Si lattice-based linewidth, as the most used calibrator in the semiconductor industry, failed to meet the nanoscale demands of critical dimensions (CD). In 2018, the Si{220} lattice spacing was recommended as a secondary realization of the meter definition, however, Si lattices as nanoscale rulers can only be used in ultra-high vacuum (UHV) environments. For the first time, we designed two-dimensional (2D) supramolecular self-assembly monolayers (SAMs) as a new generation of nanoscale rulers using scanning tunneling microscopy (STM) technology in atmospheric environment. Three SAMs nanoscale rulers were selected among seven types of SAMs based on their self-assembly behaviors and thermodynamic stability. One of these SAMs nanoscale rulers was used to calibrate the STM images through lattice perspective transformation method, and directly determine the lattice length along the nanoscale rulers’ lattice direction without calibration, proving the feasibility of SAMs nanoscale rulers in nanometrology. The construction of SAMs nanoscale rulers was straightforward and manageable in the atmosphere, significantly lowering the complexity of producing nano precise measurement tools. Identifying the ideal SAMs for use as nanoscale rulers holds immense potential to significantly reduce the cost of calibration in chip industries.

Extensive efforts have been made to pursue a low-friction state with promising applications in many fields, such as mechanical and biomedical engineering. Among which, the load capacity of the low-friction state has been considered to be crucial for industrial applications. Here, we report a low friction under ultrahigh contact pressure by building a novel self-assembled fluorinated azobenzene layer on an atomically smooth highly-oriented pyrolytic graphite (HOPG) surface. Sliding friction coefficients could be as low as 0.0005 or even lower under a contact pressure of up to 4 GPa. It demonstrates that the low friction under ultrahigh contact pressure is attributed to molecular fluorination. The fluorination leads to effective and robust lubrication between the tip and the self-assembled layer and enhances tighter rigidity which can reduce the stress concentration in the substrate, which was verified by density functional theory (DFT) and molecular dynamics (MD) simulation. This work provides a new approach to avoid the failure of ultralow friction coefficient under relatively high contact pressure, which has promising potential application value in the future.

The interaction between organic photoelectric molecules leads to the formation of a certain aggregation structure, which plays a pivotal role in the charge transport at the intermolecular interface. In view of this, we investigated the mechanism and law of intermolecular interaction by detecting the self-assembled behaviors between organic photoelectric molecules at the interface by scanning tunneling microscopy (STM). In this work, the structural transformations of tetraphenylethylene acids (H₄ETTCs) on graphite surface induced by temperature and triazine derivatives (zcy-19, zcy-27, and zcy-38 molecules) were studied by STM technology and density functional theory (DFT) calculations. At room temperature, zcy-19 and H₄ETTC molecules formed a small range of ordered co-assembled nanostructure, while for zcy-27 or zcy-38 molecules, no co-assembled nanostructures were observed and only their own self-assembled structures existed on graphite surface, individually. In the thermal annealing trials, the original co-assembled H₄ETTC/zcy-19 structure disappeared, and only zcy-19 and H₄ETTC self-assembled in separate domains. Nevertheless, new well-ordered H₄ETTC/zcy-27 or H₄ETTC/zcy-38 co-assembled structures appeared at different annealing temperatures, respectively. Combined with DFT calculations, we further analyzed the mechanism of such structural transformations by triazine derivatives and temperature. Results reveal that triazine derivatives could interact with H₄ETTC by N–H···O and O–H···N hydrogen bondings, and whether temperature or zcy series compounds could achieve successful regulation of H₄ETTC assembly behavior is closely associated with the conjugated skeleton length of zcy series compounds.

Controlling friction by the electric field is a promising way to improve the tribological performance of a variety of movable mechanical systems. In this work, the assembly structure and microscale superlubricity of a host–guest assembly are effectively controlled by the electric field. With the help of the scanning tunneling microscopy (STM) technique, the host–guest assembly structures constructed by the co-assembly of fullerene derivative (Fluorene-C₆₀) with macrocycles (4B2A and 3B2A) are explicitly characterized. Combined with density functional theory (DFT), the distinct different assembly behaviors of fullerene derivatives are revealed at different probe biases, which is attributed to the molecular polarity of the fullerene derivative. Through the control on the adsorption behavior, the friction coefficient of host–guest assembly is demonstrated to be controllable in the electric field by using atomic force microscopy (AFM). At positive probe bias, the friction coefficient of the host–guest assembly is significantly reduced and achieves superlubricity (μ_min = 0.0049). The efforts not only help us gain insight into the host–guest assembly mechanism controlled by the electric field, but also promote the further application of fullerene in micro-electro-mechanical systems (MEMS).

Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor. The morphologies, co-assembly behavior, interaction sites, and charge transfer of BTID-nF (n = 1, 2)/PC₇₁BM donor–acceptor system in the active layer of organic solar cell have been studied employing scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), density functional theory (DFT) calculations, and transient absorption (TA) spectroscopy. The results show that BTID-1F and BTID-2F form bright strip structures, whereas BTID-nF (n = 1, 2)/PC₇₁BM form ridge-like structures with each complex composed of one BTID-nF (n = 1, 2) molecule and four PC₇₁BM molecules which adsorbed around the BTID-nF (n = 1, 2) molecule by S···π interaction. With the assistance of S···π interaction between BTID-nF (n = 1, 2) and PC₇₁BM, BTID-nF (n = 1, 2)/PC₇₁BM co-assembled ridge-like structures are more stable than the BTID-nF (n = 1, 2) ridge structures. To investigate the charge transfer of BTID-nF (n = 1, 2)/PC₇₁BM system, STS measurements, DFT calculation, and TA spectroscopy are further performed. The results show that charge transfer occurs in BTID-nF (n = 1, 2)/PC₇₁BM system with the electron transferring from BTID-nF (n = 1, 2) molecules to PC₇₁BM.

The prediction of two-dimensional molecular self-assembly structures has always been a problem to be solved. The molecules with meta-dicarboxyl groups can self-assemble into a specific hexagonal cavity, which has an important influence on the prediction of molecular self-assembly structures and the application of functional molecules with meta-dicarboxyl groups. Two kinds of molecules with four pairs of meta-dicarboxyl groups, 1,3,6,8-tetrakis(3,5-isophthalic acid)pyrene (H₈TIAPy) and 4',4''',4''''',4'''''''-(ethene-1,1,2,2-tetrayl)tetrakis(([1,1’-biphenyl]-3,5-dicarboxylic acid)) (H₈ETTB) molecules were chosen to observe the self-assembly behavior at the heptanoic acid/highly oriented pyrolytic graphite (HA/HOPG) interface. H₈TIAPy molecules self-assembled into well-ordered quadrilateral structures and could be regulated into kagomé networks with hexagonal pores by coronene (COR) molecules. H₈ETTB molecules self-assembled into lamellar structures and transformed into acid-COR-acid-COR co-assembled structures at low concentration of COR solution and acid-COR dimer-acid-COR dimer co-assembled structures at high concentration of COR solution. The reason that H₈ETTB molecules could not be regulated into hexagonal porous architecture was attributed to the steric hindrance by the similar length and width of H₈ETTB molecules. The H₈ETTB templates had stronger adsorption for COR than that of hexaphenylbenzene (HPB), regardless of the order of molecular introduction.

Fullerene derivatives as a kind of star carbon materials have received intense investigation because of their three-dimensional shape, anisotropic electron mobility, and high electron affinity. Indeed, the cutting-edge developments of fullerene nanomaterials have had a tremendous impact on a wide range of applications, such as organic solar cells, field effect transistors, and photodetectors. To explore their full potential applications, research into fullerene-based multilevel nanostructures relying on hierarchical interactions from bottom to top is rapidly expanding. It is of great theoretical and practical significance to prepare multilevel fullerene nanostructures with structural and properties controlled by optimizing the influencing factors. This review would offer several aspects including the chemical structures of organic molecules and the nanostructures of the organic molecules and fullerene-organic complexes. Whether monolayers or multilayers, fullerene molecules tend to fall into a space of suitable size, in which the located positions are affected by the intermolecular interactions. For the covered surfaces, fullerenes are more likely to approach the electron-withdrawing units through the donor–acceptor and charge transfer interaction. Through the implementation of this review, an exhaustive analysis on the chemical modification, including the molecular backbone and substituents, preformed network synergies, and adsorption sites is presented. In addition, the relationship between the molecules and structures that illustrates the importance of the molecular design for the controlled fullerenes hybrid nanostructures can be further understood based on the results of the joined experimental and computational investigations.

Here, the structural transformations of H₄ETTC induced by coronene (COR) and selective adsorption behaviors of COR in different templates were investigated by scanning tunnelling microscope (STM). It was discovered that the assembled architecture of H₄ETTC at the HOPG/ heptanoic acid interface depended on the concentration of COR, and the clusters of COR were obtained in the kagomé nanoporous network of H₄ETTC molecules at a high concentration of COR solution. In addition, COR clusters can also be formed in the hexagonal porous structure of hexaphenylbenzene (HPB) molecules modified by alkyl chains at the HOPG/heptanoic acid interface. When both H₄ETTC and HPB assembly structures, based on hydrogen bonding and van der Waals force respectively, were selected as the host templates, COR showed selectivity for HPB template to form HPB/COR hexagonal host–guest architecture. Density functional theory (DFT) calculations were also performed to disclose the mechanisms involved.

The two-dimensional self-assembly behaviors of tetraphenylethylene (TPE) molecules are significant for further applications, but reports are rare. The self-assembled structures of two C₂-symmetry TPE derivatives (H₄TCPE and H₄ETTC) possessing propeller structures and their stimulus responses to the addition of vinylpyridine derivatives were thoroughly studied with the assistance of scanning tunneling microscopy (STM) technique in combination with density functional theory (DFT) calculations. Although their chemical structures were similar, the H₄TCPE and H₄ETTC molecules self-assembled into closely packed lamellar and quadrilateral structures, respectively, at the 1-heptanoic acid/HOPG interface. After the addition of pyridine derivatives (DPE, PEBP-C4, and PEBP-C8), H₄TCPE and H₄ETTC showed different responsiveness resulting in different co-assembly structures. The results indicated that the structures of pyridine derivatives—including backbones and substituents—affected the intermolecular interactions of both H₄TCPE/pyridine and H₄ETTC/pyridine systems. The modification of the self-assembly behaviors of propeller-shaped H₄TCPE and H₄ETTC would contribute to the construction of more complex multilevel nanostructures.