Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2001-10-29
2004-08-31
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
Reexamination Certificate
active
06784428
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to an apparatus and method for determining an IR spectrum of a sample material. More particularly, the disclosed invention relates to spectroscopically determining the IR spectrum of a sample using an apparatus and method that operate in real-time, and which do not require the use of any moving parts. Still further, the apparatus and method of the disclosed invention do not require extensive mathematical transformation of the detected spectral information to analyze the composition of the sample material.
The disclosed invention has industrial applicability to, for example, a real-time method to monitor manufacturing processes. Such processes include, but are not limited to measurement of thickness, chemical structure, and orientation of coatings on surfaces (solid, liquid, chemically bound, physically adsorbed). These measurements include, but are not limited to those made on biological materials, polymers, superconductors, semiconductors, metals, dielectrics, and minerals. Further applicability is found to a real-time apparatus and method to measure and detect a chemical species present in a chemical reaction involving various processing of materials in any of a gaseous, liquid, or solid state.
BACKGROUND OF THE INVENTION
As industry continues on its path of cost reductions in core technologies, more emphasis will be placed on the optimization of processes and performance. This retrenchment will necessitate the development and introduction of a whole new class of sophisticated instrumentation that is portable, rugged, reliable, and capable of operation over long periods of time in an aggressive industrial or other non-laboratory environment.
Spectrometric techniques are often used in analysis of materials. Classically, spectroscopy is the measurement of the selective absorption, emission, or scattering of light (energy) of specific colors by matter. Visible white light can be separated into its component colors, or spectrum, by a prism, for example. The principal purpose of a spectroscopic measurement is usually to identify the chemical composition of an unknown material, or to elucidate details of the structure, motion, or environmental characteristics (e.g., internal temperature, pressure, magnetic field strength, etc.) of a “known” material or object. Spectroscopy's widespread technical importance to many areas of science and industry can be traced back to nineteenth-century successes, such as characterizing natural and synthetic dyes, and determining the elemental compositions of stars.
Modern applications of spectroscopy have generalized the meaning of “light” to include the entire range or spectrum of electromagnetic radiation, which extends from gamma- and x-rays, through ultraviolet, visible, and infrared light, to microwaves and radio waves. All these various forms (or wavelength ranges) of electromagnetic radiation have their own characteristic methods of measurement. These different methods give rise to various types of spectroscopic apparatus and techniques that are outwardly very different from each other, and which often rely upon difference physical phenomena to make measurements of material characteristics. Further, the various experts and other researchers in these diverse fields, more often than not, do not cross the technical boundaries between these areas of specialization, as different and somewhat compartmentalized knowledge bases and “rules of thumb” are used.
The use of infrared (IR) is one of numerous spectroscopic techniques for analyzing the chemistry of materials. In all cases, spectroscopic analysis implies a measurement of a very specific wavelength of light energy, either in terms of the amount absorbed or reflected by the sample in question, or the amount emitted from the sample when suitably energized.
In the case of IR, an absorption form of spectrometric analysis is relied upon. IR radiation does not have enough energy to induce transitions between different electronic states, i.e., between molecular orbitals, as seen with ultraviolet (UV), for example. Unlike atomic absorption, IR spectroscopy examines vibrational transitions within a single electronic state of a molecule, and is not concerned with specific elements, such as Pb, Cu, etc. Such vibrations fall into one of three main categories, i.e., stretching, which results from a change in inter-atomic distance along the bond axis; bending, which results from a change in the angle between two bonds; and torsional coupling, which relates to a change in angle and separation distance between two groups of atoms. Almost all materials absorb IR radiation, except homonuclear diatomic molecules, e.g., O
2
, H
2
, N
2
, Cl
2
, F
2
, or noble gases.
IR typically covers the range of the electromagnetic spectrum between 0.78 and 1000 &mgr;m. Within the context of IR spectroscopy, temporal frequencies are measured in “wavenumbers” (in units of cm
−1
), which are calculated by taking the reciprocal of the wavelength (in centimeters) of the radiation. Although not precisely defined, the IR range is sometimes further delineated by three regions having the wavelength and corresponding wavenumber ranges indicated:
“near-IR”:
0.78-2.5
&mgr;m
12800-4000
cm
−1
;
“mid-IR”
2.5-50
&mgr;m
4000-200
cm
−1
; and
“far-IR”
50-1000
&mgr;m
200-10
cm
−1
For a molecule to absorb IR, the vibrations or rotations within the molecule must cause a net change in the dipole moment of the molecule. The alternating electric field of the incident IR radiation interacts with fluctuations in the dipole moment of the molecule and, if the frequency of the radiation matches the vibrational frequency of the molecule, then radiation will be absorbed, causing a reduction in the IR band intensity due to the molecular vibration.
An electronic state of a molecular functional group may have many associated vibrational states, each at a different energy level. Consequently, IR spectroscopy is concerned with the groupings of atoms in specific chemical combinations to form what are known as “functional groups”, or molecular species. These various functional groups help to determine a material's properties or expected behavior by the absorption characteristics of associated types of chemical bonds. These chemical bonds undergo a change in dipole moment during a vibration. Examples of such functional groups and their respective energy bands include, for example, hydroxl (O—H) (3610-3640 cm
−1
), amines (N—H) (3300-3500 cm
−1
), aromatic rings (C—H) (3000-3100 cm
−1
), alkenes (C—H) (3020-3080 cm
−1
), alkanes (C—H) (2850-2960 cm
−1
), nitrites (C=-N) (2210-2260 cm
−1
), carbonyl (C═O) (1650-1750 cm
−1
), or amines (C—N) (1180-1360 cm
−1
). The IR absorption bands associated with each of these functional groups act as a type of “fingerprint” which is very useful in composition analysis, particularly for identification of organic and organometallic molecules.
By knowing which wavelengths are absorbed by each functional group of interest, an appropriate wavelength can be directed at the sample being analyzed, and then the amount of energy absorbed by the sample can be measured. The intensity of the absorption is related to the concentration of the component. The more energy that is absorbed, the more of that particular functional group exists in the sample. Results can therefore be numerically quantified. Further, the absence of an absorption band in a sample can often provide equally useful information.
Intensity and frequency of sample absorption are depicted in a two-dimensional plot called a spectrum. Intensity is generally reported in terms of absorbance, the amount of light absorbed by a sample, or percent transmittance, the amount of light that passes through it. In IR spectroscopy, frequency is usually reported in terms of wavenumbers, as defined above.
Infrared spectrometers may be built using a light source (e.g., the sun), a wavelength discriminating unit or optically dispersive el
Rabolt John F.
Tsao Mei-Wei
Connolly Bove & Lodge & Hutz LLP
Hannaher Constantine
Hume Larry J.
UD Technology Corporation
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