Yande Que - Academia.edu (original) (raw)

Papers by Yande Que

Physical Chemistry Chemical Physics

Rear-earth on metal may form two-dimensional (2D) intermetallic compound whose properties can be ... more Rear-earth on metal may form two-dimensional (2D) intermetallic compound whose properties can be further modulated by the underlying substrate periodicity and coupling. Here, we present a combinational and systematic investigation...

Review of Scientific Instruments

The highest frequency of the electric signal that a conventional scanning tunneling microscope (S... more The highest frequency of the electric signal that a conventional scanning tunneling microscope (STM) can process typically lies in the kilohertz regime, imposing a limitation on its temporal resolution to the submillisecond regime. When extracting (feeding) the high frequency, or radio-frequency (RF), signal out of (into) the tunnel junction, the most challenging part is that the tunnel junction has a very high impedance, causing significant reflections. Here, we present a systematic solution on the construction of RF-STM with high sensitivity. To minimize radiation loss, using coaxial cables as conducting wires, we designed an active impedance matching network (IMN) based on a field-effect transistor, which can provide impedance matching over a wide frequency range and can bridge the enormous impedance difference associated with the tunnel junction. To shorten the signal cable before amplification, the STM probe itself was directly mounted on the IMN as the input pin, which is an unprecedented attempt to minimize the undesired parasitic capacitances. Furthermore, we employed a two-stage cryogenic SiGe low noise amplifier and a high-end spectrum analyzer to amplify and subsequently analyze the RF signal of interest. After this systematic engineering, the bandwidth of our STM has been improved to the gigahertz regime, implying a six orders of magnitude improvement. The sensitivity level of our newly built RF-STM is measured to be better than 1.0 pA/ √ Hz at 200 MHz at 78 K. The RF-STM also finds its application in nanoscale thermometry. Our efforts in its instrumentation should contribute to the development of high frequency scanning tunneling microscopy.

Science

The construction of atomically precise carbon nanostructures holds promise for developing materia... more The construction of atomically precise carbon nanostructures holds promise for developing materials for scientific study and nanotechnology applications. Here, we show that graphene origami is an efficient way to convert graphene into atomically precise, complex nanostructures. By scanning tunneling microscope manipulation at low temperature, we repeatedly fold and unfold graphene nanoislands (GNIs) along an arbitrarily chosen direction. A bilayer graphene stack featuring a tunable twist angle and a tubular edge connection between the layers is formed. Folding single-crystal GNIs creates tubular edges with specified chirality and one-dimensional electronic features similar to those of carbon nanotubes, whereas folding bicrystal GNIs creates well-defined intramolecular junctions. Both origami structural models and electronic band structures are computed to complement analysis of the experimental results. The present atomically precise graphene origami provides a platform for construc...

The Journal of Physical Chemistry C

Energy Science & Engineering

Cu(In,Ga)Se 2 (CIGS) thin film solar cells have achieved great success in laboratory in the past ... more Cu(In,Ga)Se 2 (CIGS) thin film solar cells have achieved great success in laboratory in the past few decades and are now entering the large-scale commercial production stage. 1 In the laboratory, researchers at Stuttgart's Center for Solar Energy and Hydrogen Research (ZSW) and Solar Frontier have obtained a conversion efficiency of 22.6% and 22.9%, respectively. 2,3 CIGS is considered as the most promising thin film solar cell technology by many researchers due to its numerous advantages such as high conversion efficiency, low cost, and low toxicity. 4-6 However, there still remain many fundamental issues to be addressed even after many decades of study on CIGS solar cells. One question is that how the alkali atoms in the soda lime glass (SLG) get incorporated into the CIGS absorption layer. Alkali element plays a vital role in the development of CIGS solar cells as well as other solar cells like kesterite-based Cu 2 ZnSn(S,Se) 4 solar cells. 7-10 The importance of Na in the electrical performance of CIGS solar cells was first reported in 1993 by Hedstrom et al 11 Since then, many researchers have investigated the effects of alkali elements in different

The Journal of Physical Chemistry B

The growth of polycyclic aromatic hydrocarbon (PAH) molecular coronene film on various substrates... more The growth of polycyclic aromatic hydrocarbon (PAH) molecular coronene film on various substrates and the subsequent doping of potassium under ultrahigh vacuum (UHV) conditions have been systematically investigated by low-temperature scanning tunneling microscopy and spectroscopy (STM/STS). The crystalline structures and molecular orientations of coronene thin films are both thickness-dependent and substrate-sensitive due to the competition between molecule-substrate interaction and intermolecular interaction. In mono- or bilayer films, coronene molecules are flat-lying on the surface with hexagonal lattice, whereas in multilayer films, the topmost molecules are in a standing-up but tilted configuration with rectangular lattice. In particular, a 2 × 1 superstructure with respect to that of bulk coronene is formed on thick KCl film. Furthermore, we have studied the potassium doped coronene monolayer and multilayer on Ag(100) and KCl/Ag(100) surface. For K-doped coronene monolayer, at certain doping ratio x = 3, the lowest unoccupied molecular orbital (LUMO) of coronene film moves to the Fermi level, and a splitting of the LUMO state is observed. Increased potassium doping would result in a filled LUMO state below the Fermi level. By contrast, no well-ordered structures are obtained in the K-doped coronene multilayers which are vulnerable to rather moderate annealing processes owing to their relatively weak bonding with the supporting substrates, implying a big challenge of growth of PAH thick films in vacuum. The differences in the crystal structures of coronene thin films compared with that in bulk crystals might shed insight on the controversies in the experimental results on the electronic properties of alkali-metal-doped PAHs.

Nano letters, Jan 23, 2017

Applied Physics Letters, 2016

Silica (SiO 2) islands with a dendritic structure were prepared on polycrystalline copper foil, u... more Silica (SiO 2) islands with a dendritic structure were prepared on polycrystalline copper foil, using silane (SiH 4) as a precursor, by annealing at high temperature. Assisted by copper vapor from bare sections of the foil, single-layer hexagonal graphene domains were grown directly on the SiO 2 islands by chemical vapor deposition. Scanning electron microscopy, atomic force microscopy, Raman spectra, and X-ray photoelectron spectroscopy confirm that hexagonal graphene domains, each measuring several microns, were synthesized on the silica islands. Published by AIP Publishing.

Nano letters, Feb 23, 2017

Silicon-based two-dimensional (2D) materials are uniquely suited for integration in Si-based elec... more Silicon-based two-dimensional (2D) materials are uniquely suited for integration in Si-based electronics. Silicene, an analogue of graphene, was recently fabricated on several substrates and was used to make a field-effect transistor. Here, we report that when Ru(0001) is used as a substrate, a range of distinct monolayer silicon structures forms, evolving toward silicene with increasing Si coverage. Low Si coverage produces a herringbone structure, a hitherto undiscovered 2D phase of silicon. With increasing Si coverage, herringbone elbows evolve into silicene-like honeycomb stripes under tension, resulting in a herringbone-honeycomb 2D superlattice. At even higher coverage, the honeycomb stripes widen and merge coherently to form silicene in registry with the substrate. Scanning tunneling microscopy (STM) was used to image the structures. The structural stability and electronic properties of the Si 2D structures, the interaction between the Si 2D structures and the Ru substrate, a...

Applied Physics Letters, 2015

The growth, atomic structure and electronic property of trilayer graphene (TLG) on Ru(0001) were ... more The growth, atomic structure and electronic property of trilayer graphene (TLG) on Ru(0001) were studied by low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) 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 are 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 stackingdependent electronic properties of graphene.