Tracking Invisible Transformations of Physisorbed Monolayers: LDI-TOF and MALDI-TOF Mass Spectrometry as Complements to STM Imaging
| Autor: | Chen Fang, Jian He, Matthew B. Zimmt, Russell A. Shelp |
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| Rok vydání: | 2016 |
| Předmět: |
Aryl
Polyatomic ion Analytical chemistry 02 engineering and technology Surfaces and Interfaces 010402 general chemistry 021001 nanoscience & nanotechnology Condensed Matter Physics Mass spectrometry 01 natural sciences 0104 chemical sciences law.invention chemistry.chemical_compound Crystallography chemistry Fragmentation (mass spectrometry) law Desorption Monolayer Electrochemistry Molecule General Materials Science Scanning tunneling microscope 0210 nano-technology Spectroscopy |
| Zdroj: | Langmuir : the ACS journal of surfaces and colloids. 33(2) |
| ISSN: | 1520-5827 |
| Popis: | Triphenyleneethynylene (TPEE) derivatives bearing one long aliphatic chain on each terminal aryl ring and two short aliphatic chains on the central aryl ring (core chains) self-assemble single component and 1-D patterned, two-component, crystalline monolayers at the solution-graphite interface. The monolayer morphology directs the core chains off the graphite, making them accessible for chemical reactions but invisible to imaging by scanning tunneling microscopy (STM). This precludes using STM to monitor transformations of the core chains, either by reaction or solution-monolayer exchange of TPEE molecules. Laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) successfully identifies TPEE compounds within physisorbed monolayers. The LDI-TOF spectra of TPEE monolayer-graphite samples exhibit strong molecular ion peaks and minimal fragmentation or background. LDI-TOF and STM techniques are combined to evaluate monolayer composition and morphology, track solution-monolayer exchange, to identify reaction products and to measure kinetics of chemical reactions at the solution-monolayer interface. LDI-TOF MS provides rapid qualitative evaluation of monolayer composition across a graphite substrate. Challenges to quantitative composition evaluation by LDI-TOF include compound-specific light absorption, surface desorption/ionization and fragmentation characteristics. For some, but not all, compounds, applying matrix onto a self-assembled monolayer increases molecular ion intensities and affords more accurate assessment of monolayer composition via matrix assisted laser desorption/ionization (MALDI) MS. Matrix addition precludes subsequent chemical or STM studies of the monolayer, whereas reactions and STM may be performed at nonirradiated regions following LDI-TOF measurements. LDI- and MALDI-TOF MS are useful complements to STM and are easily implemented tools for study of physisorbed monolayers. |
| Databáze: | OpenAIRE |
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