Mr. Aveek Bid Profile

Aveek Bid

at Indian Institute of Science

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Proceedings Article | 23 May 2005 Paper

Experimental study of Rayleigh instability in metallic nanowires using resistance fluctuations measurements from 77K to 375K

Aveek Bid, Achyut Bora, Arup Raychaudhuri

Proceedings Volume 5843, (2005) https://doi.org/10.1117/12.609419

KEYWORDS: Resistance, Silver, Copper, Temperature metrology, Metals, Polymers, Interference (communication), Digital signal processing, Transformers, Nanowires

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Nanowires with high aspect ratio can become unstable due to Rayleigh-Plateau instability. The instability sets in below a certain minimum diameter when the force due to surface tension exceeds the limit that can lead to plastic flow as determined by the yield stress of the material of the wire. This minimum diameter is given d_m ≈ 2σ_S/σ_Y , where σ_S is the surface tension and σ_Y is the Yield force. For Ag and Cu we estimate that d_m ≈ 15nm. The Rayleigh instability (a classical mechanism) is severely modified by electronic shell effect contributions. It has been predicted recently that quantum-size effects arising from the electron confinement within the cross section of the wire can become an important factor as the wire is scaled down to atomic dimensions, in fact the Rayleigh instability could be completely suppressed for certain values of k_F r₀. Even for the stable wires, there are pockets of temperature where the wires are unstable. Low-frequency resistance fluctuation (noise) measurement is a very sensitive probe of such instabilities, which often may not be seen through other measurements. We have studied the low-frequency resistance fluctuations in the temperature range 77K to 400K in Ag and Cu nanowires of average diameter ≈ 15nm to 200nm. We identify a threshold temperature T* for the nanowires, below which the power spectral density S_V(f) ~1/f. As the temperature is raised beyond T* there is onset of a new contribution to the power spectra. We link this observation to onset of Rayleigh instability expected in such long nanowires. T* ~ 220K for the 15nm Ag wire and ~ 260K for the 15nm Cu wire. We compare the results with a simple estimation of the fluctuation based on Rayleigh instability and find good agreement.

Proceedings Article | 25 May 2004 Paper

Study of conductance fluctuations (1/f alpha noise) in metallic nanowires

Aveek Bid, Arup Raychaudhuri

Proceedings Volume 5469, (2004) https://doi.org/10.1117/12.545333

KEYWORDS: Silver, Temperature metrology, Diffusion, Resistance, Motion models, Data modeling, Metals, Transformers, Polymers, Nanowires

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We have studied the conductance fluctuations in silver nanowires in the temperature range 4K to 375K. The nanowires with an average diameter of 15nm were electrochemically deposited using polycarbonate membrane as template. Principal motivation is to study low frequency defect relaxations in the nanowires that give rise to conductance fluctuations with a spectral power S(f) ∝ 1/f^α. The Ag nanowires, stabilized at 400K with a current of few mA, show metallic temperature dependence. The S(f) was measured with a psuedo 4 probe ac technique with rms current of few tens of μA. We find that S_V(f) (which is ∝1/f^α) shows a rapid rise at around 220K as T is increased along with an enhancement in the exponent α. The exponent α≈1-1.1 for T<220 and it increases to ≈1.4 at T=375K. In the same temperature range S(f) rises by an order of magnitude. We analyze the data using a model assuming that there are two components to the 1/f^α fluctuations--one arising from relaxation of local defects give α≈1. The other arises from the long-range diffusion of defects characterized by α≈3/2. It is seen that for T < 220K the noise arises mainly from local defect relaxation and the temperature dependence of a follows the Dutta-Horn model. Above this temperature the contribution from long-range diffusion dominates with the noise becoming thermally activated with an activation energy (~300meV). Interestingly the activation energy is similar to but somewhat higher than that seen in micron sized films.

Proceedings Article | 9 May 2003 Paper

Low-frequency noise in charge-ordered system Pr0.63Ca0.37MnO3 near the charge-ordering transition and in the current-induced destabilized state

Aveek Bid, Arup Raychaudhuri

Proceedings Volume 5112, (2003) https://doi.org/10.1117/12.497030

KEYWORDS: Resistance, Temperature metrology, Spectroscopy, Picosecond phenomena, Carbon monoxide, Amplifiers, Commercial off the shelf technology, Crystals, Transformers, Ferromagnetics

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We have investigated the dynamics of co-existing phases in the Charge Ordered (CO) manganite Pr_0.63Ca_0.37MnO₃ using the technique of conductance noise spectroscopy. We note that close to the CO transition temperature T_co the spectral power of S_v(f)/V² deviates significantly from the 1/f frequency dependence for f≤0.12Hz. Our analysis shows that this deviation can be described by a single frequency Lorentzian with corner frequency f_c in addition to the usual broadband 1/f noise. Such a Lorentzian contribution to S_v(f)/V² can come from a two level system (TLS). In the time serioues this shows up as RTN. For T≤T_co the system shows the onset of a non-linear conduction close to a threshold value J_dc = J_th the noise spectra is mainly 1/f in nature. For J > J_th a large low frequency component of noise (characterized again by a frequency f_c) appears. We associate f_c with the relaxation time tc of the TLS fluctuator so the tc = 1/f_c. For thermal activation of the TLS the temperature dependence of f_c will follow f_c=f_oexp(-E_a/k_BT) where E_a is an energy barrier. The value of f_c shows an increase with J_dc showing that the value of the activation energy E_a is being lowered by the applied bias.

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