In this work, we studied the evolution and transport of the native oxides during the atomic layer deposition (ALD) of TiO2 on GaAs(100) from tetrakis dimethyl amino titanium and H2O. Arsenic oxide transport through the TiO2 film and removal during the ALD process was investigated using transmission Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Experiments were designed to decouple these processes by utilizing their temperature dependence. A 4 nm TiO2 layer was initially deposited on a native oxide surface at 100 °C. Ex situ XPS confirmed that this step disturbed the interface minimally. An additional 3 nm TiO2 film was subsequently deposited at 150 to 250 °C with and without an intermediate thermal treatment step at 250 °C. Arsenic and gallium oxide removal was confirmed during this second deposition, leading to the inevitable conclusion that these oxides traversed at least 4 nm of film so as to react with the precursor and its surface reaction/decomposition byproducts. XPS measurements confirmed the relocation of both arsenic and gallium oxides from the interface to the bulk of the TiO2 film under normal processing conditions. These results explain the continuous native oxide removal observed for alkyl-amine precursor-based ALD processes on III-V surfaces and provide further insight into the mechanisms of film growth.

Atomic layer deposition (ALD) was used to deposit Ta2O5 on etched and native oxide-covered InAs(100) using pentakis dimethyl amino tantalum and H2O at 200–300 °C. The transport and removal of the native oxides during the ALD process was investigated using x-ray photoelectron spectroscopy (XPS). Depositions above 200 °C on etched surfaces protected the interface from reoxidation. On native oxide-covered surfaces, depositions resulted in enhanced native oxide removal at higher temperatures. The arsenic oxides were completely removed above 250 °C after 3 nm of film growth, but some of the As2O3 remained in the film at lower temperatures. Angle-resolved and sputter depth profiling XPS confirmed indium and arsenic oxide migration into the Ta2O5 film at deposition temperatures as low as 200 °C. Continuous removal of both arsenic and indium oxides was confirmed even after the deposition of several monolayers of a coalesced Ta2O5 film, and it was demonstrated that native oxide transport is a prevalent component of the interface “clean-up” mechanism.

This manuscript describes a simple process for fabricating gold-based, multi-layered, surface-enhanced Raman scattering (SERS) substrates that can be applied to a variety of different nanostructures, while still providing multi-layer enhancement factors comparable to those previously achieved only with optimized silver/silver oxide/silver substrates. In particular, gold multi-layered substrates generated by atomic layer deposition (ALD) have been fabricated and characterized in terms of their optimal performance, revealing multi-layer enhancements of 2.3-fold per spacer layer applied. These substrates were fabricated using TiO2 as the dielectric spacer material between adjacent gold layers, with ALD providing a conformal thin film with high surface coverage and low thickness. By varying the spacer layer thicknesses from sub-monolayer (non-contiguous) films through multiple TiO2 layer thick films, the non-monotonic spacer layer thickness response has been elucidated, revealing the importance of thin, contiguous dielectric spacer layers for optimal enhancement. Furthermore, the extended shelf life of these gold multi-layered substrates was characterized, demonstrating usable lifetimes (i.e. following storage in ambient conditions) of greater than five months, with the further potential for simple limited electrochemical regeneration even after this time.

Atomic Layer Deposition has been used to deposit a series of TiO 2 films on native oxide Si(100) at temperatures ranging from 100 to 300 • C using tetrakis(dimethylamino) titanium and H 2 O. The films were subjected to post-deposition thermal treatment and their structure, morphology and composition was examined. As-deposited films were amorphous and began to crystallize after thermal treatment at 500 • C. The films deposited at 100 • C and treated thermally at temperatures up to 900 • C for 10 min crystallized exclusively in the anatase phase forming crystallites with lateral size in excess of 200 nm. The films deposited at higher temperatures formed rutile crystallites with no mixing of the two phases. The films containing anatase grains exhibited significantly higher surface activity as evidenced by the detection of surface bound species such as carbonates (CO), carbon-nitrogen (CN) and nitrosyls. Although 100 • C is not within the ALD window for optimal film growth, it appears that the poor film adhesion to the substrate as well as the low film density and possibly the presence of carbon containing impurities result in the stabilization of anatase crystallites with lateral size at least one order of magnitude higher than it is widely reported in the literature.

In this manuscript we compare the interaction of alkyl (trimethyl aluminum) and alkyl amine (tetrakis dimethylamino titantium) precursors during thermal atomic layer deposition with III-V native oxides. For that purpose we deposit Al 2 O 3 and TiO 2 , using H 2 O as the oxidizer, on GaAs(100) and InAs(100) native oxide surfaces. We find that there are distinct differences in the behavior of the two films. For the Al 2 O 3 ALD very little native oxide removal happens after the first few ALD cycles while the interaction of the alkyl amine precursor for TiO 2 and the native oxides continues well after the surface has been covered with 2 nm of TiO 2. This difference is traced to the superior properties of Al 2 O 3 as a diffusion barrier. Differences are also found in the behavior of the arsenic oxides of the InAs and GaAs substrates. The arsenic oxides from the InAs surface are found to mix more efficiently in the growing dielectric film than those from the GaAs surface. This difference is attributed to lower native oxide stability as well as an initial diffusion path formation by the indium oxides.