Direct bandgap type-I Ge quantum dots/GeSnSi for SWIR and MWIR lasers

Liyao Zhang,Peng Yu,Shuang Yao,Duo Feng,Jinmeng Dai 대한금속·재료학회 2022 ELECTRONIC MATERIALS LETTERS Vol.18 No.1

A direct bandgap type-I Ge QDs/Ge1−y−zSnySiz double-heterostructure on Ge1−xSnx virtual substrates is proposed for SWIRand MWIR lasers. The Ge1−y−zSnySiz barrier is lattice-matched to Ge1−xSnx. The band structures are calculated with differentto Sn contents in Ge1−y−zSnySiz and Ge1−xSnx. The band edge energies of Ge QDs vary linearly with x, and independent withy. The Γ-valley is below L-valley when x exceeds 7.5%. The ground states of electrons of Γ- and L-conduction band varieswith both x and y. High x and y can increase the conduction band offsets and decrease the valence band offsets. Emissionwavelengths range from 1.91 to 4.6 μm are achieved from the proposed structure with proper Sn contents.

GaAsBi Quantum Dots for 1.55 μm Laser Diode

Mingxuan Zhang,Liyao Zhang,Zhongyue Zhang,Peng Yu,Shuang Yao 대한금속·재료학회 2021 ELECTRONIC MATERIALS LETTERS Vol.17 No.2

Bi incorporations can reduce the bandgap of GaAs1-xBix. With a Bi content of 10.5%, GaAsBi is predicted to emit light at1.55 μm. However, high Bi incorporation is difficult for material growth and deteriorates the optical property of GaAsBi. In this work, a GaAsBi quantum dot (QD)/InAlAs structure on InP platform is proposed to fabricate 1.55 μm laser diodes. Strain distributions and band structures are calculated with different Bi contents and QD sizes using finite element method. High Bi contents and large QD sizes are beneficial for achieving long wavelengths. GaAsBi QD/InAlAs structures with alow Bi content of 5.6% and proper QD sizes, such as a diameter of 30 nm and a height of 6 nm, can emit light at 1.55 μm. The proposed structure can be realized by migration enhanced epitaxy and droplet epitaxy and provides a feasible way forfabricating GaAsBi based 1.55 μm laser diodes applied in fiber-optic communications.

An Algorithm for Traffic Flow Prediction Based on Improved SARIMA and GA

Xianglong Luo,Liyao Niu,Shengrui Zhang 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.10

The traffic flow prediction plays a key role in modern Intelligent Transportation Systems (ITS). Although great achievements have been made in traffic flow prediction, it is still a challenge to improve the prediction accuracy and reduce the operation time simultaneously. In this paper, we proposed a hybrid prediction methodology combined with improved seasonal autoregressive integrated moving average (ISARIMA) model and multi-input autoregressive (AR) model by genetic algorithm (GA) optimization. Since traffic flow data has strong spatio-temporal correlation with neighboring stations, GA is used to select those stations which are highly correlated with the prediction station. The ISARIMA model is used to predict the traffic flow in test station at first. A multiinput AR model with traffic flow data in optimal selected stations is built to predict the traffic flow in test station as well. The final prediction result can be gained by combining with the results of ISARIMA and multi-input AR model. The test results from traffic data provided by TDRL at UMD Data Center demonstrate that proposed algorithm has almost the same prediction accuracy with artificial neural networks (ANNS). However, its operation time is almost the same with SARIMA model. It is proved to be an effective method to perform traffic flow prediction.

Influence of Thermal Processing Conditions on Mechanical and Material Properties of 3D Printed Thin-Structures Using PEEK Material

Han Qu,Wei Zhang,Zihan Li,Liyao Hou,Guiwei Li,Jerry YH Fuh,Wenzheng Wu 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.23 No.6

Poly-ether-ether-ketone (PEEK) was one of the most promising engineering plastics, which had been widely employed in the aerospace, biomedical and automotive industry and manufacturing. The design of various 3D printing (3DP) parameters had a significant impact on its mechanical and thermal properties. This study aimed to investigate the thermodynamic properties of thin-structure PEEK samples by printing them under various conditions, including varying substrate and ambient temperature parameters, under a control- method. Numerous critical properties such as interlayer bonding force, tensile and bending properties, dynamic mechanical properties, and crystallization had been investigated in this work. The results indicated that the maximum relative interlayer bonding force was 989.91 N, while comparing to the lowest initial ambient and substrate temperature 60 °C and 90 °C, the optimal tensile and bending strengths both increased by 28.46% and 13.86% to 86.62 MPa and 113.21 MPa under ambient and substrate temperature 90 °C and 160 °C, respectively. Concurrently, the crystallinity increased by 6.67% to 31.56%. Mechanical and thermal properties had been significantly improved when appropriate substrate temperature parameters were used during the printing process, demonstrating the enormous potential in printing PEEK material. Thermal processing was another critical factor in achieving higher performance of 3D printing PEEK components.

Carbon-coated SnO₂@C with hierarchically porous structures and graphite layers inside for a high-performance lithium-ion battery

Li, Yao,Zhu, Shenmin,Liu, Qinglei,Gu, Jiajun,Guo, Zaiping,Chen, Zhixin,Feng, Chuanliang,Zhang, Di,Moon, Won-Jin The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.6

<P>A high-performance anode material was prepared from a hierarchically structured activated carbon which contains <I>in situ</I> graphene and nano-graphite. The activated carbon was immersed in a solution of SnCl<SUB>2</SUB>·2H<SUB>2</SUB>O and subjected to ultrasound. As a result, nanoparticles of SnO<SUB>2</SUB> were uniformly deposited on the surface of the activated carbon. The composite material was then coated with a thin layer of carbon by soaking it in a sucrose solution, followed by carbonization of the adsorbed sucrose at 500 °C. The resulting composite showed an outstanding high-rate cycling performance that can deliver an initial discharge capacity of 1417 mAh g<SUP>−1</SUP> and maintain a discharge capacity of more than 400 mAh g<SUP>−1</SUP> after 100 cycles at a high current density of 1000 mA g<SUP>−1</SUP>. This outstanding electrochemical performance is likely to be related to a unique combination of the excellent electrical conductivity of the activated carbon with graphite layers formed inside, its hierarchical pore structure which enhances lithium-ion transportation, and the carbon coating which alleviates the effects of volume changes, shortens the distance for Li<SUP>+</SUP> diffusion, facilitates the transmission of electrons, and keeps the structure stable.</P> <P>Graphic Abstract</P><P>Carbon-coated SnO<SUB>2</SUB>@C nanocomposite with hierarchically porous structures and graphite layers inside was prepared by ultrasound and hydrothermal treatment, which showed an outstanding high-rate cycling performance for lithium-ion battery. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1jm14290a'> </P>

Combination of dispersive solid phase extraction with dispersive liquid–liquid microextraction for the sequential speciation and preconcentration of Cr(III) and Cr(VI) in water samples prior to graphite furnace atomic absorption spectrometry determination

Li Yao,Yongqun Zhu,Wenzhi Xu,Hong Wang,Xie Wang,Jianhua Zhang,Haitao Liu,Chaowen Lin 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.72 No.-

In this study, the combination of dispersive solid phase extraction (DSPE) with dispersive liquid–liquidmicroextraction (DLLME) was proposed as a novel sequential speciation method for Cr determination bygraphite furnace atomic absorption spectrometry. In thefirst step, the selective extraction of Cr(III) byDSPE was achieved using graphene oxide (GO) nanoparticles as the adsorbent. The difficulty of separationand collection of GO in analytical performance was solved by the introduction of the syringe nanofilter. Then Cr(VI) was enriched by DLLME using [Omim] [PF6] as the extraction solvent. The experimentalparameters affecting the performance of both preconcentration methods were investigated andoptimized. Under the optimal conditions including the initial pH value of 7, 150 mg GO, 2 min ultrasoundtime, 210 mL elution solvent (first step), secondary pH value of 4, 0.15% (m/v) Aliquat-336, 120 mL of[Omim] [PF6] and 3 min ultrasound time (second step), the linear range of 0.06–5 ng/mL (R > 0.997), thelimits of detection of 0.015 and 0.02 ng/mL were achieved for Cr(III) and Cr(VI), respectively. The relativestandard deviations (n = 5) of 0.6 ng/mL Cr(III) and Cr(VI) were 3.2% and 4.6%, respectively. Finally, thisnewly developed method was applied for the speciation and determination of Cr species in differentwater samples and satisfactory results were obtained.

Emergent Topological Hall Effect in La_0.7Sr_0.3MnO₃/SrIrO₃ Heterostructures

Li, Yao,Zhang, Lunyong,Zhang, Qinghua,Li, Chen,Yang, Tieying,Deng, Yu,Gu, Lin,Wu, Di American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.23

<P>Recently, perovskite oxide heterostructures have drawn great attention because multiple and complex coupling at the heterointerface may produce novel magnetic and electric phenomena that are not expected in homogeneous materials either in the bulk or in films. In this work, we report for the first time that an emergent giant topological Hall effect (THE), associated with a noncoplanar (NC) spin texture, can be induced in ferromagnetic (FM) La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> thin films in a wide temperature range of up to 200 K by constructing La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB>/SrIrO<SUB>3</SUB> epitaxial heterostructures on (001) SrTiO<SUB>3</SUB> substrates. This THE is not observed in La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> single-layer films or La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB>/SrTiO<SUB>3</SUB>/SrIrO<SUB>3</SUB> trilayer heterostructures, indicating the relevance of the La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB>/SrIrO<SUB>3</SUB> interface, where the Dzyaloshinskii-Moriya interaction due to strong spin-orbital coupling in SrIrO<SUB>3</SUB> may play a crucial role. The fictitious field associated with THE is independent of temperature in La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB>/SrIrO<SUB>3</SUB> heterostructures, suggesting that the NC spin texture may be magnetic skyrmions. This work demonstrates the feasibility of using SrIrO<SUB>3</SUB> to generate novel magnetic and transport characteristics by interfacing with other correlated oxides, which might be useful to novel spintronic applications.</P> [FIG OMISSION]</BR>