Annealing Of Films Research Articles

Fabrication of ultrasensitive hexagonal disc structured ZnO thin film sensor to trace nitric oxide

ABSTRACT ZnO thin films were deposited on glass substrate using simple and cost-effective spin coating technique. Further, the deposited sample was annealed in air at various temperatures, such as 400°C, 500°C, 600°C and 700°C. As-prepared and annealed ZnO thin films were characterized for structural, morphological, optical and gas sensing properties. All the films have shown polycrystalline nature with hexagonal wurtzite phase of ZnO. The grain size and the crystalline nature of the film improved with increase in annealing temperature. FESEM results showed a transformation into two-dimensional flower-like structures, enhancing the sensing property of the film with the more improved surface area for gas adsorption as compared to the as-prepared ZnO thin film. Optical band gaps were determined using Tauc’s plot. The gas sensing study toward Nitric oxide is carried out at a low concentration level of 2.75 ppm. At an operating temperature of 150°C, the ZnO film annealed at 400°C has shown a good sensitivity of 1.4 with response and recovery time of 52 sec and 19 seconds respectively.

Ultrafast and Scalable Laser‐Induced Crystallization of Titanium Dioxide Films for Planar Perovskite Solar Cells

A conventional annealing method to fabricate metal oxide films used for perovskite solar cells (PSCs) is a time‐consuming batch process. Herein, a near‐IR fiber laser process with a unique design of power ramping program and beam configuration is developed to achieve ultrafast and scalable processing of TiO2 films for PSCs. Highly crystalline anatase TiO2 films can be synthesized in only 18.5 s by the laser process with a peak annealing temperature up to 800–850 °C, compared with that of the furnace‐annealing at 500 °C for 30 min and an overall processing time of 3 h. Then, a unique capability of using this laser process is presented to anneal stacked layers of substrates coated with the TiO2 films simultaneously, with a uniform annealing area up to 15.2 cm2, thereby potentially achieving an in‐line production rate of over 43 cm2 min−1 (1 cm2 in ≈1.4 s). Planar PSCs fabricated under a high relative humidity of 60–70% based on the TiO2 films annealed under optimal laser conditions show enhanced photovoltaic performance than the furnace‐annealed samples. This laser process potentially opens a new avenue for scalable annealing and rapid production of thin films.

Investigation of the Optical and Dielectric Behaviour of SnO2-CuO Mixed Oxides Thin Films

The effects of CuO on the optical and dielectric properties of SnO2 thin film were studied to achieve improved light photon absorption and conversion. The films were deposited using airblast chemical spray pyrolysis. Rutherford Backscattering Spectrometric analysis using the Windows SIMNRA software gave the compositions of as-deposited and annealed films and their thicknesses. The optical and dielectric parameters were evaluated from the transmittance data obtained from UV – Visible spectrophotometer. The optical band gap of as-deposited SnO2-CuO film was evaluated to be 3.4 eV. The value of Urbach tail width of the as-deposited mixed oxide is higher (296 meV) compared to that of the annealed (252 meV) indicating the presence of more disordered states in the as-deposited film. The analysis also showed that the presence of CuO in the matrix of SnO2 led to a decrease in optical bandgap, refractive index, and by extension dielectric constants of SnO2. Our investigation led to the conclusion that the addition of CuO into SnO2 increased its electromagnetic photon absorption and also delay its speed thereby enhancing photon interaction with free charge carriers in the mixed oxide film. We opined that the mixed oxide will perform better in photocatalysis, photodegradation of pollutants and other lightharvesting applications since the CuO inclusion has extended its absorption edge towards the visible light range.

Research of nanopore structure of Ga2O3 film in MOCVD for improving the performance of UV photoresponse

Using the mechanism of self-reactive etching between Ga and Ga2O3, Ga2O3 nanopore films were fabricated. The self-reactive etching effects based on as-grown and annealed Ga2O3 films by metal organic chemical vapor deposition were compared. It was found that the nanopore film based on as-grown Ga2O3 film has a uniform size, high density and a small diameter. Ultraviolet-visible light reflection spectra and transmission spectra show that the nanopore film could effectively reduce the reflectivity of light and enhance the light absorption. Based on the as-grown Ga2O3 film and its nanopore film, metal-semiconductor-metal structure solar blind ultraviolet photodetectors (PD) were fabricated. Under 5 V bias, the light-dark current ratio of the nanopore film PD is about 2.5 × 102 times that of the film PD, the peak responsivity of the nanopore film PD is about 49 times that of the film PD. The rejection ratio is 4.6 × 103, about 1.15 × 102 times that of the film PD. The nanopore structure effectively increases the surface-volume ratio of film. The photoelectric detection performance and response performance of the nanopore film PD could be significantly enhanced.

Influence of Annealing Temperature Variations on the Properties of Chemically Deposited Nanocrystalline Zinc Selenide Thin Films

In the present report, influence of annealing temperature variations on the optical, morphological, and structural properties of chemically deposited nanocrystalline zinc-selenide thin films is studied employing an X-ray diffractometer, scanning electron microscope, and UV spectroscope. As-synthesized and annealed films exhibit nanocrystalline nature with cubic structure. The result shows that ZnSe thin films contain spherical particles that are composed of nanocrystals ranging from 3 to 7 nm crystallite size. The SEM studies reveal that the inter-crystalline spaces have been found to be reduced with an increase in grain size as annealing temperature increases. The EDS data reveal that the obtained thin films are rich in selenium. However, thermal annealing assisted to reduce the non-stoichiometric nature of the films by reducing selenium content that was found to be reduced with a rise in annealing temperature. The reduction in strains and dislocation density was observed after the annealing process. The band-gap energy was found to be raised from 2.56 to 2.76 eV with a rise in annealing temperature. The transmittance of more than 80% was recorded by as-synthesized and annealed films as well.

High-temperature annealing of AlN films grown on 4H–SiC

The effect of high-temperature annealing (HTA) at 1700 °C on AlN films grown on 4H–SiC substrates by metalorganic vapor phase epitaxy has been studied. It is shown that the structural quality of the AlN layers improves significantly after HTA similar to what has been demonstrated for AlN grown on sapphire. Dislocation densities reduce by one order of magnitude resulting in 8 × 108 cm−2 for a-type and 1 × 108 cm−2 for c-type dislocations. The high-temperature treatment removes pits from the surface by dissolving nanotubes and dislocations in the material. XRD measurements prove that the residual strain in AlN/4H–SiC is further relaxed after annealing. AlN films grown at higher temperature resulting in a lower as-grown defect density show only a marginal reduction in dislocation density after annealing. Secondary ion mass spectrometry investigation of impurity concentrations reveals an increase of Si after HTA probably due to in-diffusion from the SiC substrate. However, C concentration reduces considerably with HTA that points to an efficient carbon removal process (i.e., CO formation).

Optical Spectroscopy of Schottky Nanostructures Au/GaAs: Plasmon Resonances and Anisotropy

The Schottky nanostructures Au/GaAs with Au nanoclusters are prepared by annealing of thin gold films deposited on nitridized GaAs(001) surface. The nanostructures are diagnosed nanoscopically and investigated by optical reflection anisotropy spectroscopy. The Au nanoclusters arrays of two types are found to be formed respectively under and over GaAs surface. The energies of local plasmons of the arrays are detected at 1.6 and 2.15 eV, respectively. The latter plasmons possess in-surface anisotropy which causes in optical anisotropy spectra the intensive resonant feature at energy about 2 eV. The plasmon anisotropy is studied comprehensively, and the results are interpreted theoretically.

Tunable indium tin oxide for metamaterial perfect absorbers and nonlinear devices

Indium tin oxide (ITO) has become a very useful plasmonic and nonlinear optical material because of its highly tunable electrical and optical properties and strong optical nonlinearity. In this work, the authors conducted detailed fabrication process studies by using high-temperature reactive sputtering to finely tune the optical properties of ITO thin films, particularly the epsilon-near-zero (ENZ) wavelength in the near and mid-IR spectrum. Sputtered ITO thin films are characterized by using spectroscopic ellipsometry, surface profilometry, Hall measurements, and 4-point probe testing. Additionally, the effect of post-deposition annealing of ITO films is also investigated.

Anisotropic plasmons in Au/GaAs(001) structures with gold nanoclusters

The structures Au/GaAs(001) with gold nanoclusters are created by annealing of Au films deposited onto GaAs surface. The samples are diagnosed stepwise by scanning probe microscopy. Using reflectance anisotropy spectroscopy, Au clusters are established to possess plasmons with the in-surface anisotropy. The measured anisotropy spectrum consists of a resonant feature near the energy of 2 eV typical of local plasmons of Au clusters. The results are explained theoretically, and the new spectral feature is assigned to anisotropic plasmons of Au nanoclusters located on GaAs surface.

INFLUENCE OF POST-DEPOSITION ANNEALING ON THE INDIUM TIN OXIDE THIN FILMS GROWN BY PULSED LASER DEPOSITION

Transparent thin-film Indium Tin Oxides (ITO) were prepared on glass substrates using a pulsed laser deposition (PLD) process with an average thickness of 150 nm. Post-deposition annealing was performed on the samples in a wide range of temperatures from 250 to 650 0C. The surface structures of as-deposited and annealed ITO films were analyzed using the x-ray diffraction (XRD). Atomic Force Microscopy (AFM) was carried out on all samples to verify any change in the grain sizes, and in the roughness of the oxide thin film surfaces. The transmittance spectra of the annealed samples were also investigated using spectrophotometer measurements. Energy band gaps Eg were calculated from the optical spectra for all films. It was found that the optical band gap values decreased as the annealing temperature was increased. To compare the effect of the annealing on refractive index n and extinction coefficient k properties, additional measurements were done on the samples pre and post annealing using an ellipsometer. It is noted that the annealed ITO films resulted in a noticeable improvement in the crystalline structure and an increase in the surface roughness. Furthermore, their maintained good optical properties made them very favorable to be used in different disciplines such as anodes of the solar cells and as protective coatings in space windows.

Effects of different treatments of films of PIM-1 on its gas permeation parameters and free volume

Polymer of intrinsic microporosity (PIM-1) was prepared according to a new procedure – precipitation polycondensation in DMSO solution. The permeability coefficients were determined in the “as cast” and ethanol treated samples of this material. It was shown that permeability of the novel polymer is higher than that of PIM-1 samples prepared according to the traditional methods, while selectivity was lower. Free volume in the novel PIM-1 was studied using the PALS technique. Positron life time parameters and the radii of free volume elements were virtually the same as in PIM-1 samples investigated earlier. The samples of novel PIM-1 were subjected to treatment by supercritical CO2 and annealing of free films and films in strained state. The treatment with scCO2 leads qualitatively to the same results as insertion of the films into EtOH (increase in gas permeability) although the observed Pi values are somewhat lower. Annealing of the films in strained and free state causes significant decrease in gas permeability with respect to all the gases but increase in selectivity. This effect is rather strong, so some the data points are even located above the Upper Bound 2008 in Robeson diagrams. Aging of PIM-1 samples for 30–60 days was also studied, and its mechanism is considered.

Atomic layer deposition of tungsten sulfide using a new metal-organic precursor and H2S: thin film catalyst for water splitting

Transition metal dichalcogenides (TMDs) are extensively researched in the past few years due to their two-dimensional layered structure similar to graphite. This group of materials offers tunable optoelectronic properties depending on the number of layers and therefore have a wide range of applications. Tungsten disulfide (WS2) is one of such TMDs that has been studied relatively less compared to MoS2. Herein, WS x thin films are grown on several types of substrates by atomic layer deposition (ALD) using a new metal-organic precursor [tris(hexyne) tungsten monocarbonyl, W(CO)(CH3CH2C≡CCH2CH3)3] and H2S molecules at a relatively low temperature of 300 °C. The typical self-limiting film growth by varying both, precursor and reactant, is obtained with a relatively high growth per cycle value of ∼0.13 nm. Perfect growth linearity with negligible incubation period is also evident in this ALD process. While the as-grown films are amorphous with considerable S-deficiency, they can be crystallized as h-WS2 film by post-annealing in the H2S atmosphere above 700 °C as observed from x-ray diffractometry analysis. Several other analyses like Raman and x-ray photoelectron spectroscopy, transmission electron microscopy, UV–vis. spectroscopy are performed to find out the physical, optical, and microstructural properties of as-grown and annealed films. The post-annealing in H2S helps to promote the S content in the film significantly as confirmed by the Rutherford backscattering spectrometry. Extremely thin (∼4.5 nm), as-grown WS x films with excellent conformality (∼100% step coverage) are achieved on the dual trench substrate (minimum width: 15 nm, aspect ratio: 6.3). Finally, the thin films of WS x (as-grown and 600/700 °C annealed) on W/Si and carbon cloth substrate are investigated for electrochemical hydrogen evolution reaction (HER). The as-grown WS x shows poor performance towards HER and is attributed to the S-deficiency, amorphous character, and oxygen contamination of the WS x film. Annealing the WS x film at 700 °C results in the formation of a crystalline layered WS2 phase, which significantly improves the HER performance of the electrode. The study reveals the importance of sulfur content and crystallinity on the HER performance of W-based sulfides.

Highly Porous Magnesium Silicide Honeycombs Prepared by Magnesium Vapor Annealing of Silica-Coated Polymer Honeycomb Films toward Ultralightweight Thermoelectric Materials

Magnesium silicide (Mg2Si) is one of the few thermoelectric materials that is composed of high Clark number elements and exhibits an optimum temperature near 700 K. The advantage of Mg2Si is that i...

(Invited) Conformal Deposition of Li-Based Thin Films for 3D Lithium-Ion Microbatteries

Lithium-ion batteries have been the premiere power source in the mobile electronics industry due to their superior energy density and cycle life as compared to other battery chemistries. In the Era of the Internet of Things (IoT) there is an increasing need to find a viable power source to support millimeter-size and smaller scale devices in the fields of environmental sensing, biomedical devices, and wearable electronics. Three-dimensional battery architectures mitigate the limitations of traditional thin film batteries through improvement of ion transport properties allowing for higher areal loading of active materials. Atomic layer deposition not only offers the ability to synthesize a wide range of functional materials, but crucially is a non-line-of-sight deposition technique that allows for conformal deposition necessary for fabrication of 3D lithium-ion batteries. In this work, two ALD processes were developed to synthesize conformal thin films applicable to 3D battery fabrication—LiAlSiO4, a solid-state electrolyte, and LiMn2O4, a high-rate thin film cathode.LiAlSiO4 is a solid-electrolyte of interest, in which its quartz-like framework produces unique 1D channels for Li-ion transport along the c-axis, exhibiting ionic conductivities as high as 4.7x10-5 S/cm at room temperature,1, 2 where the ionic conductivity in its thin film form has shown to increase upon decreasing thicknesses, 3 In this work, ALD of LixAlySizO was demonstrated with careful tuning of the stoichiometry to allow for crystallization into the ionically conductive β-Eucryptite LiAlSiO4 phase. The rapid thermal annealed ALD film developed a well-defined epitaxial relationship to the silicon substrate: β-LiAlSiO4 (12 ̅10) || Si (100) and β-LiAlSiO4 (101 ̅0) || Si(001). The extrapolated room temperature ionic conductivity was found to be 1.2 x 10-7 S/cm in the [12 ̅10] direction with an activation energy of 0.63 eV, as compared to amorphous ALD LASO films with ionic conductivities on the order of 10-9 S/cm.Beyond the electrolyte layer, an equally crucial material is a thin film cathode with optimal interfacial properties to ensure homogeneous active material utilization, adequate cycle-life, and high rate performance. To realize this goal, LiMn2O4 was demonstrated utilizing O2 plasma and Tris(2,2,6,6Tetramethyl-3,5-heptanedione) Mn(III), where lithium incorporation was performed through a thermal ALD LiOtBu/H2O process. Thin films with stoichiometries of Li1+xMn2-xO4, where x>0 were observed (as-characterized via XPS) with LiOH ALD sub-cycle percentages lower than 1% of the total ALD supercycle. LiMn2O4 thin films exhibited great rate capability (66% capacity retention after increasing the rate from C/2 to 50C) as well as capacity retention (97% capacity retention after 100 cycles at 5C).Lastly, a proof-of-concept nanobattery consisting of a SiGe nanowire (anode) coated with LixAlySizO (electrolyte) and LiMn2O4 (cathode) was fabricated. Both materials show great promise for direct integration with three-dimensional lithium-ion microbatteries.1. V. Thangadurai and W. Weppner, Ionics 8 (3), 281-292 (2002). 2. P. G. Bruce, Solid State Electrochemistry. (Cambridge University, Press, 1995).3. S.-i. Furusawa, H. Tabuchi and T. Tsurui, Solid State Ionics 178 (15), 1033-1038 (2007).

Enhanced Magneto-Optic Properties in Sputtered Bi- Containing Ferrite Garnet Thin Films Fabricated Using Oxygen Plasma Treatment and Metal Oxide Protective Layers.

Magneto-optic (MO) imaging and sensing are at present the most developed practical applications of thin-film MO garnet materials. However, in order to improve sensitivity for a range of established and forward-looking applications, the technology and component-related advances are still necessary. These improvements are expected to originate from new material system development. We propose a set of technological modifications for the RF-magnetron sputtering deposition and crystallization annealing of magneto-optic bismuth-substituted iron-garnet films and investigate the improved material properties. Results show that standard crystallization annealing for the as-deposited ultrathin (sputtered 10 nm thick, amorphous phase) films resulted in more than a factor of two loss in the magneto-optical activity of the films in the visible spectral region, compared to the liquid-phase grown epitaxial films. Results also show that an additional 10 nm-thick metal-oxide (Bi2O3) protective layer above the amorphous film results in ~2.7 times increase in the magneto-optical quality of crystallized iron-garnet films. On the other hand, the effects of post-deposition oxygen (O2) plasma treatment on the magneto-optical (MO) properties of Bismuth substituted iron garnet thin film materials are investigated. Results show that in the visible part of the electromagnetic spectrum (at 532 nm), the O2 treated (up to 3 min) garnet films retain higher specific Faraday rotation and figures of merit compared to non-treated garnet films.

Conducting Polymers for Optoelectronic Devices and Organic Solar Cells: A Review.

In this review paper, we present a comprehensive summary of the different organic solar cell (OSC) families. Pure and doped conjugated polymers are described. The band structure, electronic properties, and charge separation process in conjugated polymers are briefly described. Various techniques for the preparation of conjugated polymers are presented in detail. The applications of conductive polymers for organic light emitting diodes (OLEDs), organic field effect transistors (OFETs), and organic photovoltaics (OPVs) are explained thoroughly. The architecture of organic polymer solar cells including single layer, bilayer planar heterojunction, and bulk heterojunction (BHJ) are described. Moreover, designing conjugated polymers for photovoltaic applications and optimizations of highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy levels are discussed. Principles of bulk heterojunction polymer solar cells are addressed. Finally, strategies for band gap tuning and characteristics of solar cell are presented. In this article, several processing parameters such as the choice of solvent(s) for spin casting film, thermal and solvent annealing, solvent additive, and blend composition that affect the nano-morphology of the photoactive layer are reviewed.

Annealing effect on the structure relaxation and mechanical properties of a Polytetrafluoroethylene film by RF-magnetron sputtering

In the current work, a Polytetrafluoroethylene (PTFE) film with thickness of 3.4 μm was prepared by RF-magnetron sputtering on a silicon substrate. By annealing at different temperatures (100–300 °C), the structure relaxations of PTFE film were systematically investigated via the variations of physical properties, i.e., atomic bonding, density and surface morphology. It was unfolded that inner atomic arrangement and surface morphology changed little whilst film density was greatly increased with increasing annealing temperature. Relying on nanoindentation technology, the mechanical properties including hardness, elastic modulus, creep resistance and friction coefficient were measured in the as-prepared and annealed PTFE films. By increasing annealing temperature, hardness and elastic modulus were enhanced at 100 °C and then gradually declined at higher temperatures. The room-temperature creep resistance was promoted in the annealed films and nearly independent on annealing temperature. During the scratch test, the residual depth of scratches increased and the elastic recovery ratio decreased by further increasing annealing temperature.

Rapid Thermal Annealing of Double Perovskite Thin Films Formed by Polymer Assisted Deposition.

The annealing process is an important step common to epitaxial films prepared by chemical solution deposition methods. It is so because the final microstructure of the films can be severely affected by the precise features of the thermal processing. In this work we analyze the structural and magnetic properties of double perovskite La2CoMnO6 and La2NiMnO6 epitaxial thin films prepared by polymer-assisted deposition (PAD) and crystallized by rapid thermal annealing (RTA). It is found that samples prepared by RTA have similar values of saturation magnetization and Curie temperature to their counterparts prepared by using conventional thermal annealing (CTA) processes, thus indicating low influence of the heating rates on the B-B’ site cationic ordering of the A2BB’O6 double perovskite structure. However, a deeper analysis of the magnetic behavior suggested some differences in the actual microstructure of the films.

Nanoscale Mapping of Morphology of Organic Thin Films.

We determine precise nanoscale information about the morphologies of several organic thin film structures using Fourier plane imaging microscopy (FIM). We used FIM microscopy to detect the orientation of molecular transition dipole moments from an extremely low density of luminescent dye molecules, which we call "morphology sensors". The orientation of the sensor molecules is driven by the local film structure and thus can be used to determine details of the host morphology without influencing it. We use symmetric planar phosphorescent dye molecules as the sensors that are deposited into the bulk of organic film hosts during the growth. We demonstrate morphological mapping with a depth resolution to a few Ångstroms that is limited by the ability to determine thickness during deposition, along with an in-plane resolution limited by optical diffraction. Furthermore, we monitor morphological changes arising from thermal annealing of metastable organic films that are commonly employed in photonic devices.

Boosting carrier mobility and stability in indium\u2013zinc\u2013tin oxide thin-film transistors through controlled crystallization

We investigated the effect of film thickness (geometrical confinement) on the structural evolution of sputtered indium-zinc-tin oxide (IZTO) films as high mobility n-channel semiconducting layers during post-treatment at different annealing temperatures ranging from 350 to 700 °C. Different thicknesses result in IZTO films containing versatile phases, such as amorphous, low-, and high-crystalline structures even after annealing at 700 °C. A 19-nm-thick IZTO film clearly showed a phase transformation from initially amorphous to polycrystalline bixbyite structures, while the ultra-thin film (5 nm) still maintained an amorphous phase. Transistors including amorphous and low crystalline IZTO films fabricated at 350 and 700 °C show reasonable carrier mobility (µFE) and on/off current ratio (ION/OFF) values of 22.4–35.9 cm2 V−1 s−1 and 1.0–4.0 × 108, respectively. However, their device instabilities against positive/negative gate bias stresses (PBS/NBS) are unacceptable, originating from unsaturated bonding and disordered sites in the metal oxide films. In contrast, the 19-nm-thick annealed IZTO films included highly-crystalline, 2D spherulitic crystallites and fewer grain boundaries. These films show the highest µFE value of 39.2 cm2 V−1 s−1 in the transistor as well as an excellent ION/OFF value of 9.7 × 108. Simultaneously, the PBS/NBS stability of the resulting transistor is significantly improved under the same stress condition. This promising superior performance is attributed to the crystallization-induced lattice ordering, as determined by highly-crystalline structures and the associated formation of discrete donor levels (~ 0.31 eV) below the conduction band edge.