Ex situ characterization techniques in molecular beam epitaxy(MBE)have inherent limitations,such as being prone to sample contamination and unstable surfaces during sample transfer from the MBE chamber.In recent years...Ex situ characterization techniques in molecular beam epitaxy(MBE)have inherent limitations,such as being prone to sample contamination and unstable surfaces during sample transfer from the MBE chamber.In recent years,the need for improved accuracy and reliability in measurement has driven the increasing adoption of in situ characterization techniques.These techniques,such as reflection high-energy electron diffraction,scanning tunneling microscopy,and X-ray photoelectron spectroscopy,allow direct observation of film growth processes in real time without exposing the sample to air,hence offering insights into the growth mechanisms of epitaxial films with controlled properties.By combining multiple in situ characterization techniques with MBE,researchers can better understand film growth processes,realizing novel materials with customized properties and extensive applications.This review aims to overview the benefits and achievements of in situ characterization techniques in MBE and their applications for material science research.In addition,through further analysis of these techniques regarding their challenges and potential solutions,particularly highlighting the assistance of machine learning to correlate in situ characterization with other material information,we hope to provide a guideline for future efforts in the development of novel monitoring and control schemes for MBE growth processes with improved material properties.展开更多
A second order accurate(in time)numerical scheme is analyzed for the slope-selection(SS)equation of the epitaxial thin film growth model,with Fourier pseudo-spectral discretization in space.To make the numerical schem...A second order accurate(in time)numerical scheme is analyzed for the slope-selection(SS)equation of the epitaxial thin film growth model,with Fourier pseudo-spectral discretization in space.To make the numerical scheme linear while preserving the nonlinear energy stability,we make use of the scalar auxiliary variable(SAV)approach,in which a modified Crank-Nicolson is applied for the surface diffusion part.The energy stability could be derived a modified form,in comparison with the standard Crank-Nicolson approximation to the surface diffusion term.Such an energy stability leads to an H2 bound for the numerical solution.In addition,this H2 bound is not sufficient for the optimal rate convergence analysis,and we establish a uniform-in-time H3 bound for the numerical solution,based on the higher order Sobolev norm estimate,combined with repeated applications of discrete H¨older inequality and nonlinear embeddings in the Fourier pseudo-spectral space.This discrete H3 bound for the numerical solution enables us to derive the optimal rate error estimate for this alternate SAV method.A few numerical experiments are also presented,which confirm the efficiency and accuracy of the proposed scheme.展开更多
Fabrication of metal-organic frameworks(MOFs)thin films has been an efficient way to expand their functionalities and applications.Here,we use the vapor-assisted deposition(VAD)method to epitaxially grow a porphyrin-b...Fabrication of metal-organic frameworks(MOFs)thin films has been an efficient way to expand their functionalities and applications.Here,we use the vapor-assisted deposition(VAD)method to epitaxially grow a porphyrin-based MOF PCN-222 film.That is,vapor source assists to deposit pre-treated precursor solution on quartz substrate to form a continuous PCN-222 film.Furthermore,utilizing the post-treated encapsulation of functional carbon-based nanoparticles,the carbon nanodots(CND)and Pt doped CND(Pt/CND)are well loaded into the pores of PCN-222 film,the size(~3.1 nm)of which is highly close to the pore size of the corresponding MOF(~3.7 nm).The Z-scan results reveal that PCN-222 film exhibits high reverse saturable absorption.In addition,encapsulation of carbon based nanodots into PCN-222 film could enhance the nonlinear optical limiting effect benefiting from the host-guest combination.This study serves to present both the available toolbox of thin film preparation and high potential for precise synthetic nanocomposite films in optical limiting devices.展开更多
The research and development of high temperature superconducting （HTS） films, especially ReBa2Cu3- O7-δ （REBCO or RE123; RE=Y, Gd, or other rare earths） yttrium-based coated conductors, has generated widespread i...The research and development of high temperature superconducting （HTS） films, especially ReBa2Cu3- O7-δ （REBCO or RE123; RE=Y, Gd, or other rare earths） yttrium-based coated conductors, has generated widespread interest for the potential applications of the second generation superconducting films. In view of commercialization, however, the maximum superconducting currents for coated conductors should be increased further. Unfortunately, it has been frequently observed that the average critical current density Jc decreases with an increase in film thickness. The thickness effect is still a hurdle for largescale production, especially in pulsed laser deposition and metal organic deposition processes. An engineering current of more than 1 000 A/cm is desired owing to the high cost of 2G superconducting materials. The present work attempts to review the evolution of various issues subject to the thickness effect, including the microstructure, epitaxial texture, surface roughness, pinning force, oxygen deficiency, residual stress, copper-rich layers, and segregation of elements. Furthermore, recent progress in enhancing the performance of superconductors especially in terms of critical current density is illustrated, such as the use of heavy doping. Further understanding of the thickness effect is extremely important for large-scale commercial development of the second generation high temperature superconductors.展开更多
The growth conditions of La0.7Ca0.3MnO3(LCMO) epitaxial thin film are investigated.The results indicate that the deposition temperature plays a crucial role on the growth mode of LCMO thin film.There is an optimal dep...The growth conditions of La0.7Ca0.3MnO3(LCMO) epitaxial thin film are investigated.The results indicate that the deposition temperature plays a crucial role on the growth mode of LCMO thin film.There is an optimal deposition temperature,To,for the epitaxial growth of LCMO thin film.Just only at the To,the real epitaxial LCMO thin film can be obtained.When the deposition temperature deviates from the To,the thin film tends to be polycrystalline,although it orientes growth along a certain direction(a or c axis).Moreover,the experimental results show that just only for the epitaxial thin film the ferromagnetic-paramagnetic transition temperature(i.e.the Courier temperature Tc) equals to the metal-semiconductor transition temperature(Tp).The ferromagnetic state shows metallicity and the paramagnetic state exhibits semiconducting character.展开更多
Practical solar energy solutions must not only reduce the cost of the module,but also address the substantial balance of system costs.Here,we demonstrate a counter-intuitive approach based on gallium arsenide solar ce...Practical solar energy solutions must not only reduce the cost of the module,but also address the substantial balance of system costs.Here,we demonstrate a counter-intuitive approach based on gallium arsenide solar cells that can achieve extremely low-cost solar energy conversion with an estimated cost of only 3% that of conventional gallium arsenide solar cells using an accelerated,non-destructive epitaxial lift-off wafer recycling process along with a lightweight,thermoformed plastic,truncated mini-compound parabolic concentrator that avoids the need for active solar tracking.Using solar cell/concentrator assemblies whose orientations are adjusted only a few times per year,the annual energy harvesting is increased by 2.8 times compared with planar solar cells without solar tracking.These results represent a potentially drastic cost reduction in both the module and the balance of system costs compared with heavy,rigid conventional modules and trackers that are subject to wind loading damage and high installation costs.展开更多
基金supported by the National Key R&D Program of China(Grant No.2021YFB2206503)National Natural Science Foundation of China(Grant No.62274159)+1 种基金CAS Project for Young Scientists in Basic Research(Grant No.YSBR-056)the“Strategic Priority Research Program”of the Chinese Academy of Sciences(Grant No.XDB43010102).
文摘Ex situ characterization techniques in molecular beam epitaxy(MBE)have inherent limitations,such as being prone to sample contamination and unstable surfaces during sample transfer from the MBE chamber.In recent years,the need for improved accuracy and reliability in measurement has driven the increasing adoption of in situ characterization techniques.These techniques,such as reflection high-energy electron diffraction,scanning tunneling microscopy,and X-ray photoelectron spectroscopy,allow direct observation of film growth processes in real time without exposing the sample to air,hence offering insights into the growth mechanisms of epitaxial films with controlled properties.By combining multiple in situ characterization techniques with MBE,researchers can better understand film growth processes,realizing novel materials with customized properties and extensive applications.This review aims to overview the benefits and achievements of in situ characterization techniques in MBE and their applications for material science research.In addition,through further analysis of these techniques regarding their challenges and potential solutions,particularly highlighting the assistance of machine learning to correlate in situ characterization with other material information,we hope to provide a guideline for future efforts in the development of novel monitoring and control schemes for MBE growth processes with improved material properties.
文摘A second order accurate(in time)numerical scheme is analyzed for the slope-selection(SS)equation of the epitaxial thin film growth model,with Fourier pseudo-spectral discretization in space.To make the numerical scheme linear while preserving the nonlinear energy stability,we make use of the scalar auxiliary variable(SAV)approach,in which a modified Crank-Nicolson is applied for the surface diffusion part.The energy stability could be derived a modified form,in comparison with the standard Crank-Nicolson approximation to the surface diffusion term.Such an energy stability leads to an H2 bound for the numerical solution.In addition,this H2 bound is not sufficient for the optimal rate convergence analysis,and we establish a uniform-in-time H3 bound for the numerical solution,based on the higher order Sobolev norm estimate,combined with repeated applications of discrete H¨older inequality and nonlinear embeddings in the Fourier pseudo-spectral space.This discrete H3 bound for the numerical solution enables us to derive the optimal rate error estimate for this alternate SAV method.A few numerical experiments are also presented,which confirm the efficiency and accuracy of the proposed scheme.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB20000000)the National Key Research and Development Program of China(2018YFA0208600)+1 种基金the National Natural Science Foundation of China(21872148,21601189)the Youth Innovation Promotion Association of Chinese Academy of Sciences(2018339)。
文摘Fabrication of metal-organic frameworks(MOFs)thin films has been an efficient way to expand their functionalities and applications.Here,we use the vapor-assisted deposition(VAD)method to epitaxially grow a porphyrin-based MOF PCN-222 film.That is,vapor source assists to deposit pre-treated precursor solution on quartz substrate to form a continuous PCN-222 film.Furthermore,utilizing the post-treated encapsulation of functional carbon-based nanoparticles,the carbon nanodots(CND)and Pt doped CND(Pt/CND)are well loaded into the pores of PCN-222 film,the size(~3.1 nm)of which is highly close to the pore size of the corresponding MOF(~3.7 nm).The Z-scan results reveal that PCN-222 film exhibits high reverse saturable absorption.In addition,encapsulation of carbon based nanodots into PCN-222 film could enhance the nonlinear optical limiting effect benefiting from the host-guest combination.This study serves to present both the available toolbox of thin film preparation and high potential for precise synthetic nanocomposite films in optical limiting devices.
基金This work was supported in part by Shanghai Key Laboratory of High Temperature Superconductors （Grant No. 14DZ2260700）, the Science and Technology Commission of Shanghai Municipality （Grant Nos. 13111102300 and 14521102800）, and the National Natural Science Foundation of China （Grant Nos. 51572165, 11174193 and 51202141）.
文摘The research and development of high temperature superconducting （HTS） films, especially ReBa2Cu3- O7-δ （REBCO or RE123; RE=Y, Gd, or other rare earths） yttrium-based coated conductors, has generated widespread interest for the potential applications of the second generation superconducting films. In view of commercialization, however, the maximum superconducting currents for coated conductors should be increased further. Unfortunately, it has been frequently observed that the average critical current density Jc decreases with an increase in film thickness. The thickness effect is still a hurdle for largescale production, especially in pulsed laser deposition and metal organic deposition processes. An engineering current of more than 1 000 A/cm is desired owing to the high cost of 2G superconducting materials. The present work attempts to review the evolution of various issues subject to the thickness effect, including the microstructure, epitaxial texture, surface roughness, pinning force, oxygen deficiency, residual stress, copper-rich layers, and segregation of elements. Furthermore, recent progress in enhancing the performance of superconductors especially in terms of critical current density is illustrated, such as the use of heavy doping. Further understanding of the thickness effect is extremely important for large-scale commercial development of the second generation high temperature superconductors.
文摘The growth conditions of La0.7Ca0.3MnO3(LCMO) epitaxial thin film are investigated.The results indicate that the deposition temperature plays a crucial role on the growth mode of LCMO thin film.There is an optimal deposition temperature,To,for the epitaxial growth of LCMO thin film.Just only at the To,the real epitaxial LCMO thin film can be obtained.When the deposition temperature deviates from the To,the thin film tends to be polycrystalline,although it orientes growth along a certain direction(a or c axis).Moreover,the experimental results show that just only for the epitaxial thin film the ferromagnetic-paramagnetic transition temperature(i.e.the Courier temperature Tc) equals to the metal-semiconductor transition temperature(Tp).The ferromagnetic state shows metallicity and the paramagnetic state exhibits semiconducting character.
文摘Practical solar energy solutions must not only reduce the cost of the module,but also address the substantial balance of system costs.Here,we demonstrate a counter-intuitive approach based on gallium arsenide solar cells that can achieve extremely low-cost solar energy conversion with an estimated cost of only 3% that of conventional gallium arsenide solar cells using an accelerated,non-destructive epitaxial lift-off wafer recycling process along with a lightweight,thermoformed plastic,truncated mini-compound parabolic concentrator that avoids the need for active solar tracking.Using solar cell/concentrator assemblies whose orientations are adjusted only a few times per year,the annual energy harvesting is increased by 2.8 times compared with planar solar cells without solar tracking.These results represent a potentially drastic cost reduction in both the module and the balance of system costs compared with heavy,rigid conventional modules and trackers that are subject to wind loading damage and high installation costs.
