A new low-modulus β Ti−Nb alloy with low elastic modulus and excellent corrosion resistance is currently under consideration as a surgical implant material. The usefulness of such materials can be dramatically enhanced if their surface structure and surface chemistry can be controlled. This control is achieved in two stages. Electropolishing and anodic oxidation of the Ti45Nb alloy provide a surface with a uniform oxide layer that is a mixture of TiO2 and Nb2O5. The impact of each of these two steps on the morphology of the surface and on the thickness and chemistry of the oxide layer has been assessed. In addition, as a first step toward controlling the surface chemistry of this material, a self-assembled monolayer (SAM) based on hexadecylphosphonic acid (HDPA) is attached to the anodized surface. The SAM is characterized based on its wetting properties and by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. Using variable angle XPS analysis, detailed information is obtained about the orientation and structure of the SAM, its thickness, and the chemistry of its interaction with the metal oxide surface of the alloy. Further support for the creation of a true monolayer film is obtained from FTIR measurements on a model oxide surface analogous to that of the alloy. This is the first report of SAM attachment to this alloy and opens the possibility of monolayer control of its biocompatibility.

Significance Morpho butterflies are a brilliant spectacle of nature’s capability for photonic engineering. Their conspicuous appearance arises from the interference and diffraction of light within tree-like nanostructures on their scales. Scientific lessons learned from these butterflies have already inspired designs of new displays, fabrics, and cosmetics. This study reports a vertical surface polarity gradient in these tree-like structures. This biological pattern design may be applied to numerous technological applications ranging from security tags to self-cleaning surfaces, gas separators, protective clothing, and sensors. Here it has allowed us to unveil a general mechanism of selective vapor response in photonic Morpho nanostructures and to demonstrate attractive opportunities for chemically graded sensing units for high-performance sensing.

Producing large-scale graphene films with controllable patterns is an essential component of graphene-based nanodevice fabrication. Current methods of graphene pattern preparation involve either high cost, low throughput patterning processes or sophisticated instruments, hindering their large-scale fabrication and practical applications. We report a simple, effective, and reproducible approach for patterning graphene films with controllable feature sizes and shapes. The patterns were generated using a versatile photocoupling chemistry. Features from micrometres to centimetres were fabricated using a conventional photolithography process. This method is simple, general, and applicable to a wide range of substrates including silicon wafers, glass slides, and metal films.

X-ray Photoelectron Spectroscopy (XPS) was used to characterize the nitrogen species in perfluorophenylazide (PFPA) self-assembled monolayers. PFPA chemistry is a novel immobilization method for tailoring the surface properties of materials. It is a simple route for the efficient immobilization of graphene, proteins, carbohydrates and synthetic polymers onto a variety of surfaces. Upon light irradiation, the azido group in PFPA is converted to a highly reactive singlet nitrene species that readily undergoes CH insertion and C=C addition reactions. Here, the challenge of characterizing the PFPA modified surfaces was addressed by detailed XPS experimental analyses. The three nitrogen peaks detected in the XPS N1s spectra were assigned to amine/amide (400.5 eV) and azide (402.1 and 405.6 eV) species. The observed 2:1 ratio of the areas from the 402.1 eV to 405.6 eV peaks suggests the assignment of the peak at 402.1 eV to the two outer nitrogen atoms in the azido group and assignment of the peak at 405.6 eV to the central nitrogen atom in the azido group. The azide decomposition as the function of x-ray exposure was also determined. Finally, XPS analyses were conducted on patterned graphene to investigate the covalent bond formation between the PFPA and graphene. This study provides strong evidence for the formation of covalent bonds during the PFPA photocoupling process.

In the biological sciences the use of core-shell quantum dots (QDs) has gained wide usage, but analytical challenges still exist for characterizing the QD structure. The application of energydispersive x-ray spectroscopy and x-ray photoelectron spectroscopy (XPS) to bulk materials is relatively straightforward, however, for meaningful applications of surface science techniques to multilayer nanoparticles requires novel modifications and analysis methods. To experimentally characterize the elemental composition and distribution in CdSe/CdS/ZnS QDs, we first develop a XPS signal subtraction technique capable of separating the overlapped selenium 3s (core) and sulfur 2s (shell) peaks (both peaks have binding energies near 230eV) with higher precision than is typically reported in the nanoparticle literature. This method is valid for any nanoparticle containing selenium and sulfur. Then we apply a correction formula to the XPS data and determine that the 2 nm stoichiometric CdSe core is surrounded by 2 CdS layers and a stoichimetric ZnS monolayer. These findings and the multi-approach methodology represent a significant advancement in the detailed surface science study of multi-layer nanoparticles. In agreement with recent surprising findings, the time-of-flight secondary mass spectrometry measurements suggest that the surface sites of the QDs used in this study are primarily covered with a mixture of octadecylphosphonic acid and trioctylphophine oxide.

Biointegration of titanium implants in the body is controlled by their surface properties. Improving surface properties by coating with a bioactive polymer is a promising approach to improve the biological performance of titanium implants. To optimize the grafting processes, it is important to fully understand the composition and structure of the modified surfaces. The main focus of this study is to provide a detailed, multi-technique characterization of a bioactive poly(sodium styrene sulfonate) (pNaSS) thin film grafted from titanium surfaces via a two-step procedure. Thin titanium films (~50 nm thick with an average surface roughness of 0.9±0.2nm) prepared by evaporation onto silicon wafers were used as smooth model substrates. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed that the titanium film was covered with a TiO2 layer that was at least 10nm thick and contained hydroxyl groups present at the outermost surface. These hydroxyl groups were first modified with a 3-methacryloxypropyltrimethoxysilane (MPS) cross linker. XPS and ToF-SIMS showed that a monolayer of the MPS molecules were successfully attached onto the titanium surfaces. The pNaSS film was grafted from the MPS modified titanium through atom transfer radical polymerization. Again, XPS and ToF-SIMS were used to verify that the pNaSS molecules were successfully grafted onto the modified surfaces. Atomic force microscopy analysis showed that the film was smooth and uniformly covered the surface. Fourier transform infrared spectroscopy indicated an ordered array of grafted NaSS molecules were present on the titanium surfaces. Sum frequency generation vibration spectroscopy and near edge X-ray absorption fine structure spectroscopy illustrated that the NaSS molecules were grafted onto the titanium surface with a substantial degree of orientational order in the styrene rings.

Nickel titanium (NiTi, nitinol) shape memory alloy was nitrided using a powder immersion reaction assisted coating (PIRAC) method to modify its surface properties. PIRAC nitriding is based on annealing the samples in an atmosphere of highly reactive nitrogen supplied by decomposition of unstable nitride powders or, alternatively, by selective diffusion of atmospheric nitrogen to the sample surface. Since it is not line of sight limited, PIRAC nitriding of nitinol alloys allows uniform treatment of complex shapes (e.g., surgical implants). It results in the formation of a Ni-free TiN film and considerably improves the corrosion behavior of the underlying NiTi alloy. The usefulness of PIRAC nitrided nitinol could be significantly enhanced by attaching to its surface a phosphonate anchored self-assembled monolayer (SAM). Phosphonate-anchored SAMs on PIRAC nitrided nitinol and on thin films of TiN sputtered onto a silicon wafer have been characterized by FTIR, contact angle measurements, and XPS analysis. The SAM was only weakly attached to the nitride surface. However, when anodization was used to add an oxide layer on top of the TiN, a robust, uniform phosphonate-anchored SAM could be formed. Thus, anodization of the nitride surface allows it to continue functioning as a corrosion barrier while still being able to take advantage of the range of surface chemistries offered by SAM films. The composition and morphology of the nitrided TiNi surface, before and after anodization, are reported, along with an analysis of phosphonate-anchored SAM formation on these surfaces.

A new low modulus beta Ti-Nb alloy with low elastic modulus and excellent corrosion resistance is currently under consideration as a surgical implant material. The usefulness of such materials can be dramatically enhanced if their surface structure and surface chemistry can be controlled. This control is achieved by attaching a self assembled monolayer (SAM) based on 11-chloroacetyl-1-undecylphosphonic acid, CAUDPA, to the surface and immobilization of a peptide to the monolayer. The SAM is characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) at two different takeoff angles. The CAUDPA molecules were covalently bonded on the substrate in a configuration in which the phosphonic group turns toward the Ti45Nb while the acetyl chloride end group tail turns to the topmost surface. In such configuration sequential in situ reaction is possible by exchange between the chloride and a biological molecule. Such biological molecule is the arginine-glycine-aspartic acid-cysteine, RGDC, small amino acid sequence present in many molecules of the extracellular matrix. Preliminary cell culture in-vitro result shows an improvement of the response of osteoblast cells to Ti45Nb after the peptide immobilization.