitaxy, were investigated employing transmission electron microscopy related techniques. Single crystalline, single phase nanopillars were observed exhibiting a low density of crystal defects, which contribute to good crystal quality. Initial nanostructures merge through subgrain boundaries to form final nanopillars. Energy dispersive X-ray analysis revealed a very low InN mole fraction near the interface with the substrate, owing to high desorption rates from the elevated growth temperature, and gradually higher In incorporation rates near the tips of the nanopillars. This compositional fluctuation is main- tained due to poor segregation of indium adatoms along the c-axis of the nanopillars towards the Si interface. A second species of long and narrow nanopillars was found In-free