Convective heat transfer enhancement by diamond shaped micro-protruded patterns for heat sinks: Thermal fluid dynamic investigation and novel optimization methodology

In the present work, micro-protruded patterns on flush mounted heat sinks for convective heat transfer enhancement are investigated and a novel methodology for thermal optimization is proposed. Patterned heat sinks are experimentally characterized in fully turbulent regime, and the role played by geometrical parameters and fluid dynamic scales are discussed. A methodology specifically suited for micro-protruded patterns optimization is designed, leading to 73 % enhancement in thermal performance respect to commercially available heat sinks, at fixed costs. This work is expected to introduce a new methodological approach for a more systematic and efficient development of solutions for electronics cooling

Influence of the long-range ordering of gold-coated Si nanowires on SERS

Controlling the location and the distribution of hot spots is a crucial aspect in the fabrication of surface-enhanced Raman spectroscopy (SERS) substrates for bio-analytical applications. The choice of a suitable method to tailor the dimensions and the position of plasmonic nanostructures becomes fundamental to provide SERS substrates with significant signal enhancement, homogeneity and reproducibility. In the present work, we studied the influence of the long-range ordering of different flexible gold-coated Si nanowires arrays on the SERS activity. The substrates are made by nanosphere lithography and metal-assisted chemical etching. The degree of order is quantitatively evaluated through the correlation length (ξ) as a function of the nanosphere spin-coating speed. Our findings showed a linear increase of the SERS signal for increasing values of ξ, coherently with a more ordered and dense distribution of hot spots on the surface. The substrate with the largest ξ of 1100 nm showed an enhancement factor of 2.6 · 103 and remarkable homogeneity over square-millimetres area. The variability of the signal across the substrate was also investigated by means of a 2D chemical imaging approach and a standard methodology for its practical calculation is proposed for a coherent comparison among the data reported in literature

Fabrication and characterization of reference nano and micro structures for 3D chemical analysis

Industry is progressively moving towards complex 3D architectures and using advanced materials and heterogeneous systems, which includes both organic and inorganic materials. Obviously, the performance of such complex 3D systems is also determined by the 3D elemental distributions, e.g. dopants distributions, or chemical compositions at the nanometric scale. Thus, 3D metrology should provide an accurate elemental and chemical measurement solution with a 3D spatial resolution (both lateral and depth) down to the nanometric scale in accordance with the needs of the industry (e.g. down to sub nanometer scale for the semiconductor industry). In this context, time-of-flight secondary ion mass spectrometry (ToFSIMS), grazing incidence X-ray fluorescence (GIXRF) and atom probe tomography (APT) are among the potential enablers to resolve such a 3D spatial resolution. Despite the recent improvements to push ToFSIMS and GIXRF as the reliable 3D measurement techniques, the metrological assessment of such analyses has not been yet well evaluated. This is mainly due to the absence of 3D reference materials and the calibration standards. On the other hand, APT is an inherent three-dimensional technique, which enables elemental identification and quantification at a near-atomic resolution. However, similar to the other aforementioned techniques, the metrological assessment of APT analysis is also hampered due to the absence of the suitable reference materials. In this project, we have developed several well-characterized organic-inorganic 3D microstructures as the potential reference material (RM) for 3D ToFSIMS. To prepare the 3D nanostructures with the characteristic dimensions below 20 nm as a test vehicle for GIXRF analysis, we exploited the self-assembly of di-block copolymers (DBCs) as the lithography mask. We have also studied in detail the pattern transfer at sub 20 scale into the Si substrate. In order to develop a potential reference material for APT, we have studied in detail the different aspects of the APT analysis, including ion trajectories, field-of-view (FOV) and the calibration of the different reconstruction parameters. We have studied in detail the FOV for both hemispherical and UV laser-induced asymmetric tip shape. In addition, we suggested a new design for an APT specimen, which maximizes the FOV and allows to probe the entire specimen volume in APT (full tip imaging). We have proven the feasibility of full tip imaging both numerically (finite element analysis) and experimentally. To do so, a specimen preparation process was developed based on standard lithography and etching techniques which allows to prepare multiple APT specimens in a repeatable fashion and with a minimized tip to tip variations in view of the tip radius and the shank angle. The developed full tip imaging feature can pave the way for the uncertainty assessment for all the reconstruction parameters and potentially enables a more reliable 3D data reconstruction in APT with the quantifiable uncertainties. In the absence of the certified reference material for APT, we have developed a well-characterized (i.e. traceable) B doped SiGe reference system (i.e. piece of wafer). Relying on this reference, the accuracy and the repeatability of APT analysis in view of Ge and B quantification over the specimen volume has been evaluated using UV and green lasers as well as in the different experimental conditions (electric field). In addition, the feasibility of APT analysis of an organic-inorganic system based on a polyaniline (Pani) - porous silicon (PSi) nanocomposite was evaluated in detail. We demonstrated that such a complex system could be analyzed by APT, whereby the 3D compositional distribution (lateral and depth distribution) was identified according to the distribution of monoatomic ions. The remained challenges for such an analysis were addressed and a potential solution was proposed.status: publishe

Fabrication and characterization of reference nano and micro structures for 3D chemical analysis

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Automated calibration of model-driven reconstructions in atom probe tomography

Traditional reconstruction protocols in atom probe tomography frequently feature image distortions for multiphase materials, due to inaccurate geometric assumptions regarding specimen evolution. In this work, the authors' outline a new reconstruction protocol capable of correcting for many of these distortions. This new method uses predictions from a previously developed physical model for specimen field evaporation. The application of this new model-driven approach to both an experimental semiconductor multilayer system and a fin field-effect transistor device (finFET) is considered. In both systems, a significant reduction in multiphase image distortions when using this new algorithm is clearly demonstrated. By being able to quantitatively compare model predictions with experiment, such a method could also be applied to testing and validating new developments in field evaporation theory

Development and Synchrotron-Based Characterization of Al and Cr Nanostructures as Potential Calibration Samples for 3D Analytical Techniques

The continuous and aggressive scaling in semiconductor technology results in the integration of increasingly complex 3D architectures and new materials. The realization of these downscaled 3D structures requires also further improvement in 3D characterization techniques. In this work, a potential route to improve the accuracy and reliability of the quantitative analysis of 3D nano-devices is investigated. 3D organic and inorganic reference nanostructures with dimensions and structural ordering resembling those utilized in industrial applications are fabricated and characterized in detail. The 3D organic nanostructures are fabricated exploiting the self-assembly capability of di-block copolymers. Subsequent deposition of a thin Al film lead to the formation and realization of nanostructured Al. In addition, different inorganic nanostructures are fabricated using electron beam lithography. The various nanostructures are characterized with respect to their dimensions as well as composition using various analytical techniques namely reference-free grazing incidence X-ray fluorescence, grazing incidence small angle X-ray scattering, scanning electron microscopy, and spectroscopic ellipsometry