Siloxane Self-assembled Monolayers Research Articles

Surface energy patterning for ink-independent process optimization of inkjet-printed electronics

The applicability of inkjet-printed (opto-)electrical devices are hindered by their low lateral resolution, when compared to conventional techniques. The low lateral resolution is mainly caused by the flow and spreading of the functional ink on the substrate, which is determined by the substrate-ink-interaction. Recent approaches, that confine and control the spreading, have been developed. However, they suffer from low lateral resolution or the usage of physical barriers. The later needs an adjustment of the ink or may contain an overlaid height information. Both cases are not always applicable when fabricating functional devices. Herein, we report the utilization of a surface energy patterning approach based on siloxane self-assembled monolayers. The obtained energetic differences control the flow and suppress the spreading of the ink, without creating the necessity to alter the ink composition. Furthermore this approach leads to an improved structural fidelity and printing resolution of arbitrary shapes. With that, we were able to print silver- and gold-electrodes for organic filed-effect transistors with a channel length of <25 µm, fabricating feature sizes below the footprint of a single drop. The electrical characterization of these transistors revealed that the utilization of this surface energy patterning has no negative influence on the device performance. The introduced approach facilitates the process development and improves the quality and resolution of printed features. This will facilitate the fabrication of high-quality and high resolution printed electronic devices.

Selective Crystal Growth of Theophylline-Saccharin Cocrystal on Self-Assembled Monolayer from Incongruent System

This paper seeks to extend the screening methods for cocrystal incongruent systems by using siloxane self-assembled monolayers (SAMs). The theophylline (THE)–saccharin (SAC)–methanol incongruent system was chosen as a case study. The results of cocrystallization experiments showed that siloxane SAMs with exposed Cl groups can act as templates for the selective growth of THE–SAC cocrystal on the monolayer surface with relatively high purity, which was confirmed by Powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC). The observed selectivity is rationalized on the basis of two-dimensional geometric matching and chemical interactions at the SAM/crystal interfaces using a molecular modeling method.

Surface Structures of Amine-Bearing Siloxane Self-Assembled Monolayers: Influence of Conformation on Methylene Vibrational Frequencies

Functionalized self-assembled monolayers (SAMs) are of interest for numerous applications including materials for national security and defense, chemical and biological sensing, and electronic device components. Understanding the surface structures of SAMs is important for determining the functionality and efficiency of these systems and aiding in the design of advanced materials. In this study, the surface structures of amine-bearing siloxane SAMs on fused silica were investigated by vibrational sum frequency generation (VSFG) spectroscopy and density functional theory (DFT). VSFG spectra of the SAMs were collected in the C–H and N–H stretching regions, and observed spectral features were assigned to specific vibrational modes that provided information regarding the surface structure of the deposited SAM. The molecular conformation of secondary amine moieties was determined to have a significant effect on the vibrational frequencies of methylene vibrational modes. Red-shifting of the methylene symmetric stretching mode by greater than 50 cm–1 was observed experimentally in systems containing secondary amines. This effect was confirmed by DFT calculations and found to be a consequence of molecular conformation that allowed the formation of resonance structures depending on the position of the nitrogen lone-pair electrons with respect to C–N and C–H bonding and antibonding orbitals, respectively.

Large-Area Fabrication of Patterned ZnO-Nanowire Arrays Using Light Stamping Lithography

We demonstrate selective adsorption and alignment of ZnO nanowires on patterned poly(dimethylsiloxane) (PDMS) thin layers with (aminopropyl)siloxane self-assembled monolayers (SAMs). Light stamping lithography (LSL) was used to prepare patterned PDMS thin layers as neutral passivation regions on Si substrates. (3-Aminopropyl)triethoxysilane-based SAMs were selectively formed only on regions exposing the silanol groups of the Si substrates. The patterned positively charged amino groups define and direct the selective adsorption of ZnO nanowires with negative surface charges in the protic solvent. This procedure can be adopted in automated printing machines that generate patterned ZnO-nanowire arrays on large-area substrates. To demonstrate its usefulness, the LSL method was applied to prepare ZnO-nanowire transistor arrays on 4-in. Si wafers.

Dynamics within Alkylsiloxane Self-Assembled Monolayers Studied by Sensitive Dielectric Spectroscopy

Self-assembled monolayers are a ubiquitous laboratory tool and have been the subject of many experimental investigations which have primarily focused on static properties of full coverage monolayers, with the maximum density and ordering possible. In this work, dynamics within low density, planar siloxane self-assembled monolayers are studied utilizing highly sensitive dielectric spectroscopy. Dilute, disordered films were intentionally fabricated in order to study the widest range of possible motions. At low coverage, an interacting relaxation is observed, which has similar dynamics to polyethylene-like glass transitions observed in phase-segregated side-chain polymers, despite the rigidity of the substrate and the constraint of ethyl groups in relatively short chains. As density is increased, a second local relaxation, previously observed in three-dimensional SAMs and associated with rotation within a small segment of the alkyl chain, is also observed.

A Quick Route to Imaging Siloxane Self Assembled Monolayers(SAM)on Nanostructured Metal Oxides(NSMO)

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Formation of Aromatic Siloxane Self-Assembled Monolayers

We describe reproducible protocols for the chemisorption of self-assembled monolayers (SAMs), useful as imaging layers for nanolithography applications, from p-chloromethylphenyltrichlorosilane (CMPS) and 1-(dimethylchlorosilyl)-2-(p,m-chloromethylphenyl)ethane on native oxide Si wafers. Film chemisorption was monitored and characterized using water contact angle, X-ray photoelectron spectroscopy, and ellipsometry measurements. Atomic force microscopy was used to monitor the onset of multilayer deposition for CMPS films, ultimately allowing film macroscopic properties to be correlated with their surface coverage and nanoscale morphologies. Although our results indicate the deposition of moderate coverage, disordered SAMs under our conditions, their quality is sufficient for the fabrication of sub-100-nm-resolution metal features. The significance of our observations on the design of future imaging layers capable of molecular scale resolution in nanolithography applications is briefly discussed.

Perfecting Imperfect “Monolayers”: Removal of Siloxane Multilayers by CO2 Snow Treatment

Self-assembled monolayers (SAMs) of N-(3-triethoxysilylpropyl)-4-hydroxybutyramide were prepared on silicon oxide on silicon (Si/SiO(2)). Initial silane adsorption and high-temperature annealing led to a stable base monolayer with many large over-lying islands of disordered multilayers as a result of the non-self-limited growth process. The disordered multilayers were hydrolyzed and subsequently removed by CO(2) snow treatment. The resulting films were one monolayer thick as measured by ellipsometry. Atomic force microscopy, attenuated total reflection Fourier transform infrared spectroscopy, and contact angle analysis showed that the films were composed of monolayers with full and uniform surface coverage rather than nonuniform coverage by islands or patches of multilayers. Monolayers of octadecyltrichlorosilane were also prepared by multilayer removal via CO(2) treatment, showing the general applicability of the technique toward siloxane SAMs. We believe that CO(2) is an excellent solvent for weakly bound and hydrolyzed molecules that compose multilayers, and this ability to prepare near-perfect monolayer films from imperfect ones allows for less stringent formation conditions.

The effect of liquid-induced adhesion changes on the interfacial shear strength between self-assembled monolayers

Friction between chemically-modified tips and surfaces has been studied with chemical force microscopy (CFM) to evaluate the effect of changing solid/liquid free energy on energy dissipation in sliding tip-surface contact. Well-controlled conditions were necessary to attain a single asperity contact in these experiments. We found that in a series of methanol- water mixtures the interfacial shear strength between CH3-terminated surfaces of the siloxane self-assembled monolayers (SAMs) was independent of the adhesion force. The shear strength value of 10.2 ± 1.0 MPa found for this interface under methanol-water media is consistent with the previous studies of similar systems under dry gas conditions. A comparison to available data on interfacial shear strengths demonstrated that siloxane monolayers were much more effective in reducing friction than various carbon coatings.

Edge Transfer Lithography of Molecular and Nanoparticle Materials

A simple and general method which we call edge transfer lithography has been developed for large-area patterning of molecular and nanoparticle materials with line widths as small as 60 nm. The procedure employs standard “ink” and “stamp” microcontact printing techniques and takes advantage of the intrinsic topographic character of micropatterned elastomeric stamps and discontinuous dewetting behavior of ink solutions to selectively apply ink within the recesses of the stamp. In this way, molecules or particles are delivered from the stamp to a solid substrate of interest selectively along the edges of the stamp features. Siloxane self-assembled monolayers (SAMs) and titanium dioxide (TiO2) nanoparticle materials are directly patterned on glass substrates at nanometer resolution. Alkyl siloxane patterned SAM surfaces are used as a template structure for the guided self-assembly of molecular and nanoparticle materials. The surfaces are characterized by lateral force microscopy and noncontact atomic force mi...