Martin Hÿtch

Bio: Martin Hÿtch is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Electron holography & High-resolution transmission electron microscopy. The author has an hindex of 29, co-authored 111 publications receiving 5930 citations.

Synthesis and Micrometer-Scale Assembly of Colloidal CdSe/CdS Nanorods Prepared by a Seeded Growth Approach

Abstract: Key limitations of the colloidal semiconductor nanorods that have been reported so far are a significant distribution of lengths and diameters as well as the presence of irregular shapes produced by the current synthetic routes and, finally, the poor ability to fabricate large areas of oriented nanorod arrays. Here, we report a seeded-growth approach to the synthesis of asymmetric core−shell CdSe/CdS nanorods with regular shapes and narrow distributions of rod diameters and lengths, the latter being easily tunable up to 150 nm. These rods are highly fluorescent and show linearly polarized emission, whereby the emission energy depends mainly on the core diameter. We demonstrate their lateral alignment as well as their vertical self-alignment on substrates up to areas of several square micrometers.

Measurement of the displacement field of dislocations to 0.03 Å by electron microscopy

Abstract: Defects and their associated long-range strain fields are of considerable importance in many areas of materials science. For example, a major challenge facing the semiconductor industry is to understand the influence of defects on device operation, a task made difficult by the fact that their interactions with charge carriers can occur far from defect cores, where the influence of the defect is subtle and difficult to quantify. The accurate measurement of strain around defects would therefore allow more detailed understanding of how strain fields affect small structures-in particular their electronic, mechanical and chemical properties--and how such fields are modified when confined to nanometre-sized volumes. Here we report the measurement of displacements around an edge dislocation in silicon using a combination of high-resolution electron microscopy and image analysis inherited from optical interferometry. The agreement of our observations with anisotropic elastic theory calculations is better than 0.03 A. Indeed, the results can be considered as an experimental verification of anisotropic theory at the near-atomic scale. With the development of nanostructured materials and devices, we expect the use of electron microscopy as a metrological tool for strain analysis to become of increasing importance.

Nanoscale holographic interferometry for strain measurements in electronic devices

Abstract: Strained silicon is now an integral feature of the latest generation of transistors and electronic devices because of the associated enhancement in carrier mobility. Strain is also expected to have an important role in future devices based on nanowires and in optoelectronic components. Different strategies have been used to engineer strain in devices, leading to complex strain distributions in two and three dimensions. Developing methods of strain measurement at the nanoscale has therefore been an important objective in recent years but has proved elusive in practice: none of the existing techniques combines the necessary spatial resolution, precision and field of view. For example, Raman spectroscopy or X-ray diffraction techniques can map strain at the micrometre scale, whereas transmission electron microscopy allows strain measurement at the nanometre scale but only over small sample areas. Here we present a technique capable of bridging this gap and measuring strain to high precision, with nanometre spatial resolution and for micrometre fields of view. Our method combines the advantages of moire techniques with the flexibility of off-axis electron holography and is also applicable to relatively thick samples, thus reducing the influence of thin-film relaxation effects.

Effects of elastic anisotropy on strain distributions in decahedral gold nanoparticles

Abstract: Metallic nanoparticles exhibit exceptional optoelectronic properties with applications in plasmonics, biosensing and nanomedicine1,2,3,4,5. Recently, new synthesis techniques have enabled precise control over the sizes and shapes of metal nanoparticles6,7,8, occasionally leading to morphologies that cannot be properly characterized using standard techniques. An example is five-fold-twinned decahedral Au nanoparticles, which are intrinsically strained as a result of their unique geometry. Various competing models have been proposed to predict the strain states of such nanoparticles. Here, we present a detailed analysis of the internal structure of a decahedral Au nanoparticle using aberration-corrected high-resolution electron microscopy and strain mapping. Our measurements confirm the presence of a disclination, which is consistent with the commonly accepted strain model. However, we also observed shear gradients, which are absent from the models. By comparing our local strain determinations with finite-element calculations, we show the effect of elastic anisotropy on the strain state in these nanoparticles.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Synthesis and Characterization of Monodisperse Nanocrystals and Close-Packed Nanocrystal Assemblies

Abstract: ▪ Abstract Solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤5%, are presented. Preparation of monodisperse samples enables systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close-packed, glassy, and ordered nanocrystal assemblies (superlattices, colloidal crystals, supercrystals). Rigorous structural characterization is critical to understanding the electronic and optical properties of both nanocrystals and their assemblies. At inter-particle separations 5–100 A, dipole-dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. At separations <5 A, exchange interactions cause otherwise insulating ass...

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Abstract: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

High-performance bulk thermoelectrics with all-scale hierarchical architectures

Abstract: Controlling the structure of thermoelectric materials on all length scales (atomic, nanoscale and mesoscale) relevant for phonon scattering makes it possible to increase the dimensionless figure of merit to more than two, which could allow for the recovery of a significant fraction of waste heat with which to produce electricity.