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arXiv 1902.01908cond-mat.mtrl-sci
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氮氩混合气体中溅射纳米晶钨薄膜的超导电性

Superconductivity in nanocrystalline tungsten thin films growth by sputtering in a nitrogen-argon mixture

J. A. Hofer, Nestor Haberkorn

摘要:

本文报道了在室温下用N2:Ar混合气体(N2从3%到50%)溅射法生长的纳米晶钨薄膜的结构和超导特性。通过比较原始的和热退火的薄膜来鉴定结晶相。当N_2/(Ar+ N_2)为3 ~ 10%时,薄膜呈现纳米晶β-W相。在N2含量为20%~ 40%的混合气体中观察到β-W和W2 N相共存。详细研究了在8%N2混合气体中生长的W膜的超导特性随厚度的变化。对于该浓度,氮原子增加了纳米级的无序,减小了晶粒尺寸并避免了α-W的结晶。超导临界温度(Tc = 4.7 K)对厚度大于17 nm的薄膜是不依赖的。低于此厚度,Tc值系统地降低为3.1 K为4 nm厚的膜。我们的研究为制备纳米晶β-W薄膜提供了一种简单的方法,在超导器件中具有潜在的应用价值。

英文摘要:

We report on the structural and superconducting properties of nanocrystalline tungsten thin films growth by sputtering at room temperature with an N2:Ar mixture (N2 from 3% to 50%). The crystalline phases were identified by comparing pristine and thermal annealed thin films. For N2/(Ar+N2) mixtures between 3 and 10 %, the films display nanocrystalline beta-W phase. Coexistence of beta-W and W2N phases are observed for gas mixtures with N2 between 20 % and 40%. A detailed study of the superconducting properties as function of the thickness was performed for W films growth with 8 % N2 mixtures. For this concentration, the nitrogen atoms increase the disorder at the nanoscale reducing the grain size and avoiding the crystallization of alpha-W. The superconducting critical temperature (Tc = 4.7 K) is thickness independent for films thicker than ~ 17 nm. Below this thickness, the Tc value decreases systematically being 3.1 K for 4 nm thick films. Our study provides a simple method for the fabrication of nanocrystalline beta-W thin films with potential applications in superconducting devices.

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