Alejandro Cruz

Heterointerface engineered electronic and magnetic phases of NdNiO 3 thin films

Mott physics is characterized by an interaction-driven metal-to-insulator transition in a partially filled band. In the resulting insulating state, antiferromagnetic orders of the local moments typically develop, but in rare situations no long-range magnetic order appears, even at zero temperature, rendering the system a quantum spin liquid. A fundamental and technologically critical question is whether one can tune the underlying energetic landscape to control both metal-to-insulator and Néel transitions, and even stabilize latent metastable phases, ideally on a platform suitable for applications. Here we demonstrate how to achieve this in ultrathin films of NdNiO3 with various degrees of lattice mismatch, and report on the quantum critical behaviours not reported in the bulk by transport measurements and resonant X-ray spectroscopy/scattering. In particular, on the decay of the antiferromagnetic Mott insulating state into a non-Fermi liquid, we find evidence of a quantum metal-to-insulator transition that spans a non-magnetic insulating phase.

Impact of high biomass loading on ionic liquid pretreatment

BackgroundIonic liquid (IL) pretreatment has shown great potential as a novel pretreatment technology with high sugar yields. To improve process economics of pretreatment, higher biomass loading is desirable. The goal of this work is to establish, the impact of high biomass loading of switchgrass on IL pretreatment in terms of viscosity, cellulose crystallinity, chemical composition, saccharification kinetics, and sugar yield.ResultsThe pretreated switchgrass/IL slurries show frequency dependent shear thinning behavior. The switchgrass/IL slurries show a crossover from viscous behavior at 3 wt% to elastic behavior at 10 wt%. The relative glucan content of the recovered solid samples is observed to decrease with increasing levels of lignin and hemicelluloses with increased biomass loading. The IL pretreatment led to a transformation of cellulose crystalline structure from I to II for 3, 10, 20 and 30 wt% samples, while a mostly amorphous structure was found for 40 and 50 wt% samples.ConclusionsIL pretreatment effectively reduced the biomass recalcitrance at loadings as high as 50 wt%. Increased shear viscosity and a transition from ‘fluid’ like to ‘solid’ like behavior was observed with increased biomass loading. At high biomass loadings shear stress produced shear thinning behavior and a reduction in viscosity by two orders of magnitude, thereby reducing the complex viscosity to values similar to lower loadings. The rheological properties and sugar yields indicate that 10 to 50 wt% may be a reasonable and desirable target for IL pretreatment under certain operating conditions.

Modular soft x-ray spectrometer for applications in energy sciences and quantum materials

Over the past decade, the advances in grating-based soft X-ray spectrometers have revolutionized the soft X-ray spectroscopies in materials research. However, these novel spectrometers are mostly dedicated designs, which cannot be easily adopted for applications with diverging demands. Here we present a versatile spectrometer design concept based on the Hettrick-Underwood optical scheme that uses modular mechanical components. The spectrometers optics chamber can be used with gratings operated in either inside or outside orders, and the detector assembly can be reconfigured accordingly. The spectrometer can be designed to have high spectral resolution, exceeding 10 000 resolving power when using small source (∼1μm) and detector pixels (∼5μm) with high line density gratings (∼3000 lines/mm), or high throughput at moderate resolution. We report two such spectrometers with slightly different design goals and optical parameters in this paper. We show that the spectrometer with high throughput and large energy window is particularly useful for studying the sustainable energy materials. We demonstrate that the extensive resonant inelastic X-ray scattering (RIXS) map of battery cathode material LiNi1/3Co1/3Mn1/3O2 can be produced in few hours using such a spectrometer. Unlike analyzing only a handful of RIXS spectra taken at selected excitation photon energies across the elemental absorption edges to determine various spectral features like the localized dd excitations and non-resonant fluorescence emissions, these features can be easily identified in the RIXS maps. Studying such RIXS maps could reveal novel transition metal redox in battery compounds that are sometimes hard to be unambiguously identified in X-ray absorption and emission spectra. We propose that this modular spectrometer design can serve as the platform for further customization to meet specific scientific demands.

Restricting lignin and enhancing sugar deposition in secondary cell walls enhances monomeric sugar release after low temperature ionic liquid pretreatment

BackgroundLignocellulosic biomass has the potential to be a major source of renewable sugar for biofuel production. Before enzymatic hydrolysis, biomass must first undergo a pretreatment step in order to be more susceptible to saccharification and generate high yields of fermentable sugars. Lignin, a complex, interlinked, phenolic polymer, associates with secondary cell wall polysaccharides, rendering them less accessible to enzymatic hydrolysis. Herein, we describe the analysis of engineered Arabidopsis lines where lignin biosynthesis was repressed in fiber tissues but retained in the vessels, and polysaccharide deposition was enhanced in fiber cells with little to no apparent negative impact on growth phenotype.ResultsEngineered Arabidopsis plants were treated with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate 1-ethyl-3-methylimidazolium acetate ([C2C1im][OAc]) at 10 % wt biomass loading at either 70 °C for 5 h or 140 °C for 3 h. After pretreatment at 140 °C and subsequent saccharification, the relative peak sugar recovery of ~26.7 g sugar per 100 g biomass was not statistically different for the wild type than the peak recovery of ~25.8 g sugar per 100 g biomass for the engineered plants (84 versus 86 % glucose from the starting biomass). Reducing the pretreatment temperature to 70 °C for 5 h resulted in a significant reduction in the peak sugar recovery obtained from the wild type to 16.2 g sugar per 100 g biomass, whereas the engineered lines with reduced lignin content exhibit a higher peak sugar recovery of 27.3 g sugar per 100 g biomass and 79 % glucose recoveries.ConclusionsThe engineered Arabidopsis lines generate high sugar yields after pretreatment at 70 °C for 5 h and subsequent saccharification, while the wild type exhibits a reduced sugar yield relative to those obtained after pretreatment at 140 °C. Our results demonstrate that employing cell wall engineering efforts to decrease the recalcitrance of lignocellulosic biomass has the potential to drastically reduce the energy required for effective pretreatment.

Solubilization and Upgrading of High Polyethylene Terephthalate Loadings in a Low-Costing Bifunctional Ionic Liquid

The solubilization and efficient upgrading of high loadings of polyethylene terephthalate (PET) are important challenges, and most solvents for PET are highly toxic. Herein, a low-cost (ca.

Identification of the operational frequencies of 300+ bridges using smartphones

1.2 kg-1 ) and biocompatible ionic liquid (IL), cholinium phosphate ([Ch]3 [PO4 ]), is demonstrated for the first time to play bifunctional roles in the solubilization and glycolytic degradation of PET. A high loading of PET (10 wt %) was readily dissolved in [Ch]3 [PO4 ] at relatively low temperatures (120 °C, 3 h) and under water-rich conditions. In-depth analysis of the solution revealed that high PET solubilization in [Ch]3 [PO4 ] could be ascribed to significant PET depolymerization. Acid precipitation yielded terephthalic acid as the dominant depolymerized monomer with a theoretical yield of approximately 95 %. Further exploration showed that in the presence of ethylene glycol (EG), the [Ch]3 [PO4 ]-catalyzed glycolysis of PET could efficiently occur with approximately 100 % conversion of PET and approximately 60.6 % yield of bis(2-hydroxyethyl)terephthalate under metal-free conditions. The IL could be reused at least three times without an apparent decrease in activity. NMR spectroscopy analysis revealed that strong hydrogen-bonding interactions between EG and the IL played an important role in the activation of EG and promotion of the glycolysis reaction. This study opens up avenues for exploring environmentally benign and efficient IL technology for solubilizing and recycling postconsumer polyester plastics.

Resonant soft x-ray scattering endstation for time-resolved pump-probe measurements at LCLS

A country’s economic development depends heavily on transportation networks and hence, as a vital aspect, bridge structures must function safely at all times. Structural Health Monitoring (SHM) and Damage Prognosis (DP) of bridges should be a priority in order to prevent deterioration, avoid collapse and ensure user’s safety. One objective of SHM for civil structures is the behavior assessment due to ambient, operational and seismic excitations, for which acceptable ranges are established for the variation of dynamic properties. Through Operational Modal Analysis (OMA) it is possible to estimate operational frequencies of a bridge and provide a measure of its current dynamic behavior. These frequencies can then be used for future comparisons to revise if the structure has been damaged or has experienced changes due to environmental conditions. In this paper, vertical and horizontal operational frequencies of more than 300 vehicular and pedestrian bridges of the transportation network of Santiago de Cali, Colombia, were estimated using ambient vibration tests. Data were obtained using smartphones and processed using frequency domain analyses. Correlations of these frequencies with the structural characteristics of the bridges are presented. The results of this study represent the current state of each bridge and provide a baseline for future evaluations of changes due to environmental conditions or damage.

Identification of Prestress Forces using Genetic Algorithms and Generic Element Matrices

Localized charge, spin and orbital degrees of freedom can compete with electronic itinerancy and such competition lies at the heart of emergent material properties. To study these electronic orderings, resonant soft X-ray scattering (RSXS) spectroscopy has been demonstrated as one of the most powerful direct probes, and its time-resolved capability can be implemented through pump-probe technique. The ultrafast/ultra-intense X-ray pulses from LCLS can be used as the probe in the time-resolved RSXS experiments, but the inherent fluctuations in intensity and timing between pulses can degrade the superior temporal resolution. To overcome such fluctuations, a compact fast CCD (cFCCD) was developed to enable shot-by-shot data acquisitions and a dedicated RSXS endstation, constructed to house this cFCCD and other single-channel photon detectors, has been extensively used at both ALS and LCLS. Time-resolved RSXS experiments on La1.75Sr0.25 NiO4 nickelate have revealed an unexpected transient behavior of charge and spin ordering (CO/SO) states. After 800nm laser excitation, the CO can be fully suppressed at higher pump fluence while SO remains detectable, creating a transient state that is not accessible by tuning thermodynamic variables. Furthermore, two distinct time scales are identified in the recovery of CO and can be attributed to the amplitude (fast) and phase (slow) dynamics of order parameter. A new version of cFCCD, with eight times the detection area and the readout electronics moved into vacuum side to minimize the pickup noise, has been developed and will be incorporated into the RSXS endstation.

Surface Defects: Possible Source of Room Temperature Ferromagnetism in Co-Doped ZnO Nanorods

Prestressing is a technology that enhances the capabilities of concrete through application of counteracting forces. The strength of prestressed beams depends on the tension of the steel tendons, which experiences short‐term and long‐term losses due to elastic deformations, anchorage friction, creep of concrete and tendon relaxation. This paper presents a method for the identification of axial prestress forces in simply supported beams. Numerical results are presented which show the effectiveness of the proposed method. The strategy uses a genetic algorithm to minimize the difference between the measured and the predicted dynamic response at a single point; the former is obtained from an accelerometer that records the acceleration induced by an external dynamic force, and the latter is calculated from a finite element model of the beam. The uncertainty of model parameters is handled through the inclusion of generic element matrices in the model so that the axial prestress force and the generic parameters ...