Simultaneous measurement of structure and XUF dielectric constant of nanoscale objects using diffraction of high harmonic radiation

XUV diffraction using radiation generated by high harmonic generation is used simultaneously to determine both the structure and the complex refractive index of a partially ordered array of 196 nm diameter polystyrene spheres

XUV diffraction from a self-assembled 2D array of hexagonal close-packed 200nm diameter PMMA spheres

Laser-generated XUV and soft x-ray radiation sources using high-harmonic generation, typically producing 108 photons per pulse per harmonic (~5 nm to ~50 nm) in a coherent low-divergence beam, are a promising source for nanometer scale imaging. Here we present XUV diffraction from a single-layer self-assembled hexagonal close-packed (HCP) array of 200 nm diameter PMMA nanospheres. Such a lattice is too small to diffract from using visible light, and hence XUV wavelengths are required. We observe a hexagonal diffraction pattern for three diffraction orders - the result of illuminating a single crystal. The observed interference peaks are a convolution of a Bragg peak with both the distribution of lattice planes (due to crystal defects) and the harmonic spectra. However, as these convolutions are in orthogonal directions, they can be independently resolved hence providing useful information on the quality of the crystal and the generated wavelengths. The far-field diffraction pattern from a single-layer HCP array of spheres is the Fourier Transform (FT) of a hexagonal grid of delta functions multiplied by the FT of the scattering function from a single sphere, which can be calculated using the Mie solution to Maxwell's equations. We compare the measured intensity for each of the eighteen observed interference peaks for the harmonic at 27.6 nm, against the theoretical intensity. The excellent agreement over four orders of magnitude indicates that Mie scattering predicts an appropriate form factor for this analysis and also enables us to extract the complex refractive index of PMMA at this wavelength

XUV diffraction from a self-assembled 2D array of close-packed 200nm diameter PMMA spheres

Laser-generated XUV and soft x-ray radiation sources using high-harmonic generation (HHG), typically producing 108 photons per pulse per harmonic (~5nm to ~50nm) in a coherent low-divergence beam [1], are a promising source for nanometer scale imaging [2]. Here we present XUV diffraction from a single-layer self-assembled hexagonal-close-packed (HCP) array of 200nm diameter PMMA nanospheres. Such a lattice is too small to diffract from using visible light, and hence XUV wavelengths are required. Figure (a) shows the far-field pattern from the single crystal at a 22µm focus, and overlaid with 100 mrad contours. The interference peaks are a convolution of a Bragg peak with both the distribution of lattice planes (due to crystal defects) and the harmonic spectra. However, as these convolutions are in orthogonal directions, they can be independently resolved (figures b & c), providing information on the crystal quality and generated wavelengths.The far-field diffraction pattern from a single-layer HCP array of spheres is the Fourier Transform (FT) of a hexagonal grid of delta functions multiplied by the FT of a the scattering function from a single sphere, which can be calculated using Mie theory. Figure (d) shows, (+) the measured intensity for each of the eighteen interference peaks for the harmonic at 27.6nm, (.) the theoretical intensity versus angle distribution for a single sphere, and (o) the predicted intensity at each interference peak. The excellent agreement indicates that Mie scattering predicts an appropriate form factor for this analysis and enables us to extract the complex refractive index of PMMA at this wavelength

Welding shape memory alloys with NdYAG lasers Soldadura de ligas de memória de forma com laser Nd-YAG

The demand of emerging joining techniques for shape memory alloys (SMA) has become of great importance, as their functional properties namely shape memory effect (SME) and superelasticity (SE) present unique solutions for state-of-the-art applications. Welding of SMAs is a challenge due to the risk of reduced mechanical performance after laser processing. The wider application of these alloys in various sectors as aerospace, medical or electronic industry is hindered by the limitations in its processing. The need to weld SMAs to other materials is pressing for applications in the above referred sectors. In dissimilar joints the need to understand materials behavior is even more challenging since base materials have different physical properties leading to different heat flow, convection processes and residual stress distribution. The chemical composition across the weld pool varies and intermetallic compounds are formed. Research detailing the effects of laser processing on NiTi is essential to overcome many of these challenges. The objectives of the current study are to analyze the effects of laser welding in the weld shape of both similar and dissimilar joints of NiTi to stainless steel and titanium alloys.<br>A procura de técnicas de ligação para ligas de memória de forma tem-se revetido de importância crescente, devido ao desenvolvimento de aplicações deste material com particulares propriedades de memória de forma e superelasticidade. A soldadura de ligas de memória de forma é um desafio devido ao risco de emporbrecimento das propriedades mecânicas depois do processamento laser. A aplicação alargarda destas ligas em vários sectores como o aeroespacial, medico ou electrónico é prejudicado pelas limitações de processamento. A necessidade de soldar ligas de memória de forma a outros materiais é premente para estes sectores. Em juntas dissimilares, o entendimento do comportamento dos materaias é um desafio ainda maior uma vez que os materias base têm propriedades diferentes com consquentes diferenças no escoamento térmico, movimentação de fuido e distribuição de tensões residuais. A composição química varia ao longo do banho de fusão e formam-se compostos intermetálicos. É essencial realizar-se investigação sobre estes efeitos do processamento laser de NiTi para ultrapassar este desafio. O presente estudo visa analisar os efeitos da soldadura a laser na forma do cordão de soldadura em juntas similares e dissimilares de NiTi com aço inoxidável e ligas de titâneo