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We have investigated the structural and magnetic properties of (Zn,Fe)Te:N thin films grown under Zn-rich condition with Fe composition fixed at 1.4% and N concentrations varying in the range [N] = 1.8 × 1018–5.1 × 1019 cm−3. Structural analysis by x-ray diffraction (XRD) detects some additional extrinsic diffraction peaks possibly from Fe-N compounds in the N-doped film with [N] = 5.1 × 1019 cm−3 only. Accordingly, x-ray absorption fine structure (XAFS) analysis reveals the shifting of Fe atoms from substitutional position for N-doped films with high N concentrations, [N] ≥ 1.8 × 1019 cm−3, whereas N-doped films with intermediate N concentrations [N] ≤ 4.3 × 1018 cm−3 are composed of pure diluted phase with substitutional Fe atoms in the valence state deviating from Fe2+. Magnetization measurement using SQUID confirms drastic change of magnetic properties; the linear dependence of magnetization on magnetic field, typical of van Vleck-type paramagnetism in the film without N-doping changes into room temperature ferromagnetic behaviors with hysteretic magnetization curves for N-doped films. The observed weak room temperature ferromagnetic behavior of the N-doped films with [N] ≤ 4.3 × 1018 cm−3 may reflect the deviation of substitutional Fe valence state from Fe2+ to Fe2+/3+ mixed states. On the other hand, the robust room temperature ferromagnetic behavior exhibited by N-doped films with [N] ≥ 1.8 × 1019 cm−3 may originate from precipitates of Fe-N compounds with Fe being in Fe2+/3+ or other valence state.

We study a new diluted magnetic semiconductor system based on the spin of the ionized acceptor Cr$^+$. We show that the negatively charged Cr$^+$ ion, an excited state of the Cr in II-VI semiconductor, can be stable when inserted in a CdTe quantum dot (QD). The Cr$^+$ attracts a heavy-hole in the QD and form a stable hole-Cr$^+$ complex. Optical probing of this system reveals a ferromagnetic coupling between heavy-holes and Cr$^+$ spins. At low temperature, the thermalization on the ground state of the hole-Cr$^+$ system with parallel spins prevents the optical recombination of the excess electron on the 3$d$ shell of the atom. We study the dynamics of the nano-magnet formed by the hole-Cr$^+$ exchange interaction. The ferromagnetic ground states with M$_z$=$\pm$4 can be controlled by resonant optical pumping and a spin relaxation time in the 20 $\mu$s range is obtained at T=4.2 K. This spin memory at zero magnetic field is limited by the interaction with phonons.

We have investigated the effect of co-doping of nitrogen (N) acceptor impurity on the structural and magnetic properties of (Zn,Fe)Te. We grew (Zn,Fe)Te:N thin films by molecular beam epitaxy (MBE) with a fixed Fe composition 1.5% and varied N concentrations in the range of [N] = 8 × 1017– 4 × 1019 cm−3. Structural analyses by using x-ray absorption fine structure (XAFS) and transmission electron microscope (TEM) reveal that N-doped films with intermediate N concentration [N] = 8 × 1017– 7 × 1018 cm−3 are mainly composed of pure diluted phase with substitutional Fe atoms in the valence state deviated from Fe2+, while Fe is dominantly incorporated in an Fe-N compound at the highest N concentration [N] = 4 × 1019 cm−3. Accordingly, the magnetization measurement using SQUID confirms a drastic change of magnetic properties; a linear dependence of magnetization of magnetic field (M-H), typical of van-Vleck paramagnetism in the film without N-doping changes into ferromagnetic behaviors with a hysteretic M-H curves at the intermediate N concentrations and comes back to a linear M-H dependence at the highest N concentration. The ferromagnetism in the intermediate [N] range may reflect a deviation of the valence state of the substitutional Fe from Fe2+, while the linear M-H at the highest [N] would be attributed to precipitates of an Fe-N compound.

Hydroxyapatite (HA) [Ca10 (PO4)6 (OH)2] has a high degree of chemical similarity with the mineral composition of animal bone. Hydroxyapatite fiber scaffold (HAF) is a biological material with a highly interconnected porous structure. We aimed to study the physical and biological characteristics of HAF and compare the osteogenic effects of HAF, natural osteogenic materials (NOM), and carbonate apatite (CO3Ap-DP) in the parietal defects of a rabbit's skull. X-ray analysis and histological assessment showed that HAF followed a trend of early initial osteogenesis and bone trabecular structure formation, especially at the cortical bone portion.Compared to the other two materials, HAF was more absorptive. Results indicated that HAF had the same osteoconductive and new bone formation properties as NOM and CO3Ap-DP. These findings will provide options for future material development and novel protocols for use in surgeries, ultimately leading to better patient outcomes.

This study evaluated the effects of two types of superstructures (splinted crown and non-splinted crown) on four vibration characteristics (natural frequency, damping ratio (DAR), vectors in antiphase, maximum displacement (MDP)) by using modal analysis. These structures were fabricated on three implants placed in the mandibular free-end defect model. After placing three implants on a mandibular distal extension model with missing teeth, the three-unit splinted and non-splinted crowns were designed on the CAD software. Subsequently, the zirconia disc was milled using a milling machine to produce the superstructures (n = 5). After establishing four measurement points on each crown of the prostheses, a vibration was applied to the mandible model with an impact hammer, and the transfer function of each measurement point was identified. Using the modal analysis software, the natural frequency and damping ratios were calculated from the transfer function, modal shapes at each natural frequency were observed, and maximum displacement that takes into account the lateral force during mastication was simulated. The t-test was performed for each of the averaged values of natural frequency, maximum displacement, and damping ratio (p 0.05). Mann-Whitney U test was performed on the average of the number of vectors in antiphase (p 0.05). The mean natural frequency was significantly higher in the splinted crown (758.2 ± 2.8 Hz) than that in the non-splinted crown (752.8 ± 3.7 Hz) (P = 0.047). The mean damping ratio was not significantly different for the splinted (3.3 ± 0.2%) and non-splinted crowns (3.2 ± 0.3%) (P = 0.535). The average number of vectors in antiphase was significantly smaller in the non-splinted crown (4.4 ± 0.9) than in the splinted crown (10 ± 2.5) (P = 0.008). The mean value of the maximum displacement was significantly smaller in the splinted crown (6.7 ± 1.1 μm) than that in the non-splinted crown (7.3 ± 0.6 μm) (P = 0.048). Within the limitations of this study, the vibration characteristics of the superstructures differed between designs with splinted and non-splinted crowns. Crown splinting increased the rigidity and natural frequency and decreased the MDP. However, the higher number of vectors in antiphase indicated more twists in the superstructures during vibration. The non-splinted crowns showed a lower natural frequency and a greater maximum displacement; however, they comprised fewer vectors in antiphase, indicating that the twist during vibration was less than that observed with the splinted crowns. Thus, our results suggest that crown splinting reduces the deformation of the superstructure, implants, and the surrounding tissues in comparison to the deformation observed when no splinting is performed.

International audience; We demonstrate radio-frequency tuning of the energy of individual CdTe/ZnTe quantum dots (QDs) by Surface Acoustic Waves (SAWs). Despite the very weak piezoelectric coefficient of ZnTe, SAW in the GHz range can be launched on a ZnTe surface using interdigitated transducers deposited on a c-axis oriented ZnO layer grown on ZnTe containing CdTe QDs. The photoluminescence (PL) of individual QDs is used as a nanometer-scale sensor of the acoustic strain field. The energy of QDs is modulated by SAW in the GHz range and leads to characteristic broadening of time-integrated PL spectra. The dynamic modulation of the QD PL energy can also be detected in the time domain using phase-locked time domain spectroscopy. This technique is in particular used for monitoring complex local acoustic fields resulting from the superposition of two or more SAW pulses in a cavity. Under magnetic field, the dynamic spectral tuning of a single QD by SAW can be used to generate single photons with alternating circular polarization controlled in the GHz range.

Improved osseointegration of dental implants is imperative in clinic. Effect of doxycycline on promoting bone formation after implant placement was expected due to its inhibitory properties on inflammation and osteoclastogenesis. To evaluate new bone formation on the hydroxyapatite (HA)-coated implant surface, which was treated with doxycycline, in comparison with the untreated HA surface, half of the HA-coated implants were soaked in doxycycline solution (DOX group) whereas the other HA-coated implants were untreated (HA group). Eight weeks after extracting the maxillary first molars of 4-week-old male mice, the implants of both groups were placed at the extracted site. 4 and 8 weeks after surgery, the samples were evaluated radiologically and histomorphometrically. Bone-implant contact of DOX group was statistically higher than the one of HA group at 4 and 8 weeks. New bone area between the threads of the implants also statistically increased at 8 weeks in DOX group compared to HA group.

We have performed the structural and magnetic characterization of Zn 1- x Fe x Te thin films grown by molecular beam epitaxy (MBE). Thin films of Zn 1- x Fe x Te with Fe composition up to x ~0.06 were grown by MBE with the supply of excess Zn flux over Te flux. From the structural analyses by x-ray absorption fine structure (XAFS), it is revealed that the grown film with a low Fe content x =0.015 is composed of pure diluted phase with substitutional Fe atoms while the precipitation of an extrinsic phase is suggested at higher Fe contents x =0.03~0.06. The magnetization measurement reveals a clear distinction in the magnetic-field ( M - H ) and temperature ( M - T ) dependences between the low and high Fe contents; a hysteretic M - H dependence and the blocking phenomenon in the M - T dependence at the higher Fe content. These behaviors are attributed to the superparamagnetism, originating from the formation of an extrinsic precipitate.

International audience; We study the emission of individual quantum dots in CdTe/ZnTe samples doped with a low concentration of Cr. In addition to dots with a photoluminescence (PL) split by the exchange interaction with a magnetic Cr atom, we observe another type of dots with a complex PL structure composed of a minimum of six lines on the exciton and biexciton and three lines on the charged excitons. In these dots, the linear polarization dependence and the magnetic field dependence of the PL behave like three similar quantum dots emitting at slightly different energies. Cross-correlation intensity measurements show that these emission lines are not independent but exchange intensities in a time scale of a few hundred nanoseconds depending on the optical excitation power. We attribute this PL structure to charge fluctuations of a Cr atom located in the vicinity the CdTe dots in the ZnTe barrier. We present a model which confirms that the presence of a single charge fluctuating between-e (Cr +), 0 (Cr 2+) and +e (Cr 3+) and located a few nm away from the dot explains the observation of three emission energies. We finally show that the interaction between the confined carriers and the nearby fluctuating localized charge can be modified by an applied static electric field which modulates the splitting of the emission lines.

Magneto-transport properties of (111)-oriented single-crystal thin films of SnTe were investigated. SnTe (111) thin films were epitaxially grown on a BaF2 substrate by molecular beam epitaxy. By optimizing the growth conditions and the thickness of the films, the bulk carrier density could be reduced, making it possible to detect the surface transport. In the magneto-conductance (MC) measurement, a cusp-like feature around zero magnetic field was observed, which is attributed to the weak-antilocalization effect of the transport in the topological surface state. Detailed analysis of this negative MC reveals a reduced number of transport channels contributing to the surface transport, suggesting a strong coupling between Dirac valleys on the SnTe (111) surface, as a characteristic feature of the transport in the multivalley structure of TCI., Comment: 24 pages, 7 figures

A detailed analysis of the photoluminescence (PL) intensity distribution in singly Cr-doped CdTe/ZnTe quantum dots (QDs) is performed. First of all, we demonstrate that hole-Cr flip-flops induced by an interplay of the hole-Cr exchange interaction and the coupling with acoustic phonons are the main source of spin relaxation within the exciton-Cr complex. This spin flip mechanism appears in the excitation power dependence of the PL of the exciton as well as in the intensity distribution of the resonant PL. The resonant optical pumping of the Cr spin which was recently demonstrated can also be explained by these hole-Cr flip-flops. Despite the fast exciton-Cr spin dynamics, an analysis of the PL intensity under magnetic field shows that the hole-Cr exchange interaction in CdTe/ZnTe QDs is antiferromagnetic. In addition to the Cr spin dynamics induced by the interaction with carriers' spin, we finally demonstrate using time resolved optical pumping measurements that a Cr spin interacts with nonequilibrium acoustic phonons generated during the optical excitation inside or near the QD.

We investigated the structural and magnetic properties of Cr 1 −δ Te thin films grown on CdTe(001) layers by molecular beam epitaxy (MBE) with systematic variations of the ratio between Cr and Te fluxes and the substrate temperature T s during the growth. Cr 1 −δ Te of the hexagonal structure (hex-Cr 1 −δ Te) was always formed irrespective of the growth conditions, but the growth orientation was different depending on the Cr/Te flux ratio and T s . Hex-Cr 1 −δ Te was grown in the [0001] axis in the range of small Cr/Te ratios and high T s while it was also grown in the direction normal to the (1–102) plane at larger Cr/Te ratios or lower T s . Hex-Cr 1 −δ Te films grown in the both orientations show ferromagnetism, but they exhibit a clear contrast in the field dependence of perpendicular magnetization at 2 K; a square hysteretic loop in the film grown in the [0001] axis versus a round-shape loop in the film grown in the direction normal to the (1–102) plane. Moreover, the films grown in the [0001] axis at the smallest Cr/Te ratio show variations of ferromagnetic properties with Curie temperature ( T c ) and the coercivity ( H c ) varying according to the value of T s .

Thin films of aluminum nitride (AlN) fabricated by reactive deposition were characterized in order to examine the electrical insulation properties suitable for a gate insulator. For a series of AlN films deposited with a variation of the amount of Al flux at a fixed N flux, compositional and chemical analyses were performed using X-ray photoelectron spectroscopy (XPS) and elastic recoil detection analysis (ERDA). Combined with the result of current-voltage (I-V) measurement, it is found that the insulation properties are correlated with the compositional ratio between Al and N estimated by the ERDA measurement; a good electrical insulation with a minimal leak current of the order of 10- 9 A/cm2 at a high electric field 1 MV/cm is achieved in the film of nearly stoichiometric compositional ratio of Al/N, in which the dominance of the Al-N bonding state is confirmed in the XPS measurement. On the other hand, the incorporation of oxygen, probably caused by the surface oxidization due to the exposure to the air, has little effect on the electrical properties.

A detailed knowledge of the atomic structure of magnetic semiconductors is crucial to understanding their electronic and magnetic properties, which could enable spintronic applications. Energy-dispersive X-ray spectrometry (EDX) in the scanning transmission electron microscope and atom probe tomography (APT) experiments reveal the formation of Cr-rich regions in Cd1−xCrxTe layers grown by molecular beam epitaxy. These Cr-rich regions occur on a length scale of 6–10 nm at a nominal Cr composition of x=0.034 and evolve toward an ellipsoidal shape oriented along directions at a composition of x=0.083. Statistical analysis of the APT reconstructed volume reveals that the Cr aggregation increases with the average Cr composition. The correlation with the magnetic properties of such (Cd,Cr)Te layers is discussed within the framework of strongly inhomogeneous materials. Finally, difficulties in accurately quantifying the Cr distribution in the CdTe matrix on an atomic scale by EDX and APT are discussed.

We report the electric-field modulation of magnetism of a hexagonal Cr1–δTe thin film. A gate voltage VG is ap-plied in the field effect capacitor (FEC) structure consisting of electric double-layer capacitor (EDLC) of an ion liquid and a 2nm-thick Cr1–δTe layer grown by molecular beam epitaxy (MBE) and the magnetization of the layer is directly measured using a superconducting quantum interference device (SQUID) magnetometer in the both configurations with magnetic fields perpendicular or parallel to the film plane. As a result, we observe a clear change in the magnetization vs. magnetic field (M-H) curves by applying VG at a low temperature of 15 K in the perpendicular field configuration; the magnetization increases and the coercivity decreases by applying either positive or negative gate voltage. When the temperature is increased up to 160K, slightly lower than the Curie temperature, or the magnetization was measured in the in-plane field configuration, the magnetization increases similarly by applying either positive or negative gate voltage, but the amount of the increase becomes much smaller. A possible mechanism of the electric-field modulation is discussed in relation to the Cr vacancies in the Cr1–δTe layer. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate the structural and magnetic properties of Zn1–xFex Te with an aim of discerning the intrinsic magnetism of this ternary compounds. Thin films of Zn1–xFex Te with a high Fe composition up to x = 0.2 were grown by molecular beam epitaxy (MBE) in the excess of Te flux against Zn flux. The structural analyses using X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) measurements reveal that crystals of the pure diluted phase are grown at low Fe compositions less than x = 0.02, while precipitates of extrinsic phases start to be formed at higher Fe compositions. In the magnetization measurements, the films of x ≤ 0.02, which were confirmed to be of the pure diluted phase, exhibit paramagnetic behaviors down to 2 K. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We fabricated MnBi2Se4/(n − 1) quintuple layer (QL) Bi2Se3 magnetic topological heterostructures (n = 1–6) and measured the Dirac cone dispersion with angle-resolved photoemission spectroscopy. We observed a clear gap opening for films with n = 2–6 and the gap size decreased as the film thickness increased. From magnetization measurements using SQUID, all the heterostructures showed hysteresis loops at 4 K and at room temperature, confirming that MnBi2Se4 is a room temperature van der Waals ferromagnet. We were able to distinguish the contribution of the hybridization and magnetic effects on the observed Dirac-cone gap directly using a four-band model and its implications on the behavior of the expected quantum anomalous Hall effect is discussed.

Purpose: Low intensity pulsed ultrasound stimulation (LIPUS) has been clinically applied to promote bone fracture healing in the orthopedic field. Thus, it is likely that LIPUS also stimulates bone regeneration in bone defects in the cranial-maxillofacial area. However, this has not been clearly proved. Furthermore, optimal time point and period of the application after the surgery has not been reported. The purpose of the present study was to evaluate the effect of LIPUS on bone regeneration in the rat parietal bone defects especially focusing on time and period of the application. Materials and Methods: Eighteen Wistar rats (14 weeks old) were divided into 6 groups: 5 experimental groups and a control group. Bone defect of 5 mm diameter was prepared on each side of the parietal bone and customized gelatin membranes were placed over the bone defects. LIPUS (160 mW/cm2, 15 min/day) was applied to the defect area with an active transducer externally in the experimental groups according to the schedules of the applications: Group 1 (day 6 - 12), group 2 (day 13 - 19), group 3 (day 20 - 26), group 4 (day 6 - 19) and group 5 (day 6 - 26). All the animals were sacrificed at 28 days. The defects were analyzed with micro CT and then histologically. Results: In Group 1, new bone formation was significantly promoted and the newly-formed bone was thick and matured compared to the one of the control group. In other experimental groups there were tendencies of stimulation of new bone formation; however, they were not statistically significant. Discussion and Conclusion: The present study demonstrated that amount of new bone formation in the bone defect depended on the time and period of LIPUS application. It has been suggested that application of LIPUS at an early healing period, the second week after the surgery, effectively accelerated new bone formation.

We report molecular beam epitaxial growth of a SnTe (111) layer on a CdTe template, fabricated by depositing it on a GaAs (111)A substrate, instead of BaF 2 which has been conventionally used as a substrate. By optimizing temperatures for the growth of both SnTe and CdTe layers and the SnTe growth rate, we could obtain SnTe layers of the single phase grown only in the (111) orientation and of much improved surface morphology from the viewpoint of the extension and the flatness of flat regions, compared to the layers grown on BaF 2 . In this optimal growth condition, we have also achieved a low hole density of the order of 10 17 cm −3 at 4 K, the lowest value ever reported for SnTe thin films without additional doping. In the magnetoresistance measurement on this optimized SnTe layer, we observe characteristic negative magneto-conductance which is attributed to the weak antilocalization effect of the two-dimensional transport in the topological surface state.

A sputtering technique followed by a low temperature hydrothermal treatment has been demonstrated to produce a dense-and-bioactive hydroxyapatite thin film coating. The purpose of the present study was to investigate osteoblast and osteoclast responses to the hydroxyapatite coated plates and titanium plates with similar roughness. Rat bone marrow stromal cells were cultured on these plates to induce osteoblasts. The cells showed a significantly enhanced proliferation on the hydroxyapatite surface, accompanied by increase of osteoblastic phenotypes. The co-cultured osteoclasts exhibited the significantly different cell number and morphology between the hydroxyapatite and the titanium surfaces. A series of osteoclast marker genes were more stimulated on the hydroxyapatite and thirty two percent of the hydroxyapatite surface area could be resorbed by osteoclasts. The thin film sputtered hydroxyapatite could provide a favorable surface for both osteoblast and osteoclast formation and their function, indicating its good osteoconductivity and biodegradability.

Collagen containing bone morphogenetic protein-2 (BMP-2) expression vector, which is called “gene-activated matrix,” promotes bone regeneration when transplanted to the bone defect. We speculated that hydroxyapatite fiber (HF) would be an ideal matrix for “gene-activated matrix” especially for bone regeneration, because it is oseteoconductive and has high affinity to DNA. The purpose of this study is to clarify whether HF containing BMP-2 expression vector induces ectopic bone formation. We prepared HF containing 0, 10, 50, and 100 μg BMP-2 expression vector. Wistar male rats (8 weeks) were used and each rat received two HF implants in the left and right dorsal muscle. The rats were sacrificed 4, 8, and 12 weeks after the operation, and implants were analyzed radiographically by softex, dual-energy X-ray absorptiometry, and they were histologically examined. At 4 weeks, HF containing 50 or 100 μg BMP-2 expression vector showed high bone mineral contents and large radiopaque volume compared to the other implants. At 8 and 12 weeks, HF containing 50 μg BMP-2 expression vector exerted the highest values in the radiographic analyses. Bonelike tissue was histologically observed in HF containing 50 and 100 μg BMP-2 expression vector groups but not detected in the other implants. The present results suggest that HF is potential as a matrix for “gene-activated matrix” for bone tissue engineering. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009

The extensive experimental and computational search for multifunctional materials has resulted in the development of semiconductor and oxide systems, such as (Ga,Mn)N, (Zn,Cr)Te, and HfO2, which exhibit surprisingly stable ferromagnetic signatures despite having a small or nominally zero concentration of magnetic elements. Here, we show that the ferromagnetism of (Zn,Cr)Te, and the associated magnetooptical and magnetotransport functionalities, are dominated by the formation of Cr-rich (Zn,Cr)Te metallic nanocrystals embedded in the Cr-poor (Zn,Cr)Te matrix. Importantly, the formation of these nanocrystals can be controlled by manipulating the charge state of Cr ions during the epitaxy. The findings provide insight into the origin of ferromagnetism in a broad range of semiconductors and oxides, and indicate possible functionalities of these composite systems. Furthermore, they demonstrate a bottom-up method for self-organized nanostructure fabrication that is applicable to any system in which the charge state of a constituent depends on the Fermi-level position in the host semiconductor., Comment: 22 pages, 8 figures (incl. Supplementary Information)

Raman spectroscopy has been used to study the lattice properties of plasma-assisted molecular beam epitaxy grown GaN:Mn layers (0–18% Mn). Raman spectra corresponding to the intrinsic GaN layers demonstrate three Raman active excitations at 144, 570 and 729.2 cm−1, identified as E 2 L , E 2 H and A1(LO) respectively. The Mn-doped GaN layers exhibit additional excitations attributed to defect-activated Raman scattering and Mnm–N (m =1–4) related frequency modes in the vicinity of E 2 H mode. Subsequently, detailed X-ray diffraction measurements have revealed the coexistence of cubic phases in the predominantly hexagonal GaN lattice.

Raman spectroscopy has been used to study the lattice properties of plasma-assisted molecular beam epitaxy grown Ga1−x Mnx N layers (x = 0–12%). Raman spectra corresponding to the intrinsic GaN layers demonstrate three Raman active excitations at 144, 570 and 729 cm−1 identified as E2L, E2H and A1(LO), respectively. The Mn-doped GaN layers exhibit additional excitations attributed to defect-activated Raman scattering (DARS) and Mnx–N related frequency modes in the vicinity of E2H mode. The observed frequencies associated with Mnx–N modes are in fair agreement with the standard theoretical results. Based on line shape fitting analysis, apparent free carrier concentrations in Ga1−x Mnx N layers, involving LO phonon–plasmon coupled (LOPC) mode are found in the range of 1.6 × 1017 to 1.1 × 1018 cm−3. The ferromagnetic character of the layers is discussed in view of the estimated carrier density.

Rutherford backscattering (RBS) and particle-induced X-ray emission (PIXE) experiments were performed on (Ga,Mn)N epilayers and self-organized dots grown by plasma-assisted MBE. The combined channeling RBS and Mn PIXE experiments were performed on Ga 0.949 M 0.051 N epilayer, which was confirmed to be of pure diluted phase by X-ray diffraction (XRD) in our previous study, in order to check the presence of Mn atoms in the interstitial site in wurtzite crystal. The axis scan around and axes and the plane scan around (1010) plane revealed that almost all the Mn atoms were in the substitutional site of wurtzite GaN crystal. For self-organized dots of (Ga,Mn)N grown on AlN by MBE, the PIXE spectra were measured and the Mn composition in the dot layer was estimated from the ratio of emission intensity of Mn and Ga K α lines. At a result, it was found that the Mn composition in the dots was higher by two or three times than that in thick epilayers grown with the addition of the same amount of Mn flux.

The anisotropic magnetic and magneto-transport properties of Zn1–xCoxO thin films were investigated. By pulsed laser deposition (PLD) technique, the (0001) plane (c -plane) or (11-20) plane (a -plane) Zn1–xCoxO layer was deposited on the c -surface or r -surface sapphire substrate, respectively, and magnetization and magnetoresistance (MR) measurements were performed with magnetic fields parallel or perpendicular to the film plane. It was found that the magnitudes of the magnetization and MR were larger when magnetic fields were applied along a - or b -axis than those under magnetic fields along c -axis, irrespective of the growth orientation of the films. The consistency of the anisotropy between magnetization and MR is considered to originate from the anisotropic electronic state of Co d -electrons. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magneto-optical studies of an internal transition of Mn in the diluted magnetic semiconductor (Ga,Mn)N are reported. A strong zero-phonon line (ZPL) is observed at 1.413 eV, followed by weak phonon replicas. The sharpness of the ZPL in very diluted samples allows a precise study of its Zeeman effect in magnetic fields up to 11 T in both Faraday and Voigt configurations. Some consequences concerning the analysis of the Mn3+ (3d4) configuration, the magnetic properties of the Mn system, and the spin–carrier coupling as revealed from magnetic circular dichroism at the bandgap, are briefly discussed.

A set of molecular-beam-epitaxy grown GaN:Mn films with Mn concentration from 0.03 to 5.7% was investigated by Fourier transform infrared absorption at 4 K. All the absorption spectra exhibit well-defined zero phonon lines (ZPL) at 11395 cm −1 (1.41 eV) and 11902 cm −1 (1.48 eV) and a series of phonon replicas at higher energy. The position, linewidth and integrated area of the main absorption features were analyzed versus the manganese concentration. The integrated optical cross section of the main ZPL is of 8.6×10 −16 cm/Mn, that is three orders of magnitude larger than that for Cr in II–VI semiconductors, and the intensity of the phonon-related absorption cross section is of the same order of magnitude as the ZPL. This low electron–phonon coupling suggests a delocalized hole weakly bound to the Mn 2+ ions, similar to Mn in GaAs, in contradiction with the high ionization energy. For Mn-concentration higher than 1% the integrated absorption decreases, attributed to the incorporation of Mn in non-isolated and substitutional sites, or compensated by donor growth defects. Linewidth of the main ZPL increases from 11.6 to 55 cm –1 for Mn-concentration increasing from 0.03% to 5.7%. The analysis of these absorption features indicated a peculiar behaviour of Mn in GaN compared to similar impurities in other semiconductors: it has a low electron–phonon coupling such as the shallow impurity Mn in GaAs, and a high ionization energy such as Cr in II–VI materials.

The magnetic and structural properties of MBE-grown films of Zn1−xCr x Te were investigated. The magnetization versus magnetic field (M–H) measurement of Zn1−xCr x Te (x = 0.01–0.17) showed clear hysteresis loop at low temperatures. The ferromagnetic transition temperature (TC) estimated from the Arrott-plot analysis increased almost linearly with the Cr composition (x) up to 275 K at x = 0.17. However, in the magnetization versus temperature (M–T) measurement, the irreversibility between the zero-field-cooled (ZFC) and field-cooled (FC) processes was observed. This is typically observed in the magnetic random system such as spin-glass or superparamagnetic phase. In the high resolution transmission microscopy (HRTEM) observations, structural defects such as stacking faults and polycrystalline-like structure were observed at high Cr compositions, whereas any apparent precipitates of different phases were not seen in all the range of Cr compositions examined. The correlation of the observed magnetic randomness with the local structural defects was discussed.

Magnetic properties of a novel ferromagnetic semiconductor (Zn, Cr)Te were investigated. Zn1−xCrxTe thin films, both without and with the additional hole doping by nitrogen, were grown by molecular beam epitaxy. In the magnetization measurement on Zn1−xCrxTe without carrier doping, the ferromagnetic behaviors such as a hysteresis loop in the magnetization vs. magnetic field curve were observed. Similar hysteretic behaviors in the field dependence were reproduced in the magnetic circular dichroism measurement. The ferromagnetic transition temperature TC deduced from Arrott plot increased almost linearly with Cr composition with the maximum TC=275 K at a Cr composition of x=0.17. The ferromagnetic behaviors observed in the undoped samples were found to be suppressed upon the p-type doping with nitrogen. These experimental findings are discussed based on the double exchange mechanism and the suppression of ferromagnetism by the hole doping is interpreted as due to the shift of the Fermi level in the Cr 3d level with the acceptor doping.

The influence of epitaxial growth conditions such as C/Si ratio, growth temperature and growth rate on the propagation of basal plane dislocation from a 4H-SiC substrate to the epilayer was studied by reflection X-ray topography. It was observed that the growth temperature has no effect on the propagation of basal plane dislocation. On the contrary, a large number of basal plane dislocations in the substrate tend to propagate as basal plane dislocations into the epilayer under low C/Si ratio condition. A higher growth rate at a constant C/Si ratio also enhances the propagation of basal plane dislocation.

4H-SiC homoepitaxial layers were grown on on-axis (0 0 0 1 ) C-face substrates at an inclination of 0.5° or less by horizontal hot wall chemical vapor deposition. After H 2 etching, the surface morphology of the on-axis (0 0 0 1 ) C-face substrate showed a straight step structure that had the same height as a 4H-SiC lattice constant along the c -axis. Specular surface morphology of a wide area of up to 80% of a 2-in wafer was obtained at a low C/Si ratio of 0.6. It was found that that appearance of basal plane dislocations on the epitaxial layer surface can be prevented by using an on-axis substrate. Ni/4H-SiC Schottky barrier diodes fabricated on the epitaxial layer at 1×10 16 cm −3 showed a high breakdown voltage of up to 1 kV and low leakage current.

Spatial diffusion of excitons in n-type modulation-doped (Cd,Mn)Te/(Cd,Mg)Te single quantum wells (SQWs) was studied through time- and spatially resolved photoluminescence (PL) measurements at 4.2 K under magnetic fields up to 0.5 T . The PL spatial extent exceeded the laser spot in all samples studied here, however, the detailed manners were strongly dependent upon the intrinsic 2D carrier density. We found the PL spatial extent got larger with the increase of magnetic fields in the case of the lower carrier density sample. It is the opposite result to the case of non-magnetic SQW. These phenomena are qualitatively interpreted by considering the competition of mobile neutral exciton (X), localized negatively-charged exciton (X−) and, furthermore, the suppression of a free-exciton-magnetic-polaron formation which is one of the characteristic properties of diluted magnetic semiconductor such as (Cd,Mn)Te.

Mn-doped wurtzite GaN epilayers have been grown by nitrogen plasma-assisted molecular-beam epitaxy. Correlated SIMS, structural and magnetic measurements show that the incorporation of Mn strongly depends on the conditions of the growth. Hysteresis loops which persist at high temperature do not appear to be correlated to the presence of Mn. Samples with up to 2% Mn are purely substitutional Ga1 − xMnxN epilayers, and exhibit paramagnetic properties. At higher Mn contents, precipitates are formed which are identified as GaMn3N clusters by X-ray diffraction and absorption: this induces a decrease of the paramagnetic magnetisation. Samples co-doped with enough Mg exhibit a new feature: a ferromagnetic component is observed up to Tc ~ 175 K, which cannot be related to superparamagnetism of unresolved magnetic precipitates.

Screw dislocation, threading edge dislocation and basal plane dislocation in 4H–SiC substrates and epitaxial layers were observed by X-ray topography using synchrotron radiation. Distribution of basal plane dislocation is markedly different between substrates and epitaxial layers. Basal plane dislocations in the substrate are arc-shaped and show no distribution direction. Conversely, those in the epitaxial layer are straight and directed towards the off-orientation. The propagation of dislocations from the substrate to the epitaxial layer can be directly observed. Threading edge dislocations in the substrate are propagated as threading edge dislocations into the epitaxial layer. Basal plane dislocations in the substrate are mostly deflected to threading edge dislocations, and the rest are propagated as basal plane dislocations in the epitaxial layer.

The present study demonstrates increased early mechanical fixation of titanium implants coated with a new biomimetic apatite surface in a rat model. Male Sprague- Dawley rats received unilateral femoral medullary implants for periods of 1- 4 weeks. The strength of fixation of the implant to the host bone increased more rapidly in the group receiving apatite-treated implants compared with the control group as evidenced by the apatite group's 21-fold greater fixation strength at 1 week (p 0.009), 4-fold greater fixation strength at 2 weeks (p 0.041), and 2-fold greater fixation strength at 4 weeks (p 0.093) compared with the control. Fixation strength was correlated with bone-implant contact as determined from micro computed tomography assessment of the specimens (r 2 0.338, p 0.011 in the control group and r 2 0.543, p 0.001 in the apatite group). Furthermore, for a given amount of bone-implant contact, the fixation strength was higher in the apatite group than in the control group (p 0.011), suggesting that the bone formed a stronger bond to the apatite coating than to the titanium. This difference in bonding strength accounted for the difference in mechanical behavior. © 2004 Wiley Period- icals, Inc. J Biomed Mater Res 70A: 66 -73, 2004

A systematic compositional and structural study of GaN:Mn epilayers grown by molecular beam epitaxy (MBE) was performed, with a special attention to the dependence on the growth conditions. The growth diagram related to the Ga/N flux ratio for GaN was modified by adding Mn flux. In particular, the stable Ga-bilayer coverage on the surface for the Ga-rich condition was reduced in the presence of Mn. The Mn incorporation in the epilayers was found to be strongly dependent on the Ga/N flux ratio. The X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) measurements revealed a clear contrast between the precipitation of a perovskite compound GaMn 3 N at Mn compositions higher than 1.7%, and the single phase of the wurtzite Ga 1-x Mn x N at lower Mn compositions. The single-phase epilayers (x < 1.7%) exhibited intrinsic ferromagnetic behaviors at room temperature.

We use the combination of nonequilibrium phonon and exciton luminescence techniques to study the spin dynamics in diluted magnetic semiconductor structures with (Cd,Mn)Te and (Cd,Mn)Se quantum dots (QDs). We show that the spin–lattice relaxation (SLR) of Mn ions in these structures differs strongly from the SLR in quantum wells. We explain the results by a model where SLR process in structures with QDs is modified by the spin diffusion on Mn ions from the QD to a wetting layer.

The magneto-transport properties of nitrogen-doped p-Zn1−xMnxTe films grown by MBE were studied, with an emphasis on the dependence on the Mn composition and the hole concentration. The Mn composition x and hole concentration p were varied in the range of x = 0.026–0.068 and p = 8.2 × 1018–2.6 × 1019 cm−3. In the measurement of magnetoresistance (MR), a large negative component was observed at low temperatures. In the dependence on the Mn composition, it was found the magnitude of the negative component of MR became larger and survived up to higher temperatures in the sample with a higher Mn composition. The observed negative MR is attributed to the localization of holes due to the magnetic polaron formation. The origin of the dependence on the Mn composition is discussed.

We have studied the structural properties of the phase separation in Zn1−xCrxTe films grown by MBE with a relatively high Cr composition x∼0.2. In the combined analyses using TEM and EELS, it has been revealed that the Cr-aggregated regions are composed of precipitates of the hexagonal structure, which are formed in a particular crystallographic relation with the zinc-blende (ZB) structure of the matrix that the c-plane of the hexagonal structure nearly parallel to the (1 1 1) plane of the ZB structure. In the XRD measurements, the diffraction from the hexagonal precipitates has been detected in the ω-scan. From the measurements on the series of films grown at different temperatures, it has been suggested the hexagonal precipitates were formed in a larger quantity with the increase in growth temperature.

We report the photoluminescence and excitation spectra of CdTe self-assembled quantum dots grown by molecular beam epitaxy in ZnTe. In photoluminescence excitation spectra, multiple longitudinal-op...

Some dental implants are coated with hydroxyapatite (HA), which preferentially binds to bone. Several matrix proteins have an arginine-glycine-aspartic acid (RGD) sequence where cells attach via an integrin receptor. We hypothesized that coating an HA surface with an RGD-containing peptide might enhance the attachment and differentiation of osteoblasts. The HA disks (diameter 34 mm, thickness 1 mm) were treated with a solution (50 mM Tris/HCl and 150 mM NaCl, pH 7.4) containing the peptide EEEEEEEPRGDT, in which the E repetition exerts a high affinity to HA. After washing with phosphate-buffered saline, KUSA/A1 mouse osteoblastic cells were inoculated onto the HA surface and cultured. After 30 min, the number of cells attached to the surface was counted. The DNA content and alkaline phosphatase (ALP) activity were measured after 10 days in culture. Expression of bone matrix proteins was also examined by means of reverse transcriptase-polymerase chain reaction at 7 days; the mineralized area of the culture was also evaluated by staining with Alizarin Red S after 10 days. Treatment with the peptide stimulated cell attachment and increased DNA content and ALP activity. Furthermore, matrix protein expression and mineralized nodule formation were enhanced to a greater extent on the peptide-treated surface than on the nontreated surface. Our results indicate that coating an HA surface with RGD-containing peptide enhances osteoblast attachment and differentiation. This peptide treatment of HA-coated implants may stimulate the osseointegration of the implants.

The magneto-transport properties of two-dimensional electron gas (2DEG) of n-type modulation-doped Cd 1− x Mn x Te/Cd 1− y Mg y Te single quantum wells were investigated under magnetic fields up to 7 T applied perpendicular to the 2D plane at 2 K . The 2D carrier concentration was varied in the range of 1.8– 4.6×10 11 cm −2 . Apart from the quantum behavior in the magneto- and Hall resistance, a positive and successively negative magnetoresistance (MR) appeared at low magnetic fields. This effect was not observed in non-magnetic 2DEG. This peculiar MR is interpreted as caused by the enhanced spin-splitting in magnetic 2DEG. The appearance of the positive and negative MR was more distinct in a sample with lower carrier concentrations. The positive MR was analyzed on the basis of the theoretical model of the quantum correction to the conductivity in the disordered system.

The purpose of this study was to evaluate a thin gelatin hydrogel membrane containing β-tricalcium phosphate (G-TCP) for use in guided bone regeneration, a technique that we developed. G-TCP membranes were fabricated from gelatin and β-TCP powder, freezedried, and cross-linked by heating. The resulting G-TCP membranes were as thin as collagen membranes, with high mechanical integrity. Proliferation and differentiation of rat bone marrow stromal cells (BMSCs) on G-TCP and collagen membranes were examined. On both membranes, BMSCs proliferated well and expressed alkaline phosphatase. However, more bone-like mineralized tissue formed on G-TCP membranes than on collagen membranes at 4 weeks. The effects of G-TCP and collagen membranes on bone regeneration in rat parietal bone defects were histologically examined. Bone bridges with mature uniform bone were observed under G-TCP membranes as early as 2 weeks. These results indicate that G-TCP is a GBR membrane that is comparable or superior to collagen membrane.

The purpose of the present study was to clarify the potentiality of acidic fluoride solution in treating peri-implantitis. We examined bactericidal activity of fluoride solution against periodontal pathogens; and evaluated the effects of fluoride on titanium, and the effects on cell proliferation and differentiation of rat bone marrow cells on the fluoride-treated titanium. Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis were used to determine minimal inhibitory concentration (MIC) and shorttime exposure. The cells were seeded on the titanium surface with or without fluoride treatment. Then, cellular proliferation, differentiation and mineral deposition were analyzed. The MIC values for A. actinomycetemcomitans and P. gingivalis were 225 and 900 ppm F(-), respectively. In short-time exposure test, both bacterial strains exhibited a significant decrease in a concentrationdependent manner. Cell proliferation and mineral deposition were significantly increased on the fluoride-treated surface. Within the limitation of this study, acidic sodium fluoride solution has the potentiality in treating peri-implantitis.