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DOE OSTI2016

Crystal growth methods dedicated to low solubility actinide oxalates

Two novel crystal growth syntheses dedicated to low solubility actinide-oxalate systems and adapted to glove box handling are described. These methods based on the use of precursors of either actinide metal or oxalic acid have been optimized on lanthanide systems (analogue of actinides(III)) and then assessed on real actinide systems. They allow the synthesis of several actinide oxalate single crystals, Am{sub 2}(C{sub 2}O{sub 4}){sub 3}(H{sub 2}O){sub 3}·xH{sub 2}O, Th(C{sub 2}O{sub 4}){sub 2}·6H{sub 2}O, M{sub 2+x}[Pu{sup IV}{sub 2−x}Pu{sup III}{sub x}(C{sub 2}O{sub 4}){sub 5}]·nH{sub 2}O and M{sub 1−x}[Pu{sup III}{sub 1−x}Pu{sup IV}{sub x}(C{sub 2}O{sub 4}){sub 2}·H{sub 2}O]·nH{sub 2}O. It is the first time that these well-known compounds are formed by crystal growth methods, thus enabling direct structural studies on transuranic element systems and acquisition of basic data beyond deductions from isomorphic (or not) lanthanide compounds. Characterizations by X-ray diffraction, UV–visible solid spectroscopy, demonstrate the potentialities of these two crystal growth methods to obtain oxalate compounds. - Graphical abstract: Two new single crystal growth methods dedicated to actinide oxalate compounds. - Highlights: • Use of diester as oxalate precursor for crystal growth of actinide oxalates. • Use of actinide oxide as precursor for crystal growth of actinide oxalates. • Crystal growth of Pu(III) and Am(III) oxalates. • Crystal growth of mixed Pu(III)/Pu(IV) oxalates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Growth, structure, defects and polarized absorption spectral properties of Er:Yb:YCa{sub 4}O(BO{sub 3}){sub 3} crystals

YCa{sub 4}O(BO{sub 3}){sub 3} (YCOB) crystals co-doped with 3 at% Er{sup 3+} and 20 at% Yb{sup 3+} were successfully grown by the Czochralski method. X-ray powder diffraction (XRPD) results show that the as-grown Er:Yb:YCOB crystal belongs to the monoclinic system with space group Cm. And the lattice parameters are a=8.076(8) Å, b=16.023(7) Å, c=3.528(4) Å and β=101.15(4)°. Crystal defects were revealed by chemical etching experiments. The density of etch pits, attributed to dislocations and observed on (010) planes, was found to be not uniform along the crystal diameter. The detailed polarized absorption spectra were measured. The polarized absorption cross sections at 977 nm are 1.01×10{sup −20}, 1.22×10{sup −20} and 1.05×10{sup −20} cm{sup 2} for E//X, E//Y and E//Z, respectively. And the polarized absorption cross sections at 1538 nm is about 1.86×10{sup −20} cm{sup 2} for both E//X and E//Z, but for E//Y the result is 1.03×10{sup −20} cm{sup 2}, which is much smaller. The relationship between the crystal structure and absorption spectra was discussed. - Graphical abstract: The as-grown bulk Er:Yb:YCOB crystal (the long axis is along the b-axis) and LeBail fit to the XRPD pattern of Er:Yb:YCOB (top) compared to the diffraction pattern of YCOB from the JCPDS data bank (bottom). Reflection markers indicate the calculated reflection positions. The middle trace gives the difference between observed and calculated intensity. Reflection indices corresponding to the strongest diffraction peaks are marked on the experimental pattern. - Highlights: • Er:Yb:YCOB crystal with a new composition was grown. • XRPD and FT-IR showed a certain degree of deformation in the crystal structure. • Detailed polarized absorption cross sections at 977 nm and 1538 nm were calculated. • Crystal defects were clearly revealed by chemical etching experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Tl{sub 10}Hg{sub 3}Cl{sub 16}: Single crystal growth, electronic structure and piezoelectric properties

Single crystal of the ternary halide Tl{sub 10}Hg{sub 3}Cl{sub 16} was grown using Bridgman-Stockbarger method. For the Tl{sub 10}Hg{sub 3}Cl{sub 16} crystal, we have measured X-ray photoelectron spectra for both pristine and Ar{sup +} ion-bombarded surfaces and additionally investigated photoinduced piezoelectricity. Our data indicate that the Tl{sub 10}Hg{sub 3}Cl{sub 16} single crystal surface is very sensitive with respect to Ar{sup +} ion-bombardment. In particular, Ar{sup +} ion-bombardment with energy of 3.0 keV over 5 min at an ion current density of 14 μA/cm{sup 2} causes significant changes of the elemental stoichiometry of the Tl{sub 10}Hg{sub 3}Cl{sub 16} surface resulting in an abrupt decrease of the mercury content in the top surface layers of the studied single crystal. As a result of the treatment, the mercury content becomes nil in the top surface layers. In addition, the present XPS measurements allow for concluding about very low hygroscopicity of the Tl{sub 10}Hg{sub 3}Cl{sub 16} single crystal surface. The property is extremely important for the crystal handling in optoelectronic or nano-electronic devices working at ambient conditions. The photoinduced piezoelectricity has been explored for Tl{sub 10}Hg{sub 3}Cl{sub 16} depending on nitrogen (λ=371 nm) laser power density and temperature. - Graphical abstract: As-grown single crystal boule of Tl{sub 10}Hg{sub 3}Cl{sub 16}; dependence of the effective piezoelecric coefficient d{sub 33} versus the photoinducing nitrogen laser power density, I, at different temperatures, T; and packing of the polyhedra of halide atoms around Hg atoms in the Tl{sub 10}Hg{sub 3}Cl{sub 16} structure. - Highlights: • High-quality Tl{sub 10}Hg{sub 3}Cl{sub 16} single crystal has been grown by Bridgman-Stockbarger method. • Electronic structure of Tl{sub 10}Hg{sub 3}Cl{sub 16} is studied by the XPS method. • Tl{sub 10}Hg{sub 3}Cl{sub 16} single crystal surface is sensitive with respect to Ar{sup +} ion-bombardment. • Very low hygroscopicity is characteristic of the Tl{sub 10}Hg{sub 3}Cl{sub 16} surface. • Photoinduced piezoelectricity is studied for the Tl{sub 10}Hg{sub 3}Cl{sub 16} compound.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Dual gauge field theory of quantum liquid crystals in two dimensions

We present a self-contained review of the theory of dislocation-mediated quantum melting at zero temperature in two spatial dimensions. The theory describes the liquid-crystalline phases with spatial symmetries in between a quantum crystalline solid and an isotropic superfluid: quantum nematics and smectics. It is based on an Abelian-Higgs-type duality mapping of phonons onto gauge bosons (“stress photons”), which encode for the capacity of the crystal to propagate stresses. Dislocations and disclinations, the topological defects of the crystal, are sources for the gauge fields and the melting of the crystal can be understood as the proliferation (condensation) of these defects, giving rise to the Anderson–Higgs mechanism on the dual side. For the liquid crystal phases, the shear sector of the gauge bosons becomes massive signaling that shear rigidity is lost. After providing the necessary background knowledge, including the order parameter theory of two-dimensional quantum liquid crystals and the dual theory of stress gauge bosons in bosonic crystals, the theory of melting is developed step-by-step via the disorder theory of dislocation-mediated melting. Resting on symmetry principles, we derive the phenomenological imaginary time actions of quantum nematics and smectics and analyze the full spectrum of collective modes. The quantum nematic is a superfluid having a true rotational Goldstone mode due to rotational symmetry breaking, and the origin of this ‘deconfined’ mode is traced back to the crystalline phase. The two-dimensional quantum smectic turns out to be a dizzyingly anisotropic phase with the collective modes interpolating between the solid and nematic in a non-trivial way. We also consider electrically charged bosonic crystals and liquid crystals, and carefully analyze the electromagnetic response of the quantum liquid crystal phases. In particular, the quantum nematic is a real superconductor and shows the Meissner effect. Furthermore, their special properties inherited from spatial symmetry breaking show up mostly at finite momentum, and should be accessible by momentum-sensitive spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Product-specific kinetics reveal effect of epoxy crystallization on thermoset thermal degradation

Crystallization is a common problem for epoxy resins, which are ubiquitous in industrial and commercial use. Integration of crystallized epoxy monomers into cured thermosets has been shown to alter the thermosets’ final mechanical properties. However, no studies have investigated the impact of these crystals on the thermal stability of the thermoset. Here we investigate the degradation kinetics of a bisphenol F–based epoxy thermoset with and without crystallized monomers using Product-Specific Kinetic (PSK) analysis coupled with Evolved Gas Analysis-Mass Spectrometry (EGA-MS). PSK analysis revealed significant differences in evolved product ion kinetics, suggesting changes in the degradation kinetics between thermoset configurations. Further, it was concluded that early stages of degradation are influenced most by crystal presence due to the high concentration of unreacted epoxy monomers and lower cross-linking density of the cured network. After post-cure annealing, significant changes are observed in the degradation kinetics of thermosets without crystal inclusions. Conversely, post-cure annealing procedures of crystal integrated thermosets showed little change in the thermoset degradation kinetics across all conversion extents. These findings suggest that post-cure annealing of thermosets with crystals present at the onset does not alter the cross-linking density of the polymer network enough to significantly change the degradation kinetics. We hypothesize this is because the excess monomers from the melted crystals are unable to find suitable reaction sites for complete binding into the polymer network, which has direct implications for the material properties and final thermal stability of the thermoset.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Light-Induced Macroscopic Peeling of Single Crystal Driven by Photoisomeric Nano-Optical Switching

Single-crystal optical actuators are emerging as a prospective material form for nano-optical mechanical switching, sensing, or transduction device applications in nano-technology and quantum technology. Crystal-lattice strain effects lie at the molecular origins of their macroscopic optical behavior, and linkage photoisomerization is an attractive source of optical actuation if only suitably functioning materials of this ilk could be found. In this work, we discover η 1 -SO 2 to η 1 -OSO single-crystal linkage photoisomerization in [Ru(NH 3 ) 4 (SO 2 )(3-phenylpyridine)]Cl 2 ·H 2 O, which behaves macroscopically as a single-crystal optical actuator, whereby the crystal peels in response to light-induction at 100 K. It thermally recovers, whereupon the crystal exhibits remarkable restorative properties. We apply photocrystallography alongside concerted optical microscopy and optical absorption spectroscopy to reveal how the molecular origins of photoisomerization induce crystal-lattice strain that engenders this macroscopic crystal peeling effect. Finally, linking structure and function across molecular and macroscopic length scales showcases a means by which single-crystal optically actuating materials could be systematically designed.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Diabatization with Electrostatic Embedding for Studying Photophysics in Organic Molecular Crystals

Highly emissive organic molecular crystals find applications in several areas, such as organic electronics, solar cells, and sensors. Understanding the excited-state mechanisms underlying these applications is essential for optimizing and controlling them effectively. Exciton models coupled with nonadiabatic dynamics, particularly quantum dynamics, provide crucial insights into photochemical and photophysical processes in molecular crystals. Nevertheless, there remains a lack of general tools and automated workflows to facilitate such simulations. In this paper, we present a computational strategy to investigate the photoactivated dynamics of organic molecular crystals, bridging methodologies traditionally used for molecular systems and materials science, with a particular focus on the interplay between local excitations and charge transfer (CT) processes. We have implemented an interface between the fromage and Overdia programs, enabling the construction of vibronic Hamiltonians for molecular crystals within an excited-state ONIOM(QM:QM′) framework, incorporating long-range electrostatics through a RESP-based Ewald summation. Fragment-based diabatization provides a route to quantum dynamics simulations in weak-to-intermediate coupling regimes. The method was applied to the photophysics of dibenzo[g,p]chrysene (DBC) crystals using time-dependent DFT. The fromage/ Overdia interface was employed to compute the couplings of local excitations and CT states for 18 unique DBC dimers in the crystal and to quantify the influence of electrostatic embedding, which was found to be modest (10−20%). Simulations on π-stacked dimers reproduced the small red shift observed experimentally from solution to crystal, attributed to electronic interactions among fixed monomers rather than crystal electrostatics. Quantum dynamics simulations revealed ultrafast population transfer from bright local excitations to CT states. This approach establishes a robust framework linking molecular and solid-state excited-state dynamics, with potential applications for studying excitations, defects, and impurities in molecular crystals.

Crystals↗
DOE OSTI2014

Melting processes of oligomeric α and β isotactic polypropylene crystals at ultrafast heating rates

The melting behaviors of α (stable) and β (metastable) isotactic polypropylene (iPP) crystals at ultrafast heating rates are simulated with atomistic molecular dynamics method. Quantitative information about the melting processes of α- and β-iPP crystals at atomistic level is achieved. The result shows that the melting process starts from the interfaces of lamellar crystal through random dislocation of iPP chains along the perpendicular direction of lamellar crystal structure. In the melting process, the lamellar crystal gradually expands but the corresponding thickness decreases. The analysis shows that the system expansion lags behind the crystallinity decreasing and the lagging extents for α- and β-iPP are significantly different. The apparent melting points of α- and β-iPP crystals rise with the increase of the heating rate and lamellar crystal thickness. The apparent melting point of α-iPP crystal is always higher than that of β-iPP at differently heating rates. Applying the Gibbs-Thomson rule and the scaling property of the melting kinetics, the equilibrium melting points of perfect α- and β-iPP crystals are finally predicted and it shows a good agreement with experimental result.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Glass transition and crystallization kinetics of a barium borosilicate glass by a non-isothermal method

The glass transition and crystallization kinetics of a glass with a molar composition 60BaO-30B{sub 2}O{sub 3}-10SiO{sub 2} were investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. DSC curves exhibited an endothermic peak associated with the glass transition and two partially overlapped exothermic peaks associated with the crystallization of the glass. The dependence of the glass transition temperature (T{sub g}) and of the maximum crystallization temperature (T{sub p}) on the heating rate was used to determine the activation energy associated with the glass transition (E{sub g}), the activation energy for crystallization (E{sub c}), and the Avrami exponent (n). X-ray diffraction (XRD) revealed that barium borate (β-BaB{sub 2}O{sub 4}) was the first crystalline phase to be formed followed by the formation of barium silicate (Ba{sub 5}Si{sub 8}O{sub 21}). The variations of activation energy for crystallization and of Avrami exponent with the fraction of crystallization (χ) were also examined. When the crystallization fraction (χ) increased from 0.1 to 0.9, the value of local activation energy (E{sub c}(χ)) decreased from 554 to 458 kJ/mol for the first exothermic peak and from 1104 to 831 kJ/mol for the second exothermic peak. The value determined for the Avrami exponent was near 2 indicating a similar one-dimensional crystallization mechanism for both crystalline phases. This was confirmed by the morphological studies performed by scanning electron microscopy (SEM) on glass samples heat-treated at the first and at the second crystallization temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Cationic coordination compound Cs{sub 2}Hg{sub 3}I{sub 8} for IR NLO material: Synthesis, crystal growth and characterizations

Single crystals Cs{sub 2}Hg{sub 3}I{sub 8} of dimensions 5 × 3 × 4 mm{sup 3} were grown by solution growth method at room temperature and structurally characterized by single crystal X – ray diffraction. Cs{sub 2}Hg{sub 3}I{sub 8} compound crystallizes in a noncentrosymmetric space group Cm with the crystal data of a = 7.4415 Å, b = 21.6629 Å, c = 7.6726 Å, α, β = 90°, γ = 108.05° and Z = 2. The grown crystals were characterized by powder X – ray diffraction analysis and the various diffraction planes are indexed. The presence of functional groups was identified qualitatively by Fourier transform infrared and FT – Raman spectral analyses. Ultraviolet – visible spectral analyses shows that the crystal has low UV cut off at 388 nm combined with very good transparency of 98 % in a wide range. The optical band gap was estimated to be 3 eV. Mechanical hardness of the grown crystal Cs{sub 2}Hg{sub 3}I{sub 8} was determined. The dielectric response of the crystal with varying frequencies was studied. Differential scanning calorimetry (DSC) analysis shows that the grown crystal has very good thermal stability up to 97.5°C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Translation effects on vertical Bridgman growth and optical, mechanical and surface analysis of 2-phenylphenol single crystal

2-phenylphenol optical crystals were grown in cone ampoules using vertical Bridgman technique. Single crystal of 2-phenylphenol with 150 mm length has been grown. The inclination on the conical part of the ampoule reduces the growth defects in the 2-phenylphenol single crystal. The lattice parameters and structure studied using single crystal X-ray diffraction method. 2-phenylphenol single crystal belongs to orthorhombic space group Fdd2. The micro translation rate affects crystal growth of 2-phenylphenol crystal was studied. The translation rate dependent defects present in the crystal were investigated by transmittance, indentation and etching characterizations. The dislocation induced indentation crack lengths variations were studied. Etch pits and striations observed for the selective etchants furnish significant information on growth aspects and degree of defect present in the crystal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Chiral Topological Surface States on a Finite Square Photonic Crystal Bounded by Air

Chiral, topologically protected, photonic surface states can be found at the boundary between gyrotropic photonic crystals where a changing magnetic field induces different topology across the interface. Typically, photonic crystals with either a suitable band structure on both sides of the interface to provide a band gap and evanescent decay of the surface states away from the interface, or an outer layer with engineered material properties is required. In this paper, we show the emergence of topological, unidirectional surface states at the termination of finite gyrotropic photonic crystals with a simple square lattice and C 4 rotational symmetry bounded by a vacuum, eliminating the need for an outside layer to enable chiral surface modes. Here, we start from an infinite, time-reversal-symmetry-breaking photonic crystal with a band gap associated with bands with nonzero Chern numbers, different from all-zero Chern numbers in air. We then modify the photonic crystal to move this band gap below the light line, while maintaining the Chern-number discontinuities. Band-structure calculations for a supercell approximating a photonic crystal finite in the direction normal to the surface demonstrate the existence, dispersion, and chirality of the surface mode. Extensive direct scattering calculations for a point source and spatial Fourier analysis further reveal a unidirectional free-space topological surface state, which propagates counterclockwise around the surface of a finite photonic crystal, providing a nearly foolproof way to cross-check the surface-mode band structure unaffected by backscattering from local defects. Additionally, scattering simulations allow an independent characterization of the state dispersion and unveil the robustness of the topological plasmonic mode propagation around the 90° bends of the structure, being due to only radiation leakage. In contrast to buried topological surface states, the observed surface modes at the photonic crystal–air interface have the advantage of being accessible to the outside world, allowing one to take advantage of the defect-tolerant backscattering-free surface modes to engineer emission from photonic crystal surfaces into arbitrary free-space beam shapes and directions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Small Bragg-plane slope errors revealed in synthetic diamond crystals

Wavefront-preserving X-ray diamond crystal optics are essential for numerous applications in X-ray science. Perfect crystals with flat Bragg planes are a prerequisite for wavefront preservation in Bragg diffraction. However, this condition is difficult to realize in practice because of inevitable crystal imperfections. Here, X-ray rocking curve imaging is used to study the smallest achievable Bragg-plane slope errors in the best presently available synthetic diamond crystals and how they compare with those of perfect silicon crystals. It is shown that the smallest specific slope errors in the best diamond crystals are about 0.08 (3) µrad mm -2 . These errors are only 50% larger than the 0.05 (2) µrad mm -2 specific slope errors measured in perfect silicon crystals. High-temperature annealing at 1450°C of almost flawless diamond crystals reduces the slope errors very close to those of silicon. Further investigations are in progress to establish the wavefront-preservation properties of these crystals.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

LCP crystallization and X-ray diffraction analysis of VcmN, a MATE transporter from Vibrio cholerae

A V. cholerae MATE transporter was crystallized using the lipidic cubic phase (LCP) method. X-ray diffraction data sets were collected from single crystals obtained in a sandwich plate and a sitting-drop plate to resolutions of 2.5 and 2.2 Å, respectively. Multidrug and toxic compound extrusion (MATE) transporters, one of the multidrug exporter families, efflux xenobiotics towards the extracellular side of the membrane. Since MATE transporters expressed in bacterial pathogens contribute to multidrug resistance, they are important therapeutic targets. Here, a MATE-transporter homologue from Vibrio cholerae, VcmN, was overexpressed in Escherichia coli, purified and crystallized in lipidic cubic phase (LCP). X-ray diffraction data were collected to 2.5 Å resolution from a single crystal obtained in a sandwich plate. The crystal belonged to space group P2{sub 1}2{sub 1}2{sub 1}, with unit-cell parameters a = 52.3, b = 93.7, c = 100.2 Å. As a result of further LCP crystallization trials, crystals of larger size were obtained using sitting-drop plates. X-ray diffraction data were collected to 2.2 Å resolution from a single crystal obtained in a sitting-drop plate. The crystal belonged to space group P2{sub 1}2{sub 1}2{sub 1}, with unit-cell parameters a = 61.9, b = 91.8, c = 100.9 Å. The present work provides valuable insights into the atomic resolution structure determination of membrane transporters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

The crystal acceleration effect for cold neutrons

A new mechanism of neutron acceleration is discussed and studied experimentally in detail for cold neutrons passing through the accelerated perfect crystal with the energies close to the Bragg one. The effect arises due to the following reason. The crystal refraction index (neutron-crystal interaction potential) for neutron in the vicinity of the Bragg resonance sharply depends on the parameter of deviation from the exact Bragg condition, i.e. on the crystal-neutron relative velocity. Therefore the neutrons enter into accelerated crystal with one neutron-crystal interaction potential and exit with the other. Neutron kinetic energy cannot vary inside the crystal due to its homogeneity. So after passage through such a crystal neutrons will be accelerated or decelerated because of the different energy change at the entrance and exit crystal boundaries.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

A review on the synthesis, crystal growth, structure and physical properties of rare earth based quaternary intermetallic compounds

This review highlights the synthesis and crystal growth of quaternary intermetallic compounds based on rare earth metals. In the first part of this review, we highlight briefly about intermetallics and their versatile properties in comparison to the constituent elements. In the next part, we have discussed about various synthesis techniques with more focus on the metal flux technique towards the well shaped crystal growth of novel compounds. In the subsequent parts, several disordered quaternary compounds have been reviewed and then outlined most known ordered quaternary compounds with their complex structure. A special attention has been given to the ordered compounds with structural description and relation to the parent binary and ternary compounds. The importance of electronic and structural feature is highlighted as the key roles in designing these materials for emerging applications. - Graphical abstract: Rare earth based quaternary intermetallic compounds crystallize in complex novel crystal structures. The diversity in the crystal structure may induce unique properties and can be considered them as future materials. - Highlights: • Crystal growth and crystal structure of quaternary rare earth based intermetallics. • Structural complexity of quaternary compounds in comparison to the parent compounds. • Novel quaternary compounds display unique crystal structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Organic Modulators Enable Morphological Diversity in Colloidal Crystals Engineered with DNA

Colloidal crystal engineering with DNA is a powerful way of generating a wide variety of crystals spanning over 90 different symmetries. However, in many cases, crystals with well-defined habits are difficult, if not impossible, to make, in part due to rapid crystal defect formation and propagation. This is especially true in the case of face-centered cubic (FCC) structures. Herein, we report a strategy that uses formamide as a chemical modulator to slow down colloidal crystal growth, which decreases defect formation and yields higher-quality crystals. Formamide forms hydrogen bonds with DNA bases and destabilizes the DNA duplex; in the context of colloidal crystallization, formamide leads to the disassembly of undercoordinated particles (defect architectures) and facilitates their reassembly into structures with the maximum number of nearest-neighbor contacts and DNA bonds. Here, when targeting an FCC lattice comprised of DNA-modified spherical 20 nm particles, formamide promotes the formation of its Wulff polyhedron (a truncated octahedron), never observed before in colloidal crystal engineering with DNA. Importantly, kinetic habits, including tetrahedra, octahedra, icosahedra, and decahedra, are also observed depending on formamide concentration.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Crystallization behavior in Se{sub 90}Te{sub 10} and Se{sub 80}Te{sub 20} thin films

Isothermal crystal growth kinetics in Se{sub 90}Te{sub 10} and Se{sub 80}Te{sub 20} thin films was studied by microscopy and in situ X-ray diffraction (XRD) measurements. The spherulite-like crystals grew linearly with time. In a narrow temperature range of between 65 and 85 °C, crystal growth rates exhibit simple exponential behavior with activation energies E{sub G} = 193 ± 4 kJ mol{sup −1} for Se{sub 90}Te{sub 10} and E{sub G} = 195 ± 4 kJ mol{sup −1} for Se{sub 80}Te{sub 20}. The crystal growth in both compositions is controlled by liquid-crystal interface kinetics and can be described by a screw dislocation growth model. From the XRD data, the crystallization fraction was estimated. The crystallization data were described by Johnson-Mehl-Avrami (JMA) model with Avrami exponents m = 1.4 ± 0.3 for Se{sub 90}Te{sub 10} and m = 1.6 ± 0.4 for Se{sub 80}Te{sub 20}. Activation energies were estimated from the temperature dependence of rate constant evaluated from the JMA model. The activation energies of nucleation-growth process were found to be E{sub c} = 184 ± 21 kJ mol{sup −1} for Se{sub 90}Te{sub 10} and E{sub c} = 179 ± 7 kJ mol{sup −1} for Se{sub 80}Te{sub 20}, and are comparable with activation energies of crystal growth.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗