Subsequent Annealing Processes Research Articles

Strengthening mechanisms of a heterostructured pure aluminum with extraordinary mechanical properties

To achieve superior mechanical properties in metallic materials, one promising way is to make them into heterogeneous structures (HS). In this work, a novel HS including grain size and dislocation density is developed in commercial pure aluminum through cold-rolling and subsequent partial annealing processes. Tensile tests show that the HS specimen, annealed at 150 °C for 2 min with ~31.1% recrystallized grains, have a high yield strength of ~121 MPa and a good uniform elongation of ~8.5%. The yield strength increases by 10% and the ductility increases by 7 times compared with the as-rolled specimen, respectively. Detailed microstructure characterizations confirm that a significant strain gradient was generated near the interface between the hard zone and soft zone, in which the slip and plugging of geometrically necessary dislocations act as an important role in the abnormal hardening and strengthening phenomena of the HS specimen. To quantify the specific contribution of each strengthening mechanism, we compare the experimental measurements with the theoretical calculations and confirm that the multiple deformation modes are activated by the deformation stress. The hetero-deformation-induced hardening and strengthening effects are responsible for the superior mechanical properties of the heterostructured pure aluminum.

Efficiency Optimization of Ge‐V Quantum Emitters in Single‐Crystal Diamond upon Ion Implantation and HPHT Annealing

AbstractThe authors report on the characterization at the single‐defect level of germanium‐vacancy (GeV) centers in diamond produced upon Ge− ion implantation and different subsequent annealing processes, with a specific focus on the effect of high‐pressure‐high‐temperature (HPHT) processing on their quantum‐optical properties. Different post‐implantation annealing conditions are explored for the optimal activation of GeV centers, namely, 900 °C 2 h, 1000 °C 10 h, 1500 °C 1 h under high vacuum, and 2000 °C 15 min at 6 GPa pressure. A systematic analysis of the relevant emission properties, including the emission intensity in saturation regime and the excited state radiative lifetime, is performed on the basis of a set of ion‐implanted samples, with the scope of identifying the most suitable conditions for the creation of GeV centers with optimal quantum‐optical emission properties. The main performance parameter adopted here to describe the excitation efficiency of GeV centers as single‐photon emitters is the ratio between the saturation optical excitation power and the emission intensity at saturation. The results show an up to eightfold emission efficiency increase in HPHT‐treated samples with respect to conventional annealing in vacuum conditions, suggesting a suitable thermodynamic pathway toward the repeatable fabrication of ultra‐bright GeV centers for single‐photon generation purposes.

Morphological Evolution of La2NiO4 Coatings Synthesized by Reactive Magnetron Sputtering (RMS) at High Pressure as Cathode for Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC)

This work focuses on the evolution of the morphology and structure of La2NiO4 (namely, LNO) coatings deposited by reactive magnetron sputtering (RMS) with subsequent annealing processes. The LNO coatings start to crystallize at 600 °C, and the LNO with K2NiF4 structure was formed at 700 °C. A small amount of La3Ni2O7 appeared in the La2NiO4 coatings at 1100 °C. Interestingly, the LNO coatings realize the transformation from dense to different porous morphologies due to the annealing process. The LNO coating with abundant pores was formed after annealing treatment at 1000 °C for 2 h. This porous morphology can be stably maintained after short-term thermal stability experiments at 750 °C for 120 h. The electrochemical impedance spectroscopy (EIS) measurement of the LNO/YSZ/LNO symmetrical half-cells shows that the LNO cathode coating after annealing at 1000 °C for 2 h exhibits lower polarization resistance (Rpol) and activation energy.

Controlling the beam angle spread of carbon implantation for improvement of bin map defect in V-NAND flash memory

As the shrinkage of devices accelerates and the vertical layers increase, beam angle spread of carbon ion implantation (C IIP) for the silicon selective epitaxial growth (Si-SEG) areas in V-NAND is one of the most critical parameters related with bin map defects. The roles of C IIP in Si-SEGs are that it can suppress channeling effect of boron IIP and diffusion limitation of boron dopants during subsequent annealing processes. In this study, beam angle spread was reduced by 36% and the center-to-edge beam angle skew of wafer was reduced to less than 1° by optimizing the specification of tracking magnet and the beam angle mean. After applying the improved process conditions and effective interlocks, the bin defective rate was controlled less than 0.5% successfully.

A highly controllable doping technique via interdiffusion between epitaxial germanium layers and GaAs

Interdiffusion between epitaxial Ge layers and GaAs substrates was used in this study to precisely control the doping concentration and doping type of the Ge layers. An extremely high n-type doping concentration (> 1020 cm−3) was achieved in a Ge layer grown at a low temperature of 300 °C; the layer exhibited a smooth surface morphology and excellent crystalline quality. Subsequent post-growth annealing processes led to a decrease of the n-type doping concentration followed by an n- to p-type transition because of the diffusivity difference between As and Ga atoms. Our experimental results indicated the preferential diffusion of As atoms and their consequent escape through the Ge top surface, resulting in the p-type transition via time-lagged Ga diffusion. We fabricated a Ge-on-insulator junctionless field-effect transistor using a heavily n-doped 10 nm-thick Ge channel, and the device demonstrated good performance.

Aluminium-assisted chemical etching for fabrication of black silicon

This paper investigates aluminium-assisted chemical etching (AACE) process to fabricate b-Si absorber for the first time. The AACE process combines deposition of a thin aluminium (Al) film with thickness of 12–30 nm on crystalline silicon (c-Si) wafers, followed by subsequent thermal annealing and wet chemical etching processes. The AACE process produces random nanopores on the b-Si surface. From the results, thicker Al thickness leads to lower depth of nanopores, lower surface coverage of nanopores on the b-Si and exhibits higher weighted average reflection (Ravg) within 300–1100 nm wavelength region. The b-Si fabricated by Al film of 12 nm thickness demonstrates the lowest Ravg (11.9%) and the highest broadband light absorption. The b-Si reveals nanopores with average depth of 200 nm and surface coverage of 45.1%. The findings from this work demonstrate the potential of the AACE process to produce b-Si with superior broadband light absorption, which is crucial for photovoltaic (PV) applications.

Low-pressure solid-state bonding technology using fine-grained silver foils for high-temperature electronics

A solid-state bonding technique using fine-grained silver (Ag) foils is presented. The Ag foils are manufactured using many runs of cold rolling and subsequent annealing processes to achieve the favorable microstructure. X-ray diffraction and pole figure measurement are performed to examine the crystal structure and grain orientations. Si chips are bonded to bare Cu substrates using the Ag foil as the bonding medium at 300 °C in 0.1 torr vacuum assisted by 6.9 MPa static pressure, which is much lower than that used in conventional thermal compression bonding. Cross sections prepared by focus ion beam show clear bonding interfaces with only a few voids smaller than 100 nm. The bonded structures do not crack after cooling down to room temperature, indicating that the ductile Ag layer is able to manage the strain induced by the large coefficient of thermal expansion mismatch between Si and Cu. The average shear strength of as-bonded samples is 29 MPa. High-temperature storage tests are conducted, and slight increase in strength can be observed after 300 °C aging. Fracture analyses show that the breakage occurs within the Ag foil rather than on the bonding interface. Transmission electron microscopy and energy-dispersive spectroscopy (TEM/EDX) are conducted for Ag/Cu interface after 200-h aging, and the result shows that slight diffusion proceeds during the aging. Since Ag has the highest electrical and thermal conductivities among metals, therefore the bonded structures reported in this paper probably represent the best possible design for high-temperature and high-power electronic packaging applications.

Large magnetic entropy change and magnetic phase transitions in rapidly quenched bulk Mn-Fe-P-Si alloys

Mn1.15Fe0.85P0.50Si0.45B0.05 alloys were prepared by copper mold suction casting method. Subsequent annealing processes were employed to tune the microstructures and magnetocaloric effects. Results show that Mn1.15Fe0.85P0.50Si0.45B0.05 alloys crystallize in a hexagonal phase with the Fe2P structure type. With increasing annealing temperature, the lattice parameters of a and c of Fe2P-type phase increase from 5.7988(1)Å to 6.0785(2)Å and from 3.3218(1)Å to 3.4727(2)Å for the Mn1.15Fe0.85P0.50Si0.45B0.05 alloys according to XRD. At the same time the Curie temperature and magnetic entropy change increase from 233 K to 244 K and from 8.8 J kg−1K−1 to 17.0 J kg−1K−1 (ΔH = 2 T), respectively, while the thermal hysteresis decreases. The entropy changes of these alloys are also estimated from the Clausius-Clapeyron equation, Landau theory and heat capacity, respectively. The nature of the phase transitions were studied through the Arrott plots, which indicate that the samples undergo first-order ferro-paramagnetic phase transitions. However, the universal curve of scaled magnetic entropy change reveals that during the magnetic phase transition, there exists a critical magnetic field, about 1.25 T, below which the sample undergoes a second-order phase transition and above which it displays a first-order phase transition. Furthermore, mechanisms for the large magnetic entropy change and possibilities for the room-temperature magnetic refrigeration are discussed.

Role of Solution Structure in Self-Assembly of Conjugated Block Copolymer Thin Films

Conjugated block copolymers provide a pathway to achieve thermally stable nanostructured thin films for organic solar cells. We characterized the structural evolution of poly(3-hexylthiophene)-block-poly(diketopyrrolopyrrole–terthiophene) (P3HT-b-DPPT-T) from solution to nanostructured thin films. Aggregation of the DPPT-T block of P3HT-b-DPPT-T was found in solution by small-angle X-ray scattering with the P3HT block remaining well-solvated. The nanostructure in thin films was determined using a combination of wide and small-angle X-ray scattering techniques as a function of processing conditions. The structure in solution controlled the initial nanostructure in spin-cast thin films, allowing subsequent thermal annealing processes to further improve the ordering. In contrast to the results for thin films, nanostructural ordering was not observed in the bulk samples by small-angle X-ray scattering. These results suggest the importance of controlling solvent induced aggregation in forming nanostructured th...

High-Temperature Characterization of Silicon Dioxide Films with Wafer Curvature

Amorphous silicon dioxide films used as dielectric layers in microelectronic devices are deposited using plasma-enhanced chemical vapor deposition. Because of the presence of hydrogen and nitrogen species in the precursor gases, incorporation of such species in the films can lead to crack formation during subsequent annealing processes up to 1000°C. In this study, the role of film chemistry on the thermo-mechanical behavior of silicon dioxide films is studied with in situ film stress measurements using wafer curvature to maximum temperatures of 1000°C. This is a significant advance because normal wafer curvature can only reach maximum temperatures of around 500°C. The increased temperature range allows for the stress evolution and film chemistry to be examined for the relevant processing conditions. It was found that at temperatures higher than 550°C, hydrogen bond cleavage led to a large stress increase and film chemistry change due to new bonding arrangements between nitrogen and silicon as well as subsequent film densification causing cracking of films. These changes could only be identified with wafer curvature measurements up to 1000°C.

Transformation of metallic photonic structures from nano-hole to nano-island arrays through annealing process

Large-area metallic photonic crystals (MPCs) consist of two-dimensional (2D) periodical arrays of gold nano-holes are fabricated by solution-processible gold nanoparticles using interference lithography in combination with subsequent lift-off and annealing processes. By controlling the annealing temperature, the 2D nano-hole arrays are transformed into nano-island arrays, enabling easy achievements of two different photonic devices. The microscopic characterization shows convincingly the success of the fabrication techniques and verifies our proposed mechanisms for this kind of nanoscale morphology transformation. This kind of mechanisms can be applied extensively in the metallic nanofabrication and in the realization of plasmonic photonic devices. OCIS codes: 250.0250, 100.6640, 210.4770, 180.1790. doi: 10.3788/COL201210.S12502.

Atomic force microscopy investigation of the kinetic growth mechanisms of sputtered nanostructured Au film on mica: towards a nanoscale morphology control

The study of surface morphology of Au deposited on mica is crucial for the fabrication of flat Au films for applications in biological, electronic, and optical devices. The understanding of the growth mechanisms of Au on mica allows to tune the process parameters to obtain ultra-flat film as suitable platform for anchoring self-assembling monolayers, molecules, nanotubes, and nanoparticles. Furthermore, atomically flat Au substrates are ideal for imaging adsorbate layers using scanning probe microscopy techniques. The control of these mechanisms is a prerequisite for control of the film nano- and micro-structure to obtain materials with desired morphological properties. We report on an atomic force microscopy (AFM) study of the morphology evolution of Au film deposited on mica by room-temperature sputtering as a function of subsequent annealing processes. Starting from an Au continuous film on the mica substrate, the AFM technique allowed us to observe nucleation and growth of Au clusters when annealing process is performed in the 573-773 K temperature range and 900-3600 s time range. The evolution of the clusters size was quantified allowing us to evaluate the growth exponent 〈z〉 = 1.88 ± 0.06. Furthermore, we observed that the late stage of cluster growth is accompanied by the formation of circular depletion zones around the largest clusters. From the quantification of the evolution of the size of these zones, the Au surface diffusion coefficient was evaluated in . These quantitative data and their correlation with existing theoretical models elucidate the kinetic growth mechanisms of the sputtered Au on mica. As a consequence we acquired a methodology to control the morphological characteristics of the Au film simply controlling the annealing temperature and time.

Nanoscale patterning using photo-assisted polymer transfer lithography

We successfully demonstrate photo-assisted polymer transfer lithography for submicron-size patterning to greatly simplify conventional decal transfer lithography. For a small size patterning, this process includes three main processes: fabrication of a precise polydimethylsiloxaene (PDMS) stamp, TiO 2 film deposition on substrate and subsequent annealing processes to form anatase crystalline phase, and pattern transfer process onto substrate with light illumination. The adhesion of PDMS onto TiO 2 substrate is related to the photocatalystic reaction of anatase TiO 2 film, which is caused by rapid thermal anneal at least above 300 °C. This soft lithographic technique demonstrates the formation of high line and dot patterns simultaneously without any additional adhesion-promotion and time-urgent processes.

Melt Spinning Preparation of Bismuth Telluride and Partially Alloying with IV-VI Compounds for Thermoelectric Application

AbstractThe melt spinning technique (MST) combined with post annealing processes is evaluated for the development of thermoelectric nanocomposites. The evaluated ones are based on two components almost immiscible in solid state but with crystallographic correlation. One is taken from the V-VI-components system and the other one from the IV-VI-components system. This concept was applied to p-(Bi0,2Sb0,8)2Te3 and to p-[(Bi0,2Sb0,8)2Te3]1-xPbTex composites. MST samples of all types were characterised for some structural and thermoelectric properties. All V-VI materials are clearly textured after MST and show no deterioration concerning the thermoelectric properties even after subsequent annealing processes. Structural analysis of p-[(Bi0,2Sb0,8)2Te3]1-xPbTex composites gave significant hints for oriented precipitates of a IV-VI-rich phase incorporated into the V-VI-rich matrix. The thermoelectric figure of merit of the evaluated composites could be enhanced by suitable annealing procedures of both the quenched bulk materials and the melt spin material.

Development of Stereocomplex Crystal of Polylactide in High-Speed Melt Spinning and Subsequent Drawing and Annealing Processes

High-speed melt spinning of racemate polylactide (r-PLA), which is a blend of equal amounts of poly(l-lactide) and poly(d-lactide) molecules, was performed up to the take-up velocity of 7.5 km/min. In the fiber structure analysis, particular attention was paid to the formation of stereocomplex crystals, because this crystal form has a melting temperature about 60° higher than the homocrystals. It was found that highly oriented and highly crystallized fibers containing the α-form and stereocomplex crystals were obtained when the take-up velocity exceeded about 4 km/min. The amount of stereocomplex crystal was higher under the spinning conditions of higher take-up velocity, lower throughput rate, and lower extrusion temperature. Under these conditions, higher tensile stress can be applied to the spinning line, and therefore, the orientation-induced crystallization is promoted. Annealing of the fibers obtained at high-take-up velocities, such as 6 km/min, which already have the crystalline structure with a certain amount of stereocomplex crystal, at a temperature between the melting temperatures of α-form and stereocomplex crystals, yielded the fiber structure mainly consisting of highly oriented stereocomplex crystal. The annealed fibers showed fairly high mechanical properties and good thermal stability.

Ferritic steels: Optimization of hot-rolled textures through cold rolling and annealing

This paper describes the processes used in the production of tinplate, autobody and interstitial-free (IF) steels, and examines how the microstructure and the texture of the hot-rolled stock modify the cold formability properties ( n, r m and Δ r) of the blanks through the subsequent cold-rolling and annealing processes. The process of fabrication of ferritic steel strip must comply with the specified drawing quality requirements: commercial quality (CQ), drawing quality (DQ), deep drawing quality (DDQ) or extra deep drawing quality (EDDQ). The quality level is determined by several factors, such as the chemical composition, microstructure and texture of the hot-rolled sheet, the percentage of cold reduction (CR) and the recrystallization treatment in the continuous annealing process or batch process. To a lesser degree, other parameters such as the coiling temperature in the hot strip workshop and the degree of reduction in the temper rolling (TR) mill also modify the cold workability of the strip.

Formation of buried oxide layers in molybdenum by high-fluence oxygen ion implantation

High-energy oxygen ions were implanted with fluences from 2.5×1017 up to 1.5×1018 O+-ions/cm2 into molybdenum at temperatures between −60°C and room temperature. Subsequent annealing processes were carried out at 500°C up to 60 min. The chemical composition was investigated using Rutherford backscattering spectrometry. The concentration distribution of the implanted oxygen is characterized by two kinds of profiles: gaussian profiles are observed, when the fluence is lower than the critical fluence required to form a buried molybdenum oxide layer, and a concentration plateau, when the fluence exceeds this critical concentration. Annealing reinforces the tendency to form a flat-topped distribution. Electron and X-ray diffraction studies show that the molybdenum oxide phase δ-MoO2 is formed during annealing. Cross-sectional TEM studies of the as-implanted and annealed oxygen implanted molybdenum are presented. After implantation a buried amorphous layer between strongly damaged material could be found in the near surface region. With increasing annealing time different oxide precipitate morphologies and a buried molybdenum oxide layer covered by an amorphous layer is formed.

Mechanically enhanced carbothermic synthesis of iron-TiN composite

We have previously reported [1–3] that high energy ball milling has an enhanced role on carbothermic reduction of mineral ilmenite (FeTiO3) to rutile (TiO2). Ball milling of a mixture of ilmenite with carbon at room temperature can dramatically lead to a high reduction rate and a low temperature required for full reduction of ilmenite to rutile and iron during the subsequent annealing process. Titanium carbide can also be produced at a relative low temperature (1000 8C) if sufficient carbon is supplied [4]. It has been reported that titanium nitride can be synthesized by reduction of titanium dioxide with carbon in a nitrogen atmosphere at 1150 8C [5]. In the work reported here, an assessment of the production of iron–TiN composite at a relatively low annealing temperature was made with an ilmenite–carbon mixture by using a pre-ball milling treatment and subsequent annealing process. The advantages expected of this production process are the inexpensive nature of the raw materials (ilmenite and graphite) and the one-step carbothermic reduction and simultaneously nitridation reaction, thus reducing the number of process steps. In this experiment, an upgraded ilmenite powder with a particle size of 200–300 mm was supplied by Westralian Sands Ltd. The chemical composition of this ilmenite was as follows: FeO, 20.8 wt %; Fe2O3, 20.0 wt %; TiO2, 53.6 wt % and impurities (MnO, SiO2, ZrO2, etc.), 3.5 wt %. A graphite powder with a purity of 99.8% or better was used as reducing agent. The weight ratio of ilmenite to graphite was 1:1, which gave excess carbon for full reduction of ilmenite to metal titanium and iron. Ball milling was performed at room temperature in a vertical planetary ball mill (ANUtech Pty Ltd, Canberra) using hardened steel balls with a diameter of 25.4 mm and a stainless steel cell. The cell was loaded with several grams of materials together with five balls and evacuated to vacuum (10y2 kPa) prior to milling. After milling, the structure of the samples was investigated by X-ray diffraction (XRD) using Co radiation (o ˆ 0.1789 nm) at room temperature. The thermal analysis was carried out in a thermogravimetric (TG) analyser where a sample was heated at a rate of 20 K miny1 under dry nitrogen flow (80 ml miny1). After each run the sample was left to cool to room temperature in the apparatus while the nitrogen flow was continued. An isothermal treatment was conducted in a thermal tube furnace under a dry nitrogen flow (60 ml miny1). Typical XRD patterns after milling and annealing are presented in Fig. 1. Fig. 1a shows that both ilmenite and graphite structures remained after 200 h of milling. However, the low intensity and the broadened shape of the graphite and ilmenite diffraction peaks suggest small crystallite size and a highly disordered structure. Indeed, it has been reported that grinding of graphite can lead to the structure disordering [6, 7] or amorphization [8]. The average grain size of the ilmenite crystallite estimated from the peak broadening by using the Scherrer formula [9] is about 45 nm, indicating a nanocrystalline structure of the milled ilmenite. Finally, no new diffraction peaks were found in this XRD pattern, suggesting that no chemical reaction occurred during the milling process. However, as shown later, the observed dramatic structural changes in both graphite and ilmenite structures strongly affect the thermal behaviour during the subsequent annealing processes. After annealing of the as-milled sample at 800 8C for 1 h under flowing nitrogen, the ilmenite phase was no longer detected by XRD (Fig. 1b) and essentially only rutile (TiO2) and iron solid solutions (Fe(C)) were obtained. The main iron solid solutions are AE-Fe(C) ‡ austenite Fe(C). Further annealing of the as-milled sample at a higher temperature (1000 8C) for 1 h leads to the formation of titanium nitride (TiN) phase, as indicated by the XRD pattern (Fig. 1c). Excess graphite was still detected in the XRD patterns (as represented by the weak diffraction peak c). Hence,

1 MHz dielectric constants of phosphosilicate glass films chemically vapour-deposited in the SiH4-PH3-O2-N2 system at low temperature

The a.c. relative dielectric constant (RDC) and resistivity of as-deposited and thermally annealed phosphosilicate glass (PSG) films with phosphorus concentrations in the range 0 to 9.3 wt% P were measured at a frequency of 1 MHz and at room temperature. The variations of RDC and resistivity with phosphorus concentration exhibit two regions: (i) for phosphorus concentrations in the range 0 to 4 wt% P, the RDC values of the as-deposited films are higher (above 4.5) than those of N2-annealed films (around 3.5), while the resistivity values of the as-deposited films (around 4 Mω cm) are lower than those of N2-annealed-films (around 8 Mω cm); and (ii) for phosphorus concentrations in the range 4 to 9.3 wt% P, RDC values of as-deposited films decrease to values below those of N2-annealed films, while the values of resistivity of as-deposited and N2-annealed films tend to the same value of 8.4 Mw cm at concentrations above 8 wt% P. The behaviour of the RDC and resistivity of PSG films is interpreted in terms of (i) the evolution of a content of HO, H2O, P-O and P=O polar groups as a function of phosphorus concentration and subsequent annealing processes, and (ii) the structural changes suffered by the films during subsequent annealing processes.

Study of phase transition VO 2 thin film

Vanadium dioxide thin film that has semiconductor-to-metal phase transition has been obtained by either reactive evaporation or reactive ion assisted deposition with subsequent annealing processes. Various kinds of measurement methods have been developed in investigation of phase transition properties of vanadium dioxide films. It is observed that the performance of phase transition properties strongly depends upon the stoichiometric and crystalline characteristics of the thin film.