Since graphene won the Nobel Prize in Physics in 2010, scientists and industries have been chasing graphene feverishly. The difference from graphite is that graphene has only one carbon atomic layer thickness and exhibits excellent mechanical and electrical properties. While chasing graphene, a large number of graphene-like two-dimensional materials have also been discovered one after another. From the periodic table of elements, the elements that make up these two-dimensional materials mainly include: transition metals, carbon elements, chalcogen elements and others. These nanometer-thick 2D materials, like graphene, have new properties that are distinct from those of bulk materials.

Figure 1. Various 2D materials and their structures

There is a big news recently: on the last working day of 2018, my country's first graphene national standard GB/T 30544.13-2018 was drafted by Taizhou Juna New Energy Co., Ltd. as the first unit: "Nanotechnology Terminology No. 13" Section: Graphene and Related 2D Materials" was officially released. However, you may not realize that this standard is also the first national standard in the field of two-dimensional materials. Because this standard not only defines graphene, but also defines important terms such as two-dimensional materials, so it is of great significance to the development of the entire new two-dimensional materials industry.

So, what are 2D materials?

According to the definition of the national standard, it consists of one or several layers, in which the atoms in each layer are closely bonded to the adjacent atoms in the layer, and one dimension (that is, its thickness) is at the nanometer or smaller scale, and the remaining two Materials whose two dimensions are usually on a larger scale are called two-dimensional materials.

In order to make it easier for everyone to understand this definition, the national standard has made a detailed remark on it:

1: The number of critical layers to distinguish two-dimensional materials and bulk materials is related to the measured material and its properties. Regarding the number of graphene layers, from the electrical test, when its thickness is less than or equal to 10 layers, it is a two-dimensional material, and when its thickness is greater than 10 layers, it has no obvious difference from the bulk material, that is, graphite.

2: The interlayer bonding is significantly different and weaker than the intralayer bonding.

3: Each layer can contain multiple elements.

4: The two-dimensional material can be a nanosheet.

What are the excellent properties of two-dimensional materials?

The surface atoms of single-layer two-dimensional materials are almost completely exposed, and the atom utilization rate is greatly improved compared with bulk materials. Through thickness control and element doping, the band structure and electrical properties, such as silicene and phosphorene, can be more easily regulated. Two-dimensional materials can be conductors, semiconductors, or insulators; they can be chemically inert, or they can be chemically modified at any time. To sum up, there are three main advantages:

1) It is more conducive to chemical modification and can control the catalytic and electrical properties.

2) It is more conducive to electron transfer, which is conducive to the improvement of the performance of electronic devices.

3) High flexibility and transparency, attractive prospects in wearable smart devices, flexible energy storage devices and other fields.

Five families of graphene-like 2D materials

Yury Gogotsi said: "A 50-year-old scientist playing with a new toy in the laboratory is no different from the fun of a 5-year-old child playing with a new toy at home. Two-dimensional materials are my new toy!" Beyond graphene, playful The scientists discovered five graphene-like two-dimensional material families, namely: MXenes, Xenes, Organicmaterials, TMDs (transition metal dichalcogenides) and Nitrides (nitrides). These materials involve a wide range of disciplines, a wide range and a variety of types, and have always shown an innovative trend of multiple blooms, new phenomena, and new applications. Two-dimensional materials are one of the most cutting-edge scientific research application fields, covering printed electronics, flexible electronics, supercapacitors, solar cells, quantum dots, sensors, semiconductor manufacturing, etc. The foundation for disruptive innovation in the field.

my country's first national standard for graphene and two-dimensional materials was mainly drafted by Taizhou Juna New Energy Co., Ltd., Southeast University and other units. Founded in 2010, Taizhou Juna New Energy Co., Ltd. is one of the earliest companies engaged in graphene research, testing, application and standardization in China. In 2013, the first National Graphene Standardization Forum was organized. Since 2014, he has led the drafting of two of the first four graphene national standard plan projects in my country. In May 2014, it officially undertook the standardization pilot work of strategic emerging industries in Jiangsu Province and passed the acceptance in 2016. In 2014, it was recognized as the National Torch Program Platform by the Ministry of Science and Technology. In 2015, an online store for low-dimensional materials, 91cailiao.cn, was established. Currently, it has provided nearly 10,000 scientific research and industrial customers with high-quality zero-dimensional, one-dimensional, and two-dimensional materials. In December 2016, with the approval of the National Standards Committee and the Chinese Academy of Sciences, it assumed the secretariat of the National Nanotechnology Standardization Technical Committee Low-Dimensional Nanostructure and Properties Working Group (No. SAC/TC279/WG9), responsible for coordinating and organizing the national low-dimensional nanomaterials standardization work. At the end of 2016, he assumed the secretariat of the International Standards Working Committee of China International Graphene Resources Industry Alliance. In October 2018, the first seminar on low-dimensional materials applications and standards (LDMAS2018) was successfully organized.

Figure 2. Five families of 2D materials