E. A. Schweikert

Calcium Phosphate Phase Identification Using XPS and Time-of-Flight Cluster SIMS

Reproducible time-of-flight cluster static secondary ion mass spectra (ToF-SSIMS) were obtained for various standard calcium phosphate (CP) powders, which allowed for phase identification. X-ray diffraction was not able to detect signals from microscopic amounts of CP (∼15 mmol m(-)(2)). The phases studied were α-tricalcium phosphate [α-Ca(3)(PO(4))(2)], β-tricalcium phosphate [β-Ca(3)(PO(4))(2)], amorphous calcium phosphate [Ca(3)(PO(4))(2)·xH(2)O], octacalcium phosphate [Ca(8)H(2)(PO(4))(6)·H(2)O], brushite (CaHPO(4)·2H(2)O), and hydroxyapatite [Ca(10)(PO(4))(6)(OH)(2)]. The SIMS spectra were obtained via bombardment with (CsI)Cs(+) projectiles. X-ray photoelectron spectroscopy (XPS) core levels of the P 2p, Ca 2p, and O 1s orbitals and the relative O 1s loss intensity were examined. The PO(3)(-)/PO(2)(-) ratios from ToF-SSIMS spectra in conjunction with XPS of the CP powders showed much promise in differentiating between these phases at microscopic CP coverages on the metal oxide surface.

Impact of slow gold clusters on various solids: nonlinear effects in secondary ion emission

Abstract A liquid metal ion source (LMIS) has been installed on a pulsed ion gun built at the IPN. The time of flight (TOF) spectra of the pulsed beam were recorded. With the gold source several cluster ions (up to 10 atoms in the cluster) and doubly charged ions were identified in the ion beam TOF spectra. With a second pulsation, single cluster ions can be selected as projectiles for secondary ion TOF mass spectrometry. We have studied the secondary ion emission (SIE) induced by cluster impact from a variety of targets: organic, CsI, metallic. A large enhancement of yield is observed by comparison to single atomic ion impact (e.g. factor of 30 between Au 3 + and Au + ). The secondary ion yields increase strongly with the number of constituents in the cluster. This effect is not linear. A comparison with other types of clusters and also fission fragments of 252 Cf has been performed. The rate of secondary emission stimulated by cluster is similar to SI yield induced by fission fragments.

Nanoscopic Cylindrical Dual Concentric and Lengthwise Block Brush Terpolymers as Covalent Preassembled High-Resolution and High-Sensitivity Negative-Tone Photoresist Materials

We describe a high-resolution, high-sensitivity negative-tone photoresist technique that relies on bottom-up preassembly of differential polymer components within cylindrical polymer brush architectures that are designed to align vertically on a substrate and allow for top-down single-molecule line-width imaging. By applying cylindrical diblock brush terpolymers (DBTs) with a high degree of control over the synthetic chemistry, we achieved large areas of vertical alignment of the polymers within thin films without the need for supramolecular assembly processes, as required for linear block copolymer lithography. The specially designed chemical compositions and tuned concentric and lengthwise dimensions of the DBTs enabled high-sensitivity electron-beam lithography of patterns with widths of only a few DBTs (sub-30 nm line-width resolution). The high sensitivity of the brush polymer resists further facilitated the generation of latent images without postexposure baking, providing a practical approach for controlling acid reaction/diffusion processes in photolithography.

Micropatterning of Proteins and Mammalian Cells on Indium Tin Oxide

This paper describes a novel surface engineering approach that combines oxygen plasma treatment and electrochemical activation to create micropatterned cocultures on indium tin oxide (ITO) substrates. In this approach, photoresist was patterned onto an ITO substrate modified with poly(ethylene) glycol (PEG) silane. The photoresist served as a stencil during exposure of the surface to oxygen plasma. Upon incubation with collagen (I) solution and removal of the photoresist, the ITO substrate contained collagen regions surrounded by nonfouling PEG silane. Chemical analysis carried out with time-of-flight secondary ion mass spectrometry (ToF-SIMS) at different stages in micropatterned construction verified removal of PEG-silane during oxygen plasma and presence of collagen and PEG molecules on the same surface. Imaging ellipsometry and atomic force microscopy (AFM) were employed to further investigate micropatterned ITO surfaces. Biological application of this micropatterning strategy was demonstrated through selective attachment of mammalian cells on the ITO substrate. Importantly, after seeding the first cell type, the ITO surfaces could be activated by applying negative voltage (-1.4 V vs Ag/AgCl). This resulted in removal of nonfouling PEG layer and allowed to attach another cell type onto the same surface and to create micropatterned cocultures. Micropatterned cocultures of primary hepatocytes and fibroblasts created by this strategy remained functional after 9 days as verified by analysis of hepatic albumin. The novel surface engineering strategy described here may be used to pattern multiple cell types on an optically transparent and conductive substrate and is envisioned to have applications in tissue engineering and biosensing.

Charged particle activation of medium Z elements

Excitation functions for proton energies up to 20 MeV have been measured for65Cu(p, n)65Zn; Sn (p, xn)115Sb,116mSb,117Sb,118mSb; Mo (p, xn)94Tc; Te (p, xn)121I,123I,128I,130I; Pd (p, xn)104Ag; Cd (p, xn)109In,110mIn,113mIn; Cs (p, xn)133mBa. The precision of the measurements (overall error estimated at ≤20%) and the conditions for interference-free detection of these elements at trace levels are also discussed.

Noradrenaline-functionalized hyperbranched fluoropolymer-poly(ethylene glycol) cross-linked networks as dual-mode, anti-biofouling coatings.

The strategy of decorating antibiofouling hyperbranched fluoropolymer-poly(ethylene glycol) (HBFP-PEG) networks with a settlement sensory deterrent, noradrenaline (NA), and the results of biofouling assays are presented. This example of a dual-mode surface, which combines both passive and active modes of antibiofouling, works in synergy to improve the overall antibiofouling efficiency against barnacle cyprids. The HBFP-PEG polymer surface, prior to modification with NA, was analyzed by atomic force microscopy, and a significant distribution of topographical features was observed, with a nanoscopic roughness measurement of 110 ± 8 nm. NA attachment to the surface was probed by secondary ion mass spectrometry to quantify the extent of polymer chain-end substitution with NA, where a 3- to 4-fold increase in intensity for a fragment ion associated with NA was observed and 39% of the available sites for attachment were substituted. Cytoskeletal assays confirmed the activity of tethered NA on adhering oyster hemocytes. Settlement assays showed deterrence toward barnacle cyprid settlement, while not compromising the passive biofouling resistance of the surface. This robust strategy demonstrates a methodology for the incorporation of actively antibiofouling moieties onto a passively antibiofouling network.

Kiloelectron volt cluster impacts: prospects for cluster-SIMS

Abstract This paper describes part of our continuing efforts in examining the ability of polyatomic or ‘cluster’ projectiles to improve secondary ion yields in SIMS. Negative secondary ion yields resulting from keV bombardment of lanthanum and bismuth oxide projectiles (composition (M2O3)mMO+) were measured and compared for both organic and inorganic targets. Each metal oxide projectile produces an increase in secondary ion yield when compared to the same number of Cs+ projectiles at similar energies. In addition, the nonlinear increase in secondary ion yield per number of constituent atoms in the primary ion is compared for polyatomic projectiles within a given metal oxide series. The high secondary ion yields combined with efficient time-of-flight mass analysis translate into prospects for SIMS under ‘superstatic’ conditions, which should be particularly attractive for the detection of organics. In considering analytical applications it must be recognized that when a projectile becomes more efficient at ejecting molecular or quasimolecular ions (intact emission), it may also become more efficient at ‘manufacturing’ ions (recombination processes). Moreover, the number of molecules destroyed per analyte-specific secondary ions detected varies with projectile characteristics. The challenge for the practice of ‘cluster-SIMS’ is to optimize the projectiles for maximizing sensitivity and eventually limit-of-detection.

Methodology and application of the nuclear resonance reaction 16O(α, α)16O for the profiling of titanium oxide

Abstract A method is presented for the application of the 16 O(α,α) 16 O resonance at 3.045 MeV to the depth profiling of oxide films. The resonance yield is translated into oxygen to metal stoichiometry as a function of the depth probed. The method is applied to anodic titanium oxide films grown in the absence and presence of tungsten anions. The oxygen depth profile is then utilized to obtain the profile of the dopants (W) incorporated in the oxide. A depth resolution of 6 μg/cm is achieved. The incorporation of tungsten anions of the order of 2 at.%, evaluated from the RBS yields, precludes the establishment of a constant oxygen to metal stoichiometry in the doped film. The tungsten atomic fractions have an estimated error of 5%.

Targeted surface nanocomplexity: two-dimensional control over the composition, physical properties and anti-biofouling performance of hyperbranched fluoropolymer–poly(ethylene glycol) amphiphilic crosslinked networks

A two-dimensional array of amphiphilic crosslinked networks was prepared by systematic alteration of both the composition of hyperbranched fluoropolymers (HBFPs) and the relative stoichiometries upon crosslinking with poly(ethylene glycol) (PEG). Results of physicochemical, mechanical, surface and biofouling assessment are described in full. The materials were designed to present complex surface topographies, morphologies, and chemical features over nano- and microscopic dimensions to explicitly inhibit microorganism settlement and adhesion. A multi-dimensional, tunable matrix was generated to understand and optimize the composition–structure–property relationships. The thermal properties of the crosslinked networks were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), where the onset of thermal degradation, overall thermal stability and phase transition temperatures could be controlled based on the formulation. Investigation of the mechanical properties of the coatings in the water-swollen state found that the Youngs modulus, ranging between 10.0 and 121 MPa, was dependent on both the wt% of PEG crosslinker and chemical composition of the HBFP. This result, on average, gives Youngs moduli an order of magnitude larger than that previously reported for HBFP–PEG networks. Use of atomic force microscopy (AFM) provided insight into the nanoscale topography of the networks. Interestingly, it was observed that for all networks, surface roughness increased with water swelling going from an average of 115 ± 49 nm (dry) to 214 ± 106 nm (swelled) RMS roughness. Probing the surface chemistry by optical tensiometry revealed an increase in the static water contact angle by as much as 40° after water swelling. These two findings display a counter-intuitive increase of the surface hydrophobicity. Secondary ion mass spectrometry (SIMS) confirmed migration of hydrophobic fluorocarbon units to the surface by quantifying a 24% increase in fluorine species ejected from a dry versus water-swollen surface. Selected formulations of HBFP–PEG that demonstrated complex surface features and an overall high mechanical strength were tested in biological assays and all surfaces (3 formulations × 12 replicates) completely resisted the settlement of barnacle cyprids (Balanus amphitrite). Diatoms (Navicula incerta) were two- to three-times more easily removed from the HBFP–PEG surfaces compared to a homogeneous polydimethylsiloxane elastomer (PDMSe) standard surface. In contrast, algal spores (Ulva linza) were able to colonize the surfaces and were more difficult to remove in comparison to the PDMSe standard, pointing to the challenges associated with the development of a single material that is capable of broad anti-biofouling performance.

Compact time‐of‐flight mass spectrometer using particle‐induced desorption

This paper describes the design and operation of a time‐of‐flight mass spectrometer that uses fast, heavy ions from the spontaneous fission of Cf‐252 to desorb species from the surfaces of solids. The technique provides for a simultaneous, multimass, isotope specific, elemental, and molecular surface characterization without complications due to surface charging.