Pt-induced Nanowires Research Articles

Oxidation Mechanism on One-Dimensional Pt-Induced Nanowires on Ge(001)

The oxidation mechanism on one-dimensional Pt-induced nanowires on Ge(001) (NWs/Ge(001)) was investigated on the atomic scale, by scanning tunneling microscopy and density functional theory calcula...

Quantum size stabilization of Ge3Pt nanofilms on Ge(001)

The electronic and structural properties of a Ge-Pt alloy film on Ge(001) were studied with low-energy electron microscopy. Well above 1000 K, a bulklike eutectic film forms, followed by the emergence of an ordered ${\mathrm{Ge}}_{3}\mathrm{Pt}$ alloy upon solidification, which sets in at 1004 K. This eight-layers-thick ${\mathrm{Ge}}_{3}\mathrm{Pt}$ phase is remarkably robust as it is stabilized by quantum size effects. Further cooling results in the evolution of ultrathin Pt-induced nanowires around 650 K. The process is reversible upon temperature variation around the eutectic point. The results are considered representative of an important class of surface alloys.

Unveiling Oxygen Adsorption States on One-Dimensional Pt-Induced Nanowires on Ge(001)

Oxygen adsorption on Pt-induced nanowires on Ge(001) (NWs/Ge(001)) was investigated on the atomic scale. At 77 K, we observed two disparate features based on scanning tunneling microscopy images an...

Investigation of atomic species in Pt-induced nanowires on Ge(001) surface by combined atomic force and scanning tunneling microscopy

We have studied identification of atomic species in Pt-induced nanowires self-assembled on the Ge(001) surface by combining scanning tunneling microscopy (STM) and atomic force microscopy (AFM). A small number of Sn atoms substituted in the top atomic chains were utilized as references to identify the target atomic species. Force spectroscopy data taken above single atoms on the Sn-substituted nanowires showed that the ratio between the maximum attractive forces above the Sn and the pristine chain atoms exhibited a constant value of 0.86. The obtained ratio was identical to that between Sn and Ge atoms, strongly suggestive that the top ridge of the Pt-induced nanowire was composed of Ge dimers. Our findings also demonstrate that AFM chemical identification method can be used to identify the unknown atomic species on surfaces, regardless of the homogeneity in the atomic composition, which has not been addressed so far.

Predicted Unusual Catalytic Activity of One-Dimensional Pt-Induced Atomic Nanowires on Ge(001) Surface

One dimensional (1D) metal-induced nanowires on a semiconductor surface have attracted enormous interest recently because of their unique electronic properties and great potential in device applications arising from the ideal 1D nature of the systems. Via ab initio modeling, we investigate for the first time the catalytic properties of Pt-induced nanowires (Pt-INWs) on a Ge(001) surface that have been successfully fabricated in experiments. We show that these 1D atomic wires can also be used as excellent catalysts for chemical reaction of CO oxidation. A new ground-state configuration of Pt-INWs on Ge (001) that is significantly more stable than previously reported ones is predicted. The origin of the low reaction barrier of the catalyzed CO oxidation is thoroughly discussed. These results pave the way for a new class of high-performance catalysts with 1D characteristics.

TRHEPD rocking curve analyses of Pt/Ge(001) and TiO2(110) surfaces

Recently, we developed new total reflection high-energy positron diffraction (TRHEPD) apparatus [1] on a beam line of the linac-based intense positron beam of the Slow Positron Facility at KEK, Japan. The high intensity allows us to install a brightness-enhancement section, which to observation of clear positron diffraction patterns for crystal surfaces under total reflection condition. In this work, we investigated the atomic configuration of Pt-induced nanowires formed on a Ge(001) surface [2] using the apparatus. By means of the diffraction intensity analysis based on the dynamical diffraction theory, or TRHEPD rocking curve analysis, a previously proposed theoretical model [D. E. P. Vanpoucke et al., Phys. Rev. B 77, 241308(R) (2008)], composed of Ge dimers on the top layer and buried Pt arrays in the second and fourth layers, was confirmed to be the fundamental structure of the nanowire. We also investigated the atomic configuration of a rutile-TiO2(110) surface. It is well known that the structure of this surface transforms its periodicity from (1×1) to (1×2) by elevating the sample temperature above ~1100 K, whereas the detailed structure is yet to be revealed. There is a longstanding controversy between the structure models proposed by scanning tunneling microscopy, low energy electron diffraction, surface X-ray diffraction, first-principles calculation with density functional theory results, etc. To solve the problem, we have measured TRHEPD rocking curves and determined the atomic arrangements of the topmost crystal surface [3].

Fermi gas behavior of a one-dimensional metallic band of Pt-induced nanowires on Ge(001)

We have investigated the electronic band structure of Pt-induced nanowires on Ge(001) [Pt/Ge(001) NWs] by angle-resolved photoelectron spectroscopy at 6 K. Single-domain samples of Pt/Ge(001) NWs were prepared on vicinal Ge(001) substrates. One of the bands disperses only in the nanowire direction, and its Fermi surface consists of strictly straight lines, indicating that it is an ideal one-dimensional metallic state. An energy distribution curve of the one-dimensional band is explained by a Fermi-Dirac-type spectral shape, which is against both a Luttinger liquid and Peierls instability schemes.

Self-Assembled Nanowires with Giant Rashba Split Bands

We investigated Pt-induced nanowires on the Si(110) surface using scanning tunneling microscopy (STM) and angle-resolved photoemission. High resolution STM images show a well-ordered nanowire array of 1.6 nm width and 2.7 nm separation. Angle-resolved photoemission reveals fully occupied one-dimensional (1D) bands with a Rashba-type split dispersion. Local dI/dV spectra further indicate well-confined 1D electron channels on the nanowires, whose density of states characteristics are consistent with the Rashba-type band splitting. The observed energy and momentum splitting of the bands are among the largest ever reported for Rashba systems, suggesting the Pt-Si nanowire as a unique 1D giant Rashba system. This self-assembled nanowire can be exploited for silicon-based spintronics devices as well as the quest for Majorana fermions.

一次元原子鎖Pt/Ge(001)のスピン偏極した擬一次元金属電子状態

一次元原子鎖Pt/Ge(001)のスピン偏極した擬一次元金属電子状態

角度分解光電子分光によるPt/Ge(001)表面の一次元金属的な電子状態の直接観測

角度分解光電子分光によるPt/Ge(001)表面の一次元金属的な電子状態の直接観測

Atomic configuration and phase transition of Pt-induced nanowires on a Ge(001) surface studied using scanning tunneling microscopy, reflection high-energy positron diffraction, and angle-resolved photoemission spectroscopy

The atomic configuration and electronic band structure of Pt-induced nanowires on a Ge(001) surface are investigated using scanning tunneling microscopy, reflection high-energy positron diffraction, and angle-resolved photoemission spectroscopy. A previously proposed theoretical model, composed of Ge dimers on the top layer and buried Pt arrays in the second and fourth layers [Vanpoucke et al., Phys. Rev. B 77, 241308(R) (2008)], is found to be the fundamental structure of the observed nanowires. At low temperatures ($T<80$ K), each Ge dimer is alternately tilted in the surface normal direction (asymmetric), causing a p($4\ifmmode\times\else\texttimes\fi{}4$) periodicity. At high temperatures ($T>110$ K), each Ge dimer is flat with respect to the horizontal axis (symmetric), giving rise to p($4\ifmmode\times\else\texttimes\fi{}2$) periodicity. Upon the above phase transition, the electronic band dispersion related to the Ge dimers in the deeper energy region shifts to the Fermi level.

CO adsorption on Pt-induced Ge nanowires

Using density-functional theory, we investigate the possible adsorption sites of CO molecules on the recently discovered Pt-induced Ge nanowires (NWs) on Ge(001). Calculated scanning tunneling microscope (STM) images are compared to experimental STM images to identify the experimentally observed adsorption sites. The CO molecules are found to adsorb preferably onto the Pt atoms between the Ge nanowire dimer segments. This adsorption site places the CO molecule in between two nanowire dimers, pushing them outward along the NW direction, blocking the nearest equivalent adsorption sites. This explains the observed long-range repulsive interaction between CO molecules on these Pt-induced nanowires.

Pt-induced nanowires on Ge(001): A density functional theory study

We study formation of the nanowires formed after deposition of Pt on a Ge(001) surface. The nanowires form spontaneously after high temperature annealing. They are thermodynamically stable, only one atom wide and up to a few hundred atoms long. Ab initio density functional theory calculations are performed to identify possible structures of the Pt-Ge (001) surface with nanowires on top. A large number of structures is studied. With nanowires that are formed out of Pt or Ge dimers or mixed Pt-Ge dimers. By comparing simulated scanning tunneling microscopy images with experimental ones we model the formation of the nanowires and identify the geometries of the different phases in the formation process. We find that the formation of nanowires on a Pt-Ge(001) surface is a complex process based on increasing the Pt density in the top layers of the Ge(001) surface. Most remarkably we find the nanowires to consist of germanium dimers placed in troughs lined by mixed Pt-Ge dimer rows.