Length dependence of current-induced breakdown in carbon nanofiber interconnects

Current-induced breakdown is investigated for carbon nanofibers (CNF) for potential interconnect applications. The measured maximum current density in the suspended CNF is inversely proportional to the nanofiber length and is independent of diameter. This relationship can be described with a heat transport model that takes into account Joule heating and heat diffusion along the CNF, assuming that breakdown occurs when and where the temperature reaches a threshold or critical value

Bright contrast imaging of carbon nanofiber-substrate interface

We present the contrast mechanisms of scanning electron microscopy (SEM) for visualizing the interface between carbon nanofibers (CNFs) and the underlying substrate. SEM imaging with electron beam energies higher than a certain threshold provides different image contrasts depending on whether CNFs are in contact with the substrate or suspended above the substrate. CNFs with diameters ranging from 25to250nm are examined with various electron beam energies. It is found that the threshold energy corresponds to the energy required to penetrate the CNF and its dependence on CNF diameter can be understood using the theory of electron range. This knowledge will be quite useful for interface imaging of all nanostructure devices

Bright-field transmission imaging of carbon nanofibers on bulk substrate using conventional scanning electron microscopy

The authors present scanning transmission electron microscopy (STEM) of carbon nanofibers (CNFs) on a bulk substrate using conventional scanning electron microscopy (SEM) without specimen thinning. By utilizing the electron beam tilted \u3e85° from the substrate normal, bright-field STEM contrast is obtained for the CNFs on substrate with conventional SEM. Analysis of the observed contrast using Monte Carlo simulation shows that the weakly scattered electrons transmitted from the CNF are selectively enhanced by the largely tilted substrate and result in the observed STEM contrast. This mechanism provides a useful STEM imaging technique to investigate the internal structure of materials on bulk substrates without destructive specimen thinning

Improved contact for thermal and electrical transport in carbon nanofiber interconnects

We study the performance and reliability of carbon nanofiber (CNF) interconnects under high-current stress by examining CNF breakdown for four test configurations, suspended/supported with/without tungsten deposition. The use of W is to improve the CNF-electrode contact. The supported cases show a larger current density just before breakdown than the suspended ones, suggesting an effective heat dissipation to the substrate. The W-deposited contacts reduce the initial total resistance from megaohm range without W to kilo-ohms. High-current stress does not change the total resistance of the test structures with W unlike those without W deposition

Morphological Alterations of the Eccrine Sweat Apparatus in Amputated Feet from Diabetes Mellitus Patients

Several physiological studies have demonstrated decreased or absent thermoregulatory sweating in the distal legs and feet of diabetes patients. Such hypohidrosis in diabetes patients is believed to be a clinical symptom of autonomic neuropathy. Thus, the present study sought to clarify the pathogenesis of structural alterations of the eccrine sweat apparatus in diabetes patients. For this study, we enrolled 17 patients with diabetic ulcers/gangrene who underwent amputation of the foot. Specimens were obtained 30mm from the ulcer/gangrene after amputation using a 6-mm trepan, with 12 normal human skin samples obtained from areas adjacent to pigmented nevi or benign skin tumors on the legs or feet to serve as controls. Numbers and morphological abnormalities of eccrine sweat glands and ducts were assessed by light microscopy. The pathogenesis of morphological alterations was examined by electron microscopy and immunoelectron microscopy of type IV collagen. Rates of disappearance of the lumen, shrunken morphology, and irregular outlines of eccrine sweat glands and ducts were significantly higher or more abundant in diabetes patients than in controls (P = 0.0002〜0.0001). Ultrastructurally, we observed prominent thickening of the basement membranes in eccrine sweat glands, admixed cell debris, and narrowing of the lumenal space. The thickened basement membranes resulted in the shrunken morphology and irregular outlines in eccrine sweat glands and ducts. Immunoelectron microscopy showed immunogold labeling for type IV collagen throughout the thickened basement membrane zone. These morphological alterations of the eccrine sweat apparatus in amputated feet from diabetes patients could be caused by diabetic and/or uremic neuropathy, and at least in part by angiopathy

Therapeutic angiogenesis by transplantation of induced pluripotent stem cell-derived Flk-1 positive cells

<p>Abstract</p> <p>Background</p> <p>Induced pluripotent stem (iPS) cells are the novel stem cell population induced from somatic cells. It is anticipated that iPS will be used in the expanding field of regenerative medicine. Here, we investigated whether implantation of fetal liver kinase-1 positive (Flk-1⁺) cells derived from iPS cells could improve angiogenesis in a mouse hind limb model of ischemia.</p> <p>Results</p> <p>Flk-1⁺cells were induced from iPS cells after four to five days of culture. Hind limb ischemia was surgically induced and sorted Flk-1⁺cells were directly injected into ischemic hind limbs of athymic nude mice. Revascularization of the ischemic hind limb was accelerated in mice that were transplanted with Flk-1⁺cells compared with control mice, which were transplanted with vehicle, as evaluated by laser Doppler blood flowmetry. Transplantation of Flk-1⁺cells also increased expression of VEGF mRNA in ischemic tissue compared to controls.</p> <p>Conclusions</p> <p>Direct local implantation of iPS cell-derived Flk-1⁺cells would salvage tissues from ischemia. These data indicate that iPS cells could be valuable in the therapeutic induction of angiogenesis.</p