Thermal Stability Of Thin Films Research Articles

The effect of the graded bilayer design on the strain depth profiles and microstructure of Cu/W nano-multilayers

The properties and thermal stability of thin films and nano-multilayers (NMLs) are generally governed by the in-depth stress (strain) gradients rather than the average stress state. The effect of strain gradient variation in Cu/W NMLs on the thermal stability between 400 and 800 °C was investigated. The strain distribution in the NML stacks was varied by combining Cu/W bilayers with different Cu and W thicknesses of either 3 or 10 nm. A recently developed method based on in-plane grazing X-ray diffraction was adopted to extract the strain depth profiles. In addition, the evolution of the average stress in the Cu/W NMLs during growth was monitored by an in-situ wafer curvature technique. The mean residual stresses in Cu and W were found to be independent of the disposition of the different Cu/W bilayer substacks. On the contrary, the strain depth profile of the W nanolayers was found to strongly depend on the disposition of Cu/W bilayer substacks in the Cu/W NML, which resulted in different Cu outflow characteristics upon annealing. Moreover, application of different Cu/W bilayer units within the NML stack also provides an innovative pathway for producing Cu/W nanocomposites with graded thermal and mechanical properties.

Synthesis of Optically Tunable and Thermally Stable PMMA-PVA/CuO NPs Hybrid Nanocomposite Thin Films.

We report the synthesis and comprehensive characterization of polymethylmethacrylate (PMMA)/polyvinylalcohol (PVA) polymeric blend doped with different concentrations of Copper oxide (CuO) nanoparticles (NPs). The PMMA–PVA/CuO nanocomposite hybrid thin films containing wt.% = 0%, 2%, 4%, 8%, and 16% of CuO NPs are deposited on glass substrates via dip-coating technique. Key optical parameters are measured, analyzed, and interpreted. Tauc, Urbach, Spitzer–Fan, and Drude models are employed to calculate the optical bandgap energy (Eg) and the optoelectronic parameters of PMMA–PVA/CuO nanocomposites. The refractive index and Eg of undoped PMMA–PVA are found to be (1.5–1.85) and 4.101 eV, respectively. Incorporation of specific concentrations of CuO NPs into PMMA–PVA blend leads to a considerable decrease in Eg and to an increase of the refractive index. Moreover, Fourier Transform Infrared Spectroscopy (FTIR) transmittance spectra are measured and analyzed for undoped and doped polymeric thin films to pinpoint the major vibrational modes in the spectral range (500 and 4000 cm−1) as well as to elucidate the nature of chemical network bonding. Thermogravimetric analysis (TGA) is conducted under appropriate conditions to ensure the thermal stability of thin films. Doped polymeric thin films are found to be thermally stable below 105 °C. Therefore, controlled tuning of optoelectronic and thermal properties of doped polymeric thin films by introducing an appropriate concentration of inorganic fillers leads to a smart design of scaled multifunctional devices.

Spectroscopic characterization of optical and thermal properties of (PMMA-PVA) hybrid thin films doped with SiO2 nanoparticles

Doped polymeric hybrid thin films based on Poly-Methyl-Meth-Acrylate (PMMA) and Poly-vinyl-alcohol (PVA) doped with silica nanoparticles (SiO2 NPs) are synthesized using the dip-coating technique. The as-prepared (PMMA-PVA)/SiO2 nanocomposite (wt% of SiO2 NPs = 2%, 4%, 8%, and 16%) are deposited on glass substrates. Transmittance (T%) and reflectance (R%) are measured using a UV–Vis spectrometer. Furthermore, other related optical parameters such as absorption coefficient (α), optical constants (n and k), and optical dielectric functions (ε1 and ε2) are calculated using experimental transmittance, reflectance spectra and well-established classical models such as Tauc, Urbach and Spitzer-Fan and Drude models. The Tauc model is used to estimate the optical bandgap energy. Incorporation of specific concentrations of SiO2 NPs into PMMA-PVA polymeric matrix leads to a noticeable decrease of the optical bandgap. The optical bandgap of un-doped PMMA-PVA thin-film is estimated to be 4.069 eV. Consequently, bandgap engineering and manipulation of optical properties are possible. Additionally, refractive indices (n) of undoped PMMA-PVA polymeric thin films are calculated to be in the range (1.48–1.72). To elucidate and identify vibrational modes of thin films, Fourier-transform infrared spectroscopy (FTIR) is employed in the spectral range (500 cm−1–4000 cm−1). The results obtained are useful for a better understanding of the lattice dynamics. Moreover, thermal stability of thin films is investigated using thermogravimetric (TGA) technique. Remarkably, TGA thermograms reveal that doped thin films are thermally stable below 110C. Consequently, investigated thin films may have the potential to be key candidates for real-time optical and optoelectronic devices.

Phase analysis and thermal stability of thin films synthesized via solid state reaction of Ni with Si1 − xGex substrate

The products of the solid state reaction involving ultra-thin Ni film (6nm) and Si1−xGex layers (Ge 25 and 55at.%), were analysed using sheet resistance (Rs), glancing angle X-ray diffraction (GIXRD), scanning electron and atomic force microscopy (SEM, AFM) techniques. The reaction was carried out via rapid thermal process (RTP) annealing using two different steps (RTP1 and RTP2) while applying a selective etch (SE) in between them. The intermediate and the end reaction products resulting after RTP1 and RTP2 were found to be dependent on the Ge content, forming Ni-rich silicide (Ni2Si) and NiSi on Si75Ge25, while Ni-rich germanide (Ni5Ge3) and NiGe were obtained by using Si45Ge55. Though the onset of intermediate Ni-rich silicide or germanide phase formation occurs at similar RTP1 temperature (275°C), the reaction completion to yield low resistive phase NiSi or NiGe phase results at different RTP2 temperatures (400°C vs 350°C). Based on the volume expansion, a resistivity value of 25μΩcm was obtained for the synthesized NiGe (12nm) and NiSi (14nm) layers. Independent of the phases obtained, the films were found to be closed and homogeneous and exhibit rms roughness of 0.5–0.8nm as evidenced by SEM and AFM analysis. Thermal stability studies carried out on NiSi and NiGe thin films, post RTP1/RTP2, show the latter phase to have limited stability and result in Rs degradation starting already at 475°C due to phase decomposition.

Time dependence and mechanism of Au nanostructure transformation during annealing

Melting point of thin nanostructured materials decreases with decreasing particle size. This can influence thermal stability of thin films used in electronic applications and compromise their function. Therefore it is desirable to explore connection between metal film thickness and its thermal stability. Thin films of Au were sputtered for 10–300 s (2–60 nm thick layers). Post deposition annealing was carried out at 150–300°C for 15–180 min. Sheet electrical resistance measurements were employed to investigate electrical continuousness of the Au film. A significant leap in percolation threshold was found between samples annealed at 250°C and 300°C. This suggests that phase transition occurs during annealing, however, annealing for different times suggests the structural modification is a gradual and slow process, which is a sign of diffusion in a solid state. This was further supported by UV–Vis measurements which showed slow evolution of plasmon resonance peak. Convincing direct evidence of the surface morphology evolution was obtained by AFM microscopy.

Grain boundary grooving in thin films revisited: The role of interface diffusion

Thin nickel (Ni) films were grown on c-plane-oriented sapphire substrates by electron-beam deposition. The as-deposited films exhibited a mazed bicrystal microstructure consisting of interwoven grains of two twinned orientations. Annealing of the specimens at 700°C resulted in the thickening of the Ni film. At the same time a mass deficit in the surface regions near grain boundary thermal grooves was observed. The shape of the observed grooves was very different from that predicted by the classical Mullins model. We developed a model of thermal grooving with simultaneous film thickening due to Ni diffusion along the Ni–sapphire interphase boundary, which agreed well with the experimental results. These findings demonstrate that self-diffusion of metal atoms along the metal–ceramic interface plays an important role in mass transport in thin films. Some implications of fast interphase boundary diffusion for the thermal stability of thin films are discussed.

Thermal properties of phase change material Ge2Sb2Te5 doped with Bi

The influence of Bi doping on the thermal properties and thermal stability of Ge2Sb2Te5 thin films was investigated. It was shown that Bi doping allows the change of thermal properties in wide range, and increase thermal stability of thin films. It was also shown that the doping of bismuth affects the electrical properties of the material. The existence of two Bi concentration ranges with two different doping mechanisms and influences on the film properties was established. In the range of low concentrations (0.5–1.0wt.% of Bi) the anomalous deviations of properties from main tendencies were observed. This effect is explained with the use of percolation theory when at critical concentration (percolation threshold) formation of infinite cluster is accompanied by critical phenomena.

Improved thermal stability in organic FET fabricated with a soluble BTBT derivative

We have synthesized a new benzothienobenzothiophene (BTBT) derivative, 2-octylthienylbenzothienobenzothiophene having a highly ordered liquid crystal phase of smectic E (SmE) in the temperature range next to its crystal phase, fabricated its polycrystalline thin films by spin-coating technique, and applied them to field effect transistors (FETs). Thanks to the liquid crystal phase as a precursor of polycrystalline thin films, the resulting films were molecularly flat and uniform. The thermal stability of the thin films was very much improved compared with dialkyl BTBT derivatives because of the solid-like nature of the SmE phase up to 180°C. The FETs fabricated with films after solvent vapor annealing with toluene showed high FET mobility of 1.4±0.3cm2/Vs. As expected, the FETs were not destroyed by thermal load up to 150°C. The FET mobility was recovered to 0.54cm2/Vs by the solvent vapor annealing, although the FET mobility was decreased by the thermal load. Highly ordered liquid crystalline phases provide us with easy fabrication of quality polycrystalline thin films and high thermal stability of the polycrystalline thin films.

Stability of Selected Chromophores in Biopolymer Matrix

Photochemical and thermal stability of thin films formed from selected optically responsive chromophores embedded in deoxyribonucleic acid (DNA), Collagen and in the complex formed by DNA biopolymer and the surfactant hexadecyl ammonium (CTMA) matrix was studied by UV-VIS and compared with that observed when using some synthetic polymers (polymethylmetacrylate – PMMA, polycarbonate – PC). In particular the influence of external stimuli, such as heating and UV light on the chemical degradation process was investigated.

Functionalized mesoporous silica/polyimide nanocomposite thin films with improved mechanical properties and low dielectric constant

A series of composite thin films composed of mesoporous silica (SBA-15) filled in polyimide were synthesized. The effect of SBA-15 modified with functional group of octyltrimethoxysilane (OTMS) or 3-aminopropyl trimethoxy silane (ATS) on the mechanical and dielectric properties as well as the thermal stability of thin films were investigated. The tensile strength and elongation of the composite films containing SBA-15 modified with ATS were higher than those with OTMS and pristine SBA-15. The dielectric constant was significantly reduced with increasing SBA-15 modified with ATS. The result indicates that the composite materials are potentially useful in radio-frequency/microwave substrate materials.

Effect of Substrate and Molecular Weight on the Stability of Thin Films of Semicrystalline Block Copolymers

The thermal stability of the thin film morphology of two symmetric oxyethylene/oxybutylene block copolymers (E76B38 and E114B56) on mica and silicon was investigated via atomic force microscopy (AFM). It is found that morphological transition of EmBn thin films during melting is strongly dependent on the molecular weight of the diblock copolymers and their interaction with the substrate. For E76B38 on mica, a single-layered structure transforms into a double-layered structure upon melting, but the same polymer on silicon retains a single-layered structure after melting and spreads quickly to wet-out the silicon surface. Conversely a longer polymer, E114B56, has a thin film on mica that does not change much after melting of the crystalline E block. A mechanism was proposed to explain the relative stability of E76B38 and E114B56 thin films upon melting. Internal stress is produced during melting and can be released along two directions. The release along the vertical direction is restricted by the energy barrier related to the segregation strength, and the release along the horizontal direction is dependent on the mobility of block copolymer related to the interaction between the block copolymer and the substrate. Domain size affects the release rate of the internal stress along the horizontal direction and thus the thermal stability of EmBn thin films. Switching between horizontal and vertical releases can be realized by controlling the domain size of the thin films.

Structure and thermal stability of δ-Bi2O3 thin films deposited by reactive sputtering

Nanocrystalline δ-Bi2O3 thin films have been deposited onto Si (100) and quartz substrates by reactive sputtering. The structural characteristics and thermal stability of the thin films have been investigated by x-ray diffraction and Raman spectra. It was found that the δ-Bi2O3 thin films could exist stably below 200 °C and undergo a phase transition sequence δ → β → α with increasing annealing temperature beyond 200 °C. These phase transitions were further confirmed by optical constant and optical band gap studies.

Thermal stability of TiO2, ZrO2, or HfO2 on Si(100) by photoelectron emission microscopy

The thermal stability of thin films (3nm) of transition-metal (TM) oxides (TiO2, ZrO2, and HfO2) grown on ultrathin (∼0.5nm) SiO2 buffer layers on Si(100) surfaces was investigated with ultraviolet photoelectron emission microscopy (UV-PEEM). The decomposition of the TM oxides was observed in the PEEM during ultrahigh-vacuum annealing at temperatures of ∼870, ∼900, and ∼1000°C for the TiO2, ZrO2, and HfO2, respectively. Following the decomposition reaction, atomic force microscopy measurements of the annealed surfaces revealed a high density of islands in the decomposed regions. The degradation of the TM oxide films is attributed to a reaction occurring at defects at the TM oxide/SiO2∕Si interfaces, which forms SiO species. Once a portion of the interfacial SiO2 layer is desorbed as a result of this reaction, Si from the substrate can diffuse into contact with the TM oxide layer, resulting in the formation of a TM silicide and the evolution of SiO. This process continues until the entire TM oxide layer is consumed and only silicide islands remain.

Controlling the Thermal Stability of Thin Films by Interfacial Engineering

The quantized electronic structure in Pb films on Si(111) varies substantially as the film thickness increases. The changes in electronic energy cause the thermal stability of the films to oscillate with an approximate bilayer period. The phase of the oscillations can be controlled by interfacial engineering. Comparison of Pb films prepared on Si(111) terminated by In, Au, and Pb as interfactants reveals a phase reversal. For , films made of odd numbers of atomic layers (5, 7, and 9) are more stable than the even ones. This trend is reversed for the other two cases.

Effect of annealing on CoSi 2 thin films prepared by magnetron sputtering

Cobalt disilicide (CoSi 2) thin films were prepared by radio frequency magnetron sputtering using CoSi 2 alloy target which features lower stress and more simplicity. The structure and resistivity of thin films annealed at different temperatures for different time were researched by X-ray diffraction (XRD) and four-point probe, respectively. The best electrical resistivity (23 μΩ cm), which is similar to the value of the thin films prepared by a solid state reaction, was obtained when the thin films were annealed at 600 °C in air or argon ambient. The decrease of resistivity was attributed to the grain growth and defects decrease while the increase of resistivity was ascribed to the degradation of thin films. The thermal stability of thin films was improved by oxygen.

Strongly Enhanced Thermal Stability of Crystalline Organic Thin Films Induced by Aluminum Oxide Capping Layers

The thermal stability of thin films of di-indenoperylene (DIP), an organic semiconductor is shown via thermal desorption spectroscopy (TDS) and in-situ X-ray diffraction to be strongly enhanced by aluminum oxide capping layers. Possible mechanisms for the eventual breakdown of the film (which remains crystalline up to 460 °C) at high temperatures are discussed (see Figure).

THERMAL STABILITY STUDY OF TANTALUM NITRIDE THIN FILMS BY SPECTROSCOPIC ELLIPSOMETRY

Spectroscopic ellipsometry was successfully applied in the evaluation of the thermal stability of thin films in air by detecting the changes in film optical properties and thickness. Tantalum nitride ( Ta x N y) films with a nominal thickness of 30 nm were deposited on silicon wafer and annealed at different temperatures from 200°C to 700°C. Annealing-induced changes in thickness and optical properties of Ta x N y were detected and determined by spectroscopic ellipsometry. Different approaches were adopted in the modeling and analysis of spectroscopic ellipsometric data. The results are consistent with the findings from Fourier Transform Infrared Spectroscopy (FTIR).

Roughness effects on the thermal stability of thin films

In this work, we investigate interface roughness effects on the energetic terms that play a key role on the thermal stability of thin silicide films. The roughness is modeled as a self-affine structure with power spectrum ∼σ2ξ2(1+aq2ξ2)−1−H convoluted with a domain size distribution ∝e−πR2/ζ2 to account for grain finite size effects in polycrystalline films. The parameters σ, ξ, H, and ζ denote respectively the rms roughness, the roughness correlation length, the roughness exponent, and the average domain size. The roughness effect becomes significant for small H (<0.5), and large long-wavelength roughness or σ/ξ(∼0.1). Indeed, in systems where agglomeration occurs via thermal grooving, roughness may increase significantly the critical grain sizes.

The thermal stability of AlN

The thermal stability of AlN powders and thin films has been investigated using reflection high-energy electron diffraction (RHEED) and X-ray diffraction. AlN powder was treated thermally and chemically to assess the oxidation resistance of this compound and to identify the phases formed. The results show that AlN is stable up to 1000° C in air and remains stable up to 1400° Cin vacuo. γ-AIOOH is formed when AlN is treated with water at 100° C but AlN does not react readily with atmospheric moisture at room temperature. The thermal stability of thin films of AlN on GaAs has been evaluated at temperatures between 900 and 1100° C in a nitrogen atomosphere. It was found that AlN did not oxidize under these conditions. Pure AlN is a suitable encapsulant for GaAs at high annealing temperatures in an inert atmosphere.