The high electron mobility transistor (HEMT) structures on Si (111) substrates were fabricated wi... more The high electron mobility transistor (HEMT) structures on Si (111) substrates were fabricated with heavily Fe-doped GaN buffer layers by metalorganic chemical vapor deposition (MOCVD). The heavy Fe concentrations employed for the purpose of highly insulating buffer resulted in Fe segregation and 3D island growth, which played the role of a nano-mask. The in situ reflectance measurements revealed a transition from 2D to 3D growth mode during the growth of a heavily Fe-doped GaN:Fe layer. The 3D growth mode of Fe nano-mask can effectively annihilate edge-type threading dislocations and improve transfer properties in the channel layer, and consequently decrease the vertical leakage current by one order of magnitude for the applied voltage of 1000 V. Moreover, the employment of GaN:C film on GaN:Fe buffer can further reduce the buffer leakage-current and effectively suppress Fe diffusion.
Abstract Two-dimensional (2D) β-In2S3 with a natural defective structure is a promising semicondu... more Abstract Two-dimensional (2D) β-In2S3 with a natural defective structure is a promising semiconductor for electronic and optoelectronic applications. Herein, oxidation of 2D β-In2S3 is investigated by photoluminescence, Raman scattering, and X-ray photoelectron spectroscopy studies for understanding its optoelectronic properties. Our results show that the intrinsic structural defects of sulfur vacancies induce the oxidation of β-In2S3, which can act as active sites to adsorb oxygen in air. Oxygen atoms react with indium atoms to form an inner layer of In2S3-3xO3x and outer layer of In2O3, resulting in intriguing optical properties over the exposure time to air. Moreover, the energy level diagram based on the defect-mediated oxidation process is presented. Additionally, the effect of oxidation under ambient air on β-In2S3 based photodetector and field effect transistor is investigated. Our study provides an in-depth understanding of the oxidation process of 2D β-In2S3 and paves a fundamental step for its potential applications in future electronics and optoelectronics.
Journal of Materials Science: Materials in Electronics, 2017
Gd-doped Bi 2 WO 6 nanoparticles were successfully prepared through microwave assisted synthesis.... more Gd-doped Bi 2 WO 6 nanoparticles were successfully prepared through microwave assisted synthesis. The incorporation of Gd 3+ ions into Bi 2 WO 6 crystallite was analyzed by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The optical properties of the nanoparticles were characterized by UV-Vis absorption and photoluminescence spectroscopy. The photocatalytic activity of the nanoparticleswas investigated by degradation of Rhodamine B under visiblelight irradiation. Our results showed that Gd-doping plays an important role for enhancing the visible light photocatalytic activity, and the enhanced photocatalytic activity of Gd-doped Bi 2 WO 6 nanoparticles would be mainly correlated with the effective decrease of recombination rate of photogenerated electron-hole pairs.
We demonstrated the growth of a self-assembled type-II ZnTe/ZnSe quantum dot (QD) structure coupl... more We demonstrated the growth of a self-assembled type-II ZnTe/ZnSe quantum dot (QD) structure coupled with a type-I Zn 0.88 Cd 0.12 Se/ZnSe quantum well (QW) on the (001) GaAs substrate by molecular beam epitaxy (MBE). As the spacer thickness is less than 2 nm, the carrier lifetime increasing from 20 ns to nearly 200 ns was successfully achieved. By utilizing the time-resolved photoluminescence (TRPL) and PL with different excitation power, we identify the PL emission from the coupled QDs consisting of two recombination mechanisms. One is the recombination between electrons in ZnSe barrier and holes confined within ZnTe QDs, and the other is between electrons confined in Zn 0.88 Cd 0.12 Se QW and holes confined within ZnTe QDs. According to the band diagram and power-dependent PL, both of the two recombinations reveal the type-II transition. In addition, the second recombination mechanism dominates the whole carrier recombination as the spacer thickness is less than 2 nm. A significant extension of carrier lifetime by increasing the electron and hole separation is illustrated in a type-II ZnTe/ZnSe QD structure coupling with a type-I ZnCdSe/ZnSe QW. Current sample structure could be used to increase the quantum efficient of solar cell based on the II-VI compound semiconductors.
We have shown in recent years that interatomic and interionic distances are sums of the radii of ... more We have shown in recent years that interatomic and interionic distances are sums of the radii of the adjacent atoms or ions. Many examples are provided and it is shown how the experimental bond lengths agree with the radii sums. The examples include inorganic compounds such as alkah hahdes, metal hydrides, and graphene; organic compounds such as aliphatic and aromatic compounds; and biochemical compounds such as nucleic acids, amino acids, caffeine-related compounds, and vitamins.
Metal cobaltites and ferrites have been prepared by the combusti on of an aqueo us mi xture of me... more Metal cobaltites and ferrites have been prepared by the combusti on of an aqueo us mi xture of metal nitrates and hydrazinium hyd ra zinecarboxy late in a microwave oven. The concentrated solution formed just before decomposition to the respeclive cobaltites or ferrites is removed and allowed to crystalli ze at room temperature. Composition of the complexes obtai ned from the above concentrated solutions has been found to be M I!3COm(N2H,COOh or M II3Fe2l3(N2H)COOh where M= Mg, Mn, Fe, Co, Ni or Zn. The sol id products obtained by the decomposition of the combusti on mixture and the complexes isolated from th e concentrated solutions have been characterized by chemi cal analyses, infrared spectra and X-ray powder diffraction studies. Thermal degradation of the co mplexes has also been recorded and the final residues have been found to be the respective metal cobaltites or metal ferrites.
g-C 3 N 4 /Ta 2 O 5 composites have been synthesized by a facile route in which mixtures of Ta 2 ... more g-C 3 N 4 /Ta 2 O 5 composites have been synthesized by a facile route in which mixtures of Ta 2 O 5 and urea are heated at various temperatures of 450°C, 500°C, and 550°C. The obtained materials (denoted as CN/TaO-T, where T is the heating temperature) were characterized using x-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, diffuse-reflectance ultraviolet-visible (UV-Vis) spectroscopy, thermogravimetric analysis, and x-ray photoelectron spectroscopy. The results show that the as-prepared composites are in orthorhombic Ta 2 O 5 phase coated by g-C 3 N 4. The photocatalytic activity of the composites was evaluated by photodegradation of methylene blue under visible light. Among the three materials, CN/TaO-500 exhibited the highest photocatalytic activity. The improved photocatalytic activity of the g-C 3 N 4 /Ta 2 O 5 composites is attributed to the presence of g-C 3 N 4 in the materials.
Journal of Materials Science: Materials in Electronics, 2015
Abstract Composites of carbon and W18O49 were successfully synthesized by heating the mixtures of... more Abstract Composites of carbon and W18O49 were successfully synthesized by heating the mixtures of WO3 and urea at a temperature between 600 and 800 °C in inert atmosphere. The obtained materials were characterized by XRD, SEM, TEM, Raman, XPS, TG–DTA and N2 adsorption/desorption at 77 K. The results showed that the composites consisted of W18O49 as a main phase which was coated by a thin carbon layer and exhibited a change in shape with heating temperature. The hollow form appeared from the treatment temperature of 700 °C and remained till 900 °C. However, at treatment 900 °C, the W18O49 disappeared and WO2 formed instead. The adsorption and visible-light photocatalytic degradation of methylene blue on the composites were evaluated.
We present a study of photocatalytic activities of Bi 2 WO 6 nanoparticles synthesized by fast mi... more We present a study of photocatalytic activities of Bi 2 WO 6 nanoparticles synthesized by fast microwaveassisted method. The photocatalytic activities of the nanoparticles were evaluated by the decolorization of methylene-blue under visible-light-irradiation. Our results show that the surface area of Bi 2 WO 6 nanoparticles plays a major role for improving photocatalytic activity, while visible-light absorption has only a weak effect on photocatalytic activity. This suggests efficient transportation of photo-generated electrons and holes to the oxidation active sites on the surface of nanoparticles, indicating Bi 2 WO 6 nanoparticles synthesized by fast microwave-assisted method are promising for achieving high photocatalytic activity under visible-light-irradiation.
The MnWO 4 nanoparticles encapsulated in mesoporous silica (MnWO 4 /SBA-15) was successfully synt... more The MnWO 4 nanoparticles encapsulated in mesoporous silica (MnWO 4 /SBA-15) was successfully synthesized by a fast microwave-assisted method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen absorption-desorption isotherm, and Fourier transform infrared spectroscopy (FTIR). Our results showed that the MnWO 4 /SBA-15 nanocomposites have the ordered hexagonal meso-structure of SBA-15, indicating MnWO 4 nanoparticles were successfully distributed into the channels of SBA-15. The size of MnWO 4 nanoparticles in SBA-15 is significantly smaller than the size of MnWO 4 nanoparticles prepared without SBA-15, indicating that the MnWO 4 /SBA15 nanocomposites would be very promising for improving photocatalytic activity of MnWO 4 nanoparticles.
In this paper, we present a simple microwave-assisted synthesis of Zn1−xCoxO nanopowders. With th... more In this paper, we present a simple microwave-assisted synthesis of Zn1−xCoxO nanopowders. With the advantages of the microwave-assisted method, we have successfully synthesized good crystalline quality and good surface morphology Zn1−xCoxO nanopowders. The nanopowders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–VIS absorption, and micro-Raman spectroscopy. We found, in the synthesis process, the surfactant Triethanolamine (TEA) plays an important role on the morphology of Zn1−xCoxO nanoparticles. The XRD study shows that for Co doping up to 5%, Co2+ ions are successfully incorporated into the ZnO host matrix. The absorption spectra of Zn1−xCoxO (x=1–5%) nanopowders show several peaks at 660, 611 and 565nm, indicating the presence of Co2+ ions in the tetrahedral sites. The Raman study shows that the linewidth of E2low mode increases with Co concentration, which further indicates the incorporation of Co2+ ions into the ZnO host matrix.
Co doped ZnO lms were synthesized from the precursors Zn(CH3COO)2.2H2O and Co(CH3COO)2.4H2O by us... more Co doped ZnO lms were synthesized from the precursors Zn(CH3COO)2.2H2O and Co(CH3COO)2.4H2O by using a \High Voltage Spray Pyrolysis" technique. The physical properties of the prepared lms were characterized by using scanning electron microscopy (SEM), X-ray di raction (XRD) and physical property mesurement system (PPMS) measurements. The lms studied were of a wurtzite phase with grain sizes of about 20 nm. The 5 % Co-doped ZnO lms exhibited ferromagnetic behavior at room temperature. The transmission and the optical magnetic circular dichroism (MCD) measurements con rmed that Co2+ was located at the tetrahedral sites of the ZnO wurtzite structure. MCD results showed that the observed ferromagnetism was less likely related to a carrier-induced mechanism.
... Research Article. Raman spectroscopic study of various types of tourmalines. Luc Huy Hoang 1,... more ... Research Article. Raman spectroscopic study of various types of tourmalines. Luc Huy Hoang 1,* ,; Nguyen Thi Minh Hien 2 ,; Xiang Bai Chen 3 ,; Nguyen Van Minh 1 ,; In-Sang Yang 2. Article first published online: 19 JAN 2011. DOI: 10.1002/jrs.2852. ...
The Khoi a and In-Sang Yang b The room-temperature ferromagnetism and the Raman spectroscopy of t... more The Khoi a and In-Sang Yang b The room-temperature ferromagnetism and the Raman spectroscopy of the Cu-doped Zn 1−x Co x O powders prepared by the sol-gel method are reported. The x-ray diffraction (XRD) data confirmed that the wurtzite structure of ZnO is maintained for ZnO doped with Co below 10 at%. The magnetization-field curves measured at room temperature demonstrated that all Co-doped ZnO powders were paramagnetic. Ferromagnetic ordering is observed for the samples doped with Cu in Zn 0.98 Co 0.02 O and strongly depends on the concentration of Cu. The relative strength of the second-order LO peak to the first-order one in the Raman spectra, which is related to the carrier concentration, of the Cu-doped Zn 0.98 Co 0.02 O powder is strongly correlated with the saturation magnetic moment of the system. This seems to be in favor of the Ruderman-Kittel-Kasuya-Yosida (RKKY) or double exchange mechanism of the ferromagnetism in this system.
We present the results of the temperature dependence of the Raman spectra of hexagonal HoMnO 3 th... more We present the results of the temperature dependence of the Raman spectra of hexagonal HoMnO 3 thin films in the 13-300 K temperature range. The films were grown on Pt(111)//Al 2 O 3 (0001) substrates using the laser ablation method. In the HoMnO 3 thin films, we initially observedseveral broad Raman peaks at ∼510, 760, 955, 1120, and 1410 cm −1. These broad Raman peaks display an anomalous behavior near the magnetic transition temperature, and the intensity difference of the Raman spectra at different temperatures shows several pairs of negative and positive peaks as the temperature is lowered below the Néel temperature. Our analyses indicate that all the broad peaks are correlated with magnetic ordering, and we have assigned the origin of all the broad peaks. Purely on the basis of the Raman analysis, we have deduced the Néel temperature and the spin exchange integrals of HoMnO 3 thin films. We also investigated the effects of the growth condition on the strongest broad peak at ∼760 cm −1 , which is related with pure magnetic ordering. This result indicates that the oxygen defect in the HoMnO 3 sample has negligible effect on magnetic ordering.
MnWO 4 nanoparticles were prepared using a microwave-assisted method followed by lowtemperature t... more MnWO 4 nanoparticles were prepared using a microwave-assisted method followed by lowtemperature treatment. The crystal quality and optical property of the MnWO 4 nanoparticles were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and ultraviolet-visible (UV-vis) absorption spectroscopy. Our results show that good crystal quality MnWO 4 nanoparticles can be prepared by the microwave-assisted method, and best crystal quality nanoparticles can be obtained with synthesizing pH value of 7. Furthermore, by calcination treatments, crystal quality can be further improved with less defect states and the particle size increases when the calcining temperature increases from 150 to 600 1C. In addition, our study shows that the MnWO 4 nanoparticles have strong absorption in the visible light region, suggesting that these nanoparticles are promising for photocatalytic applications.
The high electron mobility transistor (HEMT) structures on Si (111) substrates were fabricated wi... more The high electron mobility transistor (HEMT) structures on Si (111) substrates were fabricated with heavily Fe-doped GaN buffer layers by metalorganic chemical vapor deposition (MOCVD). The heavy Fe concentrations employed for the purpose of highly insulating buffer resulted in Fe segregation and 3D island growth, which played the role of a nano-mask. The in situ reflectance measurements revealed a transition from 2D to 3D growth mode during the growth of a heavily Fe-doped GaN:Fe layer. The 3D growth mode of Fe nano-mask can effectively annihilate edge-type threading dislocations and improve transfer properties in the channel layer, and consequently decrease the vertical leakage current by one order of magnitude for the applied voltage of 1000 V. Moreover, the employment of GaN:C film on GaN:Fe buffer can further reduce the buffer leakage-current and effectively suppress Fe diffusion.
Abstract Two-dimensional (2D) β-In2S3 with a natural defective structure is a promising semicondu... more Abstract Two-dimensional (2D) β-In2S3 with a natural defective structure is a promising semiconductor for electronic and optoelectronic applications. Herein, oxidation of 2D β-In2S3 is investigated by photoluminescence, Raman scattering, and X-ray photoelectron spectroscopy studies for understanding its optoelectronic properties. Our results show that the intrinsic structural defects of sulfur vacancies induce the oxidation of β-In2S3, which can act as active sites to adsorb oxygen in air. Oxygen atoms react with indium atoms to form an inner layer of In2S3-3xO3x and outer layer of In2O3, resulting in intriguing optical properties over the exposure time to air. Moreover, the energy level diagram based on the defect-mediated oxidation process is presented. Additionally, the effect of oxidation under ambient air on β-In2S3 based photodetector and field effect transistor is investigated. Our study provides an in-depth understanding of the oxidation process of 2D β-In2S3 and paves a fundamental step for its potential applications in future electronics and optoelectronics.
Journal of Materials Science: Materials in Electronics, 2017
Gd-doped Bi 2 WO 6 nanoparticles were successfully prepared through microwave assisted synthesis.... more Gd-doped Bi 2 WO 6 nanoparticles were successfully prepared through microwave assisted synthesis. The incorporation of Gd 3+ ions into Bi 2 WO 6 crystallite was analyzed by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The optical properties of the nanoparticles were characterized by UV-Vis absorption and photoluminescence spectroscopy. The photocatalytic activity of the nanoparticleswas investigated by degradation of Rhodamine B under visiblelight irradiation. Our results showed that Gd-doping plays an important role for enhancing the visible light photocatalytic activity, and the enhanced photocatalytic activity of Gd-doped Bi 2 WO 6 nanoparticles would be mainly correlated with the effective decrease of recombination rate of photogenerated electron-hole pairs.
We demonstrated the growth of a self-assembled type-II ZnTe/ZnSe quantum dot (QD) structure coupl... more We demonstrated the growth of a self-assembled type-II ZnTe/ZnSe quantum dot (QD) structure coupled with a type-I Zn 0.88 Cd 0.12 Se/ZnSe quantum well (QW) on the (001) GaAs substrate by molecular beam epitaxy (MBE). As the spacer thickness is less than 2 nm, the carrier lifetime increasing from 20 ns to nearly 200 ns was successfully achieved. By utilizing the time-resolved photoluminescence (TRPL) and PL with different excitation power, we identify the PL emission from the coupled QDs consisting of two recombination mechanisms. One is the recombination between electrons in ZnSe barrier and holes confined within ZnTe QDs, and the other is between electrons confined in Zn 0.88 Cd 0.12 Se QW and holes confined within ZnTe QDs. According to the band diagram and power-dependent PL, both of the two recombinations reveal the type-II transition. In addition, the second recombination mechanism dominates the whole carrier recombination as the spacer thickness is less than 2 nm. A significant extension of carrier lifetime by increasing the electron and hole separation is illustrated in a type-II ZnTe/ZnSe QD structure coupling with a type-I ZnCdSe/ZnSe QW. Current sample structure could be used to increase the quantum efficient of solar cell based on the II-VI compound semiconductors.
We have shown in recent years that interatomic and interionic distances are sums of the radii of ... more We have shown in recent years that interatomic and interionic distances are sums of the radii of the adjacent atoms or ions. Many examples are provided and it is shown how the experimental bond lengths agree with the radii sums. The examples include inorganic compounds such as alkah hahdes, metal hydrides, and graphene; organic compounds such as aliphatic and aromatic compounds; and biochemical compounds such as nucleic acids, amino acids, caffeine-related compounds, and vitamins.
Metal cobaltites and ferrites have been prepared by the combusti on of an aqueo us mi xture of me... more Metal cobaltites and ferrites have been prepared by the combusti on of an aqueo us mi xture of metal nitrates and hydrazinium hyd ra zinecarboxy late in a microwave oven. The concentrated solution formed just before decomposition to the respeclive cobaltites or ferrites is removed and allowed to crystalli ze at room temperature. Composition of the complexes obtai ned from the above concentrated solutions has been found to be M I!3COm(N2H,COOh or M II3Fe2l3(N2H)COOh where M= Mg, Mn, Fe, Co, Ni or Zn. The sol id products obtained by the decomposition of the combusti on mixture and the complexes isolated from th e concentrated solutions have been characterized by chemi cal analyses, infrared spectra and X-ray powder diffraction studies. Thermal degradation of the co mplexes has also been recorded and the final residues have been found to be the respective metal cobaltites or metal ferrites.
g-C 3 N 4 /Ta 2 O 5 composites have been synthesized by a facile route in which mixtures of Ta 2 ... more g-C 3 N 4 /Ta 2 O 5 composites have been synthesized by a facile route in which mixtures of Ta 2 O 5 and urea are heated at various temperatures of 450°C, 500°C, and 550°C. The obtained materials (denoted as CN/TaO-T, where T is the heating temperature) were characterized using x-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, diffuse-reflectance ultraviolet-visible (UV-Vis) spectroscopy, thermogravimetric analysis, and x-ray photoelectron spectroscopy. The results show that the as-prepared composites are in orthorhombic Ta 2 O 5 phase coated by g-C 3 N 4. The photocatalytic activity of the composites was evaluated by photodegradation of methylene blue under visible light. Among the three materials, CN/TaO-500 exhibited the highest photocatalytic activity. The improved photocatalytic activity of the g-C 3 N 4 /Ta 2 O 5 composites is attributed to the presence of g-C 3 N 4 in the materials.
Journal of Materials Science: Materials in Electronics, 2015
Abstract Composites of carbon and W18O49 were successfully synthesized by heating the mixtures of... more Abstract Composites of carbon and W18O49 were successfully synthesized by heating the mixtures of WO3 and urea at a temperature between 600 and 800 °C in inert atmosphere. The obtained materials were characterized by XRD, SEM, TEM, Raman, XPS, TG–DTA and N2 adsorption/desorption at 77 K. The results showed that the composites consisted of W18O49 as a main phase which was coated by a thin carbon layer and exhibited a change in shape with heating temperature. The hollow form appeared from the treatment temperature of 700 °C and remained till 900 °C. However, at treatment 900 °C, the W18O49 disappeared and WO2 formed instead. The adsorption and visible-light photocatalytic degradation of methylene blue on the composites were evaluated.
We present a study of photocatalytic activities of Bi 2 WO 6 nanoparticles synthesized by fast mi... more We present a study of photocatalytic activities of Bi 2 WO 6 nanoparticles synthesized by fast microwaveassisted method. The photocatalytic activities of the nanoparticles were evaluated by the decolorization of methylene-blue under visible-light-irradiation. Our results show that the surface area of Bi 2 WO 6 nanoparticles plays a major role for improving photocatalytic activity, while visible-light absorption has only a weak effect on photocatalytic activity. This suggests efficient transportation of photo-generated electrons and holes to the oxidation active sites on the surface of nanoparticles, indicating Bi 2 WO 6 nanoparticles synthesized by fast microwave-assisted method are promising for achieving high photocatalytic activity under visible-light-irradiation.
The MnWO 4 nanoparticles encapsulated in mesoporous silica (MnWO 4 /SBA-15) was successfully synt... more The MnWO 4 nanoparticles encapsulated in mesoporous silica (MnWO 4 /SBA-15) was successfully synthesized by a fast microwave-assisted method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen absorption-desorption isotherm, and Fourier transform infrared spectroscopy (FTIR). Our results showed that the MnWO 4 /SBA-15 nanocomposites have the ordered hexagonal meso-structure of SBA-15, indicating MnWO 4 nanoparticles were successfully distributed into the channels of SBA-15. The size of MnWO 4 nanoparticles in SBA-15 is significantly smaller than the size of MnWO 4 nanoparticles prepared without SBA-15, indicating that the MnWO 4 /SBA15 nanocomposites would be very promising for improving photocatalytic activity of MnWO 4 nanoparticles.
In this paper, we present a simple microwave-assisted synthesis of Zn1−xCoxO nanopowders. With th... more In this paper, we present a simple microwave-assisted synthesis of Zn1−xCoxO nanopowders. With the advantages of the microwave-assisted method, we have successfully synthesized good crystalline quality and good surface morphology Zn1−xCoxO nanopowders. The nanopowders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–VIS absorption, and micro-Raman spectroscopy. We found, in the synthesis process, the surfactant Triethanolamine (TEA) plays an important role on the morphology of Zn1−xCoxO nanoparticles. The XRD study shows that for Co doping up to 5%, Co2+ ions are successfully incorporated into the ZnO host matrix. The absorption spectra of Zn1−xCoxO (x=1–5%) nanopowders show several peaks at 660, 611 and 565nm, indicating the presence of Co2+ ions in the tetrahedral sites. The Raman study shows that the linewidth of E2low mode increases with Co concentration, which further indicates the incorporation of Co2+ ions into the ZnO host matrix.
Co doped ZnO lms were synthesized from the precursors Zn(CH3COO)2.2H2O and Co(CH3COO)2.4H2O by us... more Co doped ZnO lms were synthesized from the precursors Zn(CH3COO)2.2H2O and Co(CH3COO)2.4H2O by using a \High Voltage Spray Pyrolysis" technique. The physical properties of the prepared lms were characterized by using scanning electron microscopy (SEM), X-ray di raction (XRD) and physical property mesurement system (PPMS) measurements. The lms studied were of a wurtzite phase with grain sizes of about 20 nm. The 5 % Co-doped ZnO lms exhibited ferromagnetic behavior at room temperature. The transmission and the optical magnetic circular dichroism (MCD) measurements con rmed that Co2+ was located at the tetrahedral sites of the ZnO wurtzite structure. MCD results showed that the observed ferromagnetism was less likely related to a carrier-induced mechanism.
... Research Article. Raman spectroscopic study of various types of tourmalines. Luc Huy Hoang 1,... more ... Research Article. Raman spectroscopic study of various types of tourmalines. Luc Huy Hoang 1,* ,; Nguyen Thi Minh Hien 2 ,; Xiang Bai Chen 3 ,; Nguyen Van Minh 1 ,; In-Sang Yang 2. Article first published online: 19 JAN 2011. DOI: 10.1002/jrs.2852. ...
The Khoi a and In-Sang Yang b The room-temperature ferromagnetism and the Raman spectroscopy of t... more The Khoi a and In-Sang Yang b The room-temperature ferromagnetism and the Raman spectroscopy of the Cu-doped Zn 1−x Co x O powders prepared by the sol-gel method are reported. The x-ray diffraction (XRD) data confirmed that the wurtzite structure of ZnO is maintained for ZnO doped with Co below 10 at%. The magnetization-field curves measured at room temperature demonstrated that all Co-doped ZnO powders were paramagnetic. Ferromagnetic ordering is observed for the samples doped with Cu in Zn 0.98 Co 0.02 O and strongly depends on the concentration of Cu. The relative strength of the second-order LO peak to the first-order one in the Raman spectra, which is related to the carrier concentration, of the Cu-doped Zn 0.98 Co 0.02 O powder is strongly correlated with the saturation magnetic moment of the system. This seems to be in favor of the Ruderman-Kittel-Kasuya-Yosida (RKKY) or double exchange mechanism of the ferromagnetism in this system.
We present the results of the temperature dependence of the Raman spectra of hexagonal HoMnO 3 th... more We present the results of the temperature dependence of the Raman spectra of hexagonal HoMnO 3 thin films in the 13-300 K temperature range. The films were grown on Pt(111)//Al 2 O 3 (0001) substrates using the laser ablation method. In the HoMnO 3 thin films, we initially observedseveral broad Raman peaks at ∼510, 760, 955, 1120, and 1410 cm −1. These broad Raman peaks display an anomalous behavior near the magnetic transition temperature, and the intensity difference of the Raman spectra at different temperatures shows several pairs of negative and positive peaks as the temperature is lowered below the Néel temperature. Our analyses indicate that all the broad peaks are correlated with magnetic ordering, and we have assigned the origin of all the broad peaks. Purely on the basis of the Raman analysis, we have deduced the Néel temperature and the spin exchange integrals of HoMnO 3 thin films. We also investigated the effects of the growth condition on the strongest broad peak at ∼760 cm −1 , which is related with pure magnetic ordering. This result indicates that the oxygen defect in the HoMnO 3 sample has negligible effect on magnetic ordering.
MnWO 4 nanoparticles were prepared using a microwave-assisted method followed by lowtemperature t... more MnWO 4 nanoparticles were prepared using a microwave-assisted method followed by lowtemperature treatment. The crystal quality and optical property of the MnWO 4 nanoparticles were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and ultraviolet-visible (UV-vis) absorption spectroscopy. Our results show that good crystal quality MnWO 4 nanoparticles can be prepared by the microwave-assisted method, and best crystal quality nanoparticles can be obtained with synthesizing pH value of 7. Furthermore, by calcination treatments, crystal quality can be further improved with less defect states and the particle size increases when the calcining temperature increases from 150 to 600 1C. In addition, our study shows that the MnWO 4 nanoparticles have strong absorption in the visible light region, suggesting that these nanoparticles are promising for photocatalytic applications.
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