Photoluminescence properties of ZnO thin film on sapphire substrates fabricated by ion implantation at elevated temperature and thermal oxidation

ZnO thin films on sapphire substrate were fabricated by ion implantation combined with thermal oxidation. A sapphire substrate was implanted with 50 keV zinc ions at 350 °C with a fluence of 1.5 × 10¹⁷ ions cm^?2, then annealed in a tube furnace in oxygen ambient in 2 h at 650 °C. Photoluminescence spectra were collected at temperatures from 80 to 300 K to understand the optical properties of this film. The photoluminescence spectrum at 300 K included a UV peak at 377 nm and a broad peak from deep level emission at 500 nm. The fine spectra structure at 80 K consisted of the free exciton at 3.373 eV and the donor bound exciton at 3.357 eV. The first and second phonon replicas of free excitons were also observed and the origin of the deep level emission peak was clarified.     

A broad chemical and structural characterization of the damaged region of carbon implanted alumina

As candidate materials for future thermonuclear fusion reactors, isolating ceramics will be submitted to high energy gamma and neutron radiation fluxes together with an intense particle flux. Amorphization cannot be tolerated in ceramics for fusion applications, due to the associated volume change and the deterioration of mechanical properties. Therefore, a comprehensive study was carried out to examine the effects of carbon beam irradiation on polycrystalline aluminium oxide (Al₂O₃), a ceramic component of some diagnostic and plasma heating systems. Complementary techniques have allowed a complete chemical and structural surface analysis of the implanted alumina. Implantation with 75 keV, mono-energetic carbon ions at doses of 1 × 10¹⁷ and 5 × 10¹⁷ ions/cm² was performed on polished and thermally treated ceramic discs. The alumina targets were kept below 120 °C. The structural modifications induced during ion irradiation were studied by the GXRD and TEM techniques. Under these conditions, alumina is readily amorphized by carbon ions, the thickness of the ion-beam induced disordered area increasing with the ion dose. Matrix elements and ion implanted profiles were followed as a function of depth by using ToF-SIMS, indicating the maximum concentration of implanted ions to be in the deeper half of the amorphous region. Ion distribution and chemical modifications caused in the Al₂O₃ substrate by carbon irradiation were corroborated with XPS. The amount of oxygen in the vicinity of the implanted alumina surface was reduced, suggesting that this element was selectively sputtered during carbon irradiation. The intensity of those peaks referring to Al–O bonds diminishes, while contributions of reduced aluminium and metal carbides are found at the maximum of the carbon distribution. TEM observations on low temperature thermally annealed specimens indicate partial recovery of the initial crystalline structure.     

Temperature behavior of damage in sapphire implanted with light ions

In this study, we compare and discuss the defect behavior of sapphire single crystals implanted with different fluences (1 × 10¹⁶–1 × 10¹⁷ cm^?2) of carbon and nitrogen with 150 keV. The implantation temperatures were RT, 500 °C and 1000 °C to study the influence of temperature on the defect structures. For all the ions the Rutherford backscattering-channeling (RBS-C) results indicate a surface region with low residual disorder in the Al-sublattice. Near the end of range the channeled spectrum almost reaches the random indicating a high damage level for fluences of 1 × 10¹⁷ cm^?2. The transmission electron microscopy (TEM) photographs show a layered contrast feature for the C implanted sample where a buried amorphous region is present. For the N implanted sample the Electron Energy Loss Spectroscopy (EELS) elemental mapping give evidence for the presence of a buried damage layer decorated with bubbles. Samples implanted at high temperatures (500 °C and 1000 °C) show a strong contrast fluctuation indicating a defective crystalline structure of sapphire.     

Peculiarities of defect generation in Si+-implanted GaAs (2 1 1)

Peculiarities of the defect generation during implantation of (2 1 1) GaAs with Si⁺ ions and doses below the amorphisation dose of GaAs have been investigated by X-ray diffraction, the secondary ion mass-spectroscopy (SIMS) and transmission electron microscopy. It was shown, that in such implanted layers less radiation defects will be formed and these defects are more easily annealed by rapid photon annealing (RPA) than in (1 0 0)-oriented wafers.     

Effects of BF2+ implantation on the strain-relaxation of pseudomorphic metastable Ge0.06Si0.94 alloy layers

Metastable pseudomorphic Ge_0.06Si_0.94 alloy layers grown by molecular beam epitaxy (MBE) on Si (1 0 0) substrates were implanted at room temperature by 70 keV BF₂⁺ ions with three different doses of 3 × 10¹³, 1 × 10¹⁴, and 2.5 × 10¹⁴ cm⁻². The implanted samples were subsequently annealed at 800°C and 900°C for 30 min in a vacuum tube furnace. Observed by MeV ⁴He channeling spectrometry, the sample implanted at a dose of 2.5 × 10¹⁴ BF₂⁺ cm⁻² is amorphized from surface to a depth of about 90 nm among all as-implanted samples. Crystalline degradation and strain-relaxation of post-annealed Ge_0.06Si_0.94 samples become pronounced as the dose increases. Only the samples implanted at 3 × 10¹³ cm⁻² do not visibly degrade nor relax during anneal at 800°C . In the leakage current measurements, no serious leakage is found in most of the samples except for one which is annealed at 800°C for 30 min after implantation to a dose of 2.5 × 10¹⁴ cm⁻². It is concluded that such a low dose of 3 × 10¹³ BF₂⁺ cm⁻² can be doped by implantation to conserve intrinsic strain of the pseudomorphic GeSi, while for high dose regime to meet the strain-relaxation, annealing at high temperatures over 900°C is necessary to prevent serious leakages from occuring near relaxed GeSi/Si interfaces.     

SHI induced re-crystallization of Ge implanted SiO2 films

Ge nanocrystals embedded in SiO₂ matrix have been synthesized by swift heavy ion irradiation of Ge implanted SiO₂ films. In the present study, 400 keV Ge⁺ ions were implanted into SiO₂ films at dose of 3 × 10¹⁶ ions/cm² at room temperature. The as-implanted samples were irradiated with 150 MeV Ag¹²⁺ ions with various fluences. Similarly 400 keV Ge⁺ ions implanted into Silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au⁸⁺ ions at room temperature (RT). These samples were subsequently characterized by XRD and Raman to understand the re-crystallization behavior. The XRD results confirm the presence of Ge crystallites in the irradiated samples. Rutherford backscattering spectrometry (RBS) was used to quantify the concentration of Ge in the SiO₂ matrix. Variation in the nanocrystal size as a function of ion fluence is presented. The basic mechanism of ion beam induced re-crystallization has been discussed.     

Effect of ion-irradiation on the microstructure and microhardness of the W-2Y2O3 composite materials fabricated by sintering and hot forging

A W-2Y₂O₃ material was developed in collaboration with the Plansee Company (Austria). An ingot of the material having approximate dimension of 95 mm × 20 mm was fabricated by mixing the elemental powders followed by pressing, sintering and hot forging. The microstructure of the W-2Y₂O₃ composite was investigated using transmission electron microscopy (TEM). The microhardness was studied using nano-indentation technique. We observed that the W-grains having a mean size of about 1 μm already formed and these grains contain very low density of dislocations. The size of the yttria particles was between 300 nm and 1 μm and the Berkovich hardness was about 4.8 GPa. The specimens were irradiated/implanted with Fe and He ions at JANNuS facility located at Orsay/Saclay, France. The TEM disks kept were irradiated/implanted at 300 and 700 °C using Fe and He ions with an energy of 24 and 2 MeV, respectively. The calculated radiation dose was about 5 dpa produced by Fe ions and total He content is 75 appm at both 300 and 700 °C. From the TEM investigation of irradiated samples, few radiation loops are present on the W grains, whereas on yttria particles, the radiation induced damages appear as voids. Berkovich hardness of the irradiated sample is higher than that of the non-irradiated sample. Results on the microstructure and microhardness of the ion-irradiated W-2Y₂O₃ composites are presented in detail.     

Er+ implantation in SnO2:SiO2 layers: Structure changes and light emission

Structure changes and light emission behavior in Er⁺ implanted SnO₂:SiO₂ layers are studied, using transmission electron microscopy (TEM), Rutherford backscattering (RBS) and cathodoluminescence (CL). SnO₂:SiO₂ layers of different composition deposited with RF magnetron sputtering on Si wafers were implanted with 200 keV Er⁺ to a fluence of 3 × 10¹⁵ cm^?2 at room temperature. The implanted structures were then annealed at 600–1000 °C for 30 min, resulting in the formation of crystalline SnO₂ nanoclusters. Cross-section TEM revealed a strong reduction of the SnO₂ crystallite size down to several nanometers in the implanted area of the SnO₂:SiO₂ layer as compared to the undoped layer. In addition, a very narrow layer of SnO₂ nanocrystals appears at the SiO₂/Si interface. Several narrow CL emission peaks and wide bands were found which could be related to the decay of SnO₂ free excitons, to oxygen deficiency centers in SiO₂ and to transitions between the energy levels in the Er ions, apparently located at nanoclusters. The mechanisms of nanostructuring as well as the emission process are discussed.     

Formation of complex Al–N–C layer in aluminium by successive carbon and nitrogen implantation

The results of Auger electron spectroscopy and transmission electron microscopy of the surface layer of aluminium after successive implantation by carbon and nitrogen ions are presented in this work. The energy of implanted ions is 40 keV. The implantation dose varies in the range (3.3–6.5) × 10¹⁷ ions/cm². The findings show that successive implantation leads to the formation of two main layers in aluminium. The first layer is AlNC_x (0 < x < 0.5) layer with violated hcp. AlN structure, where carbon atoms form bonds with nitrogen atoms. The second layer contains disoriented Al₄C₃ precipitates and carbon atoms migrated from the first layer. The mechanism of migration is discussed.     

Swift heavy ion induced modifications of optical and microstructural properties of silver–fullerene C60 nanocomposite

In this paper, we study the optical and microstructural properties of silver–fullerene C₆₀ nanocomposite and their modifications induced by swift heavy ion irradiation. Silver nanoparticles embedded in fullerene C₆₀ matrix were synthesized by co-deposition of silver and fullerene C₆₀ by thermal evaporation. The nanocomposite thin films were irradiated by 120 MeV Ag ions at different fluences ranging from 1 × 10¹² to 3 × 10¹³ ions/cm². Optical absorption studies revealed that the surface plasmon resonance of Ag nanoparticles showed a blue shift of ～49 nm with increasing ion fluence up to 3 × 10¹³ ions/cm². Transmission electron microscopy and Rutherford backscattering spectroscopy were used to quantify particle size and metal atomic fraction in the nanocomposite film. Growth of Ag nanoparticles was observed with increasing ion fluence. Raman spectroscopy was used to understand the effect of heavy ion irradiation on fullerene matrix. The blue shift in plasmonic wavelength is explained by the transformation of fullerene C₆₀ matrix into amorphous carbon.     

Microstructure of ion-implanted region in TiNi alloy

TiNi alloy samples implanted with various fluences of 3 MeV Cu²⁺ ions were characterized by transmission electron microscope (TEM) and X-ray diffractometer. Cross-sectional TEM images of the samples showed that amorphous region was seen at the fluence of 10¹⁴ ions cm^?2 in case of ion implantation at 300 K of the substrate temperature, but in case of ion implantation at 100 K it did not appear even at 10¹⁵ ions cm^?2. These results were also confirmed by X-ray diffraction profiles of the same samples. Consequently, the extent of microstructure change of TiNi alloy by ion implantation was different depending on the substrate temperature.     

Hydrogen implantation defects in MgO

Deuterium and hydrogen ions with an energy of 15 keV have been implanted in virgin MgO (1 0 0) single crystals and in single crystals containing helium implantation generated microcavities. Doses were varied from 2 × 10¹⁵ to 2 × 10¹⁶ cm⁻². The samples were annealed from room temperature to 950 K. The defects produced by hydrogen and the trapping of hydrogen at the defects were monitored by photon absorption and positron beam analysis. With this novel technique a depth distribution of defects can be determined for implantation depths from 0 to 2000 nm. The technique is very sensitive for vacancy and vacancy clusters, i.e. sites with low electron density. After 950 K annealing microcavities were observed for the 2 × 10¹⁶ cm⁻² dose but not for the 10 times lower dose. During annealing up to 750 K point defects are mobile but the defect clusters remain small and filled with hydrogen. In samples which contain already microcavities, point defects and deuterium from the deuterium irradiation are accumulated by the microcavities.     

Micro-Raman depth profile investigations of beveled Al+-ion implanted 6H-SiC samples

6H-SiC single crystals were implanted with 450 keV Al⁺-ions to a fluence of 3.4 × 10¹⁵ cm^?2 , and in a separate experiment subjected to multiple Al⁺ implantations with the four energies: 450, 240, 115 and 50 keV and different fluences to obtain rectangular-like depth distributions of Al in SiC. The implantations were performed along [0 0 0 1] channeling and non-channeling (“random”) directions. Subsequently, the samples were annealed for 10 min at 1650 °C in an argon atmosphere. The depth profiles of the implanted Al atoms were obtained by secondary ion mass spectrometry (SIMS). Following implantation and annealing, the samples were beveled by mechanical polishing. Confocal micro-Raman spectroscopic investigations were performed with a 532 nm wavelength laser beam of a 1 μm focus diameter. The technique was used to determine precisely the depth profiles of TO and LO phonon lines intensity in the beveled samples to a depth of about 2000 nm. Micro-Raman spectroscopy was also found to be useful in monitoring very low levels of disorder remaining in the Al⁺ implanted and annealed 6H-SiC samples. The micro-Raman technique combined with sample beveling also made it possible the determination of optical absorption coefficient profiles in implanted subsurface layers.     

Depth-profiling of implanted 28Si by (α,α) and (α,p0) reactions

Silicon nanocrystals enclosed in thin films (Si quantum dots or Si QDs) are regarded to be the cornerstone of future developments in new memory, photovoltaic and optoelectronic products. One way to synthesize these Si QDs is ion implantation in SiO₂ layers followed by thermal annealing post-treatment.Depth-profiling of these implanted Si ions can be performed by reactions induced by α-particles on ²⁸Si. Indeed, for high incident energy, nuclear levels of ³²S and ³¹P can be reached, and cross-sections for (α,α) and (α,p₀) reactions are more intense. This can help to increase the signal for surface silicon, and therefore make distinguishing more easy between implanted Si and Si coming from the SiO₂, even for low fluences.In this work, (α,α) and (α,p₀) reactions are applied to study depth distributions of 70 keV ²⁸Si⁺ ions implanted in 200 nm SiO₂ layers with fluences of 1 × 10¹⁷ and 2 × 10¹⁷ cm^?2. Analysis is performed above E_R = 3864 keV to take advantage of resonances in both (α,α) and (α,p₀) cross-sections. We show how (α,p₀) reactions can complement results provided by resonant backscattering measurements in this complex case.     

Synthesis and characterization of SnO2 nanoparticles embedded in silica by ion implantation

Tin dioxide nanoparticles embedded in silica matrix were fabricated by ion implantation combined with thermal oxidation. Silica substrate was implanted with a 150 keV Sn⁺ ions beam with a fluence of 1.0 × 10¹⁷ ions/cm². The sample was annealed for 1 h in a conventional furnace at a temperature of 800 °C under flowing O₂ gas. According to the structural characterization performed by X-ray diffraction and transmission electron microscopy techniques, metallic tetragonal tin nanoparticles with a volume average size of 12.8 nm were formed in the as-implanted sample. The annealing in oxidizing atmosphere promotes the total oxidation of the tin nanoparticles into tin dioxide nanoparticles with a preferential migration toward the surface of the matrix, where large and coalesced nanoparticles were observed, and a small diffusion toward the bulk, where smaller nanoparticles were found.     

Er+ medium energy ion implantation into lithium niobate

Erbium-doped lithium niobate (Er:LiNbO₃) is a prospective photonics component, operating at 1.5 μm, which could find its use chiefly as an optical amplifier or waveguide laser. In this study, we have focused on the properties of the optically active Er:LiNbO₃ layers, which are fabricated by medium energy ion implantation under various experimental conditions. Erbium ions were implanted at energies of 330 and 500 keV with fluences of 1.0 × 10¹⁵, 2.5 × 10¹⁵ and 1.0 × 10¹⁶ cm^?2 into LiNbO₃ single-crystalline cuts of various orientations. The as-implanted samples were annealed in air at 350 °C for 5 h. The depth distribution and diffusion profiles of the implanted Er were measured by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He⁺ ions. The projected range R_P and projected range straggling ΔR_P were calculated employing the SRIM code. The damage distribution and structural changes were described using the RBS/channelling method. Changes of the lithium concentration depth distribution were studied by Neutron Depth Profiling (NDP). The photoluminescence spectra of the samples were measured to determine whether the emission was in the desired region of 1.5 μm. The obtained data made it possible to reveal the relations between the structural changes of erbium-implanted lithium niobate and its luminescence properties important for photonics applications.     

Lattice location and annealing behaviour of Pt and W implanted sapphire

Sapphire (α-Al₂O₃) single crystals were implanted with different doses of Pt and W ions in the range of 1 × 10¹⁴ at/cm² to 5 × 10¹⁶ at/cm² at room temperature. Detailed angular scans through the main axial directions show that up to 10¹⁵ at/cm² fluences about 80% of the W and Pt ions are incorporated into substitutional or near substitutional lattice sites. Below the amorphization threshold implantation damage show a double peak structure which anneals out partially at low temperature (800^oC). Amorphization of the implanted region starts for doses of the order of 1 × 10¹⁶ at/cm². The amorphous layer regrowths epitaxially in vacuum at 1100^oC, with a velocity of 3 Å/min and stops when the crystalline/amorphous interface reaches the region of maximum Pt concentration. When the annealing is done at ambient atmosphere the damage recovers completely at 1100^oC even for doses of the order of 5 × 10¹⁶ Pt⁺/cm² leading to the formation of Pt precipitates.     

Formation of germanium nanoparticles in silica glass studied by optical absorption and X-ray absorption fine structure analysis

We examined the relation between the 3.1 eV emission band and local structure for Ge⁺ implanted silica glass by means of photoluminescence, optical and X-ray absorption spectroscopies. In the 2 × 10¹⁵ cm^?2 implanted sample, a new emission band around 2.7 eV was observed, the origin of which was assigned to the B_2α oxygen deficient center and/or small Si clusters in silica. When the Ge⁺ fluence exceeded 2 × 10¹⁶ cm^?2, a sharp and intense 3.1 eV emission band replaced the 2.7 eV band. We found that the intense 3.1 eV PL occurred by the prolonged X-ray irradiation onto the 2 × 10¹⁵ cm^?2 implanted sample. UV–vis absorption and XAFS spectroscopies suggested that the aggregation of atomically dispersed tetravalent (Ge(IV)) atoms into Ge(0) clusters of ～1 nm exhibit strongly correlation with the generation of the 3.1 eV PL. Such nano- and/or subnano-size Ge(0) clusters formed by the X-ray radiation were oxidized and decomposed again to the isolated Ge(IV) atoms, while those produced by the higher Ge⁺ fluence were stable against the exposure to air.     

Annealing behaviour of defects in helium implanted MgO

Virgin MgO (1 1 0) single crystals have been implanted with 30 keV ³He⁺ ions to a dose of 5 × 10¹⁵ cm^-2. After implantation the samples have been annealed under air for 30 min in a tube oven. The annealing behaviour of the defects and ³He has been monitored by three experimental techniques: positron beam Doppler broadening, neutron depth profiling (NDP) and optical absorption in the UV to near-IR region. The observations in MgO lead to the conclusion that below 1000^oC the vacancy like defects are stabilised by the implanted He atoms. Above this temperature He may dissociate from these small defects, allowing the formation of larger vacancy clusters.     

Early stage of the crystallization in amorphous Fe–Si layers: Formation and growth of metastable α-FeSi2

Crystallization processes of amorphous Fe–Si layers have been investigated using transmission electron microscopy (TEM). Si(1 1 1) substrates were irradiated with 120 keV Fe ions at ?150 °C to a fluence of 1.0 × 10¹⁷ cm². An Fe-rich amorphous layer embedded in an amorphous Si was formed in the as-irradiated sample. Plan-view TEM observations revealed that a part of the amorphous Fe–Si layer crystallized to the metastable α-FeSi₂ after thermal annealing at 350 °C for 8 h. The lattice parameter of c-axis decreased with thermal annealing. It was considered that the change in the lattice parameter originates from the decrease of the Fe occupancy at (0, 0, 1/2) and its equivalent positions in the unit cell of the metastable α-FeSi₂.