A Contrast Calibration Protocol for X-ray Speckle Visibility Spectroscopy

X-ray free electron lasers, with their ultrashort highly coherent pulses, opened up the opportunity of probing ultrafast nano- and atomic-scale dynamics in amorphous and disordered material systems via speckle visibility spectroscopy. However, the anticipated count rate in a typical experiment is usually low. Therefore, visibility needs to be extracted via photon statistics analysis, i.e., by estimating the probabilities of multiple photons per pixel events using pixelated detectors. Considering the realistic X-ray detector responses including charge cloud sharing between pixels, pixel readout noise, and gain non-uniformity, speckle visibility extraction relying on photon assignment algorithms are often computationally demanding and suffer from systematic errors. In this paper, we present a systematic study of the commonly-used algorithms by applying them to an experimental data set containing small-angle coherent scattering with visibility levels ranging from below 1% to ∼60%. We also propose a contrast calibration protocol and show that a computationally lightweight algorithm can be implemented for high-speed correlation evaluation.

Accurate contrast determination for X-ray speckle visibility spectroscopy

X-ray speckle visibility spectroscopy using X-ray free-electron lasers has long been proposed as a probe of fast dynamics in noncrystalline materials. In this paper, numerical modeling is presented to show how the data interpretation of visibility spectroscopy can be impacted by the nonidealities of real-life X-ray detectors. Using simulated detector data, this work provides a detailed analysis of the systematic errors of several contrast extraction algorithms in the context of low-count-rate X-ray speckle visibility spectroscopy and their origins are discussed. Here, it was found that the finite detector charge cloud and pixel size lead to an unavoidable `degeneracy' in photon position determination, and that the contrasts extracted using different algorithms can all be corrected by a simple linear model. The results suggest that experimental calibration of the correction coefficient at the count rate of interest is possible and essential. This allows computationally lightweight algorithms to be implemented for on-the-fly analysis.

Electromagnetic-matter interactions and devices

This chapter explores electromagnetic-matter interactions from photon to extinction length scales, i.e., nanometer of X-ray and above. Starting with Casimir-Polder effect to understand interactions of metals and dielectrics at near-atomic distance scale, it stretches to larger wavelengths to explore optomechanics and its ability for energy exchange and signal transduction between PHz and GHz. This range is explored with near-quantum sensitivity limits. The chapter also develops the understanding phononic bandgaps, and for photons, it explores the use of energetic coupling for useful devices such as optical tweezers, confocal microscopes and atomic clocks. It also explores miniature accelerators as a frontier area in accelerator physics. Plasmonics—the electromagnetic interaction with electron charge cloud—is explored for propagating and confined conditions together with the approaches’ possible uses. Optoelectronic energy conversion is analyzed in organic and inorganic systems, with their underlying interaction physics through solar cells and its thermodynamic limit, and quantum cascade lasers.

Screened Coulomb interactions with non-uniform surface charge

The screened Coulomb interaction between a pair of infinite parallel planes with spatially varying surface charge is considered in the limit of small electrical potentials for arbitrary Debye lengths. A simple expression for the disjoining pressure is derived in terms of a two-dimensional integral in Fourier space. The integral is evaluated for periodic and random charge distributions and the disjoining pressure is expressed as a sum over Fourier–Bloch reciprocal lattice vectors or in terms of an integral involving the autocorrelation function, respectively. The force between planes with a finite area of uniform charge, a model for the DLVO interaction between finite surfaces, is also calculated. It is shown that the overspill of the charge cloud beyond the region immediately between the charged areas results in a reduction of the disjoining pressure, as reported by us recently in the long Debye length limit for planes of finite width.

Micrometer-resolution imaging using MÖNCH: towards G2-less grating interferometry

MÖNCH is a 25 µm-pitch charge-integrating detector aimed at exploring the limits of current hybrid silicon detector technology. The small pixel size makes it ideal for high-resolution imaging. With an electronic noise of about 110 eV r.m.s., it opens new perspectives for many synchrotron applications where currently the detector is the limiting factor,e.g.inelastic X-ray scattering, Laue diffraction and soft X-ray or high-resolution color imaging. Due to the small pixel pitch, the charge cloud generated by absorbed X-rays is shared between neighboring pixels for most of the photons. Therefore, at low photon fluxes, interpolation algorithms can be applied to determine the absorption position of each photon with a resolution of the order of 1 µm. In this work, the characterization results of one of the MÖNCH prototypes are presented under low-flux conditions. A custom interpolation algorithm is described and applied to the data to obtain high-resolution images. Images obtained in grating interferometry experiments without the use of the absorption grating G2are shown and discussed. Perspectives for the future developments of the MÖNCH detector are also presented.

DESIGN CONCEPT OF MOBILE STATIC DISCHARGER FOR HUMAN BODY ELECTROSTATIC DISCHARGE USING VAN DE GRAAFF’S GENERATORtic Discharge Using Van de Graaff’s Generator

The damage of electrostatic discharge (ESD) is a well-known problem in the semiconductor industry. When human body (operator) is in contact with electrostatic sensitive semiconductor device during manufacturing process, damage to the oxide and other active parts of the device is caused by transferring of charge between device and human body. Semiconductor industry adopts preventive and protective approaches by grounding the human body with a wrist strap connecting to utility ground to neutralize the charge and setting up ESD preventive and protective workstation. Wearing a wrist strap is impractical for the operator and it causes psychological effect as the operator would not like to be strapped. A literature search and visit of many large semiconductor manufacturing facilities have revealed that there is no alternative mean used to neutralize charge from human body besides wearing a wrist strap. This paper presents a conceptual design of a mobile static discharger for human body electrostatic discharge using Van de Graaff’s generator to generate equal amount of positive and negative charge cloud to neutral the charge of the operator. The conceptual design is a fool-proof design and it is viable to be implemented. It is also a design that will revolutionize the technique of electrostatic discharge for human body in the semiconductor industry.