Early Stage Of Deposition Research Articles

The role of surface activation prior to seeding on CVD diamond adhesion

A special surface pre-treatment protocol consisting of four steps is proposed to provide high adhesion levels for CVD diamond by hot-filament technique. In step 1, the silicon nitride ceramic substrates are surface ground with 15 µm diamond slurry and mirror-like polished with colloidal silica (0.05 µm). In step 2, plasma etching with CF 4 (PE), mechanical anchoring is promoted due to the surface roughness increment. Surface activation (SA) is the following step, where the substrates are subjected to CVD diamond growth conditions for a short time (30 min), leading to the deposition of an amorphous carbon layer responsible for enhancing the nucleation density and the further growth of diamond during early stages of deposition. The final step 4 is 0.5–1 µm diamond powder seeding in an ultrasonic bath. The results show that the Si 3 N 4 ceramic surface modified by the surface pre-treatment protocol allowed a high nucleation density promoting a continuous and homogeneous film of equally sized diamond grains, at a growth rate of ap. 1.5 µm h − 1 . Brale tip indentation tests confirmed that highly adherent films are thus produced (no delamination under 900 N).

Fluid Inclusion Constraints on the Genesis of Gold in the Darasun District (Eastern Transbaikalia), Russia

Fluid Inclusion Constraints on the Genesis of Gold in the Darasun District (Eastern Transbaikalia), Russia

Shaping Ge Islands on Si(001) Surfaces with Misorientation Angle

A complete description of Ge growth on vicinal Si(001) surfaces in the angular miscut range 0 degrees -8 degrees is presented. The key role of substrate vicinality is clarified from the very early stages of Ge deposition up to the nucleation of 3D islands. By a systematic scanning tunneling microscopy investigation we are able to explain the competition between step-flow growth and 2D nucleation and the progressive elongation of the 3D islands along the miscut direction [110]. Using finite element calculations, we find a strict correlation between the morphological evolution and the energetic factors which govern the {105} faceting at atomic scale.

Change in Surface States of Amorphous Carbon Nitride Films after Exposure to Oxygen Plasma

Amorphous carbon nitride (a-CNx) thin films were deposited by rf-reactive sputtering method using a graphite target, and after deposition the films were exposed to oxygen plasma. The effect of the oxygen plasma exposure on the morphology and chemical bonding states of the film surface has been studied. Film composition and the chemical bonding states were analyzed by X-ray photoelectron spectroscopy (XPS). Film surface was observed by atomic force microscopy (AFM). AFM observations have revealed that the as-deposited film surface is uniformly covered with particle-like features in the early stage of deposition and the surface changes to be covered with broccoli-like features with increasing the deposition time and correspondingly the surface roughness increases, while after exposure to oxygen plasma, the film surface was etched selectively and the surface roughness increases with the plasma exposure time. It should be noted that the etching behavior depends on the film deposition temperatures. XPS studies have shown that after exposure to oxygen plasma the change in the bonding states in the films prepared at 853 K is different from that in the films prepared at RT.

Expansion of the Cathaysian Oldland through the Ordovician-Silurian transition: Emerging evidence and possible dynamics

Located northwest of the Jiangshan-Shaoxing Fault Zone, western and northwestern Zhejiang and northeastern Jiangxi provinces experienced major changes in bio- and litho-facies and paleogeography through the Ordovician-Silurian transition (late Katian, Hirnantian, and early Rhuddanian), as manifested by stratigraphic, paleontologic and synecologic records. Three geographic units under consideration are South, Central, and North areas. The western margin of the South area was occupied by the Huaiyu Mountains, whereas the other two parts were covered by the Zhe-Gan Sea during late Katian (Late Ordovician) time. In the early stage of the Changwu Formation deposition (late Katian), the sea was deepening northeastward, but with shallower conditions in the southwest and deeper conditions in the northeast. During mid to late stages of Changwu Formation deposition (latest Katian), the sea became much shallower and the sea bottom was uplifted substantially, which occurred somewhat prior to the global trend. During the Hirnantian (latest Ordovician) and early Rhuddanian (earliest Silurian), the study region became a shallow bay under expansion of the Cathaysian Oldland. There occurred a major drop of sea level and great changes in benthic biota with the occurrence of many new immigrants through the Ordovician-Silurian transition, which are closely related to a unique regional orogeny. The Yangtze and Cathaysian blocks may have amalgamated within the South China Paleoplate during this interval to cause the continuous uplifting and northwestward expansion of the Cathaysian Oldland.

Copper Migration During Tungsten via Formation

AbstractA yield problem is observed with tungsten vias formed on copper interconnects. Copper migration can occur during chemical vapor deposition (CVD) of tungsten, if there are defects in the liner inside the via. Copper can react quickly with SiH4 during the early stages of tungsten deposition, when SiH4-reduction of WF6 is used. Under severe conditions, large amounts of copper diffuse out of the underlying metal layer, resulting in copper silicide formation in the via and leaving voids in the copper wire. Copper migration can be minimized by reducing the time that the wafers are exposed to SiH4.

Effect of Substrate Temperature, Biasing and Sputter Cleaning on the Structure and Properties of Nanostructured TiB<SUB>2</SUB> Coatings on High Speed Steel

Fabrication and development of TiB2-based nanostructured coatings was investigated in the present work. By varying the sputter-target power density, substrate temperature, deposition time, substrate-to-target distance, substrate biasing and substrate sputter cleaning, the relationship between the sputtered structure, properties and sputtering conditions were established. The experimental results showed that the target-to-substrate distance played a major role in the coating structure and properties. Sputter cleaning of substrate helped to improve TiB2 coating hardness and adhesion. The deposition process could be controlled to produce a TiB2 coating with both high hardness and good adhesion strength. This was achieved by introducing substrate sputter-cleaning and then biasing for the early stage of deposition, followed by deposition without biasing. [doi:10.2320/matertrans.MC200906]

Optical micro-paddle beam deflection measurement for electrostatic mechanical testing of nano-scale thin film application to MEMS

The authors describe their design for a paddle-like cantilever beam sample to relieve non-uniform stress distribution in beam-bending tests of the mechanical properties of thin film applications to MEMS. We added the sample to a custom-designed system equipped with an electrostatic panel and optical interferometer. The system overcomes problems associated with using nano-indentation for testing, and reduces errors tied to the amount of contact force required to bend the beam. Accurate paddle cantilever beam deflection was obtained using a four-step phase-shifting process with a Michelson interferometer. Film strain was determined using a simple force equilibrium equation. Residual stresses were measured at −41.3 MPa for 150 nm silver film, −3.2 MPa for 150 nm gold film, and −16.8 MPa for 150 nm copper film. We observed residual stresses for copper films at different thicknesses. The results indicate high tensile stress forms during the early deposition stage for thin copper film due to grain coalescence, and a decrease in stress with an increase in film thickness. In copper films with thicknesses greater than 153 nm, lattice relaxation associated with the surface mobility of metallic atoms changed residual stress from tension to compression.

Serum amyloid β protein in young and elderly depression: a pilot study

Depression may increase the risk of developing Alzheimer's disease (AD). Recent large cohort studies have also shown that a low plasma amyloid beta (Abeta)-42 level combined with a high Abeta40 level increases the risk of developing AD, suggesting plasma Abeta42/40 ratio as useful for identifying risk of developing mild cognitive impairment and AD. Although several studies have examined Abeta levels in the peripheral blood of elderly individuals with depression, results have been inconsistent. Furthermore, no results have been described for younger depression. Serum Abeta40, Abeta42 level and Abeta40/42 ratio were evaluated using enzyme-linked immunosorbent assay in 60 patients with major depressive disorder (MDD) and 60 healthy controls. The results were analyzed in two age groups (young, <60 years; elderly, >or=60 years). Serum Abeta40 level was significantly higher in young MDD patients compared to young controls (P < 0.001), but it was not significantly deferent in the elderly group. Serum Abeta42 level did not differ significantly in both young and elderly groups. Abeta40/42 ratio was significantly higher in both young (P < 0.001) and elderly (P < 0.001) patients with MDD compared to controls. Serum Abeta40/42 ratio was significantly higher in MDD patients than in controls, and this difference was seen for both elderly and young subjects. This may suggest that even young subjects with MDD undergo pathological changes in the very early stage of amyloid deposition.

Experimental study of the interfacial cobalt oxide inCo3O4/α−Al2O3(0001)epitaxial films

A detailed spectroscopic and structural characterization of ultrathin cobalt oxide films grown by O-assisted molecular beam epitaxy on a-Al2O3(0001) single crystals is reported. The experimental results show that the cobalt oxide films become progressively more disordered with increasing thickness, starting from the early stages of deposition. Low energy electron diffraction patterns suggest that the unit cell remains similar to that of a-Al2O3(0001) up to a thickness of 17 A, while at larger thicknesses a pattern identified with that of Co3O4(111) becomes visible. X-ray photoelectron spectroscopy reveals sudden changes in the shape of the Co 2p lines from 3.4 to 17 A cobalt oxide thickness, indicating the transition from an interfacial cobalt oxide layer towards [111]-oriented Co3O4. In particular, the absence of characteristic satellite peaks in the Co 2p lines indicates the formation of a trivalent, octahedrally coordinated, interfacial cobalt oxide layer during the early stages of growth, identified as the Co2O3 corundum phase.

Structural and Piezoelectric Properties of DC-Sputtered AlN Films Deposited on Different Si-Based Substrates

We study the DC magnetron sputtering deposition of AlN on different substrates: (100) resistive Si, Si3N4 on Si and SiO2 on Si. The growth conditions of such films have been analysed to obtain the best structural and piezoelectric properties on each substrate. We show that, while AlN follows a columnar growth from the early stage of deposition on Si, the non—crystalline nature of Si3N4 and SiO2 induces an amorphous early growth stage on such substrates. Despite this structural difference, high performances have been obtained by AlN delay lines realised on both Si3N4/Si and pure resistive Si, providing further flexibility in the development of Si-based technological applications.

Chain reaction of amyloid fibril formation with induction of basement membrane in familial amyloidotic polyneuropathy

Familial amyloidotic polyneuropathy (FAP) is characterized by extracellular deposition of amyloid fibrils caused by a point mutation in the transthyretin (TTR) gene. Despite data from a number of in vitro studies of TTR amyloidogenesis, many questions, including where and how these fibrils form in vivo and what is the impact of amyloid deposition on tissues, remain unanswered. Here, we analysed the relationship between amyloid fibril formation and micro-environmental changes by using autopsy cardiac tissues from 11 patients with FAP and a smooth muscle cell line. Ultrastructural studies of cardiomyocytes and vascular smooth muscle cells showed that amyloid fibrils formed first at the basement membrane and that amorphous non-fibrillar TTR deposits and premature fibrils predominated during the early stage of amyloid deposition. Immunohistochemical analyses revealed that expression of major components of the basement membrane, such as collagen IV, laminin, and fibronectin, increased in parallel with the accumulation of TTR amyloid fibrils. In vitro studies with a vascular smooth muscle cell line revealed that synthetic TTR aggregates increased expression of these basement membrane components. Serum levels of collagen IV in FAP patients were significantly higher than those in healthy controls. Our data thus indicate that TTR amyloid fibrils formed first at the basement membrane and that expression of basement membrane components that was induced by amyloid deposition contributed to further amyloid deposition. This chain reaction may have important implications for FAP pathogenesis.

Evolution of magnetic and structural properties from Ag nanolayers to several microns Co–Ag deposits prepared by electrodeposition

The evolution of composition, morphology, magnetic properties and crystalline structure of Co–Ag electrodeposits from nanometric to micrometric thicknesses has been analyzed. Different substrates (Si/Ti/Ni, Si/Cr/Cu and glass/ITO) have been used to electrodeposit the Co–Ag system. The same trend was observed in all cases: after a first nanometric silver layer, cobalt was gradually incorporated till constant composition was attained. Moreover, a gradual variation of the magnetic response of the films from diamagnetism to superparamagnetism and then ferromagnetism was detected by increasing the deposition charge. fcc-Ag, hcp-Co and a metastable phase hcp-CoAg 3 were present in Co–Ag micrometric deposits grown over Si/Ti/Ni from the very early deposition stages, these deposits showing coercivity values around 115 Oe. However, deposits of lower coercivities (around 50 Oe) were obtained over glass/ITO and Si/Cr/Cu substrates, these deposits being constituted by fcc-Ag and hcp-Co.

Thickness dependence of superconductivity for In/Mo thin films

We report on the superconducting characteristics of the Indium thin films on molybdenum under-layer as a function of the In film thickness. Our molybdenum under-layer with thickness of 50 Å does not cause the occurrence of superconductivity until 1.5 K and the sheet resistance has logarithmic temperature dependence observed in the present investigation. As thickness of In increased, the oscillation phenomenon of T C was observed at early stage of deposition and the value of T C is higher than the that for bulk of In. Furthermore, it is found that with increase of the In thickness, there are large differences of the strengths of the upper critical magnetic field H C2( T), resistivity and T C between films with thickness below and above 100 Å. On the other hand, the T C decreases monotonously as sheet resistance increases, when the T C is plotted against sheet resistance. To clarify the relation of superconducting characteristics and the surface structure of the films with different thickness, we have performed surface observation by atomic force microscope. As a result, we have found that the surface changes from homogeneous structure to inhomogeneous (or percolative) structure, when the thickness of in films pass through about 100 Å. Superconductivity of In/Mo films with relatively thick-inhomogeneous films cannot be explained in terms of the simple percolation theory. Therefore, we analysis the experimental data of H C2( T) near T C, using a extended Landau–Ginzburg model. It is found out that our In/Mo films must consider some factors; such as, grain size, the distance of grain space, and the strength of couplings between grains.

Photoemission study of C60-induced barrier reduction for hole injection at N, N′-bis(naphthalene-1-y1)-N, N′-bis(phenyl) benzidine/Al

Synchrotron radiation photoemission study showed that the energy level alignment at the interface between N, N′-bis(naphthalene-1-y1)-N, N′-bis(phenyl) benzidine (NPB), a typical hole transport material, and Al could be adjusted by precovering a thin C60 layer on Al. The interface dipoles so formed could shift both the highest occupied molecular orbital level of NPB and the secondary electron cutoff measured at the early stage of the NPB deposition. The barrier height for hole injection from Al to NPB could thus be lowered by as much as 0.98 eV, and the optimal thickness of the inserted C60 layer was found to be 8–12 Å.

In situ stress evolution during and after sputter deposition of Al thin films

The stress, growth, and morphology evolution of Al thin filmsup to 300 nm thick, sputter deposited at a constant rate of0.04 nm s−1 onto thermally oxidized Si(100) substrates have been investigated for varioussputter pressures in the range from 0.05 to 6 Pa. The stress evolution has beenstudied during and after the film deposition by means of in situ substrate curvaturemeasurements using an optical two-beam deflection method. In order to obtain insightinto the mechanisms of stress generation and relaxation, the microstructure ofthe films was investigated by scanning electron microscopy, focused-ion-beammicroscopy, and atomic force microscopy. The stress evolution during the early stage ofdeposition of films is consistent with the Volmer–Weber growth mode knownfor metals with high adatom mobility. For thicker films, the compressive stressincreases in the sputter pressure range of 0.05–0.5 Pa, whereas at even higher sputterpressures a transition from compressive to tensile stress takes place. This transition iscorrelated with a change from a relatively dense to a more porous microstructurecharacterized by decreasing mass density and increasing electrical resistivity withincreasing sputter pressure. The dependence of the stress and microstructure on thesputter pressure can be consistently understood through a combination of the stressmechanisms for vapor and sputter deposited films proposed in the literature.

Connection between magnetism and structure in Fe double chains on the Ir(100) surface

The magnetic ground state of nanosized systems such as Fe double chains, chains recently shown to form in the early stages of Fe deposition on Ir(100), is generally nontrivial. Using ab initio density functional theory we find that the straight ferromagnetic (FM) state typical of bulk Fe as well as of isolated Fe chains and double chains is disfavored after deposition on Ir(100) for all the experimentally relevant double chain structures considered. So long as spin-orbit coupling (SOC) is neglected, the double chain lowest energy state is generally antiferromagnetic (AFM), a state which appears to prevail over the FM state due to Fe-Ir hybridization. Successive inclusion of SOC adds two further elements, namely, a magnetocrystalline anisotropy and a Dzyaloshinskii-Moriya (DM) spin-spin interaction; the former stabilizing the collinear AFM state and the latter favoring a long-period spin modulation. We find that anisotropy is most important when the double chain is adsorbed on the partially deconstructed Ir(100)---a state which we find to be substantially lower in energy than any reconstructed structure---so that in this case the Fe double chain should remain collinear AFM. Alternatively, when the same Fe double chain is adsorbed in a metastable state onto the $(5\ifmmode\times\else\texttimes\fi{}1)$ fully reconstructed Ir(100) surface, the FM-AFM energy difference is very much reduced and the DM interaction is expected to prevail, probably yielding a helical spin structure.

On the effect of the nature and physical state of a polymer support on the stress-strain characteristics of metallic coatings

A newly proposed microscopic procedure makes it possible to estimate the strength of thin (nano-metric) coatings deposited onto various polymer supports. The strength of the deposited coating is shown to increase dramatically when the thickness of the coating decreases below 15 nm. It was also found that the strength of the coatings is controlled by the physical state of the polymer support. The Interfacial layer formed at the early stages of metal deposition onto the polymer surface is characterized by a higher strength as compared with that of a pure metal deposited onto the above interfacial layer. This observation can be explained by the following reasons: first, the dimensions of metallic grains in the interfacial layer are much smaller than those in a pure metal and, second, the intergrain space in the interfacial layer is filled with polymer matrix. At the same time, both the temperature and the adsorptionally active liquid medium affect polymer partitions in the interfacial composite layer and thus control the overall strength of thin coatings (≤15 nm). In the case of thicker coatings, the strength of the coating gradually decreases independently of the nature and state of the supporting polymer and approaches the strength of the bulk metal.

Early stages of vanadium deposition on Si(1 1 1)-7 × 7

We investigate the low-coverage regime of vanadium deposition on the Si(1 1 1)-7 × 7 surface using a combination of scanning tunnelling microscopy (STM) and density-functional theory (DFT) adsorption energy calculations. We theoretically identify the most stable structures in this system: (i) substitutional vanadium atoms at silicon adatom positions; (ii) interstitial vanadium atoms between silicon adatoms and rest atoms; and (iii) interstitial vanadium – silicon adatom vacancy complexes. STM images reveal two simple vanadium-related features near the Si adatom positions: bright spots at both polarities (BB) and dark spots for empty and bright spots for filled states (DB). We relate the BB spots to the interstitial structures and the DB spots to substitutional structures.

Morphology of Cn thin films (50 ⩽ n < 60) on graphite: Inference of energy dissipation during hyperthermal deposition

Low energy cluster beam deposition, LECBD, under UHV conditions has been used to generate thin films comprising monodispersed non-IPR fullerenes, C n, 50 ⩽ n < 60, on pyrolithic graphite surfaces (HOPG). The morphology of the resulting C n deposits has subsequently been studied by ex situ atomic force microscopy. Deposition experiments were carried out under nominally normal incidence and at hyperthermal incident kinetic energies, E 0, varied between 1 and 40 eV. Surface temperatures during deposition, T s, were varied from 300 K to the desorption onset of ∼700 K. Initial sticking of C n cages is governed by the lateral density of step edges, which act as pinning and nucleation centres for migrating cages. Consequently in the early deposition stages, the surface exhibits large areas of empty terraces, while the step edges themselves are well-decorated. The terraces in turn become decorated by dendritic C n islands in later deposition stages. Both, the mean size of these 2D islands and the mean distance between nearest islands, δ, scale with the size of the terraces. When increasing the primary kinetic energy, the fractal-like islands become smaller and less dendritic in shape. The mean initial sticking coefficient decays exponentially with increasing E 0. The island topography has also been found to depend sensitively on the deposition temperature. Instead of the dendritic/fractal islands generated at room temperature, densely packed islands terminated by smooth rims are observed upon deposition at elevated temperatures. We rationalize our findings in terms of a three step deposition process involving: (i) conversion of perpendicular E 0 into hyperthermal surface parallel gliding/sliding motion, (ii) friction–dissipation of this surface-parallel kinetic energy within an (unexpectedly large) mean free path Λ followed by (iii) thermal diffusion. Λ, is observed to scale with E 0 and T s.