Atomic layer deposition (ALD) is an attractive film growth technique for a variety of modern technologies. The method relies on sequential self-terminating gasÀsolid reactions separated by evacuation steps, i.e. purging or pumping of the deposition chamber. 1,2 The self-limiting nature of the chemical reactions allows for a layer-by-layer type growth and ensures precise thickness control and excellent conformality on substrates with complex topologies, even at the nanometer scale. So far, ALD has mainly been used in the semiconductor industry, but its ability for conformal deposition of ultrathin films could impact a broad range of additional applications, such as catalysis, fuel cells, batteries, filtration devices, etc.In order to fully exploit the unique advantages of ALD, it is important to optimize the process sequence and to understand the underlying surface reactions. In recent literature, mainly in situ diagnostics have been used to obtain fundamental information about the growth kinetics of ultrathin films deposited by ALD. In situ techniques offer the ability to monitor film properties or reaction products while ALD growth is occurring. Techniques that are often used during ALD are spectroscopic ellipsometry (SE), 3 infrared spectroscopy, 4À8 quadrupole mass spectrometry, 8À12 and quartz crystal microbalance. 9,10,13 They provide information on the thickness and optical properties of the film, the chemical surface groups, the gaseous reaction products and the mass uptake during the different process steps.

The solid-state reaction and agglomeration of thin nickel-silicide films was investigated from sputter deposited nickel films ͑1-10 nm͒ on silicon-on-insulator ͑100͒ substrates. For typical anneals at a ramp rate of 3°C / s, 5-10 nm Ni films react with silicon and form NiSi, which agglomerates at 550-650°C, whereas films with a thickness of 3.7 nm of less were found to form an epitaxylike nickel-silicide layer. The resulting films show an increased thermal stability with a low electrical resistivity up to 800°C. © 2010 American Institute of Physics. ͓doi:10.1063/1.3384997͔Nickel-silicides are currently used as contacting materials in state-of-the-art microelectronic devices.1,2 Feature size has shrunk to a few tens of nanometers, and for nickel monosilicide ͑NiSi͒ layers, this results in a particularly severe tendency to agglomerate, 3 leading to a large increase in the electrical resistance of the contact, and an increased mobility of the nickel as it starts to move on the defects, both resulting in a low yield. Since the agglomeration of thin films is driven by a minimization of interface energy, it is expected that thinner films will agglomerate faster ͑i.e., have a lower agglomeration temperature͒. 4 In this letter, we show that this holds true only for films with a thickness of at least 5 nm ͑as-deposited thickness of the nickel layer͒, while for thinner layers the resulting nickel-silicide layer is much more resistant to agglomeration.Nickel films with a thickness between 1 and 10 nm were sputter deposited onto lightly p-doped ͑ =14-22 ⍀ cm͒, Radio Corporation of America ͑RCA͒ cleaned, and HF dipped silicon-on-insulator substrates, with a top layer of 117 nm of Si ͑100͒. The deposition chamber was first evacuated to 10 −4 Pa during deposition, the samples were mounted on a rotating carousel to ensure a uniform deposition thickness. An argon pressure of 0.5 Pa and a sputtering power of 100 W were used, resulting in a deposition rate of 0.04 nm/s. After deposition, the samples were annealed in a high-purity He atmosphere, from 100 to 850°C at a rate of 3°C / s, and the surface roughness ͑using laser light scattering, recording the intensity of nonspecular reflection of the laser light͒, and the sheet resistance ͑using a four point probe͒ were recorded in situ. The thickness of both the as-deposited and annealed films was determined using x-ray reflectivity and cross section transmission electron microscopy, resulting in the reported thicknesses with a precision of Ϯ0.2 nm.An overview of the in situ sheet-resistance is shown in Fig. 1. All of the samples with more than 3.7 nm of nickel ͑6, 8, and 10 nm are shown͒, exhibit a sheet resistance qualitatively similar to what was previously reported 5 for 10 nm layers of nickel on Si ͑100͒; a complex phase sequence of high-resistive metal rich nickel-silicides at low temperatures, and the formation of the low-resistive NiSi phase at 400-450°C. This layer then agglomerates at 550-650°C, leading to the observed increase in sheet resistance. In contrast, for the thinn...

No abstract

Single crystal CaS:Eu and SrS:Eu luminescent particles were synthesized via a solvothermal route at relatively low temperature ͑200°C͒. The as-obtained suspensions were strongly photoluminescent ͑PL͒, pointing at good Eu incorporation. The phosphors showed a broad PL emission band with an emission peak at 663 and 623 nm for CaS:Eu and SrS:Eu, respectively. The synthesis method meets the growing interest in small monodisperse particles. The composition and morphology of the particles was evaluated with transmission electron microscopy, scanning electron microscopy-energy dispersive X-ray and electron backscatter diffraction, particles were found to be mostly monocrystalline. X-ray diffraction showed a cubic structure with space group Fm3m. To control the growth of the crystallites, thioglycerol was added as capping agent, narrowing the size distribution and facilitating the growth of the single crystals.

The phase formation of cobalt germanides on Ge͑100͒ and Ge͑111͒ substrates was investigated using in situ X-ray diffraction, starting from room-temperature sputter-deposited Co films. The formation temperature of the CoGe 2 phase was dependent on the substrate orientation. X-ray pole figures and electron backscatter diffraction measurements were used to identify the texture and microstructure of the CoGe 2 and the preceding Co 5 Ge 7 films. A significant difference in preferential orientation was found in the Co 5 Ge 7 films, depending on the substrate orientation. This influences the formation temperature of the CoGe 2 and results in the coexistence of Co 5 Ge 7 and CoGe 2 on Ge͑111͒ in a large temperature window.The use of self-aligned silicides is one of the enabling technologies in the production of current deep-submicrometer silicon-based electronic devices. These silicides are used as contacting materials on the active regions of field-effect transistors and are formed during the solid-state reaction of a metal with exposed silicon of the substrate. For applications where even higher switching frequencies are required than are possible with silicon, other semiconductors such as germanium ͑Ge͒, silicon germanium ͑SiGe͒, or gallium arsenide ͑GaAs͒ have an intrinsic advantage due to their higher carrier mobility. On Ge, germanides are a natural choice for the production of self-aligned contacts. 1-3 In addition to their use as self-aligned contacts, the study of germanides on single-crystal Ge substrates provides insight into the formation of germanide contacts on GaAs. Both GaAs and Ge have a cubic crystal structure with an almost identical lattice constant, which leads to a similarity in texture selection of the different germanide phases.Of all the germanides, only a fraction has the potential to be used as an electrical contact, as the electrical resistance of the phase must be low while at the same time it should exhibit a high thermal stability. A systematic overview of the phase sequence during the reaction of germanium with a wide range of metals has been reported by Gaudet et al. 4 and resulted in a list of materials that fulfill these criteria: NiGe, 5 PdGe, and CoGe 2 . In this paper, we focus on the formation of CoGe 2 . We investigate the phase sequence during reaction of Co films on Ge͑100͒ and Ge͑111͒ substrates, describe the texture of the Co 5 Ge 7 and CoGe 2 phases, and show its influence on the formation temperature of CoGe 2 . ExperimentalFilms of 30 nm Co were sputter-deposited in ultrahigh vacuum conditions on HF-cleaned, single-crystal Ge͑100͒ and ͑111͒ substrates. The samples were heated from 100 to 850°C, at a rate of 3°C/s in a high purity helium flow, during which the phase sequence was monitored using X-ray diffraction ͑XRD͒. These in situ XRD experiments were performed at the X20C beam line at the National Synchrotron Light Source ͑NSLS͒ at Brookhaven National Laboratory ͑BNL͒ using monochromatic X-rays with a wavelength of 1.78 Å and a linear detector capable of recording a 2 ran...