Jukka T. Tanskanen

Selective metal deposition at graphene line defects by atomic layer deposition

One-dimensional defects in graphene have a strong influence on its physical properties, such as electrical charge transport and mechanical strength. With enhanced chemical reactivity, such defects may also allow us to selectively functionalize the material and systematically tune the properties of graphene. Here we demonstrate the selective deposition of metal at chemical vapour deposited graphenes line defects, notably grain boundaries, by atomic layer deposition. Atomic layer deposition allows us to deposit Pt predominantly on graphenes grain boundaries, folds and cracks due to the enhanced chemical reactivity of these line defects, which is directly confirmed by transmission electron microscopy imaging. The selective functionalization of graphene defect sites, together with the nanowire morphology of deposited Pt, yields a superior platform for sensing applications. Using Pt-graphene hybrid structures, we demonstrate high-performance hydrogen gas sensors at room temperature and show its advantages over other evaporative Pt deposition methods, in which Pt decorates the graphene surface non-selectively.

Vapor transport deposition and epitaxy of orthorhombic SnS on glass and NaCl substrates

Polycrystalline SnS, Sn2S3, and SnS2 were deposited onto glass substrates by vapor transport deposition, with the stoichiometry controlled by deposition temperature. In addition, epitaxial growth of orthorhombic SnS(010) films on NaCl(100) with thicknesses up to 600 nm was demonstrated. The in-plane [100] directions of SnS and NaCl are oriented approximately 45° apart, and the translational relationship between SnS and NaCl was predicted by density functional theory. The epitaxial SnS is p-type with carrier concentration on the order of 1017 cm−3 and Hall hole mobility of 385 cm2 V−1 s−1 in-plane. It has indirect and direct bandgaps of 1.0 and 2.3 eV, respectively.

Growth characteristics, material properties, and optical properties of zinc oxysulfide films deposited by atomic layer deposition

Zinc oxysulfide—Zn(O,S)—is a wide bandgap semiconductor with tunable electronic and optical properties, making it of potential interest as a buffer layer for thin film photovoltaics. Atomic layer deposition (ALD) of ZnS, ZnO, and Zn(O,S) films from dimethylzinc, H2O, and H2S was performed, and the deposited films were characterized by means of x-ray diffraction, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry. With focus on the investigation of Zn(O,S) film growth characteristics and material properties, the ZnO/(ZnO + ZnS) ALD cycle ratios were systematically varied from 0 (ZnS ALD) to 1 (ZnO ALD). Notably, a strong effect ofthematerial properties on the optical characteristics is confirmed for the ternary films. The Zn(O,S) ALD growth and crystal structure resemble those of ZnS up to a 0.6 cycle ratio, at whichpoint XPS indicates 10% oxygen is incorporated into the film. For higher cycle ratios thefilm structure becomes amorphous, which is confirmed with XRD patterns and also reflected ...

Influence of organozinc ligand design on growth and material properties of ZnS and ZnO deposited by atomic layer deposition

Deposition of ZnS and ZnO by the atomic layer deposition technique is performed using both dimethylzinc (DMZn) and diethylzinc (DEZn) as the metal source and H2S or H2O as the counter-reactant. The deposited films are characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy, and ultraviolet-visible measurements, and particular emphasis is placed on the influence of the metal precursor on material growth and properties. The use of DMZn as the Zn source results in faster material deposition than growth with DEZn due to a less significant steric factor with DMZn. The material properties of the deposited ZnS films are nearly identical for the DMZn/H2S and DEZn/H2S processes, whereas XRD provided evidence for slight variations in the material properties of the DMZn/H2O and DEZn/H2O grown films. Overall, pure and crystalline ZnS and ZnO films can be deposited via either DMZn or DEZn, and ZnO growth is more affected by the modification of the ligand of the Zn precursor from methyl to ethyl.

ALD Growth Characteristics of ZnS Films Deposited from Organozinc and Hydrogen Sulfide Precursors

Growth characteristics of zinc sulfide thin films deposited from dialkylzinc and H(2)S reactants by the atomic layer deposition technique have been investigated by quantum chemical methods. The steady-state growth of the films was simulated by studying the reaction of the Zn precursor with the hydrogenated sulfur-terminated (111) surface of zincblende ZnS and then by investigating the chemisorption of hydrogen sulfide on the surface formed by the metal exposure. The behavior of the dissociatively chemisorbed Zn precursors on the growth surface is of particular significance for the film deposition process, since the film growth is limited by the Zn deposition step. Hydrogen sulfide exposure results in the replacement of the surface alkyl groups by SH surface species, whose vibrational features are useful in the experimental verification of the developed growth mechanisms.

Atomic layer deposition of CdxZn1−xS films

Deposition of CdxZn1−xS has been demonstrated with atomic layer deposition (ALD) using diethylzinc (DEZn), dimethylcadmium (DMCd), and hydrogen sulfide as the precursors, and DFT calculations were performed to simulate the ALD process and the properties of the deposited films. The relative ratio of the pulses is varied for DMCd and DEZn to achieve different compositions over the spectrum from pure CdS to pure ZnS. Overall, the cadmium content in the films is higher than would be expected both as a function of pulse ratio and of temperature based on the growth rates of the binary films. At 150 °C pure ZnS shows almost pure cubic nature; however, the wurtzite content increases with the presence of cadmium until the film is approximately 10% wurtzite for pure CdS. Transmission electron microscopy (TEM) with high resolution confirms the coexistence of zincblende and wurtzite within grains due to the presence of stacking faults. The roughness of the films is a function of the composition, and the band gap and index of refraction can be finely tuned with composition.

Montmorillonite interlayer surface chemistry: effect of magnesium ion substitution on cation adsorption

Montmorillonite is a clay mineral and the main component in bentonite clay, which is utilized in various applications including its planned use as a buffer material for long-term nuclear waste disposal. In the present paper, a quantum chemical study is presented providing an insight into montmorillonite structure and its surface chemistry, which plays a key role in understanding montmorillonite behavior at the molecular level. A model is first designed by calculating the positions of Mg-substitutions in the octahedral sheet of the layer structure. This model is then used to study (1) charge distribution in the system and (2) the energetics of Na+/Ca2+ cation adsorption on the interlayer surfaces. The results show and verify that the Mg-substitutions are positive charge deficits and the only significant charge defects in the structure. Therefore, the energetics of cation adsorption is found to correlate linearly with the inverse distances between cations and Mg-substitutions in a dry, fully periodic montmorillonite lattice.

Structural Characteristics of Graphane-Type C and BN Nanostructures by Periodic Local MP2 Approach

The structural characteristics of fully-hydrogenated carbon and boron nitride mono- and multilayer slabs, together with nanotubes derived from the slabs, are investigated mainly by means of periodic local second-order Møller-Plesset perturbation (LMP2) calculations and the results are compared with Hartree-Fock (HF), density functional theory (DFT), and dispersion function-augmented DFT (DFT-D) obtained ones. The investigated systems are structurally analogous to (111) and (110) slabs of diamond, where the hydrogenated (111) slab of diamond corresponds to the experimentally known graphane. Multilayering of monolayers and nanotubes is energetically favorable at the LMP2 level for both C and BN, while HF and DFT are not able to reproduce this behavior for CH systems. The work highlights the importance of utilizing methods capable of properly describing weak interactions in the investigation of dispersively-bound systems such as the multilayered graphanes and the corresponding nanotubes.

Structural Characteristics of Hydrogenated Carbon and Boron Nitride Nanotubes: Impact of H-H Interactions

The structural characteristics of perhydrogenated carbon and boron nitride nanotubes are determined by means of quantum chemical calculations. Two families of nanotubes are systematically studied for both carbon and boron nitride, the nanotubes being derived from the perhydrogenated (110) and (111) sheets of diamond and cubic boron nitride. Single-walled perhydrogenated carbon nanotubes prefer structures analogous to the (111) sheet. In clear contrast, the single-walled perhydrogenated boron nitride nanotubes prefer structures analogous to the (110) sheet. The significantly different structural characteristics are due to the polarization of hydrogen atoms in the perhydrogenated boron nitride nanotubes. The presence of attractive electrostatic H--H interactions leads to a strong preference for multilayering of the boron nitride sheets and nanotubes. The results are expected to provide new insights into the structural characteristics of main-group binary hydrides.

Growth, intermixing, and surface phase formation for zinc tin oxide nanolaminates produced by atomic layer deposition

A broad and expanding range of materials can be produced by atomic layer deposition at relatively low temperatures, including both oxides and metals. For many applications of interest, however, it is desirable to grow more tailored and complex materials such as semiconductors with a certain doping, mixed oxides, and metallic alloys. How well such mixed materials can be accomplished with atomic layer deposition requires knowledge of the conditions under which the resulting films will be mixed, solid solutions, or laminated. The growth and lamination of zinc oxide and tin oxide is studied here by means of the extremely surface sensitive technique of low energy ion scattering, combined with bulk composition and thickness determination, and x-ray diffraction. At the low temperatures used for deposition (150 °C), there is little evidence for atomic scale mixing even with the smallest possible bilayer period, and instead a morphology with small ZnO inclusions in a SnOx matrix is deduced. Postannealing of such l...