New Spectroscopic Method Enables Simple and Precise Analysis of Nanoparticle Structure

Korean researcher Sung Jun Lim suggests easy analysis method to identify the structure of semiconductor nanoparticles in solution only by measuring absorption spectrum. It is expected to present a new direction for the studies of the structure and the properties of nanoparticles.

Structural analysis of semiconductor nanoparticles in solution by measuring absorption spectrum. II-VI semiconductor nanoparticles, such as cadmium selenide (CdSe), have two different crystal structures depending on the bonding structure of atoms such as zinc-blende (red background structure) or wurtzite (green background structure). In general, X-ray diffraction has been used to analyze such crystal structure. However, the above figure shows that the two crystal structure can be distinguished through the simply measurement of absorption spectrum of nanoparticle solution. This is because the zinc-blende structure (red absorption spectrum) and the wurtzite structure (green absorption spectrum) exhibits a unique absorption peak at 4.8-4.9 eV and at 5.1 eV, respectively, due to the difference in electron energy levels produced by the two structures.

A research team of Daegu Gyeongbuk Institute of Science and Technology (DGIST), South Korea, has developed a new spectroscopic method which can more easily and accurately analyze the structure of nanoparticles than traditional methods.

Sung Jun Lim, a senior researcher at DGIST’s Intelligent Devices and Systems Research Group and a research team led by Professor Andrew M. Smith of the University of Illinois, United States, conducted a joint research and has developed a 'Optical Nano-Crystallography Analysis Method' that can analyze the crystal structure of semiconductor nanoparticles only by measuring absorption spectrum.

This study has been published in the online edition of Nature Communications, the sister journal of Nature, an international academic journal, on May 18.

Semiconductor nanoparticles, widely known as quantum dots, are unique nanomaterials whose optical and electrical properties are variously controlled by the size and shape of the particles. They are used in various science and technology fields, including LED, solar cell, photoelectric sensor, biomolecular imaging, etc.

The II-VI and III-V compound semiconductors are polymorphic materials that can have different crystal structures of Zinc Blende structure and Wurtzite structure. In order to understand and control the optical, electrical, and morphological characteristics of these nanoparticles, it is essential to accurately and efficiently analyze the crystal structure of the nanoparticles.

However, the X-ray diffraction method, which is widely used for the existing crystal structure analysis of nanoparticles, requires expensive analysis equipment and needs a large amount of refined powdery nanoparticles, which makes the analysis process cumbersome and costly. Moreover, there is a limitation that it cannot be directly applied to nanoparticle samples that are usually synthesized, purified and stored in a solution.

The researchers conducted experiments and theoretical studies on the correlation between the crystal structure and the absorption spectrum of nanoparticles, and developed the method that can distinguish the two crystal structures (zinc-blende, wurtzite) of II-VI semiconductor nanoparticles such as cadmium selenide (CdSe) only through the analysis of absorption spectrum.

This 'Nano-Optical Crystallography Analysis Method' will enable the precise observation of the crystal structure of nanoparticles of less than 2 nanometers, which is difficult to accurately analyze by X-ray diffraction technique. It can also rapidly predict the crystal structure of polytypic nanoparticles.

In addition, it is expected that the new analysis method developed by the research team is the new analytical method that can easily and accurately analyze the crystal structure of nanoparticles in solution through the spectroscopic method. Therefore, it is expected to improve the nanoparticle synthesis technology by applying the method to the study to identify the relationship between the structure and the properties of the nanoparticles.

Sung Jun Lim, a senior researcher at DGIST’s Intelligent Devices and Systems Research Group said "This method is a new analytical method that identifies not only the crystal structure of nanoparticles but also the relationship between the various structural characteristics, such as particle shape and surface state, and the optical spectrum." He added "In the future, we will continue the theoretical studies and experiments to carry out the follow-up studies for optical crystal analysis techniques with high value We will continue the theoretical research and experiments and carry out follow-up studies to develop highly usable optical crystallographic analysis method.”

Published: 06 Jul 2017

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Nature Communications (DOI : 10.1038/ncomms14849)

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