Ptychography of Organic Thin Films at Soft X-ray Energies

Abstract

The path to realizing low-cost, stable, and earth-abundant photoelectrodes can be enabled through a detailed understanding of the optoelectronic properties of these materials by combining theory and experimental techniques. Of the limited set of oxide photocathode materials currently available, CuFeO 2 has emerged as a promising candidate warranting detailed attention. In this work, highly compact thin films of rhombohedral (3R) CuFeO 2 were prepared via reactive cosputtering. Despite its 1.43 eV indirect band gap, a cathodic photocurrent of 0.85 mA/cm 2 was obtained at 0.4 V versus reversible hydrogen electrode in the presence of a sacrificial electron acceptor. This unexpected performance was related to inefficient bulk charge separation because of the ultrafast (<1 ps) self-trapping of photogenerated free carriers. The electronic structure of 3R-CuFeO 2 was elucidated through a combination of optical and X-ray spectroscopic techniques and further complemented by first-principles computational methods including a many-body approach for computing the O K-edge X-ray absorption spectrum. Through resonant inelastic X-ray scattering spectroscopy, the visible absorption edges of CuFeO 2 were found to correspond to Cu → Fe metal-to-metal charge transfer, which exhibits a high propensity toward self-trapping. Findings of the present work enable us to understand the performance bottlenecks of CuFeO 2 photocathodes and suggest feasible strategies for improving material limitations.

Resonant soft X‐ray scattering in polymer science

“…In an initial study, ptychography was performed on polymer blends that demonstrated 30-50 nm resolution with no discernable beam damage. 50 Although this is similar to the best achievable STXM resolution for similar samples, such an initial demonstration bodes well for eventual <10 nm chemically resolved images.…”

“…These techniques solve directly for the missing phase of the scattered wave to invert the scattering pattern from its Fourier transformed state back into an image of the sample itself. In an initial study, ptychography was performed on polymer blends that demonstrated 30–50 nm resolution with no discernable beam damage 50 . Although this is similar to the best achievable STXM resolution for similar samples, such an initial demonstration bodes well for eventual <10 nm chemically resolved images.…”

“…Because RSoXS in general does not exploit full coherence, RSoXS beamlines are not designed to utilize phase retrieval schemes such as coherent diffractive imaging and ptychography. Although there are some successes in certain cases, 50,92,93 the radiation damage due to the beam has significantly limited the application of these techniques in soft matter systems.…”

“…The reader is directed elsewhere for those discussions. 40,50 It is important to note that Equation (5) reduces in nonresonant form, where n is a constant proportional to the effective electron density ρ e , to…”

Control of aggregated structure of photovoltaic polymers for high‐efficiency solar cells

“…Present understanding of the aggregated structure greatly benefits from the advances in characterization tools of soft matters. [45,47,416] For instance, R-SoXS has been a very powerful tool to analyze the structural parameters (domain size, [417,418] domain purity, [419] type and degree of orientation [420,421] ) of polymers blends in solid films. Use of other techniques (e.g., in situ neutron scattering [422] and cryo-TEM [423] ) will help to understand how the aggregated structure forms in solution state.…”