AVS 66 Session AS-ThP: Applied Surface Science Poster Session

Hydrogen is frequently employed as a backfill gas during various vacuum coating processes involving metals. Hydrogen plays several roles and provides multiple benefits:

- As a carrier gas and diluent for active gases used to modify substrate surfaces

- As a cleaning and protective agent to clean deposition surfaces and prevent oxidation at high temperatures

- High purity hydrogen is relatively inexpensive, safe and effective in this application when used properly

The major challenge with hydrogen is the storage of hydrogen often required to have a source of pure hydrogen gas. Hydrogen gas for small and medium scale applications is generally delivered from far-away generating facilities and stored at the customer's site in the form of a compressed gas. Storage of hydrogen is closely controlled by national and international code guidelines and local Authorities Having Jurisdiction.

Proton Exchange Membrane (PEM fuel cell technology) hydrogen generation makes it possible to generate hydrogen at production rates and purity levels suitable for scientific and production applications. Most importantly, PEM hydrogen generation produces pure, pressurized, dry hydrogen in a load-following fashion without the need for hydrogen storage.

Poster will outline the code and cost advantages that PEM hydrogen generation can provide for scientific and production hydrogen use in vacuum applications.

The unique properties of poly(dimethylsiloxane), also known as PDMS or silicone, have allowed PDMS-based materials to proliferate in modern industry. A huge variety of applications using PDMS have been developed including structural adhesives, release agents, optical components, lubricants, anti-foam agents, and potting agents to name a few. Considering the omnipresence of PDMS in industrial settings along with its low surface energy and tendency to migrate, it comes as no surprise that PDMS is frequently encountered in industrial surface analysis laboratories. Because PDMS is readily detected and easily recognized by its characteristic fragmentation pattern, SIMS is well suited to identifying the presence of silicones on a wide range of materials.

Over the years we have observed variation in the fragmentation patterns and relative intensities of characteristic ions in the SIMS spectra from assorted PDMS-containing materials, however, the structural details that may influence the observed spectra remain poorly understood. In the past, we confirmed that endgroup type and molecular weight of PDMS fluids have a systematic influence on negative ion spectra. In addition, we determined that substrate type and thickness of the PDMS layer also greatly influence the spectra obtained, allowing us to hypothesize that the differing energy distributions and collisional cascades within the films and substrates strongly influence ion yields [1].

Using well-characterized PDMS reference materials spin-coated on a variety of substrates, the effects of cluster ion versus monoatomic ion sputtering will be presented as an extension of our past work. In addition, we previously demonstrated that spectra from a particular PDMS fluid became independent of substrate type as film thickness increased beyond the penetration depth of the primary ions, while current work further explores the sub-monolayer regime. Lastly, using thin films of various PDMS mixtures, investigation of potential layering of PDMS as a function of molecular weight or endgroup type will be presented.

[1] Vlasak, P.R.; Pacholski, M.L. (2018, October) Differentiating Silicones Using SIMS; presented at AVS 65^th International Symposium & Exhibition, Long Beach, CA.

This work presents the surface texturing of the horizontal wall of silicon micro-channels (SiMCs) using the NH4OH solution. The micro-channels are obtained on the backside of Si substrates, where the solar cells are fabricated. The micro-channels are used as heat sinks through which fluid will flow, such as water or alcohol. The texturing results in the micro-channels with roughness (in micro-pyramid shape) on horizontal surface. The roughness assists in the dilution of bubbles that can occur inside the fluid, because if the bubble excess occurs into the fluid, this can difficult the transport into the SiMC. The texturing is based on the formation of micro-pyramids with the use of NH4OH (ammonium hydroxide) alkaline solution etching, which is anisotropic. Our NH4OH solution etching can control the size of micro-pyramids on the surface into the SiMC This occurs because the etch rates are different for three [100], [110] and [111] Si crystal planes. The Si etching is due to the presence of the OH- (hydroxyl) in the NH4OH solution that reacts with Si. The micro-pyramids occurs because the (100) mono-crystalline substrates have a lower Si surface density of the plane than the (110) plane. The difference in density causes the etch rate for (100) plane to be greater than (110), which in turn, is greater than for (111). Thus, since it is a surface with lower density is easier penetration of the solution, which facilitates the Si reaction with hydroxyl (OH -). Anisotropic etching is obtained by alkaline solution of monocrystalline Si substrate, with (100) surface orientation. Exposure of [111] crystal plans occurred, forming the micro-pyramids. The obtained values of micro-pyramid height of 770 nm and 920 nm, when compared with a desired micro-channel depth of 200 µm, represent a ratio (between roughness and channel depth) lower than 5%. This ratio is considered suitable to reduce a significant impact on micro-channel performances.

Titanium alloys possess many excellent characteristics (corrosion resistance, high fatigue strength and high strength-to-weight ratio) that has led to many important applications in several field (aerospace, bioengineering, automotive, etc.). However, these same alloys have only limited use as tribological materials due to abrasion and adhesion resistance. We previously investigated the use of oxygen-diffused Ti64 (OD-Ti64) and found that, in dry sliding conditions, the oxygen diffusion treatment improved the wear resistance compared to untreated Ti64. OD-Ti64 performed better than untreated Ti64, with respect to wear resistance when a lubricant containing ZDDP because of the formation of a ZDDP-based protective triobfilm.

This study extends these previous investigations by evaluating the use of ionic liquids (ILs) as oil additives to lubricate oxygen-diffusion (OD) case-hardened titanium for improved friction and wear behavior. A base oil for boundary lubrication of an OD-treated Ti-6Al-4V sliding against a steel ball was tested using four oil-soluble ILs used as additives. This poster will present data that will show (1) the ILs improved the friction behavior to various extents; (2) two phosphate ILs clearly outperformed conventional ZDDP; (3) ILs exhibited excellent wear protection suggesting good material-chemical compatibility; and (4) the carboxylate IL protected the OD-Ti surface from any measurable wear. The morphology and chemical composition of the worn surfaces and tribofilms were examined using a combination SEM, TEM, EDS, and XPS.

Research sponsored by Vehicle Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE). Electron microscopy characterization was in part performed at ORNL’s Center for Nanophase Materials Sciences, sponsored by the Scientific User Facilities Division, Office of DOE-BES. The support by the National Natural Science Foundation of China (No. 51575402) and Chinese Academy of Sciences (CAS) during the visits of H. Duan and W. Li to ORNL, respectively, are also appreciated. This abstract has been authored by UT-Battelle, LLC under Contract No. DEAC05-00OR22725 with the U.S. Department of Energy.

Warden Soil (alkaline, fine sandy loam) from Prosser, WA was characterized by a suite of spectroscopic and microscopic techniques to gain insights into the nature of mineral-associated soil organic matter (SOM) and its stability under environmental perturbations (e.g., after spiking the soil with siderophores, fluctuating redox conditions, etc.). This approach was undertaken since: a) SOM associated with minerals has been recognized to be relatively stable with respect to biological degradation compared with particulate organic matter (POM), and b) the stability of mineral-OM moieties is primarily a function of interaction between the mineral and OM type, and their physical accessibilities by organisms, oxidants, etc.

Coupled Mössbauer spectroscopy and XRD measurements revealed that ~60-65% of total Fe (5.5 wt.%) in the soil was present in feldspars. The balance of the Fe was primarily partitioned as magnetite, ilmenite, and a suite of nano-Fe(III)-oxides. Various forms of Ca were evident in TEM as: a) “Ca-OM polymers”, b) CaCO₃ coated with Ca-OM (consistent with XPS results), and c) Ca feldspar. OM-coated magnetite particles were also evident in TEM results. XPS measurements also demonstrated various types of surface organic C (20-25× that of bulk): a) aliphatic and aromatic C-(C-H), such as C-C, C=C, C-H, b) C-(O,N) bonds as in carbohydrates and amines, c) C displaying bonds to oxygen as in aldehydes, ketones, and amides (C=O, O-C-O, O=C-N), and iv) carboxylic C (O-C=O. NanoSIMS results of ¹³C- and ¹⁵N-labeled siderophore-spiked soils showed that Ca-OM phases rather than Fe-OM phases were preferential hosts for siderophores implying weaker but quickly forming interactions were preferentially established and stable enough to exist in calcareous environments. This provides a potential explanation of the lack of pyoverdines/catechols (siderophores) observed in grassland soils, and more broadly demonstrates the importance of adsorption kinetics rather than thermodynamic equilibrium on the fate and preservation of SOM.

Low temperature nitriding of Fe-Cr-Ni austenitic stainless-steel forms a nitrogen supersaturated layer that owns a composite property of wear and corrosion resistance. It is widely used in the industry, and nuclear power plant is a very important application for its stringent performance requirements. To understand the nature of this nitrogen supersaturated layer, a serial systematically composition changed Fe-Cr-Ni austenitic stainless steel in three groups are prepared, nitrided and investigated. It is confirmed that the nitrided layers on all the Fe-Cr-Ni austenitic alloys are consistent of duplex structure of outer γ -Fe N like orderedγ^'_N and inner γ_N, althougha featureless continuous layer is observed with light-optical microscopy and a gradual decrease in nitrogen content is measured with EPMA when the alloys with a Cr-content over 12 wt. %. Cell model based on Cr-N and Fe-N interaction that considered the atomic construction of octahedral interstice is built that can explain the composition and structure evolution during the alloy composition change. The Cell Model is also used to calculated the average nearest neighbor nitrogen atoms (ANNNA) around Cr and Fe, which well explained the extended X-ray absorption fine structure (EXAFS) experiment results in both as nitrided and denitrided of 304 and 316 stainless steel. It further confirmed the reasonability of Cell Model and revealed the atomic structure of the γ^'_N and γ_N phase.

In this work was studied single-walled carbon nanotubes (SWNT) functionalized with noncovalently bonded hybrids of 3d transition metal (Me) phthalocyanines MePcs by X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT).

The transition metal Me 2p core level spectra exhibit a series of details, specifically shake-up and multiplet splitting. This latter can affect BE values for an electron from any orbital, as occurs in the links of the phthalocyanines under study, before and after interacting with the surface of the wall single-walled carbon nanotubes, in which not only the splitting occurs but, literally, bonds disappear, although its physical-chemical meaning is that its energy becomes indistinguishable.

The approximate XPS spectra measurements for neat MePcs (where Me=Co, Ni, Cu and Zn). and MePc+SWNT hybrids show very strong interactions between macrocyclic complexes and carbon nanotube sidewalls and found the existence of one N 1s component for noncovalent MePc+SWNT complexes versus three components for neat phthalocyanine β-polymorphs. As well the decrease of multiplet splitting and the increase of spectral resolution, observed for both N 1s, C 1s and Me 2p peaks as a result of phthalocyanine deposition onto SWNTs.

Density functional theory (DFT) studies, showed high absolute values of binding energies and show that the macrocycles (of MePcs) suffer strong bending distortion in order to increase the area of their contact with nanotube sidewall. The combination of XPS and DFT helps the final explanation.

A detailed description of the electrical double layer structure formed at the electrode-electrolyte interface is very important for both fundamental understanding in many electrochemical processes and further advancements in energy storage devices. However, the electrical double layer is deeply “buried” by the bulk electrolyte solution, leading to significant signal loss and low detection resolution when measuring the interface structure from the electrolyte side. Here, we report the fabrication of a novel transparent electrode made of a graphene-carbon nanotube hybrid membrane that allows us to detect the electrical double layer from the solid side of the electrode using X-ray photoelectron spectroscopy. The robust and ultrathin nature of the hybrid membrane enables the detection of different elements with excellent photoelectron signals. By in situ monitoring the concentration changes of cations and anions under different local electrical potentials, we experimentally decipher the chemical structure of the electrical double layer, which is consistent with theoretical predictions.

Silver and copper thin films were coated on commercially available 3 M water filter papers using DC high vacuum magnetron sputtering technique. The filter papers (10 X 7 cm size) are flexible structures consisting of nonconductive fibers and metallic nanoparticles were deposited with 300 nm and 1 µm thicknesses resulting in a complete coverage of the fibers surface. Both silver and copper thin films deposited on water filter paper are effectively working against common types of harmful bacteria that are found in waste water. The research is investigating the possibility of creating electrically conductive structures and the synergistic antibacterial effect obtained by using metallic thin films deposited on water filter paper and an electrical current applied to the structures. The antibacterial activity of electrically conductive structures was tested by applying an increased electrical potential. The morphology of the coatings and their adherence to the water filter paper was examined using the digital optical microscopy and Scanning Electron Microscopy and their chemical composition was investigated using the X-ray diffraction technique. A ll thin films showed good adhesion to water filter fibers and ensured a high area of exposure to contaminated water. The antibacterial effect of different conductive thin films was characterized by using the standardized membrane filtering technique for water and wastewater examination. The testing media (i.e. contaminated water) containing bacterial samples were collected from local wastewater basins. Water was tested for the bacterial content before and after the exposure to conductive thin films coated filters.

Depth profiling (1D or 3D) is often used to determine the depth distribution of species in a material. Depth profiling works well when the surface of a sample is smooth and when the depth(s) are in the nm to micron thickness range. For thicker layers, one can mount the material in epoxy and generate a cross section which can be imaged. Unfortunately, cutting and polishing often damages (or at least smears) fragile materials such Li ion batteries. Over the two past decades, Focused Ion Beam (FIB) has proven to be a viable approach to expose sub surface layers 10s of microns thick which is often analyzed by SEM or TEM in conjunction with EDS [1]. Unfortunately, most EDS detectors are not able to detect light species such as Li and C (especially at the degraded vacuum which most SEM’s operate under), and definitely can not detect H. ToF-SIMS not only detects all elements (and their isotopes), it also allows for the analysis of molecular fragments which is often critical for understanding the material. FIB/ToF-SIMS has been used to analyze other material systems [2, 3].

In this late breaking poster, we will provide preliminary in-situ FIB/ToF-SIMS results which were generated on an anode taken from a Li ion battery. In order to simultaneously obtain high lateral resolution images at high mass resolution, the delayed extraction data collection mode was utilized [4]. The advantages of multivariate statistical analysis (MVSA) for these complex data sets will be demonstrated.

[1] Lucille A. Giannuzzi, and Fred A. Stevie, Eds., “Introduction to Focused Ion Beams”, Springer-Verlag US (2005) DOI: https://doi.org/10.1007/b101190.

[2] Felix Kollmer, D. Rading, R. Moellers, H.-G. Cramer, Wolfgang Paul, Ewald Niehuis, “Novel Cluster Ion Beams For Secondary Ion Generation, Sputtering And FIB/SIMS Application”, Microscopy and Microanalysis 18(S2) (2012) 904-905; DOI: 10.1017/S143192761200637X.

[3] John S. Hammond, Gregory L. Fisher, Scott R. Bryan, Rait Kanarbik and Pritt Möller “FIB-TOF Tomography of Solid Oxide Fuel Cells”, Microscopy and Microanalysis 19 (suppl 2) (2013) 672-673, DOI:10.1017/S1431927613005357.

[4] Quentin P. Vanbellingen, Nicolas Elie, Michael J. Eller, Serge Della-Negra, David Touboul, Alain Brunelle, “Time‐of‐flight secondary ion mass spectrometry imaging of biological samples with delayed extraction for high mass and high spatial resolutions” Rapid Commun. Mass Spectrom. 29 (2015) 1187–1195, DOI: 10.1002/rcm.7210

Electrochemical measurements have shown promise for detecting biomolecules such as DNA and proteins. In this presentation, we focus on surface-immobilized DNA aptamers that can be used to bind certain species and thereby produce electrochemical signals indicating detection of desired targets. Our sensing approach is based on monitoring binding events and conformation changes that occur on reusable, temperature-controlled electrochemical microdevices. We present our findings on two “model” aptamers that bind streptavidin and platelet-derived growth factor (PDGF), respectively. The commercially-purchased aptamers were bound to the Au working electrodes of the devices through a thiol group that was synthesized at the 5’ end of the DNA. Changes in temperature caused folding and unfolding of the aptamer, altering the average distance between a terminal redox-active methylene blue moiety (at the 3’ end) and the Au surface. The resulting change in current (due to electron transfer between each methylene blue molecule and the Au surface) was monitored over a temperature range of ~10 ⁰C – 60 ⁰C. Initial studies included surface characterization using XPS and AFM in order to better understand the behavior of the aptamers under environmental stressing, such as changes in the chemical environment and temperature. Surface plasmon resonance (SPR) studies were also performed to provide instrumental analyses of the aptamer-protein binding events, to compare to results obtained with the electrochemical microdevices.