Microscopy is often underutilized as a tool for solid-state characterization. Listed below are the numerous forms of microscopy that can be performed at SSCI. We routinely use results from microscopy studies to complement analytical data from other techniques to address your solid-state characterization issues. Microscopy with appropriate sample handling is also a powerful tool for trace analysis.
Product complaints are often related to the presence of foreign material contaminants in consumer products. The foreign materials have to be identified for product safety purposes. Foreign materials may be small particulates, which require tools and techniques suitable to analyze small quantities such as particles. The stereo microscope is the analyst’s first tool. The stereo microscope is used to locate and document the original condition of the particle, assist in isolation and recovery of the particle, and to prepare the particle for other analytical techniques. An examination using a stereo microscope may provide important information about how the particle was generated, deposited, or incorporated with the product either during or after manufacturing.
Small metallic particles may be encountered due to mechanical wear or failure of machinery during manufacture. Metals such as stainless steel, aluminum, copper, or iron, for example are commonly encountered and identified by light microscopy, followed by scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM/EDS). The energy dispersive x-ray spectrometer analyzes for elemental composition, which may assist an analyst to identify metal alloys. Small polymer particles (fibers or thin films) or glass particles from reaction vessels or sample enclosures may be encountered as contaminants or product failure by-products. In addition, animal or human hairs may be identified as contaminant fibrous materials.
SSCI’s stereo microscopes are equipped with a variety of illumination sources including transmitted light, brightfield and darkfield coaxial, oblique, fiber optic, light emitting diode, or reflected polarized light for anisotropic materials, and high definition digital cameras for photomicrographs or short video to capture real-time motion pictures.
Reliable examination, isolation, and evaluation of materials using a stereo microscope followed by other analytical chemical microscopy techniques allows SSCI analysts to provide reliable identification of foreign particulates in manufactured products, allowing manufactures to respond quickly to investigations and product complaint to find accurate and preventative measures.
SSCI’s stereo microscopes include:
- Leica MZ6 on a large boom-stand to accommodate large objects.
- Leica M 80 on an MDG41 stand with polarized light capabilities.
- Leica MZ 125 on a stand with polarized light capabilities.
Polarized Light Microscopy
Microscopy is the art and science of creating, recording, and interpreting magnified images. There are two distinct parts to contaminant analyses: what is it, and from what source did it originate. Polarized light microscopy provides insight into the origin, while analytical chemical microspectroscopy addresses the composition of the material. Microscopical examination may affirm morphological detail such as striations, smears, elongation of polymers, jaggedness, tears, to name a few. A variety of light microscopy and small particle recognition, documentation, isolation, and identification techniques are available to the particulate analyst. At SSCI the polarized light microscope is used extensively in analysis of solid-state chemical entities. Microscopic particles (1 to 10s of micrometers) in a typical environment may include any of the following: minerals, animal hairs, commercial furs, synthetic and manufactured fibers, glass, paint, thin-film polymers, metals and metal alloys, to name only a few. Additional sources may include cosmetics, paper products, plastic bags or bottles, animal feed products, paint pigments and dyes, textiles, etc.
With the appropriate expertise contaminant particles can quickly be located, documented in-situ, isolated and recovered using fine forceps, sharp tungsten needles, razor blades or a variety of small micro-tools. Once the contaminant particle has been isolated, a variety of analytical chemical microscopical techniques may be used for identification. Polarized light microscopy, in many cases, may be sufficient to identify unknown particulates quickly and unambiguously. Polarized light microscopy has an inherent advantage in that it allows particles with essentially the same chemical composition to be easily distinguished based on shape or morphology, size, and numerous optical characteristics. If additional chemical information is required, then infrared microscospectrosopy may provide molecular information. Scanning electron microscopy with energy dispersive x-ray spectroscopy may provide elemental composition.
Polarized light microscopy is an extremely important and powerful tool in particle identification and characterization, and should be employed by any laboratory involved in addressing product contamination or product failure investigations. In combination with other analytical chemical microscopy techniques, it can lead to solving complex problems that otherwise go unrealized. SSCI’s analytical chemical microscopy group has several analysts with extensive expertise and experience in unknown particle identification from a diverse industrial chemistry and forensic science background.
SSCI’s polarized light microscopes:
- ZEISS Axio Imager.A2M, polarized light microscope with vertical reflected dark-field and bright-field capabilities.
- LEICA DMLP , polarized light microscopes.
- NIKON Optiphot Pol, polarized light microscope with vertical light capabilities.
- OLYMPUS BX51P, polarized light microscope.
Infrared microspectroscopy is the union of microscopy with infrared spectroscopy for the analysis of microscopic particles. The combination of microscopy and spectroscopy is extremely useful, if not mandatory, for contaminant particle examinations. Microscopy is used in selecting samples or areas within a sample for analysis, assessing the most effective and efficient spectroscopic technique, observing a sample’s micro-features, and sample preparation. Sample microstructure may differentiate samples of similar chemical composition such as cellulosic materials such as cotton, rayon or wood pulp paper. However, microspectroscopic examination may be used to determine the chemical composition of morphologically similar objects. For example, fibers that appear to be the same color and have similar cross-sectional shapes, may be colored using different dyes, which microspectroscopy could identify and differentiate. The symbiotic relationship between microscopy and spectroscopy requires the particle analyst be well versed in both microscopy and spectroscopy. SSCI employs several employees with appropriate experience and expertise.
SSCI’s Continµum™ infrared microscope attached to a bench-top spectrometer uses apertures to define a very specific region as small as 5 x 5 micrometers on the sample for examination of chemical composition. A variety of sample techniques are available: transmission, absorption-reflection-absorption, diffuse reflection (DRIFTS), attenuated total reflection (ATR), specular reflection. Samples may be prepared as a potassium bromide (KBr) pellet, directly analyzed in a compression cell or diamond anvil, mulled with Nujol or other appropriate liquid, or prepared as a thin film.
SSCI’s infrared microspectrometer:
- Continuµm FT-IR microscope interfaced with a Nicolet Magna 560 E.S.P. spectrometer.
Thermoptometry analyses consists of a group of techniques in which a physical, optical characteristic of a substance is measured as a function of temperature or time, while the sample is subjected to a predefined heating or cooling program in a specified atmosphere.
“There is almost no problem in chemistry that cannot, to at least some extent, be helped by a good microscopist and often the problem can be completely solved by microscopy.”
-Walter C. McCrone, Ph.D.
Polymorphism is the ability of any element or compound to crystallize as more than one distinct crystal species; for example, carbon as a cubic diamond or as hexagonal graphite. Different polymorphs of a given compound are generally as different in structure and properties as the crystals of two different compounds. Solubility, hardness, crystal shape, melting point, optical and electrical properties, or vapor phase all vary with the polymorphic form.
Since each phenomenon provides different information and some phenomena will not distinguish among a particular set of polymorphs, the importance of using a variety of phenomena for the identification and characterization of polymorphic systems cannot be overemphasized. The employment of polarized light microscopy with hot stage analysis allows the detection of discontinuous changes in interference (polarization) colors during the heating process; the discontinuity in any property being symptomatic of a phase change. Optically observed phase changes are negligibly detectible by other phenomenon such as differential scanning calorimetry (DSC).
|SSCI Analyses||Alternative Techniques at SSCI|
|Melting Point||DSC, Capillary method|
|Sublimation (solid – gas)||TGA|
|Transformation (solid – solid)||DSC|
|Crystallization (liquid – solid)||DSC|
|Decomposition (thermolysis)||DSC, TGA|
|Molecular Weight, Refractive Index, Chemical Reactions, ….|
SSCI’s thermomicroscopy accessories for polarized light microscopes:
- Linkam FTIR 600 hot stage with TMS 93 Temperature Controller and LNP (liquid nitrogen pump).
- Linkam FDCS 196 Freeze Dry Cryo-Stage with LNP.
- Linkam LTS 350 hot stage with TMS 94 Temperature Controller.
Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy
A scanning electron microscope (SEM) scans a focused electron beam over a surface to create an image. The electrons in the beam interact with the sample, producing various signals that can be used to obtain information about the surface topography and composition.
The FEI Quanta standard Environmental SEM (ESEM) capability delivers the extra power to accommodate difficult to handle samples and applications. The Quanta ESEM provides for in situ, dynamic experiments that cover many possibilities for materials research and examination: 1) image hydrated samples, 2) crystallization or phase transformation during humidity or thermal cycling, 3) particles in suspensions or self-assembly processes, and 4)corrosion in metals, to name only a few.
The ESEM’s versatility is well-suited for materials science. It is equally adept at performing conventional high-resolution SEM imaging/analysis and dynamic in situ experiments. The Quanta ESEM allows for the widest range of samples in their natural state for the most accurate information about structure and composition:
- oxidation/corrosion samples
- ceramics, composites, plastics
- films and coatings
- soft materials: polymers, pharmaceuticals, gels
- particles, porous materials, fibers
- metals and alloys (ferrous steels and stainless steels, brass, copper, aluminum)
SSCI’s FEI Quanta scanning electron microscopes feature three modes (high vacuum, low vacuum, and ESEM) to accommodate the widest range of samples of any SEM system. SSCI’s Quanta ESEM system is equipped with an energy dispersive x-ray spectrometer (EDX).
SSCI’s scanning electron microscope with energy dispersive x-ray spectrometer:
- FEII Quanta 200 Environmental Scanning Electron Microscope with Cryo stage capabilities.
- EDAX: Energy Dispersive X-ray Spectometer model PV77-60770 ME Sapphire.
Historically, the technique of Raman spectroscopy was established in 1928 by Professor C.V Raman. It is a light scattering technique, and can be thought of in its simplest form as a process where a photon of light interacts with a sample to produce scattered radiation of different wavelengths. Raman spectroscopy has become an important analytical and research tool. It is extremely information rich, and it is useful for chemical identification, characterization of molecular structures, and the effects of bonding, environment and stress on a sample. Raman spectroscopy can be used for a wide range of applications including pharmaceuticals, forensic science, polymers, thin films, semiconductors and even for the analysis of fullerene structures and carbon nano-materials.
The Raman microscope is one of the best instrumental techniques available for chemical characterization as it is a powerful non-destructive and non-contact method of sample analysis on a micrometer or smaller spatial resolution.
SSCI’s Raman microscope is equipped with two lasers (785 nm and 633 nm), stage mapping, and confocal configuration. Surface enhanced resonance spectroscopy (SERS) may be employed using gold or silver colloids to reduce sample fluorescence and enhance Raman signal to noise. SSCI’s spectroscopy and analytical chemical microscopy group has several analysts with extensive expertise and experience with Raman microspectroscopy.
SSCI’s Raman microspectrometer:
- RENISHAW inVia Raman Microscope