[en] The deposition of Cu at room temperature on a Cr₂O₃(0001) substrate is studied by x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and low-energy-electron diffraction. The results indicate that at RT Cu is highly dispersed on the substrate at initial deposition. X-ray induced Auger spectra, Auger parameter and ultraviolet photoelectron spectroscopy show that at the initial coverage the deposited Cu is in the Cu(I) state due to the interaction of Cu with the Cr₂O₃ substrate; Cu becomes metallic at Cu coverages of > 4 monolayer equivalent. The formation of Cu two-dimensional or quasi-2D patches is followed by the formation of Cu three-dimensional clusters. Cu grows epitaxially on the Cr₂O₃(0001) films as Cu(111)R 30 deg. as observed by low-energy-electron diffraction

[en] The interactions of V with Cr₂O₃(0001) films and Cr with V₂O₃(0001) films at room temperature are studied using x-ray photoelectron spectroscopy and low-energy-electron diffraction. The results show that the deposited V is oxidized and the Cr₂O₃(0001) surface is reduced at the initial coverage due to the interaction of V with the Cr₂O₃ substrate; V becomes metallic at V coverage greater than 5 monolayer equivalent. Full oxidization of the deposited vanadium cannot be achieved by O₂ exposure at room temperature for 20 min. However, V₂O₃(0001) films have been observed after heating the sample to 600-700 K in oxygen ambient at 1x10^-7 mbar. Similar results have been obtained for the Cr/V₂O₃(0001)/Re(0001) system. (author)

[en] We have investigated the nucleation, growth and structure of Al on an inert graphite surface at room temperature (RT) using in situ scanning tunneling microscopy. It was observed that Al initially nucleates at step edges and defect sites of graphite surfaces, due to the inertness of the substrate and weak interfacial interaction. From a diffusion and capture model, the mean adatom diffusion length before desorption was derived to be 170 ± 80 nm, correspondingly giving a lower bound of the adatom-substrate binding energy of 0.39 ± 0.03 eV. With successive Al deposition of ∼0.5 nm, the growth and coarsening of small clusters results in flat-top crystalline islands with (111)-oriented facets located at step edges as well as on defect-free terraces. The crystalline islands have essential translational and rotational mobility, which leads to the formation of craters on islands after Al deposition of ∼6 nm. A simple island-coalescence model based on fast edge diffusion and suppressed detachment from step edges was proposed for rationalizing the crater formation. It was also observed that isolated islands of Al can be stabilized by two-dimensional structures of Sb surrounding Al islands after Sb deposition at RT

[en] Iron phthalocyanine (FePc) is a p-type organic semiconductor and it has potential applications in optoelectronics, organic magnets and catalysts. The performance of the FePc-based devices essentially depends both on the properties of the FePc molecule and on the morphology of the organic thin films formed by FePc molecules. Here, using atomic force microscopy, we studied the structural properties of FePc thin films prepared with different solvents by drop-casting method. We observed the formation of large three-dimensional aggregates on Si substrates for the high-solubility solvents, while separated two-dimensional islands and multilayer islands are formed for low-solubility solvents. An identical interlayer distance of 4.3 nm is measured in such multilayer islands, suggesting a repeated unit including four molecular layers that are stacked along the direction normal to the molecular plane of FePc inclined to the ac plane with an angle of 47.7°. Meanwhile, nanorods and short linear chains along three directions are formed on graphite and mica surfaces. Our work shows that both the solvents and the substrates can exert great impact on the thin film structure that is very valuable for the preparation of high-quality FePc thin films and devices.

[en] Using in situ scanning tunneling microscopy and low-energy electron diffraction, we performed investigations on the growth of zirconium silicide on vicinal and flat Si(111)-7 x 7 surfaces. In the case of a solid-phase reaction, submonolayer zirconium deposition onto vicinal Si followed by successive annealing results in the formation of zirconium silicide nanostructures, which are distributed randomly on the surface. These nanostructures evolved into rod-shaped islands with axes running along the substrate <1-bar10> directions at the late stage of the coarsening process. When 2-3 monolayers of Zr are deposited on Si at 520 deg. C, an extended network with rod-like silicide domains was developed, which is controlled by the elastic strain-relief mechanism. The atomic structures of these silicide features were identified and they are considered to adopt C49 ZrSi₂. The reaction and growth on a flat surface with less Zr coverage at higher temperatures led to the formation of longer and narrower nanowires. The relations between the variety of nanostructures and the different growth conditions are addressed

[en] The growth, atomic structure, and electronic property of trilayer graphene (TLG) on Ru(0001) were studied by low temperature scanning tunneling microscopy and spectroscopy in combined with tight-binding approximation (TBA) calculations. TLG on Ru(0001) shows a flat surface with a hexagonal lattice due to the screening effect of the bottom two layers and the AB-stacking in the top two layers. The coexistence of AA- and AB-stacking in the bottom two layers leads to three different stacking orders of TLG, namely, ABA-, ABC-, and ABB-stacking. STS measurements combined with TBA calculations reveal that the density of states of TLG with ABC- and ABB-stacking is characterized by one and two sharp peaks near to the Fermi level, respectively, in contrast to the V-shaped feature of TLG with ABA-stacking. Our work demonstrates that TLG on Ru(0001) might be an ideal platform for exploring stacking-dependent electronic properties of graphene

[en] Large-area bilayer graphene (BG) is grown epitaxially on Ru(0001) surface and characterized by low temperature scanning tunneling microscopy. The lattice of the bottom layer of BG is stretched by 1.2%, while strain is absent from the top layer. The lattice mismatch between the two layers leads to the formation of a moiré pattern with a periodicity of ∼21.5 nm and a mixture of AA- and AB-stacking. The √3 × √3 superstructure around atomic defects is attributed to the inter-valley scattering of the delocalized π-electrons, demonstrating that the as-grown BG behaves like intrinsic free-standing graphene

[en] Multiferroic materials endowed with both dielectric and magnetic orders, are ideal candidates for a wide range of applications. In this work, we reported two phase transitions of MnI₂ at 3.45 K and 4 K by systemically measuring the magnetic-field and temperature-dependent magnetization of the MnI₂ thin flakes. Furthermore, we observed similar temperature and field-dependent behaviours for the magnetic susceptibility of MnI₂ and electronic capacitance of the Ag/MnI₂/Ag devices below 3.5 K. Considering the related theory work, we discussed the relationship between the antiferromagnetic and ferroelectric orders in MnI₂. Our work reveals the in-plane magnetic and electric properties of MnI₂ materials, which might be helpful for the further investigation and application of MnI₂ multiferroics in the future. (paper)

[en] The evolution of single-stranded DNA (ssDNA) assembly on octadecylamine (ODA) modified highly oriented pyrolytic graphite (HOPG) surface by heating and ultrasonic treatment has been studied for the first time. We have observed that DNA on the ODA coated HOPG surface underwent dramatic morphological changes as a function of heating and ultrasonic treatment. Ordered DNA firstly changed to random aggregates by heating and then changed to three-dimensional (3D) networks by ultrasonic treatment. This finding points to previously unknown factors that impact graphite–DNA interaction and opens new opportunities to control the deposition of DNA onto graphitic substrates. In this way, we built a cost-effective method to produce large-scale 3D ssDNA networks. All of these studies pave the way to understand the properties of DNA–solid interface, design novel nanomaterials, and improve the sensitivity of DNA biosensors. (paper)

[en] MnI₂ is one of the important multiferroics materials with a layered, nearly two-dimensional (2D) structure due to van der Waals bonds. In this work, we developed physical vapor deposition and mechanical exfoliation methods to prepare 2D MnI₂ flakes on amorphous SiO₂ substrates. The morphologies, composition and structure properties of the 2D MnI₂ flakes were characterized by optical microscopy, atomic force microscopy, scanning electronic microscope and Raman spectroscopy. Furthermore, we systematically studied the degradation of the MnI₂ flakes. With h-BN and PMMA as protective materials, we improved the stability of the MnI₂ flakes and slow down the degradation process under moisture conditions. In this regard, we provided MnI₂ flakes as new 2D materials with effective protection, which may pave the way for the application of low dimensional multiferroics materials in the future. (paper)