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Dominant changes in structural, optical, and magnetic properties were observed at the highest dose of implanted ions with larger ionic radii which is due to the large number of produced defects in the host.

Quantum emitters with long-lived quantum memories are a promising scalable quantum system for repeater-based quantum communications, quantum sensing, and distributed quantum computing networks. Alt...

We report high efficiency cell processing technologies for the ultra-thin Si solar cells based on crystalline Si thin foils (below a 50 µm thickness) produced by the proton implant exfoliation (PIE) technique. Shallow textures of submicrometer scale is essential for effective light trapping in crystalline Si thin foil based solar cells. In this study, we report the fabrication process of random Si nanohole arrays of ellipsoids by a facile way using low melting point metal nanoparticles of indium which were vacuum-deposited and dewetted spontaneously at room temperature. Combination of dry and wet etch processes with indium nanoparticles as etch masks enables the fabrication of random Si nanohole arrays of an ellipsoidal shape. The optimized etching processes led to effective light trapping nanostructures comparable to conventional micro-pyramids. We also developed the laser fired contact (LFC) process especially suitable for crystalline Si thin foil based PERC solar cells. The laser processing parameters were optimized to obtain a shallow LFC contact in conjunction with a low contact resistance. Lastly, we applied the random Si nanohole arrays and the LFC process to the crystalline Si thin foils (a 48 µm thickness) produced by the PIE technique and achieved the best efficiency of 17.1% while the planar PERC solar cell without the Si nanohole arrays exhibit 15.6%. Also, we demonstrate the ultra-thin wafer is bendable to have a 16 mm critical bending radius.

Conductive bridging random access memory (CBRAM) has been considered to be a promising emerging device for artificial synapses in neuromorphic computing systems. Good analog synaptic behaviors, such as linear and symmetric synapse updates, are desirable to provide high learning accuracy. Although numerous efforts have been made to develop analog CBRAM for years, the stochastic and abrupt formation of conductive filaments hinders its adoption. In this study, we propose a novel approach to enhance the synaptic behavior of a SiNx/a-Si bilayer memristor through Ge implantation. The SiNx and a-Si layers serve as switching and internal current limiting layers, respectively. Ge implantation induces structural defects in the bulk and surface regions of the a-Si layer, enabling spatially uniform Ag migration and nanocluster formation in the upper SiNx layer and increasing the conductance of the a-Si layer. As a result, the analog synaptic behavior of the SiNx/a-Si bilayer memristor, such as the nonlinearity, on/off ratio, and retention time, is remarkably improved. An artificial neural network simulation shows that the neuromorphic system with the implanted SiNx/a-Si memristor provides a 91.3% learning accuracy mainly due to the improved linearity. An approach that tweaks the structures of a new type of memory chip shows promise for neuromorphic computing applications. In conductive bridging random access memory (CBRAM) technology, nanoscale metal filaments inside special insulators are used to store data in either high or low conductance states. Inho Kim from the Korea Institute of Science and Technology in Seoul, South Korea and colleagues now report beneficial effects when germanium ions are implanted into silicon-based CBRAM using high-energy beams. The team’s microscopy experiments revealed that the implantation caused metal nanoclusters to distribute evenly within the device’s switching layer. These particles enabled smoother transitions between conductance states than conventional CBRAM, better mimicking the analog switching seen in synapses. Neural network simulations demonstrated that ion-implanted devices had significantly improved learning accuracy compared to unmodified CBRAM chips. We propose a novel approach to enhance the synaptic behavior of a SiNx/a-Si bilayer memristor through Ge implantation. The SiNx and a-Si layers serve as switching and internal current limiting layers, respectively. Ge implantation induces structural defects in the bulk and surface regions of the a-Si layer, enabling spatially uniform Ag migration and nanocluster formation in the upper SiNx layer and increasing the conductance of the a-Si layer. As a result, the analog synaptic behavior of the SiNx/a-Si bilayer memristor, such as the nonlinearity, on/off ratio, and retention time, is remarkably improved.

Si ions 2.3 MeV are implanted into nanodiamonds (NDs) at doses of 1×1012 ~ 1×1015 ions/cm2. The ion implantation not only creates silicon-vacancy (SiV) color centers but also reduces the size of the NDs from 50 nm to ~ 10 nm. As the Si dose is increased up to 1 × 1013 ions/cm2, the luminescence from the nitrogen-vacancy (NV) color centers in the ND initially increases. At higher dose rates, the luminescence from the NV color centers decreases. Due to the differences in the minimum ND size required for stable luminescence, the zero phonon line (ZPL) of the SiV color center appears after the luminescence from the NV center decreases dramatically. The ZPLs from both centers become almost negligible after Si ions have been implanted at doses higher than 5 × 1014 ions/cm2. These observations are explained by the reduced size of the NDs and the number of implanted Si ions, which is estimated based on SRIM simulations.

The present work reports the synthesis of MgO and CaO nanoparticles by using the sol-gel autocombustion method. The annealing of the precursor at 1200 °C was observed to lead the formation of MgO nanoparticles having average crystallite size of ~ 31 nm. Annealing the precursor at same temperature produced materials having a CaO phase with a minor impure phase of calcium carbonate (~ 3%). The crystallite size corresponding to the CaO phase was 38 nm. A change of thermal history in the precursor was observed not to result in an improvement of the CaO phase. The change of thermal history in the precursor gave rise to mixed phases of CaCO3 and Ca(OH)2 rather than the phase of CaO. Further, annealing at 1200 °C for 12 h resulted in the formation of the CaO phase along with almost 1 - 5% of calcium hydroxide as an impurity phase. X-ray absorption spectroscopic measurements carried out on these materials revealed that the local electronic/atomic structure of these oxides was not only affected by the impurity phases but also influenced by the carbaneous impurities attached to the crystallites.

Present work is motivated to investigate the surface and local electronic structure modifications of MgO films implanted with Zn and Fe ions. MgO film was deposited using radio frequency sputtering method. Atomic force microscopy measurements exhibit morphological changes associated with implantation. Implantation of Fe and Zn ions leads to the reduction of co-ordination geometry of Mg2+ ions in host lattice. The effect is dominant at bulk of film rather than surface as the large concentration of implanted ions resides inside bulk. Moreover, the evidences of interaction among implanted ions and oxygen are not being observed using near edge fine structure measurements.

Herein, Fe+ and Zn+ ion implantation effects in MgO single crystals were investigated. Slight improvement in the magnetic behavior of implanted single crystals was observed, however, no ferromagnetic hysteresis was observed despite the presence of Fe ions in the lattice. The effect was associated with the oxidation of these ions and possibly due to occurrence of oxygen vacancies. Angle dependent Mg K-edge near edge X-ray absorption fine structure (NEXAFS) measurements reflected the slight change in local electronic structure induced by implantation. Results obtained from O K-edge NEXAFS measurements supported the results obtained from Mg K-edge spectra. These measurements further inferred the interaction between implanted ions and lattice oxygen.

The Korea Institute of Science and Technology (KIST, Seoul, Republic of (S.) Korea) ion beam facility consists of three electrostatic accelerators: a 400 kV single ended ion implanter, a 2 MV tandem accelerator system and a 6 MV tandem accelerator system. The 400 kV and 6 MV systems were purchased from High Voltage Engineering Europa (HVEE, Netherlands) and commissioned in 2013, while the 2 MV system was purchased from National Electrostatics Corporation (NEC, USA) in 1995. These systems are used to provide traditional ion beam analysis (IBA), isotope ratio analysis (ex. accelerator mass spectrometry, AMS), and ion implantation/irradiation for domestic industrial and academic users. The main facility is the 6 MV HVEE Tandetron system that has an AMS line currently used for 10 Be, 14 C, 26 Al, 36 Cl, 41 Ca and 129 I analyses, and three lines for IBA that are under construction. Here, these systems are introduced with their specifications and initial performance results.

This work reports the effect of thermal annealing ranging from 0 to 800 °C on the various properties of zinc oxide thin film grown using radio-frequency sputtering. X-ray diffraction studies reveal the relaxation of stress up to thermal annealing of 400 °C and induction of residual stress thereafter. Zn K-edge X-ray absorption spectroscopic measurements reveal the variation of Zn–O and Zn–Zn bond distances with annealing temperature. Variation of coordination number with annealing temperature shows onset of oxygen vacancies at lower annealing temperatures. These vacancies and defects are also supported by the photoluminescence measurements. The optical band-gap of these films exhibit a significant variation with annealing temperature, which is in-line with the variation of crystallite size. Further, the magnetic behavior of these films is observed to follow the behavior of O 2p states along with defects as investigated from the X-ray magnetic circular dichroism.

Radio-frequency (RF) sputtered ZnO films were investigated as a function of the Ni-ion irradiation dose at room temperature. The prepared ZnO films were irradiated with Ni-ions at an acceleration energy of 130 MeV in the dose range from 5 × 1011 ions/cm2 to 1 × 1013 ions/cm2. The electrical properties of the irradiated ZnO films changed with changing Ni-ion irradiation dose. In order to explain the change in the electrical properties of ZnO films, we investigated the physical properties and the electronic structure, such as the physical structure, the molecular orbital in the conduction band, and the band edge state below the conduction band. The physical structure and the physical composition showed no changes, regardless of the Ni-ion irradiation dose. On the other hand, the electronic structure showed a drastic modification of the hybridized molecular orbital ordering of the Zn 4sp and the O 2p in the conduction band. In addition, two distinct band edge states below the conduction band were observed with increasing Ni-ion irradiation dose. These remarkable changes in the electronic structure could be correlated to changes in the electrical properties.

We investigate the influence of carbon-ion irradiation on the superconducting critical properties of MgB$_2$ thin films. MgB$_2$ films of two thicknesses viz. 400 nm (MB400nm) and 800 nm (MB800nm) were irradiated by 350 keV C ions having a wide range of fluence, 1 x 10$^{13}$ - 1 x 10$^{15}$ C atoms/cm$^2$. The mean projected range ($R_p$) of 350 keV C ions in MgB$_2$ is 560 nm, thus the energetic C ions will pass through the MB400nm, whereas the ions will remain into the MB800nm. The superconducting transition temperature ($T_c$), upper critical field ($H_{c2}$), $c$-axis lattice parameter, and corrected residual resistivity ($\rho_{corr}$) of both the films showed similar trends with the variation of fluence. However, a disparate behavior in the superconducting phase transition was observed in the MB800nm when the fluence was larger than 1 x 10$^{14}$ C atoms/cm$^2$ because of the different Tcs between the irradiated and non-irradiated parts of the film. Interestingly, the superconducting critical properties, such as $T_c$, $H_{c2}$, and $J_c$, of the irradiated MgB$_2$ films, as well as the lattice parameter, were almost restored to those in the pristine state after a thermal annealing procedure. These results demonstrate that the atomic lattice distortion induced by C-ion irradiation is the main reason for the change in the superconducting properties of MgB$_2$ films., Comment: 31 pages, 12 figures, submitted to Superconductor Science and Technology

The present experimental work provides the phenomenological approach to understand the dewetting in thin noble metal films with subsequent formation of nanoparticles (NPs) and embedding of NPs induced by ion irradiation. Au/polyethyleneterepthlate (PET) bilayers were irradiated with 150 keV Ar ions at varying fluences and were studied using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (X-TEM). Thin Au film begins to dewet from the substrate after irradiation and subsequent irradiation results in spherical nanoparticles on the surface that at a fluence of 5 × 1016 ions/cm2 become embedded into the substrate. In addition to dewetting in thin films, synthesis and embedding of metal NPs by ion irradiation, the present article explores fundamental thermodynamic principles that govern these events systematically under the effect of irradiation. The results are explained on the basis of ion induced sputtering, thermal spike inducing local melting and of thermodynamic driving forces by minimization of the system free energy where contributions of surface and interfacial energies are considered with subsequent ion induced viscous flow in substrate.

We report large improvement of the critical current density (Jc) of 400-nm-thick MgB2 thin films through carbon (C) ion irradiation. When 350 keV C ions with various dose levels ranging from 1 × 10...

An environment friendly, inexpensive solvothermal route is used to synthesize polycrystalline Zn x Sn 1 − x O 2 (0.0 ≤ x ≤ 0.07) nanorods with nanoflower morphology without using any organic solvents, surfactant or any catalytic agent under low hydrothermal pressure. Scanning electron microscopy (SEM) equipped with energy-dispersive x-ray spectra depicts the formation of near stoichiometric Zn x Sn 1 − x O 2 nanorods. SEM analysis reveals that Zn incorporation in SnO 2 decreases the nanorod diameter from ~ 20 nm to ~ 10 nm. High-resolution x-ray diffraction analysis reveals the rutile structure for x ≤ 0.04 samples, while for x = 0.07 a Zn 2 SnO 4 phase is observed. Near edge x-ray absorption fine structure and x-ray photoemission spectroscopy indicate that Zn atoms have been substituted for Sn sites in SnO 2 lattice without forming secondary phases and also create numerous oxygen vacancy in the structure.

1 MeV Cu2+ ions have been implanted into un-doped ZnO and Ga-doped ZnO films with a dose of 1 × 1017 ions/cm2 at room-temperature. Cu ion-implanted Ga-doped ZnO had ferromagnetism at room-temperature and the saturation magnetization of this sample was estimated to be 0.12 μB per Cu, while the Cu ion-implanted un-doped ZnO did not show ferromagnetic behavior. Near-edge X-ray fine structure (NEXAFS) spectroscopy revealed that a partial amount of implanted Cu ions existed as Cu2+ (d9) state in Ga-doped ZnO film. On the other hand, almost Cu atoms existed as Cu1+ (d10) state in un-doped ZnO film. However, the subsequent annealing at temperature above 800 °C on this ferromagnetic sample induced the annihilation of ferromagnetism due to the formation of non-ferromagnetic Cu2O phase.

RF-sputtered ZnO films were irradiated with hydrogen ions by using an ion accelerator at 110 keV. The physical and the electrical characteristics of the irradiated ZnO films were studied as functions of the hydrogen-ion irradiation dose. The Hall measurement indicated that the carrier concentration had small changes regardless of irradiated hydrogen amount, but the mobility was dramatically enhanced after irradiation of 1015 atoms/cm2. Even when the irradiated hydrogen dose was increased, the crystalline structure had no transformation and the composition was preserved. On the other hand, the electronic structure, measured by using X-ray absorption spectroscopy, exhibited a modification of the molecular orbital structure in the ZnO films irradiated at doses above 1015 atoms/cm2. These distortions of the molecular orbital in the conduction band could lead to a mobility enhancement without a structural transformation.

The dielectric properties of composition spread SiO 2 –Al 2 O 3 thin films deposited by off-axis radio-frequency magnetron sputtering at room temperature were explored to obtain optimized compositions, which have low dielectric constants and losses. The specific points (compositions) showing superior dielectric properties of low dielectric constants (8.13 and 9.12) and losses (tanδ ∼0.02) at 1 MHz were found in area of the distance of 25.0 mm (Al 2 Si 3 O 8 ) and 42 mm (Al 2.4 Si 3 O 8 ) apart from SiO 2 target side in 75 mm × 25 mm sized Pt/Ti/SiO 2 /Si(1 0 0) substrates, respectively. The specific thin films were amorphous phase and the compositions were Al 2 Si 3 O 8 ( k ∼8.13) and Al 2.4 Si 3 O 8 ( k ∼9.12).

The dielectric properties of MgO–Ta 2 O 5 continuous composition spread (CCS) thin films were investigated. The MgO–Ta 2 O 5 CCS thin films were deposited on Pt/Ti/SiO 2 /Si substrates by off-Axis RF magnetron sputtering system, and then the films were annealed at 350 °C with rapid thermal annealing system in vacuum. The dielectric constant and loss of MgO–Ta 2 O 5 CCS thin films were plotted via 1500 micron-step measuring. The specific point of Ta 2 O 5 –MgO CCS thin film (post annealed at 350 °C) showing superior dielectric properties of high dielectric constant ( k ∼ 28) and low dielectric loss (tan δ 2 O 5 side on the substrate. The cation's composition of thin film was Mg:Ta = 0.4:2 at%.

The immunotoxicity of implanted nanostructured titanium is a paramount issue for vascular, dental and orthopedic applications. However, it has been unclear whether implanted surface nanostructures can inhibit or aggrevate inflammatory responses. Herein, macrophage activation, as evidence of migration, on transparent flat and nanostructured titanium correlated with pro-inflammatory protein synthesis and cytokine release. Through the real-time monitoring of initial cytoskeleton variations, this study identified that macrophage movement was restricted on nanostructured titanium compared to flat titanium surfaces. Furthermore, nanostructured titanium elicited secretion of fewer pro-inflammatory enzyme molecules and cytokines, as well as reduced nitric oxide production. All results collectively indicated that initial macrophage activation can be mitigated by nanoscale surface topography alone, without modification of surface chemistry or stiffness.

The magnetic and structural properties of Fe ion-implanted GaN was investigated by various measurements. XRD results did not show any peaks associated with second phase formation. The magnetization curve at 5 K showed ferromagnetic behavior for 900 °C-annealed sample. In zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements, the irreversibility and a cusp-like behavior of the ZFC curve were observed for 900 °C-annealed sample. These behaviors are typically observed in superparamagnetic or spin glass phase. While the temperature dependence magnetization of 800 °C-annealed sample showed non-Brillouin-like curve and it is not exhibited ferromagnetic hysteresis at 5 K. In XPS measurement, the coexistence of metallic Fe (Fe 0 ) and Fe–N bond (Fe 2+ and Fe 3+ ) for Fe 2p core level spectra is observed in as-implanted sample. But 700–900 °C-annealed samples showed only Fe–N bond (Fe 2+ and Fe 3+ ) spectra. For Ga 3d core level spectra only Ga–N bonds showed for as implanted with 700–900 °C-annealed samples. From XPS results, it could be explained that magnetic property of our films originated from FeN structures.

Luminescent silicon oxides containing radiative centers were obtained by using two different techniques. Silicon rich silicon oxides (SRSOs) were fabricated by rf magnetron sputter deposition and Ge-implanted SiO2 films were fabricated by ion implantation following the thermal oxidation of Si. Blue and violet photoluminescence were observed from the SRSO and the Ge-implanted SiO2, respectively. However, the electroluminescence (EL) spectra from both oxides exhibited red and near-infrared luminescence bands. Strong EL was observed only under reverse bias conditions on metal-luminescent oxide–semiconductor structures. The EL intensity and peak position were varied with applied voltages. According to the EL and current–voltage measurements, it is concluded that the possible EL mechanism is the impact ionization of ground state electrons in the radiative centers.

The effect of ion irradiation on the formation of luminescent Si nanocrystals from silicon-rich silicon oxide (SRSO) films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (PECVD) whose Si content ranged from 33 to 50 at. % is investigated. As-deposited SRSO films contained a high density of irregular-shaped Si nanocrystals. Irradiating these films with 380 keV Si at room temperature to a dose of 5.7×1015 cm−2 prior to anneal at 1000 °C is found to increase the luminescence intensity due to Si nanocrystals over the films. Based on the x-ray photoemission spectra and the dependence of the luminescence intensity on the irradiating ion dose, anneal time, and the silicon content of the film, we propose the destruction of pre-existing Si clusters by ion irradiation to be an important factor responsible for the observed enhancement of luminescence, and suggest that preanneal irradiation may be a viable method to control the formation of luminescent Si nanocrystals in PECVD-dep...

SiO x layers were fabricated by thermal evaporation of SiO powders onto p-type Si(100) substrates at 200°C to investigate the electrical and light-emitting properties of the layers. After deposition, Ni ions of 70 keV were also implanted into SiO x layers at room temperature. Then both of the as-deposited and as-implanted samples were annealed in N 2 ambient for 2 h at 500°C. Violet photoluminescence (PL) due to radiative defects was observed from all the SiO x samples but annealed ones showed more intense PL than unannealed samples. Red electroluminescence (EL) was obtained from the SiO, in metal-insulator-semiconductor (MIS) structures and the annealed SiO x layers also exhibit more intense EL than unannealed layers. Particularly, the SiO x annealed after Ni-implantation showed the most intense EL which may be caused by highly concentrated radiative defects in the implanted SiO x .

The ZnO/Si photodiodes have been fabricated depositing n-ZnO films on n- and p-Si by rf sputtering method. All the n-ZnO/p-Si diodes show strong rectifying behavior characterized by the current–voltage ( I – V ) measurement under a dark condition while the n-ZnO/n-Si diodes showed weak rectifying behaviors. Photoelectric effects have been exhibited under an illuminated condition using a red light of 670 nm. High photocurrent or responsivities are obtained under a reverse bias when the crystalline quality of n-ZnO film is good enough to transmit the light into p-Si.

We show that blue-CL ( λ = 430 nm ) can be induced in SrTiO3 single crystal at room temperature by irradiating it with 60 KeV carbon ion (C−) beam. An infrared CL-emission ( λ = 770 nm ) is induced simultaneously. Transmission electron microscopy (TEM) measurement exhibits an 200 nm thick surface layer formed by the C− irradiation. We show that the emitting region can be patterned into any desired shape by fabricating the STO surface using Pt-based micro-lithography technique.

We have irradiated SrTiO3 single crystal with 3 MeV-proton (H+) beam and found that blue ( λ = 420 nm ) -, green λ = 500 nm ) - and infrared ( λ = 800 nm ) - frequency photoluminescence (PL) are induced simultaneously at room temperature. TEM and EELS analyses show that an oxygen-deficient amorphous layer is formed at the crystal surface by the proton irradiation. Possible origin of the PL-effect is discussed.

ZnO thin films were epitaxially grown on α-Al2O3 (0001) single-crystal substrates by rf magnetron sputtering. The films were grown at substrate temperatures of 550–600 °C for 1 h at a rf power of 60–120 W and Ar/O2 ratios of 1–4. The crystalline structure of the ZnO films was analyzed by four-circle x-ray diffraction (XRD) and Rutherford backscattering (RBS)/channeling. For the ZnO films deposited at 550 °C, the full width at half maximum (FWHM) of the XRD θ-rocking curve of the ZnO (0002) plane was found to be increased from 0.16° to 0.3° as the rf power was increased from 80 to 120 W. The in-plane epitaxial relationship of the ZnO film on α-Al2O3 (0001) substrates was found to be ZnO [1010]∥α-Al2O3[1120], indicating a 30° rotation of the ZnO unit cell with respect to the α-Al2O3 (0001) substrate. For the specimen grown at 600 °C, the FWHM of the XRD θ-rocking curve was 0.13°. In RBS/channeling studies, the films, which were deposited at 600 °C and 120 W, showed good crystallinity, with a channeling yi...

Si ions were implanted into 100-nm-thick SiO2 layer thermally grown on crystalline Si at an energy of 55 keV with various doses ranging from 1×1014 to 1×1017 Si/cm2 at room temperature. Si ions go through the interface between SiO2 layer and Si substrate generating defects in SiO2 layer and Si substrate as well. Defect-related phenomena were characterized by photoluminescence (PL) and electron spin resonance (ESR) measurements. The PL experiment shows that there exists a dose window for a maximum intensity of luminescence related to radiative defects, while the ESR exhibits that nonradiative defects change from E′ centers to Pb centers as the dose increases. It is considered that the intensity is controlled by the density ratio of radiative to nonradiative defects induced by ion implantation.

Boron ion implantation for edge termination of Au/n-Si Schottky diode has been studied to enhance the breakdown voltages of the diodes. Ion energies of 30 and 50 keV were adopted to achieve edge-terminated Schottky diodes. Four doses of 1×10 13 , 1×10 14 , 1×10 15 and 1×10 16 B cm −2 were used for each energy. The Schottky diodes with edge termination show much higher breakdown voltages than the diodes without edge termination if the ion dose is controlled. For instance the diodes treated with low doses achieve high breakdown voltages while the diodes with high doses of 1×10 15 and 1×10 16 B cm −2 easily fail at low voltages showing early breakdown and high current leakage. According to the results from current–voltage ( I – V ), the current leakage is reasoned to result from deep level defects introduced by B ion implantation and the leakage at a reverse bias of −40 V is maintained low up to an elevated temperature of 160°C.

B and Si ion implantation for edge termination of Au Schottky diodes have been studied to enhance the breakdown voltages of the diodes. B ions of 30 keV were implanted with three doses of 1×10 13 , 1×10 14 , and 1×10 15 B cm −2 to achieve edge-terminated Schottky diodes. For Si implantation, the energy of 70 keV was used with the same doses. Au Schottky diode implanted with a dose of 1×10 13 B cm −2 shows the best results of the edge termination: a reverse leakage of about 1.5×10 −3 A cm −2 at the breakdown voltage, 386 V. Unimplanted Schottky diode shows only 216 V at the breakdown event. Si implantation and high dose B implantation result in early breakdown and high current leakage compared to the low dose B implantation. It is concluded that the early breakdown and the high leakage are closely related to the density of ion-beam-induced defects near the end-of-range (EOR) region.

Ge ions of 100 keV were implanted into a 120-nm thick SiO 2 layer at room temperature (RT), 300, and 500°C. The employed doses of Ge ion were 5×10 15 , 1×10 16 , 5×10 16 , and 1×10 17 cm −2 . Maximum intensity of sharp violet photoluminescence (PL) from the sample implanted at room temperature with a dose of 1×10 16 cm −2 is observed after the sample has been annealed at 500°C for 2 h. Broad orange luminescence is also shown in hot-implanted samples besides the violet. Both are known as defect-related luminescences. As observed by current-voltage (I–V) characteristics, the defect-related samples exhibit large leakage currents with electoluminescence (EL) at only reverse bias region while a nanocrystal-related sample obtained by an annealing at 1100°C for 4 h shows the leakages at both the reverse and the forward region. The carrier-transport and EL mechanisms are explained from the PL and I–V results.

Photoluminescence (PL) from the Si ion irradiated SiO2/Si/SiO2 layers on Si substrate at room temperature and elevated substrate temperatures has been studied to elucidate the luminescence origins. The irradiation of Si ions into SiO2/Si/SiO2 layers instead of SiO2 films was performed to improve the PL intensity by increasing the number of proper-sized Si nanocrystals. Before annealing at high temperature, a luminescence band around 450 nm is observed. This luminescence band was found to originate from the diamagnetic defect known as B2 band generated by Si ion irradiation. The intensity of this band increases when ion irradiation is carried out at high substrate temperature. After annealing at high temperature, the PL peaks originating from the B2 band disappear and a new PL peak appears around 700 nm. This luminescence band is associated with ∼5-nm sized Si nanocrystals. Also it can be found that the PL peak intensity around 700 nm is significantly increased with the high substrate temperature during ion irradiation. Therefore, it is concluded that ion irradiation into SiO2/Si/SiO2 layers is more effective than ion implantation into SiO2 films to obtain an intensive PL peak originating from Si nanocrystals.

Visible photoluminescence from silicon nanocrystals embedded in SiO2 matrix by ion beam mixing was investigated. Photoluminescence spectra of ion beam mixed SiO2/Si/SiO2 films excited by an Ar-laser (457.9 nm) showed more intense luminescence with a peak centered at 720 nm than that prepared by the conventional ion implantation method. The formation of nanocrystals in SiO2 matrix was confirmed by cross-sectional high resolution transmission electron microscopy. The red luminescence is attributed to the silicon nanocrystals produced by ion beam mixing.

Cu thin film was deposited by a self-ion assisted beam source (SIAB) and the assessment of the Cu films was given. Some characteristics of the source and the experimental procedure are described at various conditions such as total power, ionization efficiency, and ion current vs. deposition rate. The dependence of crystalline structure, impurity concentration, and resistivity of the Cu films deposited by SIAB on acceleration voltage are discussed. q 1999 Elsevier Science S.A. All rights reserved.

We report on the fabrication of a photo-detector and a photo-inverter adopting ZnO thin-film transistors (TFTs) that have been electrically isolated by implanting B ions onto peripheral ZnO area around active ZnO channel. Our isolated ZnO-TFT exhibited a fine mobility of 0.8 cm2/(Vs) and on/off current ratio of ~104. Since the device also showed quite a high threshold voltage of 21 V, it was effective to be a photo-detector under a zero gate bias. When our photo-devices were composed of a ZnO-TFT and a 100 MΩ resistor, a minimum response time of ~5 ms under 364 nm ultraviolet light was achieved, thereby dynamically showing photo-inverting and detecting behaviors.

The structural and optical properties of Co ion-implanted GaN were investigated by various measurements. HRXRD, TEM, and SADP results did not show any peaks associated with second phase formation. XPS depth measurements showed the metallic Co 2p core levels for 700– 900 ∘ C annealed-samples. From XPS results, it could be explained that magnetic property of our films originated from Co or CoGa magnetic clusters. The PL spectra obtained at 10 K display a clear intensity modulation, indicating that the optical interference effect occurs in the layers.

Silicon nanocrystals have been synthesized in SiO 2 matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO 2 films grown on crystalline Si at energies of 30–55 keV, and with doses of 5×10 15 , 3×10 16 , and 1×10 17 cm −2 . Implanted samples were subsequently annealed in an N 2 ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×10 17 cm −2 at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO 2 sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a low dose of 5×10 15 cm −2 . It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO 2 .

Ge ions were implanted at 100 keV with 3×1016 cm−2 into a 300 nm thick SiO2 layer on Si. Visible photoluminescence (PL) around 2.1 eV from an as-implanted sample is observed, and faded out by subsequent annealing at 900°C for 2 h. However, PL shows up again after annealing above 900°C at the same peak position. Compared with the as-implanted sample, significant increase of Ge–Ge bonds is measured in X-ray photoelectron spectroscopy, and the formation of Ge nanocrystals with a diameter of 5 nm are observed in transmission electron microscopy from the sample annealed at 1100°C. We conclude that the PL peak from the sample annealed above 900°C is caused by the quantum confinement effects from Ge nanocrystals, while the luminescence from the as-implanted sample is due to some radiative defects formed by Ge implantation.

Crystallographic features of the heteroepitaxially grown yttrium oxide films on Si (1 0 0) and Si (1 1 1) substrates by ultra-high vacuum ionized cluster beam (UHV-ICB) were investigated by non-Rutherford backscattering spectrometry/channeling. The heteroepitaxially grown Y2O3 films with 1080 A thick on Si (1 0 0) and Si (1 1 1) were completely stoichiometric with the composition ratio of Y/O=1/1.5 regardless of substrates. Channeling minimum yields of Y2O3 films on Si (1 0 0) and Si (1 1 1) are 0.39 and 0.10, respectively, which were much smaller values than the minimum values (>0.8) of Y2O3 films on Si substrates deposited by other methods. The results of non-Rutherford backscattering spectrometry/channeling show that the oxygen atoms in heteroepitaxially grown Y2O3 on Si (1 1 1) substrates have reasonable crystallinity, but those on Si (1 0 0) substrates are displaced from the regular sub-lattice sites.

The heteroepitaxially grown yttrium oxide layer by an ionized cluster beam (ICB) on a Si(100) substrate was investigated by Rutherford backscattering spectrometry (RBS)/channeling. The channeling minimum value (χmin) of the Y2O3 layer on Si(100) is 0.28, and this is the smallest value among those reported. From the channeling polar plots, it is found that Y2O3 film grown on Si(100) oriented with (110) direction and has a double domain structure. The 〈110〉 axis of Y2O3 layer is exactly parallel to the (100) axis of the Si substrate. It is also observed that the interface region of Y2O3 film has more crystalline defects than the surface region.

A GaN epilayer was grown on Al/sub 2/O/sub 3/ substrate by metal-organic chemical vapor deposition, and Co/sup -/ ions with a dose of 3/spl times/10/sup 16/ cm/sup -2/ were implanted into GaN at 350/spl deg/C. The implanted samples were postannealed at 700/spl deg/C-900/spl deg/C to recrystallize the samples and to remove implantation damage. We have investigated the magnetic and structural properties of Co ion-implanted GaN by using X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, and X-ray photoelectron spectroscopy (XPS). XRD results did not show any peaks associated with the second phase formation, and only the diffraction from the GaN layer and substrate structure were observed. The temperature dependence of magnetization taken in zero-field-cooling and field-cooling conditions showed the features of superparamagnetic system in films annealed at 700/spl deg/C-900/spl deg/C. The magnetization curves at 5 K for samples annealed at 700/spl deg/C-900/spl deg/C exhibits ferromagnetic hysteresis loops, and the highest residual magnetization (M/sub R/) and coercivity (H/sub c/) of M/sub R/=1.5/spl times/10/sup -4/ emu/g and H/sub c/=107 Oe were found in the 800/spl deg/C annealed sample. XPS measurement showed the metallic Co 2p core levels and the metallic valence band spectra for as-implanted and 700/spl deg/C-900/spl deg/C annealed samples. From these, it could be explained that the magnetic property of our films originated from Co and CoGa magnetic clusters.

We have studied the spin-reorientation transition of Cu/Ni/Cu (001) system by measuring the strain, coercive field, and magnetic anisotropy of epitaxial Cu/Ni/Cu (001) films. We found that the critical thickness (tc) of Ni for the coherent growth of Ni on Cu is below 25 A and does not occur at the peak in the effective magnetic anisotropy constant (Keff) versus 1/t curve, where t is the Ni thickness. The 60-A Ni film, which is highly strained and shows out-of-plane magnetization, has been irradiated by 1-MeV C ions. After irradiation, the magnetization lies in the plane and the strain in the Ni film is almost released. This shows the close relationship between strain and out-of-plane magnetization in this system.

Subnano, nano and sub-micron surface features can selectively activate integrin receptors and induce osteoblast differentiation of bone marrow mesenchymal stem cells. Although it is widely accepted that nanoscale titanium surface roughness may promote differentiation of various osteoblast lineages, there has been no clear report on the threshold dimension of surface features and the optimized dimensions of surface features for triggering integrin activation and stem cell differentiation. This study systematically controlled titanium surface features from the sub-nano to sub-micron scales and investigated the corresponding effects on stem cell responses, such as integrin activation, cyclins, key transcriptional genes of osteoblast differentiation and osteoblastic phenotype genes. Surface features with sub-nano surface dimensions were insufficient to increase integrin activation compared to pure nanoscale titanium surface features. Although both pure nanoscale and nano-submicron hybrid scales of titanium surface features were sufficient for activating integrin-ligand proteins interactions through the α integrin subunits, only nano-submicron hybrid titanium surface features significantly accelerated subsequent osteoblast differentiation of primary mouse bone marrow stromal cells after 2 weeks. In addition, live cell analysis of human bone marrow mesenchymal stem cells on transparent titanium demonstrated rapid cytoskeletal re-organization on the nanoscale surface features, which ultimately induced higher expression of osteoblast phenotype genes after 3 weeks.