Dina Carbone

X-ray Nanodiffraction on a Single SiGe Quantum Dot inside a Functioning Field-Effect Transistor

For advanced electronic, optoelectronic, or mechanical nanoscale devices a detailed understanding of their structural properties and in particular the strain state within their active region is of utmost importance. We demonstrate that X-ray nanodiffraction represents an excellent tool to investigate the internal structure of such devices in a nondestructive way by using a focused synchotron X-ray beam with a diameter of 400 nm. We show results on the strain fields in and around a single SiGe island, which serves as stressor for the Si-channel in a fully functioning Si–metal–oxide semiconductor field-effect transistor.

Imaging of strain and lattice orientation by quick scanning X-ray microscopy combined with three-dimensional reciprocal space mapping

Numerous imaging methods have been developed over recent years in order to study materials at the nanoscale. Within this context, scanning X-ray diffraction microscopy has become a routine technique, giving access to structural properties with sub-micrometre resolution. This article presents an optimized technique and an associated software package which have been implemented at the ID01 beamline (ESRF, Grenoble). A structural scanning probe microscope with intriguing imaging qualities is obtained. The technique consists in a two-dimensional quick continuous mapping with sub-micrometre resolution of a sample at a given reciprocal space position. These real space maps are made by continuously moving the sample while recording scattering images with a fast two-dimensional detector for every point along a rocking curve. Five-dimensional data sets are then produced, consisting of millions of detector images. The images are processed by the user-friendly X-ray strain orientation calculation software (XSOCS), which has been developed at ID01 for automatic analysis. It separates tilt and strain and generates two-dimensional maps of these parameters. At spatial resolutions of typically 200–800 nm, this quick imaging technique achieves strain sensitivity below Δa/a = 10−5 and a resolution of tilt variations down to 10−3° over a field of view of 100 × 100 µm.

Coherent x-ray wavefront reconstruction of a partially illuminated Fresnel zone plate

A detailed characterization of the coherent x-ray wavefront produced by a partially illuminated Fresnel zone plate is presented. We show, by numerical and experimental approaches, how the beam size and the focal depth are strongly influenced by the illumination conditions, while the phase of the focal spot remains constant. These results confirm that the partial illumination can be used for coherent diffraction experiments. Finally, we demonstrate the possibility of reconstructing the complex-valued illumination function by simple measurement of the far field intensity in the specific case of partial illumination.

Scanning X-ray strain microscopy of inhomogeneously strained Ge micro-bridges.

A scanning X-ray strain microscopy technique using a micro-focused beam is demonstrated.

Ion-induced nanopatterns on semiconductor surfaces investigated by grazing incidence x-ray scattering techniques

In this review we cover and describe the application of grazing incidence x-ray scattering techniques to study and characterize nanopattern formation on semiconductor surfaces by ion beam erosion under various conditions. It is demonstrated that x-rays under grazing incidence are especially well suited to characterize (sub)surface structures on the nanoscale with high spatial and statistical accuracy. The corresponding theory and data evaluation is described in the distorted wave Born approximation. Both ex situ and in situ studies are presented, performed with the use of a specially designed sputtering chamber which allows us to follow the temporal evolution of the nanostructure formation. Corresponding results show a general stabilization of the ordering wavelength and the extension of the ordering as a function of the ion energy and fluence as predicted by theory. The in situ measurements are especially suited to study the early stages of pattern formation, which in some cases reveal a transition from dot to ripple formation. For the case of medium energy ions crystalline ripples are formed buried under a semi-amorphous thick layer with a ripple structure at the surface being conformal with the crystalline/amorphous interface. Here, the x-ray techniques are especially advantageous since they are non-destructive and bulk-sensitive by their very nature. In addition, the GI x-ray techniques described in this review are a unique tool to study the evolving strain, a topic which remains to be explored both experimentally and theoretically.

Correlation of electrical and structural properties of single as-grown GaAs nanowires on Si (111) substrates.

We present the results of the study of the correlation between the electrical and structural properties of individual GaAs nanowires measured in their as-grown geometry. The resistance and the effective charge carrier mobility were extracted for several nanowires, and subsequently, the same nano-objects were investigated using X-ray nanodiffraction. This revealed a number of perfectly stacked zincblende and twinned zincblende units separated by axial interfaces. Our results suggest a correlation between the electrical parameters and the number of intrinsic interfaces.

Nanobeam x-ray scattering : probing matter at the nanoscale

INTRODUCTION X-RAY DIFFRACTION PRINCIPLES -Introduction -Beam Coherence -Specific Properties of Different Sources: Laboratory vs Synchrotron vs FEL FOCUSING OF X-RAYS -Beam Propagation and Modeling -Focusing Principles Available for the Hard X-Ray Regime -Clasic Microfocusing Devices -Practical Issues SCATTERING EXPERIMENTS USING NANOBEAMS -From the Ensemble Average Approach Towards the Single Nanostructure Study -Diffraction from Single Nanostructures -Scanning X-Ray Diffraction Microscopy -Other Types of Contrast -Local X-Ray Probe Experiments from Organic Samples -Local X-Ray Probe Experiments from Biological Samples NANOBEAM DIFFRACTION SETUPS -Beam Positioning on the Nanoscale -Stability Issues: Maintaining the Spot on the Sample During Scanning Angles, Vibrations -Active Systems to Maintain the Beam Position on the Sample Constant -Restriction of Different Setups -Detector Issues: Resolution in Real and Reciprocal Space, Dynamic Range, Time Resolution SPECTROSCOPIC TECHNIQUES USING FOCUSED BEAMS -Micro/Nano-EXAFS, XANES. Fluorescence -A Side Glance on Soft X-Ray Applications COHERENT DIFFRACTION -More on Coherence Properties of Focused X-Ray Beams -The Use of Phase Retrieval Instead of Modeling Approaches -Different Retrieval Algorithms -Shape Determination of Single Structures (Retrieving the Modulus of Electron Density) -Strain Determination (Retrieving the Phase of Electron Density) -Fresnel Coherent Diffractive Imaging -Holographic Approaches (Using a Reference Wave Instead of Numerical Phase Retrieval) -Ptychography (For Extended Objects with Nanoscale Structure) -Particular Advantages and Problems when Using Coherent Diffraction Imaging in the Bragg Case THE POTENTIAL AND THE LIMITS OF THE METHOD -Limits in Beam Size -Limits in Intensity/Brilliance -Resolution Limits in Real and Reciprocal Space -Combinations with Other Local Probe Techniques FUTURE DEVELOPMENTS -Detector Developments -Beamlines at Third Generation Synchrotron Sources -The Role of Free Electron Lasers

Imaging the displacement field within epitaxial nanostructures by coherent diffraction: a feasibility study

We investigate the feasibility of applying coherent diffraction imaging to highly strained epitaxial nanocrystals using finite-element simulations of SiGe islands as input in standard phase retrieval algorithms. We discuss the specific problems arising from both epitaxial and highly strained systems and we propose different methods to overcome these difficulties. Finally, we describe a coherent microdiffraction experimental setup using extremely focused x-ray beams to perform experiments on individual nanostructures.

Ion beam sputtered surface dynamics investigated with two-time correlation functions: a model study.

Ion beam sputtering is a widely used technique to obtain patterned surfaces. Despite the wide use of this approach on different materials to create surface nanostructures, the theoretical model to explain the time evolution of the erosion process is still debated. We show, with the help of simulations, that two-time correlation functions can serve to assess the validity of different models. These functions can be measured experimentally with the x-ray photon correlation spectroscopy technique.

Ageing dynamics of ion bombardment induced self-organization processes

Instabilities caused during the erosion of a surface by an ion beam can lead to the formation of self-organized patterns of nanostructures. Understanding the self-organization process requires not only the in-situ characterization of ensemble averaged properties but also probing the dynamics. This can be done with the use of coherent X-rays and analyzing the temporal correlations of the scattered intensity. Here, we show that the dynamics of a semiconductor surface nanopatterned by normal incidence ion beam sputtering are age-dependent and slow down with sputtering time. This work provides a novel insight into the erosion dynamics and opens new perspectives for the understanding of self-organization mechanisms.