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This paper reviews our contributions and the development of an instrument for X-ray photoelectron diffraction (XPED) and X-ray holography. XPED and X-ray holography have been extensively applied in materials analysis over the past decades. We made pioneering contributions in this area that fueled the development of the corresponding instrumentation and technology. In this review, we briefly discuss the theory of XPED and X-ray holography instrument, the genesis, and applications. The instruments comprise a high-power soft and hard X-ray source as well as a diffraction aperture; further, they are capable of high-angular-resolution detection and patterning. The applications of these instruments for practical surface analysis are also reviewed for ultrathin insulators, catalysts, and magnetic materials. Finally, possibilities for the differential photoelectron holography (DPH) approach are premiered based on a novel approach. • This paper reviews our contributions and the development of instruments for XPED and X-ray holography over the last decades. • We demonstrated our original laboratory-level XPED instruments from the perspectives of a high-power soft and hard X-ray source, diffraction aperture, and high-angular-resolution detection. • We also demonstrated applications of practical surface analysis for ultrathin insulators, catalysts, and magnetic materials. • We premiered possibilities for differential photoelectron holography (DPH) based on the atomic reconstruction method using typical four-wave numbers. [ABSTRACT FROM AUTHOR]

Abstract: Thin-film solar cells based on compound semiconductors consist of a multilayer structure with various interfaces and contain a multitude of elements and impurities, etc. A rapid progress of these photovoltaic technologies can only be achieved by an insight-driven optimization/development. Hence it is crucial to characterize and understand the relationship between the chemical and electronic properties of these components. This paper reviews some examples of our recent work characterizing compound semiconductor thin films using laboratory- and synchrotron-based electron and soft X-ray spectroscopic characterization methods. It is demonstrated how these different analytical techniques are extraordinarily powerful to reveal the material characteristics from many different perspectives, ultimately resulting in a comprehensive picture of the related electronic and chemical properties. As examples, the paper will discuss the electronic surface structure of chalcopyrite thin-film solar cell absorbers, the chemical structure of the CdS/chalcopyrite interface, present the band alignment at the CdS/kesterite interface, and report on how post-deposition treatments cause chemical interaction/interdiffusion processes in CdTe/CdS thin-film solar cell structures. [Copyright &y& Elsevier]

Spectroptychography is being used to realize a significant improvement in the spatial resolution of x-ray spectromicroscopy, allowing chemical microanalysis at finer spatial scales. The chemical sensitivity of near edge X-ray absorption fine structure (NEXAFS) is familiar to most researchers who use x-ray spectromicroscopy for chemical microanalysis. However, the additional phase information available through ptychography provides additional and tantalizing data, and potentially additional chemical information. This paper explores the chemical information available in phase for a system of silicon dioxide nanospheres. • Soft x-ray spectroptychography provides chemical information through absorption and phase. • Phase spectra reveal chemical information in an indirect manner. • The Kramers–Kronig relation is useful for understanding contrast in ptychography chemical analysis. [ABSTRACT FROM AUTHOR]

In this paper, we give an overview of the nanoscale spectromicroscopy studies performed with the full-field X-ray microscope at the BESSY II electron storage ring. We do not consider spectromicroscopy studies performed with X-ray microscopes operated at other synchrotron sources. Such studies can be found in the literature. To our knowledge, the full-field X-ray microscope at the BESSY II storage ring is the first one operating with both a plane-grating-monochromator (PGM) beamline equipped with multi-layer optics for the tender X-ray range, as well as with standard optical elements for the soft X-ray range. We discuss how this instrument has been used in various published NEXAFS-TXM studies to probe low dimensional nanostructures. This research work paves the way for understanding electronic structures approaching the atomic scale, and will thereby help in the design of tailored functional systems. • Nanoscale X-ray spectromicroscopy with a full-field X-ray microscope. • Nanoscale oxides in catalysis and light harvesting/storage applications. • X-ray spectromicroscopy studies of microelectronic devices. • X-ray spectromicroscopy studies of graphene based materials. • X-ray spectromicroscopy studies of nanomaterials for different sensor types. [ABSTRACT FROM AUTHOR]

The beamline, BL4U, in UVSOR-III Synchrotron is dedicated to scanning transmission X-ray microscopy (STXM) based on 2-dimensional soft X-ray absorption and has been in operation since 2013, to enable both academic and industrial users to carry out advanced chemical analysis under various sample environments. In this paper, we have summarized our major developments for the last decade; especially, expansion of the photon energy range down to the Li K-edge (55 eV), sample cryo-cooling to reduce radiation damage, 3-dimensional computer tomography, and air-free sample transfer. • Lithium K absorption edge around 55 eV is available for STXM by reducing higher order harmonics. • Cryo-cooling setup is developed to reduce X-ray radiation damage to samples. • By using computer tomography, 3-dimensional X-ray absorption spectroscopy of an isolated cell nucleus was performed. • Air-free sample transfer system is developed for samples which are highly reactive with oxygen or water. [ABSTRACT FROM AUTHOR]

Time-resolved X-ray spectroscopies have the potential of unveiling ultrafast processes with chemical sensitivity, but their widespread application is still withheld by technical and experimental constraints on two levels: the count rate and the amount of signal to be measured. In this paper, we will give a brief overview of the available pulsed X-ray sources focusing in particular on those delivering photons with energies inside the water window (280–550 eV), thus allowing to access the C1s, N1s and O1s core levels which are relevant for the characterization of thin organic films and small molecules adsorbed on surfaces. We will mainly discuss the photon fluxes delivered by such sources in relation to their repetition rates, and we will see how these factors affect time-resolved measurements. The main purpose of this work is to discuss the most crucial parameter to adjust in pump-probe spectroscopies: the excitation density, which corresponds to the fraction of photoexcited molecules/atoms. We show that such quantity may be increased up to roughly 25% in gas phase and other robust samples, however, due to a lower damage threshold, in organic films it is typically constrained to be in the order of 1–5%. Despite the initially limited population of excited states in the latter case, we show that the evolution of the system may lead to a collective response of the material, which entirely modifies the measured core level line shape, thus providing a clear signal that may nonetheless offer valuable insights into the dynamics of the studied process. • The experimental challenges of time-resolved soft X-ray spectroscopies are outlined. • A formula for excitation density generated by optical pumping is derived. • In organic films the fraction of photoexcited molecules is usually as low as 1–5%. [ABSTRACT FROM AUTHOR]

Abstract: Progress toward a fundamental understanding of magnetism continues to be of great scientific interest and high technological relevance. To control magnetization on the nanoscale, external magnetic fields and spin polarized currents are commonly used. In addition, novel concepts based on spin manipulation by electric fields or photons are emerging which benefit from advances in tailoring complex magnetic materials. Although the nanoscale is at the very origin of magnetic behavior, there is a new trend toward investigating mesoscale magnetic phenomena, thus adding complexity and functionality, both of which will become crucial for future magnetic devices. Advanced analytical tools are thus needed for the characterization of magnetic properties spanning the nano- to the meso-scale. Imaging magnetic structures with high spatial and temporal resolution over a large field of view and in three dimensions is therefore a key challenge. A variety of spectromicroscopic techniques address this challenge by taking advantage of variable-polarization soft X-rays, thus enabling X-ray dichroism effects provide magnetic contrast. These techniques are also capable of quantifying in an element-, valence- and site-sensitive way the basic properties of ferro(i)- and antiferro-magnetic systems, such as spin and orbital moments, spin configurations from the nano- to the meso-scale and spin dynamics with sub-ns time resolution. This paper reviews current achievements and outlines future trends with one of these spectromicroscopies, magnetic full field transmission soft X-ray microscopy (MTXM) using a few selected examples of recent research on nano- and meso-scale magnetic phenomena. The complementarity of MTXM to X-ray photoemission electron microscopy (X-PEEM) is also emphasized. [Copyright &y& Elsevier]