Diffraction Oscillations Research Articles

Dissolution and recrystallization behavior of microbially induced calcium carbonate: influencing factors, kinetics and cementation effect

Microbially induced calcium carbonate precipitation (MICP) is a nature-based biomineralization method with significant potential in geotechnical engineering. Despite the extensive previous studies on this technology, the stability of calcium carbonate crystals formed during the MICP process and its impact on cementation effectiveness remains unclear. This study investigates the effects of varying curing conditions and durations on the stability of microbially induced calcium carbonate crystals. Throughout the curing period, pH levels of the solutions and the mass of calcium carbonate samples were monitored. Crystal morphology, crystalline composition, and cementation properties were examined using scanning electron microscopy, X-ray diffraction, and ultrasonic oscillation tests. The findings reveal that vaterite remained stable in MICP or bacterial solution but quickly dissolved in deionized water. While most vaterite underwent dissolution and recrystallization within the first day of curing, the presence of organic matter in the crystals led to 10-20% of the vaterite remaining undissolved after 28 days. The dissolution of vaterite tended to promote the growth of pre-existing calcite polymorph rather than forming new ones. Extended curing periods in deionized water increased the proportion of dissolved vaterite, resulting in higher calcite content and enhanced cementation properties, which provides new insights for optimizing MICP applications in geotechnical engineering.

Atom interferometers in weakly curved spacetimes using Bragg diffraction and Bloch oscillations

Atom interferometers in weakly curved spacetimes using Bragg diffraction and Bloch oscillations

A single resonance Regge pole dominates the forward-angle scattering of the state-to-state F + H2 → FH + H reaction at Etrans = 62.09 meV.

The aim of the present paper is to bring clarity, through simplicity, to the important and long-standing problem: does a resonance contribute to the forward-angle scattering of the F + H2 reaction? We reduce the problem to its essentials and present a well-defined, yet rigorous and unambiguous, investigation of structure in the differential cross sections (DCSs) of the following three state-to-state reactions at a translational energy of 62.09 meV: F + H2(vi = 0, ji = 0, mi = 0) → FH(vf = 3, jf = 0, 1, 2, mf = 0) + H, where vi, ji, mi and vf, jf, mf are the initial and final vibrational, rotational and helicity quantum numbers respectively. Firstly, we carry out quantum-scattering calculations for the Fu-Xu-Zhang potential energy surface, obtaining accurate numerical scattering matrix elements for indistinguishable H2. The calculations use a time-independent method, with hyperspherical coordinates and an enhanced Numerov method. Secondly, the following theoretical techniques are employed to analyse structures in the DCSs: (a) full and Nearside-Farside (NF) partial wave series (PWS) and local angular momentum theory, including resummations of the full PWS up to second order. (b) The recently introduced "CoroGlo" test, which lets us distinguish between glory and corona scattering at forward angles for a Legendre PWS. (c) Six asymptotic (semiclassical) forward-angle glory theories and three asymptotic farside rainbow theories, valid for rainbows at sideward-scattering angles. (d) Complex angular momentum (CAM) theories of forward and backward scattering, with the Regge pole positions and residues computed by Thiele rational interpolation. Thirdly, our conclusions for the three PWS DCSs are: (a) the forward-angle peaks arise from glory scattering. (b) A broad (hidden) farside rainbow is present at sideward angles. (c) A single Regge pole contributes to the DCS across the whole angular range, being most prominent at forward angles. This proves that a resonance contributes to the DCSs for the three transitions. (d) The diffraction oscillations in the DCSs arise from NF interference, in particular, interference between the Regge pole and direct subamplitudes.

Bloch oscillations in anti-PT-symmetric electrical circuit resonators

Bloch oscillation is a phenomenon from solid state physics, describing a wave packet in periodic potential undergoing periodic oscillations in space, returning to the initial position after one oscillation cycle, under the action of a weak constant force. This wave phenomenon pertains to many physical systems including acoustic or optical resonators, and optical waveguides. Herein, we demonstrate discrete diffraction and Bloch oscillations, in a non-Hermitian electric circuit chain with anti-parity-time (APT) symmetry. The electric circuit chain consists of an LC circuit with operational amplifiers. We theoretically investigate the time-domain dynamics in different symmetry phases of the system. The time evolution of the envelope of voltage is in excellent agreement with coupled mode theory numerical calculations.

Complete numerical description of the laser-induced thermal profile in a liquid, to explain complex self-induced diffraction patterns

In the past, laser propagation in a fluid with heat transfer has been modeled using simplistic conduction and convection conditions yielding inaccurate predictions. Here we present a detailed numerical study describing the thermal profile of the fluid and its interaction with the laser. Furthermore, we evaluate the diffraction field in the far field produced by a pump beam impinging in the fluid and the interferometric pattern obtained normal to the propagation direction to test our model. Direct comparison between experimental results and numerical simulation allows for a complete understanding of the energy transfer from the laser to the liquid and the subsequent effect on the laser propagation. Spatial self-phase modulation and propagation control from small-phase diffraction to aberration-controlled diffraction and up to diffraction oscillation are observed and explained with our modeling.

Canonical approach to cation flux calibration in oxide molecular-beam epitaxy

Molecular-beam epitaxy (MBE) is the gold standard for the epitaxial growth of complex oxides with the best material properties as determined by respective figures of merit. Unfortunately, once more than one cation is involved in the material desired, MBE growth often becomes plagued by difficulties in stoichiometry control. Instead of relying on a quartz crystal microbalance to measure the fluxes of the individual molecular beams, which lacks accuracy, or reflection high-energy electron diffraction oscillations of the targeted multication oxide in layer-by-layer growth, which lacks general applicability, here, we describe a canonical approach based on the growth of films of the constituent binary oxides or metals individually for cation flux calibration. This method can calibrate the flux of each molecular beam with an absolute accuracy of \ifmmode\pm\else\textpm\fi{}1%. After describing the growth parameters of binary oxides or metals enabling the individual fluxes of 39 elements of the periodic table to be determined, we demonstrate the efficacy of this approach by applying it to the growth of the quaternary ferromagnetic metal ${\mathrm{La}}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ to achieve films with transport properties rivalling the best reported using thin-film growth techniques providing stoichiometric transfer.

The effect of trisodium phosphate crosslinking on the diffusion kinetics of caffeine from chitosan networks

This work examines the relationship between microstructural properties of hot-moulded chitosan networks, crosslinked with trisodium phosphate, and diffusive behaviour from these networks. Analysis through infrared spectroscopy (FTIR) confirmed successful crosslinking of the polymer chains and bioactive entrapment, while X-ray diffraction (WAXD) and dynamic oscillation in-shear elucidated the higher order structural properties of each matrix, as they transitioned from solutions to amorphous gels to semi-crystalline matrices. The picture of molecular motion observed in these systems and consequent application of the Flory-Rehner theory further indicated that different extents of chitosan crosslinking yielded a distinct water infusion functionality seen in the levels of swelling. Diffusion of caffeine from these delivery vehicles showed that network structural properties (governed by crosslinker concentration) had a significant effect on the release kinetics of the entrapped bioactive. The relationship between network mesh characteristics and diffusion properties were further confirmed by correlating caffeine release rates and molecular pore size.

High-Resolution Imaging of C + He Collisions using Zeeman Deceleration and Vacuum-Ultraviolet Detection.

High-resolution measurements of angular scattering distributions provide a sensitive test for theoretical descriptions of collision processes. Crossed beam experiments employing a decelerator and velocity map imaging have proven successful to probe collision cross sections with extraordinary resolution. However, a prerequisite to exploit these possibilities is the availability of a near-threshold state-selective ionization scheme to detect the collision products, which for many species is either absent or inefficient. We present the first implementation of recoil-free vacuum ultraviolet (VUV) based detection in scattering experiments involving a decelerator and velocity map imaging. This allowed for high-resolution measurements of state-resolved angular scattering distributions for inelastic collisions between Zeeman-decelerated carbon C(3P1) atoms and helium atoms. We fully resolved diffraction oscillations in the angular distributions, which showed excellent agreement with the distributions predicted by quantum scattering calculations. Our approach offers exciting prospects to investigate a large range of scattering processes with unprecedented precision.

Specific cation stoichiometry control of SrMnO3-δ thin films via RHEED oscillations

Cubic heteroepitaxial (001) SrMnO3-δ (SMO) films were grown on SrTiO3 substrates by atomic alternating layer molecular beam epitaxy. Precise control of cation stoichiometry was achieved by in situ reflection high-energy electron diffraction (RHEED) oscillation. During SMO film growth, a correlation between RHEED oscillation features and the cation stoichiometry/monolayer dose was established. In non-stoichiometric films, there were out-of-plane lattice expansions due to off-stoichiometry-dependent defects, including Ruddlesden–Popper SrO planar faults in Sr-rich films and Sr vacancy defect clusters in Mn-rich films.

Dielectric properties of sub 20 nm homoepitaxial SrTiO3 thin film grown by molecular beam epitaxy using oxygen plasma

Epitaxial SrTiO 3 thin films were grown by molecular beam epitaxy (MBE) using an oxygen plasma source. SrO and TiO2 layers were alternately deposited on 0.5 wt% (001) Nb doped SrTiO3 substrates whose surface were terminated with TiO2. A two-dimensional (2-D) layer-by-layer growth mode was confirmed by the reflection high energy electron diffraction (RHEED) oscillation during the growth and the well-terraced SrTiO3 surface was obtained after growth. X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) analysis showed that the obtained SrTiO3 thin films had epitaxially (001) oriented and stoichiometric crystal structures without any interfacial layer. With simple MIS (Metal-Insulator-Semiconductor) capacitors using Ir top electrodes, the dielectric constants of the SrTiO3 thin film with 10, 15, 20, 100 nm were measured at room temperature, 10 kHz and zero bias.

Movable holder for a quartz crystal microbalance for exact growth rates in pulsed laser deposition.

Controlling the amount of material deposited by pulsed laser deposition (PLD) down to fractions of one atomic layer is crucial for nanoscale technologies based on thin-film heterostructures. Albeit unsurpassed for measuring growth rates with high accuracy, the quartz crystal microbalance (QCM) suffers from some limitations when applied to PLD. The strong directionality of the PLD plasma plume and its pronounced dependence on deposition parameters (e.g., background pressure and fluence) require that the QCM is placed at the same position as the substrate during growth. However, QCM sensors are commonly fixed off to one side of the substrate. This also entails fast degradation of the crystal, as it is constantly exposed to the ablated material. The design for a movable QCM holder discussed in this work overcomes these issues. The holder is compatible with standard transfer arms, enabling easy insertion and transfer between a PLD chamber and other adjoining vacuum chambers. The QCM can be placed at the same position as the substrate during PLD growth. Its resonance frequency is measured in vacuum at any location where it can be in contact with an electrical feedthrough, before and after deposition. We tested the design for the deposition of hematite (Fe2O3), comparing the rates derived from the QCM and from reflection high-energy electron diffraction oscillations during homoepitaxial growth.

State-to-state scattering of highly vibrationally excited NO at broadly tunable energies.

Experimental developments continue to challenge the theoretical description of molecular interactions. One key arena in which these advances have taken place is in rotationally inelastic scattering. Electric fields have been used with great success to select the initial quantum state and slow molecules for scattering studies, revealing novel stereodynamics, diffraction oscillations and scattering resonances. These have enjoyed excellent agreement with quantum scattering calculations performed on state-of-the-art coupled-cluster potential energy surfaces. To date these studies have largely employed reactants in the ground vibrational state (v = 0) and the lowest low-field-seeking quantum state. Here we describe the use of stimulated emission pumping to prepare NO molecules in arbitrary single rotational and parity states of v = 10 for inelastic scattering studies. These are employed in a near-copropagating molecular beam geometry that permits the collision energy to be tuned from above room temperature to 1 K or below, with product differential cross-sections obtained by velocity map imaging. This extremely nonequilibrium condition, not found in nature, tests current theoretical methods in a new regime.

High-resolution imaging of molecular collisions using a Zeeman decelerator.

We present the first crossed beam scattering experiment using a Zeeman decelerated molecular beam. The narrow velocity spreads of Zeeman decelerated NO (X2Π3/2, j = 3/2) radicals result in high-resolution scattering images, thereby fully resolving quantum diffraction oscillations in the angular scattering distribution for inelastic NO-Ne collisions and product-pair correlations in the radial scattering distribution for inelastic NO-O2 collisions. These measurements demonstrate similar resolution and sensitivity as in experiments using Stark decelerators, opening up possibilities for controlled and low-energy scattering experiments using chemically relevant species such as H and O atoms, O2 molecules, or NH radicals.

Discrete diffraction and Bloch oscillations in non-Hermitian frequency lattices induced by complex photonic gauge fields

Non-Hermitian lattice systems with unconventional transport phenomena and topological effects have attracted intensive attention recently. Non-Hermiticity is generally introduced by engineering on-site gain/loss distribution or inducing asymmetric couplings by applying an imaginary gauge field. Here, we extend the concept of non-Hermitian lattices from spatial to frequency dimension and emulate various non-Hermitian transport phenomena arising from asymmetric coupling in synthetic dimension. The non-Hermitian frequency lattice is created by introducing complex gauge potentials through appropriate complex modulations in a slab waveguide. This complex gauge potential can induce asymmetric couplings among spectral modes and give rise to various non-Hermitian transport phenomena such as amplified and decayed frequency diffraction, refraction and non-Hermitian Bloch oscillations. The latter manifest themselves as both power oscillation and asymmetric oscillation patterns, and can be exploited to probe in the bulk the non-Hermitian skin effect. Frequency-domain Bloch oscillations with both exponentially growing oscillation amplitude and energy are also predicted. Our results pave the way towards emulating non-Hermitian transport phenomena and topological effects in synthetic dimension on a photonic platform, with potential applications to spectral manipulation of optical signals and energy harvesting.

Discrete propagation of trapped modes in acoustic waveguide arrays

Arrays of evanescently coupled waveguides in which wave behavior becomes discretized exhibit unique wave dynamics, and they offer the possibility to investigate analogous fundamental quantum phenomena at accessible time and length scales. In this Rapid Communication, we investigate the discretelike propagation of trapped modes in airborne acoustic waveguide arrays. Using numerical simulations and experiments, we analyze the emergence of acoustic discrete diffraction and spatial Bloch oscillations in the array. Furthermore, exploiting the Bloch oscillations phenomenon, we demonstrate the possibility to generate diffraction-free acoustic beams and to focus the acoustic energy within a single lattice site at distances orders of magnitude larger than the operating wavelength.

Atom‐Interferometry Measurement of the Fine Structure Constant

AbstractUsing an atom interferometer to measure the quotient of the reduced Planck's constant and the mass of a cesium‐133 atom , the most accurate measurement of the fine structure constant is recorded, at an accuracy of 0.20 parts per billion (ppb). Using multiphoton interactions (Bragg diffraction and Bloch oscillations), the largest phase (12 million radians) of any Ramsey–Bordé interferometer and controlled systematic effects at a level of 0.12 ppb are demonstrated. Comparing the Penning trap measurements with the Standard Model prediction of the electron gyromagnetic anomaly based on the α measurement, a 2.5 tension is observed, rejecting dark photons as the reason for the unexplained part of the muon's gyromagnetic moment discrepancy at a 99% confidence level according to frequentist statistics. Implications for dark‐sector candidates (e.g., scalar and pseudoscalar bosons, vector bosons, and axial‐vector bosons) may be a sign of physics beyond the Standard Model. A future upgrade of the cesium fountain atom interferometer is also proposed to increase the accuracy of by 1 to 2 orders of magnitude, which would help resolve the tension.

Overlapping growth windows to build complex oxide superlattices

Perovskite oxide superlattices are of particular interest due to novel phenomena emerging at interfaces which are beyond the bulk properties of the constituent layers. However, building perovskite superlattices comprised of stoichiometric layers with sharp interfaces has proven challenging. Here, the synthesis of a series of high quality (SrTiO3)n/(CaTiO3)n superlattice structures grown on LSAT substrates is demonstrated by employing hybrid molecular beam epitaxy, where Ti was supplied using metal-organic titanium tetraisopropoxide (TTIP), and Sr and Ca were supplied using conventional effusion cells. By careful adjustment of the cation fluxes of Sr and Ca with respect to the TTIP flux, the growth windows of SrTiO3 and CaTiO3 were overlapped, allowing us to grow the individual superlattice layers with self-regulated stoichiometry. Stable and repeatable reflection high-energy electron diffraction oscillations during the entire ∼2.5 h growth period indicated good source flux stability. The structural quality of the superlattice films were determined by scanning transmission electron microscopy and synchrotron-based X-ray diffraction, revealing periodic, phase pure, homogenous superlattice structures with abrupt interfaces. Utilization of perovskite stoichiometric growth windows offers great potential for accessing and realizing interface driven phenomena in versatile perovskite superlattice materials with chemistries beyond titanates.

Interference in electron–molecule elastic scattering

General formulas describing the multiple scattering of electron by polyatomic molecules have been derived within the framework of the model of non-overlapping atomic potentials. These formulas are applied to different carbon molecules, both for fixed-in-space and randomly oriented molecules. The molecular continuum wave function is represented as a plane wave plus a linear combination of the Green’s functions for free motion and the derivatives of these functions. Far from the target the electron spherical waves interfere as in the case of the Young’s double slits experiment. This interference manifests itself as diffraction oscillations in the differential and total cross sections for elastic electron scattering. The amplitude of electron scattering by a molecule is defined by the phase shifts for each of the atoms forming the target and its geometry. The numerical calculation of the scattering amplitude in closed form (rather than in the form of S-matrix expansion) is reduced to solving a system of algebraic equations. The number of atoms in a molecule and the atomic phase shifts for the orbital angular momenta included in the calculation define the number of equations.

Chemically specific termination control of oxide interfaces via layer-by-layer mean inner potential engineering

Creating oxide interfaces with precise chemical specificity at the atomic layer level is desired for the engineering of quantum phases and electronic applications, but highly challenging, owing partially to the lack of in situ tools to monitor the chemical composition and completeness of the surface layer during growth. Here we report the in situ observation of atomic layer-by-layer inner potential variations by analysing the Kikuchi lines during epitaxial growth of strontium titanate, providing a powerful real-time technique to monitor and control the chemical composition during growth. A model combining the effects of mean inner potential and step edge density (roughness) reveals the underlying mechanism of the complex and previously not well-understood reflection high-energy electron diffraction oscillations observed in the shuttered growth of oxide films. General rules are proposed to guide the synthesis of atomically and chemically sharp oxide interfaces, opening up vast opportunities for the exploration of intriguing quantum phenomena at oxide interfaces.

Exceptional points and photonic catastrophe.

Exceptional points (EPs) with a global collapse of pairs of eigenfunctions are shown to arise in two locally coupled and spatially extended optical structures with balanced gain and loss. The global collapse at the EP deeply changes light propagation, which becomes very sensitive to small changes of initial conditions or system parameters, similar to what happens in models of classical or quantum catastrophes. The implications of global collapse for light behavior are illustrated by considering discrete beam diffraction and Bloch oscillation catastrophe in coupled waveguide lattices.