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DOE OSTI2019

Materials Data on CI2 by Materials Project

CI2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four tetraiodoethylene molecules. C2+ is bonded in a distorted trigonal planar geometry to one C2+ and two I1- atoms. The C–C bond length is 1.35 Å. There are one shorter (2.10 Å) and one longer (2.11 Å) C–I bond lengths. There are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a single-bond geometry to one C2+ atom. In the second I1- site, I1- is bonded in a single-bond geometry to one C2+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Effect of ethanol concentrations on temperature driven structural changes of chymotrypsin inhibitor 2

A series of atomistic molecular dynamics (MD) simulations of a small enzymatic protein Chymotrypsin Inhibitor 2 (CI2) in water-ethanol mixed solutions were carried out to explore the underlying mechanism of ethanol driven conformational changes of the protein. Efforts have been made to probe the influence of ethanol concentrations ranging from 0% to 75% (v/v) at ambient condition (300 K (T1)) and at elevated temperatures (375 K (T2) and 450 K (T3)) to investigate the temperature induced conformational changes of the protein further. Our study showed that the effect of varying ethanol concentrations on protein’s structure is almost insignificant at T1 and T2 temperatures whereas at T3 temperature, partial unfolding of CI2 in 10% ethanol solution followed by full unfolding of the protein at ethanol concentrations above 25% occurs. However, interestingly, at T3 temperature CI2’s native structure was found to be retained in pure water (0% ethanol solution) indicating that the cosolvent ethanol do play an important role in thermal denaturation of CI2. Such observations were quantified in the light of root-mean-square deviations (RMSDs) and radius of gyration. Although higher RMSD values of β-sheet over α-helix indicate complete destruction of the β-structure of CI2 at high ethanol concentrations, the associated time scale showed that the faster melting of α-helix happens over β-sheet. Around 60%-80% of initial native contacts of the protein were found broken with the separation of hydrophobic core consisting eleven residues at ethanol concentrations greater than 25%. This leads protein to expand with the increase in solvent accessible surface area. The interactions between protein and solvent molecules showed that protein’s solvation shell preferred to accommodate ethanol molecules as compared to water thereby excluded water molecules from CI2’s surface. Further, concentration dependent differential self-aggregation behavior of ethanol is likely to regulate the replacement of relatively fast diffused water by low diffused ethanol molecules from protein’s surface during the unfolding process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Materials Data on CI(NO)3 by Materials Project

CN2N2CI2(NO3)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight ammonia molecules, four cyanamide molecules, and two CI2(NO3)2 clusters. In each CI2(NO3)2 cluster, C4+ is bonded in a single-bond geometry to one N1+ atom. The C–N bond length is 1.25 Å. There are two inequivalent N1+ sites. In the first N1+ site, N1+ is bonded in a bent 120 degrees geometry to one C4+ and one O2- atom. The N–O bond length is 1.31 Å. In the second N1+ site, N1+ is bonded in a bent 120 degrees geometry to two O2- atoms. There is one shorter (1.20 Å) and one longer (1.36 Å) N–O bond length. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one I1- atom. The O–I bond length is 1.80 Å. In the second O2- site, O2- is bonded in a single-bond geometry to one I1- atom. The O–I bond length is 1.81 Å. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one N1+ and one I1- atom. The O–I bond length is 2.17 Å. In the fourth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three I1- atoms. There are a spread of O–I bond distances ranging from 1.95–2.64 Å. In the fifth O2- site, O2- is bonded in a single-bond geometry to one N1+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one N1+ and one I1- atom. The O–I bond length is 2.25 Å. There are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a 3-coordinate geometry to three O2- atoms. In the second I1- site, I1- is bonded in a 4-coordinate geometry to four O2- atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Irradiation induced structural change in Mo 2 Zr intermetallic phase

The Mo 2 Zr phase has been identified as a major interaction product at the interface of U-10Mo and Zr. Transmission electron microscopy in-situ irradiation with Kr ions at 200 °C with doses up to 2.0E+16 ions/cm 2 was carried out to investigate the radiation stability of the Mo 2 Zr. The Mo 2 Zr undergoes a radiation-induced structural change, from a large cubic (cF24) to a small cubic (cI2), along with an estimated 11.2% volume contraction without changing its composition. The structural change begins at irradiation dose below 1.0E+14 ions/cm 2 . Furthermore, the transformed Mo 2 Zr phase demonstrates exceptional radiation tolerance with the development of dislocations without bubble formation.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Plasma Processing of Superconducting Radio Frequency Cavities

The development of plasma processing technology of superconducting radio frequency (SRF) cavities not only provides a chemical free and less expensive processing method, but also opens up the possibility for controlled modification of the inner surfaces of the cavity for better superconducting properties. The research was focused on the transition of plasma etching from two dimensional flat surfaces to inner surfaces of three dimensional (3D) structures. The results could be applicable to a variety of inner surfaces of 3D structures other than SRF cavities. Understanding the A r/C L plasma etching mechanism is crucial for achieving the desired modification of Nb SRF cavities. In the process of developing plasma etching technology, an apparatus was built and a method was developed to plasma etch a single cell Pill Box cavity. The plasma characterization was done with the help of optical emission spectroscopy. The Nb etch rate at various points of this cavity was measured before processing the SRF cavity. Cylindrical ring-type samples of Nb placed on the inner surface of the outer wall were used to measure the dependence of the process parameters on plasma etching. The measured etch rate dependence on the pressure, rf power, dc bias, temperature, CI2 concentration and diameter of the inner electrode was determined. The etch rate mechanism was studied by varying the temperature of the outer wall, the dc bias on the inner electrode and gas conditions. In a coaxial plasma reactor, uniform plasma etching along the cylindrical structure is a challenging task due to depletion of the active radicals along the gas flow direction. The dependence of etch rate uniformity along the cylindrical axis was determined as a function of process parameters. The formation of dc self-biases due to surface area asymmetry in this type of plasma and its variation on the pressure, rf power and gas composition was measured. Enhancing the surface area of the inner electrode to reduce the asymmetry was studied by changing the contour of the inner electrode. The optimized contour of the electrode based on these measurements was chosen for SRF cavity processing.

Upadhyay, Janardan↗