Increase Of Annealing Time Research Articles

Shrinking of silicon nanocrystals embedded in an amorphous silicon oxide matrix during rapid thermal annealing in a forming gas atmosphere

We report the effect of hydrogen on the crystallization process of silicon nanocrystals embedded in a silicon oxide matrix. We show that hydrogen gas during annealing leads to a lower sub-band gap absorption, indicating passivation of defects created during annealing. Samples annealed in pure nitrogen show expected trends according to crystallization theory. Samples annealed in forming gas, however, deviate from this trend. Their crystallinity decreases for increased annealing time. Furthermore, we observe a decrease in the mean nanocrystal size and the size distribution broadens, indicating that hydrogen causes a size reduction of the silicon nanocrystals.

Measurement and optimization of atmospheric plasma sprayed CoMoCrSi coatings parameters on Ti-6Al-4V substrates affecting microstructural and properties using hybrid abductor induction mechanism

Abstract A hybrid artificial intelligence method (AIM) is used to optimize the atmospheric plasma spraying (APS) processing parameters for CoMoCrSi coatings deposited on Ti-6Al-4V substrates. In the proposed approach, the Taguchi design method is used to obtain an initial solution for the optimal set of APS parameters. The true optimal values of the spray distance, chamber pressure, current, argon gas flow rate and hydrogen gas flow rate are then obtained using an artificial neural network (ANN) and genetic algorithm (GA). The coatings deposited using the processing parameters determined using the Taguchi design method alone have a porosity of 8.5%. However, following the ANN/GA optimization procedure, the porosity reduces to just 5.6%. The XRD analysis results show that the as-sprayed coatings contain Cr 3 Si phase as a result of the high-temperature plasma flame. In addition, it is shown that the structure of the Ti phase in the coating transforms from a α-Ti crystal structure (i.e., HCP) to a β-Ti crystal structure (i.e., BCC) during thermal treatment at temperatures to 1200 °C. Finally, it is shown that the hardness of the annealed coatings increases with both an increasing annealing time and an increasing annealing temperature. The higher hardness under higher temperature conditions is attributed to the precipitation of Cr 3 Si phase. Overall, the coatings obtained in the present study using the optimal spray-coating parameters have a low porosity, a high hardness and a good thermal stability at high temperatures.

Formation of linear polyenes in poly(vinyl alcohol) films catalyzed by phosphotungstic acid, aluminum chloride, and hydrochloric acid

Formation of linear polyenes–(CH=CH)n–via acid-catalyzed thermal dehydration of polyvinyl alcohol in 9- to 40-µm-thick films of this polymer containing hydrochloric acid, aluminum chloride, and phosphotungstic acid as dehydration catalysts was studied by electronic absorption spectroscopy. The concentration of long-chain (n ≥ 8) polyenes in films containing phosphotungstic acid is found to monotonically increase with the duration of thermal treatment of films, although the kinetics of this process is independent of film thickness. In films containing hydrochloric acid and aluminum chloride, the formation rate of polyenes with n ≥ 8 rapidly drops as film thickness decreases and the annealing time increases. As a result, at a film thickness of less than 10–12 µm, long-chain polyenes are not formed at all in these films no matter how long thermal duration is. The reason for this behavior is that hydrochloric acid catalyzing polymer dehydration in these films evaporates from the films during thermal treatment, the evaporation rate inversely depending on film thickness.

Effect of Annealing by CO2 Laser on Structural and Optical Properties of CuO Thin Films Prepared by Sol – Gel Method

Laser heat treatment is one of the important industrial applications of laser and being studied at the present time as a substitute for conventional thermal annealing. In this research (CuO) thin films have been deposition on a glass by (Sol - Gel / Spin Coating) technique and annealed by two ways, the first one using a convection oven, where they were annealing with three temperatures (400 °C, 500 °C, 600 °C) for one hour, and the second way using a continuous (CO2) laser with (10.6 μm) wavelength and (10 W) power and three intervals (10 min, 15 min, 20 min), were studied structural and optical properties of membranes prepared by both ways to determine the effect of laser annealing on them, and the results of (XRD) tests showed that these membranes with the structural of multi-crystalline monoclinic type and increase the degree of oven annealing temperature, as well as increasing the duration of the laser annealing lead to increased volumes of granular membranes rates. The results of the (AFM) tests to the topography of the surfaces of the membranes to be of crystalline uniformity and homogeneity superficially good, especially for laser annealed membranes. The results of optical examinations of these membranes showed that they having high permeability, especially in the regions of the visible spectrum and the near-infrared and increased with increase the degree of oven annealing temperature and the duration of laser annealing, and less energy gap of these membranes values with increase the temperature degree of annealing or increase of laser annealing time. In addition to this, the optical properties studied in this research included absorbance, reflectivity, refractive index, coefficients of absorption and extinction, and real and imaginary dielectric constants.

Evolution in surface morphology during rapid microwave annealing of PS‐b‐PMMA thin films

ABSTRACTMicrowave annealing enables rapid (60 s) ordering and orientation of block copolymer films. The developed morphology in polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) thin films depends on details of the heating rate that is controlled by microwave output energy as well as the sample location in the microwave. Over a wide heating rate (1.1–2.7 °C/s), perpendicular orientation of the cylindrical mesostructure at the surface is >50% after 60 s, but goes through a maximum at 1.8 °C/s leading to approximately 97% perpendicular cylinders at the surface. The propagation of this perpendicular surface morphology through the film thickness is also dependent upon the microwave annealing conditions. The surface structure evolves with the microwave annealing time from imperfect ordering to perpendicular cylinders to parallel cylinders as the annealing time increases. This work demonstrates the importance of controlling the heating rate during microwave annealing, which will be critical for optimizing microwave conditions for directed self‐assembly. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1499–1506

Effects of post-annealing treatment on the structure and photoluminescence properties of CdS/PS nanocomposites prepared by sol-gel method

CdS nanocrystals have been successfully grown on porous silicon (PS) by sol-gel method. The plan-view field emission scanning electron microscopy (FESEM) shows that the pore size of PS is smaller than 5 μm in diameter and the agglomerates of CdS are broadly distributed on the surface of PS substrate. With the increase of annealing time, the CdS nanoparticles grow in both length and diameter along the preferred orientation. The cross-sectional FESEM images of ZnO/PS show that CdS nanocrystals are uniformly penetrated into all PS layers and adhere to them very well. photoluminescence (PL) spectra demonstrate that the intensity of PL peak located at about 425 nm has almost no change after the annealing time increases. The range of emission wavelength of CdS/PS is from 425 nm to 455 nm and the PL intensity is decreasing with the annealing temperature increasing from 100 °C to 200 °C.

Influence of annealing time on microstructure and dielectric properties of (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 ceramic thin films prepared by sol–gel method

(Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 dielectric ceramic thin films were fabricated on Si(100) substrates by sol–gel method followed by annealing in O2 atmosphere at 900 °C for 5, 15, 30, and 45 min. Results show that the surface morphologies of the samples are crack free and compact with well-crystallized structures. The grain sizes of the thin films increase with increased annealing time from 5 to 30 min. Thin films annealed for 30 min possess the minimum root–mean–square (RMS) value of roughness and the highest crystallinity among all samples as well as the best dielectric properties. Thus, 30 min is the optimal annealing time.

Phase structure and cycling stability of A2B7 superlattice La0.60Sm0.15Mg0.25Ni3.4 metal hydride alloy

Improvement in cycling stability is a key issue for La–Mg–Ni-based alloys to be widely applied as anode electrode materials of nickel metal hydride batteries. In this paper, we report the phase structure and melioration of cycling stability of a Sm-containing A2B7-type La–Mg–Ni-based alloy. Sm element promotes the Gd2Co7-type phase formation with increasing annealing period, which the Ce5Co19-, CaCu5- and MgCu4Sn-type phases in as-cast La0.60Sm0.15Mg0.25Ni3.4 alloy are successively eliminated as the annealing time increases from 6 to 24 h at 950 °C and forms a single A2B7-type alloy with coexistence of 73.2 wt.% Gd2Co7- and 26.8 wt.% Ce2Ni7-type phases. The single A2B7-type La0.60Sm0.15Mg0.25Ni3.4 alloy is superior in discharge capacity (382 mAh g−1) and high rate dischargeability (40% at a 1500 mA g−1 discharge current density). Especially, the cycling stability of the alloy is enhanced to 87.7% at the 100th cycle. The improved cycling stability of the single A2B7-type alloy is mainly attributed to its slower growth of inner strain during charging/discharging, which improves anti-pulverization/amorphization ability, and drops oxidation degree of the alloy. Therefore, Sm is a positive element in improvement of the cycling stability property of the La–Mg–Ni-based alloys.

Phase composition identification and microstructure of BaTiO3-containing sodium-aluminoborosilicate glass-ceramics

Bulk glasses with a composition 20.1Na2O/23.1BaO/23.0TiO2/7.6B2O3/17.4SiO2/3Al2O3/5.8Fe2O3 containing less than 30 mol% glass-forming oxides are synthesized. Information on the valency of the glass constituents is obtained by x-ray photoelectron spectroscopy and it is concluded that all species are predominantly present in their oxidized state. Glassy samples are annealed above the glass transition temperature which leads to the crystallization of BaTiO3 for all time-temperature applied schedules. The phase composition of the glass-ceramics is studied by x-ray diffraction and the formation of cubic BaTiO3 is suggested. Temperature-dependent Raman spectroscopy confirms the presence of solely cubic BaTiO3. The microstructures of all annealed samples are similar and consist of globular interconnected particles in which nanosized BaTiO3 crystals grow randomly. The mean size of the spherical formations increases with the increasing annealing time from 200 to 600 nm. Electron microscopy suggests that during the annealing process first phase separation and then crystallization of BaTiO3 occurs.

Electrical Properties of Mesoporous TiO2 Nanocomposite Thin Films Incorporated with Au Nanoparticles by Simple One-pot Synthesis

Abstract Low thermal conductivity, high electrical conductivity, and high Seebeck coefficient are required for thermoelectric materials. To independently control electrical and thermal conductivity, Au nanoparticles were incorporated into mesoporous TiO2 nanocomposite thin films. With increase of Au nanoparticle concentration and annealing time, ordered pore structure gradually collapsed. As porosity and pore structure changed, the electrical resistivity decreased from 142.9 to 41.6 Ω cm. In this work, Au nanoparticle concentration and annealing conditions were investigated to optimize the thermoelectric properties.

Reducing the nano-scale defect formation of atomic-layer-deposited SrTiO3 films by adjusting the cooling rate of the crystallization annealing of the seed layer

SrTiO3 (STO) thin films, grown by atomic layer deposition (ALD), were studied for capacitors in dynamic random access memory. The STO ALD process consisted of two steps: the growth of seed layer followed by a rapid thermal annealing (RTA) process at 650°C to crystallize it, and the deposition of the main layer on top of the seed layer at 370°C to induce the in-situ crystallization. During single cooling process after the RTA of the seed layer, voids and nano-cracks were formed due to the thermal expansion mismatch between STO film and Si substrate. This problem was well mitigated by adopting the stepwise cooling process, wherein the holding time of 30s at 500, 350, and 200°C suppressed the defect formation in the seed layer. Therefore, the main layer grown on that seed layer showed an improved microstructure with a high bulk dielectric constant of 135. However, the increase in total annealing time degraded the interface quality between the STO and the bottom electrode, which finally worsened the insulating property. As a result, the minimum equivalent oxide thicknesses with low leakage current densities (<10−7A/cm2 at 0.8V) for the single and stepwise cooling processes were 0.39nm and 0.46nm, respectively.

열처리 시간에 따른 메조기공 타이타니아의 비표면적 향상 연구: 가스센싱 특성 변화

낮은 열전도도 및 높은 비표면적 특성으로 흡착제 및 가스센서 등 여러 응용 분야로 연구되고 있는 규칙적 메조기공 세라믹 소재는 폐기공 메조기공 구조와 개기공 메조기공 구조로 나뉜다. 이중 폐기공 메조기공 세라믹 소재는 개기공 메조기공 세라믹 소재보다 높은 기계적 특성을 가짐에도 내부에 존재하는 기공을 이용한 비표면적 증가에 한계가 있어 응용에 제약을 가지고 있다. 본 연구팀은 규칙적 폐기공 메조기공 타이타니아(<TEX>$TiO_2$</TEX>)의 열처리 시간 변화에 따른 입자성장으로부터 폐기공 연결의 도입을 통하여 비표면적을 변화시키는 연구를 수행하고자 하였다. 열처리 시간 증가시 타이타니아 결정상의 변화는 없었으며 입자성장이 일어나게 되면서 기공구조의 무너짐 및 기공의 연결성 증가를 확인할 수 있었다. 24시간 열처리 시료의 경우, 기공률은 36.3%에 34.1%로 감소하였으나 기공의 연결도 증가로 인해 비표면적은 <TEX>$48m^2/g$</TEX>에서 <TEX>$156m^2/g$</TEX>으로 증가하였다. 이러한 비표면적의 증가는 CO 가스의 감응도 측정을 통하여 감응도가 약 7.4배 증가하는 것으로부터 확인될 수 있었다. Mesoporous ceramic materials were applied in various fields such as adsorbent and gas sensor because of low thermal conductivity and high specific surface area properties. This structure could be divided into open-pore structure and closed-pore structure. Although closed-pore structure mesoporous ceramic materials have higher mechanical property than open-pore structure, it has a restriction on the application because the increase of specific surface area is limited. So, in this work, specific surface area of closed-pore structure <TEX>$TiO_2$</TEX> was increased by anneal time. As increased annealing time, crystallization and grain growth of <TEX>$TiO_2$</TEX> skeleton structured material in mesoporous structure induced a collapse and agglomeration of pores. Through this pore structural change, pore connectivity and specific surface area could be enhanced. After anneal for 24 hrs, porosity was decreased from 36.3% to 34.1%, but specific surface area was increased from <TEX>$48m^2/g$</TEX> to <TEX>$156m^2/g$</TEX>. CO gas sensitivity was also increased by about 7.4 times due to an increase of specific surface area.

Thermal stability of AlN films prepared by ion beam assisted deposition

The thermal stability of AlN films deposited by ion beam assisted deposition was performed at 600°C for 192h under air ambient. The composition, morphology and optical properties were studied by X-ray photoelectron spectrometer, transmission electron microscopy, scanning electron microscopy, spectroscopic ellipsometry and UV–vis spectroscopy. The results show that the deposited film is polycrystalline, smooth, dense and homogenous. The oxidation of grain boundary takes place due to the element diffusion in the polycrystalline material. Oxidation produces amorphous oxide layers on the surface of film. As annealing time increases, surface roughness and diffuse reflection increase. Annealing has little influence on refractive index and extinction coefficient.

Effects of Film Stress and Geometry on Texture Evolution Before and After the Martensitic Transformation in a Nanocrystalline Co Thin Film

Using a transmission electron microscopy-based orientation and phase mapping technique we examine effects of film stress and geometry on texture development before and after the martensitic transformation in a nanocrystalline Co thin film. Specimens are annealed for various times at 873 K (600 °C), which is above the equilibrium martensitic transformation temperature [~693 K (~420 °C)], and then cooled to room temperature. The cooled specimens are used for texture analysis. The martensitic transformation is observed to be incomplete, and fcc and hcp structures coexist in all the specimens examined. It is deduced from the crystallographic orientation relationship of the martensitic transformation of Co that, during prolonged annealing at 873 K (600 °C), the major texture in the fcc phase is {101}, followed by {111}. In the cooled structure, the major texture component in the hcp phase is (0001), followed by {2 $$ \overline{1} \overline{1} $$ 0}. The {101} texture is clarified by assuming that the film system is perfect elastic–plastic with the help of the concept of the Taylor factor. We conclude that the (0001) texture is produced by the surface energy minimization, which, however, does not elucidate the development of the {2 $$ \overline{1} \overline{1} $$ 0} texture. The formation of the texture component is understood by considering the strain energy provided by a constraint imposed by neighboring grains. As annealing time increases, the hcp phase expands its area, dominating over the fcc phase after prolonged annealing, which is also clarified by allowing for the geometrical constraint effect. The expansion of the hcp phase supports the possibility of surface nucleation of martensites.

Reflective Ni/Ag/Ti/Au electrode with low specific contact resistivity

The specific contact resistivity and reflectivity of Ni/Ag/Ti/Au contact with p-GaN are studied. It is found that the thickness of Ag, anneal time and deposition temperature have a great effect on the performance of Ni/Ag/Ti/Au electrode. Its optical reflectivity is measured by reflectivity spectrophotometer, and its specific contact resistivity is calculated by circular transmission line model. It is observed that the contact reflectivity values of Ni (1 nm)/Ag/Ti (100 nm)/Au (100 nm), when the thickness values of Ag are 25 nm and 50 nm, are low: their values are 68.5% and 82.1% at 450 nm, respectively, and they start to increase with increasing the Ag thickness, then reach their saturated values when Ag thickness is beyond 200 nm. When the anneal time changes from 1 min to 10 min in oxygen atmosphere, the specific contact resistivity decreases at 300 ℃, decreases further and then increases at 400-600 ℃. After annealing at temperatures at 300 ℃ and 400 ℃ in oxygen atmosphere, the contact reflectivity value of Ni/Ag/Ti/Au remains almost unchanged, even when anneal time increases from 1 min to 10 min. However, The contact reflectivity of Ni/Ag/Ti/Au decreases significantly after annealing at a temperature higher than 400 ℃ and it becomes smaller with longer annealing time. After 400 ℃ annealing in oxygen atmosphere for 3 min, the specific contact resistivity reaches 3.6×10-3 Ω·cm2. Additionally, the deposition temperature of Ni/Ag is investigated. It is noticed that the specific contact resistivity decreases and the reflectivity increases with increasing the deposition temperature from room temperature to 120 ℃. The reflectivity rises to 90.1% at 450 nm and the specific contact resistivity reaches 6.4×10-3Ω·cm2 for the Ni/Ag/Ti/Au electrode at a deposition temperature of 120 ℃. However, the effects of improving the electrical and optical characteristics weaken when deposition temperature changes from 120 ℃ to 140 ℃. With a overall consideration, Ni (1 nm)/Ag (200 nm)/Ti (100 nm)/Au (100 nm) is made at a deposition temperature of 120 ℃, and then anneals at 400 ℃ for 3 min in oxygen atmosphere to achieve the optimized electrode. The vertical light emitting diode with this Ni/Ag/Ti/Au electrode is fabricated. Its working voltage is 2.95 V and the light output power is 387.1 mW at 350 mA. The electro-optical conversion efficiency reaches 37.5%.

Precipitation Behavior and Magnetic Properties of Nanoscale Particles in a Cu–10 at% Ni–5 at% Co Alloy

We investigated the relationship between the microstructure and magnetic properties of a Cu–10 at% Ni–5 at% Co alloy by using a transmission electron microscope (TEM), a SQUID magnetometer and a magnetic thermo–balance. TEM observations were performed to examine the microstructures of the Cu–Ni–Co specimens annealed at four temperatures between 873 K and 1073 K below and above the Curie point (983 K).Particles with cubic shapes were linearly arranged along the &lt;100&gt; direction of the copper matrix in specimens prepared by isothermal annealing at temperatures below the Curie point, while octahedral precipitates were sparsely formed by annealing above the Curie point. The TEM observations confirmed that the microstructural evolution in the Cu–Ni–Co specimens isothermally annealed at 1023 K. Although coherent cubic particles appeared at the initial stage of annealing, incoherent precipitates were finally formed with increased annealing time at 1023 K. The present SQUID measurements indicated that the curve of coercive force vs. annealing time had a peak at a short annealing period.

Correlating defect density with growth time in continuous graphene films.

We report that graphene flakes and films which were synthesized by copper-catalyzed atmospheric pressure chemical vapor deposition (APCVD) method using a mixture of Ar, H2, and CH4 gases. It was found that variations in the reaction parameters, such as reaction temperature, annealing time, and growth time, influenced the domain size of as-grown graphene. Besides, the reaction parameters influenced the number of layers, degree of defects and uniformity of the graphene films. The increase in growth temperature and annealing time tends to accelerate the graphene growth rate and increase the diffusion length, respectively, thereby increasing the average size of graphene domains. In addition, we confirmed that the number of pinholes reduced with increase in the growth time. Micro-Raman analysis of the as-grown graphene films confirmed that the continuous graphene monolayer film with low defects and high uniformity could be obtained with prolonged reaction time, under the appropriate annealing time and growth temperature.

Investigation of the Annealing Time Effects on the Properties of Sputtered ZnO:Al Thin Films

ZnO:Al transparent conductive films were deposited on glass substrates by RF magnetron sputtering technique and annealed by rapid thermal annealing system. The influence of annealing time on the structural, electrical, and optical properties of ZnO:Al thin films was investigated by atomic force microscopy, X-ray diffraction, Hall method and optical transmission spectroscopy. As the annealing time increases from 0 to 5 min, the crystallinity is improved, the root main square surface roughness is decreased and the sheet resistance is decreased. The lowest sheet resistance of ZnO:Al thin film is 90 ohm/sq. The reduction of sheet resistance is caused by increasing carrier concentration due to substituent Al ion. All films are transparent up to 80% in the visible wavelength range and the adsorption edge is a blue-shift due to Burstein-Moss effect with increasing annealing time.

Structure characterization and metallurgical properties of the chars formed by devolatilization of lump coals

The thermal pyrolysis of two lump coals used in the Corex process was carried out, and the structure, strength and reactivity to CO2 of the resulting chars were comprehensively investigated. The results show that the characteristic of the resulting chars is greatly affected by coal properties and carbonization conditions. XLC char forms visible pores because of its good thermoplastic property, and the bigger pores could affect the yields of volatiles. However, fissures are produced in DLC char during pyrolysis due to the non-caking property and cracks appear to decrease the production of pores. With the increasing annealing time and temperature, pore size and pore volume of chars decrease, which can be related to the shrinkage of coal char. The mechanical strength of chars is enhanced with increasing carbonization time and temperature, but the crushing strength of DLC chars is significantly influenced by cracks. Chars produced with longer time and higher temperature primarily display a lower CO2 reactivity according to the gasification tests. The results further indicate that factors affecting the CO2 reactivity are different for the two series of chars. The char reactivity index appears to have a linear correlation with the char strength after reaction.

Effect of Annealing Conditions on Microstructure of High Silicon Steel Prepared by Electrodeposition

The effect of annealing temperature and time on the microstructure, distribution of silicon,texture and magnetism of the high silicon steel prepared by electrodeposition was investigated. The results showed that after annealing at 1000℃ for 210 min, the mean grain size of steel was about 190 μm with a uniform grain size distribution, and the silicon is also uniformly distributed on the entire cross section with an average Si concentration 6.3715%(close to 6.5%); With the increasing annealing time at high temperature, the texture with double crystal planes {100} and {110} preferential oriented microstructure was enhanced, and the iron loss was lowered, implying a relatively good magnetism for the high silicon steel prepared by the proposed process.