Multiple Transmission-reflection Research Articles

Simulation of infrared spectra of trace impurities in silicon wafers based on the multiple transmission\u2013reflection infrared method

The content of trace impurities, such as interstitial oxygen and substitutional carbon, in silicon is crucial in determining the mechanical and physical characteristics of silicon wafers. The traditional infrared (IR) method is adopted as a normal means to analyse their concentration at home and abroad, but there are two problems. The first problem is the poor representativeness of a single local sampling point because the impurity distribution in a solid sample is not as uniform as that in a liquid sample. The second problem is that interference fringes appear in the infrared spectra of the sample due to the thin wafer (≤ 300 μm thick). Based on this, controversial issues existed regarding the measured trace impurity concentrations between wafer manufacturers and solar cell assembly businessmen who used silicon sheets made by the former. Therefore, multiple transmission-reflection (MTR) infrared (IR) spectroscopy was proposed to solve the problems mentioned above. In the MTR setup, because light passes through different parts of the silicon chip several times, multiple sampling points make the final result more representative. Moreover, the optical path is lengthened, and the corresponding absorbance is enhanced. In addition to amplification of weak signals, the MTR-IR method can eliminate interference fringes via the integrating sphere effect of its special configuration. The signal-to-noise ratio of the corresponding spectrum is considerably improved due to the aforementioned dual effects. Thus, the accuracy and sensitivity of the detection method for trace impurities in silicon chips are greatly increased. In this study, silicon wafers were placed in the MTR setup, and then, their relative properties at room temperature were investigated. The corresponding theoretical calculation and simulation of infrared spectra of silicon chips were provided. This affords an optional method for the semiconductor material industry to analyse trace impurities in their chips.

Comparative study on multiple transmission–reflection infrared spectroscopy and infrared methods for the measurement of substitutional carbon and interstitial oxygen contents of polycrystalline silicon

Multiple transmission–reflection (MTR) infrared (IR) spectroscopy was established as a new IR method to measure the interstitial oxygen and substitutional carbon contents of polycrystalline silicon wafers at ambient temperature. The superiority of MTR–IR to conventional IR was verified through practical measurements of polycrystalline silicon samples. With single incidence, the following characteristics of the former were superior to those of the latter. (1) The areas of the absorption peaks of interstitial oxygen at 1107 cm−1 and substitutional carbon at 605 cm−1 can be amplified linearly with transmission times N between 10 and 12, thereby extending the limit of detection of oxygen and carbon to approximately one order of magnitude lower. (2) The strength of the interference fringes of the baseline can be decreased to 5 times that of the single incidence for a 1 mm polycrystalline silicon slice. (3) In contrast to conventional IR method in which data are gathered from one sampling point at each measurement, MTR–IR collects information from many sampling points in a long sample for one-time measurement. In conclusion, MTR–IR is more sensitive, reliable, and reproducible than the conventional IR method in terms of measuring the interstitial oxygen and substitutional carbon contents of polycrystalline silicon.

PEG Brushes on Porous, PDMS-Coated Surfaces and Their Interaction with Carbon Dioxide

A porous polymeric substrate covered with a thin polydimethylsiloxane (PDMS) coating is used for the surface-initiated polymerization of polyethylene glycol (PEG)-based polymer brushes. Successful synthesis of the brushes is evidenced by several methods and their impact on the characteristics of the polymeric multilayer substrate is studied. Investigation into the behavior of PEG-based brushes using atomic force microscopy and multiple transmission-reflection infrared (MTR-FTIR) spectroscopy reveals conformational changes of the brush chains upon exposure to carbon dioxide. The results presented here highlight an elegant way to covalently modify porous, PDMS-coated substrates with polymer brushes to alter their characteristics.

Growing Embossed Nanostructures of Polymer Brushes on Wet-Etched Silicon Templated via Block Copolymers.

Block copolymer nanolithography has attracted enormous interest in chip technologies, such as integrated silicon chips and biochips, due to its large-scale and mass production of uniform patterns. We further modified this technology to grow embossed nanodots, nanorods, and nanofingerprints of polymer brushes on silicon from their corresponding wet-etched nanostructures covered with pendent SiHx (X = 1–3) species. Atomic force microscopy (AFM) was used to image the topomorphologies, and multiple transmission-reflection infrared spectroscopy (MTR-IR) was used to monitor the surface molecular films in each step for the sequential stepwise reactions. In addition, two layers of polymethacrylic acid (PMAA) brush nanodots were observed, which were attributed to the circumferential convergence growth and the diffusion-limited growth of the polymer brushes. The pH response of PMAA nanodots in the same region was investigated by AFM from pH 3.0 to 9.0.

Response of Plasma-Polymerized Hexamethyldisiloxane Films to Aqueous Environments.

Thin plasma polymer films were deposited in hexamethyldisiloxane (HMDSO) and HMDSO/O2 low-pressure discharges and their chemical structures analyzed using infrared (IR) spectroscopy and neutron reflectometry (NR). The (plasma-polymerized) ppHMDSO film exhibits hydrophobic, poly(dimethylsiloxane)-like properties, while the retention of carbon groups is reduced by O2 addition, yielding a more inorganic, hydrophilic ppSiOx film. Both films show a minor (vertical) density gradient perpendicular to the substrate, where the exposed film surface seems to be more oxidized, indicating oxidative aging reactions upon contact with air. The hydration and water uptake abilities of the films in aqueous environments were investigated in humid environments using ellipsometry, NR in D2O, and multiple transmission-reflection IR measurements after equilibration of the films in water.

Multiple Transmission-Reflection IR Spectroscopy Shows that Surface Hydroxyls Play Only a Minor Role in Alkylsilane Monolayer Formation on Silica

Multiple transmission-reflection (MTR)—a recently developed infrared spectroscopy sampling method for surfaces—has been applied to the study of silane monolayer formation on silicon oxide. Thanks to the excellent signal:noise ratio of data obtained by MTR, spectra of silane monolayers on a silica substrate could be readily obtained. This system has been previously difficult to investigate by standard sampling methods. The data is particularly important for gaining insights into the nature of the silica-silane interaction. The results support a model in which the inherent strain caused by the mismatch of alkyl-chain van der Waals radius and Si–O–Si bond distance is relieved in silane monolayers by the formation of a structure resembling snow moguls or closely packed umbrellas.

Constructing polyamidoamine dendrons from poly(poly(ethylene glycol) monomethacrylate) brushes grafted from planar silicon hydride surfaces for biomedical applications

A facile approach was established to construct polyamidoamine (PAMAM) dendrons from polymer brushes of poly(poly(ethylene glycol) monomethacrylate) (Si-g-P(PEGMA-OH)) grafted from a planar silicon hydride surface. First the Si-g-P(PEGMA-OH) brushes were grown via surface-initiated atom transfer radical polymerization with robust Si–C links on silicon surfaces. The side-chain hydroxyl groups of Si-g-P(PEGMA-OH) were chlorinated with thionyl chloride and further chlorines were substituted with amino groups of ethylenediamine, giving terminal primary amines. Borrowing the solution synthesis approach, we constructed second and third generations of PAMAM dendrons on-chip by surface-initiated alternative growth of two monomers, methyl acrylate and ethylenediamine. Two applications of silicon-based PAMAM dendrons were shown: the dense amino groups were activated via a cross-linker, N-succinimidyl-6-maleimidylhexanoate, to capture a free-thiol-carrying peptide of oxytocin and the third generation of PAMAM dendrons was used as a platform to on-chip synthesize a three amino acid peptide of Arg-Gly-Asp (RGD). The above conclusions were mainly derived from a home-built multiple transmission-reflection infrared spectroscopy, and complemented by X-ray photoelectron spectroscopy, UV–Vis spectroscopy and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry.

Microwave irradiated click reactions on silicon surfaces via derivertization of covalently grafted poly(PEGMA) brushes

Two surface chemistry approaches were realized to complete click reactions at covalently grafted polymer brushes of poly(poly(ethylene glycol) monomethacrylate) on a planar silicon surface (Si- g-P(PEGMA OH)). On one hand, the hydroxyls from Si- g-P(PEGMA OH) brushes can be replaced by chlorines of thionyl chloride and then chlorines can be substituted with azides of sodium azide to achieve azide-terminated (Si- g-P(PEGMA N 3)) brushes. On the other hand, the terminal acetylene (Si- g-P(PEGMA CH 2C CH)) brushes can be prepared easily by reaction between Si- g-P(PEGMA OH) and propargyl bromide. Model compounds of acetylene-terminated propargylamine, propiolic acid, and 10-undecynoic acid as well as azide-terminal benzyl azide were chosen to investigate the surface click reactions catalyzed with Cu(II)/sodium L-ascorbate by microwave irradiation under very mild conditions at 30 °C for 1 h. The stepwise modifications were characterized by two surface-sensitive techniques, Multiple Transmission-Reflection Infrared Spectroscopy (MTR-IR) and X-ray Photoelectron Spectroscopy (XPS), and their spectra were analyzed in detail. The triazole ring v(H C ) stretching at 3139 cm −1 and the XPS high-resolution scan of N 1s directly confirm the click reactions. By quantifying their infrared spectra before and after click reactions, we conclude that the click reactions on silicon surfaces by microwave irradiation possess high yield and efficiency. Hence, the microwave irradiated click reaction approaches might open convenient avenues to fabricate functional and hybrid organic/silicon devices.

Enhanced protein loading on a planar Si(111)–H surface with second generation NTA

A Si(111)–H surface was modified via a direct reaction between Si–H and 1-undecylenic acid (UA) under microwave irradiation to form molecular monolayers with terminal carboxyl groups. After esterifying carboxylic acid being esterified with N-hydroxysuccinimide (NHS), aminobutyl nitrilotriacetic acid (ANTA) was bound to the silicon surface through amidation (pH = 8.0) between its primary amino group and NHS-ester, producing nitrilotriacetic acid (NTA) anions. Then hexa-histidine tagged thioredoxin–urodilatin (his-tagged protein) and FITC-labeled hexa-histidine tagged thioredoxin–urodilatin (FITC-his-tagged protein) can be anchored after NTA was coordinated with Ni 2+. Furthermore, the NTA-terminated chip was acidified with 0.1 M HCl and subsequently esterified with NHS and then amidated with ANTA again to produce a second generation NTA. Thus the surface density of nitrilotriacetic acid anions was improved and resultantly that of anchored proteins was also enhanced through the iterative reactions. Both multiple transmission-reflection infrared spectroscopy (MTR-IR) and fluorescence scanning measurements demonstrated a proximate 1.63 times of anchored proteins on the second generation NTA/Ni 2+ as that on the first generation NTA/Ni 2+ monolayer.

AFM and multiple transmission-reflection infrared spectroscopy (MTR-IR) studies on formation of air-stable supported lipid bilayers.

Supported lipid bilayers (SLBs) were prepared by deposition of unilamellar vesicles on a silicon substrate. Atomic force microscopy (AFM) and a new Multiple Transmission-Reflection Infrared Spectroscopy (MTR-IR) developed by us were used to trace the dynamic formation of lipid bilayers on the silicon surfaces. The evolution from deformation of vesicles to formation of bilayers can be distinguished clearly by AFM imaging. MTR-IR provided high quality infrared spectra of ultrathin lipid bilayers with high sensitivity and high signal to noise ratio (SNR). The structural and orientational changes during vesicle’s fusion were monitored with MTR-IR. MTR-IR shows superiority over other infrared approaches for ultrathin films on standard silicon wafers in view of its economy and high sensitivity. Both MTR-IR and AFM results were consistent with each other and they provided more information for understanding the self-assembling procedure of SLBs.

Multiple Transmission−Reflection Infrared Spectroscopy for High-Sensitivity Measurement of Molecular Monolayers on Silicon Surfaces

A new infrared spectroscopic measurement involving multiple transmissions and reflections for molecular monolayers adsorbed on silicon surfaces has been established. Compared to the well-known multiple internal reflection (MIR) method, the distinctive advantage of multiple transmission-reflection infrared spectroscopy (MTR-IR) is the convenient measurement using standard silicon wafers as samples, while in the MIR setup special fabrication of geometric shapes such as 45 degrees bevel cuts on an attenuated total reflection silicon crystal is needed. Both p- and s-polarized spectra can be obtained reproducibly with the same order of sensitivity as by the MIR spectroscopy. Optimal conditions for spectral acquisition have been obtained from theoretical calculations. The ability of this methodology to gather high quality infrared spectra of adsorbed monolayers is demonstrated and the analysis of the surface packing and molecular orientation is discussed.

Evaluation of layered multiple-scattering method for antiplane shear wave scattering from gratings

The layered multiple-scattering method is based on an approximate solution for infinite gratings. In this method, an array of regularly arranged scatterers is viewed as comprising of layers of infinite grating and treated as a multiple transmission-reflection process in a multilayer panel. In this paper, this method is evaluated by comparing with exact solutions obtained by other means. One is a multiple-scattering solution. Another is the exact solution for an infinite grating, which is obtained by combining the T-matrix formulation of the multiple-scattering theory and an alternative representation of the Schlömilch series. The infinity nature enables the waves due to a planar incident wave to be expressed as planar waves and divided into propagating and evanescent modes. The layered multiple-scattering method accounts only for the propagating modes. Details of these modes are analyzed for a single grating, and it is concluded that only the first evanescent modes would have significant presence in a limited frequency range. The layered multiple-scattering method suggests that the only important geometric parameters for wave transmission and reflection are the grating distance and the interlayer distance. Numerical examples indicate that error due to evanescent modes might be significant due to interlayer interactions, such as critical frequencies of a stopband.