SAM characterization

In many respects gold is more convenient than sihcon for characterizing polymer brush films. For instance, the RAIR spectra from planar gold are usually superior to that from sihcon wafers, especially for the SAM characterization. In addition, the S - Au bond is easily cleaved by treatment in a dilute solution of iodine. This allows for the isolation of the tethered polymer and the determination of Mn and PDI. The SAMs are easily deposited from dilute solutions of thiol or disulfide precursors. The only major disadvantage to gold is the instability of the weak S - Au bond, which is unstable above 60 °C, and imder UV irradiation in air. 

SAM Characterization. TDS and XPS were performed in a UHV chamber with a base pressure of 10 10 mbar. The apparatus is equipped with a x-ray photoelectron spectrometer (Leybold Heraues, EA 10/100), a quadrupole mass spectrometer (Balzers QMA 400) with a mass range from 1 to 500, and an Ar+-sputter gun. For TDS the sample was mounted on a steel plate, which can be heated by tantalum wires spot welded on the backside of the plate [12], AFM was performed ex situ using a Nanosurf Easy scan 2 scanning probe microscope in tapping mode. 

Scanning Auger microscopy (SAM) (characterization) A scanning surface analytical technique that uses an electron beam as the sampling probe and Auger electrons as the detected species to give the composition of the surface. See also Auger electron spectroscopy (AES). 

Gu Y, Akhremitchev B B, Waiker G C and Waideck D H 1999 Structurai characterization and eiectron tunneiing at n-Si/Si02/SAM/iiquid interface J. Phys. Chem. B 103 5220-6... 

Laser ionization mass spectrometry or laser microprobing (LIMS) is a microanalyt-ical technique used to rapidly characterize the elemental and, sometimes, molecular composition of materials. It is based on the ability of short high-power laser pulses (-10 ns) to produce ions from solids. The ions formed in these brief pulses are analyzed using a time-of-flight mass spectrometer. The quasi-simultaneous collection of all ion masses allows the survey analysis of unknown materials. The main applications of LIMS are in failure analysis, where chemical differences between a contaminated sample and a control need to be rapidly assessed. The ability to focus the laser beam to a diameter of approximately 1 mm permits the application of this technique to the characterization of small features, for example, in integrated circuits. The LIMS detection limits for many elements are close to 10 at/cm, which makes this technique considerably more sensitive than other survey microan-alytical techniques, such as Auger Electron Spectroscopy (AES) or Electron Probe Microanalysis (EPMA). Additionally, LIMS can be used to analyze insulating sam-... 

The acoustic microscopy s primary application to date has been for failure analysis in the multibillion-dollar microelectronics industry. The technique is especially sensitive to variations in the elastic properties of semiconductor materials, such as air gaps. SAM enables nondestructive internal inspection of plastic integrated-circuit (IC) packages, and, more recently, it has provided a tool for characterizing packaging processes such as die attachment and encapsulation. Even as ICs continue to shrink, their die size becomes larger because of added functionality in fact, devices measuring as much as 1 cm across are now common. And as die sizes increase, cracks and delaminations become more likely at the various interfaces. 

For analytical applications it is important to realize that three distributions are involved, namely one that describes the measurement process, one that brings in the sampling error, and another that characterizes the sam-... 

Protsailo, L.V., Fawcett, W.R., Russell, D. and Meyer, R.L. (2002) Electrochemical Characterization of the Alkaneselenol-Based SAMs on Au(lll) Single Crystal Electrode. Langmuir, 18, 9342-9349. 

Relatively little work has been done on ORR catalysis by self-assembled mono-layers (SAMs) of metalloporphyrins. The advantages of this approach include a much better defined morphology, structure, and composition of the catalytic film, and the surface coverage, and the capacity to control the rate at which the electrons ate transferred from the electrode to the catalysts [CoUman et al., 2007b Hutchison et al., 1993]. These attributes are important for deriving the catal5d ic mechatfism. The use of optically transparent electrodes aUows characterization of the chemical... 

The possibility that many organic compounds could potentially be precursors of ethylene was raised, but direct evidence that in apple fruit tissue ethylene derives only from carbons of methionine was provided by Lieberman and was confirmed for other plant species. The pathway of ethylene biosynthesis has been well characterized during the last three decades. The major breakthrough came from the work of Yang and Hoffman, who established 5-adenosyl-L-methionine (SAM) as the precursor of ethylene in higher plants. The key enzyme in ethylene biosynthesis 1-aminocyclopropane-l-carboxylate synthase (S-adenosyl-L-methionine methylthioadenosine lyase, EC 4.4.1.14 ACS) catalyzes the conversion of SAM to 1-aminocyclopropane-l-carboxylic acid (ACC) and then ACC is converted to ethylene by 1-aminocyclopropane-l-carboxylate oxidase (ACO) (Scheme 1). 

Sofia HJ, Chen G, Hetzler BG, et al. 2001. Radical SAM, a novel protein superfanuly linking unresolved steps in familiar biosynthetic pathways with radical mechanisms functional characterization using new analysis and information visualization methods. Nucleic Acids Res 29 1097-106. 

A number of methods are available for the characterization and examination of SAMs as well as for the observation of the reactions with the immobilized biomolecules. Only some of these methods are mentioned briefly here. These include surface plasmon resonance (SPR) [46], quartz crystal microbalance (QCM) [47,48], ellipsometry [12,49], contact angle measurement [50], infrared spectroscopy (FT-IR) [51,52], Raman spectroscopy [53], scanning tunneling microscopy (STM) [54], atomic force microscopy (AFM) [55,56], sum frequency spectroscopy. X-ray photoelectron spectroscopy (XPS) [57, 58], surface acoustic wave and acoustic plate mode devices, confocal imaging and optical microscopy, low-angle X-ray reflectometry, electrochemical methods [59] and Raster electron microscopy [60]. 

Elemental maps obtained using an ion microprobe will be highly surface specific as in SAM. However, since ion sputtering is destructive, repeated scans over the field of particles will penetrate deeper and deeper into the particle interiors. McHugh and Stevens have demonstrated the utility of IMP elemental maps in the identification and chemical characterization of oil soot particles in the atmosphere (38). 

Lysine methyltransferases catalyze the transfer of methyl groups from the cosubstrate SAM to certain lysine residues in histone proteins. To characterize modulators of these transferases, the above-mentioned antibody-based assay protocols are also applicable. 

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