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.

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New materials, namely high-k (high-permittivity) dielectrics to replace SiO(2), Cu to replace Al, and barrier materials for Cu, are revolutionizing modern integrated circuits. These materials must be deposited as very thin films on structured surfaces. The self-limiting growth mechanism characteristic to atomic layer deposition (ALD) facilitates the control of film thickness at the atomic level and allows deposition on large and complex surfaces. These features make ALD a very promising technique for future integrated circuits. Recent ALD research has mainly focused on materials required in microelectronics. Chemistry, in particular the selection of suitable precursor combinations, is the key issue in ALD; many interesting results have been obtained by smart chemistry. ALD is also likely to find applications in other areas, such as magnetic recording heads, optics, demanding protective coatings, and micro-electromechanical systems, provided that cost-effective processes can be found for the materials required.

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Platinum thin films were grown at 300 °C by atomic layer deposition (ALD) using (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and oxygen as precursors. The films had excellent uniformity, low resistivity, and low-impurity contents. Structural studies by X-ray diffraction showed that the films were strongly (111) oriented. Growth rates of 0.45 Å cycle-1 were obtained with 4 s total cycle times. The film thickness was found to linearly depend on the number of the reaction cycles. Also, the possible reaction mechanism is discussed.

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Recently, a new approach to dihydrogen activation known as frustrated Lewis pairs (FLPs) concept has been introduced 1, 2, 3 . A combination of highly Lewis acidic boranes and sterically hindered bases can split hydrogen heterolytically generating onium (phosphonium, ammonium, etc.) borohydrides. These compounds show reduction activity resembling that of inorganic borohydrides like NaBH 4 , i. e. they are suitable mostly for reduction of polarized multiple bonds. Imines, enamines, silyl ethers 4, 5,6 , α,β-enones 7 , ynones 8 , Nalkylanilines 9 were hydrogenated using stoichiometric or catalytic amounts of FLPs. Due to heterolytic nature of FLP-H 2 adducts, hydrogenation of unactivated multiple C-C bonds using FLPs has some natural limitations, since during the respective step of the catalytic cycle a proton transfer from catalyst to substrate should take place (Fig. 1a). Although Greb et al. have implemented this approach to hydrogenation of alkenes under ambient conditions, this method is predictably restricted to the alkenes with high proton affinity 10 .

The first ansa-aminoborane N-TMPN-CH2C6H4B(C6F5)2 (where TMPNH is 2,2,6,6-tetramethylpiperidinyl) which is able to reversibly activate H2 through an intramolecular mechanism is synthesized. This new substance makes use of the concept of molecular tweezers where the active N and B centers are located close to each other so that one H2 molecule can fit in this void and be activated. Because of the fixed geometry of this ansa-ammonium-borate it forms a short N-H...H-B dihydrogen bond of 1.78 A as determined by X-ray analysis. Therefore, the bound hydrogen can be released above 100 degrees C. In addition, the short H...H contact and the N-H...H (154 degrees) and B-H...H (125 degrees) angles show that the dihydrogen interaction in N-TMPNH-CH2C6H4BH(C6F5)2 is partially covalent in nature. As a basis for discussing the mechanism, quantum chemical calculations are performed and it is found that the energy needed for splitting H2 can arise from the Coulomb attraction between the resulting ionic fragments, or "Coulomb pays for Heitler-London". The air- and moisture-stable N-TMPNH-CH2C6H4BH(C6F5)2 is employed in the catalytic reduction of nonsterically demanding imines and enamines under mild conditions (110 degrees C and 2 atm of H2) to give the corresponding amines in high yields.