Das Dhruba, Rao M S Ramachandra
Department of Physics, Quantum Centres in Diamond and Emergent Materials (QuCenDiEM)-group, Nano Functional Materials Technology Centre, Materials Science Research Centre, Indian Institute of Technology Madras Chennai 600036 India
RSC Adv. 2021 Jul 6;11(38):23686-23699. doi: 10.1039/d1ra03846j. eCollection 2021 Jul 1.
With the 200 keV N-ion implantation technique and a systematic variation of fluence, we report on the formation of highly conducting n-type diamond where insulator-to-metal transition (IMT) is observed above a certain fluence wherein the conductivity no longer obeys the hopping mechanism of transport rather, it obeys quantum corrections to Boltzmann conductivity at concentrations of ≥ 2 × 10 cm. The conductivity for ultra-nanocrystalline diamond is found to be high, ∼650 Ω cm with thermal activation energy ∼ 4 meV. Interestingly, with gradual increase in fluence, the conductivity in polycrystalline diamond films has been seen to progress from the hopping mechanism of transport in the case of low fluence implantation to a semiconducting nature with medium fluence and finally a semi-metallic conduction is observed where percolation occurs giving an insulator-to-metal transition. XANES confirms that the long-range order in diamond films remains intact when implanted with low and medium fluences; while implantation at sufficiently high fluences >5 × 10 cm leads to the formation of a disordered tetrahedral amorphous carbon network leading to metallic conduction resembling a metallic glass behaviour. XPS confirms that the sp fraction increases gradually with fluence starting from only 6% in the case of low fluence implantations and saturates at 40-50% for implantation at high fluences. A similar observation can be made for single crystal diamond when implanted at high fluence; it retains long-range order but percolative transport takes place through defects or semi-amorphized regions.
利用200 keV的氮离子注入技术以及通量的系统变化，我们报道了高导电性n型金刚石的形成情况。在一定通量以上观察到绝缘体-金属转变（IMT），其中在浓度≥2×10 cm时，电导率不再遵循跳跃传输机制，而是遵循对玻尔兹曼电导率的量子修正。发现超纳米晶金刚石的电导率很高，约为650Ω·cm，热激活能约为4 meV。有趣的是，随着通量逐渐增加，多晶金刚石薄膜中的电导率已被观察到从低通量注入时的跳跃传输机制发展到中等通量时的半导体性质，最后观察到半金属传导，此时发生渗流，出现绝缘体-金属转变。X射线吸收近边结构（XANES）证实，当以低通量和中等通量注入时，金刚石薄膜中的长程有序保持不变；而当以足够高的通量>5×10 cm注入时，会导致形成无序的四面体非晶碳网络，从而导致类似于金属玻璃行为的金属传导。X射线光电子能谱（XPS）证实，sp分数从低通量注入时仅6%开始随着通量逐渐增加，并在高通量注入时达到40 - 50%饱和。当以高通量注入时，单晶金刚石也有类似的观察结果；它保持长程有序，但渗流传输通过缺陷或半非晶化区域发生。
