Change in the magnetic properties of nanoferrihydrite with an increase in the volume of nanoparticles during low-temperature annealing

The results of the investigation into the effect of low-temperature annealing of a powder of nanoparticles of bacterial ferrihydrite on its magnetic properties have been presented. It has been found that an increase in the time (up to 240 h) and temperature (in the range from 150 to 200°C) of annealing leads to a monotonic increase in the superparamagnetic blocking temperature, the coercive force, and the threshold field of the opening of the magnetic hysteresis loop (at liquid-helium temperatures), as well as to an increase in the magnetic resonance line width at low temperatures and in the magnetic susceptibility at room temperature. At the same time, according to the results of the analysis of the Mössbauer spectra, the annealing of ferrihydrite does not lead to the formation of new iron oxide phases. Most of these features are well consistent with the fact that the low-temperature annealing of ferrihydrite causes an increase in the size of nanoparticles, which is confirmed by the results of transmission electron microscopy studies.     

Effect of thermal annealing in the microstructural and the optical properties of uncapped InAs quantum dots grown on GaAs buffer layers

The effect of thermal annealing on self-assembled uncapped InAs/GaAs quantum dots (QDs) has been investigated using transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images showed that the lateral sizes and densities of the InAs QDs were not changed significantly up to 650 °C. When the InAs/GaAs QDs were annealed at 700 °C, while the lateral size of the InAs QDs increased, their density decreased. The InAs QDs disappeared at 800 °C. PL spectra showed that the peaks corresponding to the interband transitions of the InAs QDs shifted slightly toward the high-energy side, and the PL intensity decreased with increasing annealing temperature. These results indicate that the microstructural and the optical properties of self-assembled uncapped InAs/GaAs can be modified due to postgrowth thermal annealing.     

Infrared transmission of chalcohalide glasses in the Ge–Se–Te–I system

Infrared (IR) transmission spectra in the range from 4000 to 400 cm^?1 have been measured at ambient temperature for the prepared, (Ge₂₂Se₁₄Te₆₄)_100?xI_x, glasses where x = 0, 4, 6, 8 and 10 at.%. The effects of both iodine content and the annealing of glasses at different temperatures on the transmittance and observed absorption peaks have been evaluated. Scanning electron microscope (SEM) micrographs were performed to insure the effect of annealing on the obtained IR transmission spectra.     

Electromagnetic and magnetic properties of magnetophotonic crystal based on opal matrix with Co and CoO nanoparticles

Magnetic properties of magnetophotonic crystals based on opal matrices have been studied as well as their electromagnetic properties in millimeter waveband. The particles of cobalt oxide are embedded into the inter-sphere voids of the matrix. After annealing in hydrogen the cobalt oxide particles transform to metallic cobalt. It has been shown that if antiferromagnetic cobalt oxide remains besides ferromagnetic cobalt, the low-temperature magnetic hysteresis loop is shifted along the field axis. Magnetic field influences essentially on the microwave transmission and reflection coefficients only after annealing in hydrogen that is if the ferromagnetic phase presents in the sample. The spectra of magnetic resonance and antiresonance are studied.     

Influence of low and high temperature annealing on the blue and green emission bands of ZnS crystals

After annealing at 350 °C, in the luminescence spectra of pure and Cu-doped ZnS crystals a reversible blue-green conversion has been obtained. The blue-green conversion of luminescence is correlated with analogous reversible variations in the optical transmission and thermoluminescence properties. Besides these low temperature results, in the fluorescence spectra of undoped ZnS crystals, which are annealed at 1,000 °C in sealed evacuated quartz ampoules, a reversible blue-blue conversion has been observed. All these effects, induced by distinct heat treatments, seem to be mainly controlled by changes in the structural disorder or/and by the evaporation of lattice atoms from the surface of the crystals.     

Optical and nonlinear optical properties of copper nanocomposite glasses annealed near the glass softening temperature

Copper nanocomposite glasses have been prepared by the ion-exchange method, and annealed at different temperatures up to and above the glass softening temperature. The absorption spectra, fluorescence spectra, and nonlinear optical transmission of the samples at 532 nm for nanosecond laser pulses, have been investigated. The optical and nonlinear optical properties of the glasses are found to be distinctly different below and above the glass softening temperature. For instance, thermal annealing up to the glass softening temperature makes the samples behave like saturable absorbers, while annealing at higher temperatures makes them behave like optical limiters. Such flexibility in controlling the optical nonlinearity in these materials makes them potential candidates for photonic applications.     

Hydrogen related effects in a-Si:H studied by photothermal deflection spectroscopy

A study of thermal annealing of a-Si:H samples between 300 and 600°C has been carried out. At increasing annealing temperatures, the sub-gap absorption measured by PDS increases showing two inflections, centered at 375 and 550°C. The hydrogen content measured by thermal desorption spectroscopy evolves in the same temperature range, whereas the evolution of the hydrogen content deduced from the IR transmission spectra differs, decreasing sooner and vanishing already at about 450°C.     

Influence of low and high temperature annealing on the blue and green emission bands of ZnS crystals

After annealing at 350 °C, in the luminescence spectra of pure and Cu-doped ZnS crystals a reversible blue-green conversion has been obtained. The blue-green conversion of luminescence is correlated with analogous reversible variations in the optical transmission and thermoluminescence properties. Besides these low temperature results, in the fluorescence spectra of undoped ZnS crystals, which are annealed at 1,000 °C in sealed evacuated quartz ampoules, a reversible blue-blue conversion has been observed. All these effects, induced by distinct heat treatments, seem to be mainly controlled by changes in the structural disorder or/and by the evaporation of lattice atoms from the surface of the crystals.Dedicated to Prof. Dr. Dr. Ing. E.h.W. Hanle on occasion of his 75^th birthdayPart of thesis, Gießen 1974 (D26)     

Thermoreflectance investigation of heavily doped silicon

The effect of the presence of high concentrations of dopants on the interband spectra of silicon has been studied by means of thermoreflectance. Heavy doping has been performed through ion implantation and eventually laser annealing. From the analysis of the thermoreflectance spectra a wide set of parameters characterizing in particular the E₁andE₂ structures has been obtained.     

Effect of Heating Procedure and Annealing Temperature on Transmission Spectra of sp1-Carbon Films Synthesized by the Ion-Plasma Method

Journal of Applied Spectroscopy - The influence of the heating procedure and annealing temperature in air on the transmission spectra and morphology of linear-chain carbon films synthesized by the...     

Structure and physical-mechanical properties of equiatomic ordering FeCo alloy obtained by quenching from the liquid state

The fine structure of ordering soft magnetic FeCo alloy obtained by quenching from the liquid state has been studied by transmission and scanning electron microscopy. The effect of ultrafast quenching and subsequent annealing on the structural aspects of the processes of crystallization, atomic ordering, and polymorphic transformation has been investigated. The reasons for the increase in the alloy plasticity as a result of quenching from the liquid state are established.     

The influence of annealing temperature on the structure,morphologies and optical properties of ZnO nanoparticles

ZnO nanoparticles (NPs) have been successfully synthesized by the simple solution method at low temperature. The effects of annealing temperature on the structure and optical properties of ZnO NPs were investigated in detail by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) spectroscopy and photoluminescence (PL) measurements. As the annealing temperature was increased above 180 ^°C the particles morphology evolved from spherical to hexagonal shape, indicating that the average particle size increased from 11 nm to 87 nm. The UV-vis and PL spectra showed a red-shift from 3.62 to 3.33 eV when the annealing temperature was increased.     

Structure,impurity composition,and photoluminescence of mechanically polished layers of single-crystal silicon

The introduction of optically active defects (such as atomic clusters, dislocations, precipitates) into a silicon single crystal using irradiation, plastic deformation, or heat treatment has been considered a possible approach to the design of silicon-based light-emitting structures in the near infrared region. Defects were introduced into silicon plates by traditional mechanical polishing. The changes in the defect structure and the impurity composition of damaged silicon layers during thermal annealing (TA) of a crystal were examined using transmission electronic microscopy and x-ray fluorescence. Optical properties of the defects were studied at 77 K using photoluminescence (PL) in the near infrared region. It has been shown that the defects generated by mechanical polishing transform into dislocations and dislocation loops and that SiO₂ precipitates also form as a result of annealing at temperatures of 850 to 1000°C. Depending on the annealing temperature, either oxide precipitates or dislocations decorated by copper atoms, which are gettered from the crystal bulk, make the predominant contribution to PL spectra.     

Photoluminescence studies on nanostructured cadmium sulfide thin films prepared by chemical bath deposition method and annealed at different temperatures

Nanostructured cadmium sulfide (CdS) thin films have been prepared by chemical bath deposition (CBD) method and after post deposition annealing of the thin films at different temperatures, photoluminescence (PL) property has been studied. The effects of various photoexcitation wavelengths on the PL behaviour of different annealed films of CdS were studied by recording the PL spectra. The intensity of PL, the profile of the PL spectra and the effects of photoexcitation wavelength depend drastically on the temperature of the post deposition annealing of the thin films. The XRD patterns of the films show the presence of both the hexagonal and cubic phases (mixed phases). The emission peak arises from the surface defects of the CdS nanocrystalline thin films. Significant modification in the surface morphology of the CdS films upon annealing has been observed from the FESEM images. The morphology of the thin films is expected to influence the PL behaviour of the CdS thin films. The quantum size effect and size dependant PL have been observed.     

Application of synchrotron radiation to investigation of the mechanism of increase in the yield of alkali metal ions in electron-stimulated desorption

Core-level photoelectron spectroscopy with synchrotron radiation (hv = 140 eV) has been applied to study the variation in the Si⁺ charge state in silicon films deposited on the W(100) surface after thermal annealing of the substrate. The purpose of this study is to check the mechanism responsible for the sharp increase in the yield of Na⁺ ions in electron-stimulated desorption from a sodium layer adsorbed on the Si/W(100) surface after high-temperature annealing. The evolution of the W 4f _7/2 and Si 2p photoelectron spectra and the valence band photoemission spectra is investigated for two silicon coverages (1 and 3 ML) on the W(100) surface in the temperature range 300<T<2200 K. It is shown that annealing of 1 ML Si on the W(100) surface results in the formation of a W-Si covalent bond, which can weaken the Si-Na bond and lead to an increase in the equilibrium distance X ₀ and, hence, to an increase in the yield of Na⁺ ions in electron-stimulated desorption. The variation in the photoelectron spectra under annealing of 3 ML Si differs from that observed after annealing of 1 ML Si in the direction of charge transfer, thus correlating with the opposite effect of annealing of 3 ML Si/W on the Na⁺ yield in electron-stimulated desorption.     

退火温度和退火气氛对Ni/Au与p-GaN之间欧姆接触性能的影响

研究了不同退火温度和气氛对Ni/Au与p-GaN之间欧姆接触性能的影响. 采用圆形传输线模型方法得到不同退火温度和不同退火气氛下的比接触电阻率. 结果表明, 较适宜的退火温度为500 ℃左右, 退火温度太高或太低都会导致比接触电阻率的增大; 较适宜的退火气氛为适量含氧的氮气气氛, 且氧气含量对比接触电阻率大小的影响并不显著. 经过对退火条件的优化, 得到的比接触电阻率可达7.65×10^-4 Ω·cm². 关键词： p-GaN 欧姆接触 圆形传输线模型 快速热退火     

Effect of laser annealing using high repetition rate pulsed laser on optical properties of phosphorus-ion-implanted ZnO nanorods

The effect of high repetition rate pulsed laser annealing with a KrF excimer laser on the optical properties of phosphorus-ion-implanted zinc oxide nanorods has been investigated. The recovery levels of phosphorus-ion-implanted zinc oxide nanorods have been measured by photoluminescence spectra and cathode luminescence images. Cathode luminescence disappeared over 300 nm below the surface due to the damage caused by ion implantation with an acceleration voltage of 25 kV. When the annealing was performed at a low repetition rate of the KrF excimer laser, cathode luminescence was recovered only in a shallow area below the surface. The depth of the annealed area was increased along with the repetition rate of the annealing laser. By optimizing the annealing conditions such as the repetition rate, the irradiation fluence and so on, we have succeeded in annealing the whole damaged area of over 300 nm in depth and in observing cathode luminescence. Thus, the effectiveness of high repetition rate pulsed laser annealing on phosphorus-ion-implanted zinc oxide nanorods was demonstrated.     

用模拟退火算法研究非晶硅薄膜的光学性质

在玻璃衬底上采用等离子体增强的化学气相沉积(PECVD)法制备了非晶硅薄膜(A-Si:H)。用紫外-可见-近红外分光光度计测出了其透射光谱。采用模拟退火算法研究了透射光谱,得出了薄膜的厚度、折射率和吸收系数随波长变化的关系式、光学带隙等光学常数,并对该方法的优缺点进行了讨论。     

Study of radiation-induced damage to type III–V semiconductor compounds irradiated with γ quanta and protons using positron annihilation spectroscopy

The effect of proton and ?? radiation on characteristics of the spectra for the angular distribution of annihilation photons (ADAP) have been studied in the case of positron annihilation in GaAs and GaP single crystals. Relative variations in defect accumulation and annealing under irradiation and subsequent isochronous annealing of the samples have been studied using variations in the basic parameters of the ADAP spectra. In both cases (GaAs and GaP), the variations in the ADAP spectral parameters as functions of the annealing temperature have a steplike character, which is interpreted as the formation of a certain type of defects with different annealing activation energies.     

退火温度对ZnO薄膜结构和发光特性的影响

采用反应射频磁控溅射法在 Si(100)基片上制备了高c轴择优取向的ZnO薄膜，研究了退火温度对ZnO薄膜的晶粒尺度、应力状态、成分和发光光谱的影响，探讨了ZnO薄膜的紫外发光光谱和可见发光光谱与薄膜的微观状态之间的关系.研究结果显示,在600—1000℃退火温度范围内，退火对薄膜的织构取向的影响较小，但薄膜的应力状态和成分有比较明显的变化.室温下光致发光光谱分析发现，薄膜的近紫外光谱特征与薄膜的晶粒尺度和缺陷状态之间存在着明显的对应关系；而近紫外光谱随退火温度升高所呈现的整体峰位红移是各激子峰相对比例变 关键词： ZnO薄膜 退火 光致发光 射频反应磁控溅射 可见光发射