Energetics of hydrogen adsorption and diffusion for the main surface planes and all magnetic structures of γ-iron using density functional theory

In this study, we calculated the energetics of hydrogen atoms adsorbing on and diffusing into the first few layers of γ-Fe for the (100), (110) and (111) surfaces and for the non-magnetic (NM), ferromagnetic (FM), and antiferromagnetic single (AFM1) and double layer (AFMD) structures. These studies are relevant as they atomistically simulate the early stages of hydrogen embrittlement in steels. We employed density functional theory to establish adsorption sites and energies for each plane and the minimum energy pathways for diffusion through the first few layers with associated activation barriers. Adsorption energies for all cases vary between ∼3.7 and 4.4 eV, and the energy barriers to diffusion in the bulk region vary between ∼0.2 and 1.2 eV for the twelve cases, with the highest and lowest bulk diffusion barriers occurring in the NM(111) and the FM(100) case, respectively. We conclude that the texturing of steels in order to expose certain cleavage planes or magnetic structures can decrease the likelihood of hydrogen embrittlement

Self-supervised motion descriptor for cardiac phase detection in 4D CMR based on discrete vector field estimations

Cardiac magnetic resonance (CMR) sequences visualise the cardiac function voxel-wise over time. Simultaneously, deep learning-based deformable image registration is able to estimate discrete vector fields which warp one time step of a CMR sequence to the following in a self-supervised manner. However, despite the rich source of information included in these 3D+t vector fields, a standardised interpretation is challenging and the clinical applications remain limited so far. In this work, we show how to efficiently use a deformable vector field to describe the underlying dynamic process of a cardiac cycle in form of a derived 1D motion descriptor. Additionally, based on the expected cardiovascular physiological properties of a contracting or relaxing ventricle, we define a set of rules that enables the identification of five cardiovascular phases including the end-systole (ES) and end-diastole (ED) without the usage of labels. We evaluate the plausibility of the motion descriptor on two challenging multi-disease, -center, -scanner short-axis CMR datasets. First, by reporting quantitative measures such as the periodic frame difference for the extracted phases. Second, by comparing qualitatively the general pattern when we temporally resample and align the motion descriptors of all instances across both datasets. The average periodic frame difference for the ED, ES key phases of our approach is $0.80\pm{0.85}$, $0.69\pm{0.79}$ which is slightly better than the inter-observer variability ($1.07\pm{0.86}$, $0.91\pm{1.6}$) and the supervised baseline method ($1.18\pm{1.91}$, $1.21\pm{1.78}$). Code and labels will be made available on our GitHub repository. https://github.com/Cardio-AI/cmr-phase-detectionComment: accepted for the STACOM2022 workshop @ MICCAI202

Translational and Rotational Energy Distributions of NO Photodesorbed from Au(100)

We report velocity and internal state distributions of nitric oxide photodesorbed from an Au(100) single crystal using 355 and 266 nm photons. The velocity distributions were measured in all three dimensions independently using our novel 3D-velocity map imaging setup. Combined with the internal energy distributions we reveal two distinct desorption mechanisms for the photodesorption of NO from gold dependent on the photon wavelength. The 355 nm desorption is dominated by a nonthermal mechanism due to excitation of an electron from the gold substrate to the adsorbed NO; this leads to a superthermal and noticeably narrow velocity distribution and a rotational state distribution that positively correlates with the velocity distribution and can be described by a rotational temperature appreciably above the surface temperature. Desorption with 266 nm photons leads to a slower average speed and wider angular distribution and rotational temperatures not too far off the surface temperature. We conclude that in the absence of occupied orbitals in the substrate and unoccupied orbitals on the adsorbed NO separated by 4.7 eV, corresponding to 266 nm; the shorter wavelength desorption is dominated by a thermally activated mechanism

Adsorption site, orientation and alignment of NO adsorbed on Au(100) using 3D-velocity map imaging, X-ray photoelectron spectroscopy and density functional theory

Nitric oxide adsorption on a Au(100) single crystal has been investigated to identify the type of adsorption, the adsorption site, and the orientation and alignment of the adsorbed NO relative to the surface. This was done using a combination of 3D-surface velocity map imaging, near-ambient pressure X-ray photoelectron spectroscopy, and density functional theory. NO was observed to be molecularly adsorbed on gold at ∼200 K. Very narrow angular distributions and cold rotational distributions of photodesorbed NO indicate that NO adsorbs on high-symmetry sites on the Au crystal, with the N-O bond axis close to the surface normal. Our density functional theory calculations show that NO preferentially adsorbs on the symmetric bridge (2f) site, which ensures efficient overlap of the NO π* orbital with the orbitals on the two neighbouring Au atoms, and with the N-O bond axis aligned along the surface normal, in agreement with our conclusions from the rotational state distributions. The combination of XPS, which reveals the orientation of NO on gold, with 3D-surface velocity map imaging and density functional theory thus allowed us to determine the adsorption site, orientation and alignment of nitric oxide adsorbed on Au(100)

Correction: Imaging the reactivity and width of graphene's boundary region.

Correction for 'Imaging the reactivity and width of graphene's boundary region' by Huda S. AlSalem et al., Chem. Commun., 2020, 56, 9612-9615, DOI: 10.1039/D0CC02675A

Vibrational fingerprints of residual polymer on transferred CVD-graphene

The use of vibrational sum-frequency spectroscopy (VSFS) to study transferred graphene, produced by chemical vapour deposition, is presented. The VSF spectrum shows a clear CH stretching mode at ∼2924 cm−1, which is attributed to residue of the polymer used for the transfer. This makes VSFS a powerful tool to identify adsorbates and contaminants affecting the properties of graphene