40 research outputs found
Probing Single Vacancies in Black Phosphorus at the Atomic Level
Utilizing a combination of low-temperature scanning tunneling
microscopy/spectroscopy (STM/STS) and electronic structure calculations, we
characterize the structural and electronic properties of single atomic
vacancies within several monolayers of the surface of black phosphorus. We
illustrate, with experimental analysis and tight-binding calculations, that we
can depth profile these vacancies and assign them to specific sublattices
within the unit cell. Measurements reveal that the single vacancies exhibit
strongly anisotropic and highly delocalized charge density, laterally extended
up to 20 atomic unit cells. The vacancies are then studied with STS, which
reveals in-gap resonance states near the valence band edge and a strong
p-doping of the bulk black phosphorus crystal. Finally, quasiparticle
interference generated near these vacancies enables the direct visualization of
the anisotropic band structure of black phosphorus.Comment: Nano Letters (2017
An orbitally derived single-atom magnetic memory
A single magnetic atom on a surface epitomizes the scaling limit for magnetic
information storage. Indeed, recent work has shown that individual atomic spins
can exhibit magnetic remanence and be read out with spin-based methods,
demonstrating the fundamental requirements for magnetic memory. However, atomic
spin memory has been only realized on thin insulating surfaces to date,
removing potential tunability via electronic gating or distance-dependent
exchange-driven magnetic coupling. Here, we show a novel mechanism for
single-atom magnetic information storage based on bistability in the orbital
population, or so-called valency, of an individual Co atom on semiconducting
black phosphorus (BP). Distance-dependent screening from the BP surface
stabilizes the two distinct valencies and enables us to electronically
manipulate the relative orbital population, total magnetic moment and spatial
charge density of an individual magnetic atom without a spin-dependent readout
mechanism. Furthermore, we show that the strongly anisotropic wavefunction can
be used to locally tailor the switching dynamics between the two valencies.
This orbital memory derives stability from the energetic barrier to atomic
relaxation and demonstrates the potential for high-temperature single-atom
information storage
Activating the fluorescence of a Ni(II) complex by energy transfer
Luminescence of open-shell 3d metal complexes is often quenched due to
ultrafast intersystem crossing (ISC) and cooling into a dark metal-centered
excited state. We demonstrate successful activation of fluorescence from
individual nickel phthalocyanine (NiPc) molecules in the junction of a scanning
tunneling microscope (STM) by resonant energy transfer from other metal
phthalocyanines at low temperature. By combining STM, scanning tunneling
spectroscopy, STM- induced luminescence, and photoluminescence experiments as
well as time-dependent density functional theory, we provide evidence that
there is an activation barrier for the ISC, which in most experimental
conditions is overcome. We show that this is also the case in an
electroluminescent tunnel junction where individual NiPc molecules adsorbed on
an ultrathin NaCl decoupling film on a Ag(111) substrate are probed. However,
when placing an MPc (M = Zn, Pd, Pt) molecule close to NiPc by means of STM
atomic manipulation, resonant energy transfer can excite NiPc without
overcoming the ISC activation barrier, leading to Q-band fluorescence. This
work demonstrates that the thermally activated population of dark
metal-centered states can be avoided by a designed local environment at low
temperatures paired with a directed molecular excitation into vibrationally
cold electronic states. Thus, we can envisage the use of luminophores based on
more abundant transition metal complexes that do not rely on Pt or Ir.Comment: Accepted manuscrip
Direct oriented growth of armchair graphene nanoribbons on germanium
Graphene can be transformed from a semimetal into a semiconductor if it is confined into nanoribbons narrower than 10nm with controlled crystallographic orientation and well-defined armchair edges. However, the scalable synthesis of nanoribbons with this precision directly on insulating or semiconducting substrates has not been possible. Here we demonstrate the synthesis of graphene nanoribbons on Ge(001) via chemical vapour deposition. The nanoribbons are self-aligning 3 degrees from the Ge < 110 > directions, are self-defining with predominantly smooth armchair edges, and have tunable width to <10 nm and aspect ratio to >70. In order to realize highly anisotropic ribbons, it is critical to operate in a regime in which the growth rate in the width direction is especially slow, <5 nm h(-1). This directional and anisotropic growth enables nanoribbon fabrication directly on conventional semiconductor wafer platforms and, therefore, promises to allow the integration of nanoribbons into future hybrid integrated circuits
Multifunctional porous silicon nanopillar arrays: antireflection, superhydrophobicity, photoluminescence, and surface-enhanced Raman scattering Multifunctional porous silicon nanopillar arrays: antireflection, superhydrophobicity, photoluminescence, and s
Abstract We have fabricated porous silicon nanopillar arrays over large areas with a rapid, simple, and low-cost technique. The porous silicon nanopillars show unique longitudinal features along their entire length and have porosity with dimensions on the single-nanometer scale. Both Raman spectroscopy and photoluminescence data were used to determine the nanocrystallite size to be <3 nm. The porous silicon nanopillar arrays also maintained excellent ensemble properties, reducing reflection nearly fivefold from planar silicon in the visible range without any optimization, and approaching superhydrophobic behavior with increasing aspect ratio, demonstrating contact angles up to 138 • . Finally, the porous silicon nanopillar arrays were made into sensitive surface-enhanced Raman scattering (SERS) substrates by depositing metal onto the pillars. The SERS performance of the substrates was demonstrated using a chemical dye Rhodamine 6G. With their multitude of properties (i.e., antireflection, superhydrophobicity, photoluminescence, and sensitive SERS), the porous silicon nanopillar arrays described here can be valuable in applications such as solar harvesting, electrochemical cells, self-cleaning devices, and dynamic biological monitoring
Moire-induced electronic structure modifications in monolayer V2S3 on Au(111)
Contains fulltext :
232260.pdf (Publisher’s version ) (Open Access