Electronic structure orientation as a map of in-plane antiferroelectricity in ß'-In2Se3.

Antiferroelectric (AFE) materials are excellent candidates for sensors, capacitors, and data storage due to their electrical switchability and high-energy storage capacity. However, imaging the nanoscale landscape of AFE domains is notoriously inaccessible, which has hindered development and intentional tuning of AFE materials. Here, we demonstrate that polarization-dependent photoemission electron microscopy can resolve the arrangement and orientation of in-plane AFE domains on the nanoscale, despite the absence of a net lattice polarization. Through direct determination of electronic transition orientations and analysis of domain boundary constraints, we establish that antiferroelectricity in ß'-In2Se3 is a robust property from the scale of tens of nanometers to tens of micrometers. Ultimately, the method for imaging AFE domain organization presented here opens the door to investigations of the influence of domain formation and orientation on charge transport and dynamics.

Photoemission electron microscopy for connectomics.

Detailing the physical basis of neural circuits with large-volume serial electron microscopy (EM), 'connectomics', has emerged as an invaluable tool in the neuroscience armamentarium. However, imaging synaptic resolution connectomes is currently limited to either transmission electron microscopy (TEM) or scanning electron microscopy (SEM). Here, we describe a third way, using photoemission electron microscopy (PEEM) which illuminates ultra-thin brain slices collected on solid substrates with UV light and images the photoelectron emission pattern with a wide-field electron microscope. PEEM works with existing sample preparations for EM and routinely provides sufficient resolution and contrast to reveal myelinated axons, somata, dendrites, and sub-cellular organelles. Under optimized conditions, PEEM provides synaptic resolution; and simulation and experiments show that PEEM can be transformatively fast, at Gigahertz pixel rates. We conclude that PEEM imaging leverages attractive aspects of SEM and TEM, namely reliable sample collection on robust substrates combined with fast wide-field imaging, and could enable faster data acquisition for next-generation connectomics.

Understanding and Controlling Photothermal Responses in MXenes.

MXenes have the potential for efficient light-to-heat conversion in photothermal applications. To effectively utilize MXenes in such applications, it is important to understand the underlying nonequilibrium processes, including electron-phonon and phonon-phonon couplings. Here, we use transient electron and X-ray diffraction to investigate the heating and cooling of photoexcited MXenes at femtosecond to nanosecond time scales. Our results show extremely strong electron-phonon coupling in Ti3C2-based MXenes, resulting in lattice heating within a few hundred femtoseconds. We also systematically study heat dissipation in MXenes with varying film thicknesses, chemical surface terminations, flake sizes, and annealing conditions. We find that the thermal boundary conductance (TBC) governs the thermal relaxation in films thinner than the optical penetration depth. We achieve a 2-fold enhancement of the TBC, reaching 20 MW m-2 K-1, by controlling the flake size or chemical surface termination, which is promising for engineering heat dissipation in photothermal and thermoelectric applications of the MXenes.

Accurate phase detection in time-domain heterodyne SFG spectroscopy.

Heterodyne detection is a ubiquitous tool in spectroscopy for the simultaneous detection of intensity and phase of light. However, the need for phase stability hinders the application of heterodyne detection to electronic spectroscopy. We present an interferometric design for a phase-sensitive electronic sum frequency generation (e-SFG) spectrometer in the time domain with lock-in detection. Our method of continuous phase modulation of one arm of the interferometer affords direct measurement of the phase between SFG and local oscillator fields. Errors in the path length difference caused by drifts in the optics are corrected, offering unprecedented stability. This spectrometer has the added advantage of collinear fundamental beams. The capabilities of the spectrometer are demonstrated with proof-of-principle experiments with GaAs e-SFG spectra, where we see significantly improved signal to noise ratio, spectral accuracy, and lineshapes.

Nanoimaging of the Edge-Dependent Optical Polarization Anisotropy of Black Phosphorus.

The electronic structure and functionality of 2D materials is highly sensitive to structural morphology, not only opening the possibility for manipulating material properties but also making predictable and reproducible functionality challenging. Black phosphorus (BP), a corrugated orthorhombic 2D material, has in-plane optical absorption anisotropy critical for applications, such as directional photonics, plasmonics, and waveguides. Here, we use polarization-dependent photoemission electron microscopy to visualize the anisotropic optical absorption of BP with 54 nm spatial resolution. We find the edges of BP flakes have a shift in their optical polarization anisotropy from the flake interior due to the 1D confinement and symmetry reduction at flake edges that alter the electronic charge distributions and transition dipole moments of edge electronic states, confirmed with first-principles calculations. These results uncover previously hidden modification of the polarization-dependent absorbance at the edges of BP, highlighting the opportunity for selective excitation of edge states of 2D materials with polarized light.

The experience of a severe hypoglycaemic event from the perspective of people with diabetes and their caregivers: "What am I going to do?"

AIMS: Among people with diabetes using insulin, severe hypoglycaemia (SH) can be a life-threatening complication, if untreated. The personal experiences during an SH event from the perspectives of people with diabetes and their caregivers are not well-characterized. This study assessed the perceptions of the event and the decision making processes of people with diabetes (T1D n = 36; T2D n = 24) and their caregivers during SH events. METHODS: In-depth one-on-one telephone interviews were conducted with dyads of people with diabetes and caregivers in the United States (n = 120). An initial synopsis and inductive codebook schema were used to analyse the data with two independent coders (kappa = 0.87-0.89). Themes were developed from the codes, and codes were re-mapped to the themes. RESULTS: Four themes were formed: (1) Caregivers scramble to do the right thing and support people with diabetes in treating SH; (2) Decision making capacity is impaired during an SH event, often a panicked time; (3) People learn to manage SH events through their own experiences and frequently make lifestyle changes to prevent and treat future events; and (4) Discussion with healthcare providers about SH, and particularly SH treatment, is limited. CONCLUSIONS: SH events are stressful and often evoke emotional reactions that can impair decision making. Thus, advance treatment planning of SH events needs to occur. Much of the knowledge about SH treatment derives from prior experience rather than healthcare provider guidance, suggesting a need for healthcare providers to initiate proactive discussions about SH treatment.

Toward a more comprehensive understanding of the emotional side of type 2 diabetes: A re-envisioning of the assessment of diabetes distress.

AIMS: To develop an updated, more theoretically sound system for describing and assessing diabetes-related emotional distress (DD) in adults with type 2 diabetes (T2D). METHODS: Items were developed from qualitative interviews with 11 adults with T2D and 6 clinicians, then categorized as reflecting a core emotional experience of DD or a primary source of DD. Items were then administered to a national sample of TCOYD Registry participants. Data were analyzed using both exploratory (EFA) and confirmatory (CFA) factor analyses. Reliability (alpha) and construct validity also were assessed. RESULTS: EFAs with 599 adults (258 insulin users, 341 non-insulin users) yielded a coherent DD Core scale and 7 DD Source scales (management demands, healthcare provider, hypoglycemia, long-term health, interpersonal issues, shame/stigma, healthcare access), which were confirmed by CFA. All alphas were >0.65. DD Core and DD Source scales were associated with criterion variables (all p < .001). Higher DD Core scores were linked to higher HbA1c, BMI, more frequent severe hypoglycemia, and poorer self-management (all p < .001). CONCLUSIONS: Good reliability and validity were found for this two-part T2DD Assessment System. It reflects a more contemporary and actionable approach to DD assessment that distinguishes between its key emotional dimension and its underlying contributors.

Daily Physical Education Linked to Higher Youth Aerobic Fitness Levels: A 4-Year Longitudinal Study.

PURPOSE: Physical education (PE) provides opportunities for youth physical activity during the school day, yet daily PE policies remain low. This study investigated whether daily PE was linked to youth aerobic capacity across a 4-year period in Greenville (South Carolina). METHODS: Youth in grade levels second to eighth at 2 schools providing daily PE and 2 schools that did not provide daily PE participated in the study (N = 466). The 2 schools used as comparisons provided standard PE outlined by South Carolina, which included one 50-minute session per week (elementary) and daily PE for one semester (middle school). Aerobic fitness was measured using the FITNESSGRAM® Progressive Aerobic Cardiovascular Endurance Run test (May 2011-2015). Number of Progressive Aerobic Cardiovascular Endurance Run laps completed, age, gender, ethnicity, body composition, and school attended were included in multilevel linear regression analyses. RESULTS: Across the sample, aerobic fitness increased with age. Throughout the study, males demonstrated growth in aerobic fitness compared with a slight decline for females (P < .001). Youth participation in daily PE was linked to increases in aerobic fitness compared with youth who did not receive daily PE (P < .001). CONCLUSIONS: Findings suggest that exposure to daily PE may contribute to increased aerobic fitness in youth.

Exploring Dietary Behavior Differences among Children by Race/Ethnicity and Socioeconomic Status.

BACKGROUND: In Spartanburg County, SC, nearly 33.7% of children are overweight or obese. The purpose of this study was to investigate differences in eating behavior of youth by race/ethnicity and socioeconomic status. METHODS: Students (N = 997) in 4th to 5th grades completed the School Nutrition and Physical Activity Survey. School databases categorized students as either White or racial/ethnic minority and free/reduced or full paid lunch status. Dietary behaviors included 13 composite measures: unhealthy proteins, healthy proteins, dairy, refined grains, whole grains, vegetables, fruit, fried snacks, sugar-sweetened beverages, sweets, and consumption of a breakfast, evening, and/or restaurant meal. Logistic regression, controlling for sex, was used to analyze differences in consumption for each nutrition variable. RESULTS: Minority youth were less likely to consume healthy proteins (odds ratio [OR] = 0.71, 95% confidence interval [CI] = 0.55-0.92) and more likely to eat at a restaurant (OR = 1.32, 95% CI = 1.02-1.70) compared to white youth. Lower socioeconomic status youth were less likely to eat an evening meal compared to higher socioeconomic status youth (OR = 0.59, 95% CI = 0.39-0.89). CONCLUSIONS: Differences in dietary behaviors may result from food accessibility and insecurity in minority and/or low-income neighborhoods. Future research should explore policy strategies that can help ensure all youth maintain healthy eating habits and weight status.

Multistep and multiscale electron transfer and localization dynamics at a model electrolyte/metal interface.

The lifetime, coupling, and localization dynamics of electronic states in molecular films near metal electrodes fundamentally determine their propensity to act as precursors or reactants in chemical reactions, crucial for a detailed understanding of charge transport and degradation mechanisms in batteries. In the current study, we investigate the formation dynamics of small polarons and their role as intermediate electronic states in thin films of dimethyl sulfoxide (DMSO) on Cu(111) using time- and angle-resolved two-photon photoemission spectroscopy. Upon photoexcitation, a delocalized DMSO electronic state is initially populated two monolayers from the Cu surface, becoming a small polaron on a 200 fs time scale, consistent with localization due to vibrational dynamics of the DMSO film. The small polaron is a precursor state for an extremely long-lived and weakly coupled multilayer electronic state, with a lifetime of several seconds, thirteen orders of magnitude longer than the small polaron. Although the small polaron in DMSO has a lifetime of 140 fs, its role as a precursor state for long-lived electronic states could make it an important intermediate in multistep battery reactivity.

Patient Characteristics and Outcomes Associated with Receiving an Earlier Versus Later Diagnosis of Probable Alzheimer's Disease.

BACKGROUND: Effectiveness of Alzheimer's disease (AD) treatments may depend critically on the timeliness of intervention. OBJECTIVE: To compare characteristics and outcomes of patients diagnosed with probable AD (prAD) based on time elapsed from first onset of cognitive decline. METHODS: Patients with ≥1 prAD diagnosis and ≥1 follow-up visit were selected from the National Alzheimer's Coordinating Center (NACC) Uniform Data Set (UDS; 9/2005-6/2015) and stratified based on the time between the perceived onset of cognitive decline at baseline and first prAD diagnosis (i.e., earlier versus later diagnosis). Characteristics at baseline and prAD diagnosis, clinically meaningful progression, and medication use following prAD diagnosis were compared. RESULTS: Median time from perceived onset of cognitive decline to prAD diagnosis was 4.5 years (earlier diagnosis: ≤3.46; later diagnosis: >5.71). Earlier-diagnosed patients (n = 1,476) were younger at baseline (74.3 versus 76.3 years) and had better cognitive and functional scores than later-diagnosed patients (n = 1,474). At first prAD diagnosis, earlier-diagnosed patients had lower mean global Clinical Dementia Rating (CDR) score (0.8 versus 1.1), higher mean Mini-Mental State Examination (MMSE) (22.6 versus 20.0), and lower mean Functional Activities Questionnaire (11.6 versus 17.3). Earlier- and later-diagnosed patients experienced similar time to a decrease of ≥3 points in MMSE (median 23.2 versus 23.1 months, p = 0.83), but earlier-diagnosed patients had longer time to a CDR score of ≥2 points, and longer times to initiation of AD medication and antipsychotic agents (all p < 0.01). CONCLUSION: Earlier prAD diagnosis in NACC data is associated with higher cognitive function and lower functional impairment at diagnosis.

Dynamics of dipole- and valence bound anions in iodide-adenine binary complexes: A time-resolved photoelectron imaging and quantum mechanical investigation.

Dipole bound (DB) and valence bound (VB) anions of binary iodide-adenine complexes have been studied using one-color and time-resolved photoelectron imaging at excitation energies near the vertical detachment energy. The experiments are complemented by quantum chemical calculations. One-color spectra show evidence for two adenine tautomers, the canonical, biologically relevant A9 tautomer and the A3 tautomer. In the UV-pump/IR-probe time-resolved experiments, transient adenine anions can be formed by electron transfer from the iodide. These experiments show signals from both DB and VB states of adenine anions formed on femto- and picosecond time scales, respectively. Analysis of the spectra and comparison with calculations suggest that while both the A9 and A3 tautomers contribute to the DB signal, only the DB state of the A3 tautomer undergoes a transition to the VB anion. The VB anion of A9 is higher in energy than both the DB anion and the neutral, and the VB anion is therefore not accessible through the DB state. Experimental evidence of the metastable A9 VB anion is instead observed as a shape resonance in the one-color photoelectron spectra, as a result of UV absorption by A9 and subsequent electron transfer from iodide into the empty π-orbital. In contrast, the iodide-A3 complex constitutes an excellent example of how DB states can act as doorway state for VB anion formation when the VB state is energetically available.

Electron accommodation dynamics in the DNA base thymine.

The dynamics of electron attachment to the DNA base thymine are investigated using femtosecond time-resolved photoelectron imaging of the gas phase iodide-thymine (I(-)T) complex. An ultraviolet pump pulse ejects an electron from the iodide and prepares an iodine-thymine temporary negative ion that is photodetached with a near-IR probe pulse. The resulting photoelectrons are analyzed with velocity-map imaging. At excitation energies ranging from -120 meV to +90 meV with respect to the vertical detachment energy (VDE) of 4.05 eV for I(-)T, both the dipole-bound and valence-bound negative ions of thymine are observed. A slightly longer rise time for the valence-bound state than the dipole-bound state suggests that some of the dipole-bound anions convert to valence-bound species. No evidence is seen for a dipole-bound anion of thymine at higher excitation energies, in the range of 0.6 eV above the I(-)T VDE, which suggests that if the dipole-bound anion acts as a "doorway" to the valence-bound anion, it only does so at excitation energies near the VDE of the complex.

Time-resolved radiation chemistry: dynamics of electron attachment to uracil following UV excitation of iodide-uracil complexes.

Electron attachment to uracil was investigated by applying time-resolved photoelectron imaging to iodide-uracil (I(-)U) complexes. In these studies, an ultraviolet pump pulse initiated charge transfer from the iodide to the uracil, and the resulting dynamics of the uracil temporary negative ion were probed. Five different excitation energies were used, 4.00 eV, 4.07 eV, 4.14 eV, 4.21 eV, and 4.66 eV. At the four lowest excitation energies, which lie near the vertical detachment energy of the I(-)U complex (4.11 eV), signatures of both the dipole bound (DB) as well as the valence bound (VB) anion of uracil were observed. In contrast, only the VB anion was observed at 4.66 eV, in agreement with previous experiments in this higher energy range. The early-time dynamics of both states were highly excitation energy dependent. The rise time of the DB anion signal was ∼250 fs at 4.00 eV and 4.07 eV, ∼120 fs at 4.14 eV and cross-correlation limited at 4.21 eV. The VB anion rise time also changed with excitation energy, ranging from 200 to 300 fs for excitation energies 4.00-4.21 eV, to a cross-correlation limited time at 4.66 eV. The results suggest that the DB state acts as a "doorway" state to the VB anion at 4.00-4.21 eV, while direct attachment to the VB anion occurs at 4.66 eV.

Decay dynamics of nascent acetonitrile and nitromethane dipole-bound anions produced by intracluster charge-transfer.

Decay dynamics of nascent dipole bound states of acetonitrile and nitromethane are examined using time-resolved photoelectron imaging of iodide-acetonitrile (I(-)·CH3CN) and iodide-nitromethane (I(-)·CH3NO2) complexes. Dipole-bound anions are created by UV-initiated electron transfer to the molecule of interest from the associated iodide ion at energies just below the vertical detachment energy of the halide-molecule complex. The acetonitrile anion is observed to decay biexponentially with time constants in the range of 4-900 ps. In contrast, the dipole bound state of nitromethane decays rapidly over 400 fs to form the valence bound anion. The nitromethane valence anion species then decays biexponentially with time constants of 2 ps and 1200 ps. The biexponential decay dynamics in acetonitrile are interpreted as iodine atom loss and autodetachment from the excited dipole-bound anion, followed by slower autodetachment of the relaxed metastable ion, while the dynamics of the nitromethane system suggest that a dipole-bound anion to valence anion transition proceeds via intramolecular vibrational energy redistribution to nitro group modes in the vicinity of the iodine atom.

Time-resolved photoelectron imaging of the iodide-thymine and iodide-uracil binary cluster systems.

The energetics and dynamics of thymine and uracil transient negative ions were examined using femtosecond time-resolved photoelectron imaging. The vertical detachment energies (VDEs) of these systems were found to be 4.05 eV and 4.11 eV for iodide-thymine (I(-) x T) and iodide-uracil (I(-) x U) clusters, respectively. An ultraviolet pump pulse was used to promote intracluster charge transfer from iodide to the nucleobase. Subsequent electron detachment using an infrared probe pulse monitored the dynamics of the resulting transient negative ion. Photoelectron spectra reveal two primary features: a near-zero electron kinetic energy signal attributed to autodetachment and a transient feature representing photodetachment from the excited anion state. The transient state exhibits biexponential decay in both thymine and uracil complexes with short and long decay time constants ranging from 150-600 fs and 1-50 ps, respectively, depending on the excitation energy. However, both time constants are systematically shorter for I(-) x T. Vibrational autodetachment and iodine loss are identified as the primary decay mechanisms of the transient negative ions of thymine and uracil.

Time-resolved radiation chemistry: photoelectron imaging of transient negative ions of nucleobases.

Time-resolved photoelectron imaging has been utilized to probe the energetics and dynamics of the transient negative ion of the nucleobase uracil. This species was created through charge transfer from an iodide anion within a binary iodide-uracil complex using a UV pump pulse; the ensuing dynamics were followed by photodetachment with a near-IR probe pulse. The photoelectron spectra show two time-dependent features, one from probe-induced photodetachment of the transient anion state and another from very low energy electron signal attributed to autodetachment. The transient anion was observed to decay biexponentially with time constants of hundreds of femtoseconds and tens of picoseconds, depending on the excitation energy. These dynamics are interpreted in terms of autodetachment from the initially excited state and a second, longer-lived species relaxed by iodine loss. Hydrogen loss from the N1 position may also occur in parallel.

Thermal effects on energetics and dynamics in water cluster anions (H2O)n(-).

The electron binding energies and relaxation dynamics of water cluster anions (H(2)O)(n)(-) (11 ≤ n ≤ 80) formed in co-expansions with neon were investigated using one-photon and time-resolved photoelectron imaging. Unlike previous experiments with argon, water cluster anions exhibit only one isomer class, the tightly bound isomer I with approximately the same binding energy as clusters formed in argon. This result, along with a decrease in the internal conversion lifetime of excited (H(2)O)(n)(-) (25 ≤ n ≤ 40), indicates that clusters are vibrationally warmer when formed in neon. Over the ranges studied, the vertical detachment energies and lifetimes appear to converge to previously reported values.