Dynamic strain in gold nanoparticle supported graphene induced by focused laser irradiation

Graphene on noble-metal nanostructures constitutes an attractive nanocomposite with possible applications in sensors or energy conversion. In this work we study the properties of hybrid graphene/gold nanoparticle structures by Raman spectroscopy and Scanning Probe Methods. The nanoparticles (NPs) were prepared by local annealing of gold thin films using focused laser beam. The method resulted in a patterned surface, with NPs formed at arbitrarily chosen microscale areas. Graphene grown by chemical vapour deposition was transferred onto the prepared, closely spaced gold NPs. While we found that successive higher intensity (6 mW) laser irradiation increased gradually the doping and the defect concentration in SiO2 supported graphene, the same irradiation procedure did not induce such irreversible effects in the graphene supported by gold NPs. Moreover, the laser irradiation induced dynamic hydrostatic strain in the graphene on Au NPs, which turned out to be completely reversible. These results can have implications in the development of graphene/plasmonic nanoparticle based high temperature sensors operating in dynamic regimes

Lantanida(III) dietiléntriamin-pentaacetát származékokkal képződő komplexek ligandumcsere reakcióinak kinetikája. A nemkovalens kölcsönhatások szerepe. = Kinetics of ligand exchange reactions of lanthanide(III) complexes formed with the derivatives of diethylenetriaminepentaacetate. The role of non-covalent interactions.

Hidrofób csoportot tartalmazó Gd3+-komplexek és beta-ciklodextrin vagy fehérjék nem-kovalens kölcsönhatása növeli a relaxivitást, de a komplexek stabilitását, inertségét csak kismértékben befolyásolja. A Gd(DTPA), Gd(BOPTA) és Gd(DTPA-BMA) komplexek (GdL) és a TTHA közötti ligandumcsere másodrendű reakcióként megy végbe. A GdL komplexek és Cu2+ vagy Zn2+ közötti fémioncsere reakciók citrát, foszfát, karbonát és hisztidinát jelenlétében a komplexek endogén ligandumok által segített disszociációjával folynak le. A Gd(DTPA-BMA) ligandumcsere és fémioncsere reakciói a gyorsabb intramolekuláris átrendeződések miatt sokkal gyorsabbak, mint a Gd(DTPA) és Gd(BOPTA) komplexeké. A nyolcfunkciós BCAED és BCAEP ligandumok Ln3+ komplexei logKLnL értékei nagymértékben nőnek a La-tól a Lu-ig. A Sm(EDTMP) és Ho(EDTMP) stabilitási állandói nagyok, de a fémcsere reakcióik Cu2+-citráttal gyorsan végbemennek pH 7 – 9 között a komplex proton katalizált disszociációjával. A makrociklusos DO2A2P ligandum Ln3+-komplexeinek sajátosságai (stabilitás, szerkezet, képződés és disszociáció sebesség) a Ln(DOTA) és Ln(DOTP) hasonló sajátosságai közötti értéküek. | The non-covalent interaction between the Gd3+-complexes, containing hydrophobic groups, and beta-cyclodextrin or proteins result in the increase of the relaxivities, but the stability constants and the kinetic inertness of complexes is only slightly influenced. The ligand exchange between the Gd(DTPA), Gd(BOPTA) and Gd(DTPA-BMA) complexes (GdL) and TTHA occurs in second order reactions. The metal exchange reactions between the GdL complexes and Cu2+ or Zn2+, in the presence of citrate, phosphate, carbonate and histidinate, take place with the dissociation of complexes, assisted by the endogenous ligands. The ligand and metal exchange reactions of Gd(DTPA-BMA) are much faster than those of the Gd(DTPA) and Gd(BOPTA), because the intramolecular rearrangements in Gd(DTPA-BMA) are faster. The logKLnL values obtained for the Ln3+-complexes of the octadentate BCAED and BCAEP ligands increase to a great extent from La to Lu. In spite of the high stability constants of Sm(EDTMP) and Ho(EDTMP), their exchange reactions with Cu2+-citrate are fast and occur with the proton assisted dissociation of complexes in the pH range 7 – 9. The properties of the macrocyclic Ln(DO2A2P) complexes (stability, structure, formation and dissociation rates) were found to be amongst the similar properties of Gd(DOTA) and Gd(DOTP)

Determination of the STM tip-graphene repulsive forces by comparative STM and AFM measurements on suspended graphene

Graphene grown by chemical vapour deposition is transferred on top of flat gold nanoislands and characterized by scanning tunnelling microscopy (STM) and atomic force microscopy (AFM). Graphene bubbles are formed with lateral dimensions determined by the size and shape of nanoislands. These graphene bubbles can be squeezed during STM imaging using bias voltages of less than 250 mV and tunnelling currents of 1 nA. Similarly, the graphene suspended over gold nanovoids is deflected 4-5 nm by the STM tip when imaging at low bias voltages (U = 30 mV). Nanoindentation measurements performed by AFM show that the squeezing of graphene bubbles occurs at repulsive forces of 20-35 nN, and such forces can result in deflections of several nanometres in suspended graphene parts, respectively. Comparing the AFM and STM results, this study reveals that mechanical forces of the order of 10-8 N occur between the STM tip and graphene under ambient imaging conditions and typical tunnelling parameters

Novel graphene/Sn and graphene/SnOx hybrid nanostructures: Induced superconductivity and band gaps revealed by scanning probe measurements

Abstract The development of functional composite nanomaterials based on graphene and metal nanoparticles (NPs) is currently the subject of intense research interest. In this study we report the preparation of novel type of graphene/Sn and graphene/SnOx (1 ≤ x ≤ 2) hybrid nanostructures and their investigation by scanning probe methods. First, we prepare Sn NPs by evaporating 7–8 nm tin on highly oriented pyrolytic graphite substrates. Graphene/Sn nanostructures are obtained by transferring graphene on top of the tin NPs immediately after evaporation. We show by scanning tunnelling microscopy (STM) and spectroscopy (STS) that tin NPs reduce significantly the environmental p-type doping of graphene. Furthermore, we demonstrate by low-temperature STM and STS measurements that superconductivity is induced in graphene, either directly supported by Sn NPs or suspended between them. Additionally, we prepare SnOx NPs by annealing the evaporated tin at 500 °C. STS measurements performed on hybrid graphene/SnOx nanostructures reveal the electronic band gap of SnOx NPs. The results can open new avenues for the fabrication of novel hybrid superconducting nanomaterials with designed structures and morphologies

Graphene-Encapsulated Silver Nanoparticles for Plasmonic Vapor Sensing

Graphene-covered silver nanoparticles were prepared directly on highly oriented pyrolytic graphite substrates and characterized by atomic force microscopy. UV-Vis reflectance spectroscopy was used to measure the shift in the local surface plasmon resonance (LSPR) upon exposure to acetone, ethanol, 2-propanol, toluene, and water vapor. The optical responses were found to be substance-specific, as also demonstrated by principal component analysis. Point defects were introduced in the structure of the graphene overlayer by O-2 plasma. The LSPR was affected by the plasma treatment, but it was completely recovered using subsequent annealing. It was found that the presence of defects increased the response for toluene and water while decreasing it for acetone