ToF-S-SIMS molecular 3D analysis of micro-objects as an alternative to ion beam erosion at large depth: application to single inkjet dots

Molecular depth profiling is needed to develop high-tech materials optimised to the μm or even up to the nm scale. Recent progress in time-of-flight static secondary ion mass spectrometry (ToF-S-SIMS) offers perspectives to molecular depth profiling. However, at this moment, the methodology is not yet capable to deal with a range of materials science applications because of the limited depth range, the loss of intensity in the subsurface and the loss of depth resolution at large distances from the original surface. Therefore, the purpose of this paper is to develop a complementary approach for the molecular 3D analysis at large depth, using a combination of ultra-low angle microtomy (ULAM) and surface analysis of the sectioned material with ToF-S-SIMS. Single inkjet dots with a diameter of 100 μm and height of 22 μm on a PET substrate have been used as a test system for the methodology. It is demonstrated that the use of a diamond knife allows the molecular composition and distribution of components within the microscopic feature to be probed with a lateral resolution of 300 nm. Hence the methodology approaches the physical limit for ion imaging of organic components with local concentrations in the % range. In practice, the achievable depth resolution with ULAM-S-SIMS is ultimately limited by the surface roughness of the section. Careful optimisation of the ULAM step has resulted in a surface roughness within 6 nm (R _a value) at a depth of 21 μm. This offers perspective to achieve 3D analysis with a depth resolution as good as 18 nm at such a large distance from the surface. Furthermore, the ULAM-S-SIMS approach is applicable to materials unamenable to ion beam erosion. However, the method is limited to dealing with, for instance, Si or glass substrates that cannot be sectioned with a microtomy knife. Furthermore, sufficient adhesion between stacked layers or between the coating and substrate is required. However, it is found that the approach is applicable to a wide variety of industrially important (multi)layers of polymers on a polymer substrate.     

Synthesis of Aminopyridines and Aminopyridones by Cobalt‐Catalyzed [2+2+2] Cycloadditions Involving Yne‐Ynamides: Scope,Limitations, and Mechanistic Insights

An in‐depth study of the cobalt‐catalyzed [2+2+2] cycloaddition between yne‐ynamides and nitriles to afford aminopyridines has been carried out. About 30 nitriles exhibiting a broad range of steric demand and electronic properties have been evaluated, some of which open new perspectives in metal‐catalyzed arene formation. In particular, the use of [CpCo(CO)(dmfu)] (dmfu=dimethyl fumarate) as a precatalyst made possible the incorporation of electron‐deficient nitriles into the pyridine core. Modification of the substitution pattern at the yne‐ynamide allows the regioselectivity to be switched toward 3‐ or 4‐aminopyridines. Application of this synthetic methodology to the construction of the aminopyridone framework using a yne‐ynamide and an isocyanate was also briefly examined. DFT computations suggest that 3‐aminopyridines are formed by formal [4+2] cycloaddition between the nitrile and the intermediate cobaltacyclopentadiene, whereas 4‐aminopyridines arise from an insertion pathway.     

Self-assembling Dimeric and Trimeric Aggregates Based on Solvophobic and Charge-pairing Interactions

Self-assembly processes based on shape complementarity and noncovalent binding interactions are widely recognized as a fundamental principle in nature. Besides charge pairing and hydrogen bonding, hydrophobic interactions play a crucial role in water. Here we report the self-assembly of structurally simple monomers to yield defined dimeric and trimeric aggregates in highly polar media, based on ionic and solvophobic interactions. NMR, mass spectrometry and curve fitting were used to characterize these supramolecular assemblies in water–methanol solutions.     

Sodiation as a tool for enhancing the diagnostic value of MALDI‐TOF/TOF‐MS spectra of complex astaxanthin ester mixtures from Haematococcus pluvialis

The microalga Haematococcus pluvialis produces the pigment astaxanthin mainly in esterified form with a multitude of fatty acids, which results in a complex mixture of carotenol mono‐ and diesters. For rapid fingerprinting of these esters, matrix‐assisted laser desorption ionization time of flight mass spectrometry (MALDI‐TOF/TOF‐MS) might be an alternative to traditional chromatographic separation combined with MS. Investigation of ionization and fragmentation of astaxanthin mono‐ and diester palmitate standards in MALDI‐TOF/TOF‐MS showed that sodium adduct parent masses [M + Na]⁺ gave much simpler MS² spectra than radical / protonated [M]^+● / [M + H]⁺ parents. [M + Na]⁺ fragments yielded diagnostic polyene‐specific eliminations and fatty acid neutral losses, whereas [M]^+● / [M + H]⁺ fragmentation resulted in a multitude of non‐diagnostic daughters. For diesters, a benzonium fragment, formed by polyene elimination, was required for identification of the second fatty acid attached to the astaxanthin backbone. Parents were forced into [M + Na]⁺ ionization by addition of sodium acetate, and best signal‐to‐noise ratios were obtained in the 0.1 to 1.0 mM range. This method was applied to fingerprinting astaxanthin esters in a crude H. pluvialis extract. Prior to MALDI‐TOF/TOF‐MS, the extract was fractionated by normal phase Flash chromatography to obtain fractions enriched in mono‐ and diesters and to remove pheophytin a, which compromised monoester signals. All 12 types of all‐trans esterified esters found in LC were identified with MALDI‐TOF/TOF‐MS, with the exception of two minor monoesters. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of surface roughness and chemical composition on the wetting properties of silicon-based substrates

The article reports on the wetting properties of silicon-based materials as a function of their roughness and chemical composition. The investigated surfaces consist of hydrogen-terminated and chemically modified atomically flat crystalline silicon, porous silicon and silicon nanowires. The hydrogenated surfaces are functionalized with 1-octadecene or undecylenic acid under thermal conditions. The changes occurring upon surface functionalization are characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) spectroscopy and water contact angle measurements. By increasing the surface roughness, the static water contact angle increases. The combination of high surface roughness with chemical functionalization with water repellent coating (1-octadecene) enables reaching superhydrophobicity (water contact angle greater than 150°) for silicon nanowires.     

Single molecule study of DNA collision with elliptical nanoposts conveyed by hydrodynamics

Periodic arrays of micro‐ or nanopillars constitute solid‐state matrices with excellent properties for DNA size separation. Nanofabrication technologies offer many solutions to tailor the geometry of obstacle arrays, yet most studies have been conducted with cylinders arranged in hexagonal lattices. In this report, we investigate the dynamics of single DNA collision with elliptical nanoposts using hydrodynamic actuation. Our data show that the asymmetry of the obstacles has minor effect on unhooking dynamics, and thus confirm recent predictions obtained by Brownian dynamics simulations. In addition, we show that the disengagement dynamics are correctly predicted by models of electrophoresis, and propose that this consistency is associated to the confinement in slit‐like channels. We finally conclude that elliptical posts are expected to marginally improve the performances of separation devices.