[show abstract][hide abstract] ABSTRACT: Strained semiconductors are ubiquitous in microelectronics and microelectromechanical systems, where high local stress levels can either be detrimental for their integrity or enhance their performance. Consequently, local probes for elastic strain are essential in analyzing such devices. Here, a scanning X-ray sub-microprobe experiment for the direct measurement of deformation over large areas in single-crystal thin films with a spatial resolution close to the focused X-ray beam size is presented. By scanning regions of interest of several tens of micrometers at different rocking angles of the sample in the vicinity of two Bragg reflections, reciprocal space is effectively mapped in three dimensions at each scanning position, obtaining the bending, as well as the in-plane and out-of-plane strain components. Highly strained large-area Ge structures with applications in optoelectronics are used to demonstrate the potential of this technique and the results are compared with finite-element-method models for validation.
[show abstract][hide abstract] ABSTRACT: A comprehensive overview of the possibilities and potential of X–ray scattering using nanofocused beams for probing matter at the nanoscale, including guidance on the design of nanobeam experiments. The monograph discusses various sources, including free electron lasers, synchrotron radiation and other portable and non–portable X–ray sources. For scientists using synchrotron radiation or students and scientists with a background in X–ray scattering methods in general.
[show abstract][hide abstract] ABSTRACT: We present here an unprecedented way of quantifying the number of dislocations in microcrystals. This method relies on a combination of several state-of-the-art techniques: coherent x-ray diffraction used as a local probe, together with the controlled compression of micro-objects. We demonstrate that by using this method, dislocations in the microcrystal can be detected and their number precisely quantified. This cannot be done with other techniques in a nondestructive way. Our method opens a route for the study of many small-scale systems with defect-dependent physical properties and it could become a critical tool for addressing future challenges in nanotechnology.
[show abstract][hide abstract] ABSTRACT: 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.
[show abstract][hide abstract] ABSTRACT: 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.
[show abstract][hide abstract] ABSTRACT: 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.
[show abstract][hide abstract] ABSTRACT: 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.
[show abstract][hide abstract] ABSTRACT: Three-dimensional reciprocal-space maps of a single SiGe island around the Si(004) Bragg peak are recorded using an energy-tuning technique with a microfocused X-ray beam with compound refractive lenses as focusing optics. The map is in agreement with simulated data as well as with a map recorded by an ordinary rocking-curve scan. The energy-tuning approach circumvents both the comparatively large sphere of confusion of diffractometers compared with nanostructures and vibrations induced by motors. Thus, this method offers new possibilities for novel combinations of three-dimensional micro- and nano-focused X-ray diffraction with complex in situ sample environments such as scanning probe microscopes.
[show abstract][hide abstract] ABSTRACT: SiGe islands are used to induce tensile strain in the Si channel of Field Effect Transistors to achieve larger transconductance and higher current driveabilities. We report on x-ray diffraction experiments on a single fully-processed and functional device with a TiN+Al gate stack and source, gate, and drain contacts in place. The strain fields in the Si channel were explored using an x-ray beam focused to 400 nm diameter combined with finite element simulations. A maximum in-plane tensile strain of about 1% in the Si channel was found, which is by a factor of three to four higher than achievable for dislocation-free tensile strained Si in state-of-the-art devices. Comment: The following article has been submitted to Applied Physics Letters. After it is published, it will be found at http://apl.aip.org/
[show abstract][hide abstract] ABSTRACT: 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.
New Journal of Physics 03/2010; 12(3):035006. · 4.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: 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.
[show abstract][hide abstract] ABSTRACT: A compact portable vacuum-compatible chamber designed for surface X-ray scattering measurements on beamline ID01 of the European Synchrotron Radiation Facility, Grenoble, is described. The chamber is versatile and can be used for in situ investigation of various systems, such as surfaces, nanostructures, thin films etc., using a variety of X-ray-based techniques such as reflectivity, grazing-incidence small-angle scattering and diffraction. It has been conceived for the study of morphology and structure of semiconductor surfaces during ion beam erosion, but it is also used for the study of surface oxidation or thin film growth under ultra-high-vacuum conditions. Coherent X-ray beam experiments are also possible. The chamber is described in detail, and examples of its use are given.
[show abstract][hide abstract] ABSTRACT: Silicon and Teflon substrates have been structured by wet etching and a focused ion beam (FIB) to obtain very defined, clean apertures. Planar, free-standing lipid membranes (black lipid membranes (BLM)) with enhanced long-term stability have been prepared on these apertures by the methods of Montal and Müller(1,2) as well as Müller and Rudin.(3) The stability and geometric control enables the use of X-ray analysis of free-standing single bilayers. With the presented setup, simultaneous structural and electrophysiological measurements will become feasible.
[show abstract][hide abstract] ABSTRACT: We present a study of the early stage of ripple formation on Ge(001) surfaces irradiated by a 1 keV Xe(+) ion beam at room temperature and near-normal incidence. A combination of a grazing incidence x-ray scattering technique and atomic force microscopy allowed us to observe a variation of the symmetry of the surface nanopattern upon increase of the ion fluence. The isotropic dot pattern formed during the first minutes of sputtering evolves into an anisotropic ripple pattern for longer sputtering time. These results provide a new basis for further steps in the theoretical description of the morphology evolution during ion beam sputtering.