© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 www.advmat.de www.MaterialsViews.com wileyonlinelibrary.com RESEARCH NEWS Exploring Single Semiconductor Nanowires with a Multimodal Hard X-ray Nanoprobe Gema Martínez-Criado,* Jaime Segura-Ruiz, Benito Alén, Joël Eymery, Andrei Rogalev, Rémi Tucoulou, and Alejandro Homs Dr. G. Martínez-Criado, Dr. J. Segura-Ruiz, Dr. A. Rogalev, Dr. R. Tucoulou, A. Homs European Synchrotron Radiation Facility 38043, Grenoble, France E-mail: gmartine@esrf.fr Dr. B. Alén IMM-Instituto de Microelectrónica de Madrid (CNM-CSIC) 28760, Tres Cantos, Spain Dr. J. Eymery Equipe mixte CEA-CNRS-UJF “Nanophysique et semiconducteurs”, SP2M, UMR-E CEA / UJF-Grenoble 1, INAC Grenoble 38054, France DOI: 10.1002/adma.201304345 collections of NWs, though it is rather dif- ficult to find single probes covering simul- taneously all of the above properties. [4,5] In this context, the use of synchrotron based probes in the multi-keV energy range has great potentialities and several advantages: (1) surface/deep information depths; (2) element-, site-, and orbital- selectivity with simultaneous access to K absorption edges and X-ray fluorescence emission lines of heavy, medium and light elements; (3) structural probe; (4) chemical trace sensitivity owing to the high brilliance of synchrotron sources; (5) accessibility to timing modes; and (6) orientational effects by polarization selec- tion rules. [6] Thus, existing synchrotron radiation sources have largely contributed to the rapid advance- ment of NW technology, for example by X-ray microdiffraction techniques. [7] Moreover, lens-less approaches have also been applied to the study of ZnO NWs by Bragg coherent diffrac- tion imaging. [8] The ability to map in 3D the full strain tensor with nanometer scale resolution is potentially very useful for examining complex nanostructures, but in some cases there are strong limitations in terms of spatial resolution and sensitivity (i.e. signal/background ratio), which limits insights into NW related phenomena. So far most synchrotron-related techniques are carried out in ensembles of NWs and the information is obtained via spatial averaging over macroscopic length scales. [9] As a result, nanometer-scale spatial resolving power added to X-ray fluorescence (XRF), X-ray absorption spectroscopy (XAS), or X-ray diffraction (XRD) is strongly desired in NW research for three main reasons: [10] (1) the study of small embedded domains with weak signals and/or heterogeneous structures requires the use of intense X-ray pencil nanobeams; (2) stim- ulated by the great brilliance with reduced emittance of cur- rent third-generation synchrotron sources, today it is possible to focus X-rays to spot sizes smaller than NWs with a variety of focusing devices, including Fresnel zone plates, compound refractive lenses, Kirkpatrick-Baez mirrors and tapered capil- laries; (3) thanks to the multiple photon-matter interactions, these X-ray nanoprobes can be used for manifold purposes in NWs, such as ultrasensitive elemental/chemical detection using XRF/XAS, or for identification of minority phases, and/ or strain fields by XRD with nanometer resolution. Examples of the use of X-ray (sub-)microbeams in the deter- mination of spatially-resolved properties of single NWs include the study of the mechanics and dynamics of the strain induced M1–M2 structural phase transition in individual VO 2 NWs, [11] Semiconductor nanowires offer new opportunities for optoelectronic and spintronic nanodevices. However, their full potential is ultimately dictated by our ability to control multiple property-function relationships taking place at the nanoscale in the spatial and time domains. Only a combination of high- resolution analytical techniques can provide a comprehensive understanding of their complex functionalities. Here we describe how a multimodal hard X-ray nanoprobe addresses fundamental questions in nanowire research. Selected topics ranging from cluster formation, dopant segregation, and phase separations to quantum confinement effects are investigated with sub- 100 nm spatial resolution and sub-50 ps temporal resolution. This approach opens new avenues for structural, composition and optical studies with broad applicability in materials science. 1. Introduction Interest in semiconductor nanowires (NWs) has been greatly stimulated in the last years due to their potential as basic building blocks of nanoscale devices and electronic circuits. [1–3] Investigations performed so far are driven by three unique properties of NWs. First, they simultaneously present a capa- bility for optical guiding and electrical driving. Second, their large surface to volume ratio enhances their interaction with the surrounding media, turning them into highly sensitive and selective sensors and transducers. The elastic strain relaxa- tion at free surface also allows to build new heterostructures that cannot be carried out on the planar geometry. Third, their anisotropic geometry makes their optical and electrical proper- ties strongly dependent on their orientation, allowing their use as polarization-dependent sensors. To date, most NW applica- tions rely on the ability not only to grow, but also to charac- terize structurally, optically and electronically individual and Adv. Mater. 2014, DOI: 10.1002/adma.201304345