This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Beauty and mystery—it is hard to imagine a more alluring combination, and this is precisely what we encounter when we observe phenomena in the nanoworld. But are we really sure that observations made using modern microscopic techniques do not influence what is happening there?
A comparison of images of copper oxide nanoparticles reacting with chloroauric acid, obtained using electron and photon beams, has yielded unexpected results. "We stumbled upon the clue that led to our discovery while investigating the galvanic exchange reaction between copper oxide nanocubes and chloroauric acid. We examined this phenomenon in a rather unusual way, using two sophisticated microscopic techniques: LC-TEM, or liquid-cell transmission electron microscopy, and EL-STXM, or liquid-cell electrochemical scanning transmission X-ray microscopy," explains Prof.
Magdalena Parlinska from the Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN) in Krakow, one of the lead authors of an article published in the journal Small. "In other words, at times we observed the process using electrons, and at other times using photons in the X-ray energy range—and although in both cases we were observing the same substances reacting with one another, we saw something different." In transmission electron microscopy (TEM), an electron beam in a vacuum passes through a sample no more than a few dozen nanometers thick. Unfortunately, the vacuum inside the microscope prevents the examination of samples containing water or suspended in liquid.
This problem is solved by holders featuring a liquid cell (LC) comprising two chips with windows fitted with thin silicon nitride membranes, through which the imaging electron beam passes. In the experiment carried out by physicists in Krakow, the nanocubes were placed on a membrane, and a solution of chloroauric acid was delivered to the liquid cell via capillaries designed to supply fluids to the cell. Scanning transmission X-ray microscopy (STXM) operates on a similar principle to TEM, but instead of electrons, it uses a focused beam of soft X-rays, or photons.
Given that the energies of the photons are significantly higher than those in the optical range, STXM also allows for high image magnification, albeit slightly lower than that achieved with electron microscopy. The technique does, however, have a major advantage: By scanning the sample with photon beams of appropriately selected energies, it is possible to obtain information about the material's chemical composition and even its degree of oxidation at a specific point in the image. The source of X-ray radiation for STXM microscopy in the studies was the SOLARIS synchrotron, the main facility of the National Centre for Synchrotron Radiation at Jagiellonian University in Krakow.
"In the reaction of copper oxide nanocubes with a solution of chloroauric acid that we are investigating, the cubes themselves act as templates for the gold structures that are to be formed," explains Dr. Joanna Depciuch-Czarny (IFJ PAN), co-author of the discovery. "When we observed the reaction using a photon beam, we ultimately saw a material composed of gold-rich, hollow nanoboxes.
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