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GeSe is an emerging promising light-harvesting material for photovoltaics due to its excellent optoelectronic properties, nontoxic and earth-abundant constituents, and high stability. In particular, perovskite-like antibonding states at the valence band maximum arising from Ge-4s and Se-4p coupling enable the bulk-defect-tolerant properties in GeSe. However, a fundamental understanding of surface-defect states in GeSe, another important factor for high-performance photovoltaics, is still lacking. Here, we investigate the surface-defect properties of GeSe through first-principle calculations. We find that different from common semiconductors possessing numerous surface dangling bonds, some GeSe surfaces are prone to reconstruction, thus eliminating the dangling bonds. The rearranged armchair edges exhibit unexpected benign defect properties, similar to those of bulk GeSe, arising from the formation of bulk-like [GeSe3] tetrahedrons. We further show that the stable exposed (111) surfaces are hard to reconstruct due to the stiff structure but are effectively passivated by the addition of H.

Organic-inorganic halide perovskite materials are emerging as a new class of photoelectric materials for its low cost, easy preparation, and, especially, outstanding optoelectronic properties. Although tremendous efforts have been made on the regulation and optimization of perovskite materials and their microscopic electrical properties for high-efficiency solar cells, few reports focus on the evolution of electrical properties with temperature changes, especially at the microscopic scale, which will directly affect the device performances at varying temperatures. Here, we map the contact potential difference and photocurrent distribution of MAPbI3 at different temperatures in situ by Kelvin probe force microscopy and conductive atomic force microscopy, emphasizing the different influences of variable temperature and phase transition on the photoelectric properties of grains and grain boundaries (GBs). It is discovered that both the Fermi level and photocurrent decrease as the sample is heated from 30 to 80 °C gradually because of the variation of effective carrier concentration and the degradation of carrier mobility implicated by lattice vibration scattering. The difference between the Fermi level at GBs and that on the grains ascends first and then descends, peaking at 50 °C, near which MAPbI3 transforms from a tetragonal phase to a cubic phase. This peak is speculated as a comprehensive consequence of the increasing difference of the Fermi level of semiconductors with different doping concentrations and the converging properties of grains and GBs with the temperature rising because the lower ion activation energy of the cubic phase at higher temperatures facilitates greatly the ions' movement between grains and GB. The variation trend of the difference of the photocurrent is the same. These findings advance the knowledge on the temperature-induced variations of microscopic photoelectrical properties of organic-inorganic hybrid perovskite materials, which may guide the development of strategies for improving their thermal stability.

The design and construction of stable porous networks featuring tunable cavities for selective guest inclusion remains a great challenge in construction of functional miniature devices. Herein we report on construction and guest inclusion of stable 2D porphyrin-based molecular square grids connected by imine bonds showing crystalline pattern with periodic square cavities. Diperylene diimides molecules can be decorated into the square pores of the porphyrin-based molecular template on HOPG surfaces. The periodicity control over the covalent molecular grid and thus that of guest molecules is demonstrated by changing the building block. The preparation of robust host–guest systems may facilitate the fabrication of molecular miniature devices with designable properties.

Hybrid bilayers consisting of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and meso-tetra(4-pyridyl)porphine (TPyP) have been successfully constructed on Au(111) and investigated by electrochemical scanning tunneling microscopy (ECSTM). Under the guidance of the electrostatic interaction between negatively charged sulfonate groups and positively charged pyridyl groups, the underlying HPTS arrays act as templates for the deposition of cationic TPyPs, forming two types of TPyP/HPTS complex bilayers. The present work provides a feasible way to fabricate hybrid multilayers on the electrode surface via electrostatic interaction, which has great significance for the design of molecular nanodevices.

Surface covalent organic frameworks (SCOFs), featured by atomic thick sheet with covalently bonded organic building units, are promised to possess unique properties associated with reduced dimensionality, well-defined in-plane structure, and tunable functionality. Although a great deal of effort has been made to obtain SCOFs with different linkages and building blocks via both "top-down" exfoliation and "bottom-up" surface synthesis approaches, the obtained SCOFs generally suffer a low crystallinity, which impedes the understanding of intrinsic properties of the materials. Herein, we demonstrate a self-limiting solid-vapor interface reaction strategy to fabricate highly ordered SCOFs. The coupling reaction is tailored to take place at the solid-vapor interface by introducing one precursor via vaporization to the surface preloaded with the other precursor. Following this strategy, highly ordered honeycomb SCOFs with imine linkage are obtained. The controlled formation of SCOFs in our study shows the possibility of a rational design and synthesis of SCOFs with desired functionality.

The self-assemblies of three barbituric acid compounds on highly oriented pyrolytical graphite surface were investigated using scanning tunneling microscopy. On graphite surface, 5-(4-N-hexadecylaminobenzylidene))-2,4,6-(1H,3H)-pyrimidinetrione (BA I) pairs together with head–head styles and forms chiral structure with grouping of three molecular pairs as a unit motif. 5-(4-(N,N-Dihexadecylaminobenzylidene))-2,4,6-(1H,3H)-pyrimidinetrione (BA II) also appears as head–head molecular pairs but with slight displacement between each other. The small shift destroys the symmetry of molecular pairs and introduces chirality to the molecular pairs and in turn the formation of chiral domains. In this dense packing arrangement, only one hexadecyl chain of BA II lies on graphite surface, whereas the other one hangs in air. 5-(4-(N-Methyl-N-hexadecylamin obenzylidene))-(1,3-diethyl)-2-thioxodihydro-4,6-pyrimidinedione (BA III) organized into similar structure to BA II. Single molecular lines of BA III could be found i...

The production of clean and renewable hydrogen through water splitting using photocatalysts has received much attention due to the increasing global energy crises. In this study, a high efficiency of the photocatalytic H(2) production was achieved using graphene nanosheets decorated with CdS clusters as visible-light-driven photocatalysts. The materials were prepared by a solvothermal method in which graphene oxide (GO) served as the support and cadmium acetate (Cd(Ac)(2)) as the CdS precursor. These nanosized composites reach a high H(2)-production rate of 1.12 mmol h(-1) (about 4.87 times higher than that of pure CdS nanoparticles) at graphene content of 1.0 wt % and Pt 0.5 wt % under visible-light irradiation and an apparent quantum efficiency (QE) of 22.5% at wavelength of 420 nm. This high photocatalytic H(2)-production activity is attributed predominantly to the presence of graphene, which serves as an electron collector and transporter to efficiently lengthen the lifetime of the photogenerated charge carriers from CdS nanoparticles. This work highlights the potential application of graphene-based materials in the field of energy conversion.

Hydrogen bonds with high selectivity and directionality are significant in harnessing molecules to form 2D supramolecular nanostructures. The competition and reorganization of hydrogen bond partners determine the ultimate molecular assembly and pattern in a 2D supramolecular system. In this study, multicomponent assemblies of a monodendron (5-benzyloxy-isophthalic acid derivative, BIC) and pyridylethynyl derivatives [1,4-bis(4-pyridylethynyl)-2,3-bis-dodecyloxy-benzene (PBPC12) and 1,4-bis(4-pyridylethynyl)-2,3-bis-octadecyloxy-benzene (PBPC18)] have been studied by scanning tunneling microscopy (STM) on a graphite surface. BIC molecules are able to associate with PBPC12 and PBPC18 molecules to induce the rearrangement of hydrogen bond partners and form coassembly structures. Interestingly, BIC acts as a template molecule in the coassembly process, and these multicomponent structures exhibit similar structural features to the assembly structures of BIC itself. The structural details of the coassembled structures are revealed by high-resolution STM images, and their relationship with the original BIC assemblies is discussed. These results provide important insights into the design and fabrication of hydrogen-bond-directed multicomponent molecular nanostructures on solid surfaces.

The formation of a desired nanostructure with concomitant patterns and functions is of utmost importance in the field of surface molecular engineering and nanotechnology. We here present a flexible host-guest assembly, which steers the formation of linear molecular nanostructures on surfaces by a hydrogen-bond-mediated assembly process. A linear monodendron molecular template with periodic hydrogen-bond binding sites is shown to accommodate a variety of molecules with pyridylethynyl terminals. The unit cell parameters in the transverse direction of the linear pattern can be tuned from 3.4 to 7.3 nm in response to the packing of the guest molecules with different sizes, shapes, and aggregation number. The introduction of hydrogen-bonding partners into the host template and into guest molecules is responsible for the steering of the linear pattern of guest molecules. The modular approach could greatly facilitate the ordering of guest molecules with desired functional moieties.

The adsorption of four fullerene derivatives, including Re(C60Me5)(CO)3, Ru(C60Ph5)Cp, C60(C6H4C6H4−COOH)5Me, and C60(C6H4−CC−SiMe2C12H25)5Me, on a Au(111) surface has been investigated by scanning tunneling microscopy (STM) and cyclic voltammetry. High-resolution STM images reveal that Re(C60Me5)(CO)3 forms a well-ordered (2√3 × 2√3)R30° structure. Different from C60 on Au(111), the so-called “in-phase” structure is not found with the attachment of methyl and Re(CO)3 groups. With the increase of substituent size, disordered adlayers have been observed for Ru(C60Ph5)Cp and C60(C6H4C6H4−COOH)5Me. However, the individual molecules could be distinguished in STM images, suggesting that the two molecules interact strongly with the Au(111) surface. When the substituent size is further increased, a multilayered structure is formed for C60(C6H4−CC−SiMe2C12H25)5Me. This is because of molecular aggregation in the bulk solution, which occurs at very low concentration. These results indicate that the structures of fu...

NMR and STM studies revealed that the hydrazide-quinolinone-based building block 5 exhibited a monomer-dimer-polymer equilibrium, while its acyclic analogue 6, due to conformational flexibility, exhibited a more complicated mode of aggregation and formed a gel in dichloromethane/hexane.

The adlayers formed by a series of aza- and/or oxo-bridged calix[2]arene[2]triazines on Au(111) surfaces were investigated by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. 1,3-Alternate configurations of these molecules are preserved on gold surfaces as in their three-dimensional crystals. STM images show that the cavity sizes of these molecules are finely tuned by substituting the bridging nitrogen atom with oxygen atoms, which change the strengths and densities of the intermolecular hydrogen bonds. Hydrogen bond interaction influences the molecular orientation and conformation in the adlayers, and it plays a key role in the formation of these two-dimensional supramolecular architectures. Coadsorption of calix[2]arene[2]triazine with 1,3,5-tris(5-carboxyamyloxy)benzene (TCAB) intervenes with the intermolecular hydrogen bond formations among the calix[2]arene[2]triazine molecules and consequently causes a conformational transition of the calixarene molecules from rhombic to square. These results demonstrate the role of hydrogen bonds in molecular assembly formations.

Amphiphilic organic ligands, 5-octadecyloxy-2-(2-pyridylazo)phenol (PARC18) and 1,10-bis[3‘-hydroxy-4‘-(2‘ ‘-pyridylazo)phenoloxy]decane (PAR)2C10, are coordinated with Cu(II) ions, resulting in two complexes. Scanning tunneling microscopy (STM) images provide direct structural evidence for the coordination from organic ligands to resulted complexes. The appearance and conformation differences in ligands and corresponding complexes can be clearly seen in STM images recorded from their self-organizations on highly oriented pyrolytic graphite (HOPG). The adlayer structures of PARC18−Cu and (PAR)2C10−Cu complexes are significantly different from those of their corresponding ligands. A phase separation is found in the adlayer formed with the PARC18 ligand and its complex. The results demonstrate that STM is a powerful tool in coordination chemistry in analyzing ligand and coordinated complex. The coordination from ligands to complexes with metal ions would be a facile approach to surface modification and func...

Two-dimensional assemblies of tricarboxylic acid derivatives, 1,3,5-tris(carboxymethoxy)benzene (TCMB, C6H3(OCH2COOH)3) and 1,3,5-tris(3-carboxypropoxy)benzene (TCPB, C6H3(OCH2CH2CH2COOH)3), have b...

This communication provides a facile method for distributing and dispersing molecules within a molecular template. Using the self-assembled template of oligo(phenylene-ethynylene) (OPE), organic molecules such as coronene (COR) and biomolecules such as tripeptide are controllably distributed and dispersed within this molecular template on highly oriented pyrolytic graphite (HOPG) surfaces. COR molecules were controllably distributed into various regular arrays by simply adjusting the molecular molar ratio, while tripeptide molecules were uniformly positioned at the vacancies of the OPE template.