Imaging Beams Reshape Gold Formation in Liquid Nanocubes

Microscopy beams can do more than record a reaction: in experiments on copper oxide nanocubes immersed in a chloroauric acid solution, researchers in Kraków found that an electron beam produced gold-coated structures, while a soft X-ray beam produced hollow, gold-rich nanoboxes. The same chemical system therefore developed into different forms depending on how it was observed. Numerical simulations supported the explanation that radiation-induced chemistry altered the local solution environment, affecting the reduction of gold ions and the oxidation and dissolution of copper oxide. The peer-reviewed study was published in Nano Micro Small in 2026 and used liquid-phase electron and X-ray microscopy to follow the reaction at nanometre scale.

The project was led by physicists from the Henryk Niewodniczański Institute of Nuclear Physics of the Polish Academy of Sciences, with X-ray imaging performed at the SOLARIS synchrotron facility at the Jagiellonian University. The researchers examined copper oxide nanocubes as templates for structures formed from gold in solution. Copper nanocubes were placed on a membrane, and a chloroauric acid solution was introduced through capillaries into a liquid cell. Because the reaction products differed markedly between the two imaging methods, the investigators examined not only the resulting structures but also the chemical processes that could account for the contrast.

Transmission electron microscopy, or TEM, sends a beam of electrons through a specimen in a vacuum. Samples containing water or suspended in liquid cannot ordinarily be examined in this arrangement because the microscope’s vacuum prevents that kind of preparation. A liquid cell overcomes the restriction by placing the sample between two chips with thin silicon nitride membranes, each fitted with a window through which the imaging beam can pass. In the reported experiment, the nanocubes rested on one membrane while capillaries delivered the chloroauric acid solution to the cell. The electron beam could thus pass through the liquid and the reacting material while imaging the reaction in progress.

Scanning transmission X-ray microscopy, or STXM, follows a related principle but uses focused soft X-rays, which are photons rather than electrons. The photon beam used in these studies came from the SOLARIS synchrotron, the main facility of the National Centre for Synchrotron Radiation at the Jagiellonian University. STXM can achieve high magnification, although somewhat less than electron microscopy in this setting, and it can extract information about chemical composition and oxidation state at particular positions in an image by selecting appropriate photon energies. These capabilities made it possible to compare the products formed under X-ray irradiation with those observed when electrons were used.

The structural difference was pronounced. When the researchers observed the reaction with photons, they ultimately found hollow nanoboxes composed of gold-rich material. Under the electron beam, by contrast, gold was deposited on the walls of the copper nanocubes in the form of nanoclusters, while the cubes remained visible and showed no sign of disappearing. Energy-dispersive X-ray spectroscopy mapping distinguished the distributions of gold and copper in the structures, and scanning electron microscopy provided additional views of the coated cubes. The observations show that the X-ray and electron imaging methods did not simply reveal two appearances of one identical product; they were associated with distinct reaction pathways and final morphologies.

According to the study’s interpretation, both electron and photon beams interact with water, producing reactive chemical species that change the chemistry around the nanocubes. These species influence whether the environment accepts or releases electrons, thereby affecting reduction and oxidation, and they also alter hydrogen-ion activity, which corresponds to the acidity or alkalinity of the solution measured on the pH scale. The electron beam created a locally more acidic environment. That condition inhibited oxidation and etching of the copper oxide while promoting reduction of gold ions and their deposition on the copper structures, accounting for the observed shells or coatings rather than hollow boxes.

The soft X-ray beam did not cause the same local pH decrease. Under those conditions, gold deposition could proceed alongside oxidation and dissolution of copper oxide. As the copper framework was etched away, the remaining material developed into hollow, gold-rich nanoboxes. The study therefore identifies the imaging radiation as an active participant in the chemistry rather than a passive observer. Its central experimental result is that changing the beam used to image successive stages of a liquid-phase reaction can redirect the reaction itself, with the electron and photon conditions favouring different balances among gold reduction, copper oxidation and structural dissolution.

To check the proposed mechanism, the team developed numerical models describing ion transport, reactions at material surfaces and the radiolysis, or irradiation-induced breakdown, of water. The simulations were run with computing resources from the Cyfronet AGH Academic Computing Centre. According to the researchers, the models reproduced the experimentally observed beam-dependent behaviour and supported the link between radiation chemistry, local pH, gold reduction and copper-oxide dissolution. The numerical work was thus a mechanistic test of the experimental comparison rather than a separate prediction of material performance; the study did not establish catalytic effectiveness or any other application of the resulting nanoboxes.

Lead author Magdalena Parlinska said the findings address fundamental questions about chemical reactions viewed in liquid through radiation-based microscopy. The results show that the beam used to observe successive reaction stages can influence the course of events and become an actor on the chemical stage. The team is already pursuing further work involving materials containing other elements and approaching the problem from a more applied perspective. The current evidence concerns laboratory nanocubes, controlled imaging conditions and model chemistry, so it does not demonstrate how broadly the same beam-dependent transformations occur in complex biological, industrial or environmental systems. Nevertheless, the study identifies a specific and measurable source of mismatch between electron- and X-ray-based images of dynamic samples that researchers may need to account for when interpreting in-liquid nanoscale reactions.

Subject of Research: Radiation-induced chemistry in liquid-phase electron and X-ray microscopy of copper oxide and gold nanocubes.

Article Title: Photons create golden boxes, electrons lead to shells

Article References: Photons create golden boxes, electrons lead to shells. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: electron microscopy, X-ray microscopy, gold nanoboxes, copper oxide, radiolysis, liquid-phase imaging, nanomaterials, radiation chemistry, Photons, create, golden, boxes