Condensed Phase Materials Research Articles

Erratum to: Stress tensor and current correlators of interacting conformal field theories in 2+1 dimensions: fermionic Dirac matter coupled to U(1) gauge field

We compute the central charge C T and universal conductivity C J of N F fermions coupled to a U (1) gauge field up to next-to-leading order in the 1/N F expansion. We discuss implications of these precision computations as a diagnostic for response and entanglement properties of interacting conformal field theories for strongly correlated condensed matter phases and conformal quantum electrodynamics in 2 + 1 dimensions.

Nonequilibrium Reaction Kinetics in Molecular Solids

We explore the possibility of nonstatistical chemical reactions in condensed-phase energetic materials via reactive molecular dynamics (MD) simulations. We characterize the response of nitromethane [CH3NO2], HMX [cyclic (CH2-NNO2)4], and PETN [C-(CH2-ONO2)4] to different types of insults: electric fields of various frequencies and strengths and direct heating at various rates. We find that nonequilibrium states can be created for short time scales when energy input targets specific vibrations through the electric fields and that equilibration eventually occurs even while the insults remain present. Interestingly, for strong fields these relaxation time scales are comparable to those of the initial chemical decomposition of the molecules. NM decomposes predominantly via bimolecular reactions, and while insults targeting specific modes lead to strong nonequilibrium states, they do not affect the kinetics associated with decomposition. PETN decomposes via the unimolecular formation of NO2 and, quite interest...

Advances in nonlinear optical spectroscopies: a historical perspective of developments and applications presented at ECONOS

This article reviews the contributions to the special issues of the annual European Conference on Nonlinear Optical Spectroscopy (ECONOS) since its establishment in 2002. The review does not only highlight the developments of the scientific areas related to nonlinear optical spectroscopy in Europe but also shows how different sub‐fields evolved globally because ECONOS evolved as an international meeting attracting participants from all over the world. Four main topical categories are identified: (1) theoretical and instrumental developments, (2) applications to gas‐phase and combustion systems, (3) applications to condensed phase matter, and (4) development and applications of micro‐spectroscopy methods. Copyright © 2015 John Wiley & Sons, Ltd.

Diffusion flames in condensed-phase energetic materials: Application to Titanium–Boron combustion

The characteristics of a steady diffusion flame that arises at the interfaces of two condensed phase reactant streams that form an opposed counterflow are discussed. We assume that the flow is due to deformation from compaction or local heating and thermal expansion processes in the microscale environment of composite energetic materials. As a representative example of high temperature combustion of metal/intermetallic reactants, the overall reaction of titanium and boron to create titanium diboride products is considered under near isobaric conditions. The multi-component diffusion description uses a generalized Fick formulation with coefficients related to the binary diffusivities defined in the Maxwell–Stefan relations. A fairly simple depletion form with Arrhenius temperature dependent coefficients is used to describe the reaction rate. Several types of analyses are carried out at increasing levels of complexities: an asymptotic analysis valid in the limit of low strain rates (high residence time in the reaction zone), a constant mixture density assumption that simplifies the flow description, diffusion models with equal and unequal molecular weights for the various species, and a full numerical study for finite rate chemistry, composition-dependent density and strain rates extending from low to moderate values. All are found to agree remarkably well in describing the flame structure, the flame temperature and the degree of incomplete combustion. Of particular importance is the determination of a critical strain rate beyond which steady burning may no longer be observed. The analysis has a general character and can be applied to other condensed phase energetic material systems, where reaction and diffusion occur in the presence of flow and material deformation.

Double-Well Ultracold-Fermions Computational Microscopy: Wave-Function Anatomy of Attractive-Pairing and Wigner-Molecule Entanglement and Natural Orbitals.

"Bottom-up" approaches to the many-body physics of fermions have recently demonstrated precise number and site-resolved preparations with tunability of interparticle interactions in single-well, SW, and double-well, DW, nanoscale confinements created by manipulating ultracold fermionic atoms with optical tweezers. These experiments emulate an analogue-simulator mapping onto the requisite microscopic Hamiltonian, approaching realization of Feynmans' vision of quantum simulators that "will do exactly the same as nature". Here we report on exact benchmark configuration-interaction computational microscopy solutions of the Hamiltonian, uncovering the spectral evolution, wave function anatomy, and entanglement properties of the interacting fermions in the entire parameter range, including crossover from an SW to a DW confinement and a controllable energy imbalance between the wells. We demonstrate attractive pairing and formation of repulsive, highly correlated, ultracold Wigner molecules, well-described in the natural orbital representation. The agreement with the measurements affirms the henceforth gained deep insights into ultracold molecules and opens access to the size-dependent evolution of nanoclustered and condensed-matter phases and ultracold-atoms quantum information.

High-Harmonic Generation in Solids: Bridging the Gap Between Attosecond Science and Condensed Matter Physics

We review recent progress in understanding the dominant mechanism driving high-harmonic generation in solids. Three-dimensional two-band single active electron calculations predict that the major emission arises from the recombination of electron-hole pairs upon their creation and acceleration in the laser field, in analogy to atomic high-harmonic generation. The main goal of this study is to review a simple quasi-classical trajectory formalism and use it to better understand the fundamental properties of high-harmonic generation in solids and how they compare to high-harmonic generation in atomic and molecular gases. The simple formalism presents a valuable tool for extending attosecond science from the gas to the condensed matter phase. This is demonstrated by discussing the potential synthesis of attosecond pulses from solids.

Commentary on the heat transfer mechanisms controlling propagation in nanothermites

The combustion of nanothermites is a complex multiphase process that is still not well understood. One important aspect that is in need of further examination is the heat transfer mechanisms that drive combustion. Here we present some simple calculations to critically analyze the viability of conduction, convection, and radiation mechanisms of heat transfer as it relates to reaction propagation in nanothermites. While convection has generally been accepted as the critical mechanism for heat transfer, we show that the movement of hot gases cannot account for the required energy flow. Instead, it is illustrated that the movement of condensed phase material plays the critical role in heat transfer and should be accounted for in future models.

Semiclassical analysis of high harmonic generation in bulk crystals

High harmonic generation (HHG) in solids is investigated. We find that interband emission is dominant for the midinfrared laser driver frequencies, whereas intraband emission dominates the far-infrared range. Interband HHG is similar to atomic HHG and therewith opens the possibility to apply atomic attosecond technology to the condensed matter phase. Interband emission is investigated with a quasiclassical method, by which HHG can be modeled based on the classical trajectory analysis of electron-hole pairs. This analysis yields a simple approximate cutoff law for HHG in solids. Differences between HHG in atoms and solids are identified that are important for adapting atomic attosecond technology to make it applicable to condensed matter.

Self-assembly and electrostriction of arrays and chains of hopfion particles in chiral liquid crystals.

Some of the most exotic condensed matter phases, such as twist grain boundary and blue phases in liquid crystals and Abrikosov phases in superconductors, contain arrays of topological defects in their ground state. Comprised of a triangular lattice of double-twist tubes of magnetization, the so-called ‘A-phase’ in chiral magnets is an example of a thermodynamically stable phase with topologically nontrivial solitonic field configurations referred to as two-dimensional skyrmions, or baby-skyrmions. Here we report that three-dimensional skyrmions in the form of double-twist tori called ‘hopfions’, or ‘torons’ when accompanied by additional self-compensating defects, self-assemble into periodic arrays and linear chains that exhibit electrostriction. In confined chiral nematic liquid crystals, this self-assembly is similar to that of liquid crystal colloids and originates from long-range elastic interactions between particle-like skyrmionic torus knots of molecular alignment field, which can be tuned from isotropic repulsive to weakly or highly anisotropic attractive by low-voltage electric fields.

Stress tensor and current correlators of interacting conformal field theories in 2+1 dimensions: fermionic Dirac matter coupled to U(1) gauge field

We compute the central charge $C_T$ and universal conductivity $C_J$ of $N_F$ fermions coupled to a $U(1)$ gauge field up to next-to-leading order in the $1/N_F$ expansion. We discuss implications of these precision computations as a diagnostic for response and entanglement properties of interacting conformal field theories for strongly correlated condensed matter phases and conformal quantum electrodynamics in $2+1$ dimensions.

Dibromocarbene Functionalization of Boron Nitride Nanosheets: Toward Band Gap Manipulation and Nanocomposite Applications

We report the covalent functionalization of exfoliated boron nitride nanosheets (BNNSs) using dibromocarbene (DBC) species. The functionalization of BNNSs is enabled as the nanosheets are utilized as two-dimensional phase-transfer catalysts for the migration of carbenes across the organic–aqueous phase boundary. We postulate that BNNSs stabilize carbenes by forming B-CBr2 ylides and in turn act as the reaction substrate. DBC functionalization of BNNSs results in the formation of B–C and B–N bonds to the sp2-hybridized BNNS lattice via the formation of dibromo-bridged bicyclo BCN systems. The covalent functionalization was characterized using HR-TEM, AFM, EELS, XRD, EDX, ToF-SIMS, TGA, Raman, XPS, FTIR, and UV–vis techniques. Utilization of CBr2 groups as a means by which BNNSs may be integrated and interfaced with solvents, molecular species, and condensed-phase materials was demonstrated by grafting alkyl chains from the functional groups via alkyl/halogen exchange. Alkyl-functionalized BNNSs were integr...

Photoluminescence of excitons and defects in ZnSe-based longitudinal twinning nanowires

Photoluminescence spectrum is a powerful tool to investigate the excitonic and defect-related information in condensed phase materials. Through temperature-dependent photoluminescence spectra, heavy- and light-hole free excitons, and the exciton bound to a neutral donor and the accompanied LO-phonon replicas of the zinc blende ZnSe are observed and verified in ZnSe-based longitudinal twinning nanowires. In the deep-level emission region, two peaks at 1.979 and 2.315 eV are attributed to the donor–acceptor–pair recombination and the acceptor impurity of Au, respectively.

Hydrogen Atom Abstraction from CH4 by Nanosized Vanadium Oxide Cluster Cations

Reactions of vanadium oxide cluster cations with methane in a fast-flow reactor were investigated with a time-of-flight mass spectrometer. Hydrogen atom abstraction (HAA) reactions were identified over stoichiometric cluster cations (V2O5)N+ for N as large as 11, and the relative reactivity decreases as the cluster size increases. Density functional calculations were performed to study the structural, bonding, and electronic properties of the stoichiometric oxide clusters with the size N = 2–6. The geometric structures were obtained by means of topological and structural unit analyses together with global optimizations. Two types of oxygen-centered radicals were found in these clusters, which are active sites of the clusters in reactions with CH4. The size-dependent reactivity is rationalized by the charge, spin, and structural effects. This work is among the first reports that HAA from CH4 can take place on nanosized oxide clusters, which makes a bridge between the small reactive species and inert condensed phase materials for CH4 activation under low temperature.

Structural dynamics of ionic materials mapped by femtosecond x-ray diffraction

Relocation of electronic charge plays a key role for functional processes in condensed-phase molecular materials. X-ray diffraction with a femtosecond time resolution allows for spatially resolving transient atomic arrangements and charge distributions [1]. In particular, time-dependent spatial maps of electron density have been derived from x-ray powder diffraction patterns measured with a 100 fs time resolution. In this talk, new results on electron dynamics in transition metal complexes and on field-driven charge relocations in elementary ionic materials will be presented. Crystals containing a dense array of Fe(II)-tris(bipyridine) complexes and their PF6 counterions display pronounced changes of electron density that occur within the first 100 fs after two photon excitation of a small fraction of the complexes [2]. Electron density maps reveal a transfer of electronic charge from the Fe atoms and - so far unknown - from the PF6 counterions to the bipyridine units. The charge transfer displays pronounced Coulomb-mediated many-body features, affecting approximately 30 complexes around the directly excited one. As a second topic, electron relocations induced by strong external optical fields will be discussed [1,3]. This interaction mechanism allows for generating coherent superpositions of valence and conduction band quantum states and inducing fully reversible charge dynamics. While the materials LiBH4 and NaBH4 display electron relocations from the (BH4)- ions to the neighboring Li+ and Na+ ions, LiH exhibits an electron transfer from Li to H. The latter is a manifestation of electron correlations and in agreement with theoretical calculations.

Dual echelon femtosecond single-shot spectroscopy.

We have developed a femtosecond single-shot spectroscopic technique to measure irreversible changes in condensed phase materials in real time. Crossed echelons generate a two-dimensional array of time-delayed pulses with one femtosecond probe pulse. This yields 9 ps of time-resolved data from a single laser shot, filling a gap in currently employed measurement methods. We can now monitor ultrafast irreversible dynamics in solid-state materials or other samples that cannot be flowed or replenished between laser shots, circumventing limitations of conventional pump-probe methods due to sample damage or product buildup. Despite the absence of signal-averaging in the single-shot measurement, an acceptable signal-to-noise level has been achieved via background and reference calibration procedures. Pump-induced changes in relative reflectivity as small as 0.2%-0.5% are demonstrated in semimetals, with both electronic and coherent phonon dynamics revealed by the data. The optical arrangement and the space-to-time conversion and calibration procedures necessary to achieve this level of operation are described. Sources of noise and approaches for dealing with them are discussed.

Transport in aluminized RDX under shock compression explored using molecular dynamics simulations

Shock response of energetic materials is controlled by a combination of mechanical response, thermal, transport, and chemical properties. How these properties interplay in condensed-phase energetic materials is of fundamental interest for improving predictive capabilities. Due to unknown nature of chemistry during the evolution and growth of high-temperature regions within the energetic material (so called hot spots), the connection between reactive and unreactive equations of state contain a high degree of empiricism. In particular, chemistry in materials with high degree of heterogeneity such as aluminized HE is of interest. In order to identify shock compression states and transport properties in high-pressure/temperature (HP-HT) conditions, we use molecular dynamics (MD) simulations in conjunction with the multi-scale shock technique (MSST). Mean square displacement calculations enabled us to track the diffusivity of stable gas products. Among decomposition products, H2O and CO2 are found to be the dominant diffusing species under compression conditions. Heat transport and diffusion rates in decomposed RDX are compared and the comparison shows that around 2000 K, transport can be a major contribution during propagation of the reaction front.

The limits of strength in materials in the condensed phase

There is a range of thresholds in loading for the response of condensed phase matter, starting with inelastic deformation at the yield stress. Beyond this point compression continues until the material bond strength is overcome and becomes so-called warm dense matter. In this regime formulations of solid mechanics derived in the ambient state no longer apply. Between these two limits lies a boundary that differentiates weak- from strong-shock dynamic loading. This work examines these thresholds and shows a correlation between the theoretical strength of the material and this weak shock limit for a range of metals.

Quantum Cascade Laser Based Photoacoustic Spectroscopy for Depth Profiling Investigations of Condensed-Phase Materials

We report on the development of a photoacoustic device for the detection of condensed-phase materials. A mid-infrared quantum cascade laser (QCL) was used for depth-profiling studies to distinguish among glycerol films and tetraethoxysilane (TEOS) films deposited on photoresist-coated silicon wafers. The QCL was continuously tunable from 1015 cm−1 to 1240 cm−1, allowing for collection of photoacoustic vibrational spectra for these materials. Variation of the laser pulse repetition rate allowed for identification and molecular discrimination of glycerol, TEOS, and photoresist based solely on photoacoustic spectra collected at different film depths.

ChemInform Abstract: Crystalline Molecular Machines: Function, Phase Order, Dimensionality, and Composition

AbstractReview: about 100 refs.

Far-Ultraviolet Spectroscopy in the Solid and Liquid States: A Review

Ultraviolet (UV) spectroscopy has long been used together with visible (Vis) spectroscopy to investigate electronic transitions of a molecule. Most studies of the electronic structure of molecules using UV spectroscopy have been carried out in the 190–380 nm region because commercial UV-Vis spectrometers are available only for that region. The wavelength region shorter than 190 nm is also very rich in information about the electronic states and structure of a molecule, but the absorptivity is very high in this region, and thus, this region has been employed to investigate mainly the electronic states and structure of gas molecules. Because condensed-phase materials with high molecular density do not transmit much light in the shorter wavelength region of the UV, reflection spectroscopy has been used to observe spectra of solid samples in the wavelength region shorter than 190 nm. However, for liquid samples one cannot generally use either absorption spectroscopy or specular reflection spectroscopy. Accordingly, UV spectroscopy in this region for liquid samples has been a relatively undeveloped research area. To solve the above difficulties of UV spectroscopy in the wavelength region shorter than 190 nm we have recently developed a totally new UV spectrometer based on attenuated total reflection (ATR) that enables us to measure spectra of liquid and solid samples in the 140–280 nm region. We will show that spectroscopy in the wavelength region shorter than 190 nm holds considerable promise not only in basic science but also in applications such as qualitative and quantitative analysis, on-line monitoring, environmental geochemical analysis, and surface analysis. The purpose of the present review paper is to report recent progress in UV spectroscopy of solid and liquid phases in the 140–280 nm region. In this review, we refer to the 120–200 nm region to as the far-UV (FUV) region. The term “vacuum UV region” is no longer appropriate for the 120–200 nm region because most recent spectrometers used in this region are not evacuated but instead incorporate a nitrogen purge. This review consists of eight parts: (1) introduction to FUV spectroscopy, (2) brief history of FUV spectroscopy, (3) development of new FUV spectrometers, (4) FUV studies of liquid water and aqueous solutions, (5) FUV spectra of organic molecules in the liquid states, (6) band assignments by quantum chemical calculations, (7) potential applications of FUV spectroscopy in liquid and solid states; and (8) future prospects of FUV spectroscopy.