以双金属嵌段共聚物自组装制备高密度磁性纳米阵列

With the ever-increasing data storage demands and the miniaturization of optoelectronic devices in the digital age of the 21st century, reliable, small size, high density and high-speed storage solutions are needed. As the areal density of commercial hard disk drives (HDD) is quickly approaching the terabit per inch square(Tb/in2) milestone, the strong demand in developing new functional materials or fabrication technologies to reach multi Tb/in2 level has drawn much academic and industrial attention. Traditional magnetic data storage is widely used today and the data storage density has increased rapidly. However, this still cannot fulfill the increasing need of information capacity and critically, the HDD industry is facing technical challenge for areal density of magnetic grains to be further increased. In order to further scale down the size of microscopic magnetic grains in increasing the storage capacity, the limitation imposed by their thermal stability (i.e. superparamagnetic effect) must be overcome. One of the promising technologies to relieve the problem of superparamagnetic limit is by using bit-patterned media (BPM) in which magnetic nanoarrays are fabricated and each “island” in the array forms a separate recording magnetic bit. However, the patterned media requires highly well-ordered nanoarrays with dimensions less than 12.5 nm to achieve the targeted areal density of 1 Tb/in2 and beyond, which challenges the basic state-of-the-art lithographic technologies nowadays. Herein, we propose to design and develop a new suite of metal containing block copolymers (BCPs) coupled with the usage of directed BCP self-assembly “bottom up” fabrication approach to create highly dense and ordered magnetic single domain patterns for BPM applications. As high magnetocrystalline anisotropy (Ku) and coercivity of magnetic materials are crucial for long-term stability of data storage to prevent demagnetization, metal alloys, such as FePt, FePd or FeCo metallic blocks will be pursued in the synthesis of BCPs. The connectivity constraints and the incompatibility between organic and metallic blocks in BCPs would induce spontaneous self-assembly into ordered patterns over large areas in thin film, therefore the position of metal alloy NPs is fixed and patterned to the molecular level after the selective etching and pyrolysis processes of the BCPs film. Metallic BCPs undergo microseparation into metal alloy rich nanodomains to ensure ultra-high density magnetic NPs in a single bit. This project offers versatile and cost-effective technologies and fabrication schemes to create higher areal density, greater uniformity and smaller size magnetic grains for the manufacture of BPM for future data storage devices.

人类对数据存储容量及光电器件微型化需求日益增加，急需开发新型功能材料及制备技术, 以达到小尺寸、可靠、高存储密度及速度的目标。晶格介质技术常用于制备磁性纳米阵列、有效减轻超顺磁效应。但为得到面密度超越兆位元,阵列必须高度有序及空间排列<12.5nm,对当今技术是巨大挑战。即或使用最先进的光刻技术以自下而上的模式制备金属纳米颗粒阵列,颗粒团聚现象常伴随发生,精确纳米颗粒原子组成及数量难以调控;此举使用的无机金属前驱体还需要进行相转变。故本项目將研发一系列可自组装含双金属嵌段共聚物，无需相转变,制备具有高磁录密度的有序磁单畴。引入合金嵌段确保较大磁晶各向异性常数和矫顽磁力，有利数据存储长期稳定及防止消磁。共聚物在薄膜诱导作用下可自组装成有序图案，经过对薄膜选择性刻蚀及热解,合金纳米颗粒可从分子水平上固定并图案化,确保每个位节中有超高磁录密度的纳米颗粒。为制造高密度存储设备提供廉价方法。

磁性合金纳米粒子，特别是铁铂、铁钯、钴铂等类型的纳米粒子，被视为是下一代开发超高密度磁存储系统的替代材料。本项目我们开发了一种以有机金属配合物作为前驱体一步热解制备面心四方相铁铂合金纳米粒子，并成功将该方法用于制备铁钯、钴铂、铁铜、铁镍、镍铂合金纳米粒子及铁、钴、镍、铂纳米粒子。通过调整分子结构或优化热解条件，不仅将磁性合金纳米粒子的的磁矫顽力大大提高至3.6 T，初步总结了热解条件对纳米粒子尺寸和性能的影响，而且通过对比小分子和聚合物前驱体表明分子间作用力更强的小分子配合物热解后易于形成尺寸较大的纳米粒子，通过调变聚合物前驱体中金属中心负载量可以进而调控纳米粒子的尺寸，这些研究成果为后续研究的深入开展奠定了坚实基础。此外，金属聚合物前驱体具有较好的溶液加工性，我们借助纳米压印技术可以快速制备大面积有序纳米阵列，热解后得到磁性纳米粒子组成的阵列，在磁力显微镜显现出明显的信号，可用于位元规则介质研究其磁存储性能。我们还通过嵌段共聚物自组装制备了小于25 nm的规则点阵，大大提高了其存储密度。我们还进一步将自组装和纳米压印技术结合在一起，对具有自组装性能的铁铂、铁钯配合物进行压印，成功制备了规则的自组装有序形貌。上述初步的研究成果已发表论文5篇，并有3篇文章正在投稿或者准备投稿。培养博士研究生3名。