Kristoffer Meinander

Atomic layer deposition of noble metals: Exploration of the low limit of the deposition temperature

The low limit of the deposition temperature for atomic layer deposition (ALD) of noble metals has been studied. Two approaches were taken; using pure oxygen instead of air and using a noble metal starting surface instead of Al2O3. Platinum thin films were obtained by ALD from MeCpPtMe3 and pure oxygen at deposition temperature as low as 200 °C, which is significantly lower than the low-temperature limit of 300 °C previously reported for the platinum ALD process in which air was use da s the oxygen source. The platinum films grown in this study had smooth surfaces, adhered well to the substrate, and had low impurity contents. ALD of ruthenium, on the other hand, took place at lower deposition temperatures on an iridium seed layer than on an Al2O3 layer. On iridium surface, ruthenium films were obtained from RuCp2 and oxygen at 225 °C and from Ru(thd)3 and oxygen at 250 °C, whereas no films were obtained on Al2O3 at temperatures lower than 275 and 325 °C, respectively. The crystal orientation of the ruthenium films was found to depend on the precursor. ALD of palladium from a palladium -ketoiminate precursor and oxygen at 250 and 275 °C was also studied. However, the film-growth rate did not saturate to a constant level when the precursor pulse times were increased.

Upper size limit of complete contact epitaxy

Abstract Recent developments in thin film manufacturing have given rise to an interest in the growth of nanocrystalline films on one hand, and using cluster deposition to grow epitaxial films on the other. Both kinds of films can be grown using cluster deposition at soft landing conditions. But for both kinds of growth one has to know the maximum cluster size for which a cluster becomes fully epitaxial with the substrate. Using molecular dynamics computer simulations we determine this cluster size limit for landing on a smooth surface in the temperature range 0–750 K. Below the limit completely epitaxial growth is possible, and above it a nanocrystalline phase will form.

Characterization of phosphatidylcholine/polyethylene glycol-lipid aggregates and their use as coatings and carriers in capillary electrophoresis.

PEG‐stabilized lipid aggregates are a promising new class of model membranes in biotechnical and pharmaceutical applications. CE techniques, field‐flow fractionation, light scattering, quartz crystal microbalance (QCM), and microscopic techniques were used to study aggregates composed of 1‐palmitoyl‐2‐oleyl‐sn‐glycero‐phosphatidylcholine (POPC) and PEG‐lipid conjugates. The PEG‐lipids, with PEG molar masses of 1000, 2000, and 3000, were 1,2‐diacyl‐sn‐glycero‐3‐phosphoethanolamine‐N‐[methoxy‐(PEG)] derivatives with either dimyristoyl (DM, 14:0) or distearoyl (DS, 18:0) acyl groups. The 80/20 mol% POPC/PEG‐lipid dispersions in HEPES at pH 7.4 were extruded through 100 nm size membranes. Asymmetrical flow field‐flow fractionation (AsFlFFF), photon correlation spectroscopy (PCS), and dynamic light scattering (DLS) were used to determine the sizes of POPC and the PEGylated aggregates. All methods demonstrated that the DSPEG‐lipid sterically stabilized aggregates were smaller in size than pure POPC vesicles. The zeta potentials of the aggregates were measured and showed an increase from −19 mV for pure POPC to −4 mV for the POPC/DSPEG3000 aggregates. Atomic force microscopy (AFM), electron cryo‐microscopy (EM), and multifrequency QCM studies were made to achieve information about the PEGylated coatings on silica. Lipid aggregates with different POPC/DSPEG3000‐lipid ratios were applied as capillary coating material, and the 80/20 mol% composition was found to give the most suppressed and stable EOFs. Mixtures of low‐molar‐mass drugs and FITC‐labeled amino acids were separated with the PEGylated aggregates as carriers (EKC) or as coating material (CEC). Detection was made by UV and LIF.

Atomic Layer Deposition of Crystalline MoS2 Thin Films: New Molybdenum Precursor for Low‐Temperature Film Growth

DOI: 10.1002/admi.201700123 Compared to the most well-known 2D material, graphene, which is a semi-metal, the semiconducting 2H phase of MoS2 is advantageous in having a band gap suitable for electronic applications. In bulk form, MoS2 has an indirect band gap of 1.3 eV, which increases as a function of decreasing film thickness. In monolayer MoS2 (thickness ≈0.6 nm), the band gap becomes direct with a width of 1.8 eV.[1] Importantly, to meet the requirements of different applications, properties of MoS2 and other TMDCs can be tuned by controlling the thickness,[1] doping and alloying,[5–8] surface modification and functionalization,[9–11] strain,[12,13] and by creating heterostructures with other 2D materials.[6,14–16] The appealing properties of TMDCs have led to a wide range of proposed applications. MoS2 has been extensively studied as a channel material in conventional field-effect transistors,[17–21] as well as phototransistors and other optoelectronic devices.[16,21,22] The 2D structure of TMDCs plays a crucial role in possible applications relying on more exotic quantum phenomena, such as valleytronics.[23,24] MoS2 has also shown promise in, for example, catalysis,[25] batteries,[26] photovoltaics,[27] sensors,[28] and medicine.[29] The production of high-quality, large-area MoS2 films with a thickness controllable down to a monolayer, as required in many of the aforementioned applications, still remains a major challenge. Additionally, in many cases, the processing temperature should be kept as low as possible in order to avoid damaging sensitive substrates, such as polymers or nanostructures. Initially, flakes of monolayer MoS2 were produced from natural MoS2 crystals using micromechanical exfoliation, a topdown method capable of producing high-quality monolayers, albeit with poor throughput as well as limited control over flake thickness and dimensions.[4,30,31] Liquid-phase exfoliation of bulk crystals, on the other hand, offers good scalability, but often suffers from limited flake size, poor crystallinity, or contamination.[4,31,32] Bottom-up methods offer a more controllable way to produce MoS2 films. High-quality MoS2 thin films are most commonly deposited by chemical vapor deposition (CVD) or sulfurization of metal or metal oxide thin films. The most common Molybdenum disulfide (MoS2) is a semiconducting 2D material, which has evoked wide interest due to its unique properties. However, the lack of controlled and scalable methods for the production of MoS2 films at low temperatures remains a major hindrance on its way to applications. In this work, atomic layer deposition (ALD) is used to deposit crystalline MoS2 thin films at a relatively low temperature of 300 °C. A new molybdenum precursor, Mo(thd)3 (thd = 2,2,6,6-tetramethylheptane-3,5-dionato), is synthesized, characterized, and used for film deposition with H2S as the sulfur precursor. Self-limiting growth with a low growth rate of ≈0.025 Å cycle−1, straightforward thickness control, and large-area uniformity are demonstrated. Film crystallinity is found to be relatively good considering the low deposition temperature, but the films have significant surface roughness. Additionally, chemical composition as well as optical and wetting properties are evaluated. MoS2 films are deposited on a variety of substrates, which reveal notable differences in growth rate, surface morphology, and crystallinity. The growth of crystalline MoS2 films at comparably low temperatures by ALD contributes toward the use of MoS2 for applications with a limited thermal budget.

Contact epitaxy in multiple cluster deposition

The specific properties of cluster-assembled thin films depend heavily on the size of deposited clusters as well as the energy with which they impact the substrate. When depositing at thermal energies, small enough clusters will align completely epitaxially with a smooth substrate, whereas larger clusters may form structures containing grains. As more clusters are deposited, however, they will no longer impact on a smooth surface, but rather on a surface roughened by previously deposited clusters. Using molecular dynamics simulations, the authors have determined the upper limit in cluster size for epitaxial deposition of multiple copper clusters at temperatures ranging from 0to750K.

In situ delipidation of low-density lipoproteins in capillary electrochromatography yields apolipoprotein B-100-coated surfaces for interaction studies.

An electrochromatographic method was developed for the in situ delipidation of intact low-density lipoprotein (LDL) particles immobilized on the inner wall of a 50-microm inner diameter silica capillary. In this method, the immobilized LDL particles were delipidated with nonionic surfactant Nonidet P-40 at pH 7.4 and 25 degrees C, resulting in an apolipoprotein B-100 (apoB-100)-coated capillary surface. The mobility of the electroosmotic flow marker dimethyl sulfoxide gave information about the surface charge, and the retention factors of beta-estradiol, testosterone, and progesterone were informative of the surface hydrophobicity. The calculated distribution coefficients of the steroids produced specific information about the affinity interactions of the steroids, with capillary surfaces coated either with intact LDL particles or with apoB-100. Delipidation with Nonidet P-40 resulted in a strong decrease in the hydrophobicity of the LDL coating. Atomic force microscopy images confirmed the loss of lipids from the LDL particles and the presence of apoB-100 protein coating. The in situ delipidation of LDL particles in capillaries represents a novel approach for the isolation of immobilized apoB-100 and for the determination of its pI value. The technique requires extremely low quantities of LDL particles, and it is simple and fast.

Potential gold(I) precursors evaluated for atomic layer deposition

In total, seven Au(I) compounds were synthesized and preliminarily evaluated for atomic layer deposition (ALD). One of the compounds, a liquid (bis(trimethylsilyl)amido)(triethylphosphine)gold(I) (Au(N(SiMe3)2)(PEt3)), was chosen for the ALD growth experiments. It was applied with potential reducing agents and hydrogen sulfide. The best results in respect to growth rate and film properties were achieved when Au(N(SiMe3)2)(PEt3) and dimethylamine borane [BH3(NHMe2)] were applied alternately. No perfect self-limiting growth, characteristic for ALD, was confirmed. However, the process produced polycrystalline, pure, and relatively uniform particulate Au thin films. In general, the process was well controllable, but the reduction power of BH3(NHMe2) was noticed to be dependent on the deposition temperature and on the surface in contact with it.

Isosorbide synthesis from cellulose with an efficient and recyclable ruthenium catalyst

Herein, we describe an efficient two-step pathway for isosorbide synthesis from cellulose with the use of new recyclable Ru-catalysts. We show that the oxidative and sulfonation treatments of the new Ru-catalysts increase the acidity and the hydrophilicity of the activated carbon support material, thus reducing the catalyst fouling caused by the build-up of insoluble products. Accordingly, the new Ru-catalysts are more resilient towards lignin containing cellulose than a commercial Ru/C catalyst, and the best Ru-catalyst maintains its high catalytic activity in four consecutive runs with dissolving pulp, microcrystalline cellulose and even with residual lignin containing bagasse pulp. Overall, our two-step approach provides isosorbide in high yields of 56–57 mol% (49–50 wt% of the substrate) from the cellulosic substrates.

Atomic layer deposition of tin oxide thin films from bis[bis(trimethylsilyl)amino]tin(II) with ozone and water

Tin oxide thin films were grown by atomic layer deposition (ALD) from bis[bis(trimethylsilyl)amino]tin(II) with ozone and water. The ALD growth rate of tin oxide films was examined with respect to substrate temperature, precursor doses, and number of ALD cycles. With ozone two ALD windows were observed, between 80 and 100 °C and between 125 and 200 °C. The films grown on soda lime glass and silicon substrates were uniform across the substrates. With the water process the growth rate at 100–250 °C was 0.05–0.18 A/cycle, and with the ozone process, the growth rate at 80–200 °C was 0.05–0.11 A/cycle. The films were further studied for composition and morphology. The films deposited with water showed crystallinity with the tetragonal SnO phase, and annealing in air increased the conductivity of the films while the SnO2 phase appeared. All the films deposited with ozone contained silicon as an impurity and were amorphous and nonconductive both as-deposited and after annealing. The films were further deposited ...

Low‐Temperature Wafer‐Scale Deposition of Continuous 2D SnS2 Films

Semiconducting 2D materials, such as SnS2 , hold immense potential for many applications ranging from electronics to catalysis. However, deposition of few-layer SnS2 films has remained a great challenge. Herein, continuous wafer-scale 2D SnS2 films with accurately controlled thickness (2 to 10 monolayers) are realized by combining a new atomic layer deposition process with low-temperature (250 °C) postdeposition annealing. Uniform coating of large-area and 3D substrates is demonstrated owing to the unique self-limiting growth mechanism of atomic layer deposition. Detailed characterization confirms the 1T-type crystal structure and composition, smoothness, and continuity of the SnS2 films. A two-stage deposition process is also introduced to improve the texture of the films. Successful deposition of continuous, high-quality SnS2 films at low temperatures constitutes a crucial step toward various applications of 2D semiconductors.