Synthesis of colloidal Mn2+: ZnO quantum dots and high-Tc ferromagnetic nanocrystalline thin films
Synthesis of colloidal Mn2+: ZnO quantum dots and high-Tc ferromagnetic nanocrystalline thin films
复制标题
DOI：
10.1021/ja048427j
复制
发表时间：
2004-08-04
影响因子：
15
通讯作者：
Gamelin, DR
中科院分区：
文献类型：
--
作者：
Norberg, NS;Kittilstved, KR;Gamelin, DR
本文报道了胶体Mn2+掺杂ZnO （Mn2+:ZnO）量子点的合成和室温铁磁纳米晶薄膜的制备。在DMSO中，通过水解缩合反应制备了Mn2+:ZnO纳米晶体。通过电子吸收和电子顺磁共振（EPR）光谱对合成过程进行了监测。研究发现，Zn(OAc)(2)能有效抑制O-2对Mn2+的氧化作用，从而实现了Mn2+:ZnO的好氧合成。利用十二烷基胺去除纳米晶体表面的Mn2+离子，得到高质量的内掺杂Mn2+:ZnO胶体，其形状接近球形，直径均匀（6.1 +/- 0.7 nm）。模拟高分辨的X波段和q波段纳米晶体EPR光谱，结合磁化率的定量分析，证实了锰以Mn2+的形态被取代并入ZnO纳米晶体中，且形态非常均匀，与体Mn2+:ZnO仅在d应变量级上不同。自旋涂覆纳米晶体薄膜具有较强的铁磁性，300 K饱和矩高达1.35 mu(B)/Mn2+, T-C >为350 K。在铁磁薄膜的EPR谱中观察到明显的铁磁共振信号。本文结合前人的理论和实验结果，讨论了Mn2+:ZnO中铁磁性的发生及其与合成变量的关系。
We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)(2) was found to strongly inhibit oxidation of Mn2+ by O-2, allowing the synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn2+ :ZnO colloids of nearly spherical shape and uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing from bulk Mn2+ :ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin-coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 mu(B)/Mn2+ and T-C > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.