Post-annealing Time Research Articles

Thermal instability of pseudomorphically strained phosphorus doped Si:C alloy

We study the thermal stability of P doped and undoped pseudomorphically strained Si:C alloy formed by high fluence ion implantation and subsequent solid phase epitaxial regrowth (SPER), under post-annealing conditions far below the β-SiC precipitation threshold. The strain is measured by high resolution X-ray diffractometer (HRXRD) and kinematic simulation. By plotting the differential strain relaxation with respect to post-annealing time, we found much lower deactivation energy at the near surface region while the presence of high P concentration results in more significant strain relaxation. We explain the near surface relaxation by considering the interstitials injection by surface oxide formations during the post annealing process. P in the bulk on the other hand plays the role as additional interstitial kick-out mediator and lowers the thermal stability.

Thermal evolution of surface blistering and exfoliation due to ion-implanted hydrogen monomers into Si〈1 1 1〉

This study investigated the dependence of surface blistering and exfoliation phenomena on post-annealing time in H+-implanted Si〈111〉. Czochralski-grown n-type Si〈111〉 wafers were room-temperature ion-implanted with 40keV hydrogen monomers to a fluence of 5×1016cm−2, and followed by furnace annealing treatments at 400 and 500°C for various durations ranging from 0.25 to 3h. The corresponding analysis results for Si〈100〉 [1] (Liang et al., 2008); [2] (Bai, 2007) were adopted in order to make comparisons. The evolution of blister formation and growth for Si〈111〉 at 400°C has a shorter characteristic time compared to Si〈100〉. However, there is a longer characteristic time when annealing takes place at 500°C. In addition, no craters were observed for Si〈111〉 annealed at 400°C while the opposite is true for Si〈100〉. The evolution of crater development for Si〈111〉 annealed at 500°C has a longer characteristic time compared to Si〈100〉. These results are attributed to the fact that compared to Si〈100〉, Si〈111〉 has a smaller surface binding energy of silicon atoms and a larger areal number density of silicon atoms on the plane perpendicular to the incident-ion axis. Furthermore, Si〈111〉 has a greater areal number density, smaller diameter, and a similar covered-area fraction of optically-detectable blisters compared to Si〈100〉. However, Si〈111〉 has a lower areal number density and a smaller covered-area fraction of craters than does Si〈100〉. Increasing post-annealing temperature from low (e.g. 400°C) to high (e.g. 500°C) revealed that Si〈111〉 tends to create more blisters while Si〈100〉 tends to develop larger blisters as well as create more craters.

Influence of Annealing on the Structure and 1.54 µm Photoluminescence of Er-Doped ZnO Thin Films Prepared by Sol–Gel Method

We have investigated the effects of Er concentration, post-annealing time and temperature through a sol–gel preparation method on the structure and 1.54-µm-related photoluminescence (PL) of ZnO:Er thin films. The results illustrated that the 1.54 µm emission was greatly influenced by the local structure of Er–O complex and ZnO host. The active oxygen movement during annealing process resulted in the formation of optical active center of Er ions, which probably attributed to the formation of a similar pseudo-octahedron with C4v structure around Er. The preferential orientation of ZnO host had more effect on the 1.54 µm PL intensity than the crystallinity of ZnO host. Therefore, the optimum annealing condition was about 800 °C/2 h and the appropriate concentration was about 0.05 at. % Er. A low-cost and fast formation of highly efficient Er centers in ZnO host for strong luminescence at near-infared region should be benefit for both fundamental research and also applications of light-emitting devices.

Solid-phase epitaxy of amorphous silicon films by in situ postannealing using RPCVD

Solid-phase epitaxy (SPE) of in situ As-doped amorphous Si (a-Si) deposited on SiO 2/Si 3N 4 patterned Si (1 0 0) wafers by reduced pressure chemical vapour deposition (RPCVD) using a H 2–Si 2H 6 gas system was investigated. The SPE was performed by applying in situ postannealing directly after deposition process. On the one hand, we studied the lateral SPE (L-SPE) length of As-doped Si on mask and their crystal quality by TEM/SEM characterisation for various postannealing temperatures (700–1000 °C for 60 s). We observed increase in L-SPE growth and decrease of dislocation density for higher postannealing temperatures. On the other hand, L-SPE length was also investigated for different postannealing times (0–120 min at 575 °C) and As concentrations. At these conditions the L-SPE length has increased with increasing postannealing time. For both, higher and lower annealing temperature region, crystallization has been inhibited for higher As concentrations. After modifying As-doping level, we were able to crystallize up to 500 nm of a-Si on mask to epi-Si by combination of 575 °C and 1000 °C postannealing.

Optical properties of Ag nanoparticle embedded silicate glass prepared by field-assisted diffusion

Ag nanoparticle embedded silicate glass was prepared by field-assisted diffusion, combined with post-annealing process. Surface plasmon resonance (SPR) bands were observed in the optical absorption measurement. The properties of optical absorption were strongly affected by the process parameters. With increasing electric field intensity and diffusion time, the SPR peak position and the full width at half maximum (FWHM) of the plasmon band were almost invariable. With increasing post-annealing time, the SPR peak was blue-shifted and the FWHM of SPR band decreased. The experimental results could be well simulated using modified Mie scattering theory considering the spill-out effects and the limitation of the mean free path.

Structure and magnetic properties of annealed metastable FeAg/Pt films

FeAg and FeAg/Pt films were prepared by dc magnetron sputtering at room temperature. The effects of Ag volume fraction in FeAg films and postannealing temperature and time on structure and magnetic properties of FeAg and FeAg/Pt films have been investigated. The results show that the as-deposited FeAg films are metastable. After annealing at 300°C, the phase separation of metastable FeAg films happened and the highest coercivity is obtained in Fe50Ag50/Pt film. With increasing annealing temperature, the ordering and the magnetic properties of the Fe50Ag50/Pt films were improved. When the Fe50Ag50/Pt films are annealed at 600°C for different annealing times, a long annealing time enhances the ordering of the metastable Fe50Ag50/Pt films and affects the orientation development. When the films are annealed for a long time, the grain size and the magnetic domain size also increase, which lead to an increase of correlation length due to the growth of FePt grains.

Ti3+‐Free Titanoborophosphate Glasses as Molding Glasses with High Refractive Indices

Ti3+‐free titanoborophosphate TiO2–B2O3–P2O5 (TBP)‐based glasses were produced in order to obtain glasses with low Tg (<600°C), high nd (>1.8), and a short postannealing (PA) time (less than a few days). In addition, TBP‐based glasses with low Tg (<570°C), high nd (>1.85), and a short PA time were successfully developed with the substitution of Li2O and ZnO for B2O3. Some glasses had very suitable properties for precision glass molding (Tg=553°C, nd=1.851, PA time=4 days for 6Li2O·6ZnO·55TiO2·6B2O3·27P2O5 glass; Tg=563°C, nd=1.880, PA time=2 days for 5Li2O·60TiO2·10B2O3·25P2O5 glass; Tg=566°C, nd=1.885, PA time=3 days for 2.5Li2O·2.5ZnO·60TiO2·10B2O3·25P2O5 glass; and Tg=567°C, nd=1.890, PA time=1 day for 5Li2O·5ZnO·60TiO2·5B2O3·25P2O5 glass). The λ70% of TBP‐based glasses with nd>1.85 and commercially available molding glasses with nd>1.85 are 40–41 and 44–50, respectively, which means that these new glasses have even higher transparency in the visible region than those currently on the market. Thus, TBP‐based glasses are considered to be promising materials as molding glasses with high transparency, low Tg, and high nd.

Post-annealing effects on the shallow-junction characteristics caused by high-fluence 77 keV BSi molecular ion implantations at room and liquid nitrogen temperatures

In this study, n-type <1 0 0> silicon specimens were liquid nitrogen temperature (LT) and room temperature (RT) implanted with 2 × 10 15 cm −2 77 keV BSi molecular ions to produce shallow junctions. Post-annealing methods under investigation included furnace annealing (FA) at 550 °C for 0.5, 1, 2, 3 and 5 h and rapid thermal annealing (RTA) at 1050 °C for 25 s. Post-annealing effects on the shallow-junction characteristics were examined using one-step (FA) and two-step (FA + RTA) post-annealing treatments. Secondary ion mass spectrometry (SIMS), cross-sectional transmission electron microscopy (XTEM), a four-point probe and Raman scattering spectroscopy (RSS) were employed to analyze junction depths ( x j), damage microstructures, sheet resistance ( R s) and damage characteristics, respectively. The results revealed that the shallow-junction characteristics of the LT implant are better than those of the RT one when post-annealing time in FA exceeds 1 h. A post-annealing time of 3 h in FA is needed in order to obtain the optimal one- or two-step post-annealing effects on the shallow-junction characteristics in both the LT and RT implants.

Performance of P3HT/C70-PCBM Polymer Photovoltaic Devices According to Manufacturing Conditions

In order to improve the P3HT/PCBM polymer photovoltaic devices, C70-PCBM ([6,6]-phenyl C71-butyric acid methyl ester) was employed instead of C60-PCBM ([6,6]-phenyl C61-butyric acid methyl ester). C70-PCBM showed significant increase of visible region light absorption to enhance the photocurrent. To optimize the device performance, we changed the device fabrication conditions such as atmosphere, solvents, post-annealing time, active layer materials composition, and thickness. The best power conversion efficiency of 4.7% was achieved under AM 1.5 G, 75 mA/cm2 condition.

Influence of post-annealing time on blistering evolution in Si 〈1 0 0〉 implanted with high-fluence H ions

The influence of post-annealing time on blistering characteristics induced by 5×1016cm−2 ion-implanted H in Si <100> was studied in terms of the formation and growth of blisters. Ion energies consisted of 40 and 100keV. Post-annealing treatments were carried out using furnace annealing (FA) at 400 and 500°C for a duration of 0.25–3h in a nitrogen ambient. Raman scattering spectroscopy (RSS), optical microscopy (OM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) were utilized to analyze the defect complex phases, the appearance of optically-detectable blisters and craters, the average depth of craters, and the hydrogen and oxygen depth profiles in the implanted layer, respectively. Furthermore, a characteristic time for the growth of optically-detectable blisters which was determined from the blister-covered fractions for various post-annealing times is proposed and used as a criterion to identify the effectiveness in the formation and growth of optically-detectable blisters. The results revealed that the characteristic time for the 400°C-annealed specimens in the 40keV implant is much shorter than it is in the 100keV one. However, the characteristic time for the 500°C-annealed specimens in the 40keV implant is slightly longer than it is in the 100keV implant. In addition, both the characteristic times for the 500°C-annealed specimens are much shorter than those for the 400°C ones. The above-mentioned phenomena hold true for craters.

High-throughput screening of ferroelectric materials for non-volatile random access memory using multilayer perceptrons

During the last several years, the development of combinatorial technology has enabled synthesis of a huge amount of chemical compounds in a short time. The large number of variables makes the direct human interpretation of data derived from combinatorial experimentation for high-throughput screening (HTS) very difficult. Artificial neural networks using multilayer perceptrons (MLP) have been successfully applied to the regression problems with various material data. In this work, MLP model was applied to HTS of ferroelectric materials including Bi 4− x La x Ti 3O 12 (BLT) and Bi 4− x Ce x Ti 3O 12 (BCT). The model using MLP was made to predict the ferroelectric properties of whole feasible experimental conditions. Once a neural network model with high accuracy and good generalization performance was established, we could predict the expected optimal reaction conditions with the best characteristics. The highest gradient value obtained using MLP model is higher than the maximum value found from experiments, thereby accelerating the discovery of the optimal compositions and post-annealing time of BCT and BLT.

An electrostatic force microscope study of Si nanostructures on Si(1 0 0) as a function of post-annealing temperature and time

The evolution of Si nanostructures induced by Ar + ion sputtering on Si(1 0 0) was studied with electrostatic force microscopy (EFM) as a function of post-annealing temperature ( T = room temperature–800 °C) and time ( t = 0–160 min). The post-annealing of the nanostructure was conducted in vacuum. It was found that with T increasing, the EFM contrast degraded steadily and became nearly undetectable at T = 800 °C; with t increasing at T = 800 °C, the EFM contrast fell down steadily as well. However, the surface morphology and roughness were much less affected after annealing. The results suggest that the as-formed Si nanostructures may not be epitaxially grown on Si(1 0 0) substrate as claimed before. A plane capacitance model supported this conclusion.

Dependence of Ferroelectric Properties on the Crystalline Phases of HoMnO3 Thin Film

Ferroelectric <TEX>$HoMnO_3$</TEX> thin films were deposited on the Si(100) substrate at <TEX>$700^{\circ}C$</TEX> for 2 hrs by metalorganic chemical vapor deposition (MOCVD) and post-annealed at 850oC by rapid thermal process (RTP). Electrical properties and crystalline phases of <TEX>$HoMnO_3$</TEX> thin films were investigated as a function of postannealing time. Single phase of hexagonal symmetry with c-axis preferred orientation was obtained from <TEX>$HoMnO_3$</TEX> thin films post-annealed at <TEX>$850^{\circ}C$</TEX> for 5 min, while the c-axis preferred orientation was decreased with the increase of post-annealing time, and the thin films post-annealed at <TEX>$850^{\circ}C$</TEX> for 15 min showed the mixture phases of hexagonal and orthorhombic symmetry. P-E (Polarization-Electric field) hysteresis loop of ferroelectric <TEX>$HoMnO_3$</TEX> thin films was observed only for the single phase of hexagonal symmetry, but that was not observed for the mixture phases of the hexagonal and orthorhombic symmetry, which was discussed with the bond valence of Mn ion of crystalline phase. Leakage current density was dependent on the microstructure of thin films as well as the change of valence of Mn ion.

Reversible Low‐Field Magnetoresistance in Sr2Fe2–xMoxO6–δ by Oxygen Cycling and the Role of Excess Mo (x &gt; 1) in Grain‐Boundary Regions

Oxygen cycling of Sr2Fe2-xMoxO6-delta (SFMO) samples allows the resistivity and low-field magnetoresistance (LFMR) to be precisely cycled. TEM shows that the change in resistivity with oxygen is not only a consequence of the change in oxygen stoichiometry of SFMO, but also a concomitant change in the Fe/Mo ratio in SFMO. The figure shows the change in MR and resistivity (values in m Omega cm above the data points for samples D1-D7) with increasing post-annealing time

Activation and deactivation in heavily boron-doped silicon using ultra-low-energy ion implantation

A shallow p+∕n junction was formed using an ultra-low-energy implanter. Activation annealing exhibited both solid phase epitaxy, in which the sheet resistance dropped rapidly, and reverse annealing. Deactivation phenomena were investigated for the shallow source/drain junction based on measurements of the postannealing time and temperature following the rapid thermal annealing treatments. We found that the deactivation kinetics were divided into two regions. In the first region the rate of deactivation increased exponentially with the annealing temperature of up to 850°C. In the second region it decreased as the annealing temperature exceeded 850°C. We believe that the first region is kinetically limited while the second one is thermodynamically limited. In addition, we observed “transient enhanced deactivation,” an anomalous increase in the sheet resistance during the early annealing stage where the the temperatures were higher than 800°C. The activation energy for transient enhanced deactivation was measured to be between 1.75 and 1.87eV, while that for normal deactivation was between 3.49 and 3.69eV.

Characterization of crystalline structure of ball-milled nano-Ni–Zn-ferrite by Rietveld method

Nanocrystalline Ni–Zn-ferrite is synthesized at room temperature by high-energy ball milling with the target composition 0.5 ZnO, 0.5 NiO and 1.0 α-Fe2O3 ((0.5+0.5):1 mole fraction). The formation of non-stoichiometric ferrite phase is noticed after 1 h of ball milling and its content increases with increasing milling time. The structural and microstructural evolution of nickel–zinc-ferrite caused by milling is investigated by X-ray powder diffraction. The relative phase abundances of different phases, particle size, r.m.s. (root mean square) strain, lattice parameter change, etc. have been estimated from Rietveld’s powder structure refinement analysis of XRD data. It is revealed from the XRD pattern that ZnO reflections are completely disappeared within 1 h of milling but a significant amount (∼7 wt.%) of nanocrystalline NiO and α-Fe2O3 (∼12 wt.%) remain excess even after 11 h of milling. It indicates that during ball milling a non-stoichiometric mixture of NiO, ZnO and α-Fe2O3 may lead to the formation of non-stoichiometric Ni–Zn-ferrite. A considerable amount of ferrite is formed within 11 h of ball milling with lattice parameter higher than that of stoichiometric Ni–Zn-ferrite prepared by conventional ceramic route keeping the same powder mixture at 1473 K for 2 h. The 11 h milled sample is post-annealed at 773 K for different durations to verify the solubility of both the residual parts of NiO and α-Fe2O3 in forming the target composition. The post-annealing treatment reveals that within 1 h of post-annealing, stoichiometric Ni–Zn-ferrite is formed and nanocrystalline ferrite particles become almost strain-free within 15 h of post-annealing time.

Characterization of crystalline structure of ball-milled nano-Ni–Zn-ferrite by Rietveld method

Nanocrystalline Ni–Zn-ferrite is synthesized at room temperature by high-energy ball milling with the target composition 0.5 ZnO, 0.5 NiO and 1.0 α-Fe 2O 3 ((0.5+0.5):1 mole fraction). The formation of non-stoichiometric ferrite phase is noticed after 1 h of ball milling and its content increases with increasing milling time. The structural and microstructural evolution of nickel–zinc-ferrite caused by milling is investigated by X-ray powder diffraction. The relative phase abundances of different phases, particle size, r.m.s. (root mean square) strain, lattice parameter change, etc. have been estimated from Rietveld’s powder structure refinement analysis of XRD data. It is revealed from the XRD pattern that ZnO reflections are completely disappeared within 1 h of milling but a significant amount (∼7 wt.%) of nanocrystalline NiO and α-Fe 2O 3 (∼12 wt.%) remain excess even after 11 h of milling. It indicates that during ball milling a non-stoichiometric mixture of NiO, ZnO and α-Fe 2O 3 may lead to the formation of non-stoichiometric Ni–Zn-ferrite. A considerable amount of ferrite is formed within 11 h of ball milling with lattice parameter higher than that of stoichiometric Ni–Zn-ferrite prepared by conventional ceramic route keeping the same powder mixture at 1473 K for 2 h. The 11 h milled sample is post-annealed at 773 K for different durations to verify the solubility of both the residual parts of NiO and α-Fe 2O 3 in forming the target composition. The post-annealing treatment reveals that within 1 h of post-annealing, stoichiometric Ni–Zn-ferrite is formed and nanocrystalline ferrite particles become almost strain-free within 15 h of post-annealing time.

Deactivation Kinetics in Heavily Boron Doped Silicon Using Ultra Low Energy Ion Implantation

Shallow <TEX>$p^{＋}$</TEX> n junction was formed using a ULE(ultra low energy) implanter. Deactivation phenomena were investigated for the shallow source/drain junction based on measurements of post-annealing time and temperature following the rapid thermal annealing(RTA) treatments. We found that deactivation kinetics has two regimes such that the amount of deactivation increases exponentially with annealing temperature up to <TEX>$850^{\circ}C$</TEX> and that it decreases linearly with the annealing temperature beyond that temperature. We believe that the first regime is kinetically limited while the second one is thermodynamically limited. We also observed "transient enhanced deactivation", an anomalous increase in sheet resistance during the early stage of annealing at temperatures higher than X<TEX>$/^{\circ}C$</TEX>. Activation energy for transient enhanced deactivation was measured to be 1.75-1.87 eV range, while that for normal deactivation was found to be between 3.49-3.69 eV.

Growth of superconducting MgB 2 thin films via postannealing techniques

We report the effect of annealing on the superconductivity of MgB 2 thin films as a function of the postannealing temperature in the range from 700 to 950 °C and of the postannealing time in the range from 30 to 120 min. On annealing at 900 °C for 30 min, we obtained the best-quality MgB 2 films with a transition temperature of 39 K and a critical current density of ∼10 7 A/cm 2. Using scanning electron microscopy, we also investigated the film growth mechanism. The samples annealed at higher temperatures showed larger grain sizes, well-aligned crystal structures with preferential orientation along the c-axis, and smooth surface morphologies. However, a longer annealing time prevented the alignment of grains and reduced superconductivity, indicating a strong interfacial reaction between the substrate and the MgB 2 film.

Effects of postbombardment annealing on Ti diffusion in ion prebombarded MgO(100)

The effect of postbombardment annealing, or postannealing, has been investigated for Ti diffusion in ion prebombarded MgO(100). MgO postannealing was performed in ultrahigh vacuum after ion prebombardment of MgO and prior to Ti evaporation and diffusion. For postannealing temperatures of T=800, 900, and 1000 °C, Ti diffusion in 7 keV Ar+ prebombarded MgO exhibits the expected exponential decays with postannealing time and more rapid decays with higher temperatures. Cationic diffusion in the ion prebombarded sample proceeds in a nonsteady state condition of extra defects known as nonsteady state radiation enhanced diffusion (NSRED). Thermal dissociation of small vacancy clusters is responsible for NSRED. From the data of T⩽1000 °C, the derived dissociation energy of the vacancy clusters is only ∼10% of the normal value. For some specific postannealing times at T=1100 °C, the subsequent Ti diffusion was more enhanced than that without postannealing, a phenomenon which is contrary to the usual understanding of annealing effects. This same effect was also observed for Ti diffusion in 7 keV Cl+ prebombarded MgO postannealed at 1100 °C. Previous work indicates that the small vacancy clusters for NSRED are mainly Mg divacancies. We propose a divacancy creation mechanism that is due to the thermal dissociation of larger vacancy clusters during postannealing. The dissociation energy ratio of the effective large vacancy clusters (LVC) to that of the divacancies (DIV) is ELVC/EDIV∼1.4. The monovacancy coalescence was found to be unimportant for divacancy creation. A model based on this mechanism explains the unusual diffusion enhancement observed.