Rosenberg Samantha G, Barclay Michael, Fairbrother D Howard
Department of Chemistry, Johns Hopkins University , Baltimore, Maryland 21218, United States.
ACS Appl Mater Interfaces. 2014 Jun 11;6(11):8590-601. doi: 10.1021/am501457h. Epub 2014 May 12.
The elementary processes associated with electron beam-induced deposition (EBID) and post-deposition treatment of structures created from three metal(II)(hfac)2 organometallic precursors (metal = Pt, Pd, Cu; hfac = CF3C(O)CHC(O)CF3) have been studied using surface analytical techniques. Electron induced reactions of adsorbed metal(II)(hfac)2 molecules proceeds in two stages. For comparatively low electron doses (doses <1 × 10(17) e(-)/cm(2)) decomposition of the parent molecules leads to loss of carbon and oxygen, principally through the formation of carbon monoxide. Fluorine and hydrogen atoms are also lost by electron stimulated C-F and C-H bond cleavage, respectively. Collectively, these processes are responsible for the loss of a significant fraction (≥ 50%) of the oxygen and fluorine atoms, although most (>80%) of the carbon atoms remain. As a result of these various transformations the reduced metal atoms become encased in an organic matrix that is stabilized toward further electron stimulated carbon or oxygen loss, although fluorine and hydrogen can still desorb in the second stage of the reaction under the influence of sustained electron irradiation as a result of C-F and C-H bond cleavage, respectively. This reaction sequence explains why EBID structures created from metal(II)(hfac)2 precursors in electron microscopes contain reduced metal atoms embedded within an oxygen-containing carbonaceous matrix. Except for the formation of copper fluoride from Cu(II)(hfac)2, because of secondary reactions between partially reduced copper atoms and fluoride ions, the chemical composition of EBID films and behavior of metal(II)(hfac)2 precursors was independent of the transition metal's chemical identity. Annealing studies of EBID structures created from Pt(II)(hfac)2 suggest that the metallic character of deposited Pt atoms could be increased by using post deposition annealing or elevated substrate temperatures (>25 °C) during deposition. By exposing EBID structures created from Cu(II)(hfac)2 to atomic oxygen followed by atomic hydrogen, organic contaminants could be abated without annealing.
利用表面分析技术研究了与电子束诱导沉积（EBID）以及由三种金属（II）（hfac）₂有机金属前驱体（金属 = Pt、Pd、Cu；hfac = CF₃C（O）CHC（O）CF₃）生成的结构的沉积后处理相关的基本过程。吸附的金属（II）（hfac）₂分子的电子诱导反应分两个阶段进行。对于相对较低的电子剂量（剂量 <1×10¹⁷ e⁻/cm²），母体分子的分解导致碳和氧的损失，主要是通过一氧化碳的形成。氟原子和氢原子也分别通过电子激发的C - F键和C - H键断裂而损失。总体而言，这些过程导致相当一部分（≥50%）的氧原子和氟原子损失，尽管大部分（>80%）的碳原子保留下来。由于这些各种转变，还原后的金属原子被包裹在一个有机基质中，该有机基质对进一步的电子激发的碳或氧损失具有稳定性，尽管在持续电子辐照的影响下，由于C - F键和C - H键的断裂，氟和氢在反应的第二阶段仍可分别解吸。这个反应序列解释了为什么在电子显微镜中由金属（II）（hfac）₂前驱体生成的EBID结构包含嵌入含氧碳质基质中的还原金属原子。除了由于部分还原的铜原子与氟离子之间的二次反应由Cu（II）（hfac）₂形成氟化铜外，EBID薄膜的化学成分和金属（II）（hfac）₂前驱体的行为与过渡金属的化学特性无关。对由Pt（II）（hfac）₂生成的EBID结构进行的退火研究表明，通过使用沉积后退火或在沉积过程中提高衬底温度（>25°C），可以增加沉积的Pt原子的金属特性。通过将由Cu（II）（hfac）₂生成的EBID结构暴露于原子氧，然后再暴露于原子氢，可以在不进行退火的情况下减少有机污染物。
