Probing atmoic scale interface processes using X-rays and ions

ACS Appl. Mater. Interfaces

et al. 2019

A comprehensive study on the growth of nanoscale transition metal-on-transition metal (TM-on-TM) systems is presented. The near room-temperature intermixing and segregation phenomena during growth are studied in vacuo using high-sensitivity low-energy ion scattering. The investigated TM-on-TM systems are classified into four types according to the observed intermixing and segregation behavior. Empirical rules are suggested to qualitatively predict the growth characteristics of any TM-on-TM system based on the atomic size difference, surface-energy difference, and enthalpy of mixing between the film and substrate atoms. An exponential trend is observed in the effective interface width as a function of the surface-energy difference between the film and substrate layers, with a subtrend based on the crystal structure of the TM layers. A semiempirical model that accurately describes the experimental data is presented. It serves as a scaling law to predict the effective interface width and the minimum film thickness required for full film coverage in TM-on-TM systems in general. The ability to predict the growth characteristics as well as the interface width for any TM-on-TM system significantly contributes to the process of finding the best material combination for a specific application, where layer growth characteristics are implicitly considered when selecting materials based on their functional properties.

Section: Resultsmentioning

confidence: 99%

Section: Theoretical Backgroundmentioning

confidence: 99%

Nanoscale Transition Metal Thin Films: Growth Characteristics and Scaling Law for Interlayer Formation

Chandrasekaran

Kruijs

ACS Appl. Mater. Interfaces

et al. 2019

“…This approach was followed in order to avoid misinterpretation related to preferential sputtering and a possible matrix effect present in transition metal oxides 25 . Ru tracer analysis was not possible due to rapid saturated oxide thickness (∼ 1 min, Fig.…”

Section: Resultsmentioning

confidence: 99%

“…where Ep is the energy of the relative binary collision peak, Ex a specific energy in the tail signal, S the stopping of ions by the target and the constant 2.2 is derived from the instrument geometry 23,25,27 . Assuming the reionization probability to be constant for a given surface, the intensity of the tail can be applied for determining the in-depth distribution of atoms, as, for example, in determining the interface transition between two materials of different compositions 10,17,23,25 . The interface between two layers is not expected to be sharp due to intermixing and interface roughness.…”

Section: Methodology Of Oxide Thickness Determination By Leis Static mentioning

confidence: 99%

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Oxidation of metal thin films by atomic oxygen: A low energy ion scattering study

Boas

Journal of Applied Physics

Bijkerk

2019

In this study, we combine Low Energy Ion Scattering (LEIS) static and sputter depth profiles for characterization of the oxidation kinetics on Zr, Mo, Ru and Ta films of various thicknesses, following exposure to atomic oxygen at room temperature (∼20 • C). A method for non-destructive determination of the oxide growth rate via LEIS static depth profiling (static DP) is presented in detail. This method shows high sensitivity to the oxide thickness formed, and the results are in agreement with those obtained by X-ray reflectometry (XRR) and sputter depth profiling (sputter DP). Sequential exposures of oxygen isotopes in combination with LEIS sputter DP are applied to elucidate the growth mechanism of the oxide films. The results indicate that the oxidation kinetics at the applied experimental conditions is directly influenced by the metal work function, characterizing a Cabrera-Mott growth type. The maximum thickness of the formed oxide and oxide growth rate are in the order: Zr ≈ Ta > Mo > Ru. The combining of analysis by LEIS static DP and isotope tracing sputter DP is decisive in the characterization of oxidation kinetics in the room temperature regime.

Nb Texture Evolution and Interdiffusion in Nb/Si-Layered Systems

Chandrasekaran

Kruijs

ACS Appl. Mater. Interfaces

et al. 2021

In this paper, we present a detailed study on the microstructure evolution and interdiffusion in Nb/Si-layered systems. Interlayer formation during the early stages of growth in sputter-deposited Nb-on-Si and Si-on-Nb bilayer systems is studied in vacuo using a high-sensitivity low-energy ion-scattering technique. An asymmetric intermixing behavior is observed, where the Si-on-Nb interface is ∼2× thinner than the Nb-on-Si interface, and it is explained by the surface-energy difference between Nb and Si. During Nb-on-Si growth, the crystallization of the Nb layer occurs around 2.1 nm as-deposited Nb thickness with a strong Nb(110)-preferred orientation, which is maintained up to 3.3 nm as-deposited Nb thickness. A further increase in the Nb layer thickness above 3.3 nm results in a polycrystalline microstructure with a reduced degree of texture. High-resolution cross-sectional transmission electron microscopy imaging is performed on Nb/Si multilayers to study the effect of the Nb layer texture on interdiffusion during low-temperature annealing. Nb/Si multilayers with amorphous 2 nm Nb layers and strongly textured 3 nm thick Nb layers, with limited grain-boundary pathways for diffusion, show no observable interdiffusion during annealing at 200 °C for 8 h, whereas in a Nb/Si multilayer with polycrystalline 4 nm thick Nb layers, a ∼1 nm amorphous Nb/Si interlayer is formed at the Si-on-Nb interface during annealing.