Films Of Similar Thickness Research Articles

Temperature-dependent out-of-plane anisotropy in compressively strained La0.67Sr0.33MnO3 thin films

We studied the temperature and strain dependence of the perpendicular magnetic anisotropy in La0.67Sr0.33MnO3 thin films by performing temperature- and angle-dependent magnetotransport measurements. Three films of similar thickness (14 u.c., 14 u.c. and 15 u.c.) but with different out-of-plane crystallographic strain (1.9%, 0.9% and -0.7%) are studied. The films are grown on LaAlO3 and SrTiO3 substrates by pulsed laser deposition. We observe a clear increase in the out-of-plane magnetic anisotropy with increasing out-of-plane strain in the angle-dependent magnetotransport measurements which is present up to 80 K for the highest (1.9%) strained sample. The deformation of the unit cell, as discussed in earlier reports, point to the magnetocrystalline anisotropy as the main driver altering the magnetic easy axis direction. Our results highlight the utility of the effective magnetocrystalline anisotropy as a tool to control the desired anisotropy in crystalline thin films of La0.67Sr0.33MnO3.

Nanocellulose films with combined cellulose nanofibers and nanocrystals: tailored thermal, optical and mechanical properties

Cellulose nanofibers (CNFs) and nanocrystals (CNCs) were prepared, and used to prepare thin CNF/CNC films. Rheological behavior of CNF/CNC suspensions and the other relevant properties of the films were characterized in comparison with a commercial porous polymer battery separator (PBS) film of similar thickness. The use of mixed CNFs and CNCs in the film-forming suspension led to significant variation of film morphology, and structural properties. With the addition of CNCs in hybrid nanocellulose material, the CNF/CNC suspension viscosity and zeta potential, film tensile strength, crystallinity index, and optical transparency were increased. With the increased CNF loading in the suspension, film porosity, thermal stability, and thermal expansion were enhanced. The CNF/CNC films exhibited better thermal stability, thermal expansion behavior, and optical properties than those of the commercial PBS film. The coefficient thermal expansion of the CNF/CNC and PBS films were 11.86–17.65 and 178.90 ppm/k, respectively. The CNF/CNC films had more uniform strength along all directions, whereas PBS film demonstrated anisotropic property. This work paves a new strategy to tailor the properties of nanocellulose based films.

Thermal stability of ultrathin amorphous carbon films synthesized by plasma-enhanced chemical vapor deposition and filtered cathodic vacuum arc

Ultrathin hydrogenated amorphous carbon (a-C:H) films deposited by plasma-enhanced chemical vapor deposition (PECVD) and hydrogen-free amorphous carbon (a-C) films of similar thickness deposited by filtered cathodic vacuum arc (FCVA) were subjected to rapid thermal annealing (RTA). Cross-sectional transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) were used to study the structural stability of the films. While RTA increased the thickness of the intermixing layer and decreased the sp3 content of the a-C:H films, it did not affect the thickness or the sp3 content of the a-C films. The superior structural stability of the FCVA a-C films compared with PECVD a-C:H films, demonstrated by the TEM and EELS results of this study, illustrates the high potential of these films as protective overcoats in applications where rapid heating is critical to the device functionality and performance, such as heat-assisted magnetic recording.

Friction, nanostructure, and residual stress of single-layer and multi-layer amorphous carbon films deposited by radio-frequency sputtering

Abstract

Effective reduction of graphene oxide thin films by a fluorinating agent: Diethylaminosulfur trifluoride

This paper reports the use of a fluorinating agent, diethylaminosulfur trifluoride (DAST), to effectively reduce graphene oxide (GO) thin films at a relatively low temperature (50°C). X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and sheet resistance measurement were used to investigate the reduction process. The C/O atomic ratio and sheet resistance of the GO films reduced by DAST were 9.24 and 398Ω/□ respectively, which are comparable to the reduced GO films of similar thickness (6.5μm) produced by hydrazine vapor. GO film reduction by DAST is advantageous in preserving the film intactness, owing to the mild reaction conditions involved. A small amount of fluorine (3–4 at.%) was incorporated into rGO by DAST reduction which was confirmed by XPS and FTIR, which might influence the electrical properties of rGO or render it suitable for further functionalization. Further, our findings suggest that special attention should be paid to the steric hindrance of the hydroxyl groups in GO while adapting organic chemistry methods for GO reduction and functionalization, which could alter reaction outcome significantly and could also be exploited for steric protection.

Integrating Ormosil films onto microstructured semiconductor substrates

A process of heterogeneously integrating organically modified siliceous aerogel (Ormosil) films onto microstructured substrates is presented. These substrates are architecturally designed to mimic photon detectors for remote sensing applications. Here, ultrasonically homogenized Ormosil sols are drop-cast onto silicon micropyramidal arrays then dried in the ambient to produce highly porous low-density siliceous films with excellent uniformity. The highly facile process yields films endowed with high optical transmittance, high static contact angle of 168°, excellent thermal stability up to 400°C and, to some extent, excellent adhesion to the microstructured substrates on which they sit. Additional planarization benefits are easily afforded by controlling the substrate arraignment during the ambient drying process which the sol undergoes. In contrast, only conformal films were obtained when sols were spin coated over similar microstructured substrates. In correlating the resultant macroporous films’ structural integrity with the underlying substrate topography, this study established that the weak physical bond between the facets of the microstructures and gel acts as crack nucleation points that induce and exacerbate crack propagation within the film. This phenomenon does not manifest itself when thinner films are prepared even on the same microstructured substrates as well as films of similar thickness on planar substrates. Initial studies establish that the non-homogenized sols can yield macroscopic aerogel monoliths with properties akin to those exhibited by supercritically dried monoliths. It is our belief that this study can enlighten the intricacies and pitfalls encountered when fabricating macroscopically monolithic Ormosil films over topographically structured surfaces.

Nanocrystalline chitin thin films

Elucidating the interactions between crystalline chitin and various biomacromolecules is of fundamental importance for designing and fabricating chitin-based biomaterials. This work highlights a simple method to prepare ultrathin films of chitin nanocrystals (chitin NC) by spincoating chitin NCs from a colloidal suspension onto a gold surface modified by an amine-terminated self-assembled monolayer. Atomic force microscopy confirmed that chitin NC films are reasonably smooth and homogeneous, and quartz crystal microbalance with dissipation monitoring (QCM-D) solvent exchange experiments demonstrated that chitin NC films have twice as much water as amorphous regenerated chitin (RChitin) films of similar thickness. QCM-D data also showed that chitinase-catalyzed hydrolysis of chitin NC films was much slower than that of RChitin films. Chitinase not only degraded, but also caused the swelling of the chitin nanocrystals. BSA adsorption studies demonstrated that chitin NC films have high protein loading capacity, and thus show potential applications for enzyme immobilization.

Enhanced dielectric and piezoelectric response in PZT superlattice-like films by leveraging spontaneous Zr/Ti gradient formation

Spontaneous Zr/Ti gradient formation during crystallization in sol–gel-processed Pb(ZrxTi1−x)O3 films is used to prepare superlattice-like (SL), highly (100)-oriented thin films on Pt/Ti/SiO2/Si substrates. SLs with stacking periodicity ranging from 13 up to 60nm are synthesized with compositional gradient normal to the film surface and composition centered at x≈0.53. X-ray diffraction (XRD) shows high order satellite peaks and no secondary phases. XRD structural refinement, along with XPS depth profile chemical analysis, reveals that the crystal structure alternates between rhombohedral and in-plane polarized tetragonal phases, effectively corresponding to “artificially created” phase boundaries. SL films have ∼45% and ∼20% higher d33,f piezoelectric coefficient and dielectric permittivity, respectively, with respect to compositional-gradient-free films of similar thickness, possibly due to enhanced reorientation of electrical dipoles and higher extrinsic contributions due to the motion of the “artificially created” phase boundaries in SL films. Dielectric nonlinear studies indicate a higher amount of extrinsic contributions to the dielectric response in SL and gradient-enhanced films than in conventional films of similar average composition. This processing method provides a simple chemical route to create thin ferroelectric films with enhanced dielectric and piezoelectric properties suitable for a range of miniaturized applications.

Preparation and characterization of TiO 2/carbon composite thin films with enhanced photocatalytic activity

Composite TiO 2/carbon thin films prepared by physical vapor deposition techniques on fused silica substrates show enhanced photocatalytic activity towards decomposition of methanol to CO 2 and water, as compared to pure TiO 2 films of similar thickness. Raman and XRD measurements confirm that annealed TiO 2 films exhibit anatase structure while the carbon layer becomes graphitic. Characteristic for the composite films is an enhanced optical absorption in the visible range. The presence of the carbon film causes a shift of the TiO 2 absorption edge and modifies its grain size to be smaller. We hypothesize that the observed enhancement of photocatalytic activity is due to synergy effects at the carbon/TiO 2 interface, resulting in smaller titania crystallite size and anisotropic charge carrier transport, which in turn reduces their recombination probability.

A Comparative Study of Angle Dependent Magnetoresistance in [001] and [110] La2/3Sr1/3MnO3

The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ thin films show that the anisotropy energy of [110] films is higher when compared with a [001] oriented La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ film of similar thickness. The data has been analyzed in the light of multidomain model and it is seen that this model correctly explains the observed behavior.

Ferroelastic interactions in bilayered ferroelectric thin films

We present a theoretical investigation of the elastic interactions in a heteroepitaxial bilayer consisting of a (001) tetragonal PbZrxTi1−xO3 and (001) rhombohedral PbZr1−xTixO3 on a thick (001) passive substrate. Analytical expressions for the elastic interaction energies between the layers and the resultant ferroelastic twin formation have been derived as a function of the lattice misfit strain (between layers and the substrate), composition of the ferroelectric and thickness. It is found that the elastic coupling between the tetragonal and rhombohedral layers leads to the equilibrium domain fraction in the tetragonal layer several time larger than that in single-layer films of similar thickness. Most critically, the model finds a significant change in the ferroelastic domain volume fraction in the presence of an applied electric field and hence enhanced piezoelectric properties compared to single-layered epitaxial PZT thin films.

Enhanced pyroelectric coefficient of antiferroelectric-ferroelectric bilayer thin films

In this study, the pyroelectric coefficient and the figure of merit (FOM) of the ferroelectric (FE) PbZr0.3Ti0.7O3 (PZT 30/70) thin films were found to be greatly enhanced by introducing a thin antiferroelectric (AF) PbZr0.95Ti0.05O3 (PZT 95/05) layer underneath the FE film and thus creating a bilayer structure on platinized silicon substrates. The film properties were investigated as a function of the FE layer thickness when the thickness of AF layer remained unchanged. The highest pyroelectric coefficient of 1 μm thick PZT 30/70 film was 3.18×10−4 cm−2 K−1. However, the highest pyroelectric coefficient for 1 μm thick bilayer film was 3.5×10−4 or 2.5×10−4 cm−2 K−1 for only 280 nm thick bilayer film. The enhancement of pyroelectric coefficient suggests switching of AF into FE phase during poling and following stabilization of FE phase at room temperature. The reduction in dielectric constant in bilayer films after poling, compared to pure PZT 30/70, showed a FOM of 2.94×10−5 Pa−0.5, which is the double of the FOM for pure PZT 30/70 films of similar thickness (1.45×10−5 Pa−0.5).

RF SPUTTERED BISMUTH FERRITE THIN FILMS: EFFECT OF ANNEALING DURATION

Polycrystalline BFO thin films of similar thickness but subjected to different annealing durations (2 hr and 4 hr) were deposited on SRO / Pt / TiO 2/ SiO 2/ Si substrates via RF sputtering. Phase identification by using X-ray diffractions confirms the pure BFO phase of the thin films fabricated. Polarization–Electric Field (P–E) loop study measured at different frequencies shows that a longer annealing duration led to the formation of space charges in the BFO thin films and thus caused a poor ferroelectric property observed in the hysteresis loop. The results of leakage current measurement for the two BFO films are consistent with the ferroelectric measurement, where a higher leakage current is demonstrated by the BFO film annealed for 4 hr.

Correlation between infrared transmission spectra and the interface trap density of SiO 2 films

This work is an attempt to estimate the electrical properties of SiO 2 thin films by recording and analyzing their infrared transmission spectra. In order to study a big variety of films having different infrared and electrical properties, we studied SiO 2 films prepared by low pressure chemical vapor deposition (LPCVD) from SiH 4 + O 2 mixtures at 425 °C and annealed at 750 °C and 950 °C for 30 min. In addition thermally grown gate quality SiO 2 films of similar thickness were studied in order to compare their infrared and electrical properties with the LPCVD oxides. It was found that all studied SiO 2 films have two groups of Si–O–Si bridges. The first group corresponds to bridges located in the bulk of the film and far away from the interfaces, the grain boundaries and defects and the second group corresponds to all other bridges located near the interfaces, the grain boundaries and defects. The relative population of the bulk over the boundary bridges was found equal to 0.60 for the LPCVD film after deposition and increased to 4.0 for the LPCVD films after annealing at 950 °C. Thermally grown SiO 2 films at 950 °C were found to have a relative population of Si–O–Si bridges equal to 3.9. The interface trap density of the LPCVD film after deposition was found equal to 5.47 × 10 12 eV −1 cm −2 and decreases to 6.50 × 10 10 eV −1 cm −2 after annealing at 950 °C for 30 min. The interface trap density of the thermally grown film was found equal to 1.27 × 10 11 eV −1 cm −2 showing that films with similar Si–O–Si bridge populations calculated from the FTIR analysis have similar interface trap densities.

Effect of material properties on low-energy electron transmission in thin chemical-vapor deposited diamond films

Electron transmission spectroscopy is used to measure the electron escape depth in thin diamond films and to examine how the transport characteristics are affected by the crystal quality and B concentration. In the studies, energy distribution and yield measurements are taken from several films with thicknesses ranging from ∼1.5 to 4.2μm, and the data are characterized in both the conduction-band and grain-boundary transport regimes. In the conduction-band transport regime, the escape depth increases from 0.5 to 0.85 to 1.3μm as the film thickness increases from 1.5 to 2.0 to 2.5μm due to the higher crystal quality in the thicker diamond films. However, the escape depth is relatively insensitive to different B concentrations in films of similar thickness. On the other hand, the B concentration more strongly affects the transmission stability. At sufficiently high B concentration (⩾1020cm−3), the transmission yields and energy distributions are fairly insensitive to changes in Io. However, at lower B concentration, the measurements exhibit evidence of sample charging in spite of a reasonably long escape depth and high secondary (reflection) yields. In investigations of the grain-boundary transport regime, the transmission characteristics are found to be largely insensitive to the crystal quality or doping levels of the diamond films, with low yields and broad energy distributions observed in all of the measurements. Moreover, the yields and energy distributions vary little with beam energy or current, except for measurements from the thickest 4.2-μm film that exhibit irregular variation in intensity and energy.

Stress-induced surface damage and grain boundary characteristics of sputtered and electroplated copper thin films

The morphology of the stress-induced surface damage and its relationship with the microstructure in electroplated and sputtered copper thin films is discussed. After annealing at 435 °C for 1 h, two types of surface damage were observed. In some films, grooves along the grain boundaries were formed, whereas in other films, voids at the grain boundary triple junctions were observed. In films of similar thickness, the triple junction voids were deeper than the grain boundary grooves. It was found that the high energy grain boundaries (HEGBs) or their triple junctions are the sites where damages are generated by thermal stress. The area ratio of the HEGBs to the surface area per grain, which is a function of both the grain size ( d) and the film thickness ( h), as well as the fraction of HEGB ( f), determines the morphological equilibrium between the two types of damage. It is suggested that, in general, a microstructural parameter, d/ hf, can be used to predict the damage morphology in Cu films.

Moisture-induced instability at the Al2O3/Ni3Al(110) interface: interfacial chemistry

STM, XPS, AES and LEED have been used to characterize the growth of ~ 1 nm thick Al2O3 films on Ni3Al(110), and on Ni3Al(111), and their reactivity towards H2O pressures (PH2O) >10−6 Torr, 300 K. As-grown films on Ni3Al(110) exhibit a true oxide layer with an incommensurate interface involving both aluminum and oxygen atoms in intermediate oxidation states. Upon exposure to PH2O > 10−5 Torr, this oxide film undergoes severe reorganization and reconstruction, and the eventual loss of all long-range order. This effect is specific to H2O; similar exposures to O2 have no effect. STM measurements indicate that this effect is pressure- rather than exposure- dependent, indicating that oxide reconstruction is due to a cooperative surface reaction involving multiple H2O molecules at a single surface site. This effect is not correlated with surface hydroxylation, observed only for PH2O > 1 Torr, in common with other alumina surfaces. The H2O-induced instability is also observed for the Al2O3/Ni3Al(111) films of similar thickness and composition but at much longer exposure time at a given water vapor pressure. The results suggest that the incommensurate nature of the Al2O3/Ni3Al(110) interface is important in the moisture-induced spallation of alumina scales.

Internal Oxidation and Mechanical Properties of Pt-IrO2 Thin Films

ABSTRACTPt-IrO2 films, approximately 200 nm thick, were fabricated by co-sputter deposition of Pt and Ir in an Ar-O2 mixture followed by annealing at 700°C in O2 for 4 hours. X-ray photoelectron spectroscopy and x-ray diffraction measurements indicate the presence of IrO2 throughout the thickness of the films. After a thermal cycle in vacuum to 700°C, the room temperature residual stress is significantly lower in the internally oxidized films than in pure Pt films of similar thickness subjected to identical cycling. Initial analysis of the behavior of the films during thermal cycling indicates that the primary cause for the difference in residual stress level is a decrease in the thermoelastic slope associated with the introduction of IrO2.

Novel Time-modulated Chemical Vapor Deposition Process for Growing Diamond Films

Smooth polycrystalline diamond films were deposited onto silicon substrates using a newly developed time-modulated chemical vapor deposition (TMCVD) process. The distinctive feature of the TMCVD process involves pulsing the hydrocarbon gas, methane, at different flow rates for varying durations into the vacuum reactor during the chemical vapor deposition (CVD) process. Generally, CVD diamond films display nonuniformity in the crystal sizes and surface roughness along the film growth profile. The TMCVD method was specifically developed to (i) deposit smooth films, (ii) control film microstructure and morphology, and (iii) improve film reliability. We show that the TMCVD process produces diamond films with improved surface smoothness as compared to films of similar thickness produced by conventional CVD method under similar conditions. Surprisingly perhaps, the TMCVD method gave growth rates much higher than the conventional CVD method without reducing the film quality as revealed by the SEM micrographs and micro-Raman spectra.

Nanocrystalline Ti-oxide-based solar cells made by sputter deposition and dye sensitization: Efficiency versus film thickness

Nanocrystalline TiO 2-based films with a special penniform microstructure were prepared by reactive DC magnetron sputtering followed by dye sensitization. The films were integrated in a solar cell configuration and were able to yield a higher photocurrent than sol–gel-produced Ti-oxide-based films of similar thickness. The photoelectric conversion efficiency reached 4% in ∼10-μm-thick sputter deposited films.