Suchergebnisse

Thermoelectric properties of chromium nitride (CrN)-based films grown on c-plane sapphire by dc reactive magnetron sputtering were investigated. In this work, aluminum doping was introduced in CrN (degenerate n-type semiconductor) by co-deposition. Under the present deposition conditions, over-stoichiometry in nitrogen (CrN1+delta) rock-salt structure is obtained. A p-type conduction is observed with nitrogen-rich CrN combined with aluminum doping. The Cr0.96Al0.04N1.17 film exhibited a high Seebeck coefficient and a sufficient power factor at 300 degrees C. These results are a starting point for designing p-type/n-type thermoelectric materials based on chromium nitride films, which are cheap and routinely grown on the industrial scale. (C) 2018 The Japan Society of Applied Physics ; Funding Agencies|European Research Council under the European Communitys Seventh Framework Programme (FP)/ERC [335383]; Swedish Foundation for Strategic Research (SSF) through the Future Research Leaders 5 program; Swedish Research Council (VR) [621-2012-4430, 2016-03365]; Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; M.ERA-NET project MC2 - French ANR program [ANR-13-MERA-0002-02]; CTEC project [1305-00002B]

The authors study the morphological evolution of magnetron-sputtered thin silver (Ag) films that are deposited on weakly interacting silicon dioxide (SiO2) substrates in an oxygen-containing (O-2) gas atmosphere. In situ and real-time monitoring of electrically conductive layers, along with ex situ microstructural analyses, shows that the presence of O-2, throughout all film-formation stages, leads to a more pronounced two-dimensional (2D) morphology, smoother film surfaces, and larger continuous-layer electrical resistivities, as compared to Ag films grown in pure argon (Ar) ambient. In addition, the authors data demonstrate that 2D morphology can be promoted, without compromising the Ag-layer electrical conductivity, if O-2 is deployed with high temporal precision to target film formation stages before the formation of a percolated layer. Detailed real-space imaging of discontinuous films, augmented by in situ growth monitoring data, suggests that O-2 favors 2D morphology by affecting the kinetics of initial film-formation stages and most notably by decreasing the rate of island coalescence completion. Furthermore, compositional and bonding analyses show that O-2 does not change the chemical nature of the Ag layers and no atomic oxygen is detected in the films, i.e., O-2 acts as a surfactant. The overall results of this study are relevant for developing noninvasive surfactant-based strategies for manipulating noble-metal-layer growth on technologically relevant weakly interacting substrates, including graphene and other 2D crystals. ; Funding Agencies|Linkoping University ("LiU Career Contract) [Dnr-LiU-2015-01510]; Swedish Research CouncilSwedish Research Council [VR-2015-04630]; Olle Engkvist Foundation [SOEB 190-312]; Wenner-Gren Foundations [UPD2018-0071, UPD2019-0007]; French Government Program "Investissements dAvenir" (LABEX INTERACTIFS)French National Research Agency (ANR) [ANR-11-LABX-0017-01]; Aforsk Foundation; European Consortium of Innovative Universities (ECIU)

Continued downscaling of functional layers for key enabling devices has prompted the development of characterization tools to probe and dynamically control thin film formation stages and ensure the desired film morphology and functionalities in terms of, e.g., layer surface smoothness or electrical properties. In this work, we review the combined use of in situ and real-time optical (wafer curvature, spectroscopic ellipsometry) and electrical probes for gaining insights into the early growth stages of magnetron-sputter-deposited films. Data are reported for a large variety of metals characterized by different atomic mobilities and interface reactivities. For fcc noble-metal films (Ag, Cu, Pd) exhibiting a pronounced three-dimensional growth on weakly-interacting substrates (SiO2, amorphous carbon (a-C)), wafer curvature, spectroscopic ellipsometry, and resistivity techniques are shown to be complementary in studying the morphological evolution of discontinuous layers, and determining the percolation threshold and the onset of continuous film formation. The influence of growth kinetics (in terms of intrinsic atomic mobility, substrate temperature, deposition rate, deposition flux temporal profile) and the effect of deposited energy (through changes in working pressure or bias voltage) on the various morphological transition thicknesses is critically examined. For bcc transition metals, like Fe and Mo deposited on a-Si, in situ and real-time growth monitoring data exhibit transient features at a critical layer thickness of similar to 2 nm, which is a fingerprint of an interface-mediated crystalline-to-amorphous phase transition, while such behavior is not observed for Ta films that crystallize into their metastable tetragonal beta-Ta allotropic phase. The potential of optical and electrical diagnostic tools is also explored to reveal complex interfacial reactions and their effect on growth of Pd films on a-Si or a-Ge interlayers. For all case studies presented in the article, in situ data are complemented with and benchmarked against ex situ structural and morphological analyses. ; Funding Agencies|French Government program "Investissements dAvenir" (LABEX INTERACTIFS)French National Research Agency (ANR) [ANR-11-LABX-0017-01]; French Government program "Investissements dAvenir" (EUR INTREE)French National Research Agency (ANR) [ANR-18-EURE-0010]; Linkoping University ("LiU Career Contract) [Dnr-LiU-2015-01510]; Swedish research councilSwedish Research Council [VR-2015-04630]; AForsk foundation [AF 19-137, AF 19-746]; Olle Engkvist foundation [SOEB 190-312]; Wenner-Gren foundations [UPD2018-0071, UPD2019-0007]

The ability to reverse the inherent tendency of noble metals to grow in an uncontrolled three-dimensional (3D) fashion on weakly interacting substrates, including two-dimensional (2D) materials and oxides, is essential for the fabrication of high-quality multifunctional metal contacts in key enabling devices. In this study, we show that this can be effectively achieved by deploying nitrogen (N-2) gas with high temporal precision during magnetron sputtering of nanoscale silver (Ag) islands and layers on silicon dioxide (SiO2) substrates. We employ real-time in situ film growth monitoring using spectroscopic ellipsometry, along with optical modeling in the framework of the finite-difference time-domain method, and establish that localized surface plasmon resonance (LSPR) from nanoscale Ag islands can be used to gauge the evolution of surface morphology of discontinuous layers up to a SiO2 substrate area coverage of similar to 70%. Such analysis, in combination with data on the evolution of room-temperature resistivity of electrically conductive layers, reveals that presence of N-2 in the sputtering gas atmosphere throughout all film-formation stages: (i) promotes 2D growth and smooth film surfaces and (ii) leads to an increase of the continuous-layer electrical resistivity by similar to 30% compared to Ag films grown in a pure argon (Ar) ambient atmosphere. Detailed ex situ nanoscale structural analyses suggest that N-2 favors 2D morphology by suppressing island coalescence rates during initial growth stages, while it causes interruption of local epitaxial growth on Ag crystals. Using these insights, we deposit Ag layers by deploying N-2 selectively, either during the early precoalescence growth stages or after coalescence completion. We show that early N-2 deployment leads to 2D morphology without affecting the Ag-layer resistivity, while postcoalescence introduction of N-2 in the gas atmosphere further promotes formation of three-dimensional (3D) nanostructures and roughness at the film growth front. In a broader context this study generates knowledge that is relevant for the development of (i) single-step growth manipulation strategies based on selective deployment of surfactant species and (ii) real-time methodologies for tracking film and nanostructure morphological evolution using LSPR. ; Funding Agencies|French Government program "Investissements dAvenir" (LABEX INTERACTIFS)French National Research Agency (ANR) [ANR-11-LABX-0017-01]; Linkoping University [Dnr-LiU-2015-01510]; Swedish Research CouncilSwedish Research Council [VR-2015-04630]; AForsk foundation [AF 19-137, AF 19-746]; Olle Engkvist Foundation [SOEB 190-312]; Wenner-Gren Foundation [UPD2018-0071, UPD2019-0007]; Slovenian Research AgencySlovenian Research Agency - Slovenia [BI-US/18-20-08]; project "INNOVATION-EL" - Operational Program "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) [MIS 5002772]; European Union (European Regional Development Fund)European Union (EU)