Search

This study compares and analyzes the key characteristics of the ZnO core–Si shell coaxial nanorod (Si@ZnO NR) heterostructures that were grown on semi-insulating, (100)-oriented Si substrates at Si layer temperatures of 450, 500, 550 and 600 °C for optoelectronic device applications. The Si@ZnO NRs were prepared in two separate stages. Vapor-phase transport produced the ZnO NRs, whereas rapid thermal chemical vapor deposition formed the Si layers. Results obtained from X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and Raman tests indicate that the ZnO NRs were single crystals with a zincblende configuration. The findings also reveal that the Si layer was polycrystalline in nature, poly-Si, with a wurtzite configuration. The present research is beneficial to the optoelectronic devices such as light-emitting diodes, solar cells and photodetectors in the UV–infrared range using the Si@ZnO coaxial nanostructures.

We report the effect of Mn incorporation on the structural and optical properties of GaN grown on a sapphire substrate in a plasma-enhanced molecular-beam epitaxy system followed by Mn ion implantation and annealing. The crystalline quality and phase purity were determined by high-resolution X-ray diffraction (XRD). The XRD results indicated that no macroscopic second phases were present in the Mn-implanted GaN layer after the annealing process. High-resolution transmission microscopy and energy dispersive X-ray spectroscopy revealed that the as-grown GaN epilayer and Mn-implanted GaN layer after annealing were single crystals with a hexagonal wurtzite structure, and they grew with a c-axis orientation perpendicular to the sapphire substrate. The Raman and photoluminescence spectra showed that the Mn-implanted GaN layer fabricated with a Mn ion dose of 5 × 1015 cm−2 followed by annealing at 800 °C for 30 min had higher crystalline quality than the Mn-implanted GaN layers fabricated with Mn ion doses of 5 × 1015 and 2 × 1016 cm−2 followed by annealed at 900 °C for 30 and 80 min.

We calculate the formation enthalpies of PdHx (x = 0–3) by cluster expansion (CE) and calculations based on density functional theory. CE predicts the stable palladium hydride structures PdH, PdH2.67, and PdH2.75. The band structures and density of states indicate that the amount of hydrogen in the palladium lattice does not alter the metallic character of the palladium significantly. However, all PdHx structures with x > 1 have greater formation enthalpies than that of the given reaction path 4 PdH 2 = 2 PdH + 2 Pd + 3 H 2 and thus they are thermodynamically unstable. The shorter bond length of Pd–H and the smaller bond angle of Pd–H–Pd imply a higher cohesive energy in zincblende (ZB) PdH than that in rocksalt (RS) PdH. Bader charge analysis shows a stronger electronegativity of H atoms in ZB-PdH than that in RS-PdH. This results in a stronger Pd–H bond in ZB-PdH than that in RS-PdH. Thus ZB-PdH has lower formation enthalpy than that of RS-PdH. However, regarding the dynamic stability, we conclude that hydrogen atoms prefer to occupy the octahedral sites of the palladium lattice because of the lower zero-point energy and vibration free energy than that of occupying the tetrahedral sites.

Monolayer (ML)-molybdenum disulfide (MoS2) with a direct band gap of ~1.8 eV exhibits considerable potential for advanced electronic and optical device applications. The surface electronic properties of ML-MoS2 need to be controlled for developing novel MoS2-based devices. In this study, we investigated the work function variation of chemical vapor deposition-grown ML-MoS2 that was controlled by proton irradiation. The crystallinity of the ML-MoS2 was confirmed by micro-Raman and Photoluminescence measurements. The work functions of the ML-MoS2 irradiated with varying proton beam flux were measured by Kelvin probe force microscopy. As the ML-MoS2 were exposed to the proton beam flux ranging from 1 × 1012 to 1 × 1014 protons/cm2 at the same beam energy of 10 MeV, the contact potential difference of the MoS2 increased up to about 0.108 V with increased proton beam flux. Based on the referenced value of the Au work function (≈5.1 eV), the work functions of non-treated ML-MoS2 and proton-irradiated ML-MoS2 with a proton beam flux of 1 × 1014 protons/cm2 were determined to be 5.031 eV and 4.992 eV, respectively. The decrease of the work function of the MoS2 with increased proton beam flux is due to the defect formation induced by proton irradiation. We suggest the possibility of engineering the surface potential and electronic properties of ML-MoS2 through controlling proton irradiation conditions.

The influence of quantum well structure and growth temperature on a synthesized multilayer system composed of a five-layer InMnGaAs quantum well with an InGaAs buffer layer grown on semi-insulating (100)-oriented substrates prepared by low temperature molecular beam epitaxy was studied. The magnetization measurements using a superconducting quantum interference device indicated the existence of ferromagnetism with a Curie temperature above room temperature in the five-layer InGaMnAs quantum well structure with an InGaAs buffer layer in a GaAs matrix. X-ray diffraction and secondary ion mass spectroscopy measurements confirmed the second phase formation of ferromagnetic GaMn clusters. The ferromagnetism that exists in the five-layer of the InMnGaAs quantum well with the InGaAs buffer layer results from a superposition of the ferromagnetism of the low temperature region from the substitutional Mn ions into Ga sites or interstitial Mn ions as well as the presence of manganese ions dopant clusters such as GaMn clusters.

In this paper we report the results on the study of the low-temperature photoluminescence of WO3 nanoparticles uncoated and coated by carbon. The photoluminescence spectra of WO3 nanoparticles at T = 15 K demonstrate the two sharp emission bands at 369 nm and 374 nm, respectively. The energy position, the small full width at half maximum (FWHM) of these bands and the strong quenching of the intensity with increasing temperature allowed us to attribute these emission bands to the radiative recombination of bound excitons. These excitons are localized on the donor states in the conduction band of WO3. The difference in the relative intensities of the bound exciton emission bands in the uncoated and the carbon coated WO3 nanoparticles is explained by the charge (electrons) transfer from the WO3 nanoparticles to the carbon coating layer.

We have fabricated as-grown ZnO nanorods (NRs) and carbon-assisted NR arrays on semi-insulating (100)-oriented Si substrates. We compared the structural and luminescent properties of them. High-resolution transmission microscopy, field emission scanning electron microscopy, x-ray diffraction and energy-dispersive x-ray revealed that the as-grown ZnO NRs and carbon-assisted ZnO NRs were single crystals with a hexagonal wurtzite structure, and grew with a c-axis orientation perpendicular to the Si substrate. These measurements show that the carbon-assisted ZnO NRs were better synthesized vertically on an Si substrate compared to the as-grown ZnO NRs. Photoluminescence measurements showed that luminescence intensity of the carbon-assisted ZnO NRs was enhanced compared to the as-grown ZnO NRs. The enhanced luminescence intensity of the carbon-assisted ZnO demonstrates the possible improvement in the performance of photovoltaic nanodevices based on ZnO-like materials. This method can be applied to the fabrication of well-aligned ZnO NRs used widely in optoelectronic devices.

The realization and application of optoelectronics, photonics, and sensing, such as in solar diode sensors and photodiodes, which are potentially useful from ultraviolet to infrared light sensing, is dramatically advanced when ZnO is integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Here, we compare and analyze the fundamental features of the Si-ZnO coaxial nanorod heterostructures (Si@ZnO NRs) grown on semi-insulating (100)-oriented Si substrates at growing temperatures of 500°C, 600°C, 650°C, and 700°C of the Si layer for device applications. ZnO NRs were grown by a vapor phase transport, and Si layers were made by rapid thermal chemical vapor deposition. X-ray diffraction, field emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy, and Raman experiments showed that ZnO NRs were single crystals with a wurtzite structure, while the Si layer was polysilicon with a zincblende structure. Furthermore, FESEM revealed that Si shell thickness of the Si@ZnO NRs increases with increasing growing temperatures of Si from 500°C to 700°C.

A graphene-InGaN Schottky junction has been successfully fabricated by transferring graphene layers onto n-type In0.23Ga0.77N/GaN/Al2O3 substrates. Current–voltage (I–V) measurement across the junction demonstrates the rectifying behaviour. Temperature dependent I–V characteristics in a range of 10 K to 300 K reveal that the charge transport mechanism is dominated by thermionic emission. Also, it is observed that the charge-transfer induced variation of Fermi energy of graphene affects the flow of current. This graphene/InGaN junction shows electroluminescence (EL) characteristics under a forward bias, producing bright blue emission (430 nm) at room temperature. As the temperature increases, the EL peak is shifted to a lower energy with a reduced peak intensity due to the increased nonradiative recombination rate. The dependence of EL intensity on the current of the graphene/InGaN junction confirms the band-to-band recombination mechanism in the InGaN layer by the bimolecular radiative recombination. Therefore, the observed results provide an insight for implementing graphene based Schottky-junction devices with tunable emission by utilizing the variable bandgap of the InGaN layer.

We investigated the effects of the Ti content on the structural and the magnetic properties of ZnCrO:Ti thin films (Cr: 1.0 at.%, Ti: 0 - 0.8 at.%). The samples were prepared by co-sputtering of ZnCrO and Ti and showed the Ti solution limit to be ~0.3 at.%. When the Ti additives were doped with an appropriate concentration less than the solution limit, the magnetic properties of the films were improved due to the increased magnetic moments from Ti2+ ions (i.e., 3d24s0). For the samples doped with large amounts of Ti dopants over the solution limit, however, the magnetization was gradually degraded due to the formation of metastable TiO2 and ZnCrTiO having no spins (i.e., 3d04s0).

One-dimensional ZnO nanorods were grown vertically on a (100) Si substrate using a vapor phase transport method. Following the fabrication of ZnO nanorods, Si layers were deposited by rapid thermal chemical vapor deposition (RTCVD) directly on the ZnO nanorod/Si (100) substrate. Field emission scanning electron microscopy revealed that a Si/ZnO nanorod coaxial heterostructure were synthesized vertically oriented along the (002) plane on a Si substrate. X-ray diffraction, Energy dispersive X-ray and Raman spectroscopy revealed that the ZnO nanorods were single crystals with a hexagonal structure, and grew with a c-axis orientation perpendicular to the Si substrate, whereas the Si layer was poly-silicon with cubic structure. These results demonstrated the Si/ZnO nanorod coaxial heterostructure were synthesized successfully on a (100) Si substrate and the ZnO nanorod enables the synthesis of a vertically grown well-aligned Si/ZnO coaxial nanorod heterostructure.

We investigated the effect of the Cr content on the magnetic properties of ZnCrO thin films (Cr: 1.0 - 12.5 at.%). Regardless of the Cr concentration, all of the films exhibited clear ferromagnetism even at temperatures above 350 K. For the dependence of spontaneous magnetization on the Cr concentration, however, the magnitude of effective magnetic moment (per Cr ion) was observed to exponentially decrease with increasing Cr content. We attributed the decreased spontaneous magnetization to the degraded crystal magnetic anisotropy. Namely, we found that, in a magnetic-ion-doped thin film, the high concentration of magnetic ions caused a lattice distortion and consequently degraded the ferromagnetic channeling in the solid-state material system.

Above room temperature, ferromagnetic behavior is achieved in Si through Fe ion implantation. The incorporation of Fe in Si was confirmed by an X-ray diffraction and a superconducting quantum interference device. Fe-implanted Si magnetic semiconductors annealed at 800 and 900 ∘C for 25 min were found to have a ferromagnetic ordering with a Curie temperature above room temperature. X-ray diffraction (XRD) measurements strongly revealed that iron silicide were formed, suggesting that the ferromagnetism observed in Fe-implanted Si magnetic semiconductor is due to phase segregation into iron silicide. Even at low implantation dose, we observed the formation of Fe silicide phase responsible for the high temperature magnetic behavior. These measurements strongly support the formation of Fe silicide phase and provide strong evidence of the existence of the Fe silicide phase that determines Curie temperature.

We studied the influence of Mn in multilayer system consisting of twenty layers of InMnGaAs/InGaAs quantum wells (QWs) by low-temperature molecular beam epitaxy (MBE). The incorporation of Mn in the InGaAs was confirmed by X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS). A ferromagnetic ordering with a Curie temperature over 300 K of twenty layers of InGaMnAs/InGaAs QW structure grown on high resistivity (100) p-type GaAs substrates was found. Even at low growth temperature, we observed the formation of GaMn clusters responsible for the high-temperature magnetic behavior. These measurements strongly support the formation of GaMn clusters and provide strong evidence of the existence of the GaMn clusters that determines Curie temperature.

We report a ferromagnetic graphene field-effect transistor with a band gap. The Mn-doped graphene has a coercive field (Hc) of 188 Oe and a remanent magnetization of 102 emu cm−3 at 10 K. The temperature-dependent conductivity indicates that the Mn-doped graphene has a band gap of 165 meV. A fabricated graphene FET revealed p-type semiconducting behavior, and the field effect mobility was determined to be approximately 2543 cm2 V−1 s−1 at room temperature.

InCrP:Zn was prepared using the implantation with Cr concentrations of 0.3% and 0.7%, respectively. It was confirmed that the photoluminescence peaks near 0.85(D, Cr) eV and 0.96(e,Cr) eV were Cr-correlated PL bands by the implantation of Cr. Especially, each 0.85(D, Cr) eV and 0.96(e,Cr) eV peaks were separately observed based on InP. In triple-axis x-ray diffraction patterns, the samples revealed a shoulder peak indicative of intrinsic InCrP. Ferromagnetic hysteresis loops measured at 10 K and 300 K were observed and the temperature-dependent magnetization showed ferromagnetic behavior ≥300 K, which reveals obvious and enhanced ferromagnetic spin coupling mediated by hole.

In the present study, Mn/graphene/SiO2 films have been successfully prepared by spin coating a manganese dinitrate hydrate standard solution (10,000 μg/mL Mn+2 in 2% HNO3) on a graphene/SiO2 sheet. The samples were characterized by using an X-ray diffractometer, a scanning electron microscope, a superconducting quantum interference device and an atomic force microscope. The magnetic measurement revealed that the Mn/graphene/SiO2 films exhibited a ferromagnetic behavior at 5 K and 300 K. We concluded that the ferromagnetism observed in the Mn/graphene/SiO2 sheets was associated with parasitic ferromagnetic Mn clusters imposed on the antiferromagnetic structure of MnO2, which might have resulted from a distortion of the lattice structure due to oxygen vacancies, which might have been due to the effects of magnetic and structural disorder introduced by a random incorporation and inhomogeneous distribution of Mn atoms in the graphene layer.

A ferromagnetic ordering with a Curie temperature of 50 K of fifteen layer of InGaMnAs/GaAs multi quantum wells (MQWs) structure grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE) was found. It is likely that the ferromagnetic exchange coupling of sample with Curie temperature of 50 K is hole-mediated resulting in Mn substituting In or Ga sites. Temperature and excitation power dependent PL emission spectra of InGaMnAs MQWs sample grown at temperature of 170 °C show that an activation energy of Mn ion on the first quantum confinement level in InGaAs quantum well is 36 meV and impurity Mn is partly ionized. It is found that the activation energy of 36 meV of Mn ion in the QW is lower than the activation energy of 110 meV for a substitutional Mn impurity in GaAs. These measurements provide strong evidence that an impurity band existing in the bandgap due to substitutional Mn ions and it is the location of the Fermi level within the impurity band that determines Curie temperature.

Ten layers of InGaMnAs/GaAs multiquantum wells (MQWs) structure were grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE). A presence of the ferromagnetic structure was confirmed in the InGaMnAs/GaAs MQWs structure, and have ferromagnetic ordering with a Curie temperature, T C=50 K. It is likely that the ferromagnetic exchange coupling of the sample with T C=50 K is hole-mediated resulting in Mn substituting In or Ga sites. PL emission spectra of the InGaMnAs MQWs sample grown at a temperature of 170 °C show that an activation energy of the Mn ion on the first quantum confinement level in InGaAs QW is 32 meV and impurity Mn is partly ionized. The fact that the activation energy of 32 meV of Mn ion in the QW is lower than an activation energy of 110 meV for a substitutional Mn impurity in GaAs, indicating an impurity band existing in the bandgap due to substitutional Mn ions.

We fabricated high quality epitaxial Bi 0.9 Ho 0.1 FeO 3 thin films which exhibited the tetragonally stained structure with a c / a ratio of about 1.04. The Bi 0.9 Ho 0.1 FeO 3 thin film showed a good ferroelectric property with the high remanent polarization ( P r ) of about 80 μC/cm 2 . The ferromagnetic hysteresis loop with a clear remanent magnetization was shown. The coercive field and the remanent magnetization of the Bi 0.9 Ho 0.1 FeO 3 film are 6200 Oe and 1.7 emu/g, respectively. The abrupt conduction due to space charge limited (SCL) was revealed in leakage current density versus electric field.

We investigated the carrier transition properties of the GaN/InGaN/GaN single quantum well bounded by AlGaN barriers. In order to confirm the carrier transition coming from the single quantum well, the single quantum well layer was etched by reactive ion etching method. The structural property of the samples was characterized by high resolution X-ray diffraction measurements. In micro-photoluminescence measurements, it is clearly shown that the donor bound exciton transition of the single quantum well sample was redshifted compared to the etched one due to strain. Moreover, a lot of peaks were observed below the GaN band gap energy due to carrier localization in the InGaN/GaN single quantum well, including carrier localization center and quantum confined states. The excitation power dependence and time resolved photoluminescence spectra were investigated to characterize the optical transition of the single quantum well© 2011 Elsevier B.V. All rights reserved.

We have investigated the optical properties of vertical GaN nanorods with diameters of 150 nm grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy followed by Mn ion implantation and annealing. The GaN nanorods are fully relaxed and have a very good crystal quality characterized by extremely strong and narrow photoluminescence excitonic lines near 3.47 eV. For GaMnN nanorods, Arrhenius plots of the intensities of the Mn acceptor give a thermal activation energy of Δ=350 meV, indicating that the thermal quenching of the Mn-related PL peak is due to the dissociation of an acceptor-bound hole from the temperature-dependent PL spectra. This suggests that the Mn-bound holes in GaN nanorods exhibit the impurity states predicted by the hydrogen model.

p-type InP:Zn epilayers were grown by using metalorganic chemical vapor deposition. After the growth of InP:Zn epilayers, Mn was evaporated on top of the InP:Zn epilayers by using a molecular beam epitaxy system. Then, Mn was diffused into the InP:Zn epilayers by annealing. InMnP:Zn epilayers were annealed at 600 °C for 60 s with Mn concentrations of both ∼1.5 and ∼3.0%. The optical transitions related to Mn appeared at 1.144, 1.187, and 1.212 eV and at 1.143, 1.179, and 1.205 eV for InMnP:Zn epilayers annealed at 600 °C for 60 s with Mn concentrations of ∼1.5 and ∼3.0%, respectively. Transitions related to Mn are noticeably activated due to an increase in the Mn concentration near 3.0% in comparison with transitions for Mn concentration near 1.5%. Clear ferromagnetic hysteresis loops were obtained for InMnP:Zn epilayers. The ferromagnetic hysteresis loop of the InMnP:Zn epilayers annealed with Mn concentration near 3.0% was bigger than that of epilayers with Mn concentration near 1.5%, and these results agree with the PL results that transitions related to Mn are remarkably activated upon annealing at Mn concentration near 3.0% in comparison with concentration near 1.5%. Ferromagnetic behavior persisted up Tc1 ∼ 50 K and Tc2 ∼ 291 K. Tc2 ∼ 291 K corresponds to MnP. Tc1 ∼ 50 K originates from intrinsic InMnP:Zn, which is caused by carrier-mediated ferromagnetism in the InMnP:Zn epilayer. We found that at Tc1 ∼ 50 K, a ferromagnetic semiconductor could be formed in a diluted magnetic semiconductor based on InMnP:Zn epilayers additionally co-doped with Zn.

The ferromagnetic semiconductor p-InMnP:Zn epilayers were prepared through low-temperature annealing at 250 °C by using Mn/InP:Zn bilayers. The p-type InP:Zn epilayers were prepared by using metal-organic chemical vapor deposition. Then, ultra-thin Mn layers were subsequently deposited onto the layers by using molecular beam epitaxy. The Mn/InP:Zn bilayers were annealed at a low temperature of 250 °C in order to minimize the formation of precipitates such as InMn, MnP, Mn2P, and Mn3In. No ferromagnetic precipitates were observed in the annealed InMnP:Zn; however, the sample exhibited an antiferromagnetic phase of MnO2 that might have been formed because of an unavoidable surface oxide that had been created during the sample transfer. Despite the existence of antiferromagnetic MnO2, the samples revealed clear ferromagnetic hysteresis loops and showed high ferromagnetic transition temperatures up to ∼180 K. The results suggest that a ferromagnetic semiconductor InMnP:Zn can be effectively formed through low-temperature annealing by using a Mn/InP:Zn bilayer.

The thermodynamic behavior of excitonic emission properties in manganese- and zinc-codoped indium phosphide (InMnP:Zn) diluted magnetic semiconductor (DMS) layers was investigated. Compared to the InMnP:Zn DMS layer (Mn ≈ 0.06%), the inhomogeneous thermal-broadening of the excitonic-emission line-width in InMnP:Zn DMS layer (Mn ≈ 0.29%) is dominant at lower temperatures. This is attributed to the increase of ionized impurity scattering from Mn ions and results in the increase of exciton–phonon coupling strength. As a consequence, high Mn content can lead to low excitonic emission efficiency, although generally a larger Mn content is favorable to increase the Curie temperature of a DMS material.

1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) phospholipid membrane was used to fabricate a tightly packed 2-dimensional array of Sn nanoparticles through direct deposition of Sn on the DOPC membrane. Major advantage of the proposed method was that the vertical ordering of the nanoparticles extended to a centimeter (2 cm × 2 cm substrate) scale in the as-prepared state. It was also shown that the particle size and morphology were altered depending on processing conditions. Experimental evidences indicated that the Sn nanoparticle surface, which spontaneously oxidized during deposition, was encapsulated by the DOPC molecules. After removing the encapsulating lipid layer, the oxide-covered Sn nanoparticles exhibited strong photoluminescence. It was also demonstrated that the Sn particle morphology and ordering are related to the lipid membrane structure and chemistry. The proposed method can be easily extended to other metals that are susceptible to oxidation to produce various metal oxide nanoparticles.

Ten layers of self-assembled InMnAs quantum dots with InGaAs barrier were grown on high resistivity (1 0 0) p-type GaAs substrates by molecular beam epitaxy (MBE). The presence of ferromagnetic structure was confirmed in the InMnAs diluted magnetic quantum dots. The ten layers of self-assembled InMnAs quantum dots were found to be semiconducting, and have ferromagnetic ordering with a Curie temperature, TC=80 K. It is likely that the ferromagnetic exchange coupling of sample with TC=80 K is hole mediated resulting in Mn substituting In and is due to the bound magnetic polarons co-existing in the system. PL emission spectra of InMnAs samples grown at temperature of 275, 260 and 240 °C show that the interband transition peak centered at 1.31 eV coming from the InMnAs quantum dot blueshifts because of the strong confinement effects with increasing growth temperature.

The excitation density dependent photoluminescence (PL) spectra in Ga1−xMnxN layers (where x≈0.1–0.8%) grown on sapphire (0 0 0 1) substrates using the plasma-enhanced molecular beam epitaxy technique have been investigated. The efficient PL peaks are observed in the red (1.86 eV), yellow (2.34 eV), and blue (3.29 eV) spectral ranges. By examining the dependence of PL on the excitation laser power density at 15 and 300 K, the yellow band (2.34 eV) and bandgap (3.50 eV) luminescence vary linearly with the light intensity, which are in good agreement with a simple recombination model, which assumes a density of recombination centers below the conduction band edge.

The p-type InMnP:Be epilayers, which were prepared by thermal diffusion of Mn through in-situ deposition of Mn layer using molecular beam epitaxy (MBE) onto MBE-grown InP:Be epilayers and subsequent in-situ annealing at 300–350 °C, were investigated. InMnP:Be epilayers prepared by the above sequence clearly showed the Mn-related emission band at 1.1–1.2 eV, which indicates the effective incorporation of Mn 2+ ions into the host layer InP:Be. The samples demonstrated very large ferromagnetic hysteresis loops with enhanced coercivity, and the ferromagnetic-to-paramagnetic transition of the samples was observed to occur at ∼85 K. These results suggest that InP-based ferromagnetic semiconductor layers having enhanced ferromagnetism can be effectively formed by the above-mentioned sequential in-situ processes.

Multistacked Ge quantum dots (QDs) with Si spacers of different thicknesses have been grown on (100) Si substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and post-annealing. The presence of a ferromagnetic structure was confirmed in the insulating (Si0.45Ge0.55)Mn0.03 diluted magnetic quantum dots (DMQD) and semiconducting (Si0.45Ge0.55)Mn0.05 DMQD. The DMQD materials were found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with Curie temperatures TC = 350 and 160 K respectively. The x-ray diffraction (XRD) data show that there is a phase separation of Mn5Ge3 from the MnGe nanostructure. Temperature-dependent electrical resistivity in the semiconducting DMQD material indicates that manganese introduces two acceptor levels in germanium at 0.14 eV from the valence band and 0.41 eV from the conduction band implying that Mn substitutes for Ge. Therefore, it is likely that the ferromagnetic exchange coupling of DMQD material with TC = 160 K is hole-mediated due to formation of bound magnetic polarons and the ferromagnetism in the sample with TC > 300 K is due to Mn5Ge3 phase.

One layer of self-assembled Ge quantum dots with Si barrier were grown on high resistivity (100) p-type Si substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and post-annealing. A presence of ferromagnetic structure was confirmed in the dilute magnetic quantum dots (DMQD). The DMQD through 10 min annealing was found to be homogeneous, and to exhibit p-type conductivity, insulating property, and ferromagnetic ordering with a Curie temperature, T c=170 K. On the other hand, the DMQD through 30 and 60 min annealing was found to be semi-insulating and ferromagnetic ordering with a Curie temperature over 300 K. The XRD data show that there is a phase separation of Mn rich phases Mn5Ge3 from MnGe nanostructure. Therefore, it is likely that the ferromagnetic exchange coupling of sample with T c=170 K is hole-mediated and the ferromagnetism in sample with T c>300 K is due to Mn5Ge3 phase.

We have investigated the temperature and composition dependent photoluminescence (PL) spectra in Ga 1− x Mn x N layers (where x ≈ 0.1–0.8%) grown on sapphire (0 0 0 1) substrates using the plasma-enhanced molecular beam epitaxy technique. The efficient PL is peaked in the red (1.86 eV), yellow (2.34 eV), and blue (3.29 eV) spectral range. The band-gap energy of the Ga 1− x Mn x N layers decreased with increasing temperature and manganese composition. The band-gap energy of the Ga 1− x Mn x N layers was modeled by the Varshni equation and the parameters were determined to be α = 2.3 × 10 −4 , 2.7 × 10 −4 , 3.4 × 10 −4 eV/K and β = 210, 210, and 230 K for the manganese composition x = 0.1%, 0.2%, and 0.8%, respectively. As the Mn concentration in the Ga 1− x Mn x N layers increased, the temperature dependence of the band-gap energy was clearly reduced.

Ten and twenty layers of self-assembled Ge QDs with 44 and 59-nm-thick Si barrier were grown on high resistivity (1 0 0) p-type Si substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and post-annealing. A presence of ferromagnetic structure was confirmed in the insulating GeMn diluted magnetic quantum dots (DMQD) and semiconducting GeMn DMQD. The DMQD materials were found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with a Curie temperature, T C = 350 and 230 K. The X-ray diffraction (XRD) data show that there is a phase separation of Mn 5 Ge 3 from MnGe nanostructure. Temperature dependent electrical resistivity in semiconducting DMQD material indicates that manganese introduces two acceptor levels in germanium at 0.14 eV from the valence band and 0.41 eV from the conduction band implying Mn substituting Ge. Therefore, it is likely that the ferromagnetic exchange coupling of DMQD material with T C = 230 K is hole-mediated due to formation of polarons and the ferromagnetism in sample with T C > 300 K is due to Mn 5 Ge 3 phase.

Ferromagnetic Ga 1− x Mn x As layers (where x ≈4.7–5.5%) were grown on (1 0 0) GaAs substrates by molecular beam epitaxy. These p-type (Ga,Mn)As films were revealed to have a ferromagnetic structure and ferromagnetism is observed up to a Curie temperature of 318 K, which is ascribed to the presence of MnAs secondary magnetic phases within the film. It is highly likely that the phase segregation occurs due to the high Mn cell temperature around 890–920 °C, as it is well established that GaMnAs is unstable at such a high temperature. The MnAs precipitate in the samples with x ≈4.7–5.5% has a Curie temperature T c ≈318 K, which was characterized from field-cooled and zero-field-cooled magnetization curves.

Si 1− x Mn x diluted magnetic semiconductors with x ≈5% with a ferromagnetic structure were formed through Mn ion implantation and post-annealing. The temperature- and magnetic field-dependent magnetization were measured by magnetometry using a superconducting quantum interference device. The Si 0.95 Mn 0.05 materials were found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with a Curie temperature ( T C ) above room temperature. The low-temperature ( T = 10 K ) photoluminescence spectra exhibited Mn-related free-to-donor pair transitions for the Si 1− x Mn x materials with x ≈5%. A Mn double-donor level in these samples was found to be Mn substituted for Si (Mn Si ) and located around 290 meV above the valence band, suggesting that the ferromagnetism observed in Mn-implanted Si material is hole-mediated ferromagnetism.

The magneto-transport properties of ferromagnetic Ga1−xMnxAs epilayers with Mn mole fractions in the range of x≈2.2–4.4% were investigated through Hall effect measurements. The magnetic field-dependent Hall mobility for a metallic sample with x≈2.2% in the temperature range of T=0–300 K was analyzed by magnetic field-dependent mobility model including an activation energy of Mn acceptor level. This model provides outstanding fits to the measured data up to T=300 K. It was found that the acceptor levels with activation energies of 112 meV at B=0 Oe decreased to 99 meV at B=5 kOe in the ferromagnetic region. The decrease in acceptor activation energy was due to the spin splitting of the Mn acceptor level in the ferromagnetic region, and was responsible for increase in carrier concentration.

Ferromagnetic Ga1−xMnxAs epilayers with Mn mole fraction in the range of x≈2.2–4.4% were grown on semi-insulating (100) GaAs substrates using the molecular beam epitaxy technique. The transport properties of these epilayers were investigated through Hall effect measurements. The measured hole concentration of Ga1−xMnxAs layers varied from 4.4×1019 to 3.4×1019 cm−3 in the range of x≈2.2–4.4% at room temperature. From temperature dependent resisitivity data, the sample with x≈4.4% shows typical behavior for insulator Ga1−xMnxAs and the samples with x≈2.2 and 3.7% show typical behavior for metallic Ga1−xMnxAs. The Hall coefficient for the samples with x≈2.2 and 4.4% was fitted assuming a magnetic susceptibility given by Curie–Weiss law in a paramagnetic region. This model provides good fits to the measured data up to T=300 K and the Curie temperature Tc was estimated to be 65, 83 K and hole concentration p was estimated to be 5.1×1019, 4.6×1019 cm−3 for the samples with x≈2.2 and 4.4%, respectively, confirming the existence of an anomalous Hall effect for metallic and insulating samples.

The temperature-dependent Hall resistivity and carrier concentrations of Ga1−xMnxAs epilayers grown on (100) semi-insulating GaAs substrates by molecular beam epitaxy have been investigated in the temperature range of 10–300 K. A Ga1−xMnxAs sample with x≈4.4% shows typical insulator behavior and Ga1−xMnxAs samples with x≈2.2 and 3.7 % show typical metallic behavior. A model taking into account ionized impurity and spin disorder scattering mechanisms was used to portray properly the observed features of the temperature-dependent Hall resistivity data. The value of the p-d exchange energy was J=59.4±0.5 and 71.9±0.5 eV A3 for the samples with x≈2.2 and 3.7 %, respectively. Ionized impurity scattering dominates the entire temperature range, with a temperature-independent spin disorder scattering in the paramagnetic region. It was found that the spin disorder scattering mechanism had a strong temperature dependence on 1−T2 in the ferromagnetic region.

Ferromagnetic Ga1−xMnxAs epilayers with Mn mole fraction in the range of x≈0.2–9.6% were grown successfully on semi-insulating (1 0 0) GaAs substrates using the liquid phase epitaxy technique. The ferromagnetic properties of these epilayers were investigated using superconducting quantum interference device at 5 K. The Curie temperature was determined to be 80 K. All the Ga1−xMnxAs layers had p-type conductivity through Hall effect measurements. The measured hole concentration of Ga1−xMnxAs layers decreases from 2.0×1017 cm−3 to 9.8×1015 cm−3 with increasing Mn mole fraction in the range of x≈0.2–9.6%. Cross-sectional selected area diffraction pattern of the GaMnAs films obtained through transmission electron microscopy measurement showed that the grown GaMnAs layer can be classified as a single crystal. Transitions involving shallow Mn acceptors were identified through photoluminescence measurements and the ionization energy of Mn acceptor was determined to be 104.6 meV.

Mn-doped Ga1−xMnxAs epilayers grown on semi-insulating (100) GaAs substrates using the liquid phase epitaxy technique were investigated using photoluminescence and Hall effect measurements from 20 to 300 K. Transitions involving shallow Mn acceptors were identified through photoluminescence measurements and the ionization energy of Mn acceptor was determined to be 104.6 meV which is in good agreement with values calculated from a hydrogenic hole model including sp–d exchange contribution. Also, it was concluded that Ga1−xMnxAs alloys were obtained from samples with low Mn concentration (below x≈1%) and these layers have a simple impurity band merging to the valence band.

In the original article some funding information in the Acknowledgements section was inadvertently omitted. Following is the corrected text.

We report an efficient and controllable method to introduce p-type doping in graphene by decoration with Mn3O4 nanoparticles (NPs) on mechanically exfoliated single layer graphene. A monolayer of Mn3O4 NPs, with a diameter in the range of 5–10 nm, was decorated on a graphene film using an ex-situ method, whereas by controlling the coverage of the NPs on the graphene surface, the carrier concentration could be continually adjusted. The p-type of the NP-decorated single layer graphene was confirmed by the Raman G-band. It was found that the carrier concentration could be gradually adjusted up to 26.09 × 1012 cm−2, with 90% coverage of Mn3O4 NPs. The Dirac point of the pristine graphene at the gate bias of 27 V shifted to 150 V for Mn3O4 NP decorated graphene. The p-type graphene doped with Mn3O4 NPs demonstrated significant high air-stability, even under an oxygen atmosphere for 60 days. This approach allows for the opportunity for simple, scalable, and highly stable doping of graphene for future high-perfo...

Ferromagnetic Ga 1− x Mn x As layers (where x =1.4–3.0%) grown on (1 0 0) GaAs substrates by molecular beam epitaxy were characterized using Raman spectroscopy. As Mn is introduced into GaAs, a marked increase in disorder in the material occurs, as indicated by the growth of the disorder-allowed transverse-optical Raman line. Another important result is that as the Mn concentration in Ga 1− x Mn x As increases further beyond ca. 2%, Raman-active coupled-plasmon-longitudinal-optical phonon modes arise, which signals the increasing presence of holes, and thus provides a useful tool for determining their concentration. Using the depletion-layer approach from the Raman spectroscopy data, we determined the carrier concentration for samples with x =2.2% and 3.0% was to be 7.2×10 19 and 8.3×10 20 cm −3 , respectively.

Dominant hole traps of ferromagnetic Ga1−xMnxAs and epilayers with an Mn mole fraction of x≈2.2% and 4.4% were identified employing deep-level transient spectroscopy. Three hole traps with binding energies of EA=0.38±0.01 eV at 140 K, EB=0.43±0.01 eV at 220 K, and EC=0.65±0.01 eV at 300 K above the top of the valence band were observed. Comparing with theoretical data of GaAs, it appears most likely that the trap with EA is associated with a gallium vacancy (VGa) or the arsenic antisite complex (GaAs+VAs), whereas the traps with EB and EC are associated with two charge states of arsenic antisite (AsGa) defect. The hole capture cross sections were determined as σp(A)=3.7×10−11, σp(B)=1.5×10−14, and σp(C)=1.1×10−14 cm2, respectively. The samples with x≈2.2% and x≈4.4% show typical behavior for metallic Ga1−xMnxAs and insulator Ga1−xMnxAs, respectively, through Hall measurements.

We have investigated the magnetic and optical properties of dislocation-free vertical GaN nanorods with diameters of 150 nm grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy followed by Mn ion implantation and annealing. The GaN nanorods are fully relaxed and have a very good crystal quality characterized by extremely strong and narrow photoluminescence excitonic lines near 3.47 eV. For GaMnN nanorods, it can be concluded that the ferromagnetic property of GaMnN nanorod with a Curie temperature over 300 K is associated with the formation of Mn4Si7magnetic phase which results from the effects of magnetic and structural disorder introduced by a random incorporation and inhomogeneous distribution of Mn atoms in the porous layer between the nanorods that form precipitates in the Si substrate before or during the annealing step amongst the GaN nanorods.