Microscopy is a quintessential technique used to understand the microcosm around
us. Since the 17th century, microscopes have used visible light to provide a
magnified view of miniature objects, enabling scientists to make breakthrough
discoveries. A view into the Nano world became possible in the 1930s, when a team
of scientists led by Ernst Ruska, invented a microscope using electrons
instead of visible light. Both visible light and electron microscopy provide
detailed images of a sample surface. Qualitative and quantitative analysis of
surface properties can be performed. These results allow components and
materials they are made of to be pushed to new limits. But what if analysis could
be extended beyond the surface? What if investigations could be performed deep
into the sample, revealing the three-dimensional structure? What
potential could be unlocked to push material properties even further? Or to
induce new properties? X-ray microscopy is an emerging method which allows
researchers to do just that. Based on a technology called micro-computed
tomography, XRM combines three-dimensional imaging with advanced
visualization, and 3D evaluation tools. X-ray radiation is a very high-energy
light capable of penetrating objects that are opaque to the visible spectrum.
Cone beam X-ray imaging results in a two-dimensional radiograph, showing the
transmission of X-rays through an object. Low-density volumes of the object allow
high transmission, while high density volumes allow low transmission. With a
point X-ray source, magnification and illuminated volume can be adjusted.
Larger coverage is achieved by moving the object closer to the detector, while
higher magnification is achieved by moving the object closer to the source. The
source to detector distance also plays a pivotal role in balancing magnification
and coverage. Moving the detector closer to the object results in higher coverage,
while moving the detector further away yields higher resolution. Unfortunately,
if multiple features are present inside the object, the image is hard to decipher.
This is overcome with the technique known as computed tomography.
Several projection images are collected as the object is rotated. The object is
digitally reconstructed, revealing the position of features in the object. As
with cone beam microscopy, contrast in the three-dimensional model comes from
the absorption difference of the features in the object. Micro-computed
tomography extends the resolution of CT into the submicron scale by using X-ray
sources with finer focuses, object stages with higher precision and detectors with
smaller pixels. X-ray microscopes combine micro-CT Hardware with specialized
software for quantitative analysis of three-dimensional models. This includes
object counting, size determination, size distribution and orientation analysis.
The 3D model can even be exported to a 3D printer. X-ray microscopy is used
across a wide variety of applications, from maximizing well efficiency by
determining the open and closed porosity of core samples in the petroleum industry, to measuring
the homogeneity of pharmaceutical coating thicknesses to dial in API
uptake rates. Using XRM, engineers can identify defects within the internal
structure of complex components created with additive manufacturing or maximize
the performance of composite materials by verifying the orientation of fibers
buried in the resin. Innovations and instrument design, ease-of-use and
computing power have increased the availability of X-ray microscopy.
Measurements once only available at large research centers are now
commonplace in benchtop microscopes, allowing scientists to uncover new
insights into the world around us.