Heteroepitaxial diamond on iridium: New insights on domain formation

Abstract

Topography and chemical evolutions of the iridium surface in the successive steps of bias-enhanced nucleation and growth were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), and nano-Auger analyses. This sequential approach, which was performed in localized areas at the nanoscale, provides three new experimental and complementary concepts that can enhance the knowledge of nucleation pathways on iridium. First, SEM imaging at low-acceleration voltage enables the detection of diamond nuclei or stable precursors after the BEN step. Second, domains consist of iridium furrows that are covered by an amorphous carbon overlayer, with a thickness of 6.8 nm, according to AFM and X-ray photoemission spectroscopy data. Third, SEM observations also suggest a close relationship between furrows created under ion bombardment and domains in our study conditions. These results prompted us to propose a scheme that describes the topography and surface chemistry of domains.

Heteroepitaxial Growth of Single Crystal Diamond Films on Iridium: Procedure and Mechanism

“…初级核形成后, 会重整、规范其周围碳原子排 列结构形成排列规则的金刚石晶核, 从而不断扩大 形核区, 形成次级核(图 3(b3))。可以在扫描电子显 微镜照片中观测到该明亮区域 [69] , 这是形核过程的 特征形貌, 也是之后金刚石晶核生长的区域 [70] 。 原位 观测 BEN 过程及生长过程后的衬底, 可见外延的晶 粒几乎全部位于之前形成的明亮岛状区域内, 这些 区域外部几乎没有晶粒, 如图 4 所示。 可以利用这种 现象, 在衬底上预先设置"形核区", 从而达到选区 外延效果, 这也属于一种衬底图形化的方法 [71] 。 停止施加偏压并开始金刚石的生长过程 5~10 s 后, 在生长过程最初阶段腔体内甲烷浓度升高的情 况下, 之前因离子撞击稳定沉积在衬底表面的无定 型碳薄膜被快速刻蚀 [45] , 如图 3(b4)所示。…”

“…3 Procedure of single diamond eptaxial growth on Ir substrate [16,[60][61][62][63][64] 图 4 利用二次电子探测器观测到的 SEM 照片 [72] (a) BEN 过程后铱衬底表面形貌; (b) BEN 过程后铱衬底局部 表面形貌; (c)生长过程后同一位置形貌 Fig. 4 SEM images [72] of the iridium surface after BEN treatment (a), local spots after BEN (b) and after a subsequent growth step (c) 程即新金刚石晶核与形核阶段金刚石晶核的连接与 晶体尺寸增加过程。 比较常见的晶体材料的生长机制有奥斯特瓦尔 德熟化(Ostwald Ripening, OR) [73] 、定向附着生长 (Oriented Attachment, OA) [74] 和 柯 肯 达 尔 效 应 (Kirkendall Effect, KE) [75] 等。定向附着生长是团簇 沿着特定的晶向聚集并最终形成单晶或孪晶的过程, 具有非随机性 [76] 。由于金刚石在 Ir 衬底上较高的形 核密度, 金刚石生长的最初阶段更倾向于 OA 生长 机制, 可以认为定向附着生长即为金刚石缓慢生长 阶段的微观机理。 Li 等 [77] 首次利用透射电子显微镜观测到液体 中晶粒的定向附着生长过程, 如图 5 所示。 Dong 等 [69] 在外延薄膜中观测到薄膜和过渡层晶粒的拓扑衍生 定向附着生长现象, 如图 3(c1)所示。Dideikin 等 [78] 以爆轰法制备的纳米金刚石为原料, 在高温高压条 件下, 纳米金刚石颗粒相接触并发生倾斜、 旋转, 每 两个颗粒的相同晶面通过悬挂键相连接, 最终形成 1.5 μm 的单晶金刚石颗粒, 从而验证了固体颗粒之 间的定向附着生长机制。但是对于金刚石在形核生 长过程中的原位过程还缺少相应的研究仪器和研究 方法, 以至于金刚石的生长过程难以通过直观的方 法进行观测。 定向附着生长过程中, 晶界湮没形成金刚石单 晶是小角度晶界形成的楔形向错所导致的。 图 3(c2) 为立方晶中的小角晶界及部分形成楔形向错的结构 示意图, 楔形向错对应于一个不完整的倾斜晶界 [70] 。 可以推出晶粒尺寸 R 和晶界转变为楔形向错的临界 角 ω crit 之间的关系为 [32] :…”

Free exciton luminescence from a diamond p–i–n diode grown on a substrate produced by heteroepitaxy

“…Heteroepitaxial growth of diamond is one of the most important research targets to address size issues in diamond‐based electronic devices used for various applications. Heteroepitaxy on Ir was discovered by Sawabe et al, and some other groups have developed this technique to obtain large‐size and high‐quality heteroepitaxial diamond substrates . Previous studies have evaluated the doping and activation of donors and acceptors in chemical vapour deposition (CVD) films grown on heteroepitaxial diamond substrates .…”

Porous diamond foam with nanometric diamond grains using Bias Enhanced Nucleation on iridium

“…Iridium buffer layers were epitaxially grown on SrTiO3 (001) substrates using an evaporation cell [9]. Their polar and azimuthal misorientations measured by X-ray diffraction are 0.22° and 0.26°, respectively.…”

“…BEN process includes three different steps: a surface cleaning under pure hydrogen plasma with a MW power/pressure couple of 400W/20mbar during 10 min, a stabilization of the substrate temperature by adding 4 % of methane in hydrogen plasma before the BEN step during 10 min. Details about BEN conditions such as how to apply the bias voltage and measure the bias current on Ir/SrTiO3 were elsewhere reported [9]. Briefly, the substrate holder was electrically insulated from the metallic walls of the reactor, which were maintained at ground potential; thus, it was possible to apply a negative voltage to the substrate holder during plasma exposition.…”