Octadecylphosphonic Acid Molecules Research Articles

Patterning of Hybrid Metal Halide Perovskite via Printed Molecular Templates

AbstractPatterning metal halide perovskite thin films is a necessary pathway to expand their optoelectronic applications. However, developing a suitable patterning technique is challenging as conventional lithographic processes are either detrimental to the perovskite layer or lack compatibility with scalable fabrication processes used in the manufacturing of printed electronics. In this work, a complete bottom‐up patterning method is proposed based on de‐wetting from a hydrophobic molecular template, which constrains the perovskite ink to directly crystallize in selected hydrophilic regions. Octadecylphosphonic acid molecules are used as the hydrophobic template and are effectively transferred onto metal‐oxide substrates via micro‐contact printing. This allows for a low‐cost, rapid, and scalable micron‐scale patterning of perovskite thin films. Facile control over light transmittance is demonstrated by adjusting the amount of exposed area and the corresponding spectral shape changes shift the film's appearance toward being color‐neutral. Finally, the method's scalability and versatility are shown by fabricating 25 cm2 patterned films over rigid and flexible substrates.

Role of hydrophobic side chain in urea induced protein denaturation at interface

The molecular mechanism of denaturing ability of urea is still a subject of considerable debate due to two opposing mechanisms: direct and indirect. In the direct mechanism, urea directly disrupts hydrogen bonding and hydrophobic interactions within proteins. On the other hand, the indirect mechanism suggests that urea alters the properties of water and disrupts protein-protein interactions. Our aim is to unravel the denaturing mechanism of urea by studying its interaction with the side chain of octadecylphosphonic acid (ODPA)) as a mimicking surface of a protein. We employ vibrational sum frequency generation (VSFG) spectroscopy to examine the interaction between urea, the side chain of ODPA, and water molecules at the interface. Our findings suggest that urea interacts with the side chain of ODPA, effectively reducing the hydrophobic barriers provided by the long hydrophobic chain of the ODPA molecules for the water molecules at the interface. The interaction of the urea with the side chain of the ODPA molecules results in the alignment of water molecules, increasing their SFG intensity. Our findings indicate that the interaction of urea with the side chain plays a crucial role in governing the interaction between water and ODPA molecules. These outcomes help us understand the side chain's role in urea-induced protein denaturation at the interface.

Preparation of Superhydrophobic Wood Surfaces Modified Using MIL-88(Fe) via Solvothermal Method

A superhydrophobic wood surface was produced by employing the solvothermal method to form shuttle-like, well-crystallized MIL-88(Fe) on the surface of wood and assembling a Octadecylphosphonic acid (OPA) reagent. The nanosized MIL-88(Fe) molecule caused the wood’s surface to take on a nano mastoid shape. In addition, MIL-88(Fe) provides metal sites to capture OPA molecules, preventing the long-chain alkane hydrophobic group from contacting the surface of the wood. They both make a considerable difference in the growth of a hydrophobic wood surface. The results of the experiment indicate that the water contact angle (WCA) increases with reactant concentration. The WCA of the samples prepared with 5.0 × 10−2 M FeCl3 was 140.57°. When the reactant concentration was 10.0 × 10−2 M, the greatest WCA = 153.69° reading was obtained. The research’s findings present a novel technique for producing superhydrophobic wood surfaces.

Corrosion resistance improvement of the Ti6Al4V/UHMWPE systems by the assembly of ODPA molecules by dip coating technique

Living with degenerative diseases, such as arthritis and osteoporosis, is challenging if orthopedic devices manifest adverse effects caused by corrosion processes. Ti6Al4V alloy is used to manufacture orthopedic implants due to its excellent mechanical and osseointegration properties. Nonetheless, it has poor resistance to wear and corrosion by biological fluids and mechanical activity. This degradation process generates the need to improve the corrosion resistance of metallic biomaterials used as biomedical implants. Dip-coating technique is a wet coating method used to lessen wear damage on the metal surface and can produce coatings using a wide variety of molecules at a low cost. In this work, Ti6Al4V alloys were coated with ultra-high molecular weight polyethylene (UHMWPE) and Octadecylphosphonic Acid (ODPA) films forming a UHMWPE/ODPA bilayer coating by dip-coating method to improve protection efficiency against corrosion in phosphate-buffered isotonic saline solutions and proposed it as alternative coatings to delay the failure of medical implants. The optimization of individual coated systems were obtained with an immersion time of 40 s (Ti6Al4V/UHMWPE) and 30 h (Ti6Al4V/ODPA) with corrosion current densities of 1.51 × 10−9 A cm−2 and 6.8 × 10−8 A cm−2, respectively. The formation of bilayer coatings reduces the average roughness from 19.34 nm (Ti6Al4V/UHMWPE) to 12.67 nm (Ti6Al4V/UHMWPE/ODPA). ODPA deposition on UHMWPE films changes the corrosion rate by interfering with the anodic and cathodic reactions, reducing the corrosion rate to 7.46 × 10−4 μm y−1 and an estimated corrosion protection efficiency of about 99.99 %. The results show a superior performance as a protective barrier over the individual films (1.19 μm y−1 with 97.2 %, and 0.026 μm y−1 with 99.9 %, ODPA, and UHMWPE, respectively), improving the corrosion resistance of the Ti6Al4V alloys.

Bidirectional Control of the Band Bending at the (2̅01) and (010) Surfaces of β-Ga2O3 Using Aryldiazonium Ion and Phosphonic Acid Grafting

Beta gallium oxide (β-Ga2O3) is an ultrawide-bandgap semiconductor with one of the highest-known breakdown strengths (∼8 MV/cm) making it a strong candidate for high-efficiency power electronics, deep-ultraviolet photodetectors, and transparent electronic devices. Bare β-Ga2O3 surfaces exhibit a strong upward band bending and electron depletion that is reduced by the formation of a hydroxyl termination on exposure to the atmosphere, although this effect varies with exposure conditions and the processing history of different samples. This work investigates the covalent modification of (2̅01) and (010) β-Ga2O3 surfaces with organic layers, as a mechanism for more effectively controlling their surface band bending. We compare the different electronic effects of grafted layers formed by the electrochemical reduction of 4-nitrobenzenediazonium ions and the spontaneous grafting of octadecylphosphonic acid (ODPA). Atomic force microscopy, synchrotron X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure spectroscopy confirmed the presence of few-nanometer layers of covalently attached nitrophenyl (NP) and ODPA molecules. Valence band XPS showed that NP modification produced upward band bending shifts of +0.51 and +0.53 eV on (2̅01) and (010) β-Ga2O3, respectively, with further increases of +0.35 and +0.20 eV after X-ray-induced reduction of the nitro substituent to amino-like moieties. In contrast, ODPA modification produced downward shifts in surface band bending of −0.36 and −0.07 eV on (2̅01) and (010) β-Ga2O3, respectively. Our study demonstrates that covalently bound NP and ODPA molecules can be used to significantly modify the electronic properties of β-Ga2O3 surfaces, a finding that should prove useful for electronic applications of this material.

Controlling interfacial interactions in LDPE/flax fibre biocomposites by a combined chemical and radiation-induced grafting approach

By combining chemical and gamma radiation treatments, we show that it is possible to improve the interfacial adhesion between natural fibres and a non-polar and non-reactive matrix such as low density polyethylene (LDPE), and the resulting mechanical performances of their biocomposites. To this aim, flax fibres are first functionalized with octadecylphosphonic acid (ODPA) and the quantity, effective grafting and localization of ODPA molecules on flax fibres are characterized by ICP-AES, solid state 31P NMR and SEM-EDX. ODPA molecules are effectively grafted onto flax fibres at a content of roughly 2.5 wt% and mostly localized at the fibre surface. Moreover, contact angle measurements as well as water sorption kinetics give evidence for increased hydrophobic and oleophilic character of ODPA treated fibres. Pellets of LDPE/flax fibre biocomposites obtained by melt extrusion are then submitted to gamma radiation and processed by injection moulding. Based on Soxhlet extraction experiments and SEM observations, it is shown that LDPE cross-linking rate induced by gamma radiation is locally enhanced at the fibre/matrix interface, suggesting that regio-selective cross-linking occurred between LDPE chains and the alkyl chain of ODPA grafted on flax fibre surface. Consequently, the uniaxial tensile performances of the biocomposites are enhanced by this combined chemical and radiation-induced grafting approach, especially their ultimate properties (up to 40% increase in the work of rupture). These results evidence an enhanced interfacial adhesion that is also supported by more cohesive interfacial failure and higher work of rupture through in-situ micro-mechanical tensile SEM experiments.

Self-Assembled Monolayers Get Their Final Finish via a Quasi-Langmuir-Blodgett Transfer.

The growth of self-assembled monolayers (SAMs) of octadecylphosphonic acid (ODPA) molecules on α-Al2O3(0001) and subsequent dewetting of the SAMs were studied with a combination of in situ sum-frequency generation (SFG) and molecular dynamics (MD) simulations. Although SAM growth after deposition times >8 h reduces to nearly negligible values, the resultant ODPA SAMs in solution are still not in a well-ordered state with the alkyl chains in all-trans configurations. In fact, in situ SFG spectroscopy revealed a comparatively high concentration of gauche defects of the SAM in the ODPA 2-propanol solution even after a growth time of 16 h. Here, results of the MD simulations strongly suggest that defects can be caused by ODPA molecules which are not attached to the substrate but are incorporated into the SAM layer with the polar headgroup oriented into the 2-propanol solvent. This inverted adsorption geometry of additional ODPA molecules blocks adsorption sites and thus stabilizes the SAM without improving ordering to an extent that all molecules are in the all-trans configuration. While persistent in solution, the observed defects can be healed out when the SAMs are transferred from the solvent to a gas phase. During this process, a quasi-Langmuir-Blodgett transfer of molecules takes place which drives the SAM into a higher conformational state and significantly improves its quality.

Fabrication of controllable and stable In2O3 nanowire transistors using an octadecylphosphonic acid self-assembled monolayer

The controllability and stability of nanowire transistor characteristics are essential for the development of low-noise and fast-switching nano-electronic devices. In this study, the positive shift of threshold voltage and the improvement of interface quality on In2O3 nanowire transistors were simultaneously achieved by using octadecylphosphonic acid (OD-PA) self-assembly. Following the chemical bond of OD-PA molecules on the surface of In2O3 nanowires, the threshold voltage was positively shifted to 2.95 V, and the noise amplitude decreased to approximately 87.5%. The results suggest that an OD-PA self-assembled monolayer can be used to manipulate and stabilize the transistor characteristics of nanowire-based memory and display devices that require high-sensitivity, low-noise, and fast-response.

Effect of Zn2 + Concentration on the Adsorption of Organophosphonic Acids on Nanocrystalline ZnO Surfaces

The effect of the presence of Zn2+ ions on the adsorption of octadecylphosphonic acid (ODPA) on nanocrystalline ZnO films has been studied by means of Quartz Crystal Microbalance (QCM) technique and complementary ex-situ analysis of film properties. Phosphonic acid moiety has sufficient acidity, even in organic solvents, to cause dissolution of ZnO. Dissolved Zn2+ ions form complexes with the ODPA molecules in the solution, leading to the deposition of thick and undefined precipitation layers. Our results indicate that the formation of such precipitation layers could be prevented by the addition of appropriate amounts of Zn2+ ions into the deposition solution. Bi-functional monomolecular linkers with phosphonic acid head-groups are excellent candidates for application-specific functionalization of nanostructured ZnO films as well as ZnO nanoparticles. The results presented here demonstrate a straight forward method to increase the film quality.

Chemical stabilization and improved thermal resilience of molecular arrangements: possible formation of a surface network of bonds by multiple pulse atomic layer deposition.

In this work, we make use of an atomic layer deposition (ALD) surface reaction based on trimethyl-aluminum (TMA) and water to modify O-H terminated self-assembled layers of octadecylphosphonic acid (OPA). The structural modifications were investigated by X-ray reflectivity, X-ray diffraction, and atomic force microscopy. We observed a significant improvement in the thermal stability of ALD-modified molecules, with the existence of a supramolecular packing structure up to 500 °C. Following the experimental observations, density functional theory (DFT) calculations indicate the possibility of formation of a covalent network with aluminum atoms connecting OPA molecules at terrace surfaces. Chemical stability is also achieved on top of such a composite surface, inhibiting further ALD oxide deposition. On the other hand, in the terrace edges, where the covalent array is discontinued, the chemical conditions allow for oxide growth. Analysis of the DFT results on band structure and density of states of modified OPA molecules suggests that besides the observed thermal resilience, the dielectric character of OPA layers is preserved. This new ALD-modified OPA composite is potentially suitable for applications such as dielectric layers in organic devices, where better thermal performance is required.

Oxidizing octadecylphosphonic acid molecules without disrupting their self-assembled monolayers

In examination of oxidation of octadecylphosphonic acid (OPA) self-assembled monolayers (SAMs) prepared on the native oxide of a Si wafer upon exposure to UV/ozone (UVO) for up to 5 min, atomic force microscopy studies of the surface elucidated that there were no changes in morphology of the SAMs. Surprisingly, investigations on the same samples of OPA SAMs using time-of-flight secondary ion mass spectrometry revealed that the intensity of the deprotonated molecular ion fragment decreased exponentially to approximately one fourth of that of the control. We clarify that UVO-induced oxidation of alkyl chains of the OPA molecules in their SAMs precedes the disruption of the monolayer structure, which is the basis for controlling surface chemistry of SAMs with brief UVO exposure.

Influence of preparation methods on the properties of self-assembled films of octadecylphosphonate on Nitinol: XPS and EIS studies

The NiTi alloy (Nitinol), with its favorable micro-structured properties and self-passivity (resembling that of pure Ti) is used as an implant material for arterial stents and orthodontic wires. During the long term contact of the alloy with aggressive environment of human body, corrosion by releasing Ni2+ ions can occur. Thus, the usefulness of such material can be dramatically enhanced if its interface structure and surface chemistry are controlled. The octadecylphosphonate interface (ODP) synthesis, which involves a self-assembled covalently (monodentate type) bonded film of octadecylphosphonic acid (ODPA) on the oxide covered NiTi surface, produces stable and corrosion resistant interfaces. This paper introduces integrated approach to the characterization of the NiTi/ODP interfacial architecture as well as the structure of the electrified ODP/solution interface using high-resolution XPS and in situ EIS measurements. The main focus of this work was to determine the influence of the ODPA deposition method (spray and immersion) on the depth-dependent structural characteristics and orientation of ODPA molecules in the surface film by means of angle resolved XPS. Mechanically strong and chemically stable NiTi/phosphonate interfaces have the potential for their successful implementation in stent technologies.

Thermally driven stability of octadecylphosphonic acid thin films grown on SS316L

Stainless steel 316L is widely used as a biomedical implant material; however, there is concern about the corrosion of metallic implants in the physiological environment. The corrosion process can cause mechanical failure due to resulting cracks and cavities in the implant. Alkyl phosphonic acid forms a thin film by self-assembly on the stainless steel surface and this report conclusively shows that thermal treatment of the octadecylphosphonic acid (ODPA) film greatly enhances the stability of the ODPA molecules on the substrate surface. AFM images taken from the modified substrates revealed that thermally treated films remain intact after methanol, THF, and water flushes, whereas untreated films suffer substantial loss. Water contact angles also show that the hydrophobicity of thermally treated films does not diminish after being incubated in a dynamic flow of water for a 3-hour period, whereas the untreated film becomes increasingly hydrophilic due to loss of ODPA. IR spectra taken of both treated and untreated films after water and THF flushes show that the remaining film retains its initial crystallinity. A model is suggested to explain the stability of ODPA film enhanced by thermal treatment. An ODPA molecule is physisorbed to the surface weakly by hydrogen bonding. Heating drives away water molecules leading to the formation of strong monodentate or mixed mono/bi-dentate bonds of ODPA molecule to the surface.

Revealing Different Bonding Modes of Self-Assembled Octadecylphosphonic Acid Monolayers on Oxides by Time-of-Flight Secondary Ion Mass Spectrometry: Silicon vs Aluminum

Condensed octadecylphosphonic acid (OPA) dimers, i.e., two OPA molecules combined with the loss of a water molecule, were detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) on OPA self-assembled monolayers (SAMs) that are only weakly bonded on the native oxide layer of a silicon wafer. In contrast, these condensed dimers were absent on OPA SAMs formed on the oxide layer of an aluminum film, where the OPA molecules are chemically bonded on the substrate through a P-O-Al linkage. These observations lead us to conclude that the OPA molecules in their SAMs have to be free from chemical bonding with the substrate in order for the primary ion beam to generate ion fragments of the condensed dimer. We demonstrate that the detection of condensed OPA dimers serves as an analytical criterion for TOF-SIMS to reveal the bonding mode of OPA molecules in their SAMs on different oxides.

Assembly of octadecyl phosphonic acid on the α-Al 2O 3 (0 0 0 1) surface of air annealed alumina: Evidence for termination dependent adsorption

Self-assembly of octadecyl phosphonic acid (ODPA) from solution to the (0 0 0 1) plane surface of single crystal alumina is studied using atomic force microscopy (AFM), wettability measurements, transmission infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). The crystals were annealed in air at 1300 °C to produce a surface with terraces of 0.2 nm height. This resulted in a surface comprising a mixture of terraces terminated by either oxygen or aluminium atoms. After exposure of this surface to a solution of ODPA, the XPS C1s core level reveals partial displacement of adventitious carbonaceous material by the ODPA. The phase contrast image from tapping mode AFM acquired during assembly reveals that the surface chemistries of terraces differ significantly, suggesting along with the topography images that ODPA molecules adsorbed preferentially to certain terraces. We suggest that the ODPA adsorbs preferentially to the aluminium terminated terraces that are hydroxylated in air. The adsorption to only Al-terminated terraces at the micron scale is consistent with the apparent low coverage of ODPA estimated using techniques sampling the surface on a millimetre scale including XPS and wettability measurements. This behaviour is compared to ODPA close-packed monolayer coverages formed on the amorphous oxide/hydroxide surface of aluminium metal.

ToF−SIMS Investigation of Octadecylphosphonic Acid Monolayers on a Mica Substrate

In this paper, time-of-flight secondary ion mass spectrometry (ToF-SIMS) under static conditions was used to investigate self-assembled monolayers (SAMs) of octadecylphosphonic acid (OPA) formed on freshly cleaved muscovite mica substrates. The coverage of OPA on mica ranged from 20 to 100%, with a film thickness of 1.7+/-0.2 nm, which was determined by atomic force microscopy (AFM) imaging. The relative intensity of the specific secondary ion species associated with the OPA and with the exposed mica substrate exhibited good correlation with surface coverage. An excellent correlation was also observed (R2=0.98) between the relative SIMS [OPA-H]- intensity and the surface carbon concentration (OPA C 1s, in atomic %) from XPS at the prescribed surface coverage. The observation of positive and negative OPA molecular attachment of secondary ions involving the substrate species is discussed in terms of the chemical affinity of the OPA phosphonate headgroup for the cleaved mica surface as well as the sampling depth. In addition, the OPA molecular attachment species formed with the potassium ions on the cleaved mica substrate dominated the positive secondary ion mass spectrum in the high-mass range. A temperature-dependent, ToF-SIMS study employing in situ heating of a 100% coverage OPA monolayer revealed that the molecules begin to diffuse above approximately 80 degrees C, resulting in a decrease in the relative secondary ion yield of the OPA-specific secondary ions. This observation is hypothesized to be due to a decrease in the effective coverage of the substrate by the OPA molecules, which in turn could be due to the formation of multilayers upon heating in an effort to minimize the energy of the system. The interesting behavior of the novel OPA dimer species as a function of temperature is also reported. It was observed that the relative intensity of OPA and the mica-specific secondary ion peak intensities to that of Si (mica substrate) provides an effective means to estimate the change in coverage at elevated temperatures.

Structural Investigations of Octadecylphosphonic Acid Multilayers

In this work, different multilayer conformations of a linear amphiphilic molecule, octadecylphosphonic acid (OPA), were investigated by atomic force microscopy (AFM), X-ray reflectivity, and X-ray diffraction. It was found that these molecules spontaneously pack into well-organized self-assembled bilayers (SABs) when the structures are formed inside concentrated solutions and/or after slow solvent evaporation. The molecular structure of an OPA SAB was observed to be dependent on its position along a stack of bilayers: when the SAB is at, or close to, the stack surface, OPA molecules are vertically aligned and form 5 nm thick bilayers; when it is in the middle of a stack of hundreds, or thousands, of bilayers, OPA molecules are tilted and form 3.4 nm thick bilayers. The van der Waals interactions among the long OPA alkyl chains were used to explain and also predict some features of the molecular arrangement inside both bilayer types. Using the AFM technique, which also enabled the application of pressure onto a bilayer surface, oblique and hexagonal molecular packings were observed, probably corresponding to both 5 and 3.4 nm thick bilayers, respectively.

Thermal Stability Study of Self-Assembled Monolayers on Mica

In this Letter, we report on the use of atomic force microscopy to study the thermal stability of self-assembled monolayers (SAM) of octadecylphosphonic acid (OPA) grown on mica. The samples were sequentially annealed for 30 min steps at temperatures ranging from 50 to 200 °C. A major change in the SAM morphology takes place at temperatures ∼95 °C, with the disappearance of the original flat-topped and partial-coverage SAM morphology. Concomitantly, the nucleation and growth of OPA precipitates in the investigated temperature range are observed. Two separate regimes are identified: initially, for temperatures up to ∼110 °C, nucleation of OPA precipitates occurs, increasing their number density. Then, for temperatures above ∼10 °C, growth of OPA precipitate size dominates, with the density of precipitates remaining approximately constant. A simple model used to fit the experimental data of both regimes enables an estimate of ∼9 kcal/mol as the energy required for the disorganization (Ed) of OPA molecules on mica.