Alkylphosphonic Self-assembled Monolayers Research Articles

The influence of self-assembled monolayers on tribological properties of Si-DLC coatings

The tribological properties of diamond like carbon (DLC) and silicon-incorporated diamond like carbon (Si-DLC) coatings in contact with Si3N4 counterbody were investigated using a ball-on-disc tribometer. The effect of modification by perfluoro and alkylphosphonic self-assembled monolayers was evaluated in terms of lowering the coefficient of friction (CoF) and wear rate. The tribological tests revealed that the presence of silicon decreases the CoF and slightly increases the wear rate of Si-DLC coatings in comparison with DLC. Further decrease of CoF was achieved for Si-DLC coatings after self-assembled monolayers deposition. The effectiveness of modification, stability on ultraviolet (UV) irradiation and characterization of all coatings was monitored by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy and measurements of the surface free energy (SFE). The obtained study demonstrated that self-assembled monolayers reduce friction and are highly promising candidates as a good lubricant for tribological and mechanical systems.

Impact of Perfluoro and Alkylphosphonic Self-Assembled Monolayers on Tribological and Antimicrobial Properties of Ti-DLC Coatings.

The diamond-like carbon (DLC) coatings containing 1.6%, 5.3% and 9.4 at.% of Ti deposited by the radio frequency plasma enhanced chemical vapor deposition (RF PECVD) method on the silicon substrate were modified by n-decylphosphonic acid (DP) and 1H, 1H, 2H and 2H-perfluorodecylphosphonic acid (PFDP). The presence of perfluoro and alkylphosphonic self-assembled monolayers prepared by the liquid phase deposition (LPD) technique was confirmed by Fourier transform infrared spectroscopy (FTIR). It was shown that DP and PFDP monolayers on the surface of titanium incorporated diamond-like carbon (Ti-DLC) coatings had a huge influence on their wettability, friction properties, stability under phosphate- and tris-buffered saline solutions and on antimicrobial activity. It was also found that the dispersive component of surface free energy (SFE) had a significant influence on the value of the friction coefficient and the percentage value of the growth inhibition of bacteria. The dispersive component of SFE caused a reduction in the growth of bacteria and the friction coefficient in mili- and nano-newton load range. Additionally, both self-assembled monolayers prepared on Ti-DLC coatings strongly reduced bacterial activity by up to 95% compared to the control sample.

Tribological and corrosive investigations of perfluoro and alkylphosphonic self-assembled monolayers on Ti incorporated carbon coatings

Abstract This paper presents tribological and corrosion properties of perfluoro and alkylphosphonic self-assembled monolayers formed on Ti incorporated carbon coatings. The Ti-DLC incorporated coatings were deposited on Ti6Al4V substrates by Radio Frequency Plasma Enhanced Chemical Vapour Deposition (RF PECVD) method using combination of methane (CH 4 ) and titanium (IV) isopropoxide (Ti [OCH(CH 3 ) 2 ] 4 ) atmospheres. The obtained coatings were subsequently modified by perfluoro and alkylphosphonic self-assembled layers having hydrocarbon or perfluorocarbon chains (DP and PFDP). Presented results show that application of these compounds on the top of Ti-DLC coatings significantly improves their tribological properties. After 1000 m of ball-on-disc test the DP- and PFDP- modified coatings presented low coefficient of friction, showing particularly more stable and lower value in case of PFDP while the unmodified coating was worn out already after 160 m of the test under the same conditions. The corrosion tests show varied results for both modifiers. In the case of PFDP an increased reactivity of the coating is observed, whereas for DP the results prove the anti-corrosive effect of this self-assembled layer.

Electrochemical Investigation of Nitinol/Tantalum Hybrid Surfaces Modified by Alkylphosphonic Self-Assembled Monolayers

The surface characteristics of bare and modified nickel-titanium samples (NiTi) are investigated by spectroscopic, microscopic and electrochemical techniques. The successful electrodeposition of a tantalum coating on NiTi and the effective grafting of 1-dodecylphosphonic acid SAMs on both pristine and Ta-covered NiTi surfaces are evidenced and quantified by XPS and SEM. Cyclic voltammetry performed on the different NiTi-based electrodes highlights their specificities regarding electron transfer to a redox probe present in solution (here ruthenium(III) hexamine). Finally, the samples electrochemical characteristics at a local scale are investigated by scanning electrochemical microscopy (SECM). The impact of the surface modifications on mass transport of the redox probe is analyzed through approach curves in the feedback mode, while the recording of current maps in feedback as well as in substrate-generation/tip-collection modes leads to the qualitative identification of electrochemically-active areas corresponding to precursor pitting corrosion sites.

Organophosphonates as model system for studying electronic transport through monolayers on SiO2/Si surfaces

We report electrical transport measurements made on alkylphosphonate self-assembled monolayers grown on nanometer-thin SiO2 on top of highly p-doped silicon. At small bias direct tunneling is characterized by a decay constant of β ≈ 0.7/carbon. At larger positive bias to the silicon (1.1–1.5 V) the current-voltage traces feature a prominent shoulder, reminiscent of a negative differential resistance. We attribute this feature to a significant reduction in trap-assisted tunneling, as supported by a simulation. Hence, organophosphonate monolayers are excellent model systems to study electrical transport through ordered structures; they also provide highly efficient electrical passivation of the SiO2/Si surface.

Large area nanopatterning of alkylphosphonate self-assembled monolayers on titanium oxide surfaces by interferometric lithography

We demonstrate that interferometric lithography offers a fast, simple route to nanostructured self-assembled monolayers of alkylphosphonates on the native oxide of titanium. Exposure at 244 nm using a Lloyd's mirror interferometer caused the spatially periodic photocatalytic degradation of the adsorbates, yielding nanopatterns that extended over square centimetre areas. Exposed regions were re-functionalised by a second, contrasting alkylphosphonate, and the resulting patterns were used as templates for the assembly of molecular nanostructures; we demonstrate the fabrication of lines of polymer nanoparticles 46 nm wide. Nanopatterned monolayers were also employed as resists for etching of the metal film. Wires were formed with widths that could be varied between 46 and 126 nm simply by changing the exposure time. Square arrays of Ti dots as small as 35 nm (λ/7) were fabricated using two orthogonal exposures followed by wet etching.

Photopolymerization of Self-Assembled Monolayers of Diacetylenic Alkylphosphonic Acids on Group-III Nitride Substrates

This paper describes the fabrication and characterization of photopolymerizable alkylphosphonate self-assembled monolayers (SAMs) on group-III nitride substrates including GaN and Al(x)Ga(1-x)N (AlGaN; x = 0.2 and 0.25). Contact angle goniometry, visible absorption spectroscopy, and atomic force microscopy were used to assess the formation, desorption, and photopolymerization of SAMs of diacetylenic alkylphosphonic acids (CH(3)(CH(2))(n)-C[triple bond]C-C[triple bond]C-(CH(2))(m)PO(OH)(2); (m, n) = (3, 11), (6, 8), and (9, 5)). As with GaN substrates (Ito, T.; Forman, S. M.; Cao, C.; Li, F.; Eddy, C. R., Jr.; Mastro, M. A.; Holm, R. T.; Henry, R. L.; Hohn, K.; Edgar, J. H. Langmuir 2008, 24, 6630-6635), alkylphosphonic acids formed SAMs on UV/O(3)-treated AlGaN substrates from their toluene solutions in contrast to other primary substituted hydrocarbons with a terminal -COOH, -NH(2), -OH, or -SH group. Diacetylenic alkylphosphonate SAMs on group-III nitrides could be polymerized by UV irradiation (254 nm), as indicated by the appearance of a visible absorption band around 640 nm and also by their significantly reduced desorption from the surface in a 0.1 M aqueous NaOH solution. A longer UV irradiation time was required to maximize the photopolymerization of a SAM having a diacetylene group close to the terminal phosphonate moiety, probably because of the hindrance of the topochemical polymerization due to the limited flexibility of the cross-linking moieties on an atomically rough substrate surface.

Alkylperfluorosilane Self-Assembled Monolayers on Aluminum: A Comparison with Alkylphosphonate Self-Assembled Monolayers

The performance of micro- and nanoelectromechanical systems depends on the surface properties of the substrate material, such as chemical composition, roughness, friction, adhesion, and wear. Substrates of aluminum deposited onto Si (Al/Si) have been chemically reacted with perfluorodecyldimethylchlorosilane (PFMS), octadecylphosphonic acid (ODP), decylphosphonic acid (DP), octylphosphonic acid (OP), and perfluorodecylphosphonic acid (PFDP) and then characterized by X-ray photoelectron spectroscopy (XPS), contact angle measurements, and atomic force microscopy (AFM). PFMS/Al self-assembled monolayers (SAMs) were studied by friction force microscopy, a derivative of AFM, to better understand their micro- and nanotribological properties. The adhesion forces for PFMS/Al SAMs were found to be lower when compared to those of bare Al/Si; however, the coefficient of friction for both was comparable. XPS analysis revealed the presence of the corresponding alkyl chain molecules on PFMS/Al, ODP/Al, DP/Al, OP/Al, an...