A crack-free AlN film with 4.5 μm thickness was grown on a 2-inch hole-type nano-patterned sapphire substrates(NPSSs) by hydride vapor phase epitaxy(HVPE). The coalescence, stress evolution, and dislocation annihilat...A crack-free AlN film with 4.5 μm thickness was grown on a 2-inch hole-type nano-patterned sapphire substrates(NPSSs) by hydride vapor phase epitaxy(HVPE). The coalescence, stress evolution, and dislocation annihilation mechanisms in the AlN layer have been investigated. The large voids located on the pattern region were caused by the undesirable parasitic crystallites grown on the sidewalls of the nano-pattern in the early growth stage. The coalescence of the c-plane AlN was hindered by these three-fold crystallites and the special triangle void appeared. The cross-sectional Raman line scan was used to characterize the change of stress with film thickness, which corresponds to the characteristics of different growth stages of AlN. Threading dislocations(TDs) mainly originate from the boundary between misaligned crystallites and the c-plane AlN and the coalescence of two adjacent c-plane AlN crystals, rather than the interface between sapphire and AlN.展开更多
Trapped atoms on photonic structures inspire many novel quantum devices for quantum information processing and quantum sensing.Here,we demonstrate a hybrid photonic-atom chip platform based on a Ga N-onsapphire chip a...Trapped atoms on photonic structures inspire many novel quantum devices for quantum information processing and quantum sensing.Here,we demonstrate a hybrid photonic-atom chip platform based on a Ga N-onsapphire chip and the transport of an ensemble of atoms from free space towards the chip with an optical conveyor belts.Due to our platform’s complete optical accessibility and careful control of atomic motion near the chip with a conveyor belt,successful atomic transport towards the chip is made possible.The maximum transport efficiency of atoms is about 50%with a transport distance of 500μm.Our results open up a new route toward the efficient loading of cold atoms into the evanescent-field trap formed by the photonic integrated circuits,which promises strong and controllable interactions between single atoms and single photons.展开更多
Monoclinic gallium oxide(Ga_2O_3) has been grown on(0001) sapphire(Al_2O_3) substrate by plasma-assisted molecular beam epitaxy(PA-MBE). The epitaxial relationship has been confirmed to be [010]( 2ˉ01) β-Ga_2O_3||[ ...Monoclinic gallium oxide(Ga_2O_3) has been grown on(0001) sapphire(Al_2O_3) substrate by plasma-assisted molecular beam epitaxy(PA-MBE). The epitaxial relationship has been confirmed to be [010]( 2ˉ01) β-Ga_2O_3||[ 011ˉ0](0001)Al_2O_3 via in-situ reflection high energy electron diffraction(RHEED) monitoring and ex-situ X-ray diffraction(XRD) measurement. Crystalline quality is improved and surface becomes flatter with increasing growth temperature, with a best full width at half maximum(FWHM) of XRD ω-rocking curve of( 2ˉ01) plane and root mean square(RMS) roughness of 0.68° and 2.04 nm for the sample grown at 730 °C,respectively. Room temperature cathodoluminescence measurement shows an emission at ～417 nm, which is most likely originated from recombination of donor–acceptor pair(DAP).展开更多
Single-crystal sapphire is utilized as a high-performance engineering material,especially in extreme and harsh environments.However,due to its extreme hardness and brittleness,the machinability of sapphire is still a ...Single-crystal sapphire is utilized as a high-performance engineering material,especially in extreme and harsh environments.However,due to its extreme hardness and brittleness,the machinability of sapphire is still a challenge.By means of nanoindentation and plunge-cut experiments,the anisotropic brittle-ductile transition of the prismatic M-plane and rhombohedral R-plane is examined by analyzing crack morphologies and the critical depth-of-cut(CDC).The experimental results of the nanoindentation tests are correlated to the plunge-cut experiment.Both the prism plane and the rhombohedral crystal plane exhibit a two-fold symmetry of ductility with various crack patterns along the machined grooves.The direction-dependent plasticity of the hexagonal sapphire crystal is mainly connected to a twinning process accompanied by slip dislocation.展开更多
Non-spherical colloidal silica nanoparticle was prepared by a simple new method, and its particle size distribution and shape morphology were characterized by dynamic light scattering(DLS) and the Focus Ion Beam(FIB) ...Non-spherical colloidal silica nanoparticle was prepared by a simple new method, and its particle size distribution and shape morphology were characterized by dynamic light scattering(DLS) and the Focus Ion Beam(FIB) system. This kind of novel colloidal silica particles can be well used in chemical mechanical polishing(CMP) of sapphire wafer surface. And the polishing test proves that non-spherical colloidal silica slurry shows much higher material removal rate(MRR) with higher coefficient of friction(COF) when compared to traditional large spherical colloidal silica slurry with particle size 80 nm by DLS. Besides, sapphire wafer polished by non-spherical abrasive also has a good surface roughness of 0.460 6 nm. Therefore, non-spherical colloidal silica has shown great potential in the CMP field because of its higher MRR and better surface roughness.展开更多
The professional modeling software package CrysVUn was employed to study the process of a large sapphire single crystal growth using Kyropoulos method. The influence of gas pressure on thermal field, solid-liquid inte...The professional modeling software package CrysVUn was employed to study the process of a large sapphire single crystal growth using Kyropoulos method. The influence of gas pressure on thermal field, solid-liquid interface shape, gas velocity field and von Mises stress were studied for the first time. It is found that the root of the seed melt when gas pressure equals to one atmosphere or more than one atmosphere, especially during the seeding period, this result is consistent with the experimental observation, and this paper presents three ways to solve this problem. The temperature gradient and stress decreases significantly as the gas pressure increases. The convexity of the solid-liquid interface slightly increases when the gas pressure increases. Numerical analysis was used to optimize the hot zone design.展开更多
Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamen...Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamentation and analyzed the ionization dynamics of the filamentation.Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material.The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track.By increasing laser energy,the length of the damage and filamentary track appeared to increase.In addition,the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations,but no increase in the filamentary zone diameter was observed with increasing laser energy.展开更多
InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl ...InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl indium (TMIn) and N 2 were applied as precursors of In and N, respectively. The quality of as-grown InN films were systematically investigated as a function of TMIn fluxes by means of reflection high-energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), and atomic force microscopy (AFM). The results show that the dense and uniform InN films with highly c-axis preferred orientation are successfully achieved on sapphire substrates under optimized TMIn flux of 0.8 ml min 1 . The InN films reported here will provide various opportunities for the development of high efficiency and high-performance semiconductor devices based on InN material.展开更多
In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting dir...In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting direction of resultant force. Anisotropic characteristics of crack morphology and ductility of machining depending on cutting direction were explained in detail with modified fracture cleavage and plastic deformation parameters. Through the analysis, it was concluded that crack morphologies were mainly determined by the interaction of multiple fracture systems activated while, critical depth of cut was determined by the dominant plastic deformation parameter. In addition to this, by using proportionality relationship between magnitude of resultant force and depth of cut in the ductile region, an empirical model for critical depth of cut was developed.展开更多
Diffusion of beryllium was performed on dark blue sapphire from China and Australia.The samples were heated with beryllium as a dopant in a furnace at 1 600℃ for 42 hin air.After beryllium diffusion,samples were anal...Diffusion of beryllium was performed on dark blue sapphire from China and Australia.The samples were heated with beryllium as a dopant in a furnace at 1 600℃ for 42 hin air.After beryllium diffusion,samples were analyzed by UV-Vis,FTIR,and WD-XRF spectroscopy.After heat-treatment with Be as a catalyst,the irons of the ferrous state were changed to the ferric state.Therefore,reaction of Fe^(2+)/Ti^(4+) IVCT was decreased.The absorption peaks at 3 309cm^(-1) attributed to OH radical were disappeared completely due to carry out heat treatment.Consequently,the intensity of absorption band was decreased in the visible region.Especially,decreased absorption band in the vicinity of 570 nm was responsible for the lighter blue color.Therefore,we confirmed that the dark blue sapphires from China and Australia were changed to vivid blue.展开更多
A two-dimensional model was established in the rectangular co-ordinate to study the thermal stress in the sapphire single crystal grown by the improved Kyropoulos. In the simulation, the distribution, the maximum and ...A two-dimensional model was established in the rectangular co-ordinate to study the thermal stress in the sapphire single crystal grown by the improved Kyropoulos. In the simulation, the distribution, the maximum and minimum values of the thermal stress were calculated. In addition, the relationship between the thermal stress and the shouldering angles was obtained that for lower shouldering angles, the maximum of the thermal stress value is lower and the minimum value is higher. It indicates that the distribution of the thermal stress can be improved by decreasing the shouldering angles of the crystal during the growth process. To evaluate the model, the experiment was carried out and the results are in good agreement with the calculation.展开更多
We studied the evolution of wavefront aberration(WFA) of a signal beam during amplification in a Ti:sapphire chirped pulse amplification(CPA) system. The results verified that the WFA of the amplified laser beam has l...We studied the evolution of wavefront aberration(WFA) of a signal beam during amplification in a Ti:sapphire chirped pulse amplification(CPA) system. The results verified that the WFA of the amplified laser beam has little relation with the change of the pump beam energies. Transverse parasitic lasing that might occur in CPA hardly affects the wavefront of the signal beam. Thermal effects were also considered in this study, and the results show that the thermal effect cumulated in multiple amplification processes also has no obvious influence on the wavefront of the signal beam for a single-shot frequency. The results presented in this paper confirmed experimentally that the amplification in a Ti:sapphire CPA system has little impact on the WFA of the signal beam and it is very helpful for wavefront correction of single-shot PW and multi-PW laser systems based on Ti:sapphire.展开更多
AlGaN/GaN high electron mobility transistors(HEMTs) grown on Fe-modulation-doped(AID) and unintentionally doped(UID) GaN buffer layers are investigated and compared.Highly resistive GaN buffers(10~9 Ω·cm) are in...AlGaN/GaN high electron mobility transistors(HEMTs) grown on Fe-modulation-doped(AID) and unintentionally doped(UID) GaN buffer layers are investigated and compared.Highly resistive GaN buffers(10~9 Ω·cm) are induced by individual mechanisms for the electron traps' formation:the Fe AID buffer(sample A) and the UID buffer with high density of edge-type dislocations(7.24 × 10~9 cm^(-2),sample B).The 300 K Hall test indicates that the mobility of sample A with Fe doping(2503 cm^2 V^(-1) s^(-1)) is much higher than sample B(1926cm^2V^(-1)s^(-1))due to the decreased scattering effect on the two-dimensional electron gas.HEMT devices are fabricated on the two samples and pulsed Ⅰ-Ⅴ measurements are conducted.Device A shows better gate pinch-off characteristics and a higher threshold voltage(-2.63 V) compared with device B(-3.71 V).Lower gate leakage current \Igs\ of device A(3.32 × 10^(-7) A) is present compared with that of device B(8.29 × 10^(-7) A).When the off-state quiescent points Q_2(V_(GQ2) =-8 V,V_(DQ2) = 0 V) are on,V_(th) hardly shifts for device A while device B shows +0.21 V positive threshold voltage shift,resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate.Under pulsed Ⅰ-Ⅴ and transconductance G_m-V_(GS) measurement,the device with the Fe MD-dopcd buffer shows more potential in improving reliability upon off-state stress.展开更多
We investigate the impact of different numbers of positive and negative examples on machine learning for sapphire crystals defects prediction. We obtain the models of crystal growth parameters influence on the sapphir...We investigate the impact of different numbers of positive and negative examples on machine learning for sapphire crystals defects prediction. We obtain the models of crystal growth parameters influence on the sapphire crystal growth. For example, these models allow predicting the defects that occur due to local overcooling of crucible walls in the thermal node leading to the accelerated crystal growth. We also develop the prediction models for obtaining the crystal weight, blocks, cracks, bubbles formation, and total defect characteristics. The models were trained on all data sets and later tested for generalization on testing sets, which did not overlap the training set.During training and testing, we find the recall and precision of prediction, and analyze the correlation among the features. The results have shown that the precision of the neural network method for predicting defects formed by local overcooling of the crucible reached 0.94.展开更多
This paper presents the results of our numerical shnulation,ma.de by employing Splitstep Fourier Method,of pulsewidth dependence on the physical quantities in ring cavity Ti:sapphire laser.It is revealed through the c...This paper presents the results of our numerical shnulation,ma.de by employing Splitstep Fourier Method,of pulsewidth dependence on the physical quantities in ring cavity Ti:sapphire laser.It is revealed through the computed results that Kerr-lens effect which is now quantitatively considered plays a doniniaiit role in forming ultra.short pulses and its interaction with dispersion fina.lly determines the duration of the pulse,which sheds light on further theoretical investigation of the mode locking niechanisju.Meanwhile,the self-consistent results also provide a giuc/eiine for the experimental alignment of the laser.展开更多
A high-pulse-energy high-beam-quality tunable Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated.Using a fused-silica prism as the dispersion element,a tuning range of 740-855 nm is obtained....A high-pulse-energy high-beam-quality tunable Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated.Using a fused-silica prism as the dispersion element,a tuning range of 740-855 nm is obtained.At an incident pump energy of 774 mJ,the maximum output energy of 104 mJ at 790 nm with a pulse width of100 μs is achieved at a repetition rate of 5 Hz.To the best of our knowledge,it is the highest pulse energy at790 nm with pulse width of hundred micro-seconds for an all-solid-state laser.The linewidth of output is 0.5 nm,and the beam quality factor M^2 is 1.16.The high-pulse-energy high-beam-quality tunable Ti:sapphire laser in the range of 740-855 nm can be used to establish a more accurate and consistent absolute scale of second-order optical-nonlinear coefficients for KBe_2BO_3F_2 measured in a wider wavelength range and to assess Miller's rule q uantitatively.展开更多
Zircon inclusions in two selected Kashmir sapphire reference samples and one faceted gemstone were studied by HR SIMS and LA-ICP-MS for U-Pb age determination.The two independent analytical methods result in the same ...Zircon inclusions in two selected Kashmir sapphire reference samples and one faceted gemstone were studied by HR SIMS and LA-ICP-MS for U-Pb age determination.The two independent analytical methods result in the same conclusion that the zircons have crystallization ages of 26-25 Ma.The provided result is a good reference for U-Pb age of Kashmir sapphire that can be used for origin determination in gemmological laboratories with LA-ICP-MS routine method.Additionally,cathodoluminescence imaging showed that the zircon inclusions in Kashmir sapphires have regular oscillatory zoning.High U concentrations of up to 20000 ppm have been detected in the zircon inclusions.展开更多
We design and fabricate a good performance silicon photoconductive terahertz detector on sapphire substrates at room temperature.The best voltage responsivity of the detector is 6679 V/W at frequency 300 GHz as well a...We design and fabricate a good performance silicon photoconductive terahertz detector on sapphire substrates at room temperature.The best voltage responsivity of the detector is 6679 V/W at frequency 300 GHz as well as low voltage noise of 3.8 nV/Hz1/2 for noise equivalent power 0.57 pW/Hz1/2.The measured response time of the device is about 9 μs,demonstrating that the detector has a speed of>110 kHz.The achieved good performance,together with large detector size(acceptance area is 3μm×160μm),simple structure,easy manufacturing method,compatibility with mature silicon technology,and suitability for large-scale fabrication of imaging arrays provide a promising approach to the development of sensitive terahertz room-temperature detectors.展开更多
We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser.Central wavelength tunability as broad as 89 nm(736-825 nm) is achieved by adjusting the insertion of the prism.Pulses a...We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser.Central wavelength tunability as broad as 89 nm(736-825 nm) is achieved by adjusting the insertion of the prism.Pulses as short as 17 fs are generated at a central wavelength of 736 nm with an average output power of 31 mW.The maximum output power is 46.8 mW at a central wavelength of 797 nm with a pulse duration of 46 fs.展开更多
The internal radiative contributed on heat transfer will enhance the heat transport inside the crystalline phase during growth the transparent sapphire crystal using a heat-exchanger-method (HEM). The artificially enh...The internal radiative contributed on heat transfer will enhance the heat transport inside the crystalline phase during growth the transparent sapphire crystal using a heat-exchanger-method (HEM). The artificially enhanced thermal conductivity of the solid to include the internal radiation effect was used in the present study. Numerical simulations using FIDAP were performed to investigate the effects of the thermal conductivity on the shape of the melt-crystal interface, the temperature distribution, and the velocity distribution. Heat transfer (including radiation) from the furnace to the crucible and heat extraction from the heat exchanger can be modeled by the convection boundary conditions. In the present study, we focus on the influence of the conductivity on the shape of the melt-crystal interface. Therefore, the effect of the others growth parameters during the HEM crystal growth was neglected. For the homogenous conductivity (km=kS=k), the maximum convexity decreases as k increases and the rate of maximum convexity increases for a higher conductivity is less abrupt than for a lower conductivity. For the no homogenous conductivity (km≠kS), the higher solid's kS generates lower maximum convexity and the variation in maximum convexity was less abrupt for the different melt's km. The maximum convexity decreases slightly as the enhance conductivity of the sapphire crystal increases. The effects of the anisotropic conductivity of the sapphire crystal were also addressed. The maximum convexity of the melt-crystal interface decreases when the radial conductivity (ksr) of the crystal increases. The maximum convexity increases as the axial conductivity (ksz) of the crucible increases.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 61974158)the Natural Science Fund of Jiangsu Province, China (Grant No. BK20191456)。
文摘A crack-free AlN film with 4.5 μm thickness was grown on a 2-inch hole-type nano-patterned sapphire substrates(NPSSs) by hydride vapor phase epitaxy(HVPE). The coalescence, stress evolution, and dislocation annihilation mechanisms in the AlN layer have been investigated. The large voids located on the pattern region were caused by the undesirable parasitic crystallites grown on the sidewalls of the nano-pattern in the early growth stage. The coalescence of the c-plane AlN was hindered by these three-fold crystallites and the special triangle void appeared. The cross-sectional Raman line scan was used to characterize the change of stress with film thickness, which corresponds to the characteristics of different growth stages of AlN. Threading dislocations(TDs) mainly originate from the boundary between misaligned crystallites and the c-plane AlN and the coalescence of two adjacent c-plane AlN crystals, rather than the interface between sapphire and AlN.
基金supported by the National Key R&D Program(Grant No.2021YFF0603701)the National Natural Science Foundation of China(Grant Nos.U21A20433,U21A6006,92265210,12104441,12134014,61905234,and 11974335)+1 种基金the USTC Research Funds of the Double First-Class Initiative(Grant No.YD2030002007),USTC Research Funds of the Double First-Class Initiativesupported by the Fundamental Research Funds for the Central Universities。
文摘Trapped atoms on photonic structures inspire many novel quantum devices for quantum information processing and quantum sensing.Here,we demonstrate a hybrid photonic-atom chip platform based on a Ga N-onsapphire chip and the transport of an ensemble of atoms from free space towards the chip with an optical conveyor belts.Due to our platform’s complete optical accessibility and careful control of atomic motion near the chip with a conveyor belt,successful atomic transport towards the chip is made possible.The maximum transport efficiency of atoms is about 50%with a transport distance of 500μm.Our results open up a new route toward the efficient loading of cold atoms into the evanescent-field trap formed by the photonic integrated circuits,which promises strong and controllable interactions between single atoms and single photons.
基金supported by the National Key R&D Program of China(No.2018YFB0406502)the National Natural Science Foundation of China(Nos.61734001,61521004)
文摘Monoclinic gallium oxide(Ga_2O_3) has been grown on(0001) sapphire(Al_2O_3) substrate by plasma-assisted molecular beam epitaxy(PA-MBE). The epitaxial relationship has been confirmed to be [010]( 2ˉ01) β-Ga_2O_3||[ 011ˉ0](0001)Al_2O_3 via in-situ reflection high energy electron diffraction(RHEED) monitoring and ex-situ X-ray diffraction(XRD) measurement. Crystalline quality is improved and surface becomes flatter with increasing growth temperature, with a best full width at half maximum(FWHM) of XRD ω-rocking curve of( 2ˉ01) plane and root mean square(RMS) roughness of 0.68° and 2.04 nm for the sample grown at 730 °C,respectively. Room temperature cathodoluminescence measurement shows an emission at ～417 nm, which is most likely originated from recombination of donor–acceptor pair(DAP).
基金partially supported by JSPS KAKENHI[Grant no.16K14137,2016]
文摘Single-crystal sapphire is utilized as a high-performance engineering material,especially in extreme and harsh environments.However,due to its extreme hardness and brittleness,the machinability of sapphire is still a challenge.By means of nanoindentation and plunge-cut experiments,the anisotropic brittle-ductile transition of the prismatic M-plane and rhombohedral R-plane is examined by analyzing crack morphologies and the critical depth-of-cut(CDC).The experimental results of the nanoindentation tests are correlated to the plunge-cut experiment.Both the prism plane and the rhombohedral crystal plane exhibit a two-fold symmetry of ductility with various crack patterns along the machined grooves.The direction-dependent plasticity of the hexagonal sapphire crystal is mainly connected to a twinning process accompanied by slip dislocation.
基金Funded by the National Major Scientific and Technological Special Project during the Twelfth Five-year Plan Period(No.2009ZX02030-1)the National Natural Science Foundation of China(No.51205387)the Science and Technology Commission of Shanghai(No.11nm0500300),the Science and Technology Commission of Shanghai(No.14XD1425300)
文摘Non-spherical colloidal silica nanoparticle was prepared by a simple new method, and its particle size distribution and shape morphology were characterized by dynamic light scattering(DLS) and the Focus Ion Beam(FIB) system. This kind of novel colloidal silica particles can be well used in chemical mechanical polishing(CMP) of sapphire wafer surface. And the polishing test proves that non-spherical colloidal silica slurry shows much higher material removal rate(MRR) with higher coefficient of friction(COF) when compared to traditional large spherical colloidal silica slurry with particle size 80 nm by DLS. Besides, sapphire wafer polished by non-spherical abrasive also has a good surface roughness of 0.460 6 nm. Therefore, non-spherical colloidal silica has shown great potential in the CMP field because of its higher MRR and better surface roughness.
文摘The professional modeling software package CrysVUn was employed to study the process of a large sapphire single crystal growth using Kyropoulos method. The influence of gas pressure on thermal field, solid-liquid interface shape, gas velocity field and von Mises stress were studied for the first time. It is found that the root of the seed melt when gas pressure equals to one atmosphere or more than one atmosphere, especially during the seeding period, this result is consistent with the experimental observation, and this paper presents three ways to solve this problem. The temperature gradient and stress decreases significantly as the gas pressure increases. The convexity of the solid-liquid interface slightly increases when the gas pressure increases. Numerical analysis was used to optimize the hot zone design.
基金National Natural Science Foundation of China(51575013,51275011)National Key R&D Program of China(2018 YFB1107500)
文摘Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamentation and analyzed the ionization dynamics of the filamentation.Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material.The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track.By increasing laser energy,the length of the damage and filamentary track appeared to increase.In addition,the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations,but no increase in the filamentary zone diameter was observed with increasing laser energy.
基金supported by the National Natural Science Foundation of China (No. 61040058) (No. 60976006)the Fundamental Research Funds for the Central Universities (No.DUT10LK01)the Science and Technology Foundation for Higher Education of Liaoning Province, China and Science and Technology Innovation Project Foundation for Higher Education School (No.707015)
文摘InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl indium (TMIn) and N 2 were applied as precursors of In and N, respectively. The quality of as-grown InN films were systematically investigated as a function of TMIn fluxes by means of reflection high-energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), and atomic force microscopy (AFM). The results show that the dense and uniform InN films with highly c-axis preferred orientation are successfully achieved on sapphire substrates under optimized TMIn flux of 0.8 ml min 1 . The InN films reported here will provide various opportunities for the development of high efficiency and high-performance semiconductor devices based on InN material.
基金supported by the NSF under grant No. CMMI-1844821。
文摘In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting direction of resultant force. Anisotropic characteristics of crack morphology and ductility of machining depending on cutting direction were explained in detail with modified fracture cleavage and plastic deformation parameters. Through the analysis, it was concluded that crack morphologies were mainly determined by the interaction of multiple fracture systems activated while, critical depth of cut was determined by the dominant plastic deformation parameter. In addition to this, by using proportionality relationship between magnitude of resultant force and depth of cut in the ductile region, an empirical model for critical depth of cut was developed.
基金supported by the research grant of the Kongju National University in 2011.
文摘Diffusion of beryllium was performed on dark blue sapphire from China and Australia.The samples were heated with beryllium as a dopant in a furnace at 1 600℃ for 42 hin air.After beryllium diffusion,samples were analyzed by UV-Vis,FTIR,and WD-XRF spectroscopy.After heat-treatment with Be as a catalyst,the irons of the ferrous state were changed to the ferric state.Therefore,reaction of Fe^(2+)/Ti^(4+) IVCT was decreased.The absorption peaks at 3 309cm^(-1) attributed to OH radical were disappeared completely due to carry out heat treatment.Consequently,the intensity of absorption band was decreased in the visible region.Especially,decreased absorption band in the vicinity of 570 nm was responsible for the lighter blue color.Therefore,we confirmed that the dark blue sapphires from China and Australia were changed to vivid blue.
文摘A two-dimensional model was established in the rectangular co-ordinate to study the thermal stress in the sapphire single crystal grown by the improved Kyropoulos. In the simulation, the distribution, the maximum and minimum values of the thermal stress were calculated. In addition, the relationship between the thermal stress and the shouldering angles was obtained that for lower shouldering angles, the maximum of the thermal stress value is lower and the minimum value is higher. It indicates that the distribution of the thermal stress can be improved by decreasing the shouldering angles of the crystal during the growth process. To evaluate the model, the experiment was carried out and the results are in good agreement with the calculation.
基金Project supported by the National Natural Science Foundation of China(Grant No.61775223)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB1603)
文摘We studied the evolution of wavefront aberration(WFA) of a signal beam during amplification in a Ti:sapphire chirped pulse amplification(CPA) system. The results verified that the WFA of the amplified laser beam has little relation with the change of the pump beam energies. Transverse parasitic lasing that might occur in CPA hardly affects the wavefront of the signal beam. Thermal effects were also considered in this study, and the results show that the thermal effect cumulated in multiple amplification processes also has no obvious influence on the wavefront of the signal beam for a single-shot frequency. The results presented in this paper confirmed experimentally that the amplification in a Ti:sapphire CPA system has little impact on the WFA of the signal beam and it is very helpful for wavefront correction of single-shot PW and multi-PW laser systems based on Ti:sapphire.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61204017 and 61334002the National Basic Research Program of Chinathe National Science and Technology Major Project of China
文摘AlGaN/GaN high electron mobility transistors(HEMTs) grown on Fe-modulation-doped(AID) and unintentionally doped(UID) GaN buffer layers are investigated and compared.Highly resistive GaN buffers(10~9 Ω·cm) are induced by individual mechanisms for the electron traps' formation:the Fe AID buffer(sample A) and the UID buffer with high density of edge-type dislocations(7.24 × 10~9 cm^(-2),sample B).The 300 K Hall test indicates that the mobility of sample A with Fe doping(2503 cm^2 V^(-1) s^(-1)) is much higher than sample B(1926cm^2V^(-1)s^(-1))due to the decreased scattering effect on the two-dimensional electron gas.HEMT devices are fabricated on the two samples and pulsed Ⅰ-Ⅴ measurements are conducted.Device A shows better gate pinch-off characteristics and a higher threshold voltage(-2.63 V) compared with device B(-3.71 V).Lower gate leakage current \Igs\ of device A(3.32 × 10^(-7) A) is present compared with that of device B(8.29 × 10^(-7) A).When the off-state quiescent points Q_2(V_(GQ2) =-8 V,V_(DQ2) = 0 V) are on,V_(th) hardly shifts for device A while device B shows +0.21 V positive threshold voltage shift,resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate.Under pulsed Ⅰ-Ⅴ and transconductance G_m-V_(GS) measurement,the device with the Fe MD-dopcd buffer shows more potential in improving reliability upon off-state stress.
基金supported by the Russian Foundation for Basic Research Projects under Grant No.16-52-48016ИНД_оми(R.Kumar and A.V.Filimonov)。
文摘We investigate the impact of different numbers of positive and negative examples on machine learning for sapphire crystals defects prediction. We obtain the models of crystal growth parameters influence on the sapphire crystal growth. For example, these models allow predicting the defects that occur due to local overcooling of crucible walls in the thermal node leading to the accelerated crystal growth. We also develop the prediction models for obtaining the crystal weight, blocks, cracks, bubbles formation, and total defect characteristics. The models were trained on all data sets and later tested for generalization on testing sets, which did not overlap the training set.During training and testing, we find the recall and precision of prediction, and analyze the correlation among the features. The results have shown that the precision of the neural network method for predicting defects formed by local overcooling of the crucible reached 0.94.
基金Supported by the Young Teachers'Foundation of the State Commission of Education.
文摘This paper presents the results of our numerical shnulation,ma.de by employing Splitstep Fourier Method,of pulsewidth dependence on the physical quantities in ring cavity Ti:sapphire laser.It is revealed through the computed results that Kerr-lens effect which is now quantitatively considered plays a doniniaiit role in forming ultra.short pulses and its interaction with dispersion fina.lly determines the duration of the pulse,which sheds light on further theoretical investigation of the mode locking niechanisju.Meanwhile,the self-consistent results also provide a giuc/eiine for the experimental alignment of the laser.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61275157 and 61475040the National Key Scientific Instrument and Equipment Development,Project under Grant No 2012YQ120048+1 种基金the National Development Project for Major Scientific Research Facility under Grant No ZDYZ2012-2the National Key Research and Development Program of China under Grant No 2016YFB0402003
文摘A high-pulse-energy high-beam-quality tunable Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated.Using a fused-silica prism as the dispersion element,a tuning range of 740-855 nm is obtained.At an incident pump energy of 774 mJ,the maximum output energy of 104 mJ at 790 nm with a pulse width of100 μs is achieved at a repetition rate of 5 Hz.To the best of our knowledge,it is the highest pulse energy at790 nm with pulse width of hundred micro-seconds for an all-solid-state laser.The linewidth of output is 0.5 nm,and the beam quality factor M^2 is 1.16.The high-pulse-energy high-beam-quality tunable Ti:sapphire laser in the range of 740-855 nm can be used to establish a more accurate and consistent absolute scale of second-order optical-nonlinear coefficients for KBe_2BO_3F_2 measured in a wider wavelength range and to assess Miller's rule q uantitatively.
文摘Zircon inclusions in two selected Kashmir sapphire reference samples and one faceted gemstone were studied by HR SIMS and LA-ICP-MS for U-Pb age determination.The two independent analytical methods result in the same conclusion that the zircons have crystallization ages of 26-25 Ma.The provided result is a good reference for U-Pb age of Kashmir sapphire that can be used for origin determination in gemmological laboratories with LA-ICP-MS routine method.Additionally,cathodoluminescence imaging showed that the zircon inclusions in Kashmir sapphires have regular oscillatory zoning.High U concentrations of up to 20000 ppm have been detected in the zircon inclusions.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61775060 and 61275100
文摘We design and fabricate a good performance silicon photoconductive terahertz detector on sapphire substrates at room temperature.The best voltage responsivity of the detector is 6679 V/W at frequency 300 GHz as well as low voltage noise of 3.8 nV/Hz1/2 for noise equivalent power 0.57 pW/Hz1/2.The measured response time of the device is about 9 μs,demonstrating that the detector has a speed of>110 kHz.The achieved good performance,together with large detector size(acceptance area is 3μm×160μm),simple structure,easy manufacturing method,compatibility with mature silicon technology,and suitability for large-scale fabrication of imaging arrays provide a promising approach to the development of sensitive terahertz room-temperature detectors.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFB0402105)
文摘We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser.Central wavelength tunability as broad as 89 nm(736-825 nm) is achieved by adjusting the insertion of the prism.Pulses as short as 17 fs are generated at a central wavelength of 736 nm with an average output power of 31 mW.The maximum output power is 46.8 mW at a central wavelength of 797 nm with a pulse duration of 46 fs.
文摘The internal radiative contributed on heat transfer will enhance the heat transport inside the crystalline phase during growth the transparent sapphire crystal using a heat-exchanger-method (HEM). The artificially enhanced thermal conductivity of the solid to include the internal radiation effect was used in the present study. Numerical simulations using FIDAP were performed to investigate the effects of the thermal conductivity on the shape of the melt-crystal interface, the temperature distribution, and the velocity distribution. Heat transfer (including radiation) from the furnace to the crucible and heat extraction from the heat exchanger can be modeled by the convection boundary conditions. In the present study, we focus on the influence of the conductivity on the shape of the melt-crystal interface. Therefore, the effect of the others growth parameters during the HEM crystal growth was neglected. For the homogenous conductivity (km=kS=k), the maximum convexity decreases as k increases and the rate of maximum convexity increases for a higher conductivity is less abrupt than for a lower conductivity. For the no homogenous conductivity (km≠kS), the higher solid's kS generates lower maximum convexity and the variation in maximum convexity was less abrupt for the different melt's km. The maximum convexity decreases slightly as the enhance conductivity of the sapphire crystal increases. The effects of the anisotropic conductivity of the sapphire crystal were also addressed. The maximum convexity of the melt-crystal interface decreases when the radial conductivity (ksr) of the crystal increases. The maximum convexity increases as the axial conductivity (ksz) of the crucible increases.
