FT-IR RAS Research Articles

Langmuir Nanoarchitectonics: One-Touch Fabrication of Regularly Sized Nanodisks at the Air–Water Interface

In this article, we propose a novel methodology for the formation of monodisperse regularly sized disks of several nanometer thickness and with diameters of less than 100 nm using Langmuir monolayers as fabrication media. An amphiphilic triimide, tri-n-dodecylmellitic triimide (1), was spread as a monolayer at the air-water interface with a water-soluble macrocyclic oligoamine, 1,4,7,10-tetraazacyclododecane (cyclen), in the subphase. The imide moieties of 1 act as hydrogen bond acceptors and can interact weakly with the secondary amine moieties of cyclen as hydrogen bond donors. The monolayer behavior of 1 was investigated through π-A isotherm measurements and Brewster angle microscopy (BAM). The presence of cyclen in the subphase significantly shifted isotherms and induced the formation of starfish-like microstructures. Transferred monolayers on solid supports were analyzed by reflection absorption FT-IR (FT-IR-RAS) spectroscopy and atomic force microscopy (AFM). The Langmuir monolayer transferred onto freshly cleaved mica by a surface touching (i.e., Langmuir-Schaefer) method contained disk-shaped objects with a defined height of ca. 3 nm and tunable diameter in the tens of nanometers range. Several structural parameters such as the disk height, molecular aggregation numbers in disk units, and 2D disk density per unit surface area are further discussed on the basis of AFM observations together with aggregate structure estimation and thermodynamic calculations. It should be emphasized that these well-defined structures are produced through simple routine procedures such as solution spreading, mechanical compression, and touching a substrate at the surface. The controlled formation of defined nanostructures through easy macroscopic processes should lead to unique approaches for economical, energy-efficient nanofabrication.

Synthesis and DNA binding behavior of a naphthalene diimide derivative carrying two dicobalt hexacarbonyl complexes as an infrared DNA probe

Synthetic naphthalene diimide probe 1 having two dicobalt hexacarbonyl complexes at its substituent termini, which forms a stable threading intercalate complex with double stranded DNA, could utilized in the detection of the target DNA hybridized with DNA probe immobilized on a gold surface using Fourier Transform Infrared Reflection–Absorption Spectroscopy (FT-IR RAS) technique. Naphthalene diimide having two dicobalt hexacarbonyl complexes at its substituent termini 1 was designed and synthesized as an infrared probe for double stranded DNA. Spectrophotometric and viscometric DNA binding studies of 1 and naphthalene diimide having two acetylene moieties 2 as its precursor were carried out to prove their threading intercalation binding modes. Fourier Transform Infrared Reflection–Absorption Spectroscopy (FT-IR RAS) measurements were achieved for DNA-immobilized on a gold surface before and after hybridization with complementary DNA strand. Distinguished absorption peaks assigned to the dicobalt hexacarbonyl complexes were obtained in the case of the formation of double stranded DNA after treatment with 1 . This result revealed that 1 can be used as an infrared probe for monitoring double stranded DNA.

DNA Molecules on GaP (100) Surfaces: Spectroscopic Characterization and Biospecificity Assessment

DNA-modified surfaces have been the subject of considerable research activity in the field of bionanotechnology. Such surfaces can be incorporated into novel diagnostic devices that utilize sequencing and gene mapping technologies. 3] For example, the use of DNAbased sensors shows promise for rapid, economical and accurate detection of genetic diseases. In such sensor devices it is very important to have a robust and reproducible packing of DNA molecules. Different research groups have explored the absorption of biomolecules and the integration of biological systems on inorganic materials such as gold and silicon. Recently, there has been an interest in extending such studies to III–V semiconductor substrates. Gallium phosphide (GaP) is an attractive semiconductor material due to its usage in charge storage devices and low-noise detection photodiodes. This material offers promise for the fabrication of novel biosensors. Our previous work demonstrated that GaP ACHTUNGTRENNUNG(100) remains stable after surface functionalization with well-parked adlayers and high molecular coverages. Herein, we describe the covalent functionalization and characterization of H-doped GaP ACHTUNGTRENNUNG(100) with modified DNA strands. We demonstrate that photochemical functionalization with undecylenic acid (UDA) can modify GaP substrates and that the terminal carboxylic acid groups can be used for the successful immobilzation of biomolecules (Scheme 1). In our approach, we control the orientation of modified DNAs by reacting the carboxylic acid-terminated GaP ACHTUNGTRENNUNG(100) surfaces with a mixture of amine-terminated ssDNA and a spacer, hexylamine (HA). We also confirm the bioactivity of biotin-modified DNA by the use of streptavidin-modified nanoparticles and Cy3-labeled streptavidin. The following techniques are used to complete the physical characterization of the surfaces: water contact angle (WCA), atomic force microscopy (AFM), Fourier transform infrared reflectance absorbance spectroscopy (FT–IRRAS). Prior to any spectroscopic analysis each modified surface is evaluated using WCA and AFM. The data, summarized in the Supporting Information, follows the expected hydrophicilicity trend due to the nature of the end groups. In addition, no major changes in roughness are observed after each treatment. Initial spectroscopic analysis of the modified surfaces by FT–IRRAS spectroscopy provides us with information about the adsorbates’ orientation on the GaP surface. The FT–IRRAS vibrations for H-doped, Br-modified DNA/HA, biotin-modified DNA/HA and biotin-modified DNA/HA/streptavidin nanoparticles GaP ACHTUNGTRENNUNG(100) steps are shown in Figure 1. We place a Br-label at the 5’ end of the DNA so that we can use it as a way to prove that molecules are on the surface by X-ray photoelectron spectroscopy (XPS). The FT–IRRAS spectrum of H-doped GaP ACHTUNGTRENNUNG(100) does not show any peaks in the low and high frequency regions, as one would expect to be the case immedi[a] Dr. R. Flores-Perez, Prof. A. Ivanisevic Department of Chemistry Weldon School of Biomedical Engineering, Purdue University 206 S. Martin Jischke Drive, West Lafayette, IN 47907 (USA) Fax: (+1)7654961459 E-mail : albena@purdue.edu [b] Dr. D. Y. Zemlyanov Birck Nanotechnology Center Purdue University, West Lafayette, IN 47907 (USA) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.200800166. Scheme 1. Surface coupling chemistry used to modify GaP with DNA molecules.

Sequence-Specific Control of Azobenzene Assemblies by Molecular Recognition of DNA

We investigated the molecular recognition between the amphiphile AzoAde, which is composed of azobenzene in the hydrophobic and adenine in the hydrophilic portion of the molecule, and oligonucleotides having a homogeneous base (dA30, dT30, dG30, and dC30) at the air-water interface. On the basis of the complementary base-pairing of DNA in the duplex, orderly arrangement of AzoAde on templated dT30 was examined using pi-A isotherm, UV-vis RAS, FT-IR RAS, and XPS measurements. Although there was little interaction between AzoAde and mismatched oligonucleotides (dA30, dG30, and dC30), AzoAde prepared on a dT30 subphase stoichiometrically assembled and interacted with dT30, subsequently forming a J-form assembly at the air-water interface. AFM observation of the LB films revealed the nanostructure of the J-formed AzoAde monolayer on the dT30 subphase as well as the domain structures of the H-formed monolayers on the other oligonucleotide subphases. Therefore, dT30 has a potential application as a template for assembling AzoAde at the air-water interface.

The Influence of Chemical Pre-treatment and Magnesium Surface Enrichment on Bonding of Succinic Acid Molecules to Aluminium Alloy

In the present study a combined Fourier Transform Infrared Reflection–Absorption Spectroscopy (FT-IR–RAS) and Auger electron spectroscopy (AES) analysis was performed to investigate the bonding of organic coatings to oxides formed on Al–Mg based alloys. The interfacial bonding of a model molecule, succinic acid, mimicking the functional groups used in practical coatings was studied in detail on various differently pre-treated aluminium alloy (AA5182, 4.8 wt% magnesium) surfaces. Besides these differently pre-treated alloy surfaces, also pure magnesium and aluminium were studied for reference. The surface and near-surface composition of the alloys was studied by Auger electron spectroscopy, ion-milling away the surface oxides to obtain a depth profile. The results show that after heat treatment, the oxides are as much enriched in magnesium as aluminium although the bulk concentration of magnesium is only 4.8 wt%. FT-IR–RAS shows that bonding of the succinic acid molecules takes place in a range of configurations, varying between bridging bidentates and unidentates. The relative portion of unidentates increases with the magnesium surface concentration. This is attributed to the difference in bond lengths of Mg–O and Al–O, forcing the carboxylic acid groups to stretch or to attach to only one oxide group (unidentate) instead of two (bidentate). Also the mixed OH/CO3 surface after Mg enrichment at the surface has less room for bonding with two groups, thus affecting the bonding configuration in a similar way.

Formation of oriented polypeptides on Au(111) surface depends on the secondary structure controlled by peptide length

We synthesized three different lengths of poly(L-lysine) containing an -SH group at the terminal (PLL(n)-SH, n (polymerization degree) = 4, 10, 30) and adsorbed them on an Au(111) surface. To analyze the formation process and the structure of self-assembled monolayers (SAMs), we used atomic force microscopy (AFM) and Fourier transform infrared reflection absorption spectra (FT-IR RAS). At the initial stage of SAM growth, formation of nanosize domains was confirmed by AFM imaging. The alpha-helical PLL(30)-SH exhibited a well-defined SAM structure after adsorption reached equilibrium. The alpha-helical PLL(30)-SH was almost perpendicular to the gold surface and exhibited interesting molecular packing due to the secondary structure of PLL(30)-SH and the underlying Au(111) array. The tilt angle of the helix axis from the substrate normal was estimated to be about 50 degrees (AFM) and 44 degrees (FT-IR RAS) respectively. On the other hand, PLL(4)-SH and PLL(10)-SH formed beta-sheet-type SAMs on the Au(111) surface based on the structure determined by FT-IR RAS spectrum.

Interaction Analysis of the Carcinoembryonic Antigen (CEA) with Its Monoclonal Antibody Immobilized on a Gold Surface Using Fourier Transform Infrared Reflection-Absorption Spectroscopy (FT-IR RAS)

A monoclonal antibody for the carcinoembryonic antigen (CEA) was immobilized on a gold chip surface covered by a self-assembled monolayer of 11-mercaptoundecanoic acid. Upon the addition of CEA, a Fourier transform infrared reflection-absorption spectroscopy (FT-IR RAS) measurement showed an increased absorption at around 1500 - 1700 cm(-1), corresponding to its amide structures. Another addition of CEA polyclonal antibody on this chip caused a further increase of the absorption in this region only after a treatment with CEA. This result shows that an antibody-fixed gold surface coupled with an FT-IR RAS measurement provides a new tool for detecting the antibody-antigen interaction.

Observation of Single Helical Peptide Molecule Incorporated into Alkanethiol Self-Assembled Monolayer on Gold by Scanning Tunneling Microscopy

The bicomponent self-assembled monolayers (SAMs) were formed by incorporation of helical peptides into the alkanethiol monolayer, which was prepared in advance on gold substrate, and were characterized by Fourier transform infrared reflection-absorption spectroscopy (FTIR RAS) and scanning tunneling microscopy (STM). FTIR RAS spectra showed that the helical peptides were incorporated into the defects in the alkanethiol SAM without disturbing the film structure. A single helical peptide molecule was observed clearly in the bicomponent SAMs by STM. Several helical peptides associated together in a parallel arrangement to form a helix-bundle structure. Observation of the long molecule of ∼4 nm length standing vertically on the surface indicated that electron transfer occurred over a long distance through the helical peptide under the STM conditions.

Subsurface reactions of silicon nitride in a highly selective etching process of silicon oxide over silicon nitride

In situ subsurface reaction measurements of silicon nitride in a selective etching process of silicon oxide over silicon nitride using an x-ray photoelectron spectroscopy (XPS) and a Fourier transform infrared reflection absorption spectroscopy (FTIR RAS) have been carried out. Under low selectivity etching conditions using an electron cyclotron resonance plasma employing a pure octafluorocyclobutane (C4F8) gas, a clear difference has been observed between time-evolution spectra of FTIR RAS and those of XPS on the etched silicon nitride films. From these results it has been found that the etching reaction layer is thicker than that under highly selective etching conditions and that SiF3 bonds are located in the deeper region rather than in the shallow region of the reaction layer. On the other hand, under highly selective etching conditions employing C4F8 gas diluted by Ar gas, it has been observed that the shallow region of the reaction layer in the etched silicon nitride films becomes C–C cross-linking-rich and CN sp2 bond-rich. From these results, it is concluded that the C–C cross linking prevents CN sp2 bonds from reacting with F atoms, resulting in the suppression of the etch by-products such as FCN.

Study of interaction between polyimide and Cu under a high humidity condition

Polyimide (PI) films coated on Cu films were treated under a high humidity condition. FT-IR RAS measurements have clarified the interface reactions of Cu with PI, the hydrolysis of imide functional group and formation of Cu carboxylate. From the calculation of RAS spectra measured at various incident angles, the diffusion of Cu carboxylate was confirmed from interface to the surface of PI. The diffusion length of Cu carboxylate ranges about 1 μm from Cu interface. The RAS result coincides with the ATR depth profile result and TEM-EDX image. Transmission electron microscope (TEM) images show that Cu diffuses mainly into the Cu carboxylate formation under our high humidity condition.

Formation of silicon nitride gate dielectric films at 300 °C employing radical chemical vapor deposition

Silicon nitride (SiNx) ultrathin gate dielectric films for ultralarge-scale integrated circuits have been successfully formed by radical chemical vapor deposition (R-CVD) at 300 °C. In this process, charged species incident on the silicon (Si) substrate during the growth were eliminated with the magnetic field in electron cyclotron resonance plasma-enhanced CVD employing nitrogen and silane (N2/SiH4) gases. By using R-CVD, SiNx films with very low leakage current and near-ideal dielectric constant (ε=7.2) have been obtained. In situ Fourier transform infrared reflection absorption spectroscopy (FT-IR RAS) has confirmed that the Si–N bonds are increased and the voids in films are reduced by eliminating charged species. A key factor for forming ultrathin SiNx films of high quality at 300 °C is discussed, based on characterization of films synthesized with and without charged species on the substrate using in situ x-ray photoelectron spectroscopy, in situ FT-IR RAS, and in situ atomic force microscopy.

Corrosion protection of epoxy-coated steel using different silane coupling agents

To suppress steel corrosion at elevated temperature and in humid condition, silane coupling agents N-β-aminoethyl aminopropyltrimethoxysilane (AAPS), γ-glycidoxypropyltrimethoxysilane (GPS), and bis[3-(trimethoxysilyl)-1-phenylpropyl]tetrasulfide (RC-2) were introduced as primers into an epoxy/steel system. Silane coupling agents and epoxy were coated onto the steel surface using the solution casting method. The polymer degradation and steel corrosion formation after heat and humid treatment were investigated by Fourier transform infrared reflection and absorption spectroscopy (FTIR–RAS) and scanning electron microscopy (SEM). Compared to various silane treated epoxy/steel systems, the AAPS-treated epoxy/steel (AAPS/epoxy = 6 : 4) system suppressed steel corrosion at 400°C for 10 min in air and for 5 days at 60°C in 100% relative humidity. This is due to the formation of SiOSi linkage and FeOSi bond on steel surface, which are resistant to water diffusion and thermally stable at elevated temperature. The relationship between chemical bonding at the steel–epoxy interface and corrosion protection on the steel surface was also investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 585–593, 1999

In situ FT–IRRAS study of SO 2 adlayers formed on Pt(111) electrodes from open-circuit adsorption in acidic media

The irreversible adsorption of SO 2 on Pt(111) electrodes has been studied in acid media by means of cyclic voltammetry and in situ FT–IRRA Spectroscopy. The resulting adsorbed residue presents a characteristic vibrational band at 1220 cm −1 (0.65 V) either in 0.5 M HClO 4 or 0.5 M HCl. In the potential region of constant coverage (0.65–1.0 V) the bandcentre frequency increases linearly with potential at a tuning rate of 65–75 cm −1 V −1. This shift may result from mixed contributions from Stark and/or backbonding effects. Below 0.65 V, the abrupt decrease in band frequency can be linked to the weakening of the dipole–dipole coupling effect resulting from the decrease in SO 2 surface coverage. From the vibrational data for SO 2–transition metal complexes and with the aid of the surface selection rule, the band at 1220–1240 cm −1 can be assigned to the asymmetric stretching mode of undissociated SO 2, bound to the surface via S and one of the O atoms in a η 2-bridging configuration.

In situ infrared reflection and transmission absorption spectroscopy study of surface reactions in selective chemical-vapor deposition of tungsten using WF6 and SiH4

The adsorption of tungsten hexafluoride (WF6) and monosilane (SiH4) in selective chemical-vapor deposition (CVD) of tungsten (W) is investigated in situ using Fourier-transform infrared reflection and transmission absorption spectroscopy (FTIR RAS and TMS). The selectivity for W growth is found to originate from the dissociation of SiH4 on a W surface. That is, SiH4 dissociates on a W surface to form Si-containing adsorbed species when the W surface is exposed to SiH4 at temperatures higher than 110 °C, whereas SiH4 does not dissociate on a SiO2 surface. On the other hand, when W and SiO2 surfaces are exposed to WF6 at temperatures from 20 to 300 °C, no adsorbed species are observed by FTIR RAS. However, WF6 can easily react with the Si-containing adsorbed species on a W surface to form W and byproduct gases of SiHF3 and SiF4. The main surface reaction of selective W CVD can be expressed as WF6+2SiH4=W+2SiHF3+3H2. These experimental results support the selective W-CVD mechanism previously proposed, which shows that dissociation of SiH4 and not the dissociation of WF6 has a central role in this process.

Spectroscopic studies of epoxy resin coating on imidazole copolymer treated copper surfaces

The reaction between the epoxy resin coating and copper surface modified with imidazole copolymer has been studied by FT-IR reflection-absorption spectroscopy (FT-IR RAS). Due to the catalytic effect of the copper/imidazole complex, epoxy cure reaction has occurred on the copper surface at low temperature. The cured epoxy coating has been increased gradually above 150 °C, while the imidazole complex dissolved slightly into the resin solution. Compared to poly(vinylimidazole) homopolymer, silane-based imidazole copolymer coating remains more on the copper surface due to the adhesion promotion between copper surface and coating polymer.

The inhibition of copper corrosion by azole compounds in humid environments

The ability of azole compounds, benzotriazole (BTA), 2-undecylimidazole (UDI) and poly- N-vinylimidazole (PVI-1) to inhibit copper corrosion in humid environments is studied using Fourier transform infrared reflection-absorption spectroscopy (FT-IR RAS). The corrosion product of bare Cu is shown to be Cu 2O even when moisture is present. The appearance and intensity of its characteristic vibration frequency can be used to monitor corrosion. It is found that dissolution of the Cu substrate, caused by local anodic and cathodic sites set up on the surface, accelerates the degradation process of BTA, UDI and PVI-1. The degradation of UDI on Cu apparently follows the same mechanism in both dry and wet environments while the degradation of PVI-1 on Cu does not. The BTA film is a better corrosion inhibitor than UDI or PVI-1 in this environment although some corrosion is observed. It is concluded that the inhibition ability of an inhibitor compound depends on the stability of the compound in the environment.

Polarization-modulated FT IR spectra of cyanide adsorbed on a silver electrode

Polarization-modulated Fourier transforms IR reflection-absorption spectroscopy (FT IRRAS) has been used to measure the IR spectra of cyanide species at the silver electrode-electrolyte interface. These spectra show absorption bands due to both surface and solution species and are presented as a function of the electrode potential.