低束流钕离子注入外延硅薄层的结构研究

采用金属蒸气真空弧(MEWA)离子源以低束流方式将Nd离子注入到外延硅片中，经高温快速退火处理，制备了结晶良好的钕硅掺杂层。用扫描电子显微镜(SEM)、反射式高能电子衍射(RHEED)和X射线衍射(XRD)分析了在不同退火条件下样品注入层相结构的变化。研究结果表明，经高温热处理，注入层形成结晶良好的钕硅化合物，出现由Nd5Si4相向NdSi相转变的趋势。并对其转变过程进行了初步探讨。     

Influence of UV irradiation and RTA process on optical properties of Si implanted SiO2

Si ion implantation was widely used to synthesize specimens of SiO₂ containing supersaturated Si and subsequent high temperature annealing induces the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of excimer UV-light (172 nm, 7.2 eV) irradiation and rapid thermal annealing (RTA) to enhance the photoluminescence and to achieve low temperature formation of Si nanocrystals have been investigated. The Si ions were introduced at acceleration energy of 180 keV to fluence of 7.5 × 10¹⁶ ions/cm². The implanted samples were subsequently irradiated with an excimer-UV lamp. After the process, the samples were rapidly thermal annealed before furnace annealing (FA). Photoluminescence spectra were measured at various stages at the process. We found that the luminescence intensity is strongly enhanced with excimer-UV irradiation and RTA. Moreover, effective visible photoluminescence which is not observed with a simple FA treatment, is found to be observed even after FA at 900 °C, only for specimens treated with excimer-UV lamp and RTA. Based on our experimental results, we discuss the effects of excimer-UV lamp irradiation and RTA process on Si nanocrystals related photoluminescence.     

Enhancement of luminescence from encapsulated Si nanocrystals in SiO2 with rapid thermal anneals

Potentialities of rapid thermal annealing to enhance the photoluminescence emission of Si nanocrystals in SiO₂ have been investigated. Ion implantation was used to synthesize specimens of SiO₂ containing excess Si with different concentrations. Si precipitation to form nanocrystals in implanted samples takes place with a conventional furnace anneal. The photoluminescence intensity and the peak energy of emission from Si nanocrystals depend on implanted ion fluence. Moreover, the luminescence intensity is strongly enhanced with a rapid thermal anneal prior to a conventional furnace anneal. The luminescence intensity, however, decreases with a rapid thermal anneal following a conventional furnace anneal. It is found that the order of heat treatment is an important factor in intensities of the luminescence. Moreover, the luminescence peak energy is found to be dependent, but a little, on thermal history of specimens. Based on our experimental results, we discuss about the mechanism of an enhancement of the photoluminescence, together with the mechanism of photoemission from encapsulated Si nanocrystals produced in a SiO₂ matrix by ion implantation and annealing.     

Optical and structural properties of implanted silicon nanocrystals

A novel method for the fabrication of Si nanocrystals in an amorphous SiO₂ matrix by ion implantation is reported. Transmission electron microscopy indicates the formation and growth of Si nanocrystals on annealing at 1100°C which were not observed before annealing. After annealing, a photoluminescence band around 1.7 eV is observed. The shape of the emission spectrum of the photoluminescence is found to be independent of annealing time, while the intensity of the luminescence increases and then decreases as the annealing time increases. We also show direct evidence of widening of the band-gap energy of a few nanometer-sized Si particles by employing photoacoustic spectroscopy. These results indicate that the photons are absorbed by Si nanocrystals, for which the band-gap energy is modified by the quantum confinement effects, and the emission is not simply due to direct electron-hole recombination inside Si nanocrystals but is related to defects probably at the interface between Si nanocrystals and SiO₂.     

Light particle irradiation effects in Si nanocrystals

Si nanocrystals, formed by Si ion implantation into SiO₂ layers and subsequent annealing at 1150°C, were irradiated at room temperature either with He⁺ions at energies of 30 or 130 keV, or with 400 keV electrons. Transmission electron microscopy (TEM) and photoluminescence (PL) studies were performed. TEM experiments revealed that the Si nanocrystals were ultimately amorphized (for example at ion doses ∼10¹⁶ He cm⁻²) and could not be recrystallized by annealing up to 775°C. This contrasts with previous results on bulk Si, in which electron- and very light ion-irradiation never led to amorphization. Visible photoluminescence, usually ascribed to quantum-size effects in the Si nanocrystals, was found to decrease and vanish after He⁺ ion doses as low as 3 × 10¹²–3 × 10¹³ He cm⁻² (which produce about 1 displacement per nanocrystal). This PL decrease is due to defect-induced non-radiative recombination centers, possibly situated at the Si nanocrystal/SiO₂ interface, and the pre-irradiation PL is restored by a 600°C anneal.     

Influence of annealing temperatures and time on the photoluminescence properties of Si nanocrystals embedded in SiO2

We report on the effects of annealing conditions on the photoluminescence from Si nanocrystal composites fabricated by implantation of Si ions into a SiO₂ matrix, followed by thermal treatment in a nitrogen atmosphere. The evolution of the photoluminescence under different annealing temperatures (900–1100 °C) and annealing time (0.5 up to 5 h) were systematically studied for the implanted samples. After annealing the spectra presented two photoluminescence bands: one centered at 610 nm and another around 800 nm. Combined with transmission electron microscopy, we conclude that the photoluminescence behavior of the two bands suggests different origins for their emissions. The 610 nm band has its origin related to matrix defects, while the 800 nm band can be explained by a model involving recombination via quantum confinement effects of excitons in the Si nanocrystals and the interfacial states recombination process confined in the interfacial region between nanocrystals and SiO₂ matrix.     

Effect of forming gas anneals on the photoluminescence from nanocrystalline silicon formed by Si implantation into SiO2 matrix

The blue region of the room temperature photoluminescence spectrum from Si nanocrystallites formed in SiO₂ by Si⁺ ion implantation has been observed for the first time after annealing in a forming gas (10% H₂ + 90% N₂) ambient. Thermally grown SiO₂ on Si substrates were implanted with a dose of 2 × 10¹⁷ Si⁺ cm⁻² at energies of 200 keV and 400 keV. For reference purposes, quartz silica was implanted also with the same dose of 200 keV Si⁺ ions. The implanted samples were annealed in nitrogen and forming gas at 900°C for 3 to 180 min. Both the SiO₂ and quartz samples exhibited luminescence at about 380 nm which was weak, but detectable, before annealing. During extended anneals in forming gas, the intensity increased by a factor of about 2 above that recorded after a nitrogen anneal but the peak position was unchanged. The intensity was greater in samples annealed in forming gas which is due to the additional hydrogen. It would seem that this blue luminescence originates from new luminescent centres in the matrix caused by the Si⁺ ion implantation.     

Post-annealing effect on the microstructure and photoluminescence properties of the ion beam synthesized FeSi2 precipitates in Si

FeSi₂ precipitates with various structural properties embedded within silicon matrix were formed by iron ion implantation using a metal vapor vacuum arc ion source followed by thermal annealing at various conditions. The microstructure and phase properties of the implanted samples were studied by transmission electron microscopy. The orientation relationships and thus the interfacial coherence between the FeSi₂ precipitates and the Si matrix were observed to change with the annealing conditions. A good correlation is identified in-between the structural properties and the photoluminescence properties of these samples.     

XPS and optical studies of Xe-implanted and annealed YSZ single crystals

Xe⁺ ion implantation with 200 keV was completed at room temperature up to a fluence of 1 × 10¹⁷ ion/cm² in yttria-stabilized zirconia (YSZ) single crystals. Optical absorption and X-ray photoelectron spectroscopy (XPS) were used to characterize the changes of optical properties and charge state in the as-implanted and annealed crystals. A broad absorption band centered at 522 or 497 nm was observed in the optical absorption spectra of samples implanted with fluences of 1 × 10¹⁶ ion/cm² and 1 × 10¹⁷ ion/cm², respectively. These two absorption bands both disappeared due to recombination of color centers after annealing at 250 °C. XPS measurements showed two Gaussian components of O_1s spectrum assigned to Zr–O and Y–O, respectively, in YSZ single crystals. After ion implantation, these two peaks merged into a single peak with the increasing etching depth. However, this single peak split into two Gaussian components again after annealing at 250 °C. The concentration of Xe decreased drastically after annealing at 900 °C. And the XPS measurement barely detected the Xe. There was no change in the photoluminescence of YSZ single crystals with a fluence of 1 × 10¹⁷ ion/cm² after annealing up to 900 °C.     

Surface decomposition and annealing behavior of GaN implanted with Eu

Investigations on surface decomposition of GaN implanted with low energy (80keV) Eu ion to a low dose (1×1014cm-2), and its annealing behavior under high temperature (1050℃) in N2 are performed. The as-grown, as-implanted and annealed GaN films are characterized by proton elastic scattering (PES), Rutherford backscattering spectrometry (RBS), photoluminescence (PL) and atomic force microscopy (AFM). The results show that Eu ion implantation induces radiation defects and decomposition of GaN. The GaN surface decomposition is more serious during high temperature annealing. The atomic ratio of N in as-grown, as-implanted and annealed GaN film is 47 at.%, 44 at.% and 40 at.%, respectively. As a result, a rough Ga-rich layer is formed at the surface, though the lattice defects are partly removed after high temperature annealing.     

The excitation power density effect on the Si nanocrystals photoluminescence

In the present work we have studied the photoluminescence (PL) behavior from Si nanocrystals (NCs) as a function of the excitation power density and annealing time. The NCs were produced in a SiO₂ matrix by Si implantations from room temperature (RT) up to 700 °C, followed by post-annealing in N₂ atmosphere at high temperature. With this aim we have changed the excitation power density (from 2 × 10⁻³ W/cm² up to 15 W/cm²) and the annealing time (from 10 min up to 15 h). The strong PL signal, which at 15 W/cm² is composed by a single-peak structure (650–1000 nm) centered at around 780 nm, expands up to 1200 nm showing a two-peak structure when measured at 20 × 10⁻³ W/cm². The peak structure located at the short wavelength side is kept at 780 nm, while the second peak, starting at around 900 nm, redshifts and increases its intensity with the implantation temperature and annealing time. The effect of the annealing time on the PL spectra behavior measured at low excitation power agrees by the first time with the Si NC growth according to quantum confinement effects.     

The Effect of Annealing Parameter on Corrosion Resistance of Zircaloy-2

The effects of equal ΣAi for different combinations of the annealing temperature and annealing time on corrosion resistance and evolution of precipitates of Zircaloy-2 were investigated.

Nodular corrosion resistance in the out-of-pile corrosion test was degraded with increasing ΣAi only when it was increased by extending the annealing time at 894 K but did not depend on ΣAi which was increased by raising the annealing temperature for a constant annealing time of 2.5h. Extensive observation and micro-analysis of precipitates by analytical electron microscope (AEM) suggested the cause of degradation of nodular corrosion resistance to be the remarkable increase in volume fraction of Si-containing precipitates such as Zr₃Si and Zr₂Si, which were observed more frequently in large ΣAi only when it was increased by extending the annealing time at 894K.

On the other hand, uniform corrosion resistance was improved with increasing ΣAi irrespective of the annealing conditions, but was slightly better when ΣAi was increased by extending the annealing time under constant annealing temperature at 894K. This behavior can be under-stood from the reduction in content of alloying elements such as Fe, Cr and Ni which remained as solutes in the matrix at large ΣAi.     

Gd1.6Nd0.4Zr2O7烧绿石的快速合成及其组织结构研究

为探索Gd₂Zr₂O₇烧绿石快速固化高放废物中锕系核素的新途径,实验用高温高压固相反应法在3～4GPa压力、1573～1673K温度范围内合成了Gd_1.6Nd_0.4Zr₂O₇烧绿石固化体,并利用X射线衍射仪、扫描电镜对样品进行了分析。结果表明：高温高压固相反应法可在极短时间（15min）内合成完全固溶的Gd_1.6Nd_0.4Zr₂O₇立方烧绿石固化体,较常用制备方法（一般合成时间不低于48h）快近200倍;用该技术合成的样品在常温常压下的相转变温度及压力得以显著提高,烧绿石相更趋稳定;样品晶格常数随Nd含量的增加及合成温度的升高而逐渐增大,随合成压力的增加而逐渐减小。这种快速高效的合成方法为未来开展高放核素的工业固化提供了一种新的技术途径和基本数据参考。     

Stabilisation and phase transformation of hexagonal rare-earth silicides on Si(1 1 1)

Epitaxial, hexagonal rare-earth silicides, such as ErSi_1.7, can be formed using channeled ion beam synthesis. In the case of Gd-silicide, an orthorhombic GdSi₂ phase exists at high temperature; the transition temperature is related to the thickness and crystalline quality of the silicide. In the case of the lightest rare-earth metals, such as Nd, silicides only exist in a tetragonal or orthorhombic phase, which cannot grow epitaxially on Si(1 1 1). However, introduction of a fraction of yttrium (YSi_1.7 also possesses the aforementioned hexagonal lattice) drives the Nd–Si system into a hexagonal lattice structure. A combined backscattering and channeling spectrometry (RBS/C), X-ray diffraction (XRD) and transmission electron microscopy (TEM) study shows that an epitaxial, continuous ternary silicide is formed (and not a mixture of binaries) with a hexagonal structure, which is stable up to 950°C. Further annealing, however, results in a gradual transformation into polycrystalline phases. The experimental results are compared to total energy calculations of these (meta-)stable rare-earth silicides, using the density functional theory (DFT).     

Effects of Annealing on Luminescence of ZnO Films Deposited on Si Substrates by RF Magnetron Sputtering

Effects of growth ambience, annealing ambience and temperature on the photoluminescence (PL) emission properties of ZnO films deposited on Si (100) substrates by RF magnetron sputtering have been investigated. After annealing, the crystal quality of ZnO films was markedly improved, and the intensity of UV emission peak increased obviously. By varying the flow rate ratio of O2/Ar, annealing atmosphere in oxygen-deficient or oxygen-rich ambience and heating temperature during deposition, the evolution of peak intensities and positions for blue and green emission is formed. This is attributed to the deposition and annealing parameters that control the desorptions and adsorptions of oxygen atoms on the films, and leads to the changes of concentrations of Zinc and oxygen vacancies in the films.     

Low temperature formation of luminescent Si nanocrystals with combined process of excimer UV-light irradiation and RTA

Si ion implantation was widely used to synthesize specimens of SiO₂ containing supersaturated Si and subsequent high temperature annealing induces the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of excimer UV-light (172 nm, 7.2 eV) irradiation and rapid thermal annealing (RTA) to achieve low temperature (below 1000 °C) formation of luminescent Si nanocrystals in SiO₂ have been investigated. The Si ions were introduced at acceleration energy of 180 keV to fluences of 7.5 × 10¹⁶ and 1.5 × 10¹⁷ ions/cm². The implanted samples were subsequently irradiated with an excimer-UV lamp for 2 h. After the process, the samples were rapidly thermal annealed at 1050 °C for 5 min before furnace annealing (FA) at 900 °C. Photoluminescence spectra were measured at various stages at the process. Effective visible photoluminescence is found to be observed even after FA at 900 °C, only for specimens treated with excimer-UV lamp and RTA, prior to a low temperature FA process. Based on our experimental results, we discuss the mechanism for the initial formation process of the luminescent Si nanocrystals in SiO₂, together with the effects with excimer lamp irradiation and RTA process on the luminescence.     

Radiation-Induced Changes in the Photoluminescence Spectra of Cadmium Sulfide

Radiation-induced changes in the photoluminescence spectra of cadmium sulfide have been measured over a wavelength range from 4800 to 5400 ?. Gamma-ray induced changes in the 4.2°K photoluminescence spectra show a reduction in intensity of bound exciton transitions I1 and I5 and edge emission in contrast to an enhancement of a spectral line at 4867.2 ? (which we designate as IR). These changes were measured for irradiation temperatures of 300°, 78°, and 4.2°K. The 78°K photoluminescence shows that exciton emission is more sensitive to radiation-induced changes than is edge emission. Thermal annealing takes place below room temperature, particularly in the 140° to 260°K region. The sensitivity of the luminescence intensity to radiation exposure only at cryogenic temperature anid the thermal annealing of the radiation-induced changes are attributed to the mobility of defects at and below room temperature. Studies of polarized luminescence and the temperature dependence of the luminescence show that IR is like the I2; exciton lines. Optical quenching at 4.2°K indicates that the defect responsible for IR is sensitive to its charge state. The results of electron exposures at various energies at approximately 90°K show that IR is associated with a sulfur defect, possibly SI     

Defects remaining in MeV-ion-implanted and annealed Si away from the peak of the nuclear energy deposition profile

Damage has been observed in MeV-ion-implanted Si away from the maximum of the nuclear energy deposition profile, mainly around the half of the projected ion range, R_P/2. Cu gettering has been used for the detection of irradiation defects which are formed during annealing at temperatures between 700°C and 1000°C. This damage is primarily created by the implanted ions on their trajectory and consists of intrinsic defects remaining so small that they have not yet been resolved. These defects undergo a defect evolution during annealing which results in a decrease of the width of the damage layer with increasing temperature and prolonged time of the annealing.     

The phase state at high temperatures in the MOX-SiO2 system

Influence of impurity Si on microstructure in a plutonium and uranium mixed oxide (MOX), which is used for fast breeder reactor fuel, was investigated, and phase state in 25% SiO₂ - (U_0.7Pu_0.3)O₂ was observed as a function of oxygen chemical potential. Compounds composed of Pu and Si with other elements were observed at grain boundaries of the MOX parent phase in the specimens after annealing. These compounds were not observed in the grain interior and the MOX phase was not affected significantly by impurity Si. It was found that the compounds tended to form more observably with decreasing O/M ratio and with increasing annealing temperatures.     

Endotaxial growth of InSb nanocrystals at the bonding interface of the In+ and Sb+ ion implanted SOI structure

Growth of InSb nanocrystals at the Si/SiO₂ bonding interface of silicon-on-insulator (SOI) structures has been studied as a function of the annealing temperature. SOI structures with the ion implanted regions above and below the bonding interface were produced as a result of the hydrogen transfer of the Sb⁺ ion implanted silicon layer from first silicon substrate to the In⁺ ion implanted SiO₂ layer thermally-grown on the second silicon substrate. Rutherford backscattering spectrometry and high-resolution transmission electron microscopy (XTEM) were used to study the properties of the prepared structures. Up-hill diffusion of In and Sb atoms from the implantation regions toward the bonding interface as well as subsequent interface-mediated growth of InSb nanocrystals were observed as the annealing temperature achieved 1100 °C. The strain minimizing orientations of the Si and InSb lattice heteropairs were obtained from XTEM analysis of the grown nanocrystals.