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Hardness and modulus of elasticity of atomic layer deposited Al2O3-ZrO2 nanolaminates and mixtures

This work was funded by the European Regional Development Fund project TK134 “Emerging orders in quantum and nanomaterials”, Estonian Research Agency project PRG4 “Emerging novel phases in strongly frustrated quantum magnets”.Atomic layer deposition was used to produce 90–105 nm thick alumina-zirconia mixtures and nanolaminate structures on soda-lime glass substrate. The resultant chemical and structural compositions of the thin films were characterized. Hardness and modulus of elasticity were determined by instrumented nanoindentation. The hardness of mixtures and nanolaminates were in the range of 11–15 GPa and moduli in the range of 140–180 GPa ZrO2 with 3.7 mol.-% Al2O3 crystallized in pure tetragonal phase and measured hardness reached about 15 GPa on glass substrate at indentation displacement of about 13 nm. Similar mechanical properties were measured in most thin films, except pure ZrO2, demonstrating insensitivity of mechanical properties to deposition receipt.ERDF TK134; Estonian Research Agency PRG4; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

RRAM Memories with ALD High-K Dielectrics: Electrical Characterization and Analytical Modeling

Resistive switching phenomena with adequate repetitiveness on Ta2O5-TiO2-Ta2O5 and TiO2-Ta2O5-TiO2 stacks are reported. In particular, 5–nm-thick TiO2 films embedding a monolayer of Ta2O5 show the best behavior in terms of bipolar cycles loop width, with separate low and high resistive states up to two orders of magnitude. Tantalum oxide layer increases the defect density in titania that becomes less leaky, and thus, resistive switching effects appear. Small signal ac parameters measured at low and medium frequencies, namely capacitance and conductance, also show hysteretic behavior during a whole bipolar switching cycle. This means that the memory state can be read at 0 V, without any power consumption. High-frequency measurements provide information about dipole relaxation frequency values in the dielectric bulk, and this can be connected with resistive switching behavior. Finally, a double tunneling barrier model fits I-V curves at the low-resistance state even at the bias range where reset occurs and a sharp fall takes place

Structure and behavior of ZrO2-graphene-ZrO2 stacks

Producción CientíficaZrO2-graphene-ZrO2 layered structures were built and their crystallinity was characterized before resistive switching measurements. Thin nanocrystalline ZrO2 dielectric films were grown by atomic layer deposition on chemical vapor deposited graphene. Graphene was transferred, prior to the growth of the ZrO2 overlayer, to the ZrO2 film pre-grown on titanium nitride. Nucleation and growth of the top ZrO2 layer was improved after growing an amorphous Al2O3 interface layer on graphene at lowered temperatures. Studies on resistive switching in such structures revealed that the exploitation of graphene interlayers could modify the operational voltage ranges and somewhat increase the ratio between high and low resistance states.Fondo Europeo de Desarrollo Regional (project TK134)Estonian Research Agency (grants PRG753 and PRG4)Ministerio de Economía, Industria y Competitividad (grant TEC2017-84321-C4-2-R

Aatomkihtsadestatud kilede ja nanokomposiitide mehaanilised omadused

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKäesolevas töös kasutati aatomkihtsadestamist koos teiste töövõtetega nano¬struk¬tuursete komposiitide valmistamiseks. Töö käigus valmistati kolme eri¬nevat tüüpi komposiite: kiud- või pulbertäitega ning laminaatsed komposiidid. Saadud materjalidel mõõdeti instrumentaalse nanoindenteerimisega elastsus¬moodulid ja kõvadused. Mõõtmistulemusi analüüsiti kasutades erinevaid teo¬reetilisi mudeleid. Katsed näitasid, et tõenäoliselt on kõige lihtsam valmistada laminaat¬struk¬tuuriga komposiite, mille korral ettevalmistused olid lihtsamad ja lisatöövõtteid kompaktse näidise saamiseks ei olnud vaja kasutada. Ülejäänud tüüpi struk¬tuuride korral on tõenäoliselt vaja lisauuringuid ja optimeerimist parimate tule¬muste saavutamiseks. Elastsusmoodulite mõõtmine näitas, et aatomkihtsadestatud kiled ei ole väga jäigad. Näiteks oli amorfse Al2O3 moodul umbes 3 korda väiksem korundi-tüüpi Al2O3-st (≈110 GPa vs ≈340 GPa). HfO2, Ta2O5, ZrO2 moodulid olid samuti väiksemad makroskoopiliste objektidega võrreldes. Komposiitsetel laminaatidel jäid elastsusmoodulid puhaste oksiidide moo¬dulite väärtuste vahepeale, välja arvatud ZrO2-Ta2O5 nanolaminaatide korral, milledel olid elastsumoodulid suuremad võrreldes puhaste koostisoksiididega. Nähtuse täpsed põhjused on veel välja selgitamata. Kõvaduse poolest olid puhtad Al2O3 ja HfO2 peaaegu 2 korda kõvemad klaasist alusest (vastavalt 11–12 GPa ja 6,7 GPa). Tsirkoonium- ja tantaaloksiid olid klaasile lähedase kõvadusega (≈7 GPa). Tulemustest saab järeldada, et ALD kiled on suhteliselt kõvad materjalid ja neid saaks sobitada erinevate materjalide elastsusmoodulitega kasutades erine¬vaid komposiitseid kooslusi. Viimane võib olla kasulik näiteks juhul, kui soovi¬takse kasutada ALD kilesid metallide või sulamite kaitsmiseks (nt korrosiooni¬kaitse). Samuti võimaldaks ALD kilede kasutamine muuta materjalide pindade mehaanilisi omadusi, mis võib olla vajalik näiteks mikro- või nanoelektor¬mehaaniliste seadmete (NEMS/MEMS) korral.In this study atomic layer deposition combined with several other techniques was used to produce nanostructured composites. Three structure types were realized: fiber or particle filled and laminated structures. Mechanical properties (modulus and hardness) of composites were tested using instrumented nanoindentation. The results were analyzed in the context of several theoretical models where reasonable. Tests have shown that it is probably the easiest to prepare ALD laminated composites, where preparations were simple and compact sample was obtained without additional work techniques. The remaining types of structures likely need further research and optimization for best results. The elastic modulus measurements showed that the ALD films were not very rigid. For example, an amorphous Al2O3 was about 3 times less than the modulus of corundum-type Al2O3 (i. e. about 110 GPa versus ≈340 GPa). HfO2, Ta2O5, ZrO2 modules were also lower compared to bulk objects in macroscale. Elastic moduli of the composite laminates were intermediate between the values of the pure oxides, with the exception of ZrO2-Ta2O5 nanolaminates, in which case the moduli were larger compared to pure oxides. The exact causes of the phenomenon are still unaccounted for. The hardness of pure Al2O3 and HfO2 were nearly two times harder than soda-lime-glass (11–12 GPa and 6.7 GPa, respectively). Zirconium, and tantalum oxide were close to the hardness of glass (≈7 GPa). Results suggest that ALD oxide films are relatively hard materials and they could be matched to the different elastic moduli of other materials using various composite structures. The latter may be useful, for example, if it is desired to use the ALD films on metals or alloys (e.g. for corrosion protection). ALD films also allow to change mechanical properties of material surfaces that may be necessary in, for example, micro- or nanoelectromechanical (NEMS/MEMS) devices

Atomic-Layer-Deposition-Made Very Thin Layer of Al₂O₃, Improves the Young’s Modulus of Graphene

Nanostructures with graphene make them highly promising for nanoelectronics, memristor devices, nanosensors and electrodes for energy storage. In some devices the mechanical properties of graphene are important. Therefore, nanoindentation has been used to measure the mechanical properties of polycrystalline graphene in a nanostructure containing metal oxide and graphene. In this study the graphene was transferred, prior to the deposition of the metal oxide overlayers, to the Si/SiO2 substrate were SiO2 thickness was 300 nm. The atomic layer deposition (ALD) process for making a very thin film of Al2O3 (thickness comparable with graphene) was applied to improve the elasticity of graphene. For the alumina film the Al(CH3)3 and H2O were used as the precursors. According to the micro-Raman analysis, after the Al2O3 deposition process, the G-and 2D-bands of graphene slightly broadened but the overall quality did not change (D-band was mostly absent). The chosen process did not decrease the graphene quality and the improvement in elastic modulus is significant. In case the load was 10 mN, the Young’s modulus of Si/SiO2/Graphene nanostructure was 96 GPa and after 5 ALD cycles of Al2O3 on graphene (Si/SiO2/Graphene/Al2O3) it increased up to 125 GPa. Our work highlights the correlation between nanoindentation and defects appearance in graphene

Influence of Annealing on Mechanical Behavior of Alumina-Tantala Nanolaminates

Mechanical properties of thin films are significant for the applicability of nanodevices. Amorphous Al2O3-Ta2O5 double and triple layers were atomic layer-deposited to the thickness of 70 nm with constituent single-layer thicknesses varying from 40 to 23 nm. The sequence of layers was alternated and rapid thermal annealing (700 and 800 °C) was implemented on all deposited nanolaminates. Annealing caused changes in the microstructure of laminates dependent on their layered structure. Various shapes of crystalline grains of orthorhombic Ta2O5 were formed. Annealing at 800 °C resulted in hardening up to 16 GPa (~11 GPa prior to annealing) in double-layered laminate with top Ta2O5 and bottom Al2O3 layers, while the hardness of all other laminates remained below 15 GPa. The elastic modulus of annealed laminates depended on the sequence of layers and reached up to 169 GPa. The layered structure of the laminate had a significant influence on the mechanical behavior after annealing treatments

Atomic-Layer-Deposition-Made Very Thin Layer of Al2O3, Improves the Young’s Modulus of Graphene

Nanostructures with graphene make them highly promising for nanoelectronics, memristor devices, nanosensors and electrodes for energy storage. In some devices the mechanical properties of graphene are important. Therefore, nanoindentation has been used to measure the mechanical properties of polycrystalline graphene in a nanostructure containing metal oxide and graphene. In this study the graphene was transferred, prior to the deposition of the metal oxide overlayers, to the Si/SiO2 substrate were SiO2 thickness was 300 nm. The atomic layer deposition (ALD) process for making a very thin film of Al2O3 (thickness comparable with graphene) was applied to improve the elasticity of graphene. For the alumina film the Al(CH3)3 and H2O were used as the precursors. According to the micro-Raman analysis, after the Al2O3 deposition process, the G-and 2D-bands of graphene slightly broadened but the overall quality did not change (D-band was mostly absent). The chosen process did not decrease the graphene quality and the improvement in elastic modulus is significant. In case the load was 10 mN, the Young’s modulus of Si/SiO2/Graphene nanostructure was 96 GPa and after 5 ALD cycles of Al2O3 on graphene (Si/SiO2/Graphene/Al2O3) it increased up to 125 GPa. Our work highlights the correlation between nanoindentation and defects appearance in graphene

Nanoindentation of Chromium Oxide Possessing Superior Hardness among Atomic-Layer-Deposited Oxides

Chromium (III) oxide is a technologically interesting material with attractive chemical, catalytic, magnetic and mechanical properties. It can be produced by different chemical and physical methods, for instance, by metal–organic chemical vapor deposition, thermal decomposition of chromium nitrate Cr(NO3)3 or ammonium dichromate (NH4)2Cr2O7, magnetron sputtering and atomic layer deposition. The latter method was used in the current work to deposit Cr2O3 thin films with thicknesses from 28 to 400 nm at deposition temperatures from 330 to 465 °C. The phase composition, crystallite size, hardness and modulus of elasticity were measured. The deposited Cr2O3 thin films had different structures from X-ray amorphous to crystalline α-Cr2O3 (eskolaite) structures. The averaged hardness of the films on SiO2 glass substrate varied from 12 to 22 GPa and the moduli were in the range of 76–180 GPa, as determined by nanoindentation. Lower values included some influence from a softer deposition substrate. The results indicate that Cr2O3 could be a promising material as a mechanically protective thin film applicable, for instance, in micro-electromechanical devices

Influence of α-Al2O3 Template and Process Parameters on Atomic Layer Deposition and Properties of Thin Films Containing High-Density TiO2 Phases

High-density phases of TiO2, such as rutile and high-pressure TiO2-II, have attracted interest as materials with high dielectric constant and refractive index values, while combinations of TiO2-II with anatase and rutile have been considered promising materials for catalytic applications. In this work, the atomic layer deposition of TiO2 on α-Al2O3 (0 0 0 1) (c-sapphire) was used to grow thin films containing different combinations of TiO2-II, anatase, and rutile, and to investigate the properties of the films. The results obtained demonstrate that in a temperature range of 300–400 °C, where transition from anatase to TiO2-II and rutile growth occurs in the films deposited on c-sapphire, the phase composition and other properties of a film depend significantly on the film thickness and ALD process time parameters. The changes in the phase composition, related to formation of the TiO2-II phase, caused an increase in the density and refractive index, minor narrowing of the optical bandgap, and an increase in the hardness of the films deposited on c-sapphire at TG ≥ 400 °C. These properties, together with high catalytic efficiency of mixed TiO2-II and anatase phases, as reported earlier, make the films promising for application in various functional coatings