Nanoindentation Of Si Nanostructures: Buckling And Friction At Nanoscales

A nanoindentation system was employed to characterize mechanical properties of silicon nanolines (SiNLs), which were fabricated by an anisotropic wet etching (AWE) process. The SiNLs had the linewidth ranging from 24 nm to 90 nm, having smooth and vertical sidewalls and the aspect ratio (height/linewidth) from 7 to 18. During indentation, a buckling instability was observed at a critical load, followed by a displacement burst without a load increase, then a full recovery of displacement upon unloading. This phenomenon was explained by two bucking modes. It was also found that the difference in friction at the contact between the indenter and SiNLs directly affected buckling response of these nanolines. The friction coefficient was estimated to be in a range of 0.02 to 0.05. For experiments with large indentation displacements, irrecoverable indentation displacements were observed due to fracture of Si nanolines, with the strain to failure estimated to be from 3.8% to 9.7%. These observations indicated that the buckling behavior of SiNLs depended on the combined effects of load, line geometry, and the friction at contact. This study demonstrated a valuable approach to fabrication of well-defined Si nanoline structures and the application of the nanoindentation method for investigation of their mechanical properties at the nanoscale.Microelectronics Research Cente

Triple sign reversal of Hall effect in HgBa_{2}CaCu_{2}O_{6} thin films after heavy-ion irradiations

Triple sign reversal in the mixed-state Hall effect has been observed for the first time in ion-irradiated HgBa_{2}CaCu_{2}O_{6} thin films. The negative dip at the third sign reversal is more pronounced for higher fields, which is opposite to the case of the first sign reversal near T_c in most high-T_c superconductors. These observations can be explained by a recent prediction in which the third sign reversal is attributed to the energy derivative of the density of states and to a temperature-dependent function related to the superconducting energy gap. These contributions prominently appear in cases where the mean free path is significantly decreased, such as our case of ion-irradiated thin films.Comment: 4 pages, 3 eps figures, submitted Phys. Rev. Let

Genetic diversity of Iris lactea var. chinensis germplasm detected by inter-simple sequence repeat (ISSR)

The genetic diversity of 24 Iris lactea var. chinensis were analysed by using 100 ISSR primers of which only 11 primers generated distinct amplified products. Among the 24 materials, a total of 214 bands were detected, of which 170 bands were polymorphic. The percentage of polymorphic bands (PPB) was 79%. The ISSR-based genetic similarity (GS) values among 24 accessions ranged from 0.400 to 0.929. Abundant genetic diversity among I. lactea var. chinensis accessions was revealed by ISSR markers.Based on the UPGMA cluster analysis and principal components analysis (PCA), the 24 materials investigated were divided into four groups, most of genetic variation was within a group. Genetic distance was found to be related to geographic distance among I. lactea var. chinensis

Magnetic field dependence of vortex activation energy: a comparison between MgB2, NbSe2 and Bi2Sr2Ca2Cu3O10 superconductors

The dissipative mechanism at low current density is compared in three different classes of superconductors. This is achieved by measurement of resistance as a function of temperature and magnetic field in clean polycrystalline samples of NbSe2, MgB2 and Bi2Sr2Ca2Cu3O10 superconductors. Thermally activated flux flow behavior is clearly identified in bulk MgB2. While the activation energy at low fields for MgB2 is comparable to Bi2Sr2Ca2Cu3O10, its field dependence follows a parabolic behavior unlike a power law dependence seen in Bi2Sr2Ca2Cu3O10. We analyze our results based on the Kramer's scaling for grain boundary pinning in MgB2and NbSe2

Heavy top quark from Fritzsch mass matrices

It is shown, contrary to common belief, that the Fritzsch ansatz for the quark mass matrices admits a heavy top quark. With the ansatz prescribed at the supersymmetric grand unified (GUT) scale, one finds that the top quark may be as heavy as 145 GeV, provided that tan$\beta$ (the ratio of the vacuum expectation values of the two higgs doublets) $\gg 1$. Within a non-supersymmetric GUT framework with two (one) light higgs doublets, the corresponding approximate upper bound on the top mass is $120~ (90)$ GeV. Our results are based on a general one--loop renormalization group analysis of the quark masses and mixing angles and are readily applied to alternative mass matrix ans\"{a}tze.Comment: LaTeX, 14 figures (not included, available on request