Jesse Enlow

Facile plasma-enhanced deposition of ultrathin crosslinked amino acid films for conformal biometallization.

A novel method for the facile fabrication of conformal, ultrathin, and uniform synthetic amino acid coatings on a variety of practical surfaces by plasma-enhanced chemical vapor deposition is introduced. Tyrosine, which is utilized as an agent to reduce gold nanoparticles from solution, is sublimed into the plasma field and directly deposited on a variety of substrates to form a homogeneous, conformal, and robust polyamino acid coating in a one-step, solvent-free process. This approach is applicable to many practical surfaces and allows surface-induced biometallization while avoiding multiple wet-chemistry treatments that can damage many soft materials. Moreover, by placing a mask over the substrate during deposition, the tyrosine coating can be micropatterned. Upon its exposure to a solution of gold chloride, a network of gold nanoparticles forms on the surface, replicating the initial micropattern. This method of templated biometallization is adaptable to a variety of practical inorganic and organic substrates, such as silicon, glass, nitrocellulose, polystyrene, polydimethylsiloxane, polytetrafluoroethylene, polyethylene, and woven silk fibers. No special pretreatment is necessary, and the technique results in a rapid, conformal amino acid coating that can be utilized for further biometallization.

Surface oxygen in plasma polymerized films

For plasma polymerized (PP) thin films, many practical optical, electronic, sensing, and bio-applications are closely related to their surface properties. In particular, the surfaces of many PP films have a strong affinity for oxygen and moisture. Therefore, three different types of monomers which do not contain oxygen were selected to fabricate PP films, in order to understand the mechanisms for surface oxygen absorption. These monomers were a hydrocarbon, benzene (B); ferrocene (FC), containing Fe ions which have a great affinity for oxygen; and octafluorocyclobutane (OFCB), containing the strong electronegative (and thus oxygen repellent) element fluorine. X-Ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FTIR) spectroscopy, and electron spin resonance (ESR) were used to explore the chemical composition and structure of the resulting PP films. XPS depth-profiling was also used to investigate the oxygen content in the bulk of the films by analyzing the film surface after various amounts of argon etching. The initial oxygen content on the surface of the PP-FC films was the largest of the three while PP-OFCB films only contained a trace quantity. PP-B films had an intermediate concentration. Affinity for oxygen for this latter film was determined to be due to residual activated species including free radicals and dangling bond sites on the film surface. Depth profiling disclosed little oxygen a short distance into the PP-B films, indicating that the oxygen was attracted after deposition upon exposure to ambient conditions. Although the PP-B film exhibited a high concentration of free radicals as determined by ESR, the dense and crosslinked bulk structure shielded these active centers in the film by prohibiting oxygen diffusion. For the PP-FC films, although a decrease in the amount of oxygen was observed after etching, a substantial concentration of oxygen exists with the depth, indicating incorporation of oxygen during the initial deposition. Because of the chemical nature of fluorine, the as-deposited PP-OFCB films did not exhibit significant affinity towards oxygen. However, a slightly oxygen enriched film surface was present after argon etching due to changes in the surface chemistry and structure. These results demonstrate that the formation and distribution of oxygen on and within the PP films are strongly dependent upon the chemical composition and structure of the films.

Control of interface nanoscale structure created by plasma-enhanced chemical vapor deposition.

Tailoring the structure of films deposited by plasma-enhanced chemical vapor deposition (PECVD) to specific applications requires a depth-resolved understanding of how the interface structures in such films are impacted by variations in deposition parameters such as feed position and plasma power. Analysis of complementary X-ray and neutron reflectivity (XR, NR) data provide a rich picture of changes in structure with feed position and plasma power, with those changes resolved on the nanoscale. For plasma-polymerized octafluorocyclobutane (PP-OFCB) films, a region of distinct chemical composition and lower cross-link density is found at the substrate interface for the range of processing conditions studied and a surface layer of lower cross-link density also appears when plasma power exceeds 40 W. Varying the distance of the feed from the plasma impacts the degree of cross-linking in the film center, thickness of the surface layer, and thickness of the transition region at the substrate. Deposition at the highest power, 65 W, both enhances cross-linking and creates loose fragments with fluorine content higher than the average. The thickness of the low cross-link density region at the air interface plays an important role in determining the width of the interface built with a layer subsequently deposited atop the first.

Measurement of the Deformation of Silicon Substrates Coated with a Plasma-Polymerized Acrylonitrile Film

A sensitive interferometric method is employed to quantify the deformation of silicon substrates coated with thin plasma-polymerized acrylonitrile film deposited at room temperature. This provides insight into the structural variation of plasma polymerized films.