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We employed infrared scattering-type scanning near-field optical microscopy (IR-sSNOM) to study surface plasmon polaritons (SPPs) in trilayer graphene (TLG). Our study reveals systematic differences in near-field IR spectra and SPP wavelengths between Bernal (ABA) and rhombohedral (ABC) TLG domains on SiO2, which can be explained by stacking-dependent intraband conductivities. We also observed that the SPP reflection profiles at ABA-ABC boundaries could be mostly accounted for by an idealized domain boundary defined by the conductivity discontinuity. However, we identified distinct shapes in the SPP profiles at the edges of the ABA and ABC TLG, which cannot be solely attributed to idealized edges with stacking-dependent conductivities. Instead, this can be explained by the presence of various edge structures with local conductivities differing from those of bulk TLGs. Our findings unveil a new structural element that can control SPP, and provide insights into the structures and electronic states of the edges of few-layer graphene.

Karaballi I et al. i [25] find that Cr SB 2 sb N nanoparticles synthesized by a solid-state nitridation reaction support pronounced ultraviolet (UV)-region LSPRs that would be of use for photocatalytic biodegradation and water disinfection. Qiu I et al. i [29] report the electrochemical oxidation of 4-(hydroxymethyl)benzoic acid on an Au nanoparticle-decorated electrode promoted by plasmonic excitation. Sun I et al. i [36] investigate the photoluminescence emission decay of single quantum dots located near plasmonic Au nanoparticles and find a faster decay when the excitation wavelength is spectrally overlapped with the LSPR. Seminal examples of such plasmon-driven chemistry include bond scission,[[12]] but this domain has rapidly expanded to include multielectron redox reactions,[14] nanoparticle growth,[[15]] electrochemical transformations,[[17]] and thermodynamically uphill fuel synthesis reactions,[19] thereby providing a large repertoire for the conversion of light energy to chemical energy and solar-powered chemical manufacturing. [Extracted from the article]

The demand to visualize the spatial distribution of chemical species based on vibrational spectra is rapidly increasing. Driven by such a need, various Raman and infrared spectro-microscopies with a nanometric spatial resolution have been developed over the last two decades. Despite rapid progress, a large gap still exists between the general needs and what these techniques can achieve. This Perspective highlights the key challenges and recent breakthroughs of the two vibrational nano-imaging techniques, scattering-type scanning near-field optical microscopy and tip-enhanced Raman scattering. [ABSTRACT FROM AUTHOR]

CD spectroscopy is considered an incisive tool for determining the secondary structure of proteins in solution (4-6,12,13). But biomolecules participating in chemical or biological reactions often undergo ultrafast structural changes [...], Optical activity (1-3) is the result of chiral molecules interacting differently with left versus right circularly polarized light. Because of this intrinsic link to molecular structure, the determination of optical activity through circular dichroism (CD) spectroscopy has long served as a routine method for obtaining structural information about chemical and biological systems in condensed phases (4-6). A recent development is time-resolved CD spectroscopy, which can in principle map the structural changes associated with biomolecular function (7) and thus lead to mechanistic insights into fundamental biological processes. But implementing time-resolved CD measurements is experimentally challenging because CD is a notoriously weak effect (a factor of [10.sup.-4]-[10.sup.-6] smaller than absorption). In fact, this problem has so far prevented time-resolved vibrational CD experiments. Here we show that vibrational CD spectroscopy with femtosecond time resolution can be realized when using heterodyned spectral interferometry to detect (8-10) the phase and amplitude of the infrared optical activity free-induction-decay field in time (much like in a pulsed NMR experiment). We show that we can detect extremely weak signals in the presence of large achiral background contributions, by simultaneously measuring with a femtosecond laser pulse the vibrational CD and optical rotatory dispersion spectra of dissolved chiral limonene molecules. We have so far only targeted molecules in equilibrium, but it would be straightforward to extend the method for the observation of ultrafast structural changes such as those occurring during protein folding or asymmetric chemical reactions. That is, we should now be in a position to produce 'molecular motion pictures' (11) of fundamental molecular processes from a chiral perspective.

The title reaction is investigated by co-expanding a mixture of Cl[sub 2] and CH[sub 2]D[sub 2] into a vacuum chamber and initiating the reaction by photolyzing Cl[sub 2] with linearly polarized 355 nm light. Excitation of the first C–H overtone of CH[sub 2]D[sub 2] leads to a preference for hydrogen abstraction over deuterium abstraction by at least a factor of 20, whereas excitation of the first C–D overtone of CH[sub 2]D[sub 2] reverses this preference by at least a factor of 10. Reactions with CH[sub 2]D[sub 2] prepared in a local mode containing two quanta in one C–H oscillator |2000>[sup -] or in a local mode containing one quantum each in two C–H oscillators |1100> lead to products with significantly different rotational, vibrational, and angular distributions, although the vibrational energy for each mode is nearly identical. The Cl+CH[sub 2]D[sub 2]|2000>[sup -] reaction yields methyl radical products primarily in their ground state, whereas the Cl+CH[sub 2]D[sub 2]|1100> reaction yields methyl radical products that are C–H stretch excited. The HCl(v=1) rotational distribution from the Cl+CH[sub 2]D[sub 2]|2000>[sup -] reaction is significantly hotter than the HCl(v=1) rotational distribution from the Cl+CH[sub 2]D[sub 2]|1100> reaction, and the HCl(v=1) differential cross-section (DCS) of the Cl+CH[sub 2]D[sub 2]|2000>[sup -] reaction is more broadly side scattered than the HCl(v=1) DCS of the Cl+CH[sub 2]D[sub 2]|1100> reaction. The results can be explained by a simple spectator model and by noting that the |2000>[sup -] mode leads to a wider cone of acceptance for the reaction than the |1100> mode. These measurements represent the first example of mode selectivity observed in a differential cross section, and they demonstrate that vibrational excitation can be used to direct the reaction pathway of the Cl+CH[sub 2]D[sub 2] reaction. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Irradiation of molecular oxygen O[sub 2] in the region of the Herzberg continuum between 218 nm and 239 nm results in the production of open-shell photofragments O([sup 3]P)+O([sup 3]P). Product O([sup 3]P[sub j]; j=0,1,2) atoms were ionized using resonantly enhanced multiphoton ionization (2+1 REMPI) near 225 nm and the ions collected in a velocity-sensitive time-of-flight mass spectrometer. By controlling the polarization of the photolysis and ionization radiation, we have measured alignment and orientation parameters of O-atom electronic angular momentum (j) in the molecule frame. The results show alignment from both parallel and perpendicular transitions that are cylindrically symmetric about the velocity (v) of the recoiling O atom. We also observe electronic alignment that is noncylindrically symmetric about v, resulting from coherence between multiply excited dissociative states. Photodissociation with linearly polarized light is shown to produce O atoms that are oriented in the molecule frame, resulting from interference between parallel and perpendicular dissociative states of O[sub 2]. Semiclassical calculations that include spin–orbit coupling between six excited states reproduce closely the observed polarization. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A beam containing methane and molecular chlorine is expanded into a vacuum where the methane is excited with two quanta of C-H stretching (one quantum each in two of the four C-H bonds). The reaction is initiated by fast Cl atoms generated by photolysis of Cl[sub 2] at 355 nm, and the resulting CH[sub 3] and HCl products are detected in a state-specific manner using resonance-enhanced multiphoton ionization. Speed-dependent spatial anisotropies (beta;[sub prod]) of HCl and CH[sub 3] products allow identification of three major product channels. They are in order of importance: (a) HCl (υ = 0) + CH[sub 3] [v[sub l] (symmetric stretch) or v[sub 3] (asymmetric stretch) = 1]; (b) HCl (υ = 1) + CH[sub 3] [ v[sub 2](umbrella bend) = 1)]; and (c) HCl (υ = 1) + CH[sub 3] (v[sub 1] = 1). The CH[sub 3] (υ = 0) product cannot be detected, and the HCl (υ = 2) product is minor. Channels (a) and (c) proceed in a vibrationally adiabatic manner, whereas channel (b) appears to involve the nonadiabatic interaction involving the low frequency bending mode in methane that correlates to the bending mode in the methyl radical product. The angular distributions differ markedly for the three product channels. This behavior is explained by the propensity for reactive collisions involving H-atom transfer along the line of centers and the difference in the cones of acceptance. The rotational angular momentum vector of the HCl (υ = 1, J = 1) product is aligned perpendicular to the line of centers, which is consistent with an impulsive energy release along the line of centers. Our results clearly demonstrate that the direct and local mode picture of the chemical reaction remains largely valid, which connects vibrational excitation to the scattering dynamics. [ABSTRACT FROM AUTHOR]

It has been reported that defects in molybdenum disulfide (MoS2) enable the hydrogen evolution reaction (HER). The most widely employed method of argon-plasma treatment for defect generation suffers from poor material stability and loss of conductivity. Here, we report a new method to synthesize highly polycrystalline molybdenum disulfide MoS2 bilayers with enhanced HER performance and material stability. This new method is based on metal organic chemical vapor deposition (MOCVD) followed by UV/ozone treatment to generate defects. The defect densities on MoS2 were identified by the increase in lifetime (∼76%) and intensity (∼15%) in photoluminescence (PL) as compared to those of pristine MoS2. Our fabrication and characterization methods can be further applied to optimize defect densities for catalytic effects in various transition metal dichalcogenide (TMDC) materials. [ABSTRACT FROM AUTHOR]