Dynamic topological domain walls driven by lithium intercalation in graphene

Stacking engineering in van der Waals (vdW) materials is a powerful method to control topological electronic phases for quantum device applications. Atomic intercalation into the vdW material can modulate the stacking structure at the atomic scale without a highly technical protocol. Here we report that lithium intercalation in a topologically structured graphene/buffer system on SiC(0001) drives dynamic topological domain wall (TDW) motions associated with stacking order change by using an in situ aberration-corrected low-energy electron microscope in combination with theoretical modelling. We observe sequential and selective lithium intercalation that starts at topological crossing points (AA stacking) and then selectively extends to AB stacking domains. Lithium intercalation locally changes the domain stacking order to AA and in turn alters the neighbouring TDW stacking orders, and continuous intercalation drives the evolution of the whole topological structure network. Our work reveals moving TDWs protected by the topology of stacking and lays the foundation for controlling the stacking structure via atomic intercalation. These findings open up new avenues to realize intercalation-driven vdW electronic devices.

Two-Dimensional Superconductivity of Ca-Intercalated Graphene on SiC: Vital Role of the Interface between Monolayer Graphene and the Substrate

Ca-intercalation has enabled superconductivity in graphene on SiC. However, the atomic and electronic structures that are critical for superconductivity are still under discussion. We find an essential role of the interface between monolayer graphene and the SiC substrate for superconductivity. In the Ca-intercalation process, at the interface a carbon layer terminating SiC changes to graphene by Ca-termination of SiC (monolayer graphene becomes a bilayer), inducing more electrons than a free-standing model. Then, Ca is intercalated in between the graphene layers, which shows superconductivity with the updated critical temperature (T_C) of up to 5.7 K. In addition, the relation between T_C and the normal-state conductivity is unusual, "dome-shaped". These findings are beyond the simple C₆CaC₆ model in which s-wave BCS superconductivity is theoretically predicted. This work proposes a general picture of the intercalation-induced superconductivity in graphene on SiC and indicates the potential for superconductivity induced by other intercalants.

Two-Dimensional Superconductor with a Giant Rashba Effect: One-Atom-Layer Tl-Pb Compound on Si(111)

A one-atom-layer compound made of one monolayer of Tl and one-third monolayer of Pb on a Si(111) surface having √3×√3 periodicity was found to exhibit a giant Rashba-type spin splitting of metallic surface-state bands together with two-dimensional superconducting transport properties. Temperature-dependent angle-resolved photoelectron spectroscopy revealed an enhanced electron-phonon coupling for one of the spin-split bands. In situ micro-four-point-probe conductivity measurements with and without magnetic field demonstrated that the (Tl, Pb)/Si(111) system transformed into the superconducting state at 2.25 K, followed by the Berezinskii-Kosterlitz-Thouless mechanism. The 2D Tl-Pb compound on Si(111) is believed to be the prototypical object for prospective studies of intriguing properties of the superconducting 2D system with lifted spin degeneracy, bearing in mind that its composition, atomic and electron band structures, and spin texture are already well established.

Electron-Hole Recombination Time at TiO2 Single-Crystal Surfaces: Influence of Surface Band Bending

Photocatalytic activity is determined by the transport property of photoexcited carriers from the interior to the surface of photocatalysts. Because the carrier dynamics is influenced by a space charge layer (SCL) in the subsurface region, an understanding of the effect of the potential barrier of the SCL on the carrier behavior is essential. Here we have investigated the relaxation time of the photoexcited carriers on single-crystal anatase and rutile TiO2 surfaces by time-resolved photoelectron spectroscopy and found that carrier recombination, taking a nanosecond time scale at room temperature, is strongly influenced by the barrier height of the SCL. Under the flat-band condition, which is realized in nanometer-sized photocatalysts, the carriers have a longer lifetime on the anatase surface than the rutile one, naturally explaining the higher photocatalytic activity for anatase than rutile.

Metallic transport in a monatomic layer of in on a silicon surface

We have succeeded in detecting metallic transport in a monatomic layer of In on an Si(111) surface, Si(111)-sqrt[7]×sqrt[3]-In surface reconstruction, using the micro-four-point probe method. The In layer exhibited conductivity higher than the minimum metallic conductivity (the Ioffe-Regel criterion) and kept the metallic temperature dependence of resistivity down to 10 K. This is the first example of a monatomic layer, with the exception of graphene, showing metallic transport without carrier localization at cryogenic temperatures. By introducing defects on this surface, a metal-insulator transition occurred due to Anderson localization, showing hopping conduction.

Electron-phonon interaction and localization of surface-state carriers in a metallic monolayer

Temperature-dependent electron transport in a metallic surface superstructure, Si(111)sqrt[3] x sqrt[3]-Ag, was studied by a micro-four-point probe method and photoemission spectroscopy. The surface-state conductivity exhibits a sharp transition from metallic conduction to strong localization at approximately 150 K. The metallic regime is due to electron-phonon interaction while the localization seemingly originates from coherency of electron waves. Random potential variations, caused by Friedel oscillations of surface electrons around defects, likely induce strong carrier localization.

Variable-temperature independently driven four-tip scanning tunneling microscope

The authors have developed an ultrahigh vacuum (UHV) variable-temperature four-tip scanning tunneling microscope (STM), operating from room temperature down to 7 K, combined with a scanning electron microscope (SEM). Four STM tips are mechanically and electrically independent and capable of positioning in arbitrary configurations in nanometer precision. An integrated controller system for both of the multitip STM and SEM with a single computer has also been developed, which enables the four tips to operate either for STM imaging independently and for four-point probe (4PP) conductivity measurements cooperatively. Atomic-resolution STM images of graphite were obtained simultaneously by the four tips. Conductivity measurements by 4PP method were also performed at various temperatures with the four tips in square arrangement with direct contact to the sample surface.

Four-point probe resistance measurements using PtIr-coated carbon nanotube tips

We performed four-terminal conductivity measurements on a CoSi2 nanowire (NW) at room temperature by using PtIr-coated carbon nanotube (CNT) tips in a four-tip scanning tunneling microscope. The physical stability and high aspect ratio of the CNT tips made it possible to reduce the probe spacing down to ca. 30 nm. The probe-spacing dependence of resistance showed diffusive transport even at 30 nm and no current leakage to the Si substrate.

High-yield synthesis of conductive carbon nanotube tips for multiprobe scanning tunneling microscope

We have established a fabrication process for conductive carbon nanotube (CNT) tips for multiprobe scanning tunneling microscope (STM) with high yield. This was achieved, first, by attaching a CNT at the apex of a supporting W tip by a dielectrophoresis method, second, by reinforcing the adhesion between the CNT and the W tip by electron beam deposition of hydrocarbon and subsequent heating, and finally by wholly coating it with a thin metal layer by pulsed laser deposition. More than 90% of the CNT tips survived after long-distance transportation in air, indicating the practical durability of the CNT tips. The shape of the CNT tip did not change even after making contact with another metal tip more than 100 times repeatedly, which evidenced its mechanical robustness. We exploited the CNT tips for the electronic transport measurement by a four-terminal method in a multiprobe STM, in which the PtIr-coated CNT portion of the tip exhibited diffusive transport with a low resistivity of 1.8 kOmega/microm. The contact resistance at the junction between the CNT and the supporting W tip was estimated to be less than 0.7 kOmega. We confirmed that the PtIr thin layer remained at the CNT-W junction portion after excess current passed through, although the PtIr layer was peeled off on the CNT to aggregate into particles, which was likely due to electromigration or a thermally activated diffusion process. These results indicate that the CNT tips fabricated by our recipe possess high reliability and reproducibility sufficient for multiprobe STM measurements.

Interaction between adatom-induced localized states and a quasi-two-dimensional electron gas

Using angle-resolved photoemission spectroscopy, we investigate changes in the band dispersion of a free-electron-like surface state of [FORMULA: SEE TEXT], induced by adsorption of submonolayer Au adatoms. At room temperature, where the adatoms are in a two-dimensional adatom-gas phase, electrons are transferred from the Au adatoms to the substrate, shifting the surface band downwards and causing it to deviate from a parabolic dispersion. At 135 K where the Au adatoms are frozen at specific sites of the substrate, the band splits into two. This band splitting can be explained in terms of hybridization between the unperturbed surface band and the localized virtual bound states induced by the Au adatoms.

Electrical resistance of a monatomic step on a crystal surface

We have succeeded in measuring the resistance across a single atomic step through a monatomic-layer metal on a crystal surface, Si(111)(sqrt[3]xsqrt[3])-Ag, using three independent methods, which yielded consistent values of the resistance. Two of the methods were direct measurements with monolithic microscopic four-point probes and four-tip scanning tunneling microscope probes. The third method was the analysis of electron standing waves near step edges, combined with the Landauer formula for 2D conductors. The conductivity across a monatomic step was determined to be about 5 x 10(3) Omega(-1) m(-1). Electron transport across an atomic step is modeled as a tunneling process through an energy-barrier height approximately equal to the work function.

Anisotropy in conductance of a quasi-one-dimensional metallic surface state measured by a square micro-four-point probe method

We have devised a "square micro-four-point probe method" using an independently driven ultrahigh-vacuum four-tip scanning tunneling microscope, and succeeded for the first time to directly measure anisotropic electrical conductance of a single-atomic layer on a solid surface. A quasi-one-dimensional metal of a single-domain Si(111)4 x 1-In had a surface-state conductance along the metallic atom chains (sigma(axially)) to be 7.2(+/-0.6) x 10(-4) S/square at room temperature, which was larger than that in the perpendicular direction (sigma(radially)) by approximately 60 times. The sigma(axially) was consistently interpreted by a Boltzmann equation with the anisotropic surface-state band dispersion, while the sigma(radially) was dominated by a surface-space-charge-layer conductance.

Efficacy of treatment with chimeric monoclonal antibody (Infliximab) to tumor necrosis factor-alpha for Crohn's disease in Japan: evaluation by rapid turnover proteins, and radiologic and endoscopic findings

BACKGROUND

Several studies have reported that the chimeric monoclonal antibody to tumor necrosis factor (TNF)-alpha (Infliximab) is extremely valuable in the treatment of Crohn's disease. The aim of this study was to clarify the efficacy of this treatment in Japanese patients with Crohn's disease.

METHODS

A 12-week multicenter, open trial of Infliximab was carried out and involved 25 patients with moderate to severe Crohn's disease who were resistant to conventional treatment. Patients received a single 2-h intravenous infusion of Infliximab at a dose of 1, 3, 5 or 10 mg/kg bodyweight. Clinical evaluation of this treatment response was defined as a reduction in the index of the inflammatory bowel disease (IOIBD) and of the Crohn's disease activity index scores (CDAI), and in serum levels of C-reactive protein (CRP) at 2, 4, 8 and 12 weeks, and as an increase in serum levels of rapid turnover proteins as well as improvement of radiologic and endoscopic findings at 4 weeks.

RESULTS

The IOIBD score was reduced after 4 weeks in 66.7% of the group receiving 1 mg/kg Infliximab, 71.4% in the group receiving 3 mg/kg, 80.0% in the group receiving 5 mg/kg, and 85.7% in the group receiving 10 mg/kg. Improvement was better maintained over 12 weeks in the 5 and 10 mg/kg groups compared with the 1 and 3 mg/kg groups. Similar results were obtained for the CDAI scores. Serum levels of rapid turnover proteins significantly increased to within the normal ranges after infusion in all groups. Seven of the 11 (63.6%) patients evaluated showed improvement of radiologic and endoscopic findings.

CONCLUSIONS

A single infusion of Infliximab was effective for the treatment of Japanese patients with Crohn's disease. Serum rapid turnover proteins reflected the clinical response to antibody for TNF-alpha well.

[Intestinal permeability in Crohn's disease and effects of elemental dietary therapy]

Enteral intake of non-metabolic monosacharide and disaccharide, followed by measurement of the urinary excretion ratio of the two, is a method used to investigate intestinal permeability. L/R ratio (lactulose/1-rhamnose urinary excretion ratio) is considered an indicator of permeability of the small intestine. An increased L/R ratio is caused by mucosal disorders of the small intestine. The L/R ratio in all patients (n = 92) with Crohn's disease was 0.079 +/- 0.081 (mean +/- S.D.), which was significantly higher than the value in normal controls (0.027 +/- 0.009, n = 20, p < 0.05). In 39 patients with Crohn's disease, we assessed intestinal permeability before after treatment with an elemental diet, and during remission. The L/R ratio was 0.120 +/- 0.092, before treatment and 0.065 +/- 0.097 after treatment (p < 0.05), showing increased intestinal permeability before elemental dietary treatment. During remission, the L/R ratio was 0.035 +/- 0.028; this did not differ significantly from the value obtained after treatment. We conclude that intestinal permeability is useful for investigating disease activity in patients with Crohn's disease.

Investigation of the association between infection with Helicobacter pylori and with TT virus, a novel DNA virus, in patients with gastroduodenal ulcer or ulcer scar

OBJECTIVE

Recently, a novel DNA virus (TT virus; TTV) has been isolated. Enteric transmission is suggested as a route of transmission of TTV, with high prevalence of this virus infection in the general population, and age and geographical distributions of TTV prevalence very similar to those of Helicobacterpylori infection. We analysed an association between TTV and H. pylori infection in patients with gastroduodenal ulcer or ulcer scar.

METHODS

In 181 patients with a gastroduodenal ulcer or ulcer scar (102 with a gastric lesion, 60 with a duodenal lesion, and 19 with both sites involved), specimens were cultured for H. pylori and TTV infection was sought in serum by a polymerase chain reaction.

RESULTS

H. pylori infection was demonstrated in 152 patients (84.0%) and TTV was detected in 168 patients (92.8%). Patients with TTV were significantly older than those without TTV (P = 0.0001), while no age difference was observed between patients with and without H. pylori infection. No difference was apparent in the prevalence of TTV infection between patients with and without H. pylori infection, and vice versa.

CONCLUSIONS

We found no association between TTV infection and H. pylori infection in patients with peptic ulcer diseases, which is consistent with a lack of association between TTV infection and peptic ulcer. However, larger studies including surveys of the general population will be required to analyse the overall association between TTV and H. pylori.

[Unusual form of ulcerative colitis]

Segmental colitis which showed the similar findings of ulcerative colitis and right-sided colitis with back-wash ileitis has been considered as the unusual form of ulcerative colitis. Today, we have few opportunities to come across those cases, because modern diagnosis of colon disease could make differential diagnosis easily with the sense of broad spectrum of IBD. We presented three cases of segmental colitis and one case of so-called indeterminate colitis associated of carcinoma in the cecum and discussed the clinical significance for diagnosis and finding the step of studying the etiology of IBD. Especially, in the third case, thirteen years old man was showing the sign of early stage of Crohn disease with non-caseating granuloma in the biopsy specimen at first, the findings of the segmental ulcerative colitis with crypt abscess were seen after six months in the second examination. To observe the detail changes of the mucosal lesion in this kind of cases will present the new idea for studying the etiology of IBD.

[Treatment of advanced gastric and colorectal cancer with 5-FU, leucovorin and interferon-alpha]

Twenty-four patients with advanced or relapsed gastric or colorectal cancer were treated with a combination of 5-fluorouracil (5-FU), leucovorin (LV) and interferon-alpha (IFN-alpha). 5-FU was administered by rapid intravenous infusion at 350 mg/m2 for 5 consecutive days. Intravenous bolus administration of LV 20 mg/m2 was given before each 5-FU administration. This combination was repeated every 3 to 4 weeks. IFN-alpha (HLBI), 6MU, was administered subcutaneously daily. Of 13 patients with gastric cancer, there were 2 PR, 4 NC and 7 PD, and among 11 patients with colorectal cancer, there were 1 CR, 8 NC and 2 PD. All 16 previously treated patients had no clinical response. Responses were seen in patients with no prior chemotherapy and with good performance status. Most common toxicities observed were leucopenia, fever, stomatitis and diarrhea, which were all tolerable and reversible.

Effect of thiamine and thiamine levels on experimental alloxan induced diabetes mellitus

The effects of thiamine (T) on diabetes mellitus (DM) and the T levels in the brain, heart, liver, kidneys pancreas, muscle, adipose tissue and blood were measured. For the experimental DM model, alloxan (170 mg/kg, i.v.) was injected into male ddY mice and insulin was also administered for 5 days to prevent death by hyperglycemia (DM group). After 14 days, blood glucose level increased to 455 mg/dl, compared to 166 mg/dl in the normal control group (NC group). In the DM mice, the T level in the liver decreased to 7.71 micrograms/g, compared to 16.29 micrograms/g in the NC group. The T levels in the heart, pancreas, muscle and adipose tissue increased to 18.63 micrograms/g, 3.99 micrograms/g, 2.53 micrograms/g and 5.07 micrograms/g in the DM group, compared to 14.99 micrograms/g, 3.27 micrograms/g, 1.98 micrograms/g and 4.04 micrograms/g in the NC group, respectively. The T levels in the brain and kidney were 2.38 micrograms/g and 14.00 micrograms/g in the DM group, compared to 2.34 micrograms/g and 13.72 micrograms/g in the NC group, respectively. But, in the heart, an active form of a T co-enzyme decreased to 27%, compared to 95% for the NC group. These results indicate a T deficiency or an endogenous T deficiency in the DM group. All DM mice without insulin treatment died within 7 days but about 40% of the mice survived up to 14 days with the administration of T.

[Effect of oxythiamine and pyrithiamine on thiamine levels in the blood, liver and urine of rats (author's transl)]

Thiamine (T) deficient state and various functional and morphological changes in rat liver were induced, after several days, with T antagonists, oxythiamine (OT) or pyrithiamine (PT), and a thiamine deficient diet (TDD). The relationship between the extent of liver damage and T levels in blood, liver and urine were studied in OT treated rats fed a TDD (OTD group). PT treated rats fed a TDD (PTD group), OT treated rats (OT group), PT treated rats (PT group) and rats fed a TDD (TDD group). The T levels in blood and liver of OT group, PT group, OTD group, PTD group and TDD group were 89% and 91%, 76% and 88%, 25% and 14%, 33% and 16%, 24% and 15% compared with the data in the control group, respectively. Effects of OT or PT on T levels were not remarkable in some cases, and such may be due to the duration time of T antagonists, which was considered to be 3-15 hours in PT treated rats, and 0-18 hours in PT treated rats, as assessed by urinary T measurements. Treatment of T antagonist twice daily is recommended to obtain a definite T deficient state. Our results suggest that the extent of liver damage is related to the T levels in tissue.

Erythrocytosis in thiamine deficient rats

A thiamine (T) deficient state in rats was produced by feeding the rats a T deficient diet (TDD). At the stage of 13 days (TDD13 group), the number of red blood cells (RBC) and white blood cells (WBC), hematocrit (Ht) and hemoglobin (Hb) values decreased. On the other hand, after 30 days on the TDD (TDD30 group), the number of RBC was 819 x 10(4)/mm3 as against 631 x 10(4)/mm3 in the normal control group (NC group). Ht and Hb values also increased in the TDD30 group. These changes observed in the TDD30 group were significantly different from findings in the equal weight control group (EWC group) or in the pair fed control group (PFC group). The number of reticulocytes increased, the levels of 2,3-diphosphoglycerate (2,3-DPG) of RBC decreased and plasma erythropoietin levels increased in the TDD30 group. T levels of blood in the TDD13 group were 62 (39-79) ng/ml as against 275 (196-412) ng/ml in the NC group. T levels of blood in the TDD30 group were 102 (17-365) ng/ml, and widely varied. Decrease in 2,3-DPG produces an increase in O2 affinity to Hb, and hypoxia is induced in the peripheral tissues. Furthermore these conditions stimulate erythropoietin production and finally the number of RBC increases. T deficiency produces anemia at an early stage and absolute erythrocytosis occurs at the late stage of T deficiency. The increased osmotic resistance of RBC in hypotonic solution was also observed in the TDD30 group. This increase in osmotic resistance correlated with the decrease in cholesterol and phospholipid levels in the membrane of RBC.

[Effect of pyrithiamine on rat sciatic nerve. (I) Morphological changes during the early stage of thiamine deficiency (author's transl)]

We observed under light and electron microscopes morphological changes in the rat sciatic nerve during the early stages of a thiamine deficient state as induced by a pyrithiamine (PT: 50 microgram/100g X 6 days) and thiamine deficient diet (TDD). We simultaneously determined thiamine levels in the whole sciatic nerve of rats. Experiments were undertaken with normal control, TDD (rats fed a TDD), PT (PT treated rats) and PTD (PT treated rats fed a TDD) groups. Microscopically, there were numerous shrunken myelinated axons with myelin ovoids of folds in the PT group and many swollen ones in the PTD group. Electron microscopically, we found more advanced lesions in the PTD group than in the other groups. These ultrastructural changes were swelling of Schwann cells, enlarged rough-surfaced endoplasmic reticulum, axonal degeneration with shrinkage, loss of organelle or abnormal myelin sheath, and proliferation of fibroblasts. The thiamine level in the PTD group decreased to 18 approximately 30% that of control in proportion to the morphological changes. On the other hand, the thiamine level in the PT group (55 approximately 61%) decreased slightly more than that of the TDD group (50 approximately 56%), but changes in morphology were vice versa. These results suggest that the morphological changes in the sciatic nerve caused by PT-induced thiamine deficiency differs from changes seen in cases of dying-back neuropathy caused by TDD-induced deficiency, and that PT itself directly affects the nervous system

[Effect of oxythiamine and pyrithiamine on rat brain--morphological changes in the thiamine deficient rat brain (author's transl)]

We observed under light and electron microscopes morphological changes in the brains of rats in a thiamine deficient state as induced by an oxythiamine, pyrithiamine and thiamine deficient diet (OT, PT and TDD). We simultaneously determined thiamine levels in the whole brain of rats. The rats were separated into six groups-normal control, OT or PT treated rats (OT or PT group), OT or PT treated rats fed a TDD (OTD or PTD group), rats fed a TDD (TDD group)-. Microscopically, there were symmetrically distributed lesions containing spongy reticulation mainly in the vestibular nucleus. Electron microscopically, we found more advanced lesions in the OTD and PTD groups than in the TDD group. These ultrastructural changes were seen in the vicinity of capillaries and such consisted of abnormal endothelial cells and pericytes, excrescence of microglias, swelling or vacuolation of astrocytes, nerve cells containing distorted organelle and myelin degeneration, besides extracellular edema. The thiamine level in the TDD group decreased to 56% that of control. No effect of OT on the thiamine level was observed either in case of ingestion of a regular diet or when TDD was given. On the other hand, the thiamine level decreased to 43% in the PT group and to 17-23 in PTD. These results suggest that encephalopathy caused by the OT or PT-induced thiamine deficiency has the same selective vulnerable site as does the TDD-induced deficiency, however cellular sensitivity may differ slightly with the various ultrastructural changes.