Non linear volume expansion in helium implanted erbium metal films

Large dimensional expansion has been observed at room temperature in erbium metal films implanted at room temperature with high fluences of helium. The interferometrically measured film thickness increases linearly with fluence up to a critical dose of 3 × 10¹⁷ He+/cm² (E = 160 keV) and is superlinear at higher fluences. Annealing at 400°C causes a reduction of the induced expansion for fluences below the critical dose without apparent release of helium. Annealing of samples implanted to fluences greater than 3.5 × 10¹⁷ He⁺/cm² causes accentuated expansion which is accompanied by formation and rupture of bubbles at the film surface.     

Mg+注入对GaN晶体辐射损伤的研究

在蓝宝石衬底上通过金属有机物化学气相沉积(metal-organic chemical vapor deposition，MOCVD)方法外延生长的GaN薄膜具有良好的结晶品质，χ_min达到2.00%. 结合卢瑟福背散射/沟道(Rutherford backscattering/channeling，RBS/C)和高分辨X射线衍射(high-resolution X-ray diffraction，HXRD)的实验测量，研究了不同剂量和不同角度Mg⁺注入GaN所造成的辐射损伤. 实验结果表明，随注入剂量的增大，晶体的辐射损伤也增大，注入剂量在1×10¹⁵atom/cm²以下，χ_min小于4.78%，1×10¹⁶atom/cm²是Mg⁺注入GaN的剂量阈值，超过这个阈值，结晶品质急剧变差，χ_min达到29.5%；随机注入比沟道注入的辐射损伤大，且在一定范围内随注入角度的增大，损伤也增大，在4×10¹⁵atom/cm²剂量下偏离〈0001〉沟道0°，4°，6°，9°时的χ_min(%)分别为6.28，8.46，10.06，10.85；经过700℃/10min+1050℃/20s两步退火和1000℃/30s高温快速退火后，晶体的辐射损伤都有一定程度的恢复，而且1000℃/30s高温快速退火的效果更好，晶体的辐射损伤可以得到更好的恢复. 关键词： GaN 卢瑟福被散射/沟道 高分辨X射线衍射 辐射损伤     

Roles of local He concentration and Si sample orientation on cavity growth in amorphous silicon

(111)- and (100)-oriented Si samples were implanted with Si⁺ ions at 1 MeV to a dose of 1?×?10¹⁶?cm^?2 and with 5?×?10¹⁶ He⁺ cm^?2 at 10?keV or 50?keV and eventually annealed in the 800–1000°C temperature range. Sample characterisation was carried out by cross-section transmission electron microscopy, positron annihilation spectroscopy and nuclear reaction analysis. In addition to the formation of He bubbles at the projected range of He, bubbles were observed after solid-phase epitaxial growth (SPEG) of the embedded amorphous Si layer. The He threshold concentration required to obtain thermally stable bubbles in amorphised Si is between one and four orders of magnitude lower than in c-Si. Since bubble formation and growth take place in the a-Si phase, the interaction with SPEG during annealing was studied by considering (100) and (111) Si. Both the SPEG velocity and the resulting defects play a role on bubble spatial distribution and size, resulting in bigger bubbles in (111) Si with respect to (100) Si.     

Formation of ordered helium pores in amorphous silicon subjected to low-energy helium ion irradiation

Thin transparent (for transmission electron microscopy, TEM) self-supported Si(001) films are irradiated on the (110) end face by low-energy (E=17 keV) He⁺ ions at doses ranging from 5×10¹⁶ to 4.5×10¹⁷ cm⁻² at room temperature. The TEM study of the irradiated Si films along the ion range shows that an a-Si layer forms in the most heavily damaged region and helium pores (bubbles) with a density of up to 3×10¹⁷ cm⁻³ and 2–5 nm in diameter nucleate and grow across the entire width of this layer. The growth of nanopores in the a-Si layer is accompanied by their linear ordering into chains oriented along the ion tracks. The absence of pores in the region that remains crystalline and has the maximal concentration of implanted helium is explained by the desorption of helium atoms from the thin film during the irradiation. After annealing at 600°C, the volume of immobile pores in the remaining a-Si layer increases owing to the capture of helium atoms from the amorphous matrix. Solid solution is shown to be the prevalent state of the helium implanted into the amorphous silicon. Linear features with a diameter close to 1 nm and density of about 10⁷ cm⁻¹ discovered in the helium-doped a-Si layer are identified as low-energy He⁺ ion tracks.     

Resonance Raman study of He+ ion implanted nanostructured ZnS

ZnS nanocrytsals of size ∼2.5 nm were prepared by chemical precipitation technique. Pressed pellets of nanostructured ZnS were implanted with He⁺ ions at doses of 5 × 10¹⁴, 1 × 10¹⁵ and 5 × 10¹⁵ ions/cm². Raman spectra of both unimplanted and He⁺ ion implanted samples were recorded with ultraviolet (UV) excitation. LO, 2LO, 2TO, (LO + TA) and (2TO − TA) modes of ZnS were observed in the resonance Raman spectra of the unimplanted nanostructured ZnS samples. In addition, a surface mode was observed at 294 cm⁻¹. With the implantation of He⁺ ions, the 2TO mode disappeared and 2LO mode became prominent and this observation was attributed to the decrease in band gap of ZnS nanocrytsals due to ion implantation. The exciton–LO phonon coupling strength was determined from the intensity ratio of 2LO to LO modes and it was observed that the exciton–LO phonon coupling strength increases with increase in implantation dose. In the present work, we report for the first time the observation of 2TO mode in the resonance Raman spectrum of nanostructured ZnS and also the modification of exciton–LO phonon coupling strength of semiconductor nanoparticles by ion implantation. Copyright © 2008 John Wiley & Sons, Ltd.     

Phase analysis in α-Fe after high-dose Si ion implantation by depth-selective conversion-electron Mössbauer spectroscopy (DCEMS)

Si⁺ ions of 50 keV in energy were implanted into α-Fe (95% ⁵⁷Fe) with a nominal dose of 5 × 10¹⁷ cm^?2 at 350°C. The depth distribution of the Fe-Si phases formed by ion implantation after annealing at 300 and 400°C for 1 h was studied quantitatively by depth-selective conversion-electron Mössbauer spectroscopy (DCEMS). Ordered Fe₃Si and ε-FeSi was observed.     

Nitrogen centers in GaP produced by hot implantation

Backscattering yields of 1.5 MeV?He⁺ ions and low temperature photoluminescence (PL) spectra were measured in GaP crystals implanted with 200 keV?N⁺ ions as functions of ion-dose, temperature during implantation and annealing temperature after implantation. Backscattering results indicate that hot implantation at 500°C greatly reduces radiation damage. The PL intensities of NN lines become maximum in the sample implanted with N⁺ ions of 3 × 10¹⁴cm^?2 at 500°C, and annealed at 1000°C for 1 hr with aluminum glass. The PL intensity is comparable to that of the nitrogen-doped sample during liquid phase epitaxy which is widely accepted as the best method of introducing nitrogen into GaP crystals. In the case of 500°C—hot implantation, the radiation damage produced during implantation is annealed out at 700 ~ 800°C and the implanted nitrogen substitutes for the phosphorous sites after annealing at 900 ~ 1000°C. Some kinds of defects or strains remain around the NN centers even in implanted samples with a maximum PL efficiency. These defects or strains don't seem to reduce the PL efficiency. In the case of room temperature implantation, PL efficiency decreases to one-hundredth or one-thousandth due to the formation of the non-crystalline state compared with hot implantation.     

Effect of nitrogen implantation with overlay coatings on microhardness in 4145 steel

The effect of nitrogen implantation on microhardness in 4145 steel was investigated. Practically no increase in microhardness for 10, 20 and 40 gm loads was observed in samples implanted with a dose of 6.5×10¹⁷N⁺ ions cm^?2 at 94 keV. The effect of ion-beam induced intermixing of aluminium and titanium film (400Å), due to nitrogen implantation was also studied. A noticeable increase of 15% in microhardness was observed. Annealing at temperature ∽300°C proved effective, while a decreasing trend in hardness could be observed for annealing temperatures >300°C. Furthermore, preliminary test indicated that these samples were more suitable for wear-protection.     

Influence of Cr<Superscript>+</Superscript> ion implantation and pulsed ion-beam annealing on the formation and optical properties of Si/CrSi<Subscript>2</Subscript>/Si(111) heterostructures

The effect of pulsed ion-beam annealing on the surface morphology, structure, and composition of single-crystal Si(111) wafers implanted by chromium ions with a dose varying from 6 × 10¹⁵ to 6 × 10¹⁶ cm⁻² and on subsequent growth of silicon is investigated for the first time. It is found that pulsed ion-beam annealing causes chromium atom redistribution in the surface layer of the silicon and precipitation of the polycrystalline chromium disilicide (CrSi₂) phase. It is shown that the ultrahigh-vacuum cleaning of the silicon wafers at 850°C upon implantation and pulsed ion-beam annealing provides an atomically clean surface with a developed relief. The growth of silicon by molecular beam epitaxy generates oriented 3D silicon islands, which coalesce at a layer thickness of 100 nm and an implantation dose of 10¹⁶ cm⁻². At higher implantation doses, the silicon layer grows polycrystalline. As follows from Raman scattering data and optical reflectance spectroscopy data, semiconducting CrSi₂ precipitates arise inside the silicon substrate, which diffuse toward its surface during growth.     

Positron annihilation studies of defects in 3CSiC hot-implanted with nitrogen and aluminum ions

2 ⁺ and Al⁺ at temperatures from room temperature (RT) to 1200 °C at doses of 10¹³ and 10¹⁵/cm². It is found from Doppler broadening spectra of annihilation gamma-rays obtained by varying the incident positron energy that hot-implantation gives rise to clustering of vacancies, whereas it suppresses amorphization and diminishes the thickness of damaged layers. The average size of such clusters increases with increasing implantation dose and temperature. Vacancy clustering by hot-implantation can be interpreted by the combination of vacancies during implantation. Vacancy type defects in the low-dose (10¹³/cm²) implanted samples are found to be removed by annealing at 1400 °C, whereas large vacancy clusters still remain after 1400 °C annealing in the high-dose (1 0¹⁵/cm²) implanted samples. It is also derived from the depth profile of positron diffusion length that positron scattering centers are produced after annealing at 1400 °C in all implanted samples. Received: 7 March 1997/Accepted: 6 May 1997     

Influence of ion-irradiation parameters on defect formation in silicon films

It is shown that unlike bulk silicon, for which amorphization is observed at an irradiation dose of 5 × 10¹⁶ ion/cm², thin silicon films on sapphire are amorphized at lower critical doses (10¹⁵ ion/cm²). An undamaged surface layer remains when the silicon films are irradiated with Si⁺ ion beams. Its thickness depends on the current density of the incident beam. Rutherford backscattering studies show that annealing at 950°C improves the crystallinity of the irradiated silicon film. Annealing of the films at 1100°C leads to mixing of the silicon-sapphire interface.     

Investigation of irradiated and annealed high-temperature superconducting films with the Umka nanotechnological complex

Superconducting YBa₂Cu₃O_{7 ? x} films were fabricated by dc magnetron sputtering. They were irradiated with 1.2-MeV He⁺ ions to doses of 4 × 10¹⁵, 8 × 10¹⁵, 16 × 10¹⁵, and 32 × 10¹⁵ cm^?2. The irradiated films were subjected to stepwise (30 min per step) vacuum annealing at 500, 600, 700, 800, and 900°C. After vacuum annealing, the samples irradiated to doses of 4 × 10¹⁵, 8 × 10¹⁵, and 16 × 10¹⁵ cm^?2 exhibited partial recovery of their critical temperature, whereas the sample with a dose of 32 × 10¹⁵ cm^?2 exhibited no signs of partial recovery of T _C. Investigation of the irradiated annealed samples with the Umka nanotechnological complex has revealed damaged surface regions extended to a relatively large (several tenths of a micrometer) depth.     

57Fe conversion electron Mössbauer spectrometric study of boron and carbon ion implanted irons

Amorphous layers produced at the surface of iron by B⁺ and C⁺ implantation (50 kV, 1×10¹⁸ ions cm⁻²) were analyzed by CEMS. The CEM spectrum of B⁺ implanted layer was composed of broad doublet and sextet. Spread hyperfine field distribution, P(H), indicates the formation of extremely disordered FeB layer. Annealing at 400°C brought about precipitation of FeB, which was converted to Fe₂B by annealing at 500°C. The P(H) for C⁺ implanted iron was resolved to 3 subpeaks with H values of 11.0, 18.0 and 22.5 T. The amorphous FeC phase was strongly correlated to crystalline Fe₅C₂ and Fe₂C, which precipitated at 300°C and were transformed into Fe₃C at 500°C. The amorphous layer disappeared by annealing at 600°C.     

Recrystallization behavior of high-dose Mn+-implanted GaAs

Raman spectroscopy was used to study the evolution of host lattice recrystallization in Mn⁺-implanted GaAs. A high dose of Mn⁺-ions (>10¹⁵ cm^-2) was introduced into semi-insulating GaAs by the combinatorial implantation method. Subsequent thermal annealing at 920 °C was carried out to re-grow the implantation-induced amorphous layers. The dependence of the recrystallization behavior on the Mn content was systematically observed. The lattice orientation of recrystallized layers in the surface changed after high-dose implantation (>1.6×10¹⁵ cm^-2) and annealing. The size of the recrystallized crystallites decreased with increasing Mn⁺ dose, as indicated by images from atomic force microscopy. The decrease in the phonon frequency of the Raman lines with the size reduction of microcrystals was in good agreement with the spatial correlation model. However, at higher doses (>7×10¹⁶ cm^-2), a blue shift of the frequency was observed due to the compressive stress exerted on the microcrystals. Received: 5 March 2002 / Accepted: 29 August 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +86-21/658-30734, E-mail: jqwang@mail.sitp.ac.cn     

Nitrogen implantation in GaAs1−xPx (x=0.4; 0.65)

Nitrogen ions were implanted in GaAs_1−xP_x (x=0.4; 0.65) at room temperature at various doses from 5×10¹² cm⁻² to 5×10¹⁵ cm⁻² and annealed at temperatures from 600°C up to 950°C using a sputtered SiO₂ encapsulation to investigate the possibility of creating isoelectronic traps by ion implantation. Photoluminescence and channeling measurements were performed to characterize implanted layers. The effects of damage induced by optically inactive neon ion implantation on photoluminescence spectrum were also investigated. By channeling measurements it was found that damage induced by nitrogen implantation is removed by annealing at 800°C. A nitrogen induced emission intensity comparable to the intensity of band gap emission for unimplanted material was observed for implanted GaAs_0.6P_0.4 after annealing at 850°C, while an enhancement of the emission intensity by a factor of 180 as compared with an unimplanted material was observed for implanted GaAs_0.35P_0.65 after annealing at 950°C. An anomalous diffusion of nitrogen atoms was found for implanted GaAs_0.6P_0.4 after annealing at and above 900°C.     

Electrical properties of Cd,Zn and S ion-implanted layers in GaAs

The electrical properties of cadmium, zinc, and sulfur ion-implanted layers in gallium arsenide have been measured by the van der Pauw-Hall technique. Ion implantation was performed with the substrates held at room temperature. The dependence of sheet resistivity, surface carrier concentration, and mobility on ion dose and on post-implantation anneal temperature was determined. In the case of 60 keV Cd⁺ ions implanted into n-type substrates, a measurable p-type layer resulted when samples were annealed for 10 minutes at a temperature in the range 600—900°C. After annealing at 300—900°C for 10 minutes, 100 per cent electrical activity of the Cd ions resulted for ion doses ≤ 10¹⁴/cm².

The properties of p-type layers produced by implantation of 85 keV Zn⁺ ions were similar to those of the 60 keV cadmium-implanted layers, in that no measurable p-type behavior was observed in samples annealed below a relatively high temperature. However, in samples implanted with 20 keV Zn⁺ ions a p-type layer was observed after annealing for 10 minutes at temperatures as low as 300°C.

Implantation of sulfur ions into p-type GaAs substrates at room temperature resulted in the formation of a high resistivity n-type layer, evcn before any annealing was performed. Annealing at temperatures up to 200°C or above 600°C lowered the resistivity of the layer, while annealing in the range 300—500°C eliminated the n-type layer.     

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.     

Effect of simultaneous helium implantation on the microstructure evolution of Inconel X-750 superalloy during dual-beam irradiation

This study focuses on investigation into the effect of helium implantation on microstructure evolution in Inconel X-750 superalloy during dual-beam (Ni⁺/He⁺) irradiation. The 1 MeV Ni⁺ ions with the damage rate of 10^?3 dpa/s as well as 15 keV He⁺ ions using rate of 200 appm/dpa were simultaneously employed to irradiate specimens at 400 °C to different doses. Microstructure characterization has been conducted using high-resolution analytical transmission electron microscopy (TEM). The TEM results show that simultaneous helium injection has significant influence on irradiation-induced microstructural changes. The disordering of γ′ (Ni₃ (Al, Ti)) precipitates shows noticeable delay in dose level compared to mono heavy ion irradiation, which is attributed to the effect of helium on promoting the dynamic reordering process. In contrast to previous studies on single-beam ion irradiation, in which no cavities were reported even at high doses, very small (2–5 nm) cavities were detected after irradiation to 5 dpa, which proved that helium plays crucial role in cavity formation. TEM characterization also indicates that the helium implantation affects the development of dislocation loops during irradiation. Large 1/3 〈1?1?1〉 Frank loops in the size of 10–20 nm developed during irradiation at 400 °C, whereas similar big loops detected at higher irradiation temperature (500 °C) during sole ion irradiation. This implies that the effect of helium on trapping the vacancies can help to develop the interstitial Frank loops at lower irradiation temperatures.     

Characterization of silicon doped with sodium upon high-voltage implantation

The depth distribution profiles of sodium atoms in silicon upon high-voltage implantation (ion energy, 300 keV; implantation dose, 5 × 10¹⁴ and 3 × 10¹⁵ cm ^?2) are investigated before and after annealing at temperatures in the range T _ann = 300–900°C (t _ann = 30 min). Ion implantation is performed with the use of a high-resistivity p-Si (ρ= 3–5 kΩ cm) grown by floating-zone melting. After implantation, the depth distribution profiles are characterized by an intense tail attributed to the incorporation of sodium atoms into channels upon their scattering from displaced silicon atoms. At an implantation dose of 3 × 10¹⁵ ions/cm², which is higher than the amorphization threshold of silicon, a segregation peak is observed on the left slope of the diffusion profile in the vicinity of the maximum after annealing at a temperature T _ann = 600°C. At an implantation dose of 5 × 10¹⁴ ions/cm², which is insufficient for silicon amorphization, no similar peak is observed. Annealing at a temperature T _ann = 700°C leads to a shift of the profile toward the surface of the sample. Annealing performed at temperatures T _ann ≥ 800°C results in a considerable loss of sodium atoms due to their diffusion toward the surface of the sample and subsequent evaporation. After annealing, only a small number of implanted atoms that are located far from the region of the most severe damages remain electrically active. It is demonstrated that, owing to the larger distance between the diffusion source and the surface of the sample, the superficial density of electrically active atoms in the diffusion layer upon high-voltage implantation of sodium ions is almost one order of magnitude higher than the corresponding density observed upon low-voltage implantation (50–70 keV). In this case, the volume concentration of donors near the surface of the sample increases by a factor of 5–10. The measured values of the effective diffusion parameters of sodium at annealing temperatures in the range T _ann = 525–900°C are as follows: D ₀ = 0.018 cm²/s and E _a = 1.29 eV/kT. These parameters are almost identical to those previously obtained in the case of low-voltage implantation.     

Lattice disorder produced in GaAs by 60 keV Cd ions and 70 keV Zn ions

Abstract

We have used the standard channeling technique with a 1.0 MeV He⁺ analyzing beam to investigate the lattice disorder produced in GaAs by 60 keV Cd and 70 keV Zn ion implantations made at room temperature. The amount of disorder produced increases linearly with dose and saturates at a dose of approximately 1–2 × 10¹³ Cd ions/cm². The disorder present in low dose implants (～5 × 10¹² Cd ions/cm²) anneals appreciably by 150 °C. With increasing doses of Cd or Zn the samples show a continuous increase in the anneal temperature required to remove a substantial amount of lattice disorder. There is no apparent difference between the anneal of Zn and Cd implants. The rate at which lattice disorder is produced in GaAs by heavy ion implantations and the doses of heavy ions required to saturate the lattice disorder observed are significantly different from the values of the corresponding quantities for Si and Ge.