Post-deposition Processing Research Articles

Nanostructured nanofibers based on PBT and POSS: Effect of POSS on the alignment and macromolecular orientation of the nanofibers

Electrospun well aligned nanofibers based on poly(butylene terephtalate) (PBT) and polyhedral oligomeric silesquioxane (POSS) were prepared starting from polymeric solutions at different POSS contents (namely 0, 3, 6 and 10wt.%). The chemical and physical properties as well as the orientation and the polymorphic behavior of the nanostructured nanofibers were investigated by several experimental techniques, including scanning electron microscopy, wide and small angle synchrotron X-ray scattering and differential scanning calorimetry. Morphological characterization demonstrated the possibility to obtain defect free PBT/POSS nanofibers, with silsesquioxane dispersion at a submicron level, conversely to cast films where the presence of μm-sized POSS crystals was evident. Moreover, the nanofiber alignment was improved in presence of POSS.Furthermore, real time WAXS and SAXS investigations during the annealing of nanofibrous films demonstrated that electrospun nanofibers suffer from retarded crystallization. In order to assess the role played by POSS in the macromolecules self organization and packing, the post-deposition cold crystallization process of the porous films was investigated. We found that the presence of POSS affects not only the fiber alignment but also the macromolecular orientation during the annealing process.

Accelerating disorder–order transitions of FePt by preforming a metastable AgPt phase

Many approaches had been reported to successfully reduce the transition temperature of FePt from A1 to L10 phase, though without detailed knowledge. In this work, we deposited the metastable AgPt layer adjacent to the Fe layer and addressed the importance of vacancies in the disorder–order transition of FePt at reduced temperatures on the basis of a kinetic diffusion model. The decomposition of the metastable AgPt phase, creating excess vacancies during the post-deposition annealing process, accelerated the intermixing between Fe and Pt and the nucleation of L10 FePt. The evolution of phase transformation from AgPt–Fe to L10 FePt–Ag was monitored by in situ high temperature X-ray diffractometry and was also validated by first-principles calculations. The intermixing between Fe and Pt and the nucleation of L10 FePt after annealing at 230°C were directly observed by transmission electron microscopy and grazing incidence X-ray diffractometry, respectively. With the assistance of the decomposition of AgPt, we obtained a (001)-dominated L10 FePt film with an out-of-plane coercivity as large as 13.3 kOe after annealing at a temperature as low as 350°C. The principles of the proposed method can be applied for versatile disorder–order phase transitions.

Influence of annealing temperature on microstructural and electrochemical properties of rf-sputtered LiMn2O4 film cathodes

The microstructural and electrochemical properties of rf-sputtered LiMn2O4 films were investigated as a function of post-deposition process. The degree of crystallization in the films gradually increased with the increase of annealing temperature (Ta). The films annealed at Ta = 973 K exhibited characteristic peaks with predominant (111) orientation representing the cubic spinel structure of Fd3m symmetry. The estimated Mn–Mn and Mn–O distances obtained from the X-ray diffraction data were observed to be increased slightly with Ta. Characteristic changes in surface morphological features were observed as a function of Ta as evidenced from scanning electron microscopy. The estimated root mean square (RMS) roughness of the films increased from 97 to 161 nm with augmentation of Ta. The electrochemical studies, viz. cyclic voltammetry (CV), specific discharge capacity and Li ion diffusion coefficient were carried out for annealed LiMn2O4 films in saturated aqueous electrolyte (Li2SO4) in the potential window of 0–1.2 V and correlated with surface morphology and grain size. The LiMn2O4 films annealed at Ta = 973 K exhibited better electrochemical performance and demonstrated a discharge capacity of about 53.5 μA h cm−2 μm−1 with diffusion coefficient of 1.2 × 10−13 cm2 s−1.

Nanoassembly control and optical absorption in CdTe-ZnO nanocomposite thin films

The spatial distribution of CdTe nanoparticles within a ZnO thin-film matrix was manipulated using a dual-source, sequential radio-frequency (RF)-sputter deposition technique to produce nanocomposite materials with tuned spectral absorption characteristics. The relative substrate exposure time to each sputtering source was used to control the semiconductor phase connectivity, both within the film plane and along the film growth direction, to influence the degree of photocarrier confinement and the resulting optical transition energies exhibited by the CdTe phase. Significant changes (up to ΔE ≈ 0.3 eV) in the absorption onset energy for the CdTe nanoparticle ensemble were produced through modification in the extended structure of the semiconductor phase. Raman spectroscopy, cross-sectional transmission electron microscopy, and x-ray diffraction were used to confirm the phase identity of the CdTe and ZnO and to characterize the nanostructures produced in these composite films. Isochronal annealing for 5 min at temperatures up to 800 °C further indicated the potential to improve film crystallinity as well as to establish the post-deposition thermal processing limits of stability for the semiconductor phase. The study highlights the significance of ensemble behavior as a means to influence quantum-scale semiconductor optical characteristics of import to the use of such materials as the basis for a variety of optoelectronic devices, including photosensitized heterojunction components in thin film photovoltaics.

Atomic Layer Deposition and Characterization of Amorphous ErxTi1-xOy Dielectric Ultra-Thin Films

Er1-xTixOy dielectric thin films were deposited on Si(100) substrates by atomic layer deposition (ALD) using tris(methylcyclopentadienyl)erbium [(CpMe)3Er] and tetrakis(diethylamino)titanium [TDEAT] as metal precursors, and O3 as oxidant. The deposition temperature dependence of both Er2O3 and TiO2 film growths showed the overlapping ALD window of 175–250°C. Compositional tunability of Er1-xTixOy films was obtained through deposition process control. Carbon and nitrogen impurities in as-deposited films were found to be below X-ray photoelectron spectroscopy detection level. Glancing incidence X-ray diffraction and phase-shifting interferometry results showed that ErxTi1-xOy films with ALD cycle ratios (Er2O3/TiO2) of 1:8 or higher have a good thermal stability and remain amorphous with unchanged surface roughness after post-deposition rapid thermal processing (RTP) at 700°C in O2. Electrical measurements showed that optimized amorphous Er1-xTixOy films after RTP exhibited a dielectric constant of ∼36, a hysteresis voltage of less than 10 mV, and a leakage current density of 10−8 A/cm2 at −1 MV/cm; such properties compare favorably with the properties of other reported amorphous titanium-based ternary dielectrics on Si. The sizable reduction of leakage current density of Er1-xTixOy found in our study suggests that amorphous Er1-xTixOy thin films are promising future dielectrics in Si integrated circuit technology.

High electrode activity of nanostructured, columnar ceria films for solid oxide fuel cells

Highly porous oxide structures are of significant importance for a wide variety of applications in fuel cells, chemical sensors, and catalysis, due to their high surface-to-volume ratio, gas permeability, and possible unique chemical or catalytic properties. Here we fabricated and characterized Sm0.2Ce0.8O1.9−δ films with highly porous and vertically oriented morphology as a high performance solid oxide fuel cell anode as well as a model system for exploring the impact of electrode architecture on the electrochemical reaction impedance for hydrogen oxidation. Films are grown on single crystal YSZ substrates by means of pulsed laser deposition. Resulting structures are examined by SEM and BET, and are robust up to post-deposition processing temperatures as high as 900 °C. Electrochemical properties are investigated by impedance spectroscopy under H2–H2O–Ar atmospheres in the temperature regime 450–650 °C. Quantitative connections between architecture and reaction impedance and the role of ceria nanostructuring for achieving enhanced electrode activity are presented. At 650 °C, pH2O = 0.02 atm, and pH2 = 0.98 atm, the interfacial reaction resistance attains an unprecedented value of 0.21 to 0.23 Ω cm2 for porous films 4.40 μm in thickness.

Single-step solution processing of small-molecule organic semiconductor field-effect transistors at high yield

Here, we report a simple, alternative route towards high-mobility structures of the small-molecular semiconductor 5,11-bis(triethyl silylethynyl) anthradithiophene that requires one single processing step without the need for any post-deposition processing. The method relies on careful control of the casting temperature of the semiconductor and allows rapid production of transistors with uniform and reproducible device performance over large areas.

Cellular and transcriptomic analysis of human mesenchymal stem cell response to plasma-activated hydroxyapatite coating

Atmospheric pressure plasma has recently emerged as a technique with a promising future in the medical field. In this work we used the technique as a post-deposition modification process as a means to activate hydroxyapatite (HA) coatings. Contact angle goniometry, optical profilometry, scanning electron microscopy morphology imaging and X-ray photoelectron spectroscopy analysis demonstrate that surface wettability is improved after treatment, without inducing any concomitant damage to the coating. The protein adsorption pattern has been found to be preferable for MSC, and this may result in greater cell attachment and adhesion to plasma-activated HA than to untreated samples. Cell cycle distribution analysis using flow cytometry reveals a faster transition from G1 to S phase, thus leading to a faster cell proliferation rate on plasma-activated HA. This indicates that the improvement in surface wettability independently enhances cell attachment and cell proliferation, which is possibly mediated by FAK phosphorylation. Pathway-specific polymerase chain reaction arrays revealed that wettability has a substantial influence on gene expression during osteogenic differentiation of human MSC. Plasma-activated HA tends to enhance this process by systemically deregulating multiple genes. In addition, the majority of these deregulated genes had been appropriately translated, as confirmed by ELISA protein quantification. Lastly, alizarin red staining showed that plasma-activated HA is capable of improving mineralization for up to 3weeks of in vitro culture. It was concluded from this study that atmospheric pressure plasma is a potent tool for modifying the biological function of a material without causing thermal damage, such that adhesion molecules and drugs might be deposited on the original coating to improve performance.

Optical and Structural Features of Silicon-Rich Hydrogenated Amorphous Silicon Nitride Thin Films

A systematic study of fabrication and effect of post-deposition processing on the optical and structural features of silicon-rich hydrogenated amorphous silicon nitride thin films deposited by Hg-sensitized Photo-Chemical Vapour Deposition technique is presented. Both deposition parameters and post-deposition thermal treatment resulted into substantial change in the refractive index associated with the densification of the film. Our studies reveal that the presence of hydrogen and its out-diffusion upon thermal treatment play a crucial role in the overall structural evolution, specially the stabilization of individual phases such as Si and Si3N4. We further report the room-temperature photoluminescence from as-deposited films, which is due to formation of silicon nanostructures in crystalline and amorphous forms. These studies are of great interest from the prospective of commercially viable Si-based technology.

In-situ x-ray diffraction studies on post-deposition vacuum-annealing of ultra-thin iron oxide films

A maghemite (γ-Fe2O3) film of 8.3 nm thickness is epitaxially grown on MgO(001) single crystal substrate by reactive molecular beam epitaxy. Chemical composition and crystal structure of the surface was studied by x-ray photoelectron spectroscopy and low energy electron diffraction, respectively. Afterwards the sample was moved to a heating cell for in situ x-ray diffraction experiments on the post-deposition annealing process in high-vacuum to study structural phase transitions of the iron oxide film. The iron oxide film is reduced with increasing temperature. This reduction occurs in two steps that are accompanied by structural transitions. The first step is a reduction from γ-Fe2O3 to Fe3O4 at 360 °C and the second step is the reduction from Fe3O4 to FeO at 410 °C.

Low Equivalent Oxide Thickness TiO2 Based Capacitors for DRAM Application

Properties of TiO2 based DRAM capacitors with equivalent oxide thickness of 0.5 nm are described. It is shown, that dielectric constant values more than 100 can be obtained in these structures for the TiO2 films with the thickness down to 10 nm. Leakage current density below 10-7 A/cm2 at 0.8 V can be obtained after post-deposition processing for the films with the thickness of 16 nm (EOT ≈ 0.5 nm). Al doping of the TiO2 films decreases dielectric constant, but improves leakage current density. Al-doped TiO2 films with the thickness of 10 nm (EOT = 0.46 nm) exhibit leakage current density below 10-7 A/cm at 0.8 V.

Remote plasma-deposited GeO 2 with quartz-like Ge- and O-local bonding: Band-edge state and O-vacancy comparisons with SiO 2

X-ray absorption spectroscopy (XAS) and many-electron theory are combined to describe symmetries and degeneracies for intrinsic bonding defects in remote plasma-deposited (rpd-) non-crystalline (nc-), rpd-nc-GeO 2 and rpd-nc-SiO 2, hereafter simply GeO 2 and SiO 2. GeO 2 is emerging as an alternative gate dielectric for nano-CMOS devices. High resolution O-vacancy spectral features in O K pre-edge spectra for SiO 2 have been assigned to multiplet transitions and negative ion states based on an extended d 2 equivalent model, including both weaker singlet and as well the stronger triplet transitions discussed in previous publications. This has revealed predominantly mid-gap Ge and Si singlet and triplet bonding arrangements for the electrons in O-vacancy sites. These have been examined as a function of post deposition rapid thermal annealing in Ar ambients for GeO 2 deposited at 300 °C on both Si and Ge substrates, identifying different post-deposition thermal budget processing windows for low defect density GeO 2 on Si and Ge substrates. For ultra thin nitrided SiO x , x < 2 interfacial layers on Si, this is at least 700 °C, but on Ge, independent of surface processing it less than 600 °C.

Leakage Current Reduction Mechanism of Oxide–Nitride–Oxide Inter-Poly Dielectrics through the Post Plasma Oxidation Treatment

High quality oxide–nitride–oxide (ONO) inter-poly dielectrics were successfully fabricated by the optimized plasma oxidation without H2. The bottom low pressure chemical vapor deposition (LPCVD) oxides treated by the conventional N2O annealing step were subjected to the post deposition process using a plasma treatment. This process reduces both the leakage current and the stress-induced leakage current (SILC), while no thickness increase of the bottom LPCVD oxides was observed due to the plasma treatment. Based on the photo electron injection technique, it is found that the O2 plasma oxidation method significantly reduces the defect centers located at 1.67 nm away from the bottom oxide/floating gate interface.

Post-deposition processing and oxygen content of TiO 2-based capacitors

Properties of TiO 2-based capacitors with RuO 2 bottom electrode were examined. It is shown that post-deposition room temperature plasma treatment and oxygen annealing at 300 °C significantly reduces amount of impurities in the TiO 2 layer. Leakage current density of the capacitors is suppressed due to improvement of oxygen stoichiometry and increase of Schottky barrier height at the TiO 2-dielectric/metal electrode interface after post-deposition processing. Leakage current density below 10 −7 A/cm 2 was achieved for capacitor with equivalent oxide thickness of 0.58 nm.

Layer structure variations of ultra-thin HfO 2 films induced by post-deposition annealing

To meet challenges for a smaller transistor feature size, ultra-thin HfO 2 high- k dielectric has been used to replace SiO 2 for the gate dielectric. In order to accurately analyze the ultra-thin HfO 2 films by grazing incidence X-ray reflectivity (GIXRR), an appropriate material model with a proper layer structure is required. However, the accurate model is difficult to obtain, since the interfaces between layers of the ultra-thin HfO 2 films are not easily identified, especially when post-deposition annealing process is applied. In this paper, 3.0 nm HfO 2 films were prepared by atomic layer deposition on p-type silicon wafer, and annealed in Ar environment with temperatures up to 1000 °C. The layer structures and the role of the interfacial layer of the films in the post-deposition annealing processes were evaluated by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The experimental results and analysis showed that layer thicknesses, crystal phases and chemical structures of the ultra-thin HfO 2 films were significantly dependent on annealing temperatures. The binding energy shifts of Hf 4 f, O 1 s, and Si 2 p elements revealed the formation of Hf silicate (Hf–O–Si bonding) with increasing annealing temperatures. Due to the silicate formation and increasing silicon oxide formation, the interface broadening is highly expected. The structure analysis of the GIXRR spectra using the modified material structure model from the XPS analysis confirmed the interfacial broadening induced by the post-deposition annealing.

RF-Sputtered ZnO Thin Films: The Tailoring of Structural, Electrical and Optical Properties

ABSTRACTWe report on the influence of radio-frequency magnetron sputtering variables (working pressure and deposition atmosphere) and post-deposition thermal treatment processing upon the structural, optical and electrical properties of c-axis highly textured ZnO thin films. The films’ crystallinity increased progressively with argon pressure for the inert atmosphere experiments and with the oxygen dilution in the working atmosphere (up to 10%) for the reactive atmosphere experiments. The post-deposition annealing treatment at 450°C/1h in air reduced the strain in the ZnO films and enhanced their crystallinity and texturing. The ZnO films had an average transmittance of ∼90% in visible range and an average band-gap of ∼3.4 eV, regardless of the sputtering variables used. The samples prepared at the higher argon pressure (0.45 Pa) had a resistivity with one order of magnitude smaller than the samples prepared at the lower pressures.

Effect of hydrogen on hardness of amorphous silicon

A comparative study of hardness of thin films of hydrogenated amorphous silicon (a-Si:H) and hydrogen-free amorphous silicon (a-Si) was carried out to reveal the role of hydrogen in the plastic properties of amorphous silicon. In addition, the effect of hydrogen on hardness was established by changing hydrogen concentration in the material using post-deposition processing of the samples. The hydrogen concentration in a-Si:H was decreased by thermal annealing. In a-Si hydrogen was introduced by plasma hydrogenation. The values of hardness of the as-prepared a-Si and a-Si:H films were determined by nanoindentation using depth profiling. Low-depth indentation was applied to evaluate the effect of post-hydrogenation. The results obtained show that the presence of hydrogen in the amorphous silicon network leads to the increase in hardness. The conducted experiments demonstrate that plasma hydrogenation can be used as an effective tool to increase the hardness of amorphous silicon. Hardness of a-Si:H of about 12.3–12.7 GPa is as high as of crystalline silicon, suggesting a-Si:H can be a substitute for crystalline silicon in some MEMS.

Electrical and optical properties of ITO and ITO/Cr-doped ITO films

In this paper we report on the effects of the insertion of Cr atoms on the electrical and optical properties of indium tin oxide (ITO) films to be used as electrodes in spin-polarized light-emitting devices. ITO films and ITO(80 nm)/Cr-doped ITO(20 nm) bilayers and Cr-doped ITO films with a thickness of 20 nm were grown by pulsed ArF excimer laser deposition. The optical, structural, morphological and electrical properties of ITO films and ITO/Cr-doped structures were characterized by UV–Visible transmission and reflection spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and Hall-effect analysis. For the different investigations, the samples were deposited on different substrates like silica and carbon coated Cu grids. ITO films with a thickness of 100 nm, a resistivity as low as ∼4×10−4 Ω cm, an energy gap of ∼4.3 eV and an atomic scale roughness were deposited at room temperature without any post-deposition process. The insertion of Cr into the ITO matrix in the upper 20 nm of the ITO matrix induced variations in the physical properties of the structure like an increase of average roughness (∼0.4–0.5 nm) and resistivity (up to ∼8×10−4 Ω cm). These variations were correlated to the microstructure of the Cr-doped ITO films with particular attention to the upper 20 nm.

Controlling the photoluminescence of ZnO:Si nano-composite films by heat-treatment

Nano-composite thin films of silicon and zinc oxide were deposited on glass substrates using thermal co-evaporation. On heating the films at different temperatures and different atmospheric pressures, the photoluminescence (PL) emission spectra become broad, giving emissions in UV-Blue, Green and Red region. Analyses reveal that defect-dominated structure of ZnO contributes to the broad PL spectra observed. X-ray diffraction and Raman spectra analysis show that the defects caused by oxygen vacancies decrease with heating which is accompanied by a competing process of decrease in grain size made possible by surrounding silicon reacting at the surface of the ZnO nano-cluster grains giving new bonds, possibly O–Si–Zn bonds. Crystallinity of nano-grains and defects contribute different emission peaks that depending on relative contributions can give comparable peaks resulting in broad emission spectra. The study shows that simple post-deposition process can lead to fabrication of white light emitting devices based on these nano-composites. Best emission spectra are obtained by heating at a temperature of 250 °C in low vacuum.

Interfacial electronic structure of vanadyl naphthalocyanine on highly ordered pyrolytic graphite

We present a core and valence region spectroscopic analysis of the interfacial electronic structure of thin films of vanadyl naphthalocyanine (VONc) deposited onto highly oriented pyrolytic graphite (HOPG). X-ray photoelectron spectroscopy indicates the predominantly ionic character of the vanadyl metal center coordinated by the heterocycle and affords the bandgap in the thin VONc films. Valence band photoelectron spectroscopy points to the existence of three different adsorption geometries of VONc on the HOPG surface. The distribution of the different geometries can be systematically influenced in a simple post-deposition processing step, with an immediate effect on the interfacial electronic environment. We find spectroscopic evidence in the valence levels that VONc grows on HOPG most likely in a 2D-gas fashion rather than by nucleation and growth of islands. These data allow us to predict accurately the interface dipole in the case of a broad class of dipolar organic semiconductors, based simply on molecular dipole moment, polarizability and molecular diameter. This ability provides an important step towards rational optimization of energy level alignment in organic electronics.