Lauri Aarik

Atomic layer deposition of aluminum oxide films on graphene

Seed-layer approach was studied to initiate atomic layer deposition (ALD) of Al2O3 films on graphene. Low-temperature ALD and electron beam evaporation (EBE) were applied for seed-layer preparation before deposition of the dielectric at 200 °C using trimethyl-aluminum and water or ozone as precursors. To characterize nucleation of the films and possible influence of the ALD processes on the quality of graphene, properties of graphene and Al2O3 films were investigated by Raman spectroscopy, X-ray fluorescence and X-ray photoelectron spectroscopy methods. The results suggest that seed layer formation by low-temperature ALD was more efficient in the O3-based process than in the H2O-based one while EBE seed layer provided fastest growth of Al2O3 together with minimum incubation period.

Dysprosium oxide and dysprosium-oxide-doped titanium oxide thin films grown by atomic layer deposition

Dysprosium oxide and dysprosium-oxide-doped titanium oxide thin films were grown by atomic layer deposition on silicon substrates. For depositing dysprosium and titanium oxides Dy(thd)3-O3 and TiCl4-O3 were used as precursors combinations. Appropriate parameters for Dy(thd)3-O3 growth process were obtained by using a quartz crystal microbalance system. The Dy2O3 films were deposited on planar substrates and on three-dimensional substrates with aspect ratio 1:20. The Dy/Ti ratio of Dy2O3-doped TiO2 films deposited on a planar silicon substrate ranged from 0.04 to 0.06. Magnetometry studies revealed that saturation of magnetization could not be observed in planar Dy2O3 films, but it was observable in Dy2O3 films on 3D substrates and in doped TiO2 films with a Dy/Ti atomic ratio of 0.06. The latter films exhibited saturation magnetization 10−6 A cm2 and coercivity 11 kA/m at room temperature.

Atomic Layer Deposition of Zirconium Oxide on Carbon Nanoparticles

In this report we describe preparation of structures containing carbon nanoparticles for potential applications in nonvolatile memories. The carbon nanoparticles were synthesized from 5-methylresorcinol and formaldehyde via base catalysed polycondensation reaction, and were distributed over substrates by dip-coating the substrates into an organic solution. Before deposition of nanoparticles the substrates were covered with 2 nm thick Al2O3 layer grown by atomic layer deposition (ALD) from Al(CH3)3 and O3. After deposition of nanoparticles the samples were coated with ZrO2 films grown from C5H5Zr[N(CH3)2]3 and H2O. Both dielectrics were grown in two-temperature ALD processes starting deposition of Al2O3 at 25 °C and ZrO2 at 200 °C, thereafter completing both processes at a substrate temperature of 300 °C. Deposition of ZrO2 changed the structure of C-nanoparticles, which still remained in a Si/Al2O3/C/ZrO2 structure as a separate layer. Electrical characterization of nanostructures containing Al2O3 as tunnel oxide, C-nanoparticles as charge traps and ZrO2 as control oxide showed hysteretic flat-band voltage shift of about 1V.