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Supported Two-Dimensional Metal Clusters
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Highly oriented pyrolytic graphite (HOPG) is a typical substrate used for the study of nucleation and growth of metal clusters. The basal plane of HOPG provides an atomic flat substrate, which is convenient for STM imaging. Due to the weak interaction between the metal atoms and the HOPG substrate, metal deposition usually leads to the formation of 3D clusters. Figure 5.1 shows Fe, Co and Ni clusters grown on HOPG [31–33]. Similar 3D clusters are also found when metals are deposited onto metal oxide substrates such as TiO2 [34,35]. The stability of the clusters depends on the cluster size. Clusters below a certain size are unstable and hence not observed at a specific temperature.
Graphene
Published in Rajendra Kumar Goyal, Nanomaterials and Nanocomposites, 2017
It involves the exfoliation of the individual graphene sheets by using scotch tape onto graphite and then they are transferred by pressing them onto a substrate (Si, SiO2, or Ni). For this, typically highly ordered pyrolytic graphite (HOPG) is chosen in order to get high-quality graphene crystallites. Crystallites larger than 1 mm, which are visible to the naked eye, can be obtained [2]. This method has the advantage of synthesizing graphene at room temperature using low-cost equipment. However, this method has poor scalability. A sharp single-crystal diamond wedge can also be used to exfoliate graphene layers from the HOPG [3]. The shear mixing of graphite both in the N-methyl-2-pyrrolidone (NMP) and in aqueous surfactant solutions (sodium cholate, NaC) results in large-volume suspensions. After centrifugation, these suspensions contain high-quality graphene nanosheets, including some monolayers [4].
Quantum Mechanics of Graphene
Published in Andre U. Sokolnikov, Graphene for Defense and Security, 2017
Synthetically, graphite has been produced from carbonaceous materials at high temperatures and pressure. The process is called HOPG (Highly Oriented Pyrolytic Graphite) which means that pyrolytic graphite is received by thermal decomposition of hydrocarbon gas on a heated substrate. Pressure is also applied in order to improve the quality. The subsequent annealing under compression gives HOPG. The typical temperatures range from 2800°C to 3500°C and pressures are in the range of 4000 to 5000 psi. Pyrolytic graphite (carbon) is a material which is close to graphite that has covalent bonding between the layers as a result of defects in its production. The typical production process includes heating of hydrocarbon almost to its temperature of decomposition and then permitting the graphite to crystallize. The angular misalignment of the crystal is improved by annealing of the graphite at temperature of 3300°C. As a result, we have a specimen about 1 mm long (0.1 μm in c-direction). Graphite in general has a lamellar structure, i.e. a microstructure that is composed of thin, alternating layers of various materials which exist in the form of lamellae. Similar to other layered materials, it consists of stacked planes. The forces within the lateral planes are much stronger than between the planes. Because of this, HOPG cleaves like mica. In an atomic resolution scanning tunneling microscopy there are several typical images: one is a close-packed array where each atom is surrounded by six nearest neighbors. The distance between them is 0.246 nm. The hexagonal rings have the center to center distance of 0.1415 nm (see Fig. 4.6).
1,2,3-Triazole lamellar liquid crystal and its non-covalent palladium complex dimer: structure, mesomorphism and self-assembly properties
Published in Liquid Crystals, 2022
Meihao Xia, Yao Chen, Ziran Chen, Wenhao Yu, Haomin Cheng, Chun Feng, Hailiang Ni, Biqin Wang, Keqing Zhao, Ping Hu
All Scanning tunnelling microscopy (STM) experiments were performed with a Nanoscope III D scanning probe microscope system (Bruker, USA) in constant current mode under ambient conditions. STM tips were prepared by mechanically cutting of Pt/Ir wire (80/20). The STM image provided is raw data and was calibrated by referring the underlying graphite lattice. Detailed tunnelling condition was given in the corresponding figure caption. The solvent used was phenyloctane (J&K Scientific) without further purification. The 1,2,3-triazole heterocyclic LC L and its palladium complex PdCl2-L2 were dissolved separately with concentration less than 1.0 × 10−4 M CH2Cl2. Highly oriented pyrolytic graphite (HOPG, grade ZYB, brukerafmprobes, US) substrates were freshly cleaved using adhesive tape. A droplet of solution containing the sample was deposited on one piece of HOPG substrate. Then the sample was heated to 60°C and retaining for 10 minutes. After the samples cooled to room temperature, they were been studied by STM with its tips immersed directly in the droplet.
Platinum nanoparticles on HOPG surface modified by 380 keV Ar+ irradiation: TEM and Raman studies
Published in Radiation Effects and Defects in Solids, 2020
Tetsuya Kimata, Kenta Kakitani, Shunya Yamamoto, Tetsuya Yamaki, Takayuki Terai, Kazutaka G. Nakamura
We recently found the unique interaction between platinum (Pt) nanoparticles and Ar-irradiated glassy carbon substrate, namely the Pt–C interfacial interaction (7). The Pt nanoparticles on Ar-irradiated glassy carbon substrate had a higher catalytic activity than those on a non-irradiated one (8). The theoretical calculation and X-ray absorption measurement suggested that the Pt–C interfacial interaction would be the origin of the activity enhancement (9,10). Quite recently, the Pt nanoparticles on the Ar-irradiated highly oriented pyrolytic graphite (HOPG) was investigated by Raman spectroscopy. We found that the Ar-irradiated HOPG would affect the electronic structure of Pt nanoparticles, and then estimated the number of defects interacting with a Pt nanoparticle from the phonon correlation length (11).
One step synthesis of graphene
Published in Inorganic and Nano-Metal Chemistry, 2020
Chemical methods have also been used to extract graphene from graphite. In[16] a method was described to produce graphene from natural graphite. They used a series of oxidation and purification process followed by dilution in methanol and several centrifugation steps to extract sheets. In a different approach sulfuric and nitric acid were intercalated between layers of graphite and followed by heating up to 1000 °C results in graphitic sheets.[17] Thermal decomposition approach was another popular one to produce graphene. As an example, thermal decomposition of silicon on the surface plane of a single crystal of 6H-SiC was discussed on.[18] Graphene monolayers were grown on Ru single crystal at ultra-high vacuum conditions.[19] A comparatively new method of unzipping carbon nanotubes was reported by opening up multi-wall nanotubes longitudinally by using intercalation of lithium and ammonia followed by exfoliation in acid and abrupt heating.[20] Highly oriented pyrolytic graphite (HOPG) has been cleaved using a microcantilever to form graphitic sheets.[21] The sheet was 10 to 100 nm thick.