Synthesis of nanowires via helium and neon focused ion beam induced deposition with the gas field ion microscope.

The ion beam induced nanoscale synthesis of platinum nanowires using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPt(IV)Me3) precursor is investigated using helium and neon ion beams in the gas field ion microscope. The He(+) beam induced deposition resembles material deposited by electron beam induced deposition with very small platinum nanocrystallites suspended in a carbonaceous matrix. The He(+) deposited material composition was estimated to be 16% Pt in a matrix of amorphous carbon with a large room-temperature resistivity (∼3.5 × 10(4)-2.2 × 10(5) µΩ cm) and temperature-dependent transport behavior consistent with a granular material in the weak intergrain tunnel coupling regime. The Ne(+) deposited material has comparable composition (17%), however a much lower room-temperature resistivity (∼600-3.0 × 10(3) µΩ cm) and temperature-dependent electrical behavior representative of strong intergrain coupling. The Ne(+) deposited nanostructure has larger platinum nanoparticles and is rationalized via Monte Carlo ion-solid simulations which show that the neon energy density deposited during growth is much larger due to the smaller ion range and is dominated by nuclear stopping relative to helium which has a larger range and is dominated by electronic stopping.

Precision cutting and patterning of graphene with helium ions.

We report nanoscale patterning of graphene using a helium ion microscope configured for lithography. Helium ion lithography is a direct-write lithography process, comparable to conventional focused ion beam patterning, with no resist or other material contacting the sample surface. In the present application, graphene samples on Si/SiO2 substrates are cut using helium ions, with computer controlled alignment, patterning, and exposure. Once suitable beam doses are determined, sharp edge profiles and clean etching are obtained, with little evident damage or doping to the sample. This technique provides fast lithography compatible with graphene, with approximately 15 nm feature sizes.

Transformations in methane hydrates.

Detailed study of pure methane hydrate in a diamond cell with in situ optical, Raman, and x-ray microprobe techniques reveals two previously unknown structures, structure II and structure H, at high pressures. The structure II methane hydrate at 250 MPa has a cubic unit cell of a = 17.158(2) A and volume V = 5051.3(13) A(3); structure H at 600 MPa has a hexagonal unit cell of a = 11.980(2) A, c = 9.992(3) A, and V = 1241.9(5) A(3). The compositions of these two investigated phases are still not known. With the effects of pressure and the presence of other gases in the structure, the structure II phase is likely to dominate over the known structure I methane hydrate within deep hydrate-bearing sediments underlying continental margins.

Angioscopy in endovascular surgery: recent technical advances to enhance intervention selection and failure analysis.

Recent technical and procedural modifications have greatly enhanced the usefulness of angioscopy during angioplasty. A pulsed irrigation system, proximal and distal blood flow control by pressure, and attention to sheath/vessel diameter ratio were incorporated into a study in which angioscopy was used for pretreatment assessment in 23 patients with symptomatic peripheral vascular disease presenting for initial (8 patients) evaluation or repeat treatment (15 patients) following a previous vascular procedure. Twenty-five lesions were examined with a 2.3 mm flexible angioscope equipped with an irrigating lumen; there were no complications attributable to angioscopy. The angioscope was useful in the characterization of lesions for selection of the recanalization technique. Lesions more amenable to initial atherectomy were visualized in 12 patients; 7 occlusions were successfully treated with laser/balloon angioplasty, with angioscopy assisting in probe and/or wire passage in 4 cases. Three late reocclusions were identified angioscopically as due solely to thrombosis, indicating the need for thrombolytic therapy. Angioscopy also identified 4 cases of incomplete recanalization despite a satisfactory arteriographic image. Angioscopy was also used to evaluate stenotic lesions unaccompanied by thrombus formation in patients previously treated with laser-assisted angioplasty. Histologic evaluation of the biopsied plaques identified intimal hyperplasia as the etiology, matching identically similar specimens harvested from a lesion treated with balloon dilation only.

Mantle phase changes and deep-earthquake faulting in subducting lithosphere.

Inclined zones of earthquakes are the primary expression of lithosphere subduction. A distinct deep population of subduction-zone earthquakes occurs at depths of 350 to 690 kilometers. At those depths ordinary brittle fracture and frictional sliding, the faulting processes of shallow earthquakes, are not expected. A fresh understanding of these deep earthquakes comes from developments in several areas of experimental and theoretical geophysics, including the discovery and characterization of transformational faulting, a shear instability connected with localized phase transformations under nonhydrostatic stress. These developments support the hypothesis that deep earthquakes represent transformational faulting in a wedge of olivine-rich peridotite that is likely to persist metastably in coldest plate interiors to depths as great as 690 km. Predictions based on this deep structure of mantle phase changes are consistent with the global depth distribution of deep earthquakes, the maximum depths of earthquakes in individual subductions zones, and key source characteristics of deep events.

Intraoperative coronary excimer laser angioplasty: preliminary clinical experience.

Diffuse coronary artery atherosclerosis is generally recognized as a deterrent to successful revascularization if it cannot be adequately treated. Mechanical endarterectomy can be useful, but it is not the optimal solution owing to the associated higher incidences of perioperative infarction and mortality. The use of laser energy as an endarterectomy tool appears promising. To investigate the application of excimer laser radiation to intraoperative coronary artery endarterectomy, 15 stenotic lesions in 13 patients were treated with excimer irradiation during coronary artery bypass grafting. Eleven (73%) of the lesions were enlarged by the excimer probe (6 of the successes were in calcified lesions). The 4 arteries not enlarged by the excimer laser all demonstrated calcified lesions. There were 3 perforations and 2 dissections, all but 1 in heavily calcified arteries. The results of this phase 1 safety and efficacy study indicate that excimer irradiation can recanalize most arteries, including total and subtotal occlusions and some calcified lesions. Further evaluation with better delivery systems is needed to determine whether the perforation rate can be reduced.