Structure and nanostructure in ionic liquids.

Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends

Plasma-assisted atomic layer deposition (ALD) is an energy-enhanced method for the synthesis of ultra-thin films with A-level resolution in which a plasma is employed during one step of the cyclic deposition process. The use of plasma species as reactants allows for more freedom in processing conditions and for a wider range of material properties compared with the conventional thermally-driven ALD method. Due to the continuous miniaturization in the microelectronics industry and the increasing relevance of ultra-thin films in many other applications, the deposition method has rapidly gained popularity in recent years, as is apparent from the increased number of articles published on the topic and plasma-assisted ALD reactors installed. To address the main differences between plasma-assisted ALD and thermal ALD, some basic aspects related to processing plasmas are presented in this review article. The plasma species and their role in the surface chemistry are addressed and different equipment configurations, including radical-enhanced ALD, direct plasma ALD, and remote plasma ALD, are described. The benefits and challenges provided by the use of a plasma step are presented and it is shown that the use of a plasma leads to a wider choice in material properties, substrate temperature, choice of precursors, and processing conditions, but that the processing can also be compromised by reduced film conformality and plasma damage. Finally, several reported emerging applications of plasma-assisted ALD are reviewed. It is expected that the merits offered by plasma-assisted ALD will further increase the interest of equipment manufacturers for developing industrial-scale deposition configurations such that the method will find its use in several manufacturing applications.

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Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

Removal of methylene blue from aqueous solution by a solvothermal-synthesized graphene/magnetite composite.

Persistent aromatic pollutants are widely found in the effl uents from the pharmaceutical, petrochemical, dyestuff, pesticide, and other industries. Because of their high solubility in water, they transport into the environment widely and do harm to human health. Many studies have focused on the effi cient elimination of organic pollutants from aqueous solutions such as by photocatalysis, [ 1 ] adsorption, [ 2 ] and electrolysis. [ 3 ] Among these methods, adsorption techniques are simple and work effectively because of the preconcentration and solidifi cation of organic pollutants on adsorbents. However, the adsorption capacities of present materials are not high enough. It is important to develop new adsorbents with high adsorption capacities for persistent organic pollutant management in the environment. The high surface area of nanomaterials brings new prospects for the management of organic pollutants, for example, carbon nanotubes are found to work effectively to remove organic contaminants. [ 4 ] Compared with carbon nanotubes, graphene is more exciting. Graphene has a large theoretical specifi c surface area (2620 m 2 g − 1 ), [ 5 ] which indicates its potential for the adsorption of organic pollutants in environmental pollution management. However, to our knowledge, no report has addressed this topic, which is probably attributable to: 1) the strong aggregation of graphene sheets, which reduces the surface area of graphene signifi cantly, and 2) the absence of effective ways to disperse graphene in aqueous solution, which makes it diffi cult to advance in pollution management. Herein, we introduce a kind of sulfonated graphene (around 3 nm thick) with high dispersion properties in aqueous solution capable of absorbing naphthalene and 1-naphthol aromatic pollutants from aqueous solutions. The adsorption capability of the prepared sulfonated

Sulfonated Graphene for Persistent Aromatic Pollutant Management

We report on an easy-to-use, successful, and reproducible route to synthesize functionalized graphite oxide (GO) and its conversion to graphene-like materials through chemical or thermal reduction of GO. Graphite oxide containing hydroxyl, epoxy, carbonyl, and carboxyl groups loses mainly hydroxyl and epoxy groups during reduction, whereas carboxyl species remain untouched. The interaction of functionalized graphene with fluorescent methylene blue (MB) is investigated and compared to graphite, fully oxidized GO, as well as thermally and chemically reduced GO. Optical absorption and emission spectra of the composites indicate a clear preference for MB interaction with the GO derivatives containing a large number of functional groups (GO and chemically reduced GO), whereas graphite and thermally reduced GO only incorporate a few MB molecules. These findings are consistent with thermogravimetric, X-ray photoelectron spectroscopic, and Raman data recorded at every stage of preparation. The optical data also indicate concentration-dependent aggregation of MB on the GO surface leading to stable MB dimers and trimers. The MB dimers are responsible for fluorescence quenching, which can be controlled by varying the pH value.

The route to functional graphene oxide.

Copper phthalocyanine (CuPc) thin films were obtained by a sublimation technique on Si wafer substrates maintained at room temperature. As-deposited CuPc films with less than 0.1 μm thickness crystallize primarily in the α-form with a preferential orientation of the crystallites in the [2 0 0] direction. The effect of randomizing of the orientation of the CuPc crystallites is observed as the film thickness increases, whereas the preference in appearance of the α-form remains. The changes in phase composition, structure, morphology and surface chemical composition of as-deposited CuPc thin films due to different heat treatment conditions were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).

Studies on phase transformations of Cu-phthalocyanine thin films

The aim of the work discussed in this paper was to characterize adsorbed self-assembled monolayers on different metal oxide substrates with angle-resolved XPS measurements. The substrates used were silicon wafers (100) coated with 300 nm Al, Ta, or Ti. They were coated with acids by immersing them in an ethanol solution. The orientation of long-chain organic acids adsorbed on metal oxides has been successfully identified by angle-resolved XPS. On Al, Ta, and Ti substrates, C11 chains are orientated in the right manner, i.e. with the phosphonic group at the bottom and the thiophene group on top. The orientations of the C2 and C6 chains are not clear. The thickness of the layers could be obtained by using Tougaard nanostructure analysis, and it shows monolayers. A model of the chemical bonds between the phosphonic group and the metal could be developed from the chemical shift. For titanium, all three P–O bonds bind to the metal substrate, whereas only the P–O(H) bond binds to the metal on aluminium and tantalum.

Characterization of the adsorption of ω -(thiophene-3-yl alkyl) phosphonic acid on metal oxides with AR-XPS

Germanium is a promising material for future very large scale integration transistors, due to its superior hole mobility. However, germanium-based devices typically suffer from high reverse junction leakage due to the low band-gap energy of 0.66 eV and therefore are characterized by high static power dissipation. In this paper, we experimentally demonstrate a solution to suppress the off-state leakage in germanium nanowire Schottky barrier transistors. Thereto, a device layout with two independent gates is used to induce an additional energy barrier to the channel that blocks the undesired carrier type. In addition, the polarity of the same doping-free device can be dynamically switched between p- and n-type. The shown germanium nanowire approach is able to outperform previous polarity-controllable device concepts on other material systems in terms of threshold voltages and normalized on-currents. The dielectric and Schottky barrier interface properties of the device are analyzed in detail. Finite-element...

Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions

The electrodeposition of Ta from TaF(5) was studied in three different ionic liquids, namely in 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl sulfonyl) amide, 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) amide and 1-methyl-3-propyl imidazolium bis(trifluoromethyl sulfonyl) amide. The electrochemical quartz crystal microbalance (EQCM) was used together with electrochemical techniques for characterizing in situ the electrodeposition process. With the help of the EQCM we could identify the stoichiometry of the electrodeposited species. Furthermore, square-wave voltammery was used to study intermediate reduction processes in the potential regime where no mass change was detected. An XPS analysis proved the existence of elemental Ta, besides some oxides and Ta halide species. Both the ionic liquid and the deposition conditions influence strongly the quality and properties of the deposited layers.

B. Adolphi

Papers

The route to functional graphene oxide.

Studies on phase transformations of Cu-phthalocyanine thin films

Characterization of the adsorption of ω -(thiophene-3-yl alkyl) phosphonic acid on metal oxides with AR-XPS

Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions

On the electrodeposition of tantalum from three different ionic liquids with the bis(trifluoromethyl sulfonyl) amide anion