Multiple Internal Reflection Geometry Research Articles

Label-free detection of DNA molecules moving in micro-fluidic channels by infrared absorption spectroscopy

Infrared absorption spectroscopy (IRAS) in a multiple internal reflection (MIR) geometry is integrated with silicon-based micro-fluidic channels to allow detection and separation of DNA molecules in the micro-channels. The micro-channels were fabricated on a Si MIR-prism using the conventional silicon lithographic techniques. In the present method we can probe solution-phase biomolecular species through IR spectral profiles of those biomolecules, allowing us to detect and separate biomolecules without fluorescence labeling. The applicability of this approach is demonstrated with a representative test case: transport of single-stranded DNA molecules (oligonucleotides) in the micro-fluidic channels.

Interaction of plasma-generated water cluster ions with chemically-modified Si surfaces investigated by infrared absorption spectroscopy

We have investigated the interaction of water cluster ions generated by discharge plasma, with chemically modified Si surfaces using infrared absorption spectroscopy in the multiple internal reflection geometry. We observe that water cluster ions readily adsorb on SiO2-covered Si surfaces to form water droplets. We demonstrate that positively- and negatively-charged cluster ions adsorb on the SiO2-covered Si surface in different manners, indicating ionic interaction of the water droplets with the negatively-charged SiO2 surface. Water droplets formed on the protein-coated surface rupture the amide bond of the proteins, suggesting the function of protein decomposition of water cluster ions.

Molecular doping of regioregular poly(3-hexylthiophene) layers by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane investigated by infrared spectroscopy and electrical measurements

Molecular doping is a charge-transfer process intended to improve the performance of organic electronic devices such as organic transistors. We have investigated molecular doping of regioregular poly(3-hexylthiophene) (P3HT) layers by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS) and conductivity measurements. IRAS data confirm that F4-TCNQ acts as an effective p-type dopant for P3HT; highly doped P3HT displayed an intense, broad absorption band due to polaron (“polaron band”) and a high carrier (hole) density which are indicative of the charge transfer between F4-TCNQ and P3HT. We demonstrate that the charge (hole) transferred from the dopant molecule is distributed along the P3HT polymer chain and spreads over at least 10 thiophene monomer units on the chain. From a comparison of the measured conductivity of F4-TCNQ-doped P3HT layers with the carrier density, we show that the carrier mobility is proportional to the concentration of carriers (holes), which suggests that F4-TCNQ doping induces the conformational change of P3HT polymer chains to enhance the mobility of holes in the films of the doped P3HTs.

Infrared Absorption Spectroscopic Study on Reaction between Self-Assembled Monolayers and Atmospheric-Pressure Plasma

Plasma is becoming increasingly adopted in bioapplications such as plasma medicine and agriculture. This study investigates the interaction between plasma and molecules in living tissues, focusing on plasma-protein interactions. To this end, the reaction of air-pressure air plasma with NH2-terminated self-assembled monolayer is investigated by infrared spectroscopy in multiple internal reflection geometry. The atmospheric-pressure plasma decomposed the NH2components, the characteristic units of proteins. The decomposition is attributed to water clusters generated in the plasma, indicating that protein decomposition by plasma requires humid air.

Infrared spectroscopic study of the reactions between an octadecyltrichlorosilane self-assembled monolayer and plasma

Reactions involving hydrogen plasma and oxygen plasma with a self-assembled monolayer (SAM) of octadecyltrichlorosilane were investigated by infrared absorption spectroscopy in multiple internal reflection geometry. The rate of decrease of the CH3 peak intensity is smaller than that of the CH2 peak intensity when the SAM is exposed to hydrogen plasma. This is attributed to the formation of CH3 components as intermediate states of the hydrogenation of the SAM during hydrogen plasma exposure. Peak intensities due to CH2 and CH3 components in the SAM decreased at the same rate during oxygen plasma exposure. C=O components, detected during plasma exposure, are indicated as the intermediate states of film oxidation.

Adsorption of hydrocarbon components generated in deuterated benzene plasma studied by in situ real-time infrared absorption spectroscopy

In situ, real-time infrared absorption spectroscopy in the multiple internal reflection geometry was employed to investigate the evolution of hydrocarbon components deposited during plasma-enhanced chemical vapor deposition with a deuterated benzene source. We detected a peak attributed to the C–D stretching vibration of the deuterated phenyl group, which indicated a mode in which the benzene ring structure is retained on the substrate during the adsorption. The evolution of each peak during the plasma exposure suggests that the addition reaction occurs during the adsorption. Furthermore, we observed that with increasing substrate bias applied, the benzene ring structures in the film were disrupted and the amount of alkane components increased. This addition reaction proceeded on the film surface, regardless of the substrate bias.

Recent Trends of Plasma Engineering

We describe recent trends of plasma engineering on two topics - the infrared spectroscopy of plasma process and plasma processing technologies in graphene research. First, we show the measurement of plasma process with the infrared absorption spectroscopy in multiple internal reflection geometry (MIR-IRAS). This method is a very powerful tool of monitoring of plasma process, because the method has high detection sensitivity and the method can be applied to “in-situ” and “real-time” monitoring of interaction of plasma with material surface. We describe the monitoring method, acquired IR spectra and analysis methods. Second, we show plasma technologies for graphene; graphene has been considered one of key materials in a 21st century industries. For the achievement of graphene applications, various processing technologies have been required. Plasma processings are expected to become essential tools in graphene industries because they can provide answers to the requirement for low-temperature processing and the desirability of dry process.

Development of an In situ Infrared Spectroscopic Measurement of Plasma-Induced Reactions in Ethanol

An in situ monitoring system for plasma-induced reactions in ethanol was developed by infrared absorption spectroscopy in multiple internal reflection geometry. We monitored in situ the preferential decrease in the IR peak intensity of CH3 and OH groups in liquid ethanol. In addition, we monitored in situ the preferential inclusion of OCH3 and free OH groups deposited on a multiple internal reflection prism. Unlike optical emission spectroscopy, the IR-based technique detects non-light-emitting compounds. It presents as a powerful alternative tool for monitoring liquid-phase plasma reactions.

Investigation of TiO2 Surface Modification with [6,6]-Phenyl-C61-butyric Acid for Titania/Polymer Hybrid Solar Cells

We have investigated modification of TiO2 surfaces with [6,6]-phenyl-C61-butyric acid (PCBA) used for fabrication of TiO2/poly(3-hexylthiophene-2,5-diyl) (P3HT) hybrid solar cells. The surface modification process was monitored using in-situ infrared absorption spectroscopy in the multiple-internal reflection geometry (MIR-IRAS). IR data showed that longer exposure of TiO2 surfaces to an organic solution of PCBA leads to undesirable formation of a physisorbed PCBA overlayer that cannot be removed by rinsing the surface in pure solvent. We found that ultrasonic cleaning of the TiO2 surface removed most of the physisorbed PCBA molecules. Modification of TiO2 surfaces with PCBA molecules drastically increased the short circuit current of TiO2/P3HT-based hybrid solar cells, which is ascribed to improved charge separation efficiency at the TiO2/P3HT interface. The physisorbed PCBA molecules decreased the open circuit voltage and the fill factor. We demonstrated that the power conversion efficiency is improved by ultrasonic cleaning following PCBA deposition.

Evolution of Hydride Components Generated by Hydrogen Plasma Irradiation of a Si(110) Surface Investigated With In Situ Infrared Absorption Spectroscopy in Multiple Internal Reflection Geometry

The process of hydrogen plasma reacting with a Si(110) surface is investigated. The reaction process is measured with in situ infrared absorption spectroscopy (IRAS) in multiple internal reflection geometry. We monitor the evolution of hydride components in the Si(110) surface exposed to the hydrogen plasma. IRAS data show that the surface atomic arrangement of a Si(110) surface is distorted by plasma exposure. H is inserted into Si crystal and defects and vacancies are generated. Further, hydrogen plasma exposure creates silicon dihydride $({\rm SiH}_{2})$ components in an amorphous layer. The ${\rm SiH}_{2}$ formation rate is 0.5, by a comparison with the hydrogen plasma exposure time.

Label-free and real time monitoring of adipocyte differentiation by surface infrared spectroscopy

Abstract We have investigated in situ real-time monitoring of cell differentiation to adipocytes by using infrared absorption spectroscopy with the multiple internal reflection (MIR-IRAS) geometry. Preadipocyte 3T3-L1 cells were cultured on a silicon prism and their adipogenesis was monitored with MIR-IRAS for seven days. Differentiated cells showed a C O stretching band of triacylglycerides, together with the protein amide I and amide II bands. The C O stretching band appeared before optical microscopic confirmation of fat droplet formation, a typical morphological marker for adipocytes, demonstrating that MIR-IRAS is particularly useful for non-destructive monitoring of early adipogenesis. An effect of genistein, an antiadipogenic agent, was also investigated based on the peak intensity of the C O stretching and amide bands. Thus, MIR-IRAS has a potential to evaluate antiadipogenic agents in terms of their effects on fat and protein synthesis during adipogenesis.

IR study of fundamental chemical reactions in atomic layer deposition of HfO2 with tetrakis(ethylmethylamino)hafnium (TEMAH), ozone, and water vapor

The fundamental reactions in HfO2 atomic layer deposition (ALD) with the precursors tetrakis(ethylmethylamino)hafnium (TEMAH), ozone, and water vapor on Si (100) surfaces at room temperature (RT) were studied by infrared absorption spectroscopy (IRAS) with a multiple internal reflection geometry. The IRAS results indicated that TEMAH can be adsorbed at OH sites on Si surfaces at RT. Ozone irradiation on the TEMAH-adsorbed Si surface at RT effectively removes hydroaminocarbon adsorbates introduced in the course of TEMAH adsorption, although this treatment provides no OH-group adsorption sites for TEMAH on the Si surface at RT. For further adsorption, water–vapor treatment at around 160°C is effective in restoring the adsorption sites. The IR study suggests that the cyclic process of TEMAH adsorption and ozone treatment at RT followed by OH restoration with water vapor at a temperature of 160°C allows continuous HfO2 deposition.

Real-time monitoring of mitochondrial adenosine 5′-triphosphate synthesis and hydrolysis by surface infrared spectroscopy

We have developed a method for in situ real-time monitoring of adenosine 5′-triphosphate (ATP) synthesis in mitochondria using infrared absorption spectroscopy with the multiple internal reflection geometry. Spectral changes corresponding to ATP synthesis and hydrolysis were monitored under oxygenation and constant stirring condition. It was demonstrated that the reversible process of ATP synthesis in mitochondria can be monitored by analyzing stretching modes of α- and β-PO2− in adenine nucleotides. Our method has potential to evaluate mitochondrial toxicity in terms of mitochondrial activities of ATP synthesis and hydrolysis.

IR Study on N719 Dye Adsorption with High Temperature Dye Solution for Highly Efficient Dye-Sensitized Solar Cells

N719 dye adsorption by immersing electrodes in a high temperature N719 solution for dye-sensitized solar cells (DSCs) was investigated by IR absorption spectroscopy using a multiple internal reflection geometry. In this study, an N719 dye solution of a mixture of 10 mL acetonitorile and 10 mL tertiary-butyl alcohol containing N719 at a concentration of 0.36 mg/mL was examined. When the solution temperature for dye adsorption was increased from 20 to , the N719 dye chemisorbed on with the bidentate bond was increased and this high temperature dye adsorption was effective in promoting power generation in the DSCs. Decreasing the solution temperature from room temperature to resulted in an increase in the physisorbed dye on the surface, which may rather deteriorate power generation. The IR absorption spectroscopy indicates the presence of an activation barrier for N719 to chemisorb on the surface. A dye adsorption method using a high temperature dye solution for higher power generation efficiency is discussed in this paper.

Atomic layer deposition of SiO 2 from Tris(dimethylamino)silane and ozone by using temperature-controlled water vapor treatment

Atomic layer deposition of SiO 2 from tris(dimethylamino)silane (TDMAS) and ozone as precursors on Si(100) surfaces at near-room temperatures was studied by infrared absorption spectroscopy with a multiple internal reflection geometry. TDMAS can be adsorbed at OH sites on hydroxylated Si surfaces at room temperature. Ozone oxidation of the TDMAS-treated Si surface is effective in removing hydroaminocarbon adsorbates introduced during TDMAS adsorption at room temperature. After oxidation by ozone, treatment with H 2O vapor at a substrate temperature of around 160 °C causes regeneration of OH sites for TDMAS adsorption. Cycles involving TDMAS adsorption and ozonization at room temperature followed by H 2O treatment at 160 °C permit the buildup of layers of SiO 2. The amount of residual hydroaminocarbon at the interface between the growing SiO 2 film and the substrate can be reduced with the ozone treated Si surface as a starting surface.

Infrared Spectroscopy of Amorphous Carbon Film Deposition Process using Acetylene Plasma

We have investigated the acetylene-plasma deposition of amorphous carbon film using “in-situ”, “real-time” infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We showed that sp-hydrocarbons are dominant species at the initial stages of deposition, while sp3-hydrocarbon components increase their densities with film growth. IRAS data obtained for the deposited amorphous carbon film exposed to deuterium plasma showed that the density of the sp-hydrocarbon components is relatively high in the vicinity of the film surface. On the basis of the present experimental results, we suggest that the sp-hydrocarbons are transformed into the sp2-, sp3-hydrocarbon components at the film surface through the addition reaction.

Observation of Plasma Chemical Vapor Deposition Process of Amorphous Carbon Film

Understanding and controlling of plasma-induced surface reactions are quite important for developing the future plasma processing including thin film deposition. We used “in-situ”, “real-time” infrared absorption spectroscopy in multiple internal reflection geometry (MIR-IRAS), to elucidate the mechanism of plasma-induced surface reactions during plasma enhanced chemical vapor deposition of amorphous carbon film. We examined the influence of substrate temperature on the surface reaction process, by analyzing infrared absorption spectra of Si surfaces during deposition of amorphous carbon film. We found that the deposition rate and the growth mode drastically change with varying the substrate temperature. We suggest that at low substrate temperature the film growth depends predominantly on the gas phase reaction, while at high temperature the film growth mode depends on the surface reaction as well as the gas phase reactions.

Surfactant Adsorption on Single-Crystal Silicon Surfaces in TMAH Solution: Orientation-Dependent Adsorption Detected by In Situ Infrared Spectroscopy

This paper focuses on two aspects, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">macroscopic and microscopic</i> , of pure and surfactant-added tetramethylammonium hydroxide (TMAH) wet etching. The macroscopic aspects deal with the technological/engineering applications of pure and surfactant-added TMAH for the fabrication of microelectromechanical systems (MEMS). The microscopic view is focused on the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> observation of the silicon surface during etching in pure and surfactant-added TMAH solutions using Fourier transform infrared (FT-IR) spectroscopy in the multiple internal reflection geometry. The latter is primarily aimed at investigating the causes behind the change in the orientation-dependent etching behavior of TMAH solution when the surfactant is added. Silicon prisms having two different orientations ({110} and {100}) were prepared for comparison of the amount of adsorbed surfactant using FT-IR. Stronger and weaker adsorptions were observed on {110} and {100}, respectively. Moreover, ellipsometric spectroscopy (ES) measurements of surfactant adsorption depending on the crystallographic orientation are also performed in order to gain further information about the differences in the silicon-surfactant interface for Si{100} and Si{110}. In this paper, we determine the differences in surfactant adsorption characteristics for Si{110} and Si{100} using FT-IR and ES measurements for the first time, focusing both on the mechanism and on the technological/engineering applications in MEMS.

Difference of deposition process of an amorphous carbon film due to source gases

We compared the deposition process of an amorphous carbon film using acetylene as a source gas with the deposition process using methane. The process was investigated by using infrared absorption spectroscopy in multiple internal reflection geometry (MIR-IRAS). The infrared spectra showed that sp 3-hydrocarbon species was observed in both cases: on the other hand, the sp- and sp 2-carbon and/or hydrocarbon species was clearly observed in the film deposited using acetylene. Moreover, we observed the changes in predominant adsorbed species with film thickness in both cases; these facts suggest that an amorphous carbon film grows with the structural changes of adsorbed species in both deposition processes.

Substrate temperature effects on amorphous carbon film growth, investigated by infrared spectroscopy in multiple internal reflection geometry

The substrate temperature effects on the amorphous carbon film growth were investigated, by using the deposition rates and in situ and “real-time” infrared spectroscopy in multiple internal reflection geometry. The deposition rates were decreased, in contrast with the increases of substrate temperature. The growth mode was also changed with substrate temperatures: the film growth depends on the gas phase reaction at low substrate temperature; on the other hand, at high temperature the film grows with the decomposition of the CH3 species.