No abstract

We have measured the resistances (and resistivities) of Ag and Cu nanowires of diameters ranging from 15 nm to 200 nm in the temperature range 4.2 K-300 K with the specific aim to assess the applicability of the Bloch-Grüneisen formula for electron phonon resistivity in these nanowires. The wires were grown within polymeric templates by electrodeposition. We find that in all the samples the resistance reaches a residual value at T=4.2 K and the temperature dependence of resistance can be fitted to the Bloch-Grüneisen formula in the entire temperature range with a well defined transport Debye temperature (ΘR). The value of Debye temperature obtained from the fits lie within 8% of the bulk value for Ag wires of diameter 15 nm while for Cu nanowires of the same diameter the Debye temperature is significantly lesser than the bulk value. The electron-phonon coupling constants (measured by α el−ph or αR) in the nanowires were found to have the same value as that of the bulk. The resistivities of the wires were seen to increase as the wire diameter was decreased. This increase in the resistivity of the wires may be attributed to surface scattering of conduction electrons. The specularity p was estimated to be about 0.5. The observed results allow us to obtain the resistivities exactly from the resistance and gives us a method of obtaining the exact numbers of wires within the measured array (grown within the template).

We have measured the low frequency (1mHz ≤ f ≤ 10Hz) resistance fluctuations in metallic nanowires (diameter 15nm to 200nm) in the temperature range 77K to 400K. The nanowires were grown electrochemically in polycarbonate membranes and the measurements were carried out in arrays of nanowires by retaining them in the membrane. A large fluctuation in excess of conventional 1/f noise which peaks beyond a certain temperature was found. The fluctuations with a significant low frequency component (≃ 1/f 3/2 ) arise when the diameter of the wire ≃ 15nm and vanishes rapidly as the diameter is increased. We argue that Rayleigh-Plateau instability is the likely cause of this excess noise.

We have measured the low-frequency resistance fluctuations (1 mHz< f<10 Hz) in Ag nanowires of diameter 15 nm ≤d≤200 nm at room temperature. The power spectral density (PSD) of the fluctuations has a 1/fα character as seen in metallic films and wires of larger dimension. Additionally, the PSD has a significant low-frequency component and the value of α increases from the usual 1 to as the diameter d is reduced. The value of the normalized fluctuation also increases as the diameter d is reduced. We observe that there are new features in the 1/f noise as the size of the wire is reduced and they become more prominent as the diameter of the wires approaches 15 nm. It is important to investigate the origin of the new behaviour as 1/f noise may become a limiting factor in the use of metal wires of nanometre dimensions as interconnects.

Inductively coupled plasma (ICP) cryogenic dry etching was used to etch submicron pores, nano contact lines, submicron diameter pillars, thin and thick cantilevers, membrane structures and anisotropic deep structures with high aspect ratios in silicon for bio-nanoelectronics, optoelectronics and nano-micro electromechanical systems (NMEMS). The ICP cryogenic dry etching gives us the advantage of switching plasmas between etch rates of 13 nm min−1 and 4 µm min−1 for submicron pores and for membrane structures, respectively. A very thin photoresist mask can endure at −75 °C even during etching 70 µm deep for cantilevers and 300 µm deep for membrane structures. Coating the backsides of silicon membrane substrates with a thin photoresist film inhibited the lateral etching of cantilevers during their front release. Between −95 °C and −140 °C, we realized crystallographic-plane-dependent etching that creates facets only at the etch profile bottom. By varying the oxygen content and the process temperature, we achieved good control over the shape of the etched structures. The formation of black silicon during membrane etching down to 300 µm was delayed by reducing the oxygen content.