Browsing by Author "Julin, Jaakko"
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- Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-01-01) Ylivaara, Oili M E; Kilpi, Lauri; Liu, Xuwen; Sintonen, Sakari; Ali, Saima; Laitinen, Mikko; Julin, Jaakko; Haimi, Eero; Sajavaara, Timo; Lipsanen, Harri; Hannula, Simo-Pekka; Ronkainen, Helena; Puurunen, RiikkaAtomic layer deposition (ALD) is based on self-limiting surface reactions. This and cyclic process enable the growth of conformal thin films with precise thickness control and sharp interfaces. A multilayered thin film, which is nanolaminate, can be grown using ALD with tuneable electrical and optical properties to be exploited, for example, in the microelectromechanical systems. In this work, the tunability of the residual stress, adhesion, and mechanical properties of the ALD nanolaminates composed of aluminum oxide (Al2O3) and titanium dioxide (TiO2) films on silicon were explored as a function of growth temperature (110-300 °C), film thickness (20-300 nm), bilayer thickness (0.1-100 nm), and TiO2 content (0%-100%). Al2O3 was grown from Me3Al and H2O, and TiO2 from TiCl4 and H2O. According to wafer curvature measurements, Al2O3/TiO2 nanolaminates were under tensile stress; bilayer thickness and growth temperature were the major parameters affecting the stress; the residual stress decreased with increasing bilayer thickness and ALD temperature. Hardness increased with increasing ALD temperature and decreased with increasing TiO2 fraction. Contact modulus remained approximately stable. The adhesion of the nanolaminate film was good on silicon. - Atomic Layer Deposition of Intermetallic Fe4Zn9 Thin Films from Diethyl Zinc
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-06-14) Ghiyasi, Ramin; Philip, Anish; Liu, Ji; Julin, Jaakko; Sajavaara, Timo; Nolan, Michael; Karppinen, MaaritWe present a new type of atomic layer deposition (ALD) process for intermetallic thin films, where diethyl zinc (DEZ) serves as a coreactant. In our proof-of-concept study, FeCl3 is used as the second precursor. The FeCl3 + DEZ process yields in situ crystalline Fe4Zn9 thin films, where the elemental purity and Fe/Zn ratio are confirmed by time-of-flight elastic recoil detection analysis (TOF-ERDA), Rutherford backscattering spectrometry (RBS), atomic absorption spectroscopy (AAS), and energy-dispersive X-ray spectroscopy (EDX) analyses. The film thickness is precisely controlled by the number of precursor supply cycles, as expected for an ALD process. The reaction mechanism is addressed by computational density functional theory (DFT) modeling. We moreover carry out preliminary tests with CuCl2 and Ni(thd)2 in combination with DEZ to confirm that these processes yield Cu−Zn and Ni−Zn thin films with DEZ as well. Thus, we envision an opening of a new ALD approach based on DEZ for intermetallic/metal alloy thin films. - Comparison of mechanical properties and composition of magnetron sputter and plasma enhanced atomic layer deposition aluminum nitride films
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-09-01) Sippola, Perttu; Pyymaki Perros, Alexander; Ylivaara, Oili M.E.; Ronkainen, Helena; Julin, Jaakko; Liu, Xuwen; Sajavaara, Timo; Etula, Jarkko; Lipsanen, Harri; Puurunen, Riikka L.A comparative study of mechanical properties and elemental and structural composition was made for aluminum nitride thin films deposited with reactive magnetron sputtering and plasma enhanced atomic layer deposition (PEALD). The sputtered films were deposited on Si (100), Mo (110), and Al (111) oriented substrates to study the effect of substrate texture on film properties. For the PEALD trimethylaluminum-ammonia films, the effects of process parameters, such as temperature, bias voltage, and plasma gas (ammonia versus N2/H2), on the AlN properties were studied. All the AlN films had a nominal thickness of 100 nm. Time-of-flight elastic recoil detection analysis showed the sputtered films to have lower impurity concentration with an Al/N ratio of 0.95, while the Al/N ratio for the PEALD films was 0.81-0.90. The mass densities were ∼3.10 and ∼2.70 g/cm3 for sputtered and PEALD AlN, respectively. The sputtered films were found to have higher degrees of preferential crystallinity, whereas the PEALD films were more polycrystalline as determined by x-ray diffraction. Nanoindentation experiments showed the elastic modulus and hardness to be 250 and 22 GPa, respectively, for sputtered AlN on the (110) substrate, whereas with PEALD AlN, values of 180 and 19 GPa, respectively, were obtained. The sputtered films were under tensile residual stress (61-421 MPa), whereas the PEALD films had a residual stress ranging from tensile to compressive (846 to −47 MPa), and high plasma bias resulted in compressive films. The adhesion of both films was good on Si, although sputtered films showed more inconsistent critical load behavior. Also, the substrate underneath the sputtered AlN did not withstand high wear forces as with the PEALD AlN. The coefficient of friction was determined to be ∼0.2 for both AlN types, and their wear characteristics were almost identical. - Droplet slipperiness despite surface heterogeneity at molecular scale
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-04) Lepikko, Sakari; Morais Jaques, Ygor; Junaid, Muhammad; Backholm, Matilda; Lahtinen, Jouko; Julin, Jaakko; Jokinen, Ville; Sajavaara, Timo; Sammalkorpi, Maria; Foster, Adam; Ras, RobinFriction determines whether liquid droplets slide off a solid surface or stick to it. Surface heterogeneity is generally acknowledged as the major cause of increased contact angle hysteresis and contact line friction of droplets. Here we challenge this long-standing premise for chemical heterogeneity at the molecular length scale. By tuning the coverage of self-assembled monolayers (SAMs), water contact angles change gradually from about 10° to 110° yet contact angle hysteresis and contact line friction are low for the low-coverage hydrophilic SAMs as well as high-coverage hydrophobic SAMs. Their slipperiness is not expected based on the substantial chemical heterogeneity of the SAMs featuring uncoated areas of the substrate well beyond the size of a water molecule as probed by metal reactants. According to molecular dynamics simulations, the low friction of both low- and high-coverage SAMs originates from the mobility of interfacial water molecules. These findings reveal a yet unknown and counterintuitive mechanism for slipperiness, opening new avenues for enhancing the mobility of droplets. - Enhancing electrocatalytic activity in metallic thin films through surface segregation of carbon
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-12-12) Kousar, Ayesha; Quliyeva, Ulviyya; Pande, Ishan; Sainio, Jani; Julin, Jaakko; Sajavaara, Timo; Karttunen, Antti J.; Laurila, TomiThin layers of commonly used adhesion metals i.e., Cr and Ti were annealed to investigate and estimate their impact on the electrochemical properties of the carbon nanomaterials grown on top of them. The microstructure, surface chemistry, and electrochemical activities of these materials were evaluated and compared with those of as-deposited thin films. The results from X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, grazing incidence X-ray diffraction (GIXRD), time-of-flight elastic recoil detection analysis (TOF-ERDA), and conductive atomic force microscopy (C-AFM) indicated the formation of a catalytic graphite layer on Cr following annealing, while no such layer was formed on Ti. This is attributed to the formation of the Cr2O3 layer on annealed Cr, which acts as a barrier to carbon diffusion into the underlying Cr. Conversely, Ti exhibits a high solubility for both carbon and oxygen, preventing the formation of the graphite layer. Cyclic voltammetry results showed that annealed Cr electrodes are electrochemically active towards both dopamine (DA) and ascorbic acid (AA) while no electrochemical activity is exhibited by annealed Ti. Quantum chemical calculations suggested that the presence of carbon as graphene or an amorphous form is critical for the oxidation reaction of probes. These results are significant for comprehending how the distinct solubilities of typical interstitial solutes influence the microstructure of adhesion metal layers and consequently yield diverse electrochemical properties. - Mechanical and optical properties of as-grown and thermally annealed titanium dioxide from titanium tetrachloride and water by atomic layer deposition
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-08-31) Ylivaara, Oili M.E.; Langner, Andreas; Liu, Xuwen; Schneider, Dieter; Julin, Jaakko; Arstila, Kai; Sintonen, Sakari; Ali, Saima; Lipsanen, Harri; Sajavaara, Timo; Hannula, Simo-Pekka; Puurunen, Riikka L.The use of thin-films made by atomic layer deposition (ALD) is increasing in the field of optical sensing. ALD TiO2 has been widely characterized for its physical and optical properties, but systematic information about the influence of thermal history to optical and mechanical properties of the film is lacking. Optical applications require planar surface and tunability of the refractive index and residual stress. In addition, mechanical properties such as elastic modulus and film hardness influence the performance of the layer, especially, when optics is integrated with microelectromechanical systems. In this work, optical properties, density, elemental analysis, residual stress, elastic modulus and hardness of as-grown ALD TiO2 thin films on silicon were studied at temperature range from 80 to 350 °C and influence of post-ALD thermal annealing was studied on films annealed up to 900 °C. ALD TiO2 films were under tensile stress in the scale of hundreds of MPa. The stress depended both on the ALD temperature and film thickness in a complex way, and onset of crystallization increased the residual stress. Films grown at 110 and 300 °C were able to withstand post-ALD annealing at 420 °C without major change in residual stress, refractive index or extinction coefficient. Elastic modulus and hardness increased upon crystallization with increasing ALD temperature. The results presented here help to improve the design of the optical devices by choosing films with desired optical properties, and further help to design the post-ALD thermal budget so that films maintain their desired features. - Ni Drastically Modifies the Microstructure and Electrochemistry of Thin Ti and Cr Layers
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-01-25) Kousar, Ayesha; Quliyeva, Ulviyya; Pande, Ishan; Sainio, Jani; Julin, Jaakko; Sajavaara, Timo; Jiang, Hua; Laurila, TomiThere is a significant lack of literature addressing changes in the microstructure of different interfacial metal layer combinations employed in fabricating electrochemical sensors based on carbon nanomaterials. This research gap extends to analyzing their influence on the electrochemical performance, which, in turn, impacts the understanding of the properties of materials incorporating these layers. In this study, microstructural variations and electrochemical activity of chromium and titanium adhesion layers, in combination with nickel catalyst layers (designated as TiNi and CrNi), on silicon wafers were analyzed post annealing. Interestingly, during a brief annealing period of 5 min, TiNi developed a surface layer comprising graphitic carbon, alongside the formation of TiO2, TiC, and NiSi, and exhibited electrochemical activity toward both dopamine (DA) and ascorbic acid (AA). Conversely, CrNi annealed for 5 min did not show the presence of such a carbon layer and displayed no discernible electrochemical activity toward the target molecules. Only after an extended annealing time of 20 min, signs of a carbon layer appear on CrNi, displaying a moderate electrochemical activity toward DA and AA. The formation of a carbon layer on CrNi is delayed due to the presence of Ni near the surface, which disrupts the local equilibrium. Consequently, the formation of the Cr2O3 barrier layer is delayed, which in turn permits carbon diffusion into the underlying Cr layer. Conversely, Ni stabilizes the β-Ti form and markedly decreases the solubility of carbon and oxygen within the TiNi system. By providing a comprehensive analysis of microstructural changes and their impact on the surface chemistry and electrochemical responses of commonly used interfacial metal layers, this paper offers invaluable insights in selecting suitable adhesion and catalyst layer combinations for carbon nanomaterial fabrication. - Thermomechanical properties of aluminum oxide thin films made by atomic layer deposition
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-12-01) Ylivaara, Oili M.E.; Langner, Andreas; Ek, Satu; Malm, Jari; Julin, Jaakko; Laitinen, Mikko; Ali, Saima; Sintonen, Sakari; Lipsanen, Harri; Sajavaara, Timo; Puurunen, Riikka L.In microelectromechanical system devices, thin films experience thermal processing at temperatures some cases exceeding the growth or deposition temperature of the film. In the case of the thin film grown by atomic layer deposition (ALD) at relatively low temperatures, post-ALD thermal processing or high device operation temperature might cause performance issues at device level or even device failure. In this work, residual stress and the role of intrinsic stress in ALD Al2O3 films grown from Me3Al and H2O, O3, or O2 (plasma ALD) were studied via post-ALD thermal processing. Thermal expansion coefficient was determined using thermal cycling and the double substrate method. For some samples, post-ALD thermal annealing was done in nitrogen at 300, 450, 700, or 900 °C. Selected samples were also studied for crystallinity, composition, and optical properties. Samples that were thermally annealed at 900 °C had increased residual stress value (1400-1600 MPa) upon formation of denser Al2O3 phase. The thermal expansion coefficient varied somewhat between Al2O3 made using different oxygen precursors. For thermal-Al2O3, intrinsic stress decreased with increasing growth temperature. ALD Al2O3 grown with plasma process had the lowest intrinsic stress. The results show that ALD Al2O3 grown at 200 and 300 °C is suitable for applications, where films are exposed to post-ALD thermal processing even at temperature of 700 °C without a major change in optical properties or residual stress. - Tuning of emission wavelength of CaS:Eu by addition of oxygen using atomic layer deposition
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-10-01) Rosa, José; Lahtinen, Jouko; Julin, Jaakko; Sun, Zhipei; Lipsanen, HarriAtomic layer deposition (ALD) technology has unlocked new ways of manipulating the growth of inorganic materials. The fine control at the atomic level allowed by ALD technology creates the perfect conditions for the inclusion of new cationic or anionic elements of the already-known materials. Consequently, novel material characteristics may arise with new functions for applications. This is especially relevant for inorganic luminescent materials where slight changes in the vicinity of the luminescent centers may originate new emission properties. Here, we studied the luminescent properties of CaS:Eu by introducing europium with oxygen ions by ALD, resulting in a novel CaS:EuO thin film. We study structural and photoluminescent properties of two different ALD deposited Eu doped CaS thin films: Eu(thd)3 which reacted with H2S forming CaS:Eu phosphor, or with O3 originating a CaS:EuO phosphor. It was found that the emission wavelength of CaS:EuO was 625.8 nm whereas CaS:Eu was 647 nm. Thus, the inclusion of O2- ions by ALD in a CaS:Eu phosphor results in the blue-shift of 21.2 nm. Our results show that ALD can be an effective way to introduce additional elements (e.g., anionic elements) to engineer the physical properties (e.g., inorganic phosphor emissions) for photonics and optoelectronics.