S. L. Nikiforov

On the mechanism of laser-induced desorption–ionization of organic compounds from etched silicon and carbon surfaces

The laser-induced desorption/ionization of organic compounds from etched carbon and silicon substrate surfaces was investigated. Two different etching procedures were used. Silicon surfaces were etched either by galvanostatic anodization to produce porous silicon or by a hyperthermal (∼5 eV) F-atom beam to produce nonporous silicon. Atomic force microscopy (AFM) images showed that both etching procedures yielded surfaces with sub-micrometer structures. Highly oriented pyrolytic graphite was etched with hyperthermal O atoms. A 337 nm ultraviolet (UV) laser and a 3.28 μm infrared (IR) laser were used for desorption. Analytes were deposited on the substrates either from the liquid or the gas phase. Mass spectra were obtained provided that three conditions were fulfilled. First, sufficient laser light had to be absorbed. When the IR laser was employed, a thin physisorbed solvent layer was required for sufficient laser light absorption to occur. Though the required fluence of IR and UV light differed by a fact...

On the role of defects and surface chemistry for surface-assisted laser desorption ionization from silicon

The generation of ions from silicon substrates in surface-assisted laser desorption ionization (SALDI) has been studied using silicon substrates prepared and etched by a variety of different methods. The different substrates were compared with respect to their ability to generate peptide mass spectra using standard liquid sample deposition. The desorption/ionization processes were studied using gas-phase analyte deposition. Mass spectra were obtained from compounds with gas-phase basicities above 850 kJmol and with molecular weights up to 370 Da. UV, VIS, and IR lasers were used for desorption. Ionization efficiencies were measured as a function of laser fluence and accumulated laser irradiance dose. Solvent vapors were added to the ion source and shown to result in fundamental laser-induced chemical and physical changes to the substrate surfaces. It is demonstrated that both the chemical properties of the substrate surface and the presence of a highly disordered structure with a high concentration of dangling bonds or deep gap states are required for efficient ion generation. In particular, amorphous silicon is shown to be an excellent SALDI substrate with ionization efficiencies as high as 1%, while hydrogen-passivated amorphous silicon is SALDI inactive. Based on the results, a novel model for SALDI ion generation is proposed with the following reaction steps: (1) the adsorption of neutral analyte molecules on the SALDI surface with formation of a hydrogen bond to surface Si-OH groups, (2) the electronic excitation of the substrate to form free electron/hole pairs (their relaxation results in trapped positive charges in near-surface deep gap states, causing an increase in the acidity of the Si-OH groups and proton transfer to the analyte molecules), and (3) the thermally activated dissociation of the analyte ions from the surface via a loose transition state.

The degradation of submarine permafrost and the destruction of hydrates on the shelf of east arctic seas as a potential cause of the “Methane Catastrophe”: some results of integrated studies in 2011

On the basis of the analysis of published data and in the course of the authors’ long-term geochemical and acoustic surveys performed in 1995–2011 on the East Siberian shelf (ESS) and aimed to research the role of the Arctic shelf in the processes of massive methane outbursts into the Earth’s atmosphere, some crucially new results were obtained. A number of hypotheses were proposed concerning the qualitative and quantitative characterization of the scale of this phenomenon. The ESS is a powerful supplier of methane to the atmosphere owing to the continued degradation of the submarine permafrost, which causes the destruction of gas hydrates. The emission of methane in several areas of the ESS is massive to the extent that growth in the methane concentrations in the atmosphere to values capable of causing a considerable and even catastrophic warning on the Earth is possible. The seismic data were compared to those of the drilling from ice performed first by the authors in 2011 in the southeastern part of the Laptev Sea to a depth of 65 m from the ice surface. This made it possible to reveal some new factors explaining the observed massive methane bursts out of the bottom sediments.

Gas Chromatography/Surface-Assisted Laser Desorption Ionization Mass Spectrometry of Amphetamine-like Compounds

A variety of amphetamine-like compounds were analyzed by gas chromatography/surface-assisted laser desorption ionization mass spectrometry, GC/SALDI-MS. In the SALDI method, compounds are adsorbed on a solid SALDI substrate and directly ionized from the substrate by means of a laser pulse. The interfacing of a SALDI ion source with a gas chromatograph is presented here for the first time. The end of the GC column is situated 20 mm from the silicon substrate in the vacuum of the ion source of a time-of-flight mass spectrometer, and the compounds eluted from the GC capillary are adsorbed onto the nanostructured silicon surface. The mass spectra show very low levels of background noise and no reagent ions. GC/SALDI-MS detection limits are several orders of magnitude lower than those previously reported for GC/MS analysis of amphetamine-like compounds. The extent of fragmentation is under experimental control by changing the laser fluence.

Mechanisms responsible for degradation of submarine permafrost on the eastern arctic shelf of Russia

In 2011, a marine interdisciplinary expedition on the R/V Akademik M.A. Lavrentyev was carried out in the eastern Arctic seas. The expedition was conducted within the framework of the project of targeted basic investigations under the aegis of the Russian Founda� tion for Basic Research. These investigations regis� tered intense methane blowouts related to degradation of submarine permafrost (SMPF) in these basins. The mechanisms responsible for their degradation are determined by paleogeographic factors and recent sedimentation, as well as by structural features of the Arctic region. Under continuing degradation of sub� marine permafrost, methane emission should inten� sify. This process results in the formation of significant values of both gas and water, which migrate upward through the sedimentary section of the shelf and along the bedding surfaces from coastal heated areas to colder deeper parts of the basins forming subhorizon� tal convective cells, thus, stimulating permafrost deg� radation even under negative bottom temperatures. Submarine permafrost rocks are widespread mostly on the shelf in the eastern sector of the Russian Arctic region. This is explained by the peculiar paleogeo� graphic development of the region: due to the absence of the ice shield during the Quaternary glacial epochs, the shelf was dominated by subaerial settings with low temperatures. Alternation of subaerial and marine environments on the shelf resulted in the formation of a stratified sedimentary sequence. The regressive cycles (cooling epochs) were accompanied by intense frosting of the primary surface and formation of com� pact dehydrated members (for example, during the last Late Quaternary regression). On the contrary, the transgressive cycles (warming epochs) were marked by accumulation of unconsolidated sediments. In these periods, stable negative temperatures of the bottom water favored conservation of the stratified structure in the sedimentary section [1, 2].

Determination of rhenium and osmium complexes by surface-assisted laser desorption/ionization coupled to Orbitrap mass analyzer

AbstractA surface-assisted laser desorption/ionization (SALDI) source is coupled to the Orbitrap mass analyzer; the instrumental approach is tested for the analysis of rhenium (Re) and osmium (Os) complexes with 8-mercaptoquinoline. Silicon (Si) material obtained by laser treatment of monocrystalline Si is used as SALDI substrate. All studied complexes are detected as radical cations, with no protonated molecules. The comparison of SALDI, matrix-assisted laser desorption/ionization (MALDI), and direct laser desorption/ionization (LDI) on metal plates in the same instrumental setup demonstrated that the detection of the studied complexes using SALDI provides the highest sensitivity. The ability to analyze samples rapidly, high purity of spectra, and good analytical parameters make SALDI coupled to the Orbitrap mass analyzer a potentially powerful tool for the detection of Re and Os complexes and related organic, UV-absorbing compounds.n Figureᅟ

Surface‐assisted laser desorption/ionization mass spectrometry with a rotating ball interface

A rotating ball interface for surface-assisted laser desorption/ionization (SALDI) mass spectrometry was designed and tested. One side of the ball was exposed to atmospheric pressure and the other to the vacuum in a time-of-flight mass spectrometer. Analytes (arginine, atenolol, reserpine, tofisopam, and chloropyramine) were applied using electrospray to a silicon substrate on the atmospheric side, the ball was rotated 180°, and the analyte was desorbed on the vacuum side using a pulsed, 200u2009Hz, 355u2009nm laser. In order to increase the desorption area, the laser focus was scanned over the substrate in a raster pattern repeated once every second. The design allows for rapid sample throughout with a sample turn-around time as short as 5u2009s. Newly produced porous silicon substrates initially yielded very low ion signals, and they required several hundred laser shots to attain maximum sensitivity. In contrast, amorphous silicon did not require such activation. Quantitative analysis showed a sample-to-sample reproducibility of about 10%. The sensitivities with model analytes were in the 1000 to 10,000 ions/fmole range and detection limits in the low fg range.

Sea-ice ploughmarks in the eastern Laptev Sea, East Siberian Arctic shelf

One of the major observations during marine interdisciplinary expeditions in 2011 and 2012 on the RV Akademik M.A. Lavrentyev and RV Viktor Buinitskii was the occurrence of a large number of ice scours in the East Siberian Arctic shelf (Lobkovsky et al. 2013). The scours vary in size, depth, spatial arrangement and age of generation. Maximum water depth for sea-ice ploughing of the shallow continental shelf depends on sea-ice ridge keel depth (Ogorodov 2011). Linear and curvilinear scours on the floor of the eastern Laptev Sea shelf at water depths ≤40 m are interpreted here as ploughmarks generated by sea-ice pressure ridges (Fig. 1). Ice ploughmarks in the Laptev Sea were first discovered in 1970 during the East Siberian Arctic shelf transect by US Navy nuclear submarine USS Queenfish (McLaren 2008).nnnn Fig. 1. nSea-ice ploughmarks on the eastern Laptev Sea continental shelf. ( a ) General bathymetric map of the study area from digitized navigation charts (Nikiforov et al. 2004). ( b ) Location of study area (red box; map from IBCAO v. 3.0). ( c , e , f , i ) Side-scan sonar sonographs of sea-ice …

Gas extraction and degradation of the submarine permafrost rocks on the Laptev Sea shelf

In 2011 and 2012, the interdisciplinary oceanic cruises of the R/V Akademik M.A. Lavrent’ev and R/V Viktor Buinitskii were conducted in the framework of the project of targeted basic research of the Russian Foundation for Basic Research. These studies identified strong methane jets because of the degradation of submarine permafrost rocks (SPRs), which is related to paleogeographical and modern factors of formation of the upper sedimentary sequence and also to structural peculiarities of the Arctic region. Large gas and water volumes are formed at the expense of the SPR defrosting; move along the upper sedimentary shelf sequence and along the surface of one or another layer (from coastal warmed areas to cooler deep areas); and form horizontally elongated convective cells, which activates destruction even at negative bottom temperatures. The methane emission will increase and become massive during the continuing SPR degradation.

General forecast of the evolution of the coastal zone of the Eurasian Arctic seas in the 21st century

Principal regularities of the evolution of the Arctic coasts of Eurasia in the 21st century related to the climate warming and sea level rise are assessed. It is stated that the most significant changes may be expected in the most ice-covered seas of the Arctic Ocean, where the area of the ice cover may significantly decrease while the duration of the ice-free periods will grow. Thermoabrasive coasts will be the most subjected to the changes; the rate of their recession will increase 1.5–2.5 fold. The further development of accumulative coasts in the Arctic seas will proceed against the background of a transgression; meanwhile, in the 21st century, one can expect no catastrophic changes such as washing away of coastal accumulative features.