Infrared surface plasmons on a Au waveguide electrode open new redox channels associated with the transfer of energetic carriers.

Plasmonic catalysis holds promise for opening new reaction pathways inaccessible thermally or for improving the efficiency of chemical processes. We report a gold stripe waveguide along which infrared (λ ~ 1350 nanometers) surface plasmon polaritons (SPPs) propagate, operating simultaneously as an electrochemical working electrode. Cyclic voltammograms obtained under SPP excitation enable oxidative processes involving energetic holes to be investigated separately from reductive processes involving energetic electrons.

Non-specific adsorption of protein to microfluidic materials.

Non-specific adsorption of proteins to the surfaces of microfluidic channels poses a serious problem in lab-on-a-chip devices involving complex biological fluids. Materials commonly used in the formation of microfluidic channels include CYTOP, silica and SU-8. CYTOP is a transparent fluoropolymer (Poly[perfluoro(4-vinyloxy-1-butene)]) with a low refractive index that approximately matches the refractive index of biologically compatible fluids, and is useful in optical biosensors.

Long-Range Surface Plasmon-Polariton Waveguide Biosensors for Human Cardiac Troponin I Detection.

Straight long-range surface plasmon-polariton (LRSPP) waveguides as biosensors for label-free detection are discussed. The sensors consist of 5-μm-wide 35-nm-thick gold stripes embedded in a low-index optical-grade fluoropolymer (CYTOP) with fluidic channels etched to the Au surface of the stripes. This work demonstrates the application of the LRSPP biosensors for the detection of human cardiac troponin I (cTnI) protein.

Visible light driven plasmonic photochemistry on nano-textured silver.

Plasmon assisted generation of silver sulfate from dodecanethiol is demonstrated on a nano-textured silver substrate with a strong surface plasmon resonance in the visible range. The observed photo-physical processes are attributed to hot charge carriers that are generated from the excitation of surface plasmon resonances using 532 nm laser light. Excited charge carriers are responsible for cleaving the alkane chain, and for generating reactive oxygen species which rapidly photooxidize the exposed sulfur atoms.

Fermi Surface of Metallic V_{2}O_{3} from Angle-Resolved Photoemission: Mid-level Filling of e_{g}^{π} Bands.

Using angle resolved photoemission spectroscopy, we report the first band dispersions and distinct features of the bulk Fermi surface (FS) in the paramagnetic metallic phase of the prototypical metal-insulator transition material V_{2}O_{3}. Along the c axis we observe both an electron pocket and a triangular holelike FS topology, showing that both V 3d a_{1g} and e_{g}^{π} states contribute to the FS. These results challenge the existing correlation-enhanced crystal field splitting theoretical explanation for the transition mechanism and pave the way for the solution of this mystery.

Ultrafast dynamics of localized magnetic moments in the unconventional Mott insulator Sr2IrO4.

We report a time-resolved study of the ultrafast dynamics of the magnetic moments formed by the [Formula: see text] states in Sr2IrO4 by directly probing the localized iridium 5d magnetic state through resonant x-ray diffraction. Using optical pump-hard x-ray probe measurements, two relaxation time scales were determined: a fast fluence-independent relaxation is found to take place on a time scale of 1.5 ps, followed by a slower relaxation on a time scale of 500 ps-1.

Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer.

Vacuum space charge induced kinetic energy shifts of O 1s and Ru 3d core levels in femtosecond soft X-ray photoemission spectra (PES) have been studied at a free electron laser (FEL) for an oxygen layer on Ru(0001). We fully reproduced the measurements by simulating the in-vacuum expansion of the photoelectrons and demonstrate the space charge contribution of the high-order harmonics in the FEL beam. Employing the same analysis for 400 nm pump-X-ray probe PES, we can disentangle the delay dependent Ru 3d energy shifts into effects induced by space charge and by lattice heating from the femtosecond pump pulse.

Detection of leukemia markers using long-range surface plasmon waveguides functionalized with Protein G.

A novel optical biosensor based on long-range surface plasmon-polariton (LRSPP) waveguides is demonstrated for the detection of leukemia markers in patient serum using a functionalization strategy based on Protein G. The sensor consists of thin straight Au waveguides (5 μm × 35 nm × 3.2 mm) embedded in fluoropolymer CYTOP™ with a fluidic channel etched into the top cladding.

Selective detection of bacteria in urine with a long-range surface plasmon waveguide biosensor.

Experimentation demonstrates long-range surface plasmon polariton waveguides as a useful biosensor to selectively detect gram negative or gram positive bacteria in human urine having a low concentration of constituents. The biosensor can detect bacteria at concentrations of 10(5) CFU/ml, the internationally recommended threshold for diagnostic of urinary tract infection. Using a negative control urine solution of bacterial concentration 1000☓ higher than the targeted bacteria, we obtain a ratio of 5.

Atomic-Scale Perspective of Ultrafast Charge Transfer at a Dye-Semiconductor Interface.

Understanding interfacial charge-transfer processes on the atomic level is crucial to support the rational design of energy-challenge relevant systems such as solar cells, batteries, and photocatalysts. A femtosecond time-resolved core-level photoelectron spectroscopy study is performed that probes the electronic structure of the interface between ruthenium-based N3 dye molecules and ZnO nanocrystals within the first picosecond after photoexcitation and from the unique perspective of the Ru reporter atom at the center of the dye. A transient chemical shift of the Ru 3d inner-shell photolines by (2.

The Soft X-ray Research instrument at the Linac Coherent Light Source.

The Soft X-ray Research instrument provides intense ultrashort X-ray pulses in the energy range 280-2000 eV. A diverse set of experimental stations may be installed to investigate a broad range of scientific topics such as ultrafast chemistry, highly correlated materials, magnetism, surface science, and matter under extreme conditions. A brief description of the main instrument components will be given, followed by some selected scientific highlights.

Absolute pulse energy measurements of soft x-rays at the Linac Coherent Light Source.

This paper reports novel measurements of x-ray optical radiation on an absolute scale from the intense and ultra-short radiation generated in the soft x-ray regime of a free electron laser. We give a brief description of the detection principle for radiation measurements which was specifically adapted for this photon energy range. We present data characterizing the soft x-ray instrument at the Linac Coherent Light Source (LCLS) with respect to the radiant power output and transmission by using an absolute detector temporarily placed at the downstream end of the instrument.

Superconductivity. Fermi arcs in a doped pseudospin-1/2 Heisenberg antiferromagnet.

High-temperature superconductivity in cuprates arises from an electronic state that remains poorly understood. We report the observation of a related electronic state in a noncuprate material, strontium iridate (Sr2IrO4), in which the distinct cuprate fermiology is largely reproduced. Upon surface electron doping through in situ deposition of alkali-metal atoms, angle-resolved photoemission spectra of Sr2IrO4 display disconnected segments of zero-energy states, known as Fermi arcs, and a gap as large as 80 millielectron volts.

Melting of charge stripes in vibrationally driven La(1.875)Ba(0.125)CuO4: assessing the respective roles of electronic and lattice order in frustrated superconductors.

We report femtosecond resonant soft x-ray diffraction measurements of the dynamics of the charge order and of the crystal lattice in nonsuperconducting, stripe-ordered La1.875Ba0.125CuO4.

Serological diagnosis of dengue infection in blood plasma using long-range surface plasmon waveguides.

We present a compact, cost-effective, label-free, real-time biosensor based on long-range surface plasmon polariton (LRSPP) gold (Au) waveguides for the detection of dengue-specific immunoglobulin M (IgM) antibody, and we demonstrate detection in actual patient blood plasma samples. Two surface functionalization approaches are proposed and demonstrated: a dengue virus serotype 2 (DENV-2) functionalized surface to capture dengue-specific IgM antibody in blood plasma and the reverse, a blood plasma functionalized surface to capture DENV-2. The results obtained via these two surface functionalization approaches are comparable to, or of greater quality, than those collected by conventional IgM antibody capture enzyme linked immunosorbent assay (MAC-ELISA).

Selective capture of human red blood cells based on blood group using long-range surface plasmon waveguides.

An optical biosensor based on long-range surface plasmon-polariton waveguides is applied to the detection of blood group antigen A on whole erythrocytes. The biosensor consists of straight gold waveguides embedded in CYTOP with an etched fluidic channel. The gold waveguides were functionalized with immunoglobulin G against blood group A (anti-A IgG) by forming a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (16-MHA) and then conjugating the anti-A IgG through carbodiimide chemistry.

Speed limit of the insulator-metal transition in magnetite.

As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown, magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible.

Selective ultrafast probing of transient hot chemisorbed and precursor states of CO on Ru(0001).

We have studied the femtosecond dynamics following optical laser excitation of CO adsorbed on a Ru surface by monitoring changes in the occupied and unoccupied electronic structure using ultrafast soft x-ray absorption and emission. We recently reported [M. Dell'Angela et al.

Real-time manifestation of strongly coupled spin and charge order parameters in stripe-ordered La(1.75)Sr(0.25)NiO(4) nickelate crystals using time-resolved resonant x-ray diffraction.

We investigate the order parameter dynamics of the stripe-ordered nickelate, La(1.75)Sr(0.25)NiO(4), using time-resolved resonant x-ray diffraction.

Real-time observation of surface bond breaking with an x-ray laser.

We used the Linac Coherent Light Source free-electron x-ray laser to probe the electronic structure of CO molecules as their chemisorption state on Ru(0001) changes upon exciting the substrate by using a femtosecond optical laser pulse. We observed electronic structure changes that are consistent with a weakening of the CO interaction with the substrate but without notable desorption. A large fraction of the molecules (30%) was trapped in a transient precursor state that would precede desorption.

Biosensing using straight long-range surface plasmon waveguides.

Straight long-range surface plasmon waveguides are demonstrated as biosensors for the detection of cells, proteins and changes in the bulk refractive index of solutions. The sensors consist of 5 μm wide 22 nm thick Au stripes embedded in polymer (CYTOP™) with microfluidic channels etched into the top cladding. Bulk sensing is demonstrated by sequentially injecting six solutions of different refractive indices in 2 × 10(-3) RIU increments; such index steps were detected with a signal-to-noise ratio of ~1000.

Phase fluctuations and the absence of topological defects in a photo-excited charge-ordered nickelate.

The dynamics of an order parameter's amplitude and phase determines the collective behaviour of novel states emerging in complex materials. Time- and momentum-resolved pump-probe spectroscopy, by virtue of measuring material properties at atomic and electronic time scales out of equilibrium, can decouple entangled degrees of freedom by visualizing their corresponding dynamics in the time domain. Here we combine time-resolved femotosecond optical and resonant X-ray diffraction measurements on charge ordered La(1.

Temporal cross-correlation of x-ray free electron and optical lasers using soft x-ray pulse induced transient reflectivity.

The recent development of x-ray free electron lasers providing coherent, femtosecond-long pulses of high brilliance and variable energy opens new areas of scientific research in a variety of disciplines such as physics, chemistry, and biology. Pump-probe experimental techniques which observe the temporal evolution of systems after optical or x-ray pulse excitation are one of the main experimental schemes currently in use for ultrafast studies. The key challenge in these experiments is to reliably achieve temporal and spatial overlap of the x-ray and optical pulses.

The soft x-ray instrument for materials studies at the linac coherent light source x-ray free-electron laser.

The soft x-ray materials science instrument is the second operational beamline at the linac coherent light source x-ray free electron laser. The instrument operates with a photon energy range of 480-2000 eV and features a grating monochromator as well as bendable refocusing mirrors. A broad range of experimental stations may be installed to study diverse scientific topics such as: ultrafast chemistry, surface science, highly correlated electron systems, matter under extreme conditions, and laboratory astrophysics.

Femtosecond dynamics of the collinear-to-spiral antiferromagnetic phase transition in CuO.

We report on the ultrafast dynamics of magnetic order in a single crystal of CuO at a temperature of 207 K in response to strong optical excitation using femtosecond resonant x-ray diffraction. In the experiment, a femtosecond laser pulse induces a sudden, nonequilibrium increase in magnetic disorder. After a short delay ranging from 400 fs to 2 ps, we observe changes in the relative intensity of the magnetic ordering diffraction peaks that indicate a shift from a collinear commensurate phase to a spiral incommensurate phase.