Advanced manufacturing, especially of functional materials, requires careful mapping of properties to the underlying microstructure. In technologies such as microfluidics,composites and electronics the features are either too small or too complex to be imaged using optical microscopes. Alternative imaging techniques are necessary so that the relation between material structure and materials properties can be understood.
X rays are an indispensable tool to look at micro and nano structure of materials both functional like electronics and structural like composites. Historically Xrays, since their discovery in 1895, have provided many breakthroughs in imaging that have enabled scientists to advance both material and medical fields. Bone imaging is the most well known application of X rays but the application of X ray diffraction also led to the confirmation of atomic structure in materials and the invention of x ray crystallography. This new technique was later used to identify the structure of DNA and other complex biomolecules that revolutionized the field of biology.
I was excited therefore to join a webinar by Zeiss highlighting the capabilities of their x-ray machines after having interacted with them several times in new delhi during electronics and semiconductor conferences. XRM is important for detecting faults in surface mount components and chip packaging step especially of components that are micrometers in size (solder joints and micro vias). It's even more useful for conducting inspection at the chip level.
X-ray microscopes have now become highly complex as they have Integrated several technical aspects spanning image detection and analysis with precise movement,beam generation and focussing. Every piece of this technology requires highly advanced manufacturing. X-ray generation relies on electron beams striking a high atomic number (Z) material like tungsten. Because most materials are transparent to x-rays, beam focussing requires production of zone plates that achieve focus via diffraction instead of refraction with feature size of the diffracting spots in single digit nanometers. A movement of precise nm steps is achieved via piezoelectric stepper motors or via magnetic drive motors.
All of these technologies that make XRM work are marvels of engineering. The real star of the show here is the underlying software that can take those signals,which are generated via detection of light produced when Xrays strike scintillators like Cerium-doped Lutetium Aluminum Garnet,and convert them into an image that can be analysed by both machines and humans.
The big problem with XRM is the high bar it sets for manufacturing making the technology almost impossible to be replicated by those who don’t have access to manufacturing techniques or materials. On the generation side, electron beams can still be used to produce x-rays on common materials like steel. Detection is also possible via capturing of photo electrons ,though with less efficiency. But still good enough for security checks and medical as well as material imaging.
However, electron beam imaging offers other significant advantages. First it's way more efficient than xray generation which tops out at 1-2% efficiency at best, second it can be steered electrostatically requiring no complex motors—pneumatics work fine. Third it gives just as detailed sub nano-meter picture ,right up to the measurement of crystal lattice parameters. The obvious disadvantage being it's limited to surface level only.
For deep material and human body imaging mid freq ultrasonics combined with microbubbles offer a potential alternative. Electric field tomography also offers new possibilities for applying the technology in a domain that was traditionally dominated by X-rays. It's important to keep pushing the boundaries of what's possible and find cheap low - cost alternatives to expensive technologies.
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