Search for: All records

Real-time detection of intermediate species and final products at the surface and near-surface in interfacial solid–gas reactions is critical for an accurate understanding of heterogeneous reaction mechanisms. In this article, an experimental method that can simultaneously monitor the ultrafast dynamics at the surface and above the surface in photoinduced heterogeneous reactions is presented. This method relies on a combination of mass spectrometry and femtosecond pump–probe spectroscopy. As a model system, the photoinduced reaction of methyl iodide on and above a cerium oxide surface is investigated. The species that are simultaneously detected from the surface and gas-phase present distinct features in the mass spectra, such as a sharp peak followed by an adjacent broad shoulder. The sharp peak is attributed to the species detected from the surface, while the broad shoulder is due to the detection of gas-phase species above the surface, as confirmed by multiple experiments. By monitoring the evolution of the sharp peak and broad shoulder as a function of the pump–probe time delay, transient signals are obtained that describe the ultrafast photoinduced reaction dynamics of methyl iodide on the surface and in the gas-phase. Finally, SimION simulations are performed to confirm the origin of the ions produced on the surface and in the gas-phase.

 

Real-time detection of intermediate species and final products at the surface and near-surface in interfacial solid-gas reactions is critical for an accurate understanding of heterogeneous reaction mechanisms. In this contribution, an experimental method that can simultaneously monitor the ultrafast dynamics at the surface and above the surface in photoinduced heterogeneous reactions is presented. The method relies on a combination of mass spectrometry and femtosecond pump-probe spectroscopy. As a model system, the photoinduced reaction of methyl iodide on and above a cerium oxide surface is investigated. The species that are simultaneously detected from the surface and gas-phase present distinct features in the mass spectra, such as a sharp peak followed by an adjacent broad shoulder. The sharp peak is attributed to the species detected from the surface while the broad shoulder is due to the detection of gas-phase species above the surface, as confirmed by multiple experiments. By monitoring the evolution of the sharp peak and broad shoulder as a function of the pump-probe time delay, transient signals are obtained that describe the ultrafast photoinduced reaction dynamics of methyl iodide on the surface and in gas-phase. Finally, SimION simulations are performed to confirm the origin of the ions produced on the surface and gas-phase.

 

Atomic layer deposition (ALD) of ruthenium (Ru) is being investigated for next generation interconnects and conducting liners for copper metallization. However, integration of ALD Ru with diffusion barrier refractory metal nitrides, such as tantalum nitride (TaN), continues to be a challenge due to its slow nucleation rates. Here, we demonstrate that an ultraviolet-ozone (UV-O3) pretreatment of TaN leads to an oxidized surface that favorably alters the deposition characteristics of ALD Ru from islandlike to layer-by-layer growth. The film morphology and properties are evaluated via spectroscopic ellipsometry, atomic force microscopy, electrical sheet resistance measurements, and thermoreflectance. We report a 1.83 nm continuous Ru film with a roughness of 0.19 nm and a sheet resistance of 10.8 KΩ/□. The interface chemistry between TaN and Ru is studied by x-ray photoelectron spectroscopy. It is shown that UV-O3 pretreatment, while oxidizing TaN, enhances Ru film nucleation and limits further oxidation of the underlying TaN during ALD. An oxygen “gettering” mechanism by TaN is proposed to explain reduced oxygen content in the Ru film and higher electrical conductivity compared to Ru deposited on native-TaN. This work provides a simple and effective approach using UV-O3 pretreatment for obtaining sub-2 nm, smooth, and conducting Ru films on TaN surfaces.

 

We study high-order harmonic generation from epitaxial ZnO films grown on Al₂O₃substrate. We observe a saturation of the harmonic intensity for a film thickness of 30 nm. 

Rigorous coupled wave analysis (RCWA) is conducted on in situ spectroscopic ellipsometry data to understand profile evolution during film deposition inside nanotrenches. Lithographically patterned SiO 2 nanotrenches are used as test structures. The nanotrenches are 170 nm wide at the top with a taper angle of 4.5° and are 300 nm in depth. Atomic layer deposition of ZnO is used as a model process where the thickness (cycles) of the film is varied from 0 (0 cycles) to 46 nm (300 cycles). The analysis predicts transient behavior in deposition affecting film conformality and changes to the trench taper angle. In the process, the aspect ratio varies from 2.05 at the start of the process to 6.67 at the end. The model predicts changes in the refractive index of the ZnO film as a function of thickness. The real and imaginary parts of the refractive index at a wavelength of 350 nm change from 1.81 to 2.37 and 0.25 to 0.87, respectively. Scanning electron microscopy cross sections confirm thickness at the top and bottom of the trench to within 13% of those predicted by RCWA. The experimentally measured conformality degrades as film deposition proceeds from 97.3% at 100 cycles to 91.1% at 300 cycles. These results demonstrate the potential of using RCWA for continuous and in situ monitoring of growth inside 3D nanostructures. 

We study the carrier-envelope phase (CEP) dependence of high-order harmonics generated in bulk ZnO crystals. The CEP dependence measured for laser polarization oriented parallel to and perpendicular to the c-axis exhibit different periodicities.