Understanding energy distributions and kinetic processes in NxOy plasma systems is vital to realizing their potential in a range of applications, including pollution abatement. Energy partitioning between degrees of freedom and multiple molecules formed within NxOy plasma systems (N2, N2O, N2/O2) was investigated using both optical emission and broadband absorption spectroscopies. Specifically, we determined electron temperatures (Te) as well as rotational (TR) and vibrational (TV) temperatures for various N2 (B3Πg and C3Πu) and NO (X2Π and A2Σ+) states. TR and TV for both molecules (regardless of state) show a strong positive correlation with applied plasma power, as well as a negative correlation with system pressure. In all cases, TV values are significantly higher than TR for both species, suggesting vibrational modes are preferentially excited over rotational degrees of freedom. Time-resolved optical emission spectroscopy was utilized to determine rate constants, providing mechanistic insight and establishing the relationships between system parameters and plasma chemistry. Ultimately, the combination of these data allows us to glean information regarding both the kinetics and energetics of N2 and NO molecules formed within nitrogen- and oxygen-containing plasma systems for potential applications in gas remediation of pollutants.

Strategic application of an array of complementary imaging and diffraction techniques is critical to determine accurate structural information on nanomaterials, especially when also seeking to elucidate structure–property relationships and their effects on gas sensors. In this work, SnO2 nanowires and nanobrushes grown via chemical vapor deposition (CVD) displayed the same tetragonal SnO2 structure as revealed via powder X-ray diffraction bulk crystallinity data. Additional characterization using a range of electron microscopy imaging and diffraction techniques, however, revealed important structure and morphology distinctions between the nanomaterials. Tailoring scanning transmission electron microscopy (STEM) modes combined with transmission electron backscatter diffraction (t-EBSD) techniques afforded a more detailed view of the SnO2 nanostructures. Indeed, upon deeper analysis of individual wires and brushes, we discovered that, despite a similar bulk structure, wires and brushes grew with different crystal faces and lattice spacings. Had we not utilized multiple STEM diffraction modes in conjunction with t-EBSD, differences in orientation related to bristle density would have been overlooked. Thus, it is only through a methodical combination of several structural analysis techniques that precise structural information can be reliably obtained.Keywords: diffraction; growth; nanobrushes; nanowires; structure; tin oxide

Herein, we describe the surface modification of an S-nitrosated polymer derivative via H2O plasma treatment, resulting in polymer coatings that maintained their nitric oxide (NO) releasing capabilities, but exhibited dramatic changes in surface wettability. The poly(lactic-co-glycolic acid)-based hydrophobic polymer was nitrosated to achieve a material capable of releasing the therapeutic agent NO. The NO-loaded films were subjected to low-temperature H2O plasma treatments, where the treatment power (20–50 W) and time (1–5 min) were varied. The plasma treated polymer films were superhydrophilic (water droplet spread completely in <100 ms), yet retained 90% of their initial S-nitrosothiol content. Under thermal conditions, NO release profiles were identical to controls. Under buffer soak conditions, the NO release profile was slightly lowered for the plasma-treated materials; however, they still result in physiologically relevant NO fluxes. XPS, SEM-EDS, and ATR-IR characterization suggests the plasma treatment resulted in polymer rearrangement and implantation of hydroxyl and carbonyl functional groups. Plasma treated samples maintained both hydrophilic surface properties and NO release profiles after storage at −18 °C for at least 10 days, demonstrating the surface modification and NO release capabilities are stable over time. The ability to tune polymer surface properties while maintaining bulk properties and NO release properties, and the stability of those properties under refrigerated conditions, represents a unique approach toward creating enhanced therapeutic biopolymers.Keywords: nitric-oxide-releasing materials; cysteine; nitrosation; plasma treatments; PLGH

Bioresorbable polymers such as poly(ε-caprolactone) (PCL) have a multitude of potential biomaterial applications such as controlled-release drug delivery and regenerative tissue engineering. For such biological applications, the fabrication of porous three-dimensional bioresorbable materials with tunable surface chemistry is critical to maximize their surface-to-volume ratio, mimic the extracellular matrix, and increase drug-loading capacity. Here, two different fluorocarbon (FC) precursors (octofluoropropane (C3F8) and hexafluoropropylene oxide (HFPO)) were used to deposit FC films on PCL scaffolds using plasma-enhanced chemical vapor deposition (PECVD). These two coating systems were chosen with the intent of modifying the scaffold surfaces to be bio-nonreactive while maintaining desirable bulk properties of the scaffold. X-ray photoelectron spectroscopy showed high-CF2 content films were deposited on both the exterior and interior of PCL scaffolds and that deposition behavior is PECVD system specific. Scanning electron microscopy data confirmed that FC film deposition yielded conformal rather than blanket coatings as the porous scaffold structure was maintained after plasma treatment. Treated scaffolds seeded with human dermal fibroblasts (HDF) demonstrate that the cells do not attach after 72 h and that the scaffolds are noncytotoxic to HDF. This work demonstrates conformal FC coatings can be deposited on 3D polymeric scaffolds using PECVD to fabricate 3D bio-nonreactive materials.

The contributions of various gas-phase species in surface reactions are of significant value to assess and improve catalytic substrates for abatement of vehicular emissions. The impact of ions on surface scatter of NO radicals is investigated with an aim toward improving and tailoring surfaces for the reduction or removal of nitrogen oxide (NxOy) species via inductively coupled plasmas (ICPs). Nascent ions are monitored via mass spectrometry and energy analysis for a variety of NxOy precursor gases. The total average ion energy (⟨Ei⟩total) determined for all ions within each respective plasma system shows a strong positive correlation with applied rf power and a negative correlation with system pressure. The imaging of radicals interacting with surfaces (IRIS) technique was used to determine the role ions play in the surface scatter of NO radicals. The net effect of ions on substrate processing is largely dependent upon ⟨Ei⟩total. Scatter coefficients (S), determined for ion-limited and ion-rich plasma systems were used to correlate ⟨Ei⟩total and scatter. The resultant effect is that ions play a substantial role in scatter of NO only when ⟨Ei⟩total > ∼50 eV. The majority of systems studied contained ions below this energy threshold, suggesting knowledge of ion energies is integral to appropriately controlling the chemistry occurring between the gas-phase and surface.

Inductively-coupled CxFy (y/x = 2.0–4.0) plasma systems were investigated to determine relationships between precursor chemistry, CFn radical-surface reactivities, and surface properties of deposited films. The contributions of CFn (n = 1, 2) radicals to film properties were probed via gas-phase diagnostics and the imaging of radicals interacting with surfaces (IRIS) technique. Time-resolved radical emission data elucidate CF(g) and CF2(g) production kinetics from the CxFy source gases and demonstrate that CF4 plasmas inherently lag in efficacy of film formation when compared to C2F6, C3F8, and C3F6 systems. IRIS data show that as the precursor y/x ratio decreases, the propensity for CFn scatter concomitantly declines. Analyses of the composition and characteristics of fluorocarbon films deposited on Si wafers demonstrate that surface energies of the films decrease markedly with increasing film fluorine content. In turn, increased surface energies correspond with significant decreases in the observed scatter coefficients for both CF and CF2. These data improve our molecular-level understanding of CFn contributions to fluorocarbon film deposition, which promises advancements in the ability to tailor FC films to specific applications.Keywords: fluorocarbon polymers; plasma materials processing; radical surface interactions; surface energy;

Adhesion and delamination behavior of amorphous carbon nitride (a-CNx) is critical to development of wear resistant materials and protective coatings. Here, the composition and delamination behavior of a-CNx films was explored utilizing BrCN, CH3CN, and CH4 as film precursors, either alone or in combination with one another. Film delamination depends on film thickness and plasma composition as well as post deposition treatment conditions. Delamination is not observed with films deposited from 100% CH3CN discharges, whereas films of similar thickness deposited from 100% BrCN plasmas delaminate almost immediately upon exposure to atmosphere. Exploration of these differences in delamination behavior is discussed relative to contributions of humidity, hydrocarbon species, and ion bombardment during deposition in conjunction with compositional studies using X-ray photoelectron spectroscopy (XPS).Keywords: chemical vapor deposition; coatings; plasma; xps

Nitrogen doping of TiO2 films (N:TiO2) has been shown to improve the visible-light sensitivity of TiO2, thereby increasing the performance of both photovoltaic and photocatalytic devices. Inductively coupled rf plasmas containing a wide range of nitrogen precursors were used to create nitrogen-doped TiO2 films. These treatments resulted in anatase-phased materials with as high as 34% nitrogen content. As monitored with high-resolution X-ray photoelectron spectroscopy spectra, the nitrogen binding environments within the films were controlled by varying the plasma processing conditions. XPS peak assignments for multiple N 1s binding environments were made based on high resolution Ti 2p and O 1s XPS spectra, Fourier transform infrared spectroscopy (FTIR) data, and literature N 1s XPS peak assignments. The N:TiO2 films produced via plasma treatments displayed colors ranging from gray to brown to blue to black, paralleling the N/Ti ratios of the films. Three possible mechanisms to explain the color changes in these materials are presented.Keywords: photocatalysis; photovoltaic; plasma surface modification; titanium dioxide