Vedestä ja 1,2-dikloorietaanista muodostetun mikroemulsion polarisoiminen

Mikroemulsioiden polarisoitavuutta ja polarisaation mittaamista on tutkittu varsin vähän. Ylipäätään mikroemulsioiden sähkökemiaa käsitteleviä kirjallisuuslähteitä on olemassa vain kourallinen, joten aiheeseen liittyvää perustutkimusta tarvitaan. Tässä Pro Gradu -tutkielmassa käsitellään litiumkloridin vesiliuoksesta, kahtaisionisesta betaiinisulfonaattisurfaktantista ja 1,2-dikloorietaanista muodostetun o/w -mikroemulsion yleisiä ominaisuuksia ja polarisoitavuutta. Mikroemulsion polarisaatiokokeet suoritettiin potentiometrisen titrauksen avulla. Mikroemulsio polarisoitiin liuottamalla siihen joko hydrofiilisesta kationista ja oleofiilisesta anionista tai oleofiilisesta kationista ja hydrofiilisesta anionista koostuvaa suolaa. Mikroemulsion vesifaasin ja 1,2-dikloorietaanifaasin välille muodostuva potentiaaliero mitattiin faasiselektiivisten elektrodien avulla. Tutkielman tulosten perusteella voitiin osoittaa, että tutkitun mikroemulsiosysteemin 1,2-DCE -faasi voidaan varata sekä positiiviseksi että negatiiviseksi ja että varauksesta aiheutuva, eri faasien välille muodostuva potentiaaliero voidaan mitata. Lisäksi voitiin osoittaa, että mikroemulsiosysteemien polarisoitavuuden tutkimiseen kehitettyä menetelmää voidaan hyödyntää useiden eri mikroemulsiosysteemien sähkökemiallisten ominaisuuksien tutkimisessa

Charge carrier dynamics in tantalum oxide overlayered and tantalum doped hematite photoanodes

We employ atomic layer deposition to prepare 50 nm thick hematite photoanodes followed by passivating them with a 0.5 nm thick Ta2O5-overlayer and compare them with samples uniformly doped with the same amount of tantalum. We observe a three-fold improvement in photocurrent with the same onset voltage using Ta-overlayer hematite photoanodes, while electrochemical impedance spectroscopy under visible light irradiation shows a decreased amount of surface states under water splitting conditions. The Tadoped samples have an even higher increase in photocurrent along with a 0.15 V cathodic shift in the onset voltage and decreased resistivity. However, the surface state capacitance for the Ta-doped sample is twice that of the reference photoanode, which implies a larger amount of surface hole accumulation. We further utilize transient absorption spectroscopy in the sub-millisecond to second timescale under operating conditions to show that electron trapping in both Ta2O5-passivated and Ta-doped samples is markedly reduced. Ultrafast transient absorption spectroscopy in the sub-picosecond to nanosecond timescale shows faster charge carrier dynamics and reduced recombination in the Ta-doped hematite photoanode resulting in the increased photoelectrochemical performance when compared with the Ta2O5-overlayer sample. Our results show that passivation does not affect the poor charge carrier dynamics intrinsic to hematite based photoanodes. The Ta-doping strategy results in more efficient electron extraction, solving the electron trapping issue and leading to increased performance over the surface passivation strategy.Peer reviewe

Conversion of ALD CuO Thin Films into Transparent Conductive p-Type CuI Thin Films

Copper iodide (CuI) is a high-performance p-type transparent semiconductor that can be used in numerous applications, such as transistors, diodes, and solar cells. However, the lack of conformal and scalable methods to deposit CuI thin films limits its establishment in applications that involve complex-shaped and/or large substrate areas. In this work, atomic layer deposition (ALD) is employed to enable scalable and conformal thin film deposition. A two-step approach relying on ALD of CuO and its subsequent conversion to CuI via exposure to HI vapor at room temperature is demonstrated. The resulting CuI films are phase-pure, uniform, and of high purity. Furthermore, CuI films on several substrates such as Si, amorphous Al2O3, n-type TiO2, and gamma-CsPbI3 perovskite are prepared. With the resulting n-TiO2/p-CuI structure, the easy and straightforward fabrication of a diode structure as a proof-of-concept device is demonstrated. Moreover, the successful deposition of CuI on gamma-CsPbI3 proves the compatibility of the process for using CuI as the hole transport layer in perovskite solar cell applications in the nip-configuration. It is believed that the ALD-based approach described in this work will offer a viable alternative for depositing transparent conductive p-type CuI thin films in applications that involve complex high aspect ratio structures and large substrate areas.Peer reviewe

Design aspects of all atomic layer deposited TiO2–Fe2O3 scaffold-absorber photoanodes for water splitting

Iron and titanium oxides have attracted substantial attention in photoelectrochemical water splitting applications. However, both materials suffer from intrinsic limitations that constrain the final device performance. In order to overcome the limitations of the two materials alone, their combination has been proposed as a solution to the problems. Here we report on the fabrication of an atomic layer deposited (ALD) Fe2O3 coating on porous ALD-TiO2. Our results show that successful implementation requires complete mixing of the TiO2 and Fe2O3 layers via annealing resulting in the formation of a photoactive iron titanium oxide on the surface. Moreover, we found that incomplete mixing leads to crystallization of Fe2O3 to hematite that is detrimental to the photoelectrochemical performance. IPCE and transient photocurrent measurements performed using UV and visible light excitation confirmed that the iron titanium oxide extends the photocurrent generation to the visible range. These measurements were complemented by transient absorption spectroscopy (TAS), which revealed a new band absent in pristine hematite or anatase TiO2 that we assign to charge transfer within the structure. Taken together, these results provide design guidelines to be considered when aiming to combine TiO2 and Fe2O3 for photoelectrochemical applications.Peer reviewe

Atomic layer deposition of cobalt(II) oxide thin films from Co(BTSA)(2)(THF) and H2O

In this work, we have studied the applicability of Co(BTSA)(2)(THF) [BTSA = bis(trimethylsilyl)amido] (THF = tetrahydrofuran) in atomic layer deposition (ALD) of cobalt oxide thin films. When adducted with THF, the resulting Co(BTSA)(2)(THF) showed good volatility and could be evaporated at 55 degrees C, which enabled film deposition in the temperature range of 75-250 degrees C. Water was used as the coreactant, which led to the formation of Co(II) oxide films. The saturative growth mode characteristic to ALD was confirmed with respect to both precursors at deposition temperatures of 100 and 200 degrees C. According to grazing incidence x-ray diffraction measurements, the films contain both cubic rock salt and hexagonal wurtzite phases of CoO. X-ray photoelectron spectroscopy measurements confirmed that the primary oxidation state of cobalt in the films is +2. The film composition was analyzed using time-of-flight elastic recoil detection analysis, which revealed the main impurities in the films to be H and Si. The Si impurities originate from the BTSA ligand and increased with increasing deposition temperature, which indicates that Co(BTSA)(2)(THF) is best suited for low-temperature deposition. To gain insight into the surface chemistry of the deposition process, an in situ reaction mechanism study was conducted using quadrupole mass spectroscopy and quartz crystal microbalance techniques. Based on the in situ experiments, it can be concluded that film growth occurs via a ligand exchange mechanism. Published by the AVS.Peer reviewe

Role of ALD Al2O3 Surface Passivation on the Performance of p-Type Cu2O Thin Film Transistors

High-performance p- type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low hole mobility and high off-state currents. We fabricated p-type TFTs with a phase-pure polycrystalline Cu2O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al2O3 passivation layer on the Cu2O channel, followed by vacuum annealing at 300 degrees C. Detailed characterization by transmission electron microscopy-energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of Cu2O is reduced following Al2O3 deposition and indicates the formation of a 1-2 nm thick CuAlO2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al2O3, leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.Peer reviewe

Low-Temperature Atomic Layer Deposition of Cobalt Oxide as an Effective Catalyst for Photoelectrochemical Water-Splitting Devices

We have developed a low-temperature atomic layer deposition (ALD) process for depositing crystalline and phase pure spinel cobalt oxide (Co3O4) films at 120 °C using [Co(tBu2DAD)2] and ozone as coreagent. X-ray diffraction, UV–vis spectroscopy, atomic force microscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and time-of-flight elastic recoil detection analysis were performed to characterize the structure and properties of the films. The as-deposited Co3O4 films are crystalline with a low amount of impurities (<2% C and <5% H) despite low deposition temperatures. Deposition of Co3O4 onto thin TiO2 photoanodes (100 nm) for water oxidation resulted in 30% improvement of photocurrent (after 10 ALD cycles yielding small Co3O4 particles) as compared to pristine TiO2 films), and exhibited no detrimental effects on photocurrent response up to 300 deposition cycles (approximately 35 nm thick films), demonstrating the applicability of the developed ALD process for deposition of effective catalyst particles and layers in photoelectrochemical water-splitting devices.Peer reviewe

Atomic Layer Deposition of Photoconductive Cu2O Thin Films

Herein, we report an atomic layer deposition (ALD) process for Cu2O thin films using copper(II) acetate [Cu(OAc)(2)] and water vapor as precursors. This precursor combination enables the deposition of phase-pure, polycrystalline, and impurity-free Cu2O thin films at temperatures of 180-220 degrees C. The deposition of Cu(I) oxide films from a Cu(II) precursor without the use of a reducing agent is explained by the thermally induced reduction of Cu(OAc)(2) to the volatile copper(I) acetate, CuOAc. In addition to the optimization of ALD process parameters and characterization of film properties, we studied the Cu2O films in the fabrication of photoconductor devices. Our proof-of-concept devices show that approx- imately 20 nm thick Cu2O films can be used for photodetection in the visible wavelength range and that the thin film photoconductors exhibit improved device characteristics in comparison to bulk Cu2O crystals.Peer reviewe

InDEx – Industrial Data Excellence

InDEx, the Industrial Data Excellence program, was created to investigate what industrial data can be collected, shared, and utilized for new intelligent services in high-performing, reliable and secure ways, and how to accomplish that in practice in the Finnish manufacturing industry.InDEx produced several insights into data in an industrial environment, collecting data, sharing data in the value chain and in the factory environment, and utilizing and manipulating data with artificial intelligence. Data has an important role in the future in an industrial context, but data sources and utilization mechanisms are more diverse than in cases related to consumer data. Experiences in the InDEx cases showed that there is great potential in data utili zation.Currently, successful business cases built on data sharing are either company-internal or utilize an existing value chain. The data market has not yet matured, and third-party offerings based on public and private data sources are rare. In this program, we tried out a framework that aimed to securely and in a controlled manner share data between organizations. We also worked to improve the contractual framework needed to support new business based on shared data, and we conducted a study of applicable business models. Based on this, we searched for new data-based opportunities within the project consortium. The vision of data as a tradeable good or of sharing with external partners is still to come true, but we believe that we have taken steps in the right direction.The program started in fall 2019 and ended in April 2022. The program faced restrictions caused by COVID-19, which had an effect on the intensity of the work during 2020 and 2021, and the program was extended by one year. Because of meeting restrictions, InDEx collaboration was realized through online meetings. We learned to work and collaborate using digital tools and environments. Despite the mentioned hindrances, and thanks to Business Finland’s flexibility, the extension time made it possible for most of the planned goals to be achieved.This report gives insights in the outcomes of the companies’ work within the InDEx program. DIMECC InDEx is the first finalized program by the members of the Finnish Advanced Manufacturing Network (FAMN, www.famn.fi).</p

Atomic Layer Deposition of Cobalt Oxide and Copper Oxide Thin Films

The focus of this thesis is the development and optimization of atomic layer deposition (ALD) processes of cobalt oxide and copper oxide thin films. Emphasis is placed also on the characterization of the chemical and physical properties of the obtained thin films. As materials, cobalt oxides and copper oxides are semiconducting, and they also absorb visible light. Therefore, these materials are potentially useful to be utilized in various electronic, optical and catalytic applications. ALD is a chemical gas-phase thin film synthesis technique that has several advantageous features, such as the ability to produce films with exceptional conformality on three-dimensional high aspect ratio structures, excellent uniformity of film thickness over large area substrates and accurate control of film thickness in a sub-nanometer range. The origin of these features is the unique film growth mechanism based on sequential and self-limiting gas-to-solid chemical reactions. In order to enable all the useful features of ALD in thin films deposition, the precursor chemistry must be studied, developed and above all, understood. Studies related to cobalt and copper ALD precursors have largely focused on the deposition of metallic thin films due to their applicability in the microelectronics industry. ALD of cobalt oxide and copper oxide, on the other hand, has received significantly less attention. The contribution of this PhD thesis toward cobalt oxide and copper oxide thin film deposition is four ALD process development studies on these materials. The Co(BTSA)2(THF) + H2O process could be used to deposit CoO films at temperatures of 75 – 250 ºC. However, the films deposited using this precursor combination contained an increased amount of H, C and Si impurities that originated from the BTSA ligands. The amount of impurities increased with increasing deposition temperature which suggests that Co(BTSA)2(THF) is not an ideal precursor for cobalt oxide film deposition with ALD. In-situ reaction mechanism studies gave evidence toward that the film growth occurs via a ligand exchange mechanism. The Cot–Bu(DAD)2 cobalt precursor was used together with O3 to deposit cobalt oxide films. The optimal deposition temperature for this process was 120 ºC, at which polycrystalline and phase-pure Co3O4 thin films were obtained. The formation of mixed valence Co3O4 films from a Co(II) precursor occurred due to the high oxidative power of O3. The Co3O4 films deposited at 120 ºC contained only a low amount of impurities, of which H was the most prominent at approximately a low 5 at-%. In photoelectrochemical studies, cobalt oxide nanoparticles were discovered to be efficient catalysts for the photoelectrochemical oxygen evolution reaction. The Cu(OAc)2 + H2O process produced crystalline Cu2O thin films at temperatures close to 200 ºC. During the process development study, it was found that Cu(OAc)2 is reduced to the volatile copper(I) acetate (CuOAc) when heated to its source temperature in ALD conditions. According to in-situ reaction mechanism studies and post-deposition film characterization, film growth proceeds via a ligand exchange route and results in the release of acetic acid as the reaction by-product. Elemental analysis of the films revealed that the Cu:O ratio of the films is close to the stoichiometric value of 2.0 and that the films contain exceptionally low amounts of impurities, 0.4 at-% H and ≤ 0.2 at-% C. The Cu(dmap)2 copper precursor was used at deposition temperatures of 80 – 140 ºC together with O3. This ALD chemistry produced polycrystalline and phase-pure CuO thin films with relatively low amount of impurities, ≤ 3.0 at-% H, C and N at the optimal deposition temperature for this process, 120 ºC.Tämän väitöskirjatyön aiheena on kobolttioksidi- ja kuparioksidiohutkalvojen valmistaminen atomikerroskasvatuksen (Atomic Layer Deposition, ALD) avulla. ALD on kemiallinen ohutkalvojen kasvatusmenetelmä, joka perustuu itserajoittuviin, pinnalla tapahtuviin kaasumaisten lähdeaineyhdisteiden reaktioihin. Eräs ALD:n tärkeistä ominaisuuksista on se, että kasvatettavien ohutkalvojen paksuutta voidaan hallita jopa materiaalin yksittäiskerroksen tarkkuudella. Lisäksi ALD:lla valmistaa ohutkalvoja, jotka peittävät päällystettävän pinnan tasaisesti nanometrimittakaavassa. ALD on myös toistettava ja skaalattava menetelmä, joten siitä on tullut tärkeä osa modernia materiaalitutkimusta. Koboltin oksidit ja kuparin oksidit ovat puolijohtavia ja ne myös absorboivat valoa näkyvän valon aallonpituuksilla. Näiden kahden ominaisuuden vuoksi koboltin ja kuparin oksideja voidaan hyödyntää esimerkiksi elektroniikan, optiikan ja katalyysin sovelluksissa. Työn aikana kehitettiin kaksi uutta ALD-prosessia kobolttioksidiohutkalvojen kasvattamiseen sekä kaksi uutta prosessia kuparioksidiohutkalvojen kasvattamiseen. Eräs tärkeä osa työtä oli selvittää, kuinka eri lähdeaineet ja reagenssien yhdistelmät vaikuttavat kasvatettujen kobolttioksidi- ja kuparioksidiohutkalvojen kemiallisiin ja fysikaalisiin ominaisuuksiin. Kokeellisessa työssä kiinnitettiin erityistä huomiota ohutkalvojen kasvattamisen kannalta olennaisten prosessiparametrien optimointiin. Lisäksi ohutkalvojen kasvumekanismeja tutkittiin molekyylitasolla hyödyntämällä kvartsikidemikrovaakaa ja massaspektroskopiaa. Tutkimuksen aikana kartoitettiin myös kobolttioksinanopartikkelien ja ohutkalvojen katalyyttisia ominaisuuksia valosähkökemiallisessa vedenpilkkomisreaktiossa sekä vain muutamien kymmenien nanometrien paksuisten kuparioksidiohutkalvojen toimivuutta valoilmaisinsovelluksissa.