Structure Formation In Films Research Articles

Metal-induced nanocrystalline structures in Ni-containing amorphous silicon thin films

The mechanisms of silicon nanocrystal structure formation in amorphous Si films have been studied for a relative Ni impurity content varying between 0.1 and 10at.%, i.e., from a Ni doping range to the Si–Ni alloy phase. The films, deposited by the cosputtering technique at 200°C, were submitted to isochronal (15min) annealing cycles up to 800°C. Four different substrates were used to deposit the studied films: crystalline (c-) quartz, c-Si, c-Ge, and glass. Both the two orders of magnitude impurity concentration range variation and the very short annealing times were selected on purpose to investigate the first steps of the mechanism leading to the appearance of crystal seeds. The conclusions of this work are the following: (a) Ni impurity induces the low-temperature crystallization of amorphous silicon; (b) the NiSi2 silicide phase mediates, at the surface or in the bulk of the film, the crystallization process; and (c) the onset of crystallization and the crystalline fraction of the samples at each temperature depend not only on the Ni impurity concentration, but also on the nature of the substrate.

Characteristics of poly(alkyl silsesquioxane) thin films prepared from chemically linked alkyl units

Poly(alkyl silsesquioxane), PASSQ, copolymers containing the different alkyl components were synthesized by sol–gel polymerization with a bridged alkoxysilane as a matrix component, and the potential applications of low-k films were verified using TGA, FT-IR, 13C and 29Si solid state NMR after pore forming process by the thermal decomposition. As the higher alkyl groups in PASSQ were decomposed, the lower refractive indices were achieved from 1.45 to 1.27 due to the formation of nanoporous in the film. In particular, the modulus for the three different PASSQ films were significantly higher than 3.8GPa of the typical thin film of poly(methyl silsesquioxane). The enhanced moduli for the films are ascribed to the formation of rigid film structure by the introduction of bridged ethylene of BTMSE in spite of the porous structure. In addition, the partial decomposition of bridge ethylene groups was accompanied with the dominant occurrence of methyl silicon groups, which reduced the mechanical properties with microporous structure.

Pattern guided structure formation in polymer films of asymmetric blends

Two off-critical blends of poly(2-vinylpyridine) and polystyrene, 2:3 and 3:2 (w:w) PVP:PS, were spin-cast (with varied domain scale R) onto periodically ( λ = 4 μm) patterned substrate. The pattern consisted of two alternating symmetric stripes: Au attracting PVP and neutral self-assembled monolayer. The resulting droplet-type morphologies were recorded with Scanning Force Microscopy and examined with integral geometry approach. PVP-rich islands of the 2:3 PVP:PS films form, for a wide R/ λ range, strongly anisotropic morphologies. They show up, for R/ λ ∼ 0.5, a weak λ/2-substructure of smaller PVP droplets in addition to the domains periodic with λ. The 3:2 blend exhibits morphologies with dominant λ-structure of PVP ribbons, which encircle PS droplets. For R/ λ ∼ 0.5, smaller PS domains are also present but no λ/2-substructure is formed. The | χ E|-values of droplet surface density are reduced, as compared to homogeneous substrate, for the 3:2 blend (with | χ E| → 0 for R ∼ λ). This effect is absent for the 2:3 mixture.

Preparation and Its Photovoltaic Effect of Ferroelectric Film

This paper reports on the formation of film structures and the highly improved photovoltaic output current of the lead lanthanum zirconate titanate (PLZT) employed. The photovoltaic effect of ferroelectrics has the advantage of its simple mechanisms of non-bias applications which are indispensable for semiconductor p-n junctions. But the output current of PLZT bulk is too low for use as a device current source. The PLZT film structure exhibited μA output current upon light illumination. The photovoltaic current of the PLZT film was more than 102 times than that of bulk PLZT. These differences are due to the characteristics of the design of the film including the configuration of the electrode. The PLZT film also has the advantage of easy output control and suitability for use on Si. Results show that the photovoltaic effect of the ferroelectric film is useful as the current source for micro-electro-mechanical systems (MEMS).

Stress-induced domain structure formation in nanodimensional barium strontium titanate films

Thin heteroepitaxial films of BaxSr1−x TiO3 (BST) with x = 0.80 possessing high structural perfection have been grown by RF magnetron sputtering on MgO(001) substrates. The microstructure and crystallographic characteristics of the BST films of various thicknesses have been studied using electron microscopy and X-ray diffraction. It is established that there is a threshold thickness at which the BST crystal lattice parameter in the direction perpendicular to the substrate exhibits a sharp change.

Simulation of the adsorption of simple gases on transition metals (Review)

Results from simulations of the adsorption of gases on transition metal surfaces are presented. Attention is devoted mainly to the adsorption of hydrogen on the (110) surfaces of W and Mo, the structures and adsorption kinetics of oxygen and CO on the Pt(111) surface, and the catalytic reaction of CO oxidation. The choice of these systems is motivated not only by their practical importance and fundamental interest but also by the fact that substantial progress has been made toward understanding the processes of adsorption and the formation of film structures for them with the use of the Monte Carlo method. One of the main requisites for simulation of the adsorbed film structures is to adequately incorporate the lateral interaction between adsorbed molecules, which includes both a direct interaction (electrostatic and exchange) and indirect (via electrons of the substrate). The correct description of the lateral interaction in the simulation has permitted explanation of the mechanisms of formation of the structures of CO films on platinum. At the same time, the complexity of the interaction between adsorbed atoms has at yet precluded the development of a consistent model for the formation of the structure of adsorbed oxygen on the platinum surface. It can be hoped that this problem will soon be solved, making it possible to refine the model of the catalytic reaction of CO oxidation.

Monte Carlo simulation of CO and O coadsorption and reaction on Pt(1 1 1)

Dissociative oxygen adsorption, CO adsorption on the oxygen-covered Pt(1 1 1) surface, formation and stability of the p(2 × 2) structure of adsorbed oxygen and of O–CO coadsorbed layers, and reaction kinetics have been simulated by a refined Monte Carlo method. Results of the simulations are in good agreement with experiments, which suggests validity of the concepts of the precursor states in the dissociative adsorption, indirect lateral interaction between adsorbed particles, and reveals important role of mobility of the species in formation of film structures and in reaction between adsorbed CO molecules and O atoms. A new model of catalytic CO oxidation reaction, in which only oxygen atoms in hcp-type threefold adsorption sites on the Pt(1 1 1) surface are chemically active, is suggested. Within this model, the TPD (temperature programmed desorption) spectra of the coadsorbed CO–O films, which represent the rate of CO oxidation, do resemble experimental data for CO adsorption on a perfectly ordered p(2 × 2) oxygen film as well as on the oxygen layer with domain walls.

Industrially-styled room-temperature pulsed laser deposition of titanium-based coatings

Titanium-based compounds are widely used as coating materials for mechanical, tribological, electrical, optical, catalytic, sensoric, micro-electronical applications due to their exceptionally physical and chemical properties. Recently, the trend of using temperature-sensitive materials like polymers and tool steels with the highest hardness demands new low-temperature coating techniques for protective surface finishing as well as for surface functionalization, but up to now there is lack of industrially scaled vacuum coating techniques at temperatures below 50 °C. An alternative for overcoming this problem is the pulsed laser deposition (PLD) technique, which was up-scaled for industrial demands at Laser Center Leoben of JOANNEUM RESEARCH Forschungsgesellschaft mbH. The current paper summarizes the application of the industrially-scaled PLD technique on the deposition of the presently most important Ti-based coatings: metallic titanium, titanium nitride (TiN), titanium oxide (TiO 2) and titanium carbonitride (TiCN). PLD coating allows, even at room temperature, the formation of film structures of Zone-T type of Thornton's structure zone model, both on substrates aligned normal and parallel to the incident vapor flux. The high-energetic deposition conditions are revealed by the occurrence of (2 2 0) textures for the fcc TiN-based films. The dense grown structure affects advantageously the tribological behavior—generally, low wear rates and (for TiCN) very low friction coefficients were found. For TiO 2 coatings, growing as a mixture of β -TiO 2 and amorphous phases, the easily reproducible change of deposition parameters in the room-temperature PLD allows large differences in the optical transmission and electrical resistance.

Characteristics of Photovoltaic Lead Lanthanum Zirconate Titanate Ceramics in a Layered Film Structure Design

This paper reports on the formation of a new layered film structure and the highly improved photovoltaic output of PLZT. The photovoltaic current of the PLZT film was more than 102 times of magnitude higher than that of bulk PLZT. The improved photovoltaic effect of layered film structure is good for the power sources of wireless transducers and ultraviolet sensing systems.

Cryogenic deposition of carbon nitride thin solid films by reactive magnetron sputtering; suppression of the chemical desorption processes

Nanostructured fullerene-like carbon nitride (FL CNx) is commonly grown by reactive magnetron sputtering of carbon in a nitrogen-containing atmosphere. The film structure formation for this technique is presumably due to the existence of preformed molecular CxNy (x,y≤2) species in the deposition flux, which act as growth templates and enhance the selectivity of chemical desorption processes. In the present study, the extent of the desorption processes and the implications on the resulting film have been investigated in detail, addressing in particular the structure evolution and the origin of the incorporated nitrogen. This was studied by varying the N2-fraction in the discharge from 0 to 1 and the substrate temperature from 600 °C (873 K) down to minus 130 °C (143 K). The results show that the incorporation rate of carbon and nitrogen into the film increases substantially with an increased N2-content in the plasma and decreasing substrate temperature, thus indicating that the chemistry and magnitude of the arriving flux is substantially altered with the N2-fraction in the discharge. It is concluded that the chemically activated desorption in conjunction with the varying chemistry of the film-forming flux affects the sensitive structural balance, determined by incorporation and desorption of film forming CxNy (x,y≤2) species.

Structure formation in films of weakly charged block polyelectrolyte solutions

A mean-field dynamic density functional theory is used to describe a phase diagram of concentrated solutions of weakly charged flexible block polyelectrolytes in a film. Electrostatics is taken into account by applying the local electroneutrality constraint (the Donnan membrane equilibrium approach). In the Donnan limit it is assumed that a salt added to the solution perfectly screens long-range electrostatic interactions. The phase diagram of a solution of a triblock polyelectrolyte in a film as a function of the solvent concentration and the charge of the polyelectrolyte (solvophilic) block is calculated for a given film thickness. The phase behavior of the block polyelectrolyte film arises from the interplay between surface-induced alignment and the electrostatically-driven structure formation. The observed mesoscopic structures (lamellar, perforated lamellar, cylindrical, micellar, and mixed phases) are oriented parallel to the surfaces for the considered case of morphologies unfrustrated by the film thickness. Structures with connections between parallel layers (bicontinuous, etc.) are not formed. As a result of surface-induced ordering, the region of ordered phases in a film is wider than in bulk and the phase boundary between ordered and disordered phases is more diffuse. As in the case of unconfined block polyelectrolyte solution, the solution in a film does not follow the lyotropic sequence of phases of such a block copolymer upon increase in the charge of the polyelectrolyte block. Upon changing the charge of the solvophilic copolymer block, transformations of copolymer morphology take place via change in curvature of polymeric domains. Due to confinement of a polyelectrolyte film, no swelling of solvophilic domains is observed.

Effect of Acidification and Heating on the Rheological Properties of Oil-Water Interfaces with Adsorbed Milk Proteins

The behavior of casein and whey proteins at the oil-water interface was studied using a dynamic drop tensiometer (DDT). The dilational modulus of the interface was measured for aqueous solutions of skim milk powder (SMP) and whey protein concentrate (WPC) with various additions (salt, calcium, lactose) and (order of) various processing steps. Acidification or heating was performed before or after creation of the interface. The elastic properties of oil-water interfaces with adsorbed milk proteins could partly determine the rate of partial coalescence and resulting product instability.For WPC, preacidification slows down the adsorption, but the modulus is not affected. This is probably because, although the whey proteins change conformation more slowly at the interface, still a homogeneous film is formed. If postacidification is applied, coarsening of the protein film leads to loss of interfacial rigidity. Preheating of the aqueous phase with WPC leads to denaturation and aggregation, but the aggregates formed are still surface active and give high moduli. If preheating of a WPC solution is followed by postacidification, the resulting modulus is high (∼60 mN/m).The oil-water interfacial properties of SMP are only minimally affected by preheating or by choice of powder (low, medium, or high heat). At low pH, however, aggregates are formed that are less surface active, and interfacial moduli are lower.If measurements are performed at high temperature (i.e., if postheating is applied), for both SMP and WPC systems, moduli became much lower (∼10 mN/m). This is probably because of accelerated rearrangements, leading to the formation of inhomogeneous film structures.

Structures Formed in Spin-Cast Films of Polystyrene Blends with Poly(butyl methacrylate) Isomers

For polystyrene blends with poly(butyl methacrylate), replacing poly(n-butyl methacrylate) by poly(tert-butyl methacrylate) results in modified topography of spin-cast films (holes dominating at a surface are exchanged with islands, or vice versa, such individual surface features are increased), decreased PBMA surface excess, but similar overall domain structure. Two series (PS/PnBMA and PS/PtBMA) of films with constant thickness and PBMA fraction 0 < Φ < 1, cast from toluene onto silicon wafers, were examined with atomic force microscopy, X-ray photoelectron spectroscopy, profiling and mapping mode of dynamic secondary ion mass spectrometry. Topography was analyzed with the integral geometry approach. Film structure formation was postulated to involve surface segregation, phase separation, and instability of the transient PBMA layer [a linear relation between Φ2 and averaged size of holes (islands) was observed for PS/PnBMA (PS/PtBMA)]. Structural changes caused by isomer exchange are related to glass tr...

Role of the composition and type of film-forming species in film structure formation

We present the results of an investigation into correlation between the type of film-forming species (FFS) (atoms and molecules) and the structure of the films deposited by reactive magnetron sputtering of W-30 at.%Ti alloy in an Ar–N2 working gas. Mass-spectrometric studies have revealed that the FFS flux contains both atomic (W, Ti, N) and molecular (WN, TiN) species and the flux composition depends on the nitrogen partial pressure in a working gas. At low nitrogen partial pressures (PN2<0.1 Pa) the FFS flux is mainly composed of W, Ti atoms and WN, TiN molecules and the film deposited from such flux is formed of biphase [W+(W,Ti)2 N] composite material with extremely small (approx. 10 nm) grain size. The films deposited from the flux containing mostly metal and nitrogen atoms (higher nitrogen partial pressures PN2>0.2 Pa) are formed from monophase (W,Ti)2 N material with 2–4 times larger crystallite size. The microhardness of the films deposited from the FFS flux containing mainly metal atoms and nitride molecules was noticeably higher than that of the films formed mostly from metal and nitrogen atoms.

Role of the composition and type of film-forming species in film structure formation

We present the results of an investigation into correlation between the type of film-forming species (FFS) (atoms and molecules) and the structure of the films deposited by reactive magnetron sputtering of W-30 at.%Ti alloy in an Ar–N 2 working gas. Mass-spectrometric studies have revealed that the FFS flux contains both atomic (W, Ti, N) and molecular (WN, TiN) species and the flux composition depends on the nitrogen partial pressure in a working gas. At low nitrogen partial pressures ( P N2<0.1 Pa) the FFS flux is mainly composed of W, Ti atoms and WN, TiN molecules and the film deposited from such flux is formed of biphase [W+(W,Ti) 2 N] composite material with extremely small (approx. 10 nm) grain size. The films deposited from the flux containing mostly metal and nitrogen atoms (higher nitrogen partial pressures P N2>0.2 Pa) are formed from monophase (W,Ti) 2 N material with 2–4 times larger crystallite size. The microhardness of the films deposited from the FFS flux containing mainly metal atoms and nitride molecules was noticeably higher than that of the films formed mostly from metal and nitrogen atoms.

Photovoltaic properties of lead lanthanum zirconate titanate ceramics in a layered film structure design

This paper reports on the formation of a new layered film structure and the highly improved photovoltaic output of the lead lanthanum zirconate titanate (PLZT) employed. The new structure design is described using a top transparent indium tin oxide (ITO) electrode. The PLZT film structure exhibited V and mA output. This means that the photovoltaic current of the PLZT film per unit width was more than 10 2 times larger than that of bulk PLZT, while the photovoltaic voltage per unit thickness in the layered film structure was almost the same as that in bulk ceramics and single crystal. These differences are due to the characteristics of the film structure and configuration of the electrode. PLZT film also has the advantage of its easily controllable parameters: film thickness, illuminated area, and illumination intensity. A simple model is used for the phenomenological explanation of the improved photovoltaic effect of the PLZT film.

Effects of Fluorination on Self-Assembled Monolayer Formation from Alkanephosphonic Acids on Aluminum: Kinetics and Structure

We have used infrared spectroscopy, ellipsometry, and contact angle measurements to study self-assembled monolayer (SAM) formation on aluminum native oxide from three alkanephosphonic acids: CF3(CF2)7(CH2)11PO3H2 (F8H11PA), and CH3(CH2)nPO3H2 (n = 15 (H16PA); n = 21 (H22PA)). These compounds show significant differences in film structure and film formation kinetics. Strikingly, the methylene segment of the semifluorinated F8H11PA SAM never reaches an ordered state even at long assembly times. This contrasts with the ordered chains in equilibrium films from H16PA and H22PA. We attribute this behavior to steric effects of the fluorocarbon segment and the phosphonic acid headgroup. F8H11PA represents an amphiphile in which bulky head and tail groups prevent an interposed hydrocarbon segment from ordering. For all three phosphonic acids, negative peaks attributed to loss of Al−OH groups in the infrared spectra of the monolayers are consistent with a condensation reaction between the acids and surface hydroxy...

Film-thickness dependence of structure formation in ultra-thin polymer blend films

We investigated the film-thickness dependence of structure formation in ultra-thin polymer blend films prepared from solution. As a model system we used binary blends of statistical poly(styrene-co-p-bromostyrene) copolymers of different degrees of bromination. Ultra-thin-film samples differing in miscibility and film thickness were prepared via spin coating of common toluene solutions onto silicon (100) substrates. The resulting morphologies were investigated with scanning force microscopy, reflectometry and grazing-incidence scattering techniques using both X-rays and neutrons in order to obtain a picture of the sample structure at and below the sample surface.

Nanostructured Thin Films via Self-Assembly of Block Copolymers

Thin films of incompatible block copolymers self-assemble into highly regular supramolecular structures with characteristic dimensions in the 10-100 nm regime. There is increasing interest in controlling the resulting structures and utilizing them, for instance in the area of nanotechnology. So far, research has concentrated mainly on exploiting the melt structure of diblock copolymers. Recent work on block copolymer solutions and more complex co- and terpolymer architectures has revealed a rich variety of novel thin-film structures, some of which exhibit high complexity and order. In addition, by use of mean field dynamic density functional theory along with well-controlled experiments, the fundamentals of thin film structure formation have been elucidated. We highlight some aspects of these studies and point to future directions in this lively field of materials science.

Pulsed laser deposition of CNx films: role of r.f. nitrogen plasma activation for the film structure formation

Thin CNx films were deposited by pulsed laser deposition (PLD) equipped with KrF excimer laser. An additional radio-frequency discharge of the nitrogen gas was applied. The role of atomic nitrogen in CN radical formation was studied using optical emission spectroscopy (OES). The composition of the films was measured by WDX. The N/C ratio of all films was approximately 1 and did not vary greatly with nitrogen pressure.