Dusan Velic

Electronic states of the C6H6/Cu{111} system: Energetics, femtosecond dynamics, and adsorption morphology

Two-photon-photoemission (2PPE) spectroscopy is employed to characterize electronic states of a bilayer C6H6/Cu{111} system at 85 K. The unoccupied benzene π* e2u state is observed with a binding energy of 4.6 eV above the Fermi level. This result agrees with inverse-photoemission (IPE) data and provides a case where the determination of the binding energy is identical for 2PPE and IPE. The π* e2u state is assigned in the 2PPE scheme as a final state which is the first observed final state in 2PPE of adsorbate-surface systems. The dependence of the electron dynamics on the morphology of an incomplete adsorption layer is also investigated. Two (n=1)-like image potential states A and B are observed which presumably originate from two different C6H6 adsorption geometries in the bilayer regime. The two image states A and B are characterized by electron effective masses of 1.1 and 1.9 me, binding energies of 3.30 and 3.45 eV above the Fermi level, and lifetimes of 40 and 20 fs, respectively. The dielectric con...

Carboxybetaine Modified Interface for Electrochemical Glycoprofiling of Antibodies Isolated from Human Serum

Impedimetric lectin biosensors capable of recognizing two different carbohydrates (galactose and sialic acid) in glycans attached to antibodies isolated from human serum were prepared. The first step entailed the modification of a gold surface by a self-assembled monolayer (SAM) deposited from a solution containing a carboxybetaine-terminated thiol applied to the subsequent covalent immobilization of lectins and to resist nonspecific protein adsorption. In the next step, Sambucus nigra agglutinin (SNA) or Ricinus communis agglutinin (RCA) was covalently attached to the SAM, and the whole process of building a bioreceptive layer was optimized and characterized using a diverse range of techniques including electrochemical impedance spectroscopy, cyclic voltammetry, quartz crystal microbalance, contact angle measurements, zeta-potential assays, X-ray photoelectron spectroscopy, and atomic force microscopy. In addition, the application of the SNA-based lectin biosensor in the glycoprofiling of antibodies isolated from the human sera of healthy individuals and of patients suffering from rheumatoid arthritis (RA) was successfully validated using an SNA-based lectin microarray. The results showed that the SNA lectin, in particular, is capable of discriminating between the antibodies isolated from healthy individuals and those from RA patients based on changes in the amount of sialic acid present in the antibodies. In addition, the results obtained by the application of RCA and SNA biosensors indicate that the abundance of galactose and sialic acid in antibodies isolated from healthy individuals is age-related.

Selective collision‐induced desorption: Measurement of the π‐bonded C2H4 binding energy on Pt{111} precovered with atomic oxygen

Collision‐induced desorption (CID) is used to selectively probe the well depth of one particular adsorbate–surface potential energy surface in the presence of multiple adsorbates. Ethylene adsorbed at saturation coverage on Pt{111} precovered with atomic oxygen represents a system with three adsorbates: oxygen and two different adsorption forms of ethylene. Both the π‐bonded ethylene (π‐C2H4) and di‐σ‐bonded ethylene (di‐σ‐C2H4) species are formed at coverages of 0.25 ML preadsorbed atomic oxygen and 0.15 ML ethylene on Pt{111} at 100 K. Deconvolution of Al Kα x‐ray photoelectron (XP) spectra suggests that C(1s) XP binding energy is 283.1 eV for π‐C2H4 and is 283.7 eV for di‐σ‐C2H4. The C(1s) XP spectra together with the CID result reveal that the coverage ratio of π‐C2H4 and di‐σ‐C2H4 at saturation at 100 K is ∼1:1. The selectivity of CID is demonstrated by desorbing only π‐C2H4 using a neutral Xe atomic beam with translational energies ranging from 2.1 to 4.1 eV. In this translational energy range, di‐σ...

Electrochemical performance of Ti3C2Tx MXene in aqueous media: towards ultrasensitive H2O2 sensing

An extensive characterization of pristine and oxidized Ti3C2Tx (T: =O, -OH, -F) MXene showed that exposure of MXene to an anodic potential in the aqueous solution oxidizes the nanomaterial forming TiO2 layer or TiO2 domains with subsequent TiO2 dissolution by F- ions, making the resulting nanomaterial less electrochemically active compared to the pristine Ti3C2Tx. The Ti3C2Tx could be thus applied for electrochemical reactions in a cathodic potential window i.e. for ultrasensitive detection of H2O2 down to nM level with a response time of approx. 10 s. The manuscript also shows electrochemical behavior of Ti3C2Tx modified electrode towards oxidation of NADH and towards oxygen reduction reactions.

TERAHERTZ TIME-DOMAIN SPECTROSCOPY OF SELECTED LAYERED SILICATES

Micaceous layer silicate clay minerals are attractive materials for applications involving non-linear optics because of their low cost and ability to form well ordered, platy aggregates, but such applications require precise knowledge of the dielectric behavior of the clay. The purpose of the present study was to use Terahertz time-domain spectroscopy (THz-TDS) to determine the dielectric properties of certain cleavable layered clay minerals, including muscovite, vermiculite, phlogopite, and biotite. The samples were characterized by X-ray diffraction and Fourier transform infrared spectroscopy as well as chemical analysis by Energy dispersive X-ray spectroscopy. The THz frequency window investigated was the far-infrared region of 3.3 to ∼40.0 cm−1 corresponding to 0.1 and 1.2 THz, respectively. The samples were selected so that the hydrated form of the interlayer cation, e.g. Mg2+ present in the interlayer gallery of vermiculite, could be compared to species such as phlogopite, biotite, and muscovite with the dehydrated form of interlayer cations such as K+ or Na+. The frequency-dependent complex index of refraction of these natural materials was determined to vary between 2.50 and 2.80. The presence of water in the interlayer space of vermiculite was reflected in the detection of increased values of the absorption index in comparison with the muscovite, phlogopite, and biotite.

A model for estimating the surface effective mass during collision-induced processes on Pt{111}

Abstract The number of surface lattice atoms involved in a particle-surface collision is represented by an effective mass. A model for estimating the effective mass of Pt{111} during the collision with an incident particle is proposed. The effective mass is governed by the collision time which is a function of the incident particles velocity. The effective mass is proposed to increase geometrically with collision time, based on the hexagonal close-packed structure of the Pt lattice. The effective mass model was tested using Ar and Xe scattering data from Pt{111}.

Dielectric properties of micaceous clays determined by terahertz time-domain spectroscopy

Micaceous layered clay minerals, as utilized in many electro-technical applications, were studied by terahertz time-domain spectroscopy (THz-TDS). The dielectric behavior of clay samples was investigated in a far-infrared region of 0.8 and 6.0 THz corresponding to ∼27 to 200 cm–1, respectively. The samples were also characterized by X-ray diffraction and Fourier transform infrared spectroscopy, and chemical analysis by energy dispersive X-ray spectroscopy. Muscovite with dehydrated K+ interlayer cations was compared with vermiculite having hydrated Mg2+ interlayer cations. The frequency dependence of complex index of refraction varied between 2.43 and 2.48 for muscovite and from 2.23 to 2.08 for vermiculite. The frequency dependence of the power absorption coefficient revealed clear absorption bands for muscovite at 1.95 THz (65 cm−1) and 4.60 THz (153.4 cm−1), and asymmetric band at 2.5 THz (83.4 cm−1) for vermiculite. The band positions were compared with far infrared Fourier transform spectroscopic results achieved by conventional techniques. The differences found were attributed to variations in chemical composition and the stacking order of the micaceous clays used.

Linear and nonlinear properties of multicomponent glass photonic crystal fibers

Processes resulting in supercontinuum generation in multicomponent glass photonic crystal fibers are reviewed in this paper. Multicomponent glass photonic crystal fibers are shown to have a broad transmission range, extending up to 4.5 μm in selected cases. Pumping with a 1240-nm femtosecond pulse at very low sub-nJ energies resulted in soliton formation and dispersive wave generation in a multicomponent PCF sample having a double-core square-lattice structure. These processes were described using a phase-matching model derived from the simulated dispersive properties of the fiber. Third-harmonic generation was observed in the radiation modes of a different cobweb sample with the simultaneous formation of a soliton in the NIR.

Supramolecular surface layer: coumarin/thiolated cyclodextrin/gold

Abstract A formation of supramolecular host–guest inclusion surface layer is reported. A nanostructure of this layer consists of an inclusion complex, where a guest molecule – coumarin-6 (3-(2-benzothiazolyl)-7-(diethylamino) coumarin, C20H18N2O2S) is placed into a ‘bucket’ of a host molecule – thiolated cyclodextrin (6-monodeoxy-6-monothio-β-cyclodextrin, C42H70O34S) which is attached on Au surface. The inclusion and the layer formation are determined by using time-resolved fluorescence anisotropy, second-harmonic generation (SHG), and fluorescence in combination with laser-induced thermal desorption from the surface.

Collision-induced desorption (CID) of NO from Pt{111}: a comparison between the CID binding energy and the activation energy for thermal desorption

Abstract The Xe and Kr collision-induced desorption cross-sections for NO adsorbed on Pt{111} at 100 K are reported as a function of translational energy in the range of 1.9 to 3.8 eV. The minimum energy required for desorption is extracted using extrapolation to the zero of cross-section. The measured threshold energies exhibit total energy scaling for both beams using two angles of incidence, 45° and 15°. The threshold energies required to desorb NO from Pt{111} were determined experimentally to be 2.55 eV and 2.05 eV using Xe or Kr respectively. Using a hard sphere/cube collision model the NO-Pt{111} binding energy was calculated to be 1.12 ± 0.02 eV using either the beam of Xe or Kr. Comparison of this binding energy with the measured activation energy for thermal desorption supports an adsorption/desorption model having no precursor to the chemisorption state.