Function Of Thermal Annealing Research Articles

Raman and Photoluminescence Spectroscopic Studies on Structural Disorder in Oxygen Deficient Gd2Ti2O7‐δ Single Crystals

AbstractRaman and photoluminescence spectroscopic studies on oxygen vacancy‐induced structural disorder in Gd2Ti2O7‐δ single crystals grown by optical floating zone technique under argon atmosphere are reported. The oxygen vacancies in Gd2Ti2O7‐δ wafers decrease with thermal annealing in air atmosphere. The full width at half maximum of X‐ray diffraction rocking curve decreases from 245 to 157 arcsec and the optical transmittance increases from 23% to 87% (at 1000 nm) upon post growth thermal annealing. Raman spectroscopic studies reveal a monotonic increase in intensity of O–Gd–O (Eg) and Ti–O (A1g) stretching modes with thermal annealing. Since these modes are associated with modulation of oxygen x parameter which is sensitive to Ti–O octahedron distortion, the increase in Raman intensity indicates an improvement in structural ordering of oxygen sub‐lattice in Gd2Ti2O7‐δ. Moreover, the photoluminescence studies also corroborate the Raman analysis in terms of reduction of structural defects associated with oxygen vacancies as a function of thermal annealing. This study demonstrates the effectiveness of using Raman spectroscopy to probe the structural disorder in Gd2Ti2O7‐δ crystals.

Anomalous Behavior of Magnetic Anisotropy of Amorphous Co40Fe43B17 Thin Film Sandwiched Between Mo Layers

Anomalous behavior of magnetic anisotropy in Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">43</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> film sandwiched between Mo layers has been observed as a function of thermal annealing at different temperatures. The as-deposited amorphous film exhibits a uniaxial magnetic anisotropy, the origin of which can be traced to quenched-in stresses. With thermal annealing up to 300 °C, anisotropy remains unchanged. We observe an anomalous magnetic reversal near the hard axis (HA) in the samples annealed at 350 °C and above. The anomaly of the occurrence of nonuniform magnetization near HA can be explained in terms of distribution of easy magnetization direction, as evidenced by the ripple domain structure in Kerr microscopy images.

The Correlation of Optical Transmittance with Structural Evolution in Fluorozirconate Glass (ZLANI) Thin Films as a Function of Thermal Annealing

The Correlation of Optical Transmittance with Structural Evolution in Fluorozirconate Glass (ZLANI) Thin Films as a Function of Thermal Annealing

Spectroscopic Characterization of the Electronic Structure, Chemical Bonding, and Band Gap in Thermally Annealed Polycrystalline Ga2O3 Thin Films

Gallium oxide (Ga2O3) thin films were deposited onto Si(100) substrates at 500°C by sputtering the Ga2O3 ceramic target. The effect of thermal annealing in the temperature range of 500–900°C on the crystal structure, chemical bonding, electronic structure, and bandgap of polycrystalline Ga2O3 films was evaluated. Thermal annealing induced improvement in the structural quality and packing density of the Ga2O3 films as evident from X-ray diffraction and Raman spectroscopic analyses. X-ray photoelectron spectroscopic (XPS) analyses indicate the binding energies (BE) of the Ga 2p doublet i.e., the Ga 2p3/2 and Ga 2p1/2 peaks, are located at 1118.0 and 1145.0 eV, respectively, characterizing gallium in its highest chemical oxidation state (Ga3+) in the as-deposited films. The core level XPS spectra of O 1s indicate that the peak is centered at a BE∼531 eV, which is also characteristic of Ga-O bonds in the Ga2O3 phase. No significant changes were seen in the electronic structure, especially in terms of chemical valence of Ga ions and Ga-O bonds, as function of thermal annealing in the entire temperature range of 500–900°C. However, the presence of carbonyl functional groups become evident in XPS for samples under thermal annealing. Raman analysis also reveals an obvious blueshift for the high-frequency stretching and bending of the GaO4 tetrahedra, which structurally form the β-Ga2O3, with confinement. The bandgap determined from spectrophotometry measurements varies in the range of 4.94–4.78 eV for a variation in annealing temperature in the range of 500–900°C. A correlation between annealing temperature, electronic structure, chemical bonding and bandgap in Ga2O3 films is established.

Impedance spectroscopy and capacitance – voltage measurements analysis: Impact of charge carrier lifetimes and mapping vertical segregation in bulk heterojunction P3HT: PCBM solar cells

Impedance spectroscopy measurement is employed to study the impact of thermal annealing on charge carrier lifetimes in P3HT: PCBM bulk heterojunction solar cells. Upon thermal annealing at 150 °C, a correlation between charge carrier lifetime and device performance is identified. The best power conversion efficiency reported here corresponds to the devices annealed at 150 °C, yielding the longest charge carrier life time. In addition to lateral segregation, thermal annealing promotes accumulation of PCBM molecular aggregates towards the cathode inducing vertical segregation as is evident from the analysis of results obtained from capacitance – voltage measurements. Based on Mott-Schottky relation, the measured values of the flat band potential as a function of thermal annealing is correlated to the concentration of PCBM at cathode interface and a compositional gradient profile induced by thermal annealing is proposed.

Correlation of annealing temperature, morphology, and electro-mechanical properties of electrospun piezoelectric nanofibers

Piezoelectric polymeric nanofibers, such as P(VDF-TrFE), are promising nanostructures for sensing/actuation applications where flexibility of the component is required, for example soft robotics, conformal sensors, and energy harvesting devices. A challenge in polymeric piezoelectric materials is that their electromechanical coupling efficiency must be improved to approach that of bulk piezo ceramics. The electromechanical coupling factor is proportional to Yd2 (where Y is the elastic modulus, and d is the piezoelectric constant); therefore, the investigation of inter-dependence of these properties as function of thermal annealing is important. Although effect of thermal annealing on thin film of PVDF has been studied, however, detailed investigations of correlation of annealing temperature, morphology, and electro-mechanical properties of electrospun piezoelectric nanofibers have not been reported, in particular at single nanofiber level. We report on the effect of various annealing temperatures on mechanical and piezoelectric properties at the single nanofiber level using nanoindentation and piezoresponse force microscopy (PFM). FTIR, XRD, and WAXD spectroscopies were also employed to quantitatively and qualitatively explain the enhancement of these properties.

XRD and ToF-SIMS study of intermetallic void formation in Cu-Sn micro-connects

An identified reliability challenge of significant importance to Cu–Sn bonding for 3D integration is Cu–Sn intermetallic void formation. Voids, often referred to as Kirkendall voids, form within the inter-diffusional zone between Cu and Sn, more specifically within the intermetallic compound Cu3Sn. The root-cause(s) of void formation is not well understood, therefore this study is designed to understand under what conditions voids form. The two main hypotheses for the root-causes of void formation are (i) the imbalance of diffusion rates between Cu and Sn during the formation of Cu–Sn intermetallic compounds and the resulting residual stresses and (ii) the co-deposition of impurities during Cu electroplating to void formation. Therefore, an ex- and in-situ x-ray diffraction (XRD) study is used to probe the material state as a function of thermal annealing, and a time-of-flight mass spectroscopy (ToF-SIMS) study is used to detect impurities co-deposited during Cu electroplating and to understand the effects of thermal annealing on the impurities' kinetic behaviour.

Evolution with thermal annealing of magnetic anisotropy in FeCoB thin film interfaced with Mo layers

Evolution of magnetic properties of thin FeCoB films sandwiched between two Mo layers has been studied as a function of thermal annealing at different temperatures. The as-deposited film exhibits a uniaxial magnetic anisotropy. With thermal annealing up to 300°C, anisotropy gradually decreases while coercivity exhibits a significant increase. Uniaxial anisotropy reappears after annealing at 400°C. In order to understand the origin of magnetic anisotropy in the film, in-plane and out-plane X-ray diffraction measurements have been done using Hard X-ray beamline BL-11 of INDUS-2. It is found that with thermal annealing the film exhibits significant changes in grain texture as well as internal stresses. Variation in grain texture in the film is expected to be the main cause for observed magnetic anisotropy.

Correlating photovoltaic properties of a PTB7-Th:PC71BM blend to photophysics and microstructure as a function of thermal annealing

The effect of thermal annealing on a polymer solar cell is investigated and related to changes in the photophysics and structure.

Analysis of Blockade in Charge Transport Across Polymeric Heterojunctions as a Function of Thermal Annealing: A Different Perspective

A blend of poly(3-hexylthiophene-2,5diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is popularly used as an active medium in polymeric solar devices. According to the most recent understanding, the blend is a three-phase system contrary to its earlier understanding of two-phase bicontinuous network. We have synthesized a P3HT–PCBM based layered heterostructure system by spin coating and thermal vacuum evaporations. Current density (J) was measured as a function of applied electric field (E) across the system bound between two metal electrodes. J–E relations were analyzed into the backdrop of space charge limited current model and Schottky model. The later was used to predict dc-dielectric constants from the linear slopes of ln (J) versus E 1/2. The curves were not monotonously linear, but observe a knee-bend separating into two linear segments for each curve. Thermal annealing from 40°C to 80°C was used as an activation tool for driving changes in the internal morphology via inter-diffusion of polymers and current measurements were performed at room temperature after each annealing. At the last stage of annealing the two linear slopes were highly distinct. The presence of sharp knee-bend results in approximately 20 times jump in dielectric constant as a function of electric field. Such high jumps in dielectric constant illustrate the potential for switching applications and charge storage. The high dielectric constants can be understood in terms of space charge polarization due to isolated domains which hindrance to charge transport. The high dielectric constants were confirmed by another experiment of capacitance measurements of a different set of similar samples. A study of thermal evolution of internal morphology was also carried out using x-ray diffraction and scanning electron microscopy techniques to correlate the morphological changes with the transport properties.

Atomic layer deposition synthesized TiOx thin films and their application as microbolometer active materials

This paper demonstrates the possible usage of TiOx thin films synthesized by atomic layer deposition as a microbolometer active material. Thin film electrical resistance is investigated as a function of thermal annealing. It is found that the temperature coefficient of resistance values can be controlled by coating/annealing processes, and the value as high as −9%/K near room temperature is obtained. The noise properties of TiOx films are characterized. It is shown that TiOx films grown by atomic layer deposition technique could have a significant potential to be used as a new active material for microbolometer-based applications.

Local structure around Zn and Ga in solution‐processed In–Ga–Zn–O and implications for electronic properties

We study by X‐ray absorption spectroscopy the local structure around Zn and Ga in solution‐processed In–Ga–Zn–O thin films as a function of thermal annealing. Zn and Ga environments are amorphous up to 450 °C. At 200 °C and 450 °C, the Ga atoms are in a β‐Ga2O3 like structure, mostly tetrahedral gallium oxide phase. Above 300 °C, the Zn atoms are in a tetrahedral ZnO phase for atoms inside the nanoclusters. The observed formation of the inorganic structure above 300 °C may be correlated to the rise of the mobility for IGZO TFTs. The Zn atoms localized at the nanocluster boundary are undercoordinated with O. Such ZnO cluster boundary could be responsible for electronic defect levels. Such defect levels were put in evidence in the upper half of the band gap. (© 2015 WILEY‐VCH Verlag GmbH &amp;Co. KGaA, Weinheim)

Ni-(In,Ga)As Alloy Formation Investigated by Hard-X-Ray Photoelectron Spectroscopy and X-Ray Absorption Spectroscopy

Next-generation transistors based on III-V semiconductor alloys present strong material requirements for their source and drain contacts, and Ni-In-Ga-As is a promising candidate. The authors correlate the electrical characteristics of this material, as a function of thermal annealing, with structural and chemical bonding information from x-ray spectroscopy, providing the comprehensive understanding needed for device fabrication strategies.

HR-EELS study of hydrogen bonding configuration, chemical and thermal stability of detonation nanodiamond films

Nano-diamond films composed of 3–10 nm grains prepared by the detonation method and deposited onto silicon substrates by drop-casting were examined by high resolution electron energy loss spectroscopy (HR-EELS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and secondary ion mass spectroscopy (SIMS). The impact of (i) ex-situ ambient annealing at 400 °C and (ii) ex-situ hydrogenation on hydrogen bonding and its thermal stability were examined. In order to clarify the changes in hydrogen bonding configuration detected on the different surfaces as a function of thermal annealing, in-situ hydrogenation by thermally activated atomic hydrogen was performed and examined. This study provides direct evidence that the exposure to ambient conditions and medium temperature ambient annealing have a pronounced effect on the hydrogen-carbon bonding configuration onto the nano-diamond surfaces. In-situ 1000 °C annealing results in irreversible changes of the film surface and partial nano-diamond silicidation.

Synthesis of All-Conjugated ABA and AB-type Donor-Acceptor Block Copolymers and Their Application in All-Polymer Solar Cells

ABSTRACTIn this work, we report the synthesis of all-conjugated donor-acceptor block copolymers via a externally initiated Kumada catalyst-transfer polycondensation (KCTP) method. In the first step, electron acceptor blocks, poly(naphthalene diimide)s (PNDIs), were prepared via the Stille coupling polycondensation. Then, P3HT blocks were polymerized by KCTP initiated by Ni(COD)2 activated PNDI complexes. Therefore, a series of ABA (P3HTs were initiated from both ends of PNDI) and AB-type (P3HT was initiated from one end of PNDI) block copolymers were successfully synthesized. Before fabrication of all-polymer solar cells, the morphologies and crystalline behaviors of the block copolymers were extensively investigated as a function of thermal annealing and the main chain composition of PNDI block. As a control, the crystalline behaviors of the physical blends of P3HT and PNDIs were also reported. Finally, all-polymer solar cells were fabricated by using the block copolymers as the single active component or as surfactants. A PCE of 0.11 % with Voc=0.46 V, Jsc=0.50 mA/cm2, and FF=0.46 was recorded by using the donor-acceptor all-conjugated block copolymer as the single active component.

Effects of PCBM Loading and Thermal Annealing on Nanomorphology of Blend of Polymer/Fullerene Thin Films Solar Cells: Impact on Charge Carrier Mobility and Efficiency

Blend of P3HT/Fullerene thin films solar cell with two different percentage ratio of PCBM loading is investigated. Optical absorption spectroscopy is employed to elucidate the nature of PCBM cluster formation upon thermal annealing. Sandwich structures comprising of ITO/ Cs2CO3/ P3HT: PCBM/ LiF/ Al (electron only device), and ITO/ PEDOT:PSS/ P3HT:PCBM/ Au (hole only device) are fabricated using spin coating for the investigations concerning electron and hole mobilities. The impact of charge carrier mobilities on bimolecular recombination and ultimately the power conversion efficiency for two different PCBM loading is also investigated. A direct correlation between Langev in recombination rate and short circuit current density as a function of thermal annealing is realized. The maximum power conversion efficiency is measured at 150°C for P3HT: PCBM (1:1) solar cell.

Anomalous evolution of interfaces in Fe/Ag magnetic multilayer

Interfaces greatly influence the magnetic properties of multilayer nanostructures. In the present work, the x-ray standing wave (XSW) technique along with conversion electron Mössbauer spectroscopy have been used to study the evolution of interfaces in Fe/Ag system as a function of thermal annealing. The XSW technique has sufficient depth resolution so as to determine the concentration profiles of Fe across the two interfaces, namely Fe-on-Ag and Ag-on-Fe independently. In as-deposited Ag/Fe/Ag trilayer, Fe-on-Ag interface has a substantially higher roughness of 1.3 nm as compared to 0.9 nm of Ag-on-Fe interface. It is shown that the observed difference in the roughness of the two interfaces is due to a substantial intermixing between Fe and Ag occurring preferentially at Fe-on-Ag interface. With thermal annealing, the two interfaces exhibit opposite behaviour; while Fe-on-Ag interface exhibits an initial sharpening, Ag-on-Fe interface exhibits a monotonous broadening. Two competing processes occur at the interfaces, (i) interface sharpening as a result of de-mixing, driven by a large positive heat of mixing between Fe and Ag and (ii) increase in topological roughness due to increased thermal agitation. This results in a non-monotonous variation in the roughness of Fe-on-Ag interface. At sufficiently high temperature the layered structure is completely destroyed, leading to formation of Fe and Ag nanoparticles.

Enhanced Hole Carrier Transport Due to Increased Intermolecular Contacts in Small Molecule Based Field Effect Transistors

Small molecules and oligomers can be synthesized with very high purity and precise molecular weights, but they often do not form uniform thin films while processed from solution. Decreased intermolecular contacts between the small molecules are another disadvantage. To increase the intermolecular contacts in small molecules, we have chosen i-indigo, as one of the conjugated molecular units. The electron poor i-indigo has been connected with electron rich triphenylamine to synthesize a donor-acceptor-donor type small molecule. The propeller shaped triphenylamine helps to increase the solubility of the small molecule as well as isotropic charge transport. The intermolecular spacing between the molecules has been found to be low and did not vary as a function of thermal annealing. This implies that the intermolecular contacts between the small molecules are enhanced, and they do not vary as a function of thermal annealing. Organic field effect transistors (OFET) fabricated using a small molecule exhibited a hole carrier mobility (μ) of 0.3 cm(2)/(V s) before thermal annealing. A marginal increase in μ was observed upon thermal annealing at 150 °C, which has been attributed to changes in thin film morphology. The morphology of the thin films plays an important role in charge transport in addition to the intermolecular spacing that can be modulated with a judicious choice of the conjugated molecular unit.

Elastic softening of metamict titanite CaTiSiO5: Radiation damage and annealing

We have measured the elastic response of radiation-damaged titanite, CaTiSiO5, as a function of thermal annealing. We estimate the bulk modulus of the damaged samples (-24% amorphous) to be 85 GPa, which is much softer than for undamaged crystalline titanite [131.4 GPa; Angel et al. (1999)]. Conversely, the lowest shear modulus of the radiation-damaged material is 52-58 GPa, which is harder that of the undamaged titanite, 46-52 GPa. The bulk and shear moduli of the radiation-damaged materials are close to those of thermal titanite glass, Bglass ≈ 75 GPa and Gglass ≈ 47 GPa, and are much smaller than expected based on other radiation-damaged materials such as zircon (ZrSiO4). Surprisingly, annealing of the damaged titanite in the range 600 < T < 1000 K leads to additional massive softening of the shear moduli. During annealing the shear modulus of titanite sample 1 softened from 58 to 29 GPa, and sample 2 softened from 52 to 19 GPa. The temperature range for the softening coincides with that found for crystallization of the amorphous regions, as measured previously by diffraction and spectroscopic methods. In contrast to the huge softening of the ultrasonically measured shear modulus, the calorimetrically measured Debye temperature θD increases by -5%, suggesting a small intrinsic hardening of the acoustic shear modes. Additional heating to 1473 K leads, in one titanite sample, to a steep increase of the shear modulus to values much larger than that of the initial, radiation-damaged material. Theoretical models are discussed to rationalize the massive softening due to both radiation damage and subsequent anneal.

Role of Water in Super Growth of Single-Walled Carbon Nanotube Carpets

The Ostwald ripening behavior of Fe catalyst films deposited on thin alumina supporting layers is demonstrated as a function of thermal annealing in H2 and H2/H2O. The addition of H2O in super growth of single-walled carbon nanotube carpets is observed to inhibit Ostwald ripening due to the ability of oxygen and hydroxyl species to reduce diffusion rates of catalyst atoms. This work shows the impact of typical carpet growth environments on catalyst film evolution and the role Ostwald ripening may play in the termination of carpet growth.