Investigation of amorphous states of SiO2 by Raman scattering spectroscopy

The vitreous SiO₂ samples irradiated with fast neutrons at a dose of 5×10¹⁷?2.2×10²⁰ per cm² are investigated by the Raman scattering technique. It is demonstrated that the maximum of the low-frequency Raman spectrum (boson peak) shifts with an increase in the irradiation dose, and the medium-range order size decreases from 25 Å for the initial glass to 19 Å for the sample subjected to irradiation at a maximum dose. It is revealed that the fast relaxation intensity obtained from analysis of the low-frequency Raman spectra linearly correlates with the specific volume of the studied samples.     

Ag离子注入非晶SiO2的光学吸收、拉曼谱和透射电镜研究

能量为200keV的Ag离子，以1×10¹⁶，5×10¹⁶，1×10¹⁷ cm^-2的剂量分别注入到非晶SiO₂玻璃，光学吸收谱显示：注入剂量为1×10¹⁶ cm^-2的样品的光吸收谱为洛伦兹曲线，与Mie理论模拟的曲线形状一致；注入剂量较大的5×10¹⁶，1×10¹⁷ cm^-2的谱线共振吸收增强，峰位红移并出现伴峰. 透射电镜观察分析表明，注入剂量不同的样品中形成的纳米颗粒的大小、形状、分布都不同，注入剂量较大的还会产生明显的表面溅射效应，这些因素都会影响共振吸收的峰形、峰位和峰强. 当注入剂量达到1×10¹⁷ cm^-2时，Ag纳米颗粒内部可能还形成了杂质团簇. 关键词： 离子注入 纳米颗粒 共振吸收 红移     

Formation and growth of embedded indium nanoclusters by In<Superscript>2<Emphasis Type="Bold">+</Emphasis></Superscript> implantation in silica

Indium nanoclusters are synthesized in an amorphous silica matrix using an ion-implantation technique. Indium ions (In²⁺) with energy of 890 keV are implanted on silica to fluences in the range of 3×10¹⁶–3×10¹⁷ cm^-2. The formation of indium nanoclusters is confirmed by optical absorption spectrometry and glancing incidence X-ray diffraction studies. A low frequency Raman scattering technique is used to study the growth of embedded indium nanoclusters in the silica matrix as a function of fluence and post-implantation annealing duration. Rutherford backscattering spectrometry studies show the surface segregation of implanted indium. Photoluminescence studies indicate the formation of a small quantity of indium oxide phase in the ion-implanted samples. PACS 85.40.Ry; 78.67.Bf; 73.20.Mf; 82.75.Fq     

Raman spectroscopy study of damage induced in fluorapatite by swift heavy ion irradiations

Raman spectroscopy was used to study the radiation damage of fluorapatite single crystals and sinters. Krypton and iodine ion irradiations were performed at high energies (∼1 MeV amu⁻¹) for fluences ranging between 1 × 10¹¹ and 5 × 10¹³ cm⁻². Evolution of the symmetric stretching mode of the PO₄³⁻ tetrahedral building blocks (strongest Raman mode observed at 965 cm⁻¹) versus ion fluence was investigated. After irradiation, this peak decreases in intensity and a second broader peak appears at lower wavenumber. The well‐resolved peak has been assigned to the crystalline phase, and the broader one to the amorphous phase. The integrated intensity ratios of these two peaks versus fluence are in good agreement with the damage fractions determined by X‐ray diffraction (XRD). Fits of the amorphous fraction versus fluence show that the amorphization mechanisms is dominated by a single‐impact process for iodine ions and by a double‐impact process for krypton ions in the case of single crystals and sinters. For both irradiations, complete amorphization could not be obtained. The amorphous fraction saturates at a maximum value of 88% for sinters and 72% for single crystals. This is attributed to a recrystallization effect which is more important in single crystals than in sinters. For both types of samples, the crystalline peak shifts slightly to a lower wavenumber with fluence, and then shifts back to its initial value for an amorphous fraction larger than 60%. This feature is attributed to a stress relaxation, as shown in the XRD data, which is accompanied by a decrease of the crystalline peak full‐width at half‐maximum. Copyright © 2011 John Wiley & Sons, Ltd.     

Radiation hardening in niobium-dependence of the yield stress on neutron dose

Abstract

Niobium samples were neutron-irradiated at reactor ambient temperatures (approximately 50 °C for polycrystals and 90°C for single crystals) to doses from 4 × 10¹⁵ to 8 × 10¹⁸ neutrons/cm² (E> 1 MeV). The density and size distribution of radiation-produced defect clusters, observed by transmission electron microscopy, were measured in polycrystalline niobium over a range of doses from 2 × 10¹⁷ to 4.4 × 10^l8 neutrons/cm². The TEM results were correlated with yield stress measurements as a function of dose. The radiation hardening was analyzed on the basis of a planar dispersed barrier model. It was found that the observed increases in yield stress at low doses were consistent with the measured density and size distribution of the defect clusters, with a cluster strength of (0.5–0.8) Gb² (G, shear modulus; b, Burgers vector). This corresponds to strong barrier hardening. At doses above about 10¹⁸ neutrons/cm², the hardening rate decreased sharply; this apparent saturation is discussed in terms of the coarsening of defect clusters, dislocation channeling, and the effect of interstitial impurities.     

CEMS study on aluminium implanted iron

Up to now a great deal of investigations in ion beam mixing of iron-aluminium layers are known. However, the easier way to produce such layers by direct implantation of aluminium ions in iron is less studied. In the present work aluminium implanted iron layers are studied. Iron samples were implanted with aluminium ions at 50, 100, and 200 keV, respectively, with doses between 5×10¹⁶ and 5×10¹⁷ cm⁻². Independent of energy, at doses up to 2×10¹⁷ cm⁻², besides alpha iron further magnetic fractions with a Fe₃Al-like structure are formed while at a dose of 5×10¹⁷ cm⁻² amorphous nonmagnetic components are formed.     

Recrystallization of hexagonal silicon carbide after gold ion irradiation and thermal annealing

Silicon carbide (SiC) single crystals with the 6H polytype structure were irradiated with 4.0-MeV Au ions at room temperature (RT) for increasing fluences ranging from 1?×?10¹² to 2?×?10¹⁵ cm^?2, corresponding to irradiation doses from ~0.03 to 5.3 displacements per atom (dpa). The damage build-up was studied by micro-Raman spectroscopy that shows a progressive amorphization by the decrease and broadening of 6H-SiC lattice phonon peaks and the related growth of bands assigned to Si–Si and C–C homonuclear bonds. A saturation of the lattice damage fraction deduced from Raman spectra is found for ~0.8?dpa (i.e. ion fluence of 3?×?10¹⁴ cm^?2). This process is accompanied by an increase and saturation of the out-of-plane expansion (also for ~0.8?dpa), deduced from the step height at the sample surface, as measured by phase-shift interferometry. Isochronal thermal annealing experiments were then performed on partially amorphous (from 30 to 90%) and fully amorphous samples for temperatures from 200 °C up to 1500 °C under vacuum. Damage recovery and densification take place at the same annealing stage with an onset temperature of ~200 °C. Almost complete 6H polytype regrowth is found for partially amorphous samples (for doses lower than 0.8 dpa) at 1000 °C, whereas a residual damage and swelling remain for larger doses. In the latter case, these unrelaxed internal stresses give rise to an exfoliation process for higher annealing temperatures.     

X-ray diffraction studies of silicon implanted with high-energy erbium ions

Silicon crystals after implantation of erbium ions with energies in the range 0.8–2.0 MeV and doses in the range 1×10¹²–1×10¹⁴ cm⁻² have been studied by two-and three-crystal x-ray diffraction. Three types of two-crystal reflection curves are observed. They correspond to different structural states of the implanted layers. At moderate doses (1×10¹²–1×10¹³ cm⁻²) a positive strain is observed, due to the formation of secondary radiation defects of interstitial type. An increase of the implantation dose is accompanied by the formation of an amorphous layer separating the bulk layer and a thin monocrystalline surface layer. At an implantation dose of 1×10¹⁴ cm⁻² the monocrystalline surface layer is completely amorphized. Parameters of the implantation layers are determined. A model of the transformation of structural damage is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 853–857 (May 1997)     

Fluence dependant formation of <Emphasis Type="Italic">β</Emphasis>-SiC by ion implantation and thermal annealing

The β-SiC nanocrystals were synthesized by the implantation of carbon ions (C⁻) into silicon followed by high-temperature annealing. The carbon fluences of 1×10¹⁷, 2×10¹⁷, 5×10¹⁷, and 8×10¹⁷ atoms/cm² were implanted at an ion energy of 65 keV. It was observed that the average size of β-SiC crystals decreased and the amount of β-SiC crystals increased with the increase in the implanted fluences when the samples were annealed at 1100 °C for 1 h. However, it was observed that the amount of β-SiC linearly increased with the implanted fluences up to 5×10¹⁷ atoms/cm². Above this fluence the amount of β-SiC appears to saturate. The Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, and X-ray diffraction (XRD) techniques were used to characterize the samples.     

Low frequency elastic properties of neutron-irradiated quartz. Comparison with glasses

Neutron-irradiated quartz is a promising model system to learn more about the low-energy excitations (tunneling states) in vitreous silica and in similar glasses. We present the first systematic study of the elastic properties of neutron-irradiated quartz at low frequencies and very low temperatures. Using the vibrating reed technique at frequencies of several kHz we have measured the sound velocity and internal friction of six quartz crystals irradiated with different neutron doses over a wide range of temperatures (7 mK-300 K). The results are analyzed using the tunneling model and several extensions of this theory. Comparisons are made with recent low-frequency measurements on normal and compacted vitreous silica and with ultrasound experiments on neutron-irradiated quartz. Received 23 October 1998     

离子注入ZnO薄膜的拉曼光谱研究

室温下,用80 keV N⁺和400 keV Xe⁺离子注入ZnO薄膜,注入剂量分别为5.0×10¹⁴—1.0×10¹⁷/cm²和2.0×10¹⁴—5.0×10¹⁵/cm².利用拉曼散射技术对注入前后的ZnO薄膜进行光谱测量和分析,研究了样品的拉曼光谱随离子注入剂量的变化规律.实验结果发现,未进行离子注入的样品在99,435 cm<     

Carbonization in boron-ion-implanted polymethylmethacrylate as revealed from Raman spectroscopy and electrical measurements

ABSTRACT

The results of Raman spectroscopy and electrical measurements of 40 keV boron-ion-implanted polymethylmethacrylate with ion doses from 6.25 × 10¹⁴ to 5.0 × 10¹⁶ ions/cm² are reported for the first time. The Raman spectra recorded in the 400–3800 cm^?1 range, showing the formation of new carbon–carbon bands for the as-implanted samples at higher ion doses (>10¹⁶ ions/cm²), are found to be an additional support for carbonization processes earlier revealed by slow positrons. The current–voltage dependences at 360 K testify also that the as-implanted samples examined with higher fluences (3.75 × 10¹⁶ and 5.0 × 10¹⁶ ions/cm²) have created a very thin conductive layer or conductive joints due to carbonization.     

Investigations of two-level tunneling systems in n-irradiated quartz by diffuse x-ray scattering

Abstract

Recent observation of the acoustic saturation and of phonon echoes in crystalline quartz after light irradiation with fast neutrons indicates that there are the same low-energy atomic tunnelling systems as in Si0₂ glass.

We report measurements of the diffuse X-ray scattering and of the lattice parameter change from neutron irradiated quartz single crystals studying the strength and symmetry of strain defects and their local correlations. For dose 3 × 10¹⁸ n/cm² the diffuse scattering close to the Bragg peaks together with the lattice parameter change shows that the neutrons create defective regions with a volume change of 29 mean atomic volumes. The distortion field of these regions shows no high symmetry. The radius of the heavily strained region is ～ 10 Å. For higher doses the regions grow a little bit but mainly new defective regions are built.

According to the various volume fractions of defective regions at various doses the first strong amorphous halo at about K≈ 1.5 A^?1 was detected. Since this amorphous scattering is isotropic and during annealing the regions disappear mainly without changing their size we are led to the conclusion that the defective regions are glass-like in nature. So the size of the tunnelling system has to be smaller than 20 Å.     

Doping and radiation damage profiles of P+ ions implanted in silicon along the [110] axis

Several doses of 200 KeV phosphorus ions have been implanted under channeling conditions along the [110] direction in silicon.

Range distribution has been determined for the three implant doses 10¹³, 10¹⁴, 10¹⁵ P⁺/cm² both with the electrical measurements and the neutron activation techniques.

The radiation damage distribution has been determined both with 290 KeV proton back-scattering analysis and with transmission electron microscopy (TEM) observations.

Good agreement has been found between electrical and neutron activation profiles in the samples where 100% of the implanted dose had been electrically activated by means of annealing.

Carrier concentration profiles, from samples implanted with 10¹⁵ P⁺/cm², determined after two different annealing temperatures (500°C and 700°C) have bcen compared with the radiation damage distribution and a correlation between damage and phosphorus electrical activation process seems to be possible.

Maximum damage peak, as determined by back-scattering analysis, shifts from ～0.4 μ depth in the lower dose(5 × 10¹⁴ P⁺/cm²), to ～0.22 pm depth in the higher implanted dose (4 × 10¹⁵ P⁺/cm²). Damage distribution of phosphorus ions random implanted in the same experimental conditions shows 3 peak at ～0.2 μn depth.

In accordance with the back-scattering analysis, T.E.M. observations on 10¹⁵P⁺/cm² implanted samples show the presence of amorphous regions at depth between 0.25 and 0.5 μm from the surface. In the most damaged layer ～0.3μm in depth, a surface density of ～10¹²/cm² amorphous regions 25-50 A diameter was observed.     

Raman scattering and electrical studies of the phase stability in the Hg<Subscript>1−x</Subscript>Cd<Subscript>x</Subscript>Te

Raman scattering is performed to access phase stability in the boron-implanted Hg_0.7Cd_0.3Te with fluences ranging from 1 × 10¹² to 1 × 10¹⁵ cm^?2. Threshold fluence for the formation of an amorphous phase is invoked here using Thomas–Fermi statistical model. Asymmetric broadening and red shift of the Raman active HgTe-like LO phonon mode are observed with varying fluencies. Electrical properties such as sheet carrier concentration and mobility are also changed with the fluence and reach their saturated values beyond threshold fluence of 5 × 10¹³ cm^?2. Threshold fluence for the formation of amorphous phase is also validated by the Raman measurements and electrical transport properties in the implanted layers. The excess free energy of 6.8 kJ/mole is found corresponding to the threshold fluence for phase transition.     

2.0-MeV Er+ implanted in silicon: depth distribution, damage profile and annealing behaviour

Si crystals were implanted with 2.0- MeV Er⁺ at the doses of 5×10¹² ions/cm², 1×10¹⁴ ions/cm², 5×10¹⁴ions/cm², 1×10¹⁵ ions/cm² and 2.5×10¹⁵ ions/cm². Conventional furnace thermal annealing was carried out in the temperature range from 600 °C to 1150 °C. The depth distribution of Er, associated damage profiles and annealing behavioar were investigated using the Rutherford backscattering spectrometry and channelling (RBS/C) technique. A proper convolution program was used to extract the distribution of Er from the experimental RBS spectrum. The obtained distribution parameters, projected range R_p, projected range straggling ΔR_p and skewness SK were compared with those of TRIM96 calculation.The experimental R_p and SK values agree well with the simulated values, while the experimental ΔR_p is larger than TRIM 96 simulated value by a factor of 18%. The damage profile of silicon crystal induced by 2.0-MeV Er⁺ at a dose of 1×10¹⁴ ions/cm² was extracted using the multiple-scattering dechannelling model based on Feldman’s method, which is in a good agreement with the TRIM96 calculation. For the samples with dose of 5×10¹⁴ ions/cm² and more, an abnormal annealing behavioar was found and a qualitative explaination has been given. Received: 11 October 1999 / Accepted: 28 March 2000 / Published online: 5 July 2000     

Small-angle neutron scattering study of radiation defects in synthetic quartz

The superatomic structure of synthetic quartz single crystals with dislocation densities ρ = 54 and 570 cm^?2 was studied in the initial state and after irradiation with fast neutrons with energies E _n > 0.1 MeV in a WWRM reactor (St. Petersburg Nuclear Physics Institute) in the fluence range F = 0.2 × 10¹⁷?5.0 × 10¹⁸ neutrons/cm². Weak irradiation with F = 0.2 × 10¹⁷ neutrons/cm² causes only slight structural changes, whereas appreciable generation of defects with radii of gyration r _g ～ 1–2 nm and R _G ～ 40–50 nm occurs at F = 7.7 × 10¹⁷?5.0 × 10¹⁸ neutrons/cm². As the fluence increases further, the number and volume fraction of point defects, as well as extended (channels ～2 nm in radius) and globular (amorphous phase nuclei) defects, increase.     

Structural modifications of GaN after cerium implantation

Among the family of rare earth (RE) dopants, the doping of first member Ce into GaN is the least studied system. This article reports structure properties of Ce‐doped GaN realized by technique of ion implantation. Ce ions were implanted into metal organic chemical vapor deposition grown n‐ and p‐GaN/sapphire thin films at doses 3 × 10¹⁴ and 2 × 10¹⁵ cm⁻². X‐ray diffraction scans and Raman scattering measurements exhibited expansion of lattice in the implanted portion of the samples. First order Raman scattering spectra show appearance of several disorder‐activated Raman scattering modes in addition to typical GaN features. A dose‐dependent decrease in intensity of E₂ mode was observed in Raman the spectra of the implanted samples. Ultraviolet Raman spectra of implanted samples show complete quenching of photoluminescence emission and appearance of multiple A₁(LO) phonon scattering modes up to fifth order. Moreover, a decrease in intensity and an increase in line width of LO modes as a function of wavenumber were observed for implanted samples. Copyright © 2012 John Wiley & Sons, Ltd.     

Defect and photoluminescence profiles from thermally converted Cr-doped GaAs

Specimens of Cr-doped semi-insulating (SI) GaAs have been annealed in quartz ampoules under vacuum at elevated temperatures. Some samples, depending on temperature and time of anneal, were partially or wholly converted to p-type. In these cases CV measurements have been combined with serial sectioning to produce carrier concentration profiles. The As overpressure dependencies indicate acceptors to be associated with Ga vacancies. The diffusion coefficient of the Ga vacancies was estimated to be about 3.35 × 10^-14cm²sec^-1 at 950°C. Low temperature photoluminescence on the converted samples show a reasonably good correspondence between carrier distribution profile and the intensity of copper luminescence peak on photoluminescence spectra taken at various depth in the crystals.     

Crystalline to amorphous transformations in ion implanted GaP

Abstract

The amorphization process of GaP by ion implantation is studied. The samples of 〈111〉 oriented GaP were implanted at 130 K with various doses 5 × 10¹³-2 × 10¹⁶ cm^?2 of 150 keV N⁺ ions and with the doses of 6 × 10¹²-1.5 × 10¹⁵ cm^?2 of 150 keV Cd⁺ ions. Room temperature implantations were also performed to see the influence of temperature on defect production. Rutherford backscattering and channelling techniques were used to determine damage in crystals. The damage distributions calculated from the RBS spectra have been compared with the results of Monte-Carlo simulation of the defect creation.

The estimated threshold damage density appeared to be independent on ion mass and is equal 6.5 × 10²⁰ keV/cm³. It is suggested that amorphization of GaP is well explained on the basis of a homogenous model.