Forsterite Carbonation in Zones with Transport Limited by Diffusion

Fractures in rocks could provide substantial surface area for reactions that lead to carbonate mineral precipitation in geologic carbon sequestration. Diffusion-limited transport of solutes in such zones affects the spatial and temporal distribution of mineral dissolution rates and carbonation products, thus influencing the overall carbon sequestration process. A tube with a packed bed of forsterite and exposed at one end to a solution in equilibrium with 100 bar of CO₂ at 100 °C was used to explore the timing and spatial localization of carbonate precipitation along a one-dimensional diffusion-limited zone. The identity and quantity of carbonate minerals as a function of depth were determined using Raman spectroscopy and total carbon analysis. Carbonate was observed within the packed bed as early as day 1. Hydromagnesite formed in the bed first and was replaced by magnesite within 5 days. Carbonate was spatially localized with the largest amount formed 0.5 cm into the packed bed. The overall carbonation rate in the bed did not decline until day 30

Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy

Vibrational sum frequency generation (VSFG) spectroscopy has been a powerful technique to probe molecular structures in non-centrosymmetric media. Recently developed heterodyne (HD) detection can further reveal spectral phase and molecular orientations. Adding imaging capability to an HD VSFG signal can bring spatial visualization capability into this nonlinear optical technique. However, it has been a challenge to build an HD VSFG microscope that is easy to align and has good spectral phase stability, two necessary criteria for the broad application of this technique to various areas of science. Here, we report a fully collinear HD VSFG microscope, which meets both phase stability and optical alignment requirements, that can spatially resolve images of molecular interfaces and domains, with chemical and structural sensitivities. The phase stability is more than 9 times better than a Michelson interferometric HD VSFG microscope. Using this HD VSFG microscope, we study the structures of molecular self-assembly films. Because of the superior phase sensitivity, we successfully identify two molecular domains with different molecular orientations, which we show is not possible to extract from an ensemble-averaged VSFG spectrum or homodyne-detected VSFG image

Probing Electronic Structures of Organic Semiconductors at Buried Interfaces by Electronic Sum Frequency Generation Spectroscopy

We use Electronic Sum Frequency Generation Spectroscopy (ESFG) to study the electronic structures at a buried solid/solid interface for the first time. The system is an organic thin film, poly­(3-hexylthiophene-2,5-diyl) (P3HT), supported on a silicon surface. The ESFG measurement is only in resonance with electronic (or vibronic) excitations, thus capable of yielding rich information on the band gap and electronic structures of the P3HT film at interfaces. We find the bandgap of P3HT in contact with silicon is 2.2 eV, with a narrowed bandwidth and Lorentzian line shape. This is significantly distinct from the UV–vis spectra of bulk P3HT, which contains multiple broad Gaussian peaks. Our measurement demonstrates at interfaces regioregular P3HT has a uniform electronic structure, which could improve the short circuit currents. The unique capability of ESFG to probe electronic structures at buried interface under atmosphere will be useful for investigating many buried interfaces

Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy

Vibrational sum frequency generation (VSFG) spectroscopy has been a powerful technique to probe molecular structures in non-centrosymmetric media. Recently developed heterodyne (HD) detection can further reveal spectral phase and molecular orientations. Adding imaging capability to an HD VSFG signal can bring spatial visualization capability into this nonlinear optical technique. However, it has been a challenge to build an HD VSFG microscope that is easy to align and has good spectral phase stability, two necessary criteria for the broad application of this technique to various areas of science. Here, we report a fully collinear HD VSFG microscope, which meets both phase stability and optical alignment requirements, that can spatially resolve images of molecular interfaces and domains, with chemical and structural sensitivities. The phase stability is more than 9 times better than a Michelson interferometric HD VSFG microscope. Using this HD VSFG microscope, we study the structures of molecular self-assembly films. Because of the superior phase sensitivity, we successfully identify two molecular domains with different molecular orientations, which we show is not possible to extract from an ensemble-averaged VSFG spectrum or homodyne-detected VSFG image

Comparison of path planning results by the conventional BAS algorithm on four different maps.

(a) Single regular obstacle. (b) Single irregular obstacle. (c) Multiple regular obstacles. (d) Multiple irregular obstacles.</p

Path planning performance of VBAS algorithm under different types of obstacles.

Path planning performance of VBAS algorithm under different types of obstacles.</p

Multiple irregular obstacles enlarged the view of the planned path part of the VBAS algorithm.

Multiple irregular obstacles enlarged the view of the planned path part of the VBAS algorithm.</p

Raw microsatellite genotype data

Raw genotyping data for both Ciona intestinalis spA and spB

Path planning results are synthesized by the VBAS algorithm to avoid a single regular obstacle.

(a) Motion results in a 2D plane. (b) Relationship between function and number of iterations.</p

Solving the “Magic Angle” Challenge in Determining Molecular Orientation Heterogeneity at Interfaces

It is critical to determine conformations of molecular monolayers in order to understand and control their functions and properties, such as efficiencies of self-assembly-based biosensors and turnover frequency of surface-bound electrocatalysts. However, surface molecules of the monolayers can adopt conformations with many different orientations. Thus, it is necessary to describe the orientations of surface molecular monolayers using both mean tilt angle and orientational distribution, which together we refer to as orientation heterogeneity. Orientation heterogeneity is difficult to measure. In most cases, in order to calculate the mean tilt angle, it is assumed that the orientational distribution is narrow. This assumption causes ambiguities in determining the mean tilt angle and loss of orientational distribution information, which is known as the “magic angle” challenge. Using heterodyne two-dimensional vibrational sum frequency generation (HD 2D VSFG) spectroscopy, we report a novel method to solve the “magic angle” challenge, by simultaneously measuring mean tilt angle and orientational distribution of molecular monolayers. We applied this new method to a CO₂ reduction catalyst/gold interface and found that the catalysts formed a monolayer with a mean tilt angle between its quasi-<i>C</i>₃ symmetric axis and the surface normal of 53°, with 5° orientational distribution. The narrow orientational distribution indicates that the surface molecules are rigid, which sample only limited configurations for facilitating a reaction, because of the short anchoring groups. Although applied to a specific system, this method is a general way to determine the orientation heterogeneity of an ensemble-averaged molecular interface