Application of Fourier Transform Infrared Spectroscopy in the Study of Atmospheric Heterogeneous Processes

Abstract

Atmospheric heterogeneous processes associated with the complex behavior of atmospheric particles may play a crucial role in atmospheric chemistry and global climate change. Many of these heterogeneous processes have been widely investigated in detail over the years, including heterogeneous reactions on the surface of aerosol particles, aerosol hygroscopicity, as well as aerosol chemical compositions. As a fast, sensitive, precise, nondestructive, in situ, and online experimental technique, Fourier transform infrared (FTIR) spectroscopy has played a significant role in investigating atmospheric heterogeneous processes. On the basis of the mechanisms and characteristics of various FTIR techniques, this work presents a review of the applications of in situ FTIR spectroscopy in atmospheric heterogeneous processes study, and future development directions for FTIR spectroscopy are proposed considering current and future research needs for heterogeneous processes.     

New insight on the underdrawing of 16th Flemish-Portuguese easel paintings by combined surface analysis and microanalytical techniques

This paper focusses on the study of the underdrawings of 16th century easel paintings attributed to the workshop of the Portuguese-Flemish Master Frei Carlos. This investigation encompasses multidisciplinary research that relates the results of surface exams (infrared reflectography, standard light photography and infrared photography) with analytical investigations.The surface analysis of Frei Carlos’ underdrawings by infrared reflectography has shown heterogeneous work, revealing two different situations: (1) an abundant and expressive underdrawing, revealing a Flemish influence and (2) a simple and outlined underdrawing. This preliminary research raised an important question related to this Portuguese-Flemish workshop and to the analytical approach: Is the underdrawing's heterogeneity, as observed in the reflectograms, related to different artists or is this rather an effect that is produced due to the use of different materials in the underdrawing's execution? Consequently, if different materials were used, how can we have access to the hidden underdrawings? In order to understand the reasons for this dissemblance, chemical analysis of micro-samples collected in underdrawing areas and representing both situations were carried out by optical microscopy, micro Fourier transform infrared spectroscopy (μ-FTIR), scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDX) and micro-Raman spectroscopy (μ-Raman). Taking into account the different possibilities and practical and theoretical limitations of surface and punctual examinations in the study of easel painting underdrawings, the methodology of research was adjusted, sometimes resulting in a re-analysis of experimental results. This research shows the importance of combining multispectral surface exams and chemical analysis in the understanding of the artistic creative processes of 16th century easel paintings.     

Material Studies in a High Energy Spark Gap

The chemical interactions and physical processes occurring in a high energy spark gap with different combinations of gases, electrodes, and insulators were studied. The electrodes studied were graphite and a tungsten-copper composite; the insulators were Lexan and Blue Nylon; and the gases were N2 and SF6. The gas composition was monitored with a mass spectrometer. Spectroscopic techniques were used to observe the arc channel. The electrode surfaces were studied with several surface analysis techniques, including scanning electron microscopy, electron spectroscopy for chemical analysis, Auger electron spectroscopy, and X-ray fluorescence. The breakdown voltage distribution was examined for different material combinations. The plasma chemistry processes involving the gas, electrode, and insulator materials were found to affect the voltage self-breakdown distribution. The detailed surface analysis gave information about the nature of the chemical processes. The presence of Blue Nylon seemed to have a more adverse effect than Lexan and graphite seemed to have a narrower voltage distribution than the tungsten-copper composite.     

Mechanism of chemisorption and interface penetration in reactive systems at low temperatures

In the transport mechanism discussed it is demonstrated that in the large gradients of the chemical potential that exist in reactive systems gas atoms should be able to migrate in a perpendicular direction up to several atomic distances below the surface by non-activated processes. The exponential decrease in the sticking probability s observed after an initial stage with a constant s value of about unity is correlated with the increase of the activation energy barrier between molecules in the gas phase and in the chemisorbed state on the surface. Quantitative experimental results of the kinetic of chemisorption processes recently obtained for oxygen and nitrogen systems support the qualitative and semiquantitative statements of the mechanism proposed.     

Construction of self-assembled monolayer terminated with N-heterocyclic carbene-rhodium(I) complex moiety

Functionalization of self-assembled monolayer (SAM) of alkanethiolate with metal containing unit is one of the versatile methods to obtain functional surfaces such as heterogeneous catalysts. However, organic molecules that strongly bind to transition metals at SAM terminal are limited. Recently N-heterocyclic carbenes (NHCs) such as cyclic diaminocarbenes have emerged as strongly σ-donating ligands forming a robust bond with broad spectrum of transition metals. In the present study, for the purpose of establishment of a new robust basement for heterogeneous metal catalysts, a SAM of the alkanethiolate terminated with NHC-rhodium(I) complex moiety was prepared by utilizing a newly designed disulfide molecule bearing NHC-metal complex terminals. X-ray photoelectron spectroscopy (XPS) analysis and angle resolved XPS measurement revealed successful formation of the Rh-complex-terminated SAM on a gold substrate. Infrared reflection absorption spectroscopy (IRRAS) analysis suggested that the linker methylene chains connecting the rhodium complex moiety and the gold surface are in a loosely packed structure. This unique chemical species, NHC, would be a promising candidate as a basement for the construction of functional surface.     

Ionizational mechanism of heterogeneous chemiluminescence excitation. I

The kinetics and steady characteristics of the heterogeneous chemiluminescence (HC) of crystals is considered for an ionizational mechanism of excitation as a function of the sample temperature and the concentration of atoms and molecules of the exciting gas. The characteristic differences from the corresponding dependences for a direct mechanism of HC excitation are found (HC is luminescence due to the transformation of energy liberated in exothermic events of heterogeneous chemical reaction at the surface of solids into the energy of superequilibrium radiation of a solid).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 80–86, April, 1979.     

Surface microstructures and antimicrobial properties of copper plasma alloyed stainless steel

Bacterial adhesion to stainless steel surfaces is one of the major reason causing the cross-contamination and infection in many practical applications. An approach to solve this problem is to enhance the antibacterial properties on the surface of stainless steel. In this paper, novel antibacterial stainless steel surfaces with different copper content have been prepared by a plasma surface alloying technique at various gas pressures. The microstructure of the alloyed surfaces was investigated using glow discharge optical emission spectroscopy (GDOES) and scanning electron microscopy (SEM). The viability of bacteria attached to the antibacterial surfaces was tested using the spread plate method. The antibacterial mechanism of the alloyed surfaces was studied by X-ray photoelectron spectroscopy (XPS). The results indicate that gas pressure has a great influence on the surface elements concentration and the depth of the alloyed layer. The maximum copper concentration in the alloyed surface obtained at the gas pressure of 60 Pa is about 7.1 wt.%. This alloyed surface exhibited very strong antibacterial ability, and an effective reduction of 98% of Escherichia coli (E. coli) within 1 h was achieved by contact with the alloyed surface. The maximum thickness of the copper alloyed layer obtained at 45 Pa is about 6.5 μm. Although the rate of reduction for E. coli of this alloyed surface was slower than that of the alloyed surface with the copper content about 7.1 wt.% over the first 3 h, few were able to survive more than 12 h and the reduction reached over 99.9%. The XPS analysis results indicated that the copper ions were released when the copper alloyed stainless steel in contact with bacterial solution, which is an important factor for killing bacteria. Based on an overall consideration of bacterial killing rate and durability, the alloyed surface with the copper content of 2.5 wt.% and the thickness of about 6.5 μm obtained at the gas pressure of 45 Pa is expected to be useful as antimicrobial materials that may have a promising future in antimicrobial applications.     

Fabrication of a superhydrophobic ZnO nanorod array film on cotton fabrics via a wet chemical route and hydrophobic modification

A superhydrophobic ZnO nanorod array film on cotton substrate was fabricated via a wet chemical route and subsequent modification with a layer of n-dodecyltrimethoxysilane (DTMS). The as-obtained cotton sample was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), scanning probe microscope (SPM) and X-ray photoelectron spectroscopy (XPS), respectively. The wettability of the cotton fabric sample was also studied by contact angle measurements. The modified cotton fabrics exhibited superhydrophobicity with a contact angle of 161° for 8 μL water droplet and a roll-off angle of 9° for 40 μL water droplet. It was shown that the proper surface roughness and the lower surface energy both played important roles in creating the superhydrophobic surface, in which the Cassie state dominated.     

Chemical nature of phytic acid conversion coating on AZ61 magnesium alloy

Phytic acid (PA) conversion coating on AZ61 magnesium alloy was prepared by the method of deposition. The influences of pH, time and PA concentration on the formation process, microstructure and properties of the conversion coating were investigated. Scanning electron microscopy (SEM) was used to observe the microstructure. The chemical nature of conversion coating was investigated by energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) techniques. The corrosion resistance was examined by means of potentiodynamic polarization method. The adhesive ability was tested by score experiments. The results showed that the growth and microstructure of the conversion coatings were all obviously affected by pH, time and PA concentration. In 0.5 mg/ml PA solution with a pH of 5, an optimization conversion coating formed after 20 min immersion time by deposition of PA on AZ61 magnesium alloy surface through chelating with Al³⁺. It made the corrosion potential E_corr of sample shifted positively about 171 mV than that of the untreated sample, and the adhesive ability reached to Grade 1 (in accordance with GB/T 9286).     

Fundamental processes of aluminium corrosion studied under ultra high vacuum conditions

Surface sensitive electron spectroscopy was applied to study the fundamental processes of aluminium corrosion. We used metastable induced electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS) for the investigation of the densities of states of surface and bulk, respectively. Furthermore we applied X-ray photoelectron spectroscopy (XPS) to investigate the chemical composition of the top surface layers. All measurements were performed under ultra high vacuum conditions.Al films with thicknesses of 7 nm were investigated. Both the interaction of oxygen and water with these films leads to the formation of an aluminium-oxygen layer, which is partly composed of stoichiometric Al₂O₃. Weak heat treatment at 770 K transforms the surface layer into Al₂O₃ with a thickness of about 2 nm. Further gas offer does not lead to an increase of this thickness, neither for oxygen nor for water. Additional to the oxygen offer, water exposure leads to the formation of OH species in the top aluminium-oxygen layer to a small amount. Weak heat treatment to 770 K removes this species completely. Water exposure leads to a much faster oxide formation than oxygen exposure. We try to give a model for the fundamental corrosion processes on a molecular scale.     

Laser-produced iron nitrides seen by Mössbauer spectroscopy

Mössbauer spectroscopy is a very powerful tool to investigate technological processes performed mainly at the surface of materials. Nitriding of metals and steel is well established in surface engineering, and gas nitriding is used most frequently. Laser nitriding, i.e. the nitrogen take-up from the ambient gas upon irradiation of a steel surface with short laser pulses, is presented in its application to iron, stainless steel and plain carbon steels. It will be demonstrated how Mössbauer spectroscopy in combination with complementary methods (Rutherford backscattering spectroscopy, Resonant nuclear reaction analysis, Nanoindentation) can help to reveal basic mechanisms in these processes.     

Study of the gas-phase parameters affecting the silicon-oxide film deposition induced by an ArF laser

A study of the gas-phase parameters involved in ArF laser induced chemical vapour deposition of silicon-oxide thin films is presented. A complete set of experiments has been performed showing the influence of the concentration of the precursor gases, N₂O and SiH₄, and their influence on total and partial pressures on film growth and properties. In this paper we demonstrate the ability of this LCVD method to deposit silicon oxide films of different compositions and densities by appropriate control of gas composition and total pressure. Moreover, a material specific calibration plot comprising data obtained using different preparation techniques is presented, allowing determination of the stoichiometry of SiO _x films by using FTIR spectroscopy independently of the deposition method. For the range of processing conditions examined, the experimental results suggest that chemical processes governing deposition take place mainly in the gas phase.     

CO concentration and temperature measurements in a shock tube for Martian mixtures by coupling OES and TDLAS

CO concentration and gas temperature distribution are diagnosed behind a strong shock wave simulating the Martian atmosphere entry processes by coupling optical emission spectroscopy (OES) and tunable diode laser absorption spectroscopy (TDLAS). The strong shock wave (6.31 ± 0.11 km/s) is established in a shock tube driven by combustion of hydrogen and oxygen. Temperature of the shock-heated gas is inferred through a precise analysis of the high temporal and spatial resolution experimental spectral of CN violet system (B ² Σ ⁺ →X ² Σ ⁺, Δv = 0 sequence) using OES. A CO absorption line near 2,335.778 nm is utilized for detecting the CO concentration using scanned-wavelength direct absorption mode with 50 kHz repetition rate. Combined with temperature results from OES, CO concentration in the thermal equilibrium region is derived. The current experimental results are complementary for determining an accurate rate coefficient of CO₂ dissociation and validation relevant chemical kinetics models in Mars atmosphere entry processes.     

Photoelectron spectroscopy without vacuum: nanoparticles in gas suspension

The photoelectric yield Y of nanoparticles in gas suspension delivers a fingerprint of the particle surface as it interacts with the surrounding gas, but bulk properties of the particle can also be probed. We show in three new experiments how this can be applied to acquire remarkable insight into processes of considerable general interest. In the first example, soot reduction by heterogeneous catalysis is examined. We show that fuel additives lead to the formation of transition metal oxide nuclei in the combustion zone. The carbonaceous matter preferentially condenses on the surface of the nuclei where it is burnt in the last stage of the combustion. In the second example, we present a method for the investigation of the desorption dynamics from particle surfaces using excimer laser pulses for photoemission. The kinetics of thermal perylene desorption from various types of particles is measured with a time resolution of a few milliseconds. The desorption follows a first order rate law and can be described by the Arrhenius model. In the third example, we show that there exists circular dichroism (CD) in photoemission from particles built with chiral molecules. The dependence of CD on the size of the nanoparticles shows that the crystalline order in the particles is important.     

On the chemical states of nitrogen on iron surfaces reacted with ammonia and sodium cyanide,studied by X-ray photoelectron spectroscopy

The reaction products of iron reacted with ammonia gas and molten sodium cyanide are studied using X-ray photoelectron spectroscopy. Ammonia gas dissociates on iron surfaces to form a nitride and a loosely bound NH₃-like species with N 1sB.E.'s at 397.2 and 399.8 eV, respectively. On iron specimens dipped into molten NaCN three species are found at 398.6, 397.8 and 397.2 eV. The 398.6-eV peak is ascribed to adsorbed ?CN, and the 397.8-eV peak to carbonitride formed by the reaction of the cyanide with iron. Decreasing binding energies are found for adsorbed ?CN ligand, carbonitride compound and nitride, which seem to correspond to an apparent order of stronger interaction of nitrogen with iron. An iron sample was scratched with a file and the surface species of nitrogen were observed below 400°C. The nitrogen atoms in the sample diffuse and concentrate on the surface, depending on the nitrogen content in the bulk. Desorption patterns of nitrogen from a heated iron surface are examined with a view to the determination of gaseous constituents in metal samples.     

Analysis of surface and bulk polymerization of a thin film using a chemical derivatization technique and TOF-SIMS

A chemical derivatization technique in TOF-SIMS along with ultra-low angle sample cutting technique were used to perform a quantitative study of the surface and in-depth double bond profile of the photo-initiated polymerized thin film. We found out that the characteristic peaks at m/z 185 and 199 were obtained from the thin film composed of acrylate monomer and methacrylate monomer, respectively, after reaction with bromine gas. The detection sensitivity of certain chemical indicators is affected by changing the primary ion species. The Bi₃⁺ primary ion results in the best chemical sensitivity. The surface double-bond density obtained by TOF-SIMS and the Br 3d signal intensity of XPS showed a good linear relationship in the limited region due to the effect of matrix hardness.The thin film was cut with microtome about 1° angle and was left to react with bromine and was measured using TOF-SIMS. It was clearly observed from this technique that double bond of acrylate and methacrylate monomer remained much more at the surface of the photo-initiated polymerized thin film, due to the inhibition of polymerization by oxygen. From the surface to 1 μm depth, both monomers show the same behavior, but the rate of polymerization of methacrylate monomer was lower than that of acrylate in deeper layers.     

A study on the reaction between chlorine trifluoride gas and glass-like carbon

The reaction between glass-like carbon (GC) and chlorine trifluoride (ClF₃) gas was investigated with weight measurements, surface analysis, and gas desorption measurements, where the ClF₃ gas is used for the in situ cleaning of tubes in silicon-related fabrication equipment. From Auger electron spectroscopy and X-ray photoelectron spectroscopy measurements, a carbon mono-fluoride, –(CF)_n–, film near the surface of GC is considered to be grown onto the GC surface above 400 °C by the chemical reaction with ClF₃, and this thickness of the fluoride film depends on the temperature. The grown fluoride film desorbs by annealing in a vacuum up to 600 °C. Although GC is apparently etched by ClF₃ over 600 °C, the etch rate of GC is much lower than that of SiC and quartz.     

An In Situ Testing Method for Analyzing the Changes of Active Groups in Coal Oxidation at Low Temperatures

This study details an in situ Fourier transform infrared spectroscopy analytical system that was employed to follow chemical variations in the functional groups on coal surface during the oxidation process at low temperatures. In the reported in situ Fourier transform infrared spectroscopy system, a special chamber was used to contain the coal powders, and a gas inlet tube and a programmable heater were used to simulate different reaction atmospheres and temperatures. The comparisons between in situ and ex situ Fourier transform infrared spectroscopy spectra indicate that the in situ Fourier transform infrared spectroscopy data offer a more accurate reflection of changes in the functional groups. The real-time changes of aliphatic hydrocarbon groups and oxygen-containing groups in a lignite coal sample were analyzed from 30°C to 220°C using in situ Fourier transform infrared spectroscopy. The experimental results indicate that the chemical variations in the functional groups are affected by their relative chemical activities. The results show that the presence of aliphatic groups on the coal surface varies with temperature. Over the range of 30–70°C the presence of these groups decreases, but then their abundance increases over the range of 70–180°C and finally decreases again when the temperature is increased to between 180°C and 220°C. With respect to oxygen-containing functional groups, three various trends were observed as the test temperature was varied. Our conclusion was that these variations are a function of the reaction activities of the various oxygen-containing functional groups.     

Analysis of the injection layer of PTCDA in OLEDs using x-ray photoemission spectroscopy and atomic force microscopy

Through the investigation of the sample surface and interface of 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA)/indium-tin-oxide (ITO) thin films using atomic force microscopy, it has been found that the surface is complanate, the growth is uniform and the defects cover basically the surface of ITO. Furthermore, the number of pinholes is small. The analysis of the sample surface and interface further verifies this result by using x-ray photoemission spectroscopy . At the same time, PTCDA is found to have the ability of restraining the diffusion of chemical constituents from ITO to the hole transport layer, which is beneficial to the improvement of the performance and the useful lifetime of the organic light emitting diodes (OLEDs).