Showing papers by "Ulf Helmersson published in 2000"
TL;DR: In this paper, a novel high power density pulsed plasma discharge is presented, which consists of metallic and inert gas ions, determined from time resolved Langmuir probe measurements and in situ optical emission spectroscopy data.
Abstract: Time resolved plasma probe measurements of a novel high power density pulsed plasma discharge are presented. Extreme peak power densities in the pulse (on the order of several kW cm−2) result in a very dense plasma with substrate ionic flux densities of up to 1 A cm−2 at source-to-substrate distances of several cm and at a pressure of 0.13 Pa (1 mTorr). The pulse duration was ∼100 μs with a pulse repetition frequency of 50 Hz. The plasma consists of metallic and inert gas ions, as determined from time resolved Langmuir probe measurements and in situ optical emission spectroscopy data. It was found that the plasma composition at the beginning of the pulse was dominated by Ar ions. As time elapsed metal ions were detected and finally dominated the ion composition. The effect of the process parameters on the temporal development of the ionic fluxes is discussed. The ionized portion of the sputtered metal flux was found to have an average velocity of 2500 m s−1 at 6 cm distance from the source, which conforms...
279 citations
TL;DR: In this article, a tip characterizer with close to reproducible geometry, exactly known angles of all surfaces, and sharp features with close-to-atomic dimension is presented, which has been tested on three commercial AFM probes and a laboratory-made electron-beam-deposited tip, sharpened by oxygen plasma etching.
Abstract: The imaging process of the atomic force microscope (AFM) in contact, noncontact, and intermittent contact mode is still debated after more than a decade of widespread use, in particular when imaged features are approaching atomic dimensions. Several models for the interaction between the tip and the surface have been suggested, but generally they all need an exact description of the geometry of either the tip, the surface, or both. We present here a tip characterizer with close to reproducible geometry, exactly known angles of all surfaces, and sharp features with close to atomic dimension. It has been tested on three commercial AFM probes and a laboratory-made electron-beam-deposited tip, sharpened by oxygen plasma etching. High-resolution transmission electron microscopy has been used to unambiguously verify the tip shapes down to atomic dimensions, both before and after imaging in intermittent contact mode. The effect on the recorded AFM images is shown of tip shape, tip wear, spallation, and accumulation on the tip of amorphous and crystalline debris. The imaging is shown to be a dynamic event, with a continuously changing tip and occasional catastrophic events that give abrupt changes in imaging conditions. The tips are severely worn down already after scanning a few centimeters, but accumulated amorphous material may still give it imaging capabilities in the nanometer range, even with having a tip radius exceeding 130 nm. Accumulated amorphous material seems to be more important than previously believed. Procedures for tip in situ characterization and reliable imaging are suggested.
36 citations
TL;DR: In this paper, a multilayer epitaxy with a W-VO2 top layer over a bottom layer, in which the crystal phase depends on the starting oxygen flow, was done on a-Al2O3(110) by reactively sputtering a V-W (1.6 at.% wt.)
32 citations
TL;DR: In this paper, X-Ray photoelectron spectroscopy (XPS) was used to examine the chemical states and compositions of the resultant blue-tinged xerogel powders.
Abstract: Metallic Mo powder and Ti(OBun)4 were separately dissolved in H2O2 solution and the solutions obtained mixed in different Mo/Ti atomic ratios to prepare precursor solutions. Fresh gels obtained from the precursor solutions with > 40% Mo became blue upon exposure to ambient light. X-Ray photoelectron spectroscopy (XPS) was used to examine the chemical states and compositions of the resultant blue-tinged xerogel powders. Based on the XPS results, it is proposed that TiO2 particles and surface species, including adsorbed water and organic residue, all contribute to the photochromic effect of MoO3. Mo–Ti oxide films were spin-coated on ITO-coated glass substrates using a precursor solution containing 70% Mo. The cycling behaviours of the films annealed at 150 °C for 1 h were studied using cyclic voltammetry (CV) in propylene carbonate solution containing 1 mol L−1 LiClO4. The electrochromic properties of the films upon lithium intercalation were investigated by in situ monochromatic transmittance measurements during the CV process, as well as ex situ in the UV/Vis region. The Mo–Ti oxide films were found to possess excellent electrochromic properties upon Li+ ion insertion/extraction.
26 citations
TL;DR: SrTiO3 films have been grown on LaAlO3(001) single crystal substrates using rf-sputtering and the substrates were held at temperatures ranging from 100 to 850°C as discussed by the authors.
10 citations
16 Oct 2000
TL;DR: In this article, a pulsed power supply with extremely high power in the pulses was used for ionized metal deposition from a magnetron source, where a duty factor of less than 1% was used.
Abstract: Ionized metal deposition can be obtained from a magnetron source when using a pulsed power supply with extremely high power in the pulses. We have used peak power densities of several kW cm/sup -2/ with a repetition frequency of 50 Hz. To avoid overheating of the larger and the magnetron, a duty factor of less than 1% was used. The pulsed sputtering technique was employed for deposition of Ta thin films. The sputtering results in a very dense plasma with the ionized fraction of the deposited Ta flux arriving at a substrate (50 cm away from the source) estimated to be 60% or more (for P/sub Ar/=0.13 Pa and pulse energies /spl ges/6 J). This should be compared to normal dc sputtering where the degree of ionization could not be detected (<5%). This pulsed sputtering technique has a great potential for many industrial applications. One example is front-end metallization integrated circuits with high-aspect-ratio structures.
5 citations
16 Oct 2000
TL;DR: In this paper, a planar round ruthenium target of 50 mm diameter was used to prepare RuO/sub 2/ thin films on Si substrates by reactive unbalanced magnetron sputtering.
Abstract: We prepared RuO/sub 2/ thin films on Si substrates by reactive unbalanced magnetron sputtering in Ar+O/sub 2/ mixtures using a planar round ruthenium target of 50 mm diameter. Films were sputtered in the constant voltage mode at a power of 100 W, total pressures in the range from 0.2 to 10 Pa and partial pressure of O/sub 2/ from 0 to 80% at temperatures up to 600/spl deg/C and negative bias voltage. We investigated the crystallographic nature of films by X-ray diffraction. EDX measurements confirmed the presence of Ru and O in films, RBS measurements revealed changes of composition with bias voltage. It was found that there were changes of structure, electrical and mechanical properties with the oxygen flow ratio, temperature and substrate bias voltage. Nanoindentation measurements were utilised for evaluation of the hardness and reduced modulus of films.
1 citations
TL;DR: In this paper, the grain size distribution of the Ge powder was measured before and after deposition, and the median grain size had decreased to 16m and the width decreased to 55m.
Abstract: Electrostatic powder impact deposition (EPID) is a novel method to deposit thin films by electrostatic acceleration of powder material between charged plates in vacuum. The EPID method has been used to deposit Ge films on Si and Cu substrates at room temperature. Surface morphology and microstructure as studied by SEM showed a very rough surface. XRD and RBS measurements revealed that the films were mostly nanocrystalline or amorphous Ge oxide. The grain size distribution of the Ge powder was measured before and after deposition. Initial distribution showed a median grain size of 32??m and distribution width of 80??m. After the deposition the median grain size had decreased to 16??m and the width decreased to 55??m. The grain size of the deposited film was less than 1??m.