Ultrafast Polarization Switching in BaTiO3 Nanomaterials: Combined Density Functional Theory and Coupled Oscillator Study

The challenge of achieving ultrafast switching of electric polarization in ferroelectric materials remains unsolved as there is no experimental evidence of such switching to date. In this study, we developed an enhanced model that describes switching within a two-dimensional space of generalized coordinates at THz pulses. Our findings indicate that stable switching in barium titanate cannot be achieved through a single linearly polarized pulse. When the intensity of the linearly polarized pulse reaches a certain threshold, the sample experiences depolarization but not stable switching. Our study also reveals that phonon friction plays a minor role in the switching dynamics and provides an estimate of the optimal parameters for the perturbing pulse with the lowest intensity that results in the depolarization of an initially polarized sample.

Resonant Excitation of the Ferroelectric Soft Mode by a Narrow-Band THz Pulse

This study investigates the impact of narrow-band terahertz pulses on the ferroelectric order parameter in Ba_0.8Sr_0.2TiO₃ films on various substrates. THz radiation in the range of 1-2 THz with the pulse width of about 0.15 THz was separated from a broadband pulse with the interference technique. The 375 nm thick BST film on a MgO (001) substrate exhibits enhanced THz-induced second harmonic generation when excited by THz pulses with a central frequency of 1.6 THz, due to the resonant excitation of the soft phonon mode. Conversely, the BST film on a Si (001) substrate shows no enhancement, due to its polycrystalline state. The 800 nm thick BST film on a MgO (111) substrate demonstrates the maximum of a second harmonic generation signal when excited by THz pulses at 1.8 THz, which is close to the soft mode frequency for the (111) orientation. Notably, the frequency spectrum of the BST/MgO (111) film reveals peaks at both the fundamental and doubled frequencies, and their intensities depend, respectively, linearly and quadratically on the THz pulse electric field strength.

Terahertz wave rectification in a ferroelectric triglycine sulfate single crystal

The effect of optical rectification (OR) in the terahertz range (THz rectification, TR) is experimentally demonstrated. The effect consists of generating a DC voltage on the faces of a ferroelectric triglycine sulfate (TGS) single crystal under the action of pulsed radiation with a frequency of 1.57 and 1.96 THz and an electric field strength per pulse of 1.3 and 1.5 MV/m, respectively. The FLARE FELIX free-electron laser system (Radboud University, The Netherlands) was used as a THz radiation source. The TR effect makes it possible to directly determine the nonlinear susceptibilities of media (including those under conditions of strong absorption) without any reference or optical channel calibration and also without the need of Fourier transform.

Correction to "Terahertz Magnon-Polaritons in TmFeO3"

[This corrects the article DOI: 10.1021/acsphotonics.7b01402.].

Serum Concentrations of Cotinine and Trans-3'-Hydroxycotinine in US Adults: Results From Wave 1 (2013-2014) of the Population Assessment of Tobacco and Health Study

INTRODUCTION

The Population Assessment of Tobacco and Health (PATH) Study is a nationally representative cohort of tobacco product users and nonusers. The study's main purpose is to obtain longitudinal epidemiologic data on tobacco use and exposure among the US population.

AIMS AND METHODS

Nicotine biomarkers-cotinine (COT) and trans-3'-hydroxycotinine (HCT)-were measured in blood samples collected from adult daily tobacco users and nonusers during Wave 1 of the PATH Study (2013-2014; n = 5012; one sample per participant). Participants' tobacco product use and exposure to secondhand smoke were categorized based on questionnaire responses. Nonusers were subdivided into never users and recent former users. Daily tobacco users were classified into seven tobacco product use categories: exclusive users of cigarette, smokeless tobacco, electronic cigarette, cigar, pipe, and hookah, as well as polyusers. We calculated sample-weighted geometric mean (GM) concentrations of cotinine, HCT, and the nicotine metabolite ratio (NMR) and evaluated their associations with tobacco use with adjustment for potential confounders.

RESULTS

The GMs (95% confidence intervals) of COT and HCT concentrations for daily tobacco users were 196 (184 to 208) and 72.5 (67.8 to 77.4) ng/mL, and for nonusers they were 0.033 (0.028 to 0.037) and 0.021 (0.018 to 0.023) ng/mL. Exclusive smokeless tobacco users had the highest COT concentrations of all user groups examined. The GM NMR in daily users was 0.339 (95% confidence interval: 0.330 to 0.350).

CONCLUSIONS

These nationally representative estimates of serum nicotine biomarkers could be the basis for reference ranges characterizing nicotine exposure for daily tobacco users and nonusers in the US adult population.

IMPLICATIONS

This report summarizes the serum nicotine biomarker measurements in Wave 1 of the PATH Study. We are reporting the first estimates of HCT in serum for daily tobacco users and nonusers in the noninstitutionalized, civilian US adult population; the first nationally representative serum COT estimates for daily exclusive users of different tobacco products and daily polyusers; and the first nationally representative estimate of the serum NMR in daily tobacco users by age, race/ethnicity, and sex.

The pH of Smokeless Tobacco Determines Nicotine Buccal Absorption: Results of a Randomized Crossover Trial

Nicotine absorption rate influences tobacco products' addictiveness. For smokeless tobacco, nicotine buccal absorption is associated with its free-base form; the pH of smokeless tobacco defines the proportion of free-base (i.e., unprotonated) vs. protonated nicotine. This was the first study to compare nicotine pharmacokinetics (PK) and pharmacodynamics (PD) after the use of commercial smokeless tobacco products that were experimentally manipulated to differ only in pH and percent free-base nicotine. Moist snuff users (N = 40) completed four crossover visits and used a single 2 g portion of Copenhagen Original Long Cut amended to 4 pH levels: 5.0, 7.7, 8.2, and 8.6 (free-base nicotine 0.1, 32, 60, and 79%) for 30 minutes. Nicotine PK and PD were assessed for 4 hours post-use. Nicotine PK substantially depends on its free-base proportion, with more than 4-fold increases in mean plasma nicotine maximum concentration and area under the curve over 240 minutes (3.9 to 16.7 ng/mL; 385 to 1810 ng min/mL, respectively, both P < 0.001) from pH 5.0 to 8.6. The autonomic cardiovascular effects of smokeless tobacco use reflected percent free-base nicotine, with small (albeit significant) systematic increases in heart rate and blood pressure associated with free-base nicotine. Smokeless tobacco product pH and percent free-base nicotine play a major role in the rate and extent of nicotine absorption, determining product PD effects and abuse potential. Research and regulation of smokeless tobacco products should consider both total nicotine content and product pH. Further research may address the impact of modifying pH on the addictiveness of smokeless tobacco and associated use behaviors.

Photoinduced spin dynamics in a uniaxial intermetallic heterostructure [Formula: see text]

Intermetallic heterostructures of rare-earth and transition metals exhibit physical properties prospective for various applications. These structures combine giant magnetostriction, controllable magnetic anisotropy, magneto-optical activity and allow spin reorientation transitions (SRT) induced by magnetic field at room temperature. Here, we present the results of a study of spin dynamics induced by ultrafast optical excitation in the [Formula: see text] heterostructure. The time dependence of the light polarization rotation excited by a pump optical pulse with a duration of 35 fs was measured in the total range of the SRT created by external DC magnetic field. We found hysteretic dependence of the polarization rotation on magnetizing field that is specific for spin dynamics near SRT. Enhancement of the rotation is observed in the critical points of the SRT and near the points of magnetization switch from metastable to stable spin states. In the time-domain, two characteristic delays of 20 ps and 200 ps were found, corresponding to the maximum deviation of the light polarization after excitation. The first is explained by the precession motion of spins out of the plane of the structure. The latter is accounted for the spin in-plane deviation from its initial position and thermal relaxation of the anisotropy.

Ultrafast magnetization dynamics in the vicinity of spin reorientation transition in TbCo2/FeCo heterostructures

The magnetic moment dynamics excited by 35 fs laser pulses in TbCo₂/FeCo heterostructure is experimentally investigated by pump-probe technique. The studies are carried out in two typical geometries with magnetizing field perpendicular and along to the easy magnetization axis. In the 'easy axis' orientation, high-frequency oscillations of magnetic moments odd with respect to the sign of the magnetizing field are observed using the magneto-optical Kerr effect. In the perpendicular 'hard axis' orientation corresponding to the spin reorientation phase, the experiment shows oscillations that are even with respect to the field. The maximum angle of Kerr rotation as a function of the magnetizing field strength depicts a specific hysteretic loop that reveals ultrafast optical control of uniaxial magnetic anisotropy originally induced during deposition of the heterostructure in a DC magnetic field. The results provide new ways of ultrafast control of magnetic states in exchange coupled intermetallic heterostructures designed for spintronic applications.

Terahertz Magnon-Polaritons in TmFeO3

Magnon-polaritons are shown to play a dominant role in the propagation of terahertz (THz) waves through TmFeO₃ orthoferrite, if the frequencies of the waves are in the vicinity of the quasi-antiferromagnetic spin resonance mode. Both time-domain THz transmission and emission spectroscopies reveal clear beatings between two modes with frequencies slightly above and slightly below this resonance, respectively. Rigorous modeling of the interaction between the spins of TmFeO₃ and the THz light shows that the frequencies correspond to the upper and lower magnon-polariton branches. Our findings reveal the previously ignored importance of propagation effects and polaritons in such heavily debated areas as THz magnonics and THz spectroscopy of electromagnons. It also shows that future progress in these areas calls for an interdisciplinary approach at the interface between magnetism and photonics.

Strong thermo-induced single and two-photon green luminescence in self-organized peptide microtubes

Diphenylalanine peptide nano- and microtubes formed by self-assembly demonstrate strongly enhanced and tunable single-photon and two-photon luminescence in the visible range, which appears after heat- or laser treatment of these self-organized peptide microtubes. This process significantly extends the functionality of these microstructures and can trigger a new interest in the optical properties of structures based on short peptides.

Bioinspired peptide nanotubes: deposition technology, basic physics and nanotechnology applications

Synthetic peptide monomers can self-assemble into PNM such as nanotubes, nanospheres, hydrogels, etc. which represent a novel class of nanomaterials. Molecular recognition processes lead to the formation of supramolecular PNM ensembles containing crystalline building blocks. Such low-dimensional highly ordered regions create a new physical situation and provide unique physical properties based on electron-hole QC phenomena. In the case of asymmetrical crystalline structure, basic physical phenomena such as linear electro-optic, piezoelectric, and nonlinear optical effects, described by tensors of the odd rank, should be explored. Some of the PNM crystalline structures permit the existence of spontaneous electrical polarization and observation of ferroelectricity. The PNM crystalline arrangement creates highly porous nanotubes when various residues are packed into structural network with specific wettability and electrochemical properties. We report in this review on a wide research of PNM intrinsic physical properties, their electronic and optical properties related to QC effect, unique SHG, piezoelectricity and ferroelectric spontaneous polarization observed in PNT due to their asymmetric structure. We also describe PNM wettability phenomenon based on their nanoporous structure and its influence on electrochemical properties in PNM. The new bottom-up large scale technology of PNT physical vapor deposition and patterning combined with found physical effects at nanoscale, developed by us, opens the avenue for emerging nanotechnology applications of PNM in novel fields of nanophotonics, nanopiezotronics and energy storage devices.

Ultrastructural features of the tegumental surface of a new metacercaria, Nematostrigea sp. (Trematoda: Strigeidae), with a search for potential taxonomically informative characters

The tegumental surface of a new strigeid metacercaria, Nematostrigea sp., which is a parasite of the freshwater fish Channa gachua (Hamilton) in central Vietnam, is described for the first time using scanning (SEM) and transmission (TEM) electron microscopy. In addition to the general tegumental surface in various parts of the body, details of the surface of the suckers, lappets and holdfast organ are presented, as are variations in the form and distribution of the body spines. As good taxonomic criteria are few in diplostomoid metacercariae at both specific and generic levels, a number of the ultrastructural features revealed may prove to represent taxonomically informative characters. These include the presence of: two rings of dome-shaped papillae localised at different levels on the rim of the oral sucker, a single ring of ciliated papillae on the inner margin of the ventral sucker and a band of dome-shaped papillae along the lateral margins of the broad body-fold in the ventral forebody; an unarmed oral sucker and anteroventral surface of the forebody, although the latter bears protuberant secretory pores; an armed ventral sucker covered by six-pointed spines, except on its rim; multi-pointed spines along the dorsal and ventral sides of the forebody, with the number of their teeth increasing posteriorly; multi-pointed spines on the forebody which gradually transform into single-pointed, more widely distributed spines on the hindbody, disappearing completely at posterior end of the body; the surface of the lappets with a particular distribution of pores leading to three types of secretory glands and three topographical modifications (areas where the surface is smooth, bears digitiform processes or bears recurved, dagger-shaped spines); and the surface of the holdfast organ which is covered with densely packed, straight or slightly curved, simple spines on its lateral surface but is smooth medially.

Co-adsorbtion of Cu and Keggin type polytungstates on polycrystalline Pt: interplay of atomic and molecular UPD

Second harmonic generation (SHG), electrochemical quartz microbalance (EQCM), and cyclic voltammetry are applied to clarify the structure and properties of Cu adlayers formed in the presence of Keggin polytungstate anions. For 0.02-10 mM CuSO4 solutions, no pronounced suppression of underpotential copper deposition (Cu UPD) by 0.1-10 mM H3PW12O40 (PW12) or H4SiW12O40 (SiW12) is observed in electrochemical experiments. Moreover, coadsorption with polyanions results in an increase of charge in the Cu UPD region. EQCM data demonstrate high surface coverage with polytungstate in the overall potential range and their pronounced co-adsorption with Cu2+ cations under open circuit. The unusual potential dependence of EQCM response of polytungstates is discovered and discussed in terms of anion interactions with adsorbed hydrogen. The SHG response of Cu UPD demonstrates a non-linear dependence on Cu surface coverage, which is interpreted in terms of discontinuous submonolayers consisting of 2D Cu islands. The additives of PW12 or SiW12 decrease copper SHG response at low and high CuSO4 concentrations, with minor effect for a mid range of concentrations. In all mixed solutions, the potential dependence of the SHG response remains typical for Cu UPD, not for polytungstates. SHG transients measured under potential step mode demonstrate that the initial non-steady-state SHG behavior of the adlayer is more close to the behavior of polytungstates, but typical copper features appear at longer wavelength. These facts favor the hypothesis of Cu adatom penetration through anionic adlayers and formation of a metal submonolayer at the vacant areas between large quasi-spherical polyanions, with subsequent transformation into a Pt/Cu/polytungstate layered structure.

Photoluminescence studies of oligothiophene self-assembled monolayers at low excitation energy

Photoluminescence spectroscopy studies have been performed on self-assembled monolayers (SAMs) on Au(111) of thiophene oligomers with the number of thiophen rings N=3 and N=4. Photoluminescence spectra of SAMs reveal excitonic behavior with different band resolution and temperature dependence. These differences are attributed to different SAMs structure (degree of ordering).