Search

Nonlinear, four-wave mixing vibrational spectroscopies are commonly used to probe electron-vibration coupling in isotropic media. Most of these methods rely on infrared and/or Raman transitions, but methods involving hyper-Raman transitions are also possible. Hyper difference frequency generation (HDFG) spectroscopy is an underdeveloped four-wave mixing vibrational spectroscopy based upon both infrared absorption and hyper-Raman scattering transitions. Despite several experimental reports on HDFG, its spectroscopic properties have not been fully explored. To this end, we investigate the selection rules and behavior of HDFG spectroscopy as an upconverted infrared spectroscopy and as a probe of vibronic coupling in molecular systems. We discuss the similarities between HDFG, a four-wave mixing technique, and vibrational sum frequency generation (vSFG) spectroscopy, a three-wave mixing technique. vSFG and HDFG appear to provide similar output intensities, making HDFG feasible for vSFG practitioners. HDFG is shown to be a sensitive probe of vibronic coupling in bulk systems and provides an alternative method to investigate electronic-nuclear coordinate correlations., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

Vibrational fingerprints and combination bands are a direct measure of couplings that control molecular properties. However, most combination bands possess small transition dipoles. Here we use multiple, ultrafast coherent infrared pulses to resolve vibrational coupling between CH 3 CN fingerprint modes at 918 and 1039 cm -1 and combination bands in the 2750-6100 cm -1 region via doubly vibrationally enhanced (DOVE) coherent multidimensional spectroscopy (CMDS). This approach provides a direct probe of vibrational coupling between fingerprint modes and near-infrared combination bands of large and small transition dipoles in a molecular system over a large frequency range.

Floquet state spectroscopy is an optical analogue of multiple quantum coherence nuclear magnetic resonance (MQC-NMR). Tunable ultrafast excitation pulses resonantly excite multiple states in a sample to form the Floquet state. The Floquet state emits multiple coherent beams at frequencies and in directions that conserve energy and momenta. The different output beams differ in the time ordering and coherences created by the excitation beams. They correspond to the different methodologies in the NMR family. Isolating a specific beam and monitoring the output intensity as a function of excitation frequencies creates multidimensional spectra containing cross-peaks between coupled states. The frequency range of the multidimensional spectra is limited by phase matching constraints. This paper presents a new, to the best of our knowledge, active phase matching strategy that increases the versatility of multidimensional Floquet state spectroscopy through both longer sample path lengths and larger spectral ranges.

Lateral heterostructures of two-dimensional (2D) transition metal dichalcogenides offer promise as platforms for a wide variety of applications from exotic physics to environmental control. Further development and study of these heterostructures require characterization methods that assess the quality of the heterostructures. Here, we extend current characterization strategies to create photoluminescence (PL), Raman, reflection contrast, and second harmonic generation (SHG) maps of individual monolayer core-shell WS 2 -MoS 2 lateral heterostructures that were synthesized via water vapor assisted chemical vapor transport. Together, these methods provide the correlations required to resolve the effects of excitons, trions, lattice defects, strain, and alloying. The comparisons show substantial differences, especially in the regions near and at the narrow heterointerface. Comparisons between the different spectral maps show the importance of metal alloying for understanding the electronic and spatial structures of heterostructures. The results are compared to previous work on similar lateral heterostructures created by different methods.

There is great interest in developing fully coherent multidimensional X-ray/extreme ultraviolet (XUV) spectroscopic techniques because of their capability for achieving atomic spectral selectivity. Current proposals rest on using sequentially and coherently driven core excitations with multiple X-ray/XUV excitation pulses and measuring the output using time domain Fourier transform methods. In this paper, we propose an alternative method that creates an entanglement of core and optical transitions to form a Floquet state that creates directional and coherent output beams. Multidimensional spectra are obtained by measuring the intensity of output beams while tuning the optical frequencies across resonances. This approach expands on previous optical pump-XUV probe spectroscopy of MoTe 2 by theoretically demonstrating its multidimensional capabilities. Both parametric and non-parametric pathways are proposed to optimize the resolution of inhomogeneous broadening and k -selective features.

Modern instrumentation development often involves the incorporation of many dissimilar hardware peripherals into a single unified instrument. The increasing availability of modular hardware has brought greater instrument complexity to small research groups. This complexity stretches the capability of traditional, monolithic orchestration software. In many cases, a lack of software flexibility leads creative researchers to feel frustrated, unable to perform experiments they envision. Herein, we describe Yet Another acQuisition (yaq), a software project defining a new standardized way of communicating with diverse hardware peripherals. yaq encourages a highly modular approach to experimental software development that is well suited to address the experimental flexibility needs of complex instruments. yaq is designed to overcome hardware communication barriers that challenge typical experimental software. A large number of hardware peripherals are already supported, with tooling available to expand support. The yaq standard enables collaboration among multiple research groups, increasing code quality while lowering development effort., (© 2023 Author(s). Published under an exclusive license by AIP Publishing.)

Silicon-vacancy (SiV) centers in diamond have attracted attention as highly stable fluorophores for sensing and as possible candidates for quantum information science. While prior studies have shown that the formation of hybrid diamond-metal structures can increase the rates of optical absorption and emission, many practical applications require diamond plasmonic structures that are stable in harsh chemical and thermal environments. Here, we demonstrate that Ag nanospheres, produced both in quasi-random arrays by thermal dewetting and in ordered arrays using electron-beam lithography, can be completely encapsulated with a thin diamond coating containing SiV centers, leading to hybrid core-shell nanostructures exhibiting extraordinary chemical and thermal stability as well as enhanced optical properties. Diamond shells with a thickness on the order of 20-100 nm are sufficient to encapsulate and protect the Ag nanostructures with different sizes ranging from 20 nm to hundreds of nanometers, allowing them to withstand heating to temperatures of 1000 °C and immersion in harsh boiling acid for 24 h. Ultrafast photoluminescence lifetime and super-resolution optical imaging experiments were used to study the SiV properties on and off the core-shell structures, which show that the SiV on core-shell structures have higher brightness and faster decay rate. The stability and optical properties of the hybrid Ag-diamond core-shell structures make them attractive candidates for high-efficiency imaging and quantum-based sensing applications., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Ruddlesden-Popper lead halide perovskites have emerged as a new class of two-dimensional semiconductors with tunable optoelectronic properties, potentially offering unlimited heterostructure configurations for exploration. However, the practical realization of such heterostructures is challenging because of the difficulty in achieving controllable direct synthesis or van der Waals integration of halide perovskites due to their mobile and fragile crystal lattices. Here we report direct growth of large-area nanosheets of diverse phase-pure Ruddlesden-Popper perovskites with thicknesses down to one monolayer at the solution-air interface and a reliable approach for gently transferring and stacking these nanosheets. These advances enable the deterministic fabrication of arbitrary vertical heterostructures and multi-heterostructures of Ruddlesden-Popper perovskites with greater structural degrees of freedom that define the electronic structures of the heterojunctions. Such rationally designed heterostructures exhibit interesting interlayer properties, such as interlayer carrier transfer and reduction of the photoluminescence linewidth, and could enable the exploration of exciton physics and optoelectronic applications.

Euclidean geometry is the fundamental mathematical framework of classical crystallography. Traditionally, layered materials are grown on flat substrates; growing Euclidean crystals on non-Euclidean surfaces has rarely been studied. We present a general model describing the growth of layered materials with screw-dislocation spirals on non-Euclidean surfaces and show that it leads to continuously twisted multilayer superstructures. This model is experimentally demonstrated by growing supertwisted spirals of tungsten disulfide (WS 2 ) and tungsten diselenide (WSe 2 ) draped over nanoparticles near the centers of spirals. Microscopic structural analysis shows that the crystal lattice twist is consistent with the geometric twist of the layers, leading to moiré superlattices between the atomic layers., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Layered two-dimensional Ruddlesden-Popper (RP) halide perovskites are an intriguing class of semiconductors being explored for their linear and nonlinear optical and ferroelectric properties. Second harmonic generation (SHG) is commonly used to screen for noncentrosymmetric and ferroelectric materials. However, SHG measurements of perovskites can be obscured by their intense multiphoton photoluminescence (mPL). Here, we apply multidimensional harmonic generation as a method to eliminate the complications from mPL. By scanning and correlating both excitation and emission frequencies, we unambiguously assess whether a material supports SHG by examining if an emission feature scales as twice the excitation frequency. Measurements of a series of n = 2, 3 RP perovskites reveal that, contrary to previous belief, n -butylammonium (BA) RP perovskites are not SHG-active and thus centrosymmetric, but RP perovskites with phenylethylammonium (PEA) and 2-thiophenemethylammonium (TPMA) spacer cations display SHG. This work establishes multidimensional harmonic generation as a definitive method to measure SHG in halide perovskites.

Triple sum-frequency (TSF) spectroscopy is a recently developed methodology that enables collection of multidimensional spectra by resonantly exciting multiple quantum coherences of vibrational and electronic states. This work reports the first application of TSF to the electronic states of semiconductors. Two independently tunable ultrafast pulses excite the A, B, and C features of a MoS 2 thin film. The measured TSF spectrum differs markedly from absorption and second harmonic generation spectra. The differences arise because of the relative importance of transition moments and the joint density of states (JDOS). We develop a simple model and globally fit the absorption and harmonic generation spectra to extract the JDOS and the transition moments from these spectra. Our results validate previous assignments of the C feature to a large JDOS created by band nesting.

Pedot: PSS, a transparent electrically conductive polymer, finds widespread use in electronic devices. While empirical efforts have increased conductivity, a detailed understanding of the coupled electronic and morphological landscapes in PEDOT:PSS has lagged due to substantial structural heterogeneity on multiple length-scales. We use an optical microresonator-based absorption spectrometer to perform single-particle measurements, providing a bottom-up examination of electronic structure and morphology ranging from single PEDOT:PSS polymers to nascent films. Using single-particle spectroscopy with complementary theoretical calculations and ultrafast spectroscopy, we demonstrate that PEDOT:PSS displays bulk-like optical response even in single polymers. We find highly ordered PEDOT assemblies with long-range ordering mediated by the insulating PSS matrix and reveal a preferential surface orientation of PEDOT nanocrystallites absent in bulk films with implications for interfacial electronic communication. Our single-particle perspective provides a unique window into the microscopic structure and electronic properties of PEDOT:PSS.

High-quality metal halide perovskite single crystals have low defect densities and excellent photophysical properties, yet thin films are the most sought after material geometry for optoelectronic devices. Perovskite single-crystal thin films (SCTFs) would be highly desirable for high-performance devices, but their growth remains challenging, particularly for inorganic metal halide perovskites. Herein, we report the facile vapor-phase epitaxial growth of cesium lead bromide perovskite (CsPbBr 3 ) continuous SCTFs with controllable micrometer thickness, as well as nanoplate arrays, on traditional oxide perovskite SrTiO 3 (100) substrates. Heteroepitaxial single-crystal growth is enabled by the serendipitous incommensurate lattice match between these two perovskites, and overcoming the limitation of island-forming Volmer-Weber crystal growth is critical for growing large-area continuous thin films. Time-resolved photoluminescence, transient reflection spectroscopy, and electrical transport measurements show that the CsPbBr 3 epitaxial thin film has a slow charge carrier recombination rate, low surface recombination velocity (10 4 cm s -1 ), and low defect density of 10 12 cm -3 , which are comparable to those of CsPbBr 3 single crystals. This work suggests a general approach using oxide perovskites as substrates for heteroepitaxial growth of halide perovskites. The high-quality halide perovskite SCTFs epitaxially integrated with multifunctional oxide perovskites could open up opportunities for a variety of high-performance optoelectronics devices.

Ultrafast spectroscopy is often collected in the mixed frequency/time domain, where pulse durations are similar to system dephasing times. In these experiments, expectations derived from the familiar driven and impulsive limits are not valid. This work simulates the mixed-domain four-wave mixing response of a model system to develop expectations for this more complex field-matter interaction. We explore frequency and delay axes. We show that these line shapes are exquisitely sensitive to excitation pulse widths and delays. Near pulse overlap, the excitation pulses induce correlations that resemble signatures of dynamic inhomogeneity. We describe these line shapes using an intuitive picture that connects to familiar field-matter expressions. We develop strategies for distinguishing pulse-induced correlations from true system inhomogeneity. These simulations provide a foundation for interpretation of ultrafast experiments in the mixed domain.

A spectrum-matching and look-up-table (LUT) methodology has been developed and evaluated to extract environmental information from remotely sensed hyperspectral imagery. The LUT methodology works as follows. First, a database of remote-sensing reflectance (Rrs) spectra corresponding to various water depths, bottom reflectance spectra, and water-column inherent optical properties (IOPs) is constructed using a special version of the HydroLight radiative transfer numerical model. Second, the measured Rrs spectrum for a particular image pixel is compared with each spectrum in the database, and the closest match to the image spectrum is found using a least-squares minimization. The environmental conditions in nature are then assumed to be the same as the input conditions that generated the closest matching HydroLight-generated database spectrum. The LUT methodology has been evaluated by application to an Ocean Portable Hyperspectral Imaging Low-Light Spectrometer image acquired near Lee Stocking Island, Bahamas, on 17 May 2000. The LUT-retrieved bottom depths were on average within 5% and 0.5 m of independently obtained acoustic depths. The LUT-retrieved bottom classification was in qualitative agreement with diver and video spot classification of bottom types, and the LUT-retrieved IOPs were consistent with IOPs measured at nearby times and locations.