George Chumanov

Laser Ablation of Metals: A New Method for Preparing SERS Active Colloids

Laser ablation of metals is a new and very powerful method for preparation of surface-enhanced Raman scattering (SERS) active colloids. The method is characterized by its simplicity and versatility. Stable Ag, Au, Pt, Pd, and Cu colloids are prepared by ablation of the metal for ∼10 min in water and organic solvents. An important advantage of this approach over conventional chemical procedures is that the colloids are free of organic or ionic species. Consequently, the chemical and physical effects of ions or other adsorbates can be studied under carefully controlled conditions. The SERS activity of colloidal metals prepared by laser ablation is comparable or superior to that of chemically prepared colloids.

Bioanalytical applications of SERS (surface-enhanced Raman spectroscopy)

Surface-enhanced Raman scattering (SERS) is a powerful technique for analyzing biological samples as it can rapidly and nondestructively provide chemical and, in some cases, structural information about molecules in aqueous environments. In the Raman scattering process, both visible and near-infrared (NIR) wavelengths of light can be used to induce polarization of Raman-active molecules, leading to inelastic light scattering that yields specific molecular vibrational information. The development of surface enhancement has enabled Raman scattering to be an effective tool for qualitative as well as quantitative measurements with high sensitivity and specificity. Recent advances have led to many novel applications of SERS for biological analyses, resulting in new insights for biochemistry and molecular biology, the detection of biological warfare agents, and medical diagnostics for cancer, diabetes, and other diseases. This trend article highlights many of these recent investigations and provides a brief outlook in order to assess possible future directions of SERS as a bioanalytical tool.

Low temperature epitaxial silicon film growth using high vacuum electron‐cyclotron‐resonance plasma deposition

We report on the growth technique and electrical properties of epitaxial Si films grown at low temperatures using an electron‐cyclotron‐resonance plasma deposition technique. We have used standard high vacuum apparatus to grow high quality films at 450–525 °C. A critical step in achieving high quality films is an in situ hydrogen plasma cleaning of the wafer before growth. We have systematically studied the influence of ion bombardment during growth by biasing the substrate, and find that the films are crystalline for substrate bias voltages less negative than about −15 V, but become polycrystalline as the magnitude of the negative bias is increased. The crystallinity of the film was measured using Raman spectroscopy. The undoped films are n type with carrier concentrations in the 1016–1017 cm−3 range. The Hall mobilities measured for the films are comparable to values obtained in bulk Si crystals. We can achieve abrupt profiles in carrier concentrations between the heavy doped substrate and the epilayer,...

Spectroscopic properties of Er3+ and Eu3+ doped acentric LaBO3 and GdBO3

This work studies the spectroscopic behavior of Eu3+-doped and Yb3+/Er3+-codoped single crystals of orthorhombic LaBO3 and rhombohedral GdBO3. Emissions from Er3+ at ∼1535 nm are shown to exhibit multiple narrow linewidth emissions. Luminescence from the 5D0→7F1, 7F2 transitions of Eu3+ is found to depend on the choice of LaBO3 or GdBO3 as a parent phase in a well-defined manner. Phonon sideband spectroscopy of the Eu3+ 5D2 excitation, corroborated using Raman spectroscopy, indicates that the highest energy phonon is less than 1400 cm−1 for the LaBO3 and less than 1010 cm−1 for the GdBO3. Further, absorption spectrum to 190 nm is provided for the GdBO3 clearly showing the 6I manifold, and the rarely seen 6D levels. Excitation of the 6D7/2 state at 250 nm in GdBO3 is shown to yield a strong ultraviolet emission centered at 314 nm. This work marks the lanthanide borates as candidate single crystals for active and nonlinear materials for UV, visible, and telecommunication band applications.

Silver Coated Porous Alumina as a New Substrate for Surface-Enhanced Raman Scattering

Porous alumina filters were coated by vacuum deposition with silver metal and used as substrates for surface-enhanced Raman scattering (SERS). These were studied by UV-Vis absorption spectroscopy and scanning electron microscopy. The substrates exhibit reproducible Raman enhancement for different molecules tested in this study. The mass thickness of the silver was optimized for maximal SERS signal using bipyridine as a model compound. Plasma treatment of the substrates prior to SERS measurements was identified as a crucial factor for a low background and high signal-to-noise Raman spectra. The effect of different plasma treatment conditions on the SERS signal as well as on UV-Vis absorption spectra of the substrates was investigated. After the silver deposition, the porous alumina retained its filtering abilities and could be used for preconcentrating dilute analytes on the substrate surface for SERS measurements. Corresponding tests were performed using benzotriazole and bipyridine solutions. These substrates demonstrate a potential for large-scale applications in different analytical measurements.

Solution-Processed Planar Perovskite Solar Cell Without a Hole Transport Layer

Solar cells with a structure of ITO/ZnO/CH3NH3PbI3/graphite/carbon black electrode were fabricated by spin coating at ambient conditions. PbI2 thin films were converted into CH3NH3PbI3 perovskite by reacting with CH3NH3I in solution. The incorporation of electrochemically exfoliated graphite improved the fill factor, open circuit potential and short circuit current density. The best device yielded 10.2% power conversion efficiency.

Contributions of short-range and classical electromagnetic mechanisms to surface-enhanced Raman scattering from several types of biomolecules adsorbed on cold-deposited Island films

Surface-enhanced Raman scattering (SERS) spectra of three different classes of adsorbates have been analyzed: (1) native and denatured calf thymus DNA and adenine, as examples of molecules with electronic transitions in the UV region only; (2) flavine adenine dinucleotide (FAD) and doxorubicin (DOX), as examples of chromophores with low extinction transitions in the visible region; and (3) β-carotene, as an example of a chromophore with a very high extinction coefficient for an electronic transition in the visible region. These molecules were adsorbed on silver island films that had an extinction maximum in the 450–660 nm region of the electromagnetic spectrum. The short-range mechanism of Raman enhancement has been demonstrated to contribute primarily to enhanced Raman scattering from molecules in groups 1 and 2, whereas the pure (classical) electromagnetic mechanism dominates the enhancement of β-carotene resonance Raman scattering.

Coupled planar silver nanoparticle arrays as refractive index sensors

The optical properties of plasmon coupled, planar silver nanoparticle arrays (PSNA) were studied as a function of the refractive index of the surrounding medium. The PSNA samples were fabricated by self-assembling 100 nm silver particles into a single layer on chemically modified glass substrates. The arrays exhibit an intense sharp peak in the extinction spectrum in the UV–vis spectral range originating from near-field interactions between localized surface plasmons in the nanoparticles. The spectral position of the peak appeared to be sensitive to changes in the dielectric function of the local surrounding medium. Because of this dependence, the PSNA can function as a sensor for measuring the refractive index of the host medium.

Nano-patterning with polymer brushes viasolvent-assisted polymer grafting

We report surface patterning on the nanolevel with the “grafting to” approach carried out at relatively low temperatures (40 °C). Low grafting temperatures were achieved viasolvent-assisted grafting and allowed the use of the developed approach for surface templating in a variety of ways. Specifically, two examples of the patterning are discussed. A poly-2-vinylpyridine, P2VP surface pattern was created by a combination of capillary force lithography and the solvent-assisted grafting. Silver nanoparticle arrays were created and transferred into a silicon matrix employing the P2VP pattern. Solvent-assisted grafting was also a suitable technique for manipulating thermolabile objects, e.g.proteins. Protein molecules were imprinted via the grafting. Rebinding experiments showed preferential protein adsorption onto the imprinted surface relative to a non-imprinted control sample.

Characterization of cytochurome c immobilized on modified gold and silver electrodes by surface-enhanced Raman spectroscopy

Abstract Surface-enhanced Raman scattering and surface-enhanced resonance Raman scattering spectroscopies were used to investigate the behavior of cytochrome c immobilized on the surfaces of gold and silver electrodes modified with bis (4-pyridyl) disulfide and 4-mercaptopyridine. The results are consistent with earlier models for the adsorption of cytochrome c at modified gold electrodes. At a bare silver electrode the cytochrome c is in a mixed spin state, but is in the native 6cLS state at the modified silver surface.