Russian scientists, together with foreign colleagues, have synthesized a nanomaterial based on silicon and gold, which absorbs light with an efficiency of 96%, after which it converts it into heat – thanks to this property, it can be used as a nanothermometer. Moreover, the films obtained by the authors in the form of a scattering of nanoparticles have a unique “pattern” on the surface, which will allow creating protective optical labels in a fairly simple and easily scalable way to combat counterfeit products. The results of the study, supported by a grant from the Russian Science Foundation (RNF), were published in the ACS Applied Materials & Interfaces journal.
Existing technologies that make it possible to combine silicon and gold at the nanoscale level are quite laborious and expensive, since they include many successive stages. Moreover, they make it possible to obtain the desired hybrid material only in microquantities. In this regard, scientists are striving to find a simple and easily scalable method for the synthesis of hybrid nanomaterials.
Researchers from the Institute of Automation and Control Processes, Far Eastern Branch of the Russian Academy of Sciences and the Institute of Chemistry, Far Eastern Branch of the Russian Academy of Sciences (Vladivostok), together with colleagues from Spain and Japan, synthesized a nanomaterial based on silicon and gold using a laser ablation method previously developed and tested by this scientific group. First, the authors obtained silicon microspheres by illuminating the plates of this crystal placed in an organic solvent with a laser. Then, gold ions were added to the resulting solution, and repeated irradiation with laser pulses was carried out. As a result, the surface of the silicon microspheres “overgrown” with gold nanoclusters, which gradually penetrated deep into the particles.
Experiments have shown that the resulting hybrid particles absorb up to 96% of solar radiation, converting it into heat. In this case, the samples of the material were heated up to 300°C under laser illumination. This property will make it possible to use them in solar desalination plants, since the nanomaterial, when illuminated, will effectively heat sea water, which, evaporating, will begin to condense in the form of drops of clean drinking water. In addition, scientists have found that when any molecules present in solution are deposited on the surface of silicon-gold nanospheres, their optical properties change greatly. This allows individual hybrid particles to be used as detectors for various chemicals such as hazardous gases and drugs.
The scientists then obtained several samples of the material in the form of films by applying a solution of hybrid particles to smooth glass. As a result, each film had a unique surface structure, since the nanospheres always settled on the substrate randomly and uncontrollably. Random agglomeration of particles made it possible to create unique patterns of optical signals that can be recorded and used later as security marks.
“The coding ability of such optical labels is 10 to the power of 3000, that is, this is the number of attempts that an attacker will need to randomly repeat any label. This makes it physically non-replicable,” explains Stanislav Gurbatov, head of the project, supported by a grant from the Russian Science Foundation, Candidate of Physical and Mathematical Sciences, senior researcher at IAPU FEB RAS.
“The simplicity of the proposed synthesis technology, as well as its high productivity, reaching several grams per hour, make it commercially attractive for nanosensors, solar energy conversion and anti-counterfeiting labeling. In the future, we plan to study in more detail the optical properties of the obtained nanoparticles depending on the initial concentrations of the components and the type of solvent,” says co-author of the study, Vladislav Puzikov, postgraduate student and engineer at the Institute of Control and Engineering of the Far Eastern Branch of the Russian Academy of Sciences.