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1. Electrodeposition of Ru onto Ru and Au Seed Layers from Solutions of Ruthenium Nitrosyl Sulfate and Ruthenium Chloride

   https://doi.org/10.1149/1945-7111/abff68  

   Gusley, Ryan ; Cumston, Quintin ; Coffey, Kevin R. ; West, Alan C. ; Barmak, Katayun ( May 2021 , Journal of The Electrochemical Society)

   The electrodeposition of Ru was investigated from solutions of ruthenium(III) nitrosyl sulfate and ruthenium(III) chloride onto seed layers of epitaxial and polycrystalline Ru and epitaxial Au. Using both galvanostatic and potentiostatic deposition modes, metallic Ru was found to electrodeposit as a porous layer comprised of (0001) oriented Ru crystallites, the presence of which was discovered and confirmed by X-ray and scanning transmission and transmission electron microscope (S/TEM) analyses. This finding was independent of the Ru salt and seed layer used. Using X-ray reflectivity (XRR), the average film density${\rho }_{eff}$of the porous electrodeposited Ru layer was measured as less than the density of bulk Ru${\rho }_{Ru,bulk}$(14.414 g cm⁻³). Increasing the magnitude of the applied current density from −100μA cm⁻²to −10 mA cm⁻²in solutions of Ru nitrosyl sulfate increased the${\rho }_{eff}$from 7.4 g cm⁻³to 9.7 g cm⁻²while the current efficiency decreased from 9.4% to 4.3%.
2. Influence of the Seed Layer and Electrolyte on the Epitaxial Electrodeposition of Co(0001) for the Fabrication of Single Crystal Interconnects

   https://doi.org/10.1149/1945-7111/abcd13  

   Gusley, Ryan ; Ezzat, Sameer ; Coffey, Kevin R. ; West, Alan C. ; Barmak, Katayun ( December 2020 , Journal of The Electrochemical Society)

   Co electrodeposition was performed onto single crystal Ru(0001) and polycrystalline Ru films to study the influence of such seed layers on the growth of epitaxial Co(0001). The effect of misfit strain on the electrodeposited Co(0001) films was studied using 60 and 10 nm-thick Ru(0001) seed layers, where the misfit strains of the Co layer on the two Ru(0001) seed layers are 7.9% and 9.6%, respectively. Despite a large misfit strain of 7.9%, the planar growth of Co(0001) was achieved up to a thickness of 42 nm before a transition to island growth was observed. Epitaxial Co films electrodeposited onto 10 nm Ru(0001) showed increased roughness when compared with Co electrodeposited onto the 60 nm seed layer. Co electrodeposition onto polycrystalline Ru resulted in a rough, polycrystalline film with faceted growth. Electrochemical experiments and simulations were used to study the influence of [Co²⁺] and solution pH on the throughput of the electrodeposition process. By increasing [Co²⁺] from 1 to 20 mM, the deposition rate of Co(0001) increased from 0.23 nm min⁻¹to 0.88 nm min⁻¹at an applied current density of −80μA cm⁻².
3. Flexible single-crystalline GaN substrate by direct deposition of III-N thin films on polycrystalline metal tape

   https://doi.org/10.1039/d0tc04634e  

   Shervin, Shahab ; Moradnia, Mina ; Alam, Md Kamrul ; Tong, Tain ; Ji, Mi-Hee ; Chen, Jie ; Pouladi, Sara ; Detchprohm, Theeradetch ; Forrest, Rebecca ; Bao, Jiming ; et al ( March 2021 , Journal of Materials Chemistry C)

   Flexible electronics and mechanically bendable devices based on Group III-N semiconductor materials are emerging; however, there are several challenges in manufacturing, such as cost reduction, device stability and flexibility, and device-performance improvement. To overcome these limitations, it is necessary to replace the brittle and expensive semiconductor wafers with single-crystalline flexible templates for a new-bandgap semiconductor platform. The substrates in the new concept of semiconductor materials have a hybrid structure consisting of a single-crystalline III-N thin film on a flexible metal tape substrate which provides a convenient and scalable roll-to-roll deposition process. We present a detailed study of a unique and simple direct epitaxial growth technique for crystallinity transformation to deliver single-crystalline GaN thin film with highly oriented grains along both a -axis and c -axis directions on a flexible and polycrystalline copper tape. A 2-dimensional (2D) graphene having the same atomic configuration as the (0001) basal plane of wurtzite structure is employed as a seed layer which plays a key role in following the III-N epitaxy growth. The DC reactive magnetron sputtering method is then applied to deposit an AlN layer under optimized conditions to achieve preferred-orientation growth. Finally, single-crystalline GaN layers (∼1 μm) are epitaxially grown using metal organicmore »chemical vapor deposition (MOCVD) on the biaxially-textured buffer layer. The flexible single-crystalline GaN film obtained using this method provides a new way for a wide-bandgap semiconductor platform pursuing flexible, high-performance, and versatile device technology.« less
4. The Resistivity Size Effect in Epitaxial Ru(0001) and Co(0001) Layers

   https://doi.org/10.1109/NANOTECH.2018.8653560  

   Milosevic, Erik ; Kerdsongpanya, Sit ; Gall, Daniel ( November 2018 , 2018 IEEE Nanotechnology Symposium (ANTS), Albany, NY, 2018)

   Ru(0001) and Co(0001) films with thickness d ranging from 5 to 300 nm are sputter deposited onto Al2O3(0001) substrates in order to quantify and compare the resistivity size effect. Both metals form epitaxial single crystal layers with their basal planes parallel to the substrate surface and exhibit a root-mean-square roughness < 0.4 nm for Ru and < 0.9 nm for Co. Transport measurements on these layers have negligible resistance contributions from roughness and grain boundary scattering which allows direct quantification of electron surface scattering. The measured resistivity ρ vs d is well described by the classical Fuchs-Sondheimer model, indicating a mean free path for transport within the basal plane of λ = 6.7 ± 0.3 nm for Ru and λ = 19.5 ± 1.0 nm for Co. Bulk Ru is 36% more resistive than Co; in contrast, Ru(0001) layers with d ≤ 25 nm are more conductive than Co(0001) layers, which is attributed to the shorter λ for Ru. The determined λ-values are utilized in combination with the Fuchs-Sondheimer and Mayadas-Shatzkes models to predict and compare the resistance of polycrystalline interconnect lines, assuming a grain boundary reflection coefficient R = 0.4 and accounting for the thinner barrier/adhesion layers available tomore »Ru and Co metallizations. This results in predicted 10 nm half-pitch line resistances for Ru, Co, and Cu of 1.0, 2.2, and 2.1 kΩ/µm, respectively.« less
5. In-vacuum measurements of optical scatter versus annealing temperature for amorphous Ta ₂ O ₅ and TiO ₂ :Ta ₂ O ₅ thin films

   https://doi.org/10.1364/JOSAA.415665  

   Capote, Elenna M. ; Gleckl, Amy ; Guerrero, Jazlyn ; Rezac, Michael ; Wright, Robert ; Smith, Joshua R. ( March 2021 , Journal of the Optical Society of America A)

   Optical coatings formed from amorphous oxide thin films have many applications in precision measurements. The Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo use coatings of$\mathrm{S}\mathrm{i}{\mathrm{O}}_2$(silica) and$\mathrm{T}\mathrm{i}{\mathrm{O}}_2:\mathrm{T}{\mathrm{a}}_2{\mathrm{O}}_5$(titania-doped tantala) and post-deposition annealing to 500°C to achieve low thermal noise and low optical absorption. Optical scattering by these coatings is a key limit to the sensitivity of the detectors. This paper describes optical scattering measurements for single-layer, ion-beam-sputtered thin films on fused silica substrates: two samples of$\mathrm{T}{\mathrm{a}}_2{\mathrm{O}}_5$and two of$\mathrm{T}\mathrm{i}{\mathrm{O}}_2:\mathrm{T}{\mathrm{a}}_2{\mathrm{O}}_5$. Using an imaging scatterometer at a fixed scattering angle of 12.8°, in-situ changes in the optical scatter of each sample were assessed during post-deposition annealing to 500°C in vacuum. The scatter of three of the four coated optics was observed to decrease during the annealing process, by 25–30% for tantala and up to 74% for titania-doped tantala, while the scatter frommore »the fourth sample held constant. Angle-resolved scatter measurements performed before and after vacuum annealing suggest some improvement in three of the four samples. These results demonstrate that post-deposition, high-temperature annealing of single-layer tantala and titania-doped tantala thin films in vacuum does not lead to an increase in scatter, and may actually improve their scatter.

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