Esa Puukilainen

Atomic layer deposition and characterization of vanadium oxide thin films

In this study, VOx films were grown by atomic layer deposition (ALD) using V(NEtMe)4 as the vanadium precursor and either ozone or water as the oxygen source. V(NEtMe)4 is liquid at room temperature and shows good evaporation properties. The growth was investigated at deposition temperatures from as low as 75 °C, up to 250 °C. When using water as the oxygen source, a region of constant growth rate (ca. 0.8 A/cycle) was observed between 125 and 200 °C, with the ozone process the growth rate was significantly lower (0.31–0.34 A/cycle). The effect of the process conditions and post-deposition annealing on the film structure was investigated. By varying the atmosphere under which the films were annealed, it was possible to preferably form either VO2 or V2O5. Atomic force microscopy revealed that the films were smooth (rms < 0.5 nm) and uniform. The composition and stoichiometry of the films were determined by X-ray photoelectron spectroscopy. Conformal deposition was achieved in demanding high aspect ratio structure.

Study of a novel ALD process for depositing MgF2 thin films

Magnesium fluoride is an ultraviolet (UV) transparent material which is widely used in optical applications over a wide wavelength range. We have developed a novel atomic layer deposition (ALD) process for depositing magnesium fluoride thin films for the first time. MgF2 films were grown at 250–400 °C using Mg(thd)2 and TiF4 as precursors. The crystallinity, morphology, composition, thicknesses and refractive indices of the films were analyzed by X-ray diffraction/reflection (XRD/XRR), transmission electron microscopy (TEM), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), time-of-flight elastic recoil detection analysis (TOF-ERDA), and UV-vis spectrophotometry. Electrical properties were also measured. The growth rate was temperature dependent decreasing from 1.6 A cycle−1 at 250 °C to 0.7 A cycle−1 at 400 °C. The films were polycrystalline at 250–400 °C. The refractive indices were between 1.34–1.42 and the permittivity 4.9. The impurity levels were below 0.6 at.% in the films deposited at 350–400 °C.

Atomic Layer Deposition of Ruthenium Films from (Ethylcyclopentadienyl)(pyrrolyl)ruthenium and Oxygen

Ru films were grown by atomic layer deposition in the temperature range of 275―350°C using (ethylcyclopentadienyl)(pyrrolyl)ruthenium and air or oxygen as precursors on HF-etched Si, SiO 2 , ZrO 2 , and TiN substrates. Conformal growth was examined on three-dimensional silicon substrates with 20:1 aspect ratio. ZrO 2 promoted the nucleation of Ru most efficiently compared to other substrates, but the films roughened quickly on ZrO 2 with increasing film thickness. The minimum number of cycles required to form continuous and conductive metal layers could be decreased by increasing the length of the oxygen pulse. In order to obtain well-conducting Ru films growth to thicknesses of at least 8―10 nm on any surface was necessary. Resistivities in the ranges of 30―60 and 14―16 μΩ · cm were achieved for 4―6 and 10―15 nm thick films, respectively. Delamination became an issue in the Ru films grown to thicknesses about 10 nm and higher.

Iridium metal and iridium oxide thin films grown by atomic layer deposition at low temperatures

Atomic layer deposition (ALD) of both iridium and iridium oxide films at low temperatures has been studied and the resulting films have been examined by XRD, FESEM, XRR, EDX, AFM, TOF-ERDA, and four point probe measurements. Iridium oxide films were successfully grown using (MeCp)Ir(CHD) and ozone between 100 and 180 °C, however, the density of the films substantially reduced at 120 °C and below. The density reduction was accompanied by a phase change from crystalline to amorphous IrO2. Metallic iridium films were deposited between 120 and 180 °C by adding a reductive hydrogen pulse after the oxidative ozone pulse. Comparison of these processes with the earlier process employing the same Ir precursor with molecular oxygen is also made. The (MeCp)Ir(CHD)–O3–H2 process is able to produce metallic films at about 100 °C lower temperature than the oxygen based process.

Liposomes for entrapping local anesthetics: A liposome electrokinetic chromatographic study

Bupivacaine is a lipophilic, long‐acting, amide class local anesthetic commonly used in clinical practice to provide local anesthesia during surgical procedures. Several cases of accidental overdose with cardiac arrest and death have been reported since bupivacaine was introduced to human use. Recent case reports have suggested that Intralipid (Fresenius Kabi) is an effective therapy for cardiac toxicity from high systemic concentrations of, e.g. bupivacaine, even though the mechanism behind the interaction is not fully clear yet. Our long‐term aim is to develop a sensitive, efficient, and non‐harmful lipid‐based formulation to specifically trap harmful substances in vivo. In this study, the in vitro interaction of local anesthetics (bupivacaine, prilocaine, and lidocaine) with Intralipid or lipid vesicles containing phosphatidylglycerol, phosphatidylcholine, cardiolipin, cholesterol, and N‐palmitoyl‐D‐erythro‐sphingosine (ceramide) was determined by liposome electrokinetic chromatography. The interactions were evaluated by calculating the retention factors and distribution constants. Atomic force microscopy measurements were carried out to confirm that the interaction mechanism was solely due to interactions between the analytes and the moving pseudostationary phase and not by interactions with a stationary lipid phase adsorbed to the fused‐silica wall. The heterogeneity of the liposomes was also studied by atomic force microscopy. The liposome electrokinetic chromatography results demonstrate that there is higher interaction between the drugs and negatively charged liposome dispersion than with the commercial Intralipid dispersion.

MeCp)Ir(CHD) and molecular oxygen as precursors in atomic layer deposition of iridium

Iridium thin films were grown by atomic layer deposition (ALD) between 225 and 350 °C using (MeCp)Ir(CHD) (MeCp = methylcyclopentadienyl, CHD = cyclohexadiene) and molecular oxygen as precursors. (MeCp)Ir(CHD) precursor was synthesized and characterized in-house. Also the crystal structure of (MeCp)Ir(CHD) is reported. All the ALD grown Ir films passed a common tape test indicating a good adhesion on Al2O3 nucleation layer. Quite untypically, surface roughness was the highest on films deposited at 225–250 °C and decreased strongly by increasing deposition temperature. Partial decomposition of the (MeCp)Ir(CHD) precursor resulted in defects on the film surface at 350 °C. Ir thin films with good quality were obtained at the deposition temperatures of 275 and 300 °C. A 50 nm thick film grown at 275 °C had a roughness of 1.2 nm, contained about 3 at% oxygen, 0.6 at% carbon and 1.6 at% hydrogen impurities, while the resistivity was as low as 9 µΩ cm.

Atomic layer deposition and characterization of Bi₂Te₃ thin films.

Bi2Te3 thin films were deposited by atomic layer deposition (ALD) from BiCl3 and (Et3Si)2Te at 160-300 °C. The process was studied in detail, and growth properties typical of ALD were verified. Films were stoichiometric with low impurity content. The film thickness was easily controlled with the number of deposition cycles. Properties of the ALD Bi2Te3 thin films were found to be comparable to those reported in literature for Bi2Te3 films made by other methods. Films crystallized to a rhombohedral phase, and there was a preferred orientation to the growth. Electrical and thermoelectric properties were also determined to be comparable to literature values.

Studies on atomic layer deposition of IRMOF-8 thin films

Deposition of IRMOF-8 thin films by atomic layer deposition was studied at 260–320 °C. Zinc acetate and 2,6-naphthalenedicarboxylic acid were used as the precursors. The as-deposited amorphous films were crystallized in 70% relative humidity at room temperature resulting in an unknown phase with a large unit cell. An autoclave with dimethylformamide as the solvent was used to recrystallize the films into IRMOF-8 as confirmed by grazing incidence x-ray diffraction. The films were further characterized by high temperature x-ray diffraction (HTXRD), field emission scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), time-of-flight elastic recoil detection analysis (TOF-ERDA), nanoindentation, and energy-dispersive x-ray spectroscopy. HTXRD measurements revealed similar behavior to bulk IRMOF-8. According to TOF-ERDA and FTIR, composition of the films was similar to IRMOF-8. Through-porosity was confirmed by loading the films with palladium using Pd(thd)2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) as the precursor.

Surface fingerprints of individual silicon nanocrystals in laser-annealed Si/SiO2 superlattice: Evidence of nanoeruptions of laser-pressurized silicon

Silicon nanocrystals prepared by continuous-wave laser annealing of a free-standing Si/SiO2 superlattice are studied for the first time by using methods of surface analysis (scanning electron microscopy and atomic force microscopy). The surface topology and composition are compared with transmission electron microscopy images that show a projection through the whole film, allowing us to discriminate silicon nanocrystals located near the film surface. These nanocrystals have an unusual pear-like shape with the thinner part sticking out of the laser-illuminated surface. The non-spherical shape of these nanocrystals is explained by eruption of silicon pressurized at the stage of crystallization from the melt phase. This hypothesis is supported by the micro-Raman spectra which show low stress near the surface features, in contrast to the neighbouring regions having high compressive stress.

Correlation Between Film Properties and Anhydrous HF Vapor Etching Behavior of Silicon Oxide Deposited by CVD Methods

The anhydrous HF vapor etching of sacrificial silicon dioxide films grown by plasma-enhanced and low-pressure chemical vapor deposition (PECVD and LPCVD) methods was studied. The film compositions and etch residue were analyzed as part of the study. The effects of the oxide deposition method, precursors, annealing and oxide composition on the etch rate are discussed. Annealing decreases the etch rate and removes water and other hydrogen-containing residue from the films. Films grown using a tetraethoxy-silane (TEOS) precursor etch fast, unannealed films even 30 times faster than thermal oxide and they also contain more OH-species than films from SiH 4 precursors even after annealing. The etch rate of all CVD films is close to that of thermal oxide after annealing at 1000°C, around 0.1 μm/min. Etch rate differences between CVD films are much larger than those observed during wet HF etching.