Pedestal Site Research Articles

Left ventricular assist device as destination therapy in cardiac end-stage dystrophinopathies: Midterm results

ObjectiveWe report our experience with the use of a left ventricular assist device (LVAD) as destination therapy (DT) for the management of patients with cardiac end-stage dystrophinopathies. MethodsFrom February 2011 to February 2016, 7 patients with dystrophinopathies and dilated cardiomyopathy (DCM) were treated with LVADs at our institution. Median age at surgery was 16.5 years (range, 14.2-23.4 years). All patients were preoperatively evaluated by a multidisciplinary team approach. ResultsAll patients survived to hospital discharge. The early postoperative course was characterized by abdominal bleeding (1 patient) and retropharyngeal bleeding (1 patient). Because of abdominal or retropharyngeal bleeding, both required postoperative heparin infusion discontinuation for 35 and 33 days, respectively. Among the late complications, 1 child developed osteolysis and infection at the pedestal site of the device, which required surgical displacement; 1 patient required gastrostomy as a result of poor feeding, and another had a cerebral stroke, which was treated with percutaneous thrombus aspiration. The other 2 patients did not show early or late complications. At a median follow-up time of 21.7 months (range, 3-45 months) there have been 3 deaths: 1 patient died of a lung infection after 45 months, 1 died of tracheal bleeding after 29 months, and 1 died of cerebral hemorrhage after 14 months. ConclusionsOur experience indicates that the use of an LVAD as DT in patients with dystrophinopathies with end-stage DCM is feasible, suggesting that it may be suitable as a palliative therapy for the treatment of these patients with no other therapeutic options.

Cobalt adsorption on the bare Si(100) 2 × 1 surface at low temperature (12 K)

The adsorption of Co atoms on the bare Si(100)-2×1 surface at low temperature (12K) is performed in the low coverage regime (< 0.1 monolayer). The ensuing surface is studied by means of a low temperature (9K) scanning tunneling microscope (STM). Several adsorption sites are described via STM topographies and differential conductance spectroscopy. Our study reveals that at low temperature (12K), a significant fraction of the Co atoms diffuse into the surface and form the first stage reaction sites that are relevant for the silicidation mechanism of the Si(100). Furthermore, the low temperature conditions allow to describe surface Co adatoms conformations that are stabilized on the Si(100)-c(4×2) surface. Interestingly, we have observed the irreversible transformation of the symmetric pedestal site (Ps) to the under dimer site (UD) via specific STM scanning conditions. Finally, the presence of dimer vacancy lines is discussed and reveals that the activated etching process of the silicon dimer with metals can be induced at very low temperature.

Failure of potassium dimer formation on the β-SiC(100)-c (4 × 2) surface

Using ab initio molecular dynamics, we study the formation of dimers on the β-SiC(100)-c(4 × 2) surface. According to previously published experimental results of Derycke et al. [Appl. Phys. Lett. 88(2), 022105 (2006)] (using scanning tunneling spectroscopy, core-level photoemission spectroscopy, and low-energy electron diffraction) the (100)-c(4 × 2) surface is highly prone to form potassium dimers. In their work, potassium atoms fill adjacent well-defined pedestal sites when there are lower coverages of potassium deposited onto the surface (∼0.16 monolayers). Contrary to the work by Derycke et al., we find that potassium does not prefer to form dimers on the (100)-c(4 × 2) surface, but rather potassium tends to reconstruct (after annealing simulations) by choosing distant pedestal sites in order to minimize the overlap of the ionic radii of the potassium atoms.

Magic Monatomic Linear Chains for Mn Nanowire Self-Assembly on Si(001)

Using first-principles calculations, we unveil an atomistic nucleation process of monoatomic Mn nanowire self-assembly on Si(001). We find that Mn adatoms form magic 3n+1 atom dense trimerlike linear chains (DTLCs) driven by pedestal site adsorption. Moreover, the length of DTLCs is limited by a competing process to form three-dimensional D3h-Mn5 clusters in early stages. These results establish a new structural model distinct from the dimerlike linear chains for III and IV group elements on Si(001) and provide a natural explanation for recent experimental observations.

First-principles study of indium adsorption on GaP(001)(2×1) surface

We applied first-principles calculations to investigate the structural and electronic properties of indium adsorption on the GaP(0 0 1) surface at the coverages ( Θ ) of 0.5 and 1 ML. It was found that at Θ = 0.5 ML In adatoms preferred to adsorb at the pedestal (HH) site, followed by the bridge site. This is similar to the In/GaAs (0 0 1) adsorption system. For the coverage of 1 ML, the most stable configuration is a combination of the HH and valley bridge (T3) or cave (T4) sites, with the energy difference of only 30 meV between HH-T3 and HH-T4 sites adsorption. The density of states (DOS) analysis showed that the deposition of pure indium on GaP substrate can be employed as surface passivation of underlying buffered layers. The obvious hybridization of In 5p and P 3p states was observed in the conduction bands. The work function change due to In adsorption was calculated to be −1.01 and ∼−1.66 eV at the coverages of 0.5 and 1 ML, respectively, indicating that some charges are transferred from the adsorbate to the substrate.

First Principles Study on the Adsorption of Alkali Metal on C(100)( 2×1)

First-principles calculations based on density functional theory, using PW91 functional have been performed to study the adsorption of Alkali metal (AM) on C(100)(2×1) surface. The stable geometries, adsorption energies for all adsorption configurations have been calculated on half a monolayer and one monolayer. The preferred binding sites have been determined to be valley-bridge sites at the coverage of 0.5ML. At higher coverage of 1ML, two AM adsorbates were found to reside in pedestal site and valley-bridge site, respectively. Work function analysis showed that when AMs are adsorbed on C(100)(2×1) surface, the work function decreases linearly with increasing coverage and reaches a minimum at Θ=0.5ML. At higher coverage, the work function is increased again, which may be caused by depolarization effect of the adsorbate.

Dissociative versus molecular adsorption of phenol onSi(100)2×1: A first-principles calculation

We investigated the competitive adsorption of a bifunctional molecule, phenol, on $\mathrm{Si}(100)2\ifmmode\times\else\texttimes\fi{}1$ by ab initio calculations. We performed geometry optimizations of phenol adsorbed either molecularly or dissociatively, on five possible sites (top, bridge, valley bridge, cave, and pedestal), in the low coverage regime. We found that the dissociative adsorption of phenol on top of a silicon dimer is the most favorable adsorption configuration. In the group of dissociative adsorption the phenol initially placed on the bridge or the valley-bridge sites ends up as a toplike local minima. The pedestal and cave sites remain as low-adsorption energy ``open'' sites. In the group of molecular adsorption, a higher adsorption energy is associated to the adsorption through an addition reaction and loss of the aromatic character (bridge, valley-bridge, and pedestal sites). Standard butterfly or diagonal butterfly are the corresponding optimized geometries. Retention of aromatic character and lower adsorption energy are associated to the adsorption on the top and cave sites. The ordering of adsorption sites according to the adsorption energy shows a mixture of the dissociative and the molecular sites. In the case of adsorption on the top site, the adsorption energies after a rotation of the phenoxy fragment along the bonding axis and hydrogen migration on the surface are very similar. The bend of the phenoxy fragment on the surface, instead, is not favored (the adsorption energy is $1.004\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ lower compared to the vertical position). Different electron density maps were calculated for different adsorption sites and modes. Finally, we investigated the possibility that molecularly adsorbed phenol behaves as a precursor for the dissociative one by nudged elastic band calculations. We found a barrier of the same order of magnitude of the thermodynamic energy at room temperature for the conversion of the valley-bridge molecular into the top dissociative site.

Atomic and electronic structures of the Rb–C(1 0 0) chemisorption system

First-principles calculations based on DFT–GGA method have been performed on Rb adsorption on C(1 0 0)(2×1) surface. The optimized geometries, adsorption energies have been obtained and the preferred binding sites have been determined for the coverage ( Θ) of one monolayer and half a monolayer. The calculated results have shown that Rb adsorbate preferred to occupy valley-bridge sites at the coverage of 0.5 ML. At higher coverage of 1 ML, two Rb adsorbates were found to reside in pedestal site and valley-bridge site, respectively. It was also found that when Rb was adsorbed on C(1 0 0)(2×1) surface the work function decreases linearly with increasing coverage and reaches a minimum at Θ=0.5 ML, at higher coverage, the work function is increased again, which may be caused by depolarization effect of the adsorbate. The adsorption behavior was found to be similar to that of Rb on Si(0 0 1) and Ge(0 0 1) surface.

First-principles study of lithium adsorption on Si(1 0 0)2 × 1 and Ge(1 0 0)2 × 1 surface at 1.0 monolayer coverage

First-principles calculations based on density functional theory have been carried out to determine the atomic structure and electronic properties of the Si(1 0 0)2 × 1–Li and Ge(1 0 0)2 × 1–Li adsorption systems at 1.0 monolayer (ML) coverage. For the Si(1 0 0)2 × 1–Li chemisorption system, the lowest energetic configuration is that one Li atom resides at the T3′ (which is displaced along the positive y-axis from the valley bridge (T3) site by 0.90 Å) and the other resides at pedestal (HH) site. For the Ge(1 0 0)2 × 1–Li chemisorption system, the most stable configuration is found to be that one Li atom resides at HH site and the other one will penetrate deeply into the substrate surface. Chemisorption of the lithium atoms is found to result in a minimum energy configuration characterized by symmetric dimers in agreement with the results of high-resolution core-level photoelectron spectroscopy. The adsorption systems show semiconducting surface characterization.

First principles calculations on Na and K-adsorbed diamond(1 0 0) surface

Self-consistent, periodic, density functional theory calculations, using PW91 functional, have been performed to investigate Na and K adsorption on the C(1 0 0)(2 × 1) surface. Our calculations showed that Na and K adatoms preferred to occupy valley-bridge sites at the coverage ( Θ) of 0.5 ML. For the coverage of 1 ML, the combination of pedestal site and valley-bridge site turned out to be energetically favored. These findings are found to be consistent with those obtained for alkali-metal adsorption on silicon and germanium surfaces. Two desorption peaks named α and β for K adsorption have been observed and assigned to pedestal or bridge site and valley-bridge sites experimentally, while our results showed that the α and β states should be ascribed to pedestal site and valley-bridge sites and the combination of bridge and valley-bridge site is not the local minima. Work function analysis showed that when Na and K are adsorbed on diamond surface, the work function will decrease linearly with increasing coverage, up to a minimum, and finally increase again because of the depolarization of the adsorbate, agreeing well with experiments.

From K atom pairs to K atomic chains: A semiconducting 2×3 to metallic 2×1 transition on the β-SiC(100) c(4×2) surface

We study the K∕β-SiC(100) c(4×2) surface by atom-resolved scanning tunneling microscopy and spectroscopy, and synchrotron radiation-based photoemission spectroscopy. At intermediate coverages, the K atoms are grouped by pairs around Si dimers at pedestal sites, in a 2×3 long-range ordering leaving 1∕3 of the pedestal sites unoccupied, while keeping the semiconducting c(4×2) surface unchanged as identified by tunneling through the K overlayer. At saturation, additional K atoms adsorb on remaining pedestal sites and act as atomic “contacts” between two K pairs, leading to K atom chain formation in a 2×1 metallic surface.

Band bending at the Ni/Si(100)-2×1 submonolayer interface

Band bending at the Ni/Si(100)-2×1 interface has been monitored by using Si 2p core level photoemission spectra. Two nickel-induced Si 2p components appear in the initial interaction between Ni and Si(100)-2×1, which is confined at the top surface and the first subsurface layers. At Ni coverage less than 0.0375 ML, Ni atoms prefer the adamantane interstitial sites on the first subsurface, but switch to the pedestal sites on Si dimer rows at higher Ni coverage. The change in the preferred occupation sites of Ni atoms on the Si(100)-2×1 surface strongly affects the amount of band bending shift. The shift towards higher binding energy, when Ni atoms occupy the adamantane interstitial sites, is attributed to metal-induced-gap states. While Ni atoms occupy the pedestal sites, the band bending shift is reduced which is attributed to the passivation of surface states.

Ab initiostudy of adsorption and diffusion of Ag atoms on a Si(001) surface

By employing ab initio total-energy calculations we have studied adsorption and diffusion of Ag atoms on a dimer-reconstructed Si(001) surface. For a single Ag adsorption, the twofold-coordinated cave site above the fourth Si layer atom was found to be the most stable, in agreement with previous works. Inspection of the electronic structures at the cave site revealed that the Ag-Si bonds originate from low-lying $4d$ electrons and are covalent. Our calculations also exhibit another stable adsorption at the pedestal site that is slightly higher by 0.03 eV in energy than the cave site. Further potential-energy-surface calculations showed that the surface diffusion of a single Ag adatom is unexpectedly highly isotropic and that the energy barrier is 0.5 eV. When more Ag adatoms are adsorbed on the Si surface, the Ag adatoms are expected to form dimers. Actually, we obtained an energy gain of 0.36 eV/dimer through the dimerization. The diffusion of an Ag dimer was also investigated. Surprisingly, we found a very rapid surface-dimer diffusion with an energy barrier of 0.48 eV slightly lower than that of the single Ag adatom. In contrast to the diffusion of the single Ag adatom, the dimer diffusion is anisotropic and preferably occurs along the valley between Si dimer rows by concerted flipflop processes.

Local adsorption geometry of acetylene onSi(100)(2×1):Multiple sites and the role of substrate temperature

Using C 1s scanned-energy mode photoelectron diffraction the local adsorption geometry of acetylene on the $\mathrm{Si}(100)(2\ifmmode\times\else\texttimes\fi{}1)$ surface has been investigated at both low and room temperatures. Clear differences in the data at the two sample temperatures are attributed to the co-occupation of at least two distinct local sites. Quantitative modeling based on a two-site model indicates that the majority state at low temperature is bridge site adsorption with the C-C axis of the acetylene directly above, and parallel to, Si-Si surface dimers. At room temperature a second state accounts for more than 50% of the adsorbed acetylene molecules, and the favored model places these acetylene molecules midway between pairs of Si dimers, although the azimuthal orientation of the C-C axes is ambiguous. One possible geometry for this second species is the ``pedestal site'' tetra-\ensuremath{\sigma} species previously proposed by Xu et al. [Phys. Rev. Lett. 84, 939 (2000)], although the specific geometry proposed by this group can be excluded. An alternative ``rotated pedestal'' site is comparably probable. There is no direct evidence for any occupation of a rotated bridge site across the ends of two adjacent Si dimers, but partial occupation of this site cannot be excluded.

Initial processes of a Ni adatom on the Si(001) surface: a first-principles study

We have theoretically studied the initial processes of a Ni adatom on the Si(001) surface based on the first-principles calculation. On this surface, the most stable adsorption site for Ni is the pedestal site on the Si dimer row (DR). From this site, it needs the activation energies of 0.32 and 0.86 eV for the surface diffusion in the directions parallel and perpendicular to the dimer row, respectively. While under the surface, there exist more stable sites, and the minimum value of the activation energies needed for the penetration into these sites from the pedestal site is 0.71 eV. Thus, we have concluded that a Ni atom can readily diffuse on the Si surface and also penetrate into the subsurface, then it finally becomes stable in the subsurface site, at the room temperature (RT). Furthermore, it has also been concluded that the penetration of Ni is the precursor state for silicidation.

Theoretical determination of the adsorption geometry of Na on the Si(001) surface

Ab initio total-energy calculations for Na on the Si(001) 2\ifmmode\times\else\texttimes\fi{}1 surface at coverages ranging from one-fourth to one monolayer were performed using the density-functional method with a plane-wave basis set and a slab with a 2\ifmmode\times\else\texttimes\fi{}2 surface cell. The results of these electronic structure calculations are discussed and compared with other theoretical and experimental findings. At the highest coverage of one monolayer, we obtained the lowest surface energy for the double-layer model with combined occupation of the hollow and pedestal sites. For lower coverages, the structures are more complicated, as the hollow site becomes unstable and adsorption at the cave and the pedestal site is preferred. In particular, for half a monolayer a distinct larger adsorption energy is obtained for the combination of cave and pedestal sites.

内耳奇形の小児に対する人工内耳埋込術と術後成績

Cochlear implantation in children with cochlear malformation is on the rise. However, only one case has been reported in Japan. The objective of this paper is to report the authors' experiences with cochlear implants in children with cochlear malformations and, to investigate the morphological classification of cochlear malformation, surgical procedure, complications, and speech perceptions after implantation. Five children (6 ears, including 1 Usher's syndrome and 1 CHARGE association) with congenital inner ear malformations were implanted with multichannel cochlear implants (Nucleus Mini 22 device) between 1994 and 1998. Malformations included common cavity deformity 2, and incomplete partition 4. On the other hand, 4 cases with incomplete partition deformity underwent cochlear implantation by the transmastoid facial recess approach, 2 patients with common cavity deformity received implantation by the transmastoid labyrinthotomy approach. Complications such as facial twitching, cerebrospinal fluid (CSF) gusger, and flap-related problems were encountered. Facial twitching occurred in 1 of 2 patients with common cavity where the electrode array extended into the internal auditory canal. CSF gusher was encountered in 1 of 4 patients with incomplete partition, and revision surgery was performed one week later. One patient had delayed cochlear implant infection and a split pericranial flap was used to cover the defect in the skin flap. Within 6 months, however, the revised pedestal site broke down because of recurrent flap infection. Finally, the cochlear implant was explanted, and the patient underwent a new cochlear implantation in the contralateral ear. All the patients had satisfactory speech reception and word acquisition, but still poor phonetic expression.

Atomic and electronic structure of Li-adsorbed Si(100) surfaces

We investigate the atomic and electronic structure of Li-adsorbed Si(100) surfaces through first-principles pseudopotential calculations. We find that Li adatoms interact mainly with the dangling-bond orbitals of Si dimers, however, no hydrogenlike directional bonds exist between the Li and substrate Si atoms, based on calculated scanning tunneling microscopy images. The analysis of charge densities demonstrates a large charge transfer from the Li adatom to a dangling-bond orbital of a Si dimer, which is responsible for a large decrease of work function at submonolayer coverages. The Li atoms form linear chains either by occupying the interdimer bridge sites along the dimer row direction or the dimer bridge and cave sites perpendicular to the dimer row. As Li coverage (\ensuremath{\Theta}) increases, repulsive interactions between the adatoms in the chains are also found to increase. Thus, at 1-ML Li coverage, the stable adsorptions sites are changed to either the cave and pedestal sites or the valley-bridge and pedestal sites, with all the Si dimers symmetric, resulting in a $2\ifmmode\times\else\texttimes\fi{}1$ structure. From the calculated formation energies, we find a $1\ifmmode\times\else\texttimes\fi{}1$ phase to be thermodynamically stable at $\ensuremath{\Theta}=2,$ in contrast to other alkali-metal adsorptions.

Adsorption reactions of [formula omitted] by variable-temperature STM

Monatomic adsorption of Ti on the Si(001)-2 × 1 surface has been observed by variable-temperature scanning tunneling microscopy. A Ti atom is reversibly converted between two precursor states which are pedestal site adsorption and a highly mobile state between the dimer rows. The final state, that is a vacancy site adsorption, is formed only from the pedestal site adsorption inducing ejection of Si dimer atoms. The quantitative and qualitative evaluation of the site conversion reveals that the adsorption behavior is highly affected by the local bonding properties of Ti with the Si 2 × 1 reconstruction.

Site conversion path and the kinetics of Ti on Si(001)-2 × 1 observed by scanning tunneling microscopy

We have used a variable-temperature scanning tunneling microscope to observe the site conversion path and the kinetics of Ti adsorbed on the Si(001)-2 × 1 surface. We have found that the monatomic adsorption of Ti is featured by two metastable precursory states and the final state. A Ti adatom is reversibly converted between the two precursory states, i.e., the pedestal site adsorption and a highly mobile state between the dimer rows. A conversion to the final state at the vacancy site occurs only from the pedestal site adsorption. Rates of two types of the site conversions from the pedestal site were measured by counting individual site conversion events as a function of time. The obtained activation energies and the conversion path are consistently interpreted in terms of the bonding nature of a Ti adatom on the Si dimer configuration.