Design and performance of an ultra‐high‐vacuum‐compatible artificial channel‐cut monochromator

The design and performance of a novel ultra‐high‐vacuum‐compatible artificial channel‐cut monochromator that has been commissioned at undulator beamline 8‐ID‐I at the Advanced Photon Source are presented. Details of the mechanical and optical design, control system implementation and performance of the new device are given. The monochromator was designed to meet the challenging stability and optical requirements of the X‐ray photon correlation spectroscopy program hosted at this beamline. In particular, the device incorporates a novel in‐vacuum sine‐bar drive mechanism for the combined pitch motion of the two crystals and a flexure‐based high‐stiffness weak‐link mechanism for fine‐tuning the pitch and roll of the second crystal relative to the first crystal. The monochromator delivers an exceptionally uniform and stable beam and thereby improved brilliance preservation.     

X-ray photoelectron spectroscopic investigations on cubic BaTiO3, BaTi0.9Fe0.1O3 and Ba0.9Nd0.1TiO3 systems

X-ray photoelectron spectroscopic (XPS) studies were carried out on wet-chemically synthesized cubic BaTiO₃, Ba_0.9Nd_0.1TiO₃ and BaTi_0.9Fe_0.1O_3−δ powders. The compounds were prepared by hydrothermal and gel to crystallite conversion technique; and phases formed readily at 420 K. The phase purity of the powders was confirmed from X-ray diffractometry. Chemical state and chemical environment of the constituent elements in the compositions were examined by XPS. Ba²⁺ was found to exist in two different chemical environments in these titanates. The Ti 2p_3/2 photoelectron peak in BaTi_0.9Fe_0.1O_3−δ was found to be broadened after Fe³⁺ substitution. Any resolvable broadening was not observed distinctly in the Ti 2p peak for Ba_0.9Nd_0.1TiO₃, unsintered BaTiO₃ and BaTiO₃ annealed in hydrogen (8% H₂ + Ar) at 1000 K. The prevalence of mixed-valent titanium and iron in BaTi_0.9Fe_0.1O_3−δ composition was evident from the XPS results and was further supported by the enhanced electrical conductivity at 298-550 K for BaTi_0.9Fe_0.1O_3−δ in comparison to BaTiO₃ and Ba_0.9Nd_0.1TiO₃. Hydroxyl incorporation was facilitated by substituting Nd³⁺ in Ba-sublattice. The presence of hydroxyls was observed from the broadening of the O 1s peak in XPS studies of the compounds.     

Comparative study of runaway electron diffusion in the rise phase of low qa and normal qa discharges in the SINP tokamak

The behaviour of runaway electrons in the SINP tokamak, which can be operated in a normal edge safety factor (q _a ) (NQ) discharge configuration as well as in a low q _a (LQ) configuration, was experimentally investigated, during the initial plasma generation phase. An energy analysis of the runaway electron dynamics in the rise phase of the SINP tokamak discharges was also made. A comparison of the runaway electron diffusion coefficients in NQ and LQ is carried out in this paper.     

Effect of Cyclization of Polystyrene/Polyisoprene Block Copolymers on Their Micellar Morphology

Micelles made from linear polystyrene‐block‐polyisoprene (PS/PI) in decane are spherical. The differences in the structure of micelles made from linear and cyclic PS/PI were investigated using small‐angle X‐ray scattering at rest and under shear flow. The effect of shear revealed that micelles made from cyclic copolymer chains have an elongated shape, which was confirmed by transmission electron microscopy. The cyclization of diblock copolymer chains is thus a new method to control the micellar morphology.

     

Passivation techniques for InAs/GaSb strained layer superlattice detectors

InAs/(In,Ga)Sb Strained Layer Superlattices (SLSs) have made significant progress since they were first proposed as an infrared (IR) sensing material more than three decades ago. The basic material properties of SLS provide a prospective benefit in the realization of IR imagers with suppressed interband tunneling and Auger recombination processes, as well as high quantum efficiency and responsivity. With scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels’ surface/volume ratio. This article discusses the cause of surface leakage currents and various approaches of their reduction including dielectric passivation, passivation with organic materials (polyimide or various photoresists), passivation by overgrowth of wider bandgap material, and chalcogenide passivation. Performance of SLS detectors passivated by different techniques and operating in various regions of infrared spectrum has been compared.     

Polymerizable Solvent-free Organic Liquids: A New Approach for Large Area Flexible and Foldable Luminescent Films

The high demand for light-emitting and display devices made luminescent organic materials as attractive candidates. Solvent-free organic liquids are one of the promising emitters among them due to the salient features. However, the inherent limitations of forming sticky and noncurable surfaces must be addressed to become an alternate emitter for large-area device applications. Herein, we functionalized solvent-free organic liquids having monomeric emission in bulk with polymerizable groups to improve the processability. The polymerizable group on carbazole, naphthalene monoimide, and diketopyrrolopyrrole-based solvent-free liquid emitters enabled on-surface polymerization. These emitters alone and in combinations can be directly coated on a glass substrate without the help of solvents. Subsequent photo or thermal polymerization leads to stable, non-sticky, flexible, foldable, and free-standing large-area films with reasonably high quantum yield. Our demonstration of the tunable and white light-emitting films using polymerizable solvent-free liquids might be a potential candidate in flexible/foldable/stretchable electronics. The new concept of polymerizable liquid can be extended to other functional features suitable for futuristic applications.