Oxide and carbide formation at titanium/organic monolayer interfaces.
Oxide and carbide formation at titanium/organic monolayer interfaces.
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DOI：
10.1021/ja710448e
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发表时间：
2008-03
影响因子：
15
通讯作者：
J. Blackstock;C. Donley;W. Stickle;D. Ohlberg;J. J. Yang-J.;D. Stewart;R. S. Williams
中科院分区：
文献类型：
--
作者：
J. Blackstock;C. Donley;W. Stickle;D. Ohlberg;J. J. Yang-J.;D. Stewart;R. S. Williams
X 射线光电子能谱 (XPS) 是通过超高真空 (UHV) 中的样品分层获得的一系列掩埋钛/有机单层界面得出的。这种埋入界面的传统表征需要离子铣削深度分析，这是一种经常通过化学还原铣削材料来破坏键合信息的高能过程。相比之下，我们表明，在真空中在金属/有机界面处分层样品会产生尖锐的非还原光谱，从而可以对埋入界面化学进行定量分析。使用这种 UHV 分层 XPS，我们检查了沉积在 Au、SiO2 或 PtO2 基底上的 C18 硬脂酸镉 Langmuir-Blodgett 单层上的钛蒸气。钛广泛用作有机厚膜金属化中的粘附层以及分子单层结的顶部金属接触，其中钛被认为形成几个原子厚的碳化钛覆盖层。我们在此确定，在许多条件下，钛反而会形成几纳米厚的钛氧化物覆盖层。 TiO2 和还原态 TiOx 两种物质都存在，其相对比例取决于氧气的可用性。在沉积过程中，氧气从环境、有机薄膜、尤其是基材本身中被吸收，产生取决于基材数量的氧化钛和碳化钛“损伤”。在 Au 基底上，高达 20% 的单分子层碳形成碳化钛，SiO2 基底约 15%，PtO2 基底 <5%。二氧化钛的形成也强烈依赖于沉积速率和腔室压力。
X-ray photoelectron spectra (XPS) are reported from a series of buried titanium/organic monolayer interfaces accessed through sample delamination in ultrahigh vacuum (UHV). Conventional characterization of such buried interfaces requires ion-mill depth profiling, an energetic process that frequently destroys bonding information by chemically reducing the milled material. In contrast, we show that delaminating the samples at the metal/organic interface in vacuum yields sharp, nonreduced spectra that allow quantitative analysis of the buried interface chemistry. Using this UHV delamination XPS, we examine titanium vapor deposited onto a C18 cadmium stearate Langmuir-Blodgett monolayer supported on Au, SiO2, or PtO2 substrates. Titanium is widely used as an adhesion layer in organic thick film metallization as well as a top metal contact for molecular monolayer junctions, where it has been assumed to form a few-atoms-thick Ti carbide overlayer. We establish here that under many conditions the titanium instead forms a few-nanometers-thick Ti oxide overlayer. Both TiO2 and reduced TiOx species exist, with the relative proportion depending on oxygen availability. Oxygen is gettered during deposition from the ambient, from the organic film, and remarkably, from the substrate itself, producing substrate-dependent amounts of Ti oxide and Ti carbide "damage". On Au substrates, up to 20% of the molecular-monolayer carbon formed titanium carbide, SiO2 substrates approximately 15%, and PtO2 substrates <5%. Titanium oxide formation is also strongly dependent on the deposition rate and chamber pressure.