Facile Fabrication of Single-Crystal-Diamond Nanostructures with Ultrahigh Aspect Ratio
Facile Fabrication of Single-Crystal-Diamond Nanostructures with Ultrahigh Aspect Ratio
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DOI：
10.1002/adma.201301343
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发表时间：
2013-08-07
影响因子：
29.4
通讯作者：
Degen, Christian
中科院分区：
文献类型：
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作者：
Tao, Ye;Degen, Christian
与批量制造的兼容性是NEMS应用中许多有前途的材料面临的技术挑战，包括碳纳米管，[1]石墨烯纳米带，[2，3]各种材料成分的纳米线，[4，5]和单晶金刚石。通常，多种原因阻止有前途的材料系统“批量生产”，例如材料合成期间的低产量，生长和加工期间控制几何形状、放置和取向的困难，以及成品器件质量的一致性差。单晶金刚石是具有无与伦比的材料性能的有前途的材料之一，由于其生长和加工的困难，这些材料性能尚未完全解锁。[6-9]这些困难是不幸的，因为钻石在许多尖端研究领域都有着迷人的前景。其卓越的机械性能有望通过简单的设备材料交换来推动力传感和光学机械方面的努力。[10-12]宽的光学透明窗口和高折射率对于可以集成在光网络中的等离子体和光子结构是理想的。[13]有意制造的晶格杂质和缺陷，如氮空位（NV）中心，有望用于环境条件下的单光子发生器和超灵敏磁场探测器。[14-17]单晶金刚石批量制造方法的可用性将大大加速这种集成和高质量金刚石器件的进展。单晶金刚石不能异质外延生长是金刚石纳米薄膜难以制备的主要原因。换句话说，目前没有具有微晶金刚石器件层的晶片可用。化学气相沉积（CVD）金刚石是目前工业生产中最高质量的材料，但其尺寸仅限于10× 10 mm（更常见的是4× 4 mm）以下，厚度为几百微米。该起始材料随后必须进行微机械加工和光刻处理，以获得所需的MEMS或NEMS器件。现有的制造单晶金刚石纳米结构的策略可以根据起始材料的性质大致分为三类。在没有特定的顺序，A类是直接在厚的抛光单晶的顶面上制造器件。到目前为止，采用的方法包括直接FIB加工，[8]通过对下面的牺牲层进行注入损伤，然后选择性去除，从块状金刚石中创建悬浮的表面层，[6，9，18，19]以及通过倾斜的各向异性等离子体蚀刻将电子束定义的抗蚀剂结构转移到块状金刚石。[20]类别B依赖于具有大晶粒尺寸的异质外延多晶金刚石膜。虽然是多晶的，但是如果相关的器件尺寸基本上小于晶粒尺寸，则该材料仍然可以表现出单晶质量。[21]在这里，合适的衬底层、专门的成核技术和足够的生长时间导致厚的多晶膜（> 10 μ m），其在顶表面具有富位错单晶的特征。[22]在金刚石生长和顶表面的机械抛光之后，支撑衬底和外延膜的主体部分需要经由等离子体蚀刻步骤从背侧移除以提供悬浮器件层。这种方法的优点是，
Compatibility with batch fabrication is a technological challenge facing many promising materials for NEMS applications, including carbon nanotubes,[1] graphene nanoribbons,[2, 3] nanowires of various material compositions,[4, 5] and single-crystal diamond. Often, multiple reasons prevent a promising material system from “going batch”, such as low yield during material synthesis, difficulty in controlling geometry, placement, and orientation during growth and processing, as well as poor consistency in the quality of finished devices. Single-crystal diamond is one of such promising materials with unparalleled material properties, which have not yet been fully unlocked due to difficulties associated with its growth and processing.[6–9] These difficulties are unfortunate because diamond holds fascinating promise for many cutting-edge fields of research. Its exceptional mechanical properties are poised to boost efforts in force sensing and optomechanics by a simple exchange of device material.[10–12] The wide optical transparency window and high refractive index are ideal for plasmonic and photo nic structures that may be integrated in optical networks.[13] Purposely created lattice impurities and defects, such as the nitrogen-vacancy (NV) center, hold promise for single photon generators and ultrasensitive detectors for magnetic fields under ambient conditions.[14–17] Progress toward such integrated and high-quality diamond devices would be greatly accelerated by the availability of methods for the batch-fabrication of single-crystal diamond. The main reason that makes diamond nanofabrication difficult is the fact that single-crystal diamond cannot be grown heteroepitaxially. In other words, no wafers with a singlecrystal diamond device layer are currently available. As a result, obtaining high-quality starting material that facilitates subsequent device elaboration becomes the central challenge.Chemical-vapor-deposited (CVD) diamond, the highest-quality material currently grown in industrial processes, is limited in size to< 10× 10 mm (more typically< 4× 4 mm) plates at a thickness of several hundred micrometers. This starting material must be subsequently micromachined and lithographically processed to arrive at the desired MEMS or NEMS device. Existing strategies for making single-crystal diamond nanostructures can be roughly divided into three categories based on the nature of the starting material. In no particular order, category A is the fabrication of devices directly on the top surface of a thick, polished single crystal. Methods employed so far include direct FIB machining,[8] creation of a suspended surface layer from bulk diamond via implantation damage to an underlying sacrificial layer followed by its selective removal,[6, 9, 18, 19] and transferring of ebeam-defined resist structures to the bulk diamond by angled anisotropic plasma etching.[20] Category B relies on heteroepitaxial polycrystalline diamond films with large grain size. Although polycrystalline, this material can still exhibit single-crystal quality if the relevant device dimensions are substantially smaller than the grain size.[21] Here, suitable substrate layers, specialized nucleation techniques, and sufficient growth time lead to a thick polycrystalline film (> 10 μ m) with characteristics of a dislocation-rich single-crystal at the top surface.[22] Following diamond growth and mechanical polishing of the top surface, the supporting substrate and the bulk part of the epitaxial film need to be removed from the backside via plasma etching steps to provide a suspended device layer. The advantage of this method is the possibility of