Publications
References and Links to Papers
List of publications
2023
16. Shiyang He, Amin Bahrami, Xiang Zhang, Jaakko Julin, Mikko Laitinen, Kornelius Nielsch (2023). Low-temperature ALD of highly conductive antimony films through the reaction of silylamide with alkoxide and alkylamide precursors. Materials Today Chemistry, 32, 101650.
15. Shiyang He, Amin Bahrami, Xiang Zhang, Magdalena Ola Cichocka, Jun Yang, Jaroslav Charvot, Filip Bureš, Alla Heckel, Stephan Schulz, Kornelius Nielsch. (2023). Atomic layer deposition and characterization of Bi1Se1 thin films. Journal of the European Ceramic Society, 43(11), 4808-4813.
14. Sebastian Lehmann, Fanny Mitzscherling, Shiyang He, Jun Yang, Martin Hantusch, Kornelius Nielsch, Amin Bahrami (2023). Water-Free SbOx ALD Process for Coating Bi2Te3 Particles. Coatings, 13(3), 641.
2022
13. Shiyang He, Amin Bahrami, Pingjun Ying, Lars Giebeler, Xiang Zhang, Kornelius Nielsch, Ran He. (2022). Improving the Thermoelectric Performance of Double Half-Heusler Compounds ZrNi(In, Sb). Journal of Materials Chemistry A,10, 13476-13483.
12. Shiyang He, Jun Yang, Amin Bahrami, Xiang Zhang, Ran He, Martin Hantusch, Sebastian Lehmann, Kornelius Nielsch. (2022). Surface Modification of Bismuth by ALD of Antimony Oxide for Suppressing Lattice Thermal Conductivity. ACS Applied Energy Materials, 5(4), 4041-4046.
11. Jun Yang, Amin Bahrami, Xingwei Ding, Sebastian Lehmann, Nadine Kruse, Shiyang He, Bowen Wang, Martin Hantusch, Kornelius Nielsch. (2022). Characteristics of ALD‐ZnO Thin Film Transistor Using H2O and H2O2 as Oxygen Sources. Advanced Materials Interfaces, 9(15), 2101953.
10. Jun Yang, Amin Bahrami, Xingwei Ding, Panpan Zhao, Shiyang He, Sebastian Lehmann, Mikko Laitinen, Jaakko Julin, Mikko Kivekäs, Timo Sajavaara, Kornelius Nielsch (2022). Low‐Temperature Atomic Layer Deposition of High‐k SbOx for Thin Film Transistors. Advanced Electronic Materials, 2101334.
2021
9. Shiyang He, Amin Bahrami, Xiang Zhang, Ignacio González Martínez, Sebastian Lehmann, Kornelius Nielsch.(2021). Effect of Powder ALD Interface Modification on the Thermoelectric Performance of Bismuth. Advanced Materials Technologies, 2100953.
8. Shiyang He, Sebastian Lehmann, Amin Bahrami, Kornelius Nielsch. (2021). Current State‐of‐the‐Art in the Interface/Surface Modification of Thermoelectric Materials. Advanced Energy Materials, 11(37), 2101877.
7. Shiyang He, Yang Yang, Zhili Li, Jiye Zhang, Chenyang Wang, Wenqing Zhang, Jun Luo (2021). A general strategy for high-throughput experimental screening of promising bulk thermoelectric materials. Science China Materials, 64(7), 1751-1760.
2020
6. Shiyang He, Yongbo Li, Lu Liu, Ying Jiang, Jingjing Feng, Wei Zhu, Jiye Zhang, Zirui Dong, Yuan Deng, Jun Luo, Wenqing Zhang, Gang Chen. (2020). Semiconductor glass with superior flexibility and high room temperature thermoelectric performance. Science advances, 6(15), eaaz8423.
5. Li You, Zhili Li, Quanying Ma, Shiyang He, Qidong Zhang, Feng Wang, Guoqiang Wu, Qingyi Li, Pengfei Luo, Jiye Zhang, Jun Luo. (2020). High thermoelectric performance of Cu-doped PbSe-PbS system enabled by high-throughput experimental screening. Research, 2020.
2019
4. Xingyue Qi, Jing Chen, Kai Guo, Shiyang He, Jiong Yang, Zhili Li, Juanjuan Xing, Jianfeng Hu, Hongjie Luo, Wenqing Zhang, Jun Luo. (2019). Thermal stability of Ag9GaSe6 and its potential as a functionally graded thermoelectric material. Chemical Engineering Journal, 374, 494-501.
3. Huayan Pu, Rongqing Xie, Yan Peng, Yang Yang, Shiyang He, Jun Luo, Yi Sun, Shaorong Xie. (2019). Accelerating sample preparation of graded thermoelectric materials using an automatic powder feeding system. Advances in Manufacturing, 7(3), 278-287.
2. Jun Luo, Shiyang He, Zhili Li, Yongbo Li, Feng Wang, Jiye Zhan. (2019). Progress on high-throughput synthesis and characterization methods for thermoelectric materials. Journal of Inorganic Materials, 34(3), 247.
2017
1. Xiang Zhang, Yongsheng Luo, Junfeng Li, Bowen Dun, Shiyang He, Shujie Yan, Qian Li (2017). An experimental investigation and modeling of microarray replication with Zr-based bulk metallic glass using a hot embossing process. International Journal of Machine Tools and Manufacture, 117, 11-22.
Low-temperature ALD of highly conductive antimony films through the reaction of silylamide with alkoxide and alkylamide precursors
July 07, 2023, Materials Today Chemistry
Shiyang He, Amin Bahrami, Xiang Zhang, Jaakko Julin, Mikko Laitinen, Kornelius Nielsch
Antimony (Sb) has distinct physical properties that make it a promising candidate for use in integrated phase-change photonics and tunable optical absorbers. In this work, we present atomic layer deposition (ALD) of Sb metal thin films using new precursor combinations produced from comproportionation reactions of antimony ethoxide (Sb(OEt)3) and Tris (dimethylamido)antimony (Sb(NMe2)3) with Tris (trimethylsilyl)antimony ((SiMe3)3Sb). The growth behaviors of the Sb thin films made from the Sb(OEt)3/(SiMe3)3Sb and Sb(NMe2)3/(SiMe3)3Sb precursor combinations showed different temperature dependencies at low deposition temperatures (60–80 °C). Furthermore, the deposition temperature had a significant impact on the oxidation of the deposited Sb film after exposure to air. XRD and Raman spectroscopy confirmed the high purity of the Sb films made with the Sb(OEt)3/(SiMe3)3Sb combination and deposited at 75 °C. The presence of a Sb2O3 phase deteriorated the electrical properties of deposited Sb films. However, the electrical conductivities of the purest Sb films prepared in this study were slightly higher than those previously reported for Sb-ALD films. This approach of Sb ALD can speed up actual applications of pure metals in electronic device fabrication and can potentially be extended to other main group metals.
Atomic layer deposition and characterization of Bi1Se1 thin films
April 15, 2023, Journal of the European Ceramic Society
Van der Waals (vdWs) heterostructured materials have attracted considerable interest due to their intriguing physical properties. Here, we report on the deposition of BiSe by atomic layer deposition (ALD) using Bi(NMe2)3 and Se(SnMe3)2 as volatile and reactive Bi and Se precursors, respectively. The growth rate varies from 1.5 to 2.0 Å/cycle in the deposition temperature range of 90–120 °C. Higher deposition temperatures lead to increased grain sizes and enhanced crystallinity of resulting films. Further microstructure characterization reveals the formation of crystalline domains with varying orientations and nanotwinned boundaries. The presence of Bi-Bi zigzag bilayers and the formation of the BiSe phase were confirmed by the existence of the Bi-Bi binding energy peak in the XPS spectra and Raman spectra. Furthermore, the electrical conductivity of BiSe ranged from 1420 to 1520 S/cm due to the ultrahigh carrier concentration (2–3.5 × 1021 cm−3), which is the highest among undoped bismuth selenide-based materials.
Water-Free SbOx ALD Process for Coating Bi2Te3 Particles
April 5, 2023, Coating
We developed a water-free atomic layer deposition (ALD) process to homogeneously deposit SbOx using SbCl5 and Sb-Ethoxide as precursors, and report it here for the first time. The coating is applied on Bi2Te3 particles synthesized via the solvothermal route to enhance the thermoelectric properties (i.e., Seebeck coefficient, thermal and electrical conductivity) via interface engineering. The amorphous character of the coating was shown by the missing reflexes on the X-ray diffractograms (XRD). A shift from the oxidation state +III to +V of the Sb species was observed using X-ray photoelectron spectroscopy (XPS), indicating increased thickness of the SbOx coating layer. Additionally, a peak shift of the Sb 3d5/2 + O 1s peak indicated increased n-type doping of the material. Electrical measurements of spark plasma-sintered bulk samples confirmed the doping effect on the basis of decreased specific resistivity with increasing SbOx layer thickness. The Seebeck coefficient was improved for the coated sample with 500 cycles of SbOx, while the total thermal conductivity was reduced, resulting in enhancement of the zT. The results distinctly show that surface engineering via powder ALD is an effective tool for improving key properties of thermoelectric materials like electrical conductivity and the Seebeck coefficient.
Improving the thermoelectric performance of double half-Heusler compounds ZrNi(In,Sb)
May 30, 2022, Journal of Materials Chemistry A
Shiyang He, Amin Bahrami, Pingjun Ying, Lars Giebeler, Xiang Zhang, Kornelius Nielsch, Ran He
The complexity of crystal structure displays an intriguing role in manipulating properties in thermoelectrics, spintronics, and batteries. In comparison to the widely-studied ternary half-Heusler thermoelectric compounds, the quaternary double half-Heusler compounds are promising due to their intrinsically low lattice thermal conductivities (κL). However, they received much fewer investigations due to the limited material availability. In this study, we report a new double half-Heusler based on ZrNi(In, Sb). Upon tuning the ratio of In/Sb from 0.5/0.5 to 0.4/0.6, and reducing the nominal concentration of Zr and Ni by 10%, we greatly reduce the intensities of the impurity-phase peaks in the diffraction patterns. An even better phase purity, joint with an optimized power factor is realized by substituting Co at the Ni sites. Further alloying Hf at the Zr sites enhances the point defect scattering of phonons, which yielded a minimum κL of ~1.8 W⸱m−1⸱K−1 and a maximum zT of ~0.5 for Zr0.7Hf0.2Ni0.65Co0.25In0.4Sb0.6 at 973 K. Our work thus confirms the intrinsically low κL of ZrNi(In, Sb) double half-Heusler compounds and indicates their promising applications upon further improving the electrical transport properties.
Surface Modification of Bismuth by ALD of Antimony Oxide for Suppressing Lattice Thermal Conductivity
Apr 12, 2022, ACS Applied Energy Materials
Surface modification may significantly improve the performance of thermoelectric materials by suppressing thermal conductivity. Using the powder atomic layer deposition method, the newly developed Sb2O5 thin films produced from SbCl5 and H2O2 were formed on the surfaces of Bi powders. Because of the high thermal resistance generated by Sb2O5 layers on Bi particles, a substantial decrease in κtot from 7.8 to 5.7 W m–1 K–1 was obtained with just 5 cycles of Sb2O5 layer deposition and a 16% reduction in κlat. Because of the strong phonon scattering, the maximum zT values increased by around 12% and were relocated to 423 K.
Characteristics of ALD-ZnO Thin Film Transistor Using H2O and H2O2 as Oxygen Sources
Apr 10, 2022, Advanced Materials Interfaces
ZnO thin films are deposited by atomic layer deposition (ALD) using diethylzinc as the Zn source and H2O and H2O2 as oxygen sources. The oxidant- and temperature-dependent electrical properties and growth characteristics are systematically investigated. Materials analysis results suggest that H2O2 provides an oxygen-rich environment so that the oxygen vacancies (VO) is suppressed, implying a lower carrier concentration and a higher resistivity. The lower growth rate makes it possible for the ZnO thin films to grow along the lower surface energy direction of <002>, leading to a lower Hall mobility. Furthermore, the ZnO semiconductor is integrated into thin film transistor (TFT) devices and the electrical properties are analyzed. The TFT with H2O2-ZnO grown at 150 °C shows good electrical properties, such as a high field-effect mobility of 10.7 cm2 V–1 s–1, a high ratio Ion/Ioff of 2 × 107, a sharp subthreshold swing of 0.25 V dec–1, and a low trapping state (Ntrap) of 2.77 × 1012 eV–1 cm–2, which provides a new pathway to optimize the performance of metal-oxide electronics.
Low-temperature atomic layer deposition of high-k SbOx for thin film transistors
Feb 18, 2022, Advanced Electronic Materials
SbOx thin films were deposited by atomic layer deposition (ALD) using SbCl5 and Sb(NMe2)3 as antimony reactants and H2O and H2O2 as oxidizers at low temperatures. Homogenous antimony oxide deposition can be achieved on flat silicon wafers. SbCl5 can react with both oxidizers, while no deposition was found to occur using Sb(NMe2)3 and H2O. For the first time, we systematically studied the reaction mechanism and dielectric properties of ALD-SbOx thin films, which exhibit a high breakdown field of approximately 4 MV/cm and high areal capacitance ranging from 150 nF/cm2 to 200 nF/cm2, corresponding to a dielectric constant ranging from 10 to 13. The ZnO semiconductor layer was integrated into a SbOx dielectric layer, and thin film transistors (TFTs) were successfully fabricated. A TFT with a SbOx dielectric layer deposited at 200 °C from Sb(NMe2)3 and H2O2 presents excellent performance, such as a field effect mobility (μ) of 12.4 cm2 Vs-1, Ion/Ioff ratio of 4×108, subthreshold swing (SS) of 0.22 V dec.-1, and a trapping state (Ntrap) of 1.1×1012 eV-1 cm-2. After applying a voltage stress of 10 V for a period of 3600 s, the threshold voltage shift (∆Vth) is only 1.2 V. The amorphous structure and high areal capacitance of SbOx boosts the interface between the semiconductor and dielectric layer of TFT devices and provide a strong electric field for electrons to improve the device mobility.
Effect of Powder ALD Interface Modification on the Thermoelectric Performance of Bismuth
Oct 31, 2021, Advanced Materials Technologies
Shiyang He, Amin Bahrami, Xiang Zhang, Ignacio González Martínez, Sebastian Lehmann, Kornelius Nielsch
In thermoelectric materials, phase boundaries are crucial for carrier/phonon transport. Manipulation of carrier and phonon scatterings by introducing continuous interface modification has been shown to improve thermoelectric performance. In this paper, a strategy of interface modification based on powder atomic layer deposition (PALD) is introduced to accurately control and modify the phase boundary of pure bismuth. Ultrathin layers of Al2O3, TiO2, and ZnO are deposited on Bi powder by typically 1–20 cycles. All of the oxide layers significantly alter the microstructure and suppressed grain growth. These hierarchical interface modifications aid in the formation of an energy barrier by the oxide layer, resulting in a substantial increase in the Seebeck coefficient that is superior to that of most pure polycrystalline metals. Conversely, taking advantage of the strong electron and phonon scattering, an exceptionally large decrease in thermal conductivity is obtained. A maximum figure of merit, zT, of 0.15 at 393 K and an average zT of 0.14 at 300–453 K were achieved in 5 cycles of Al2O3-coated Bi. The ALD-based approach, as a practical interfacial modification technique, can be easily applied to other thermoelectric materials, which can contribute to the development of high-performance thermoelectric materials of great significance.
Cover page: Current State-of-the-Art in the Interface/Surface Modification of Thermoelectric Materials (Adv. Energy Mater. 37/2021)
Oct 7, 2021, Advanced Energy Materials
Shiyang He, Sebastian Lehmann, Amin Bahrami, Kornelius Nielsch
Thermoelectric Materials
In article number 2101877, Amin Bahrami, Kornelius Nielsch and co-workers summarize the development of interface/surface modification in thermoelectric materials and recent advances of important research, reporting the effect of charge carrier/phonon scattering induced by the second phase on thermoelectric properties. Furthermore, current challenges and future directions for interface/surface modification approaches are suggested alongside relevant experimental demonstrations for improving the thermoelectric performance.
Current State-of-the-Art in the Interface/Surface Modification of Thermoelectric Materials
Aug. 10, 2021, Advanced Energy Materials
Shiyang He, Sebastian Lehmann, Amin Bahrami, Kornelius Nielsch
Thermoelectric (TE) materials are prominent candidates for energy converting applications due to their excellent performance and reliability. Extensive efforts for improving their efficiency in single-/multi-phase composites comprising nano/micro-scale second phases are being made. The artificial decoration of second phases into the thermoelectric matrix in multi-phase composites, which is distinguished from the second-phase precipitation occurring during the thermally equilibrated synthesis of TE materials, can effectively enhance their performance. Theoretically, the interfacial manipulation of phase boundaries can be extended to a wide range of materials. High interface densities decrease thermal conductivity when nano/micro-scale grain boundaries are obtained and certain electronic structure modifications may increase the power factor of TE materials. Based on the distribution of second phases on the interface boundaries, the strategies can be divided into discontinuous and continuous interfacial modifications. The discontinuous interfacial modifications section in this review discusses five parts chosen according to their dispersion forms, including metals, oxides, semiconductors, carbonic compounds, and MXenes. Alternatively, gas- and solution-phase process techniques are adopted for realizing continuous surface changes, like the core–shell structure. This review offers a detailed analysis of the current state-of-the-art in the field, while identifying possibilities and obstacles for improving the performance of TE materials.
A general strategy for high-throughput experimental screening of promising bulk thermoelectric materials
Feb. 4, 2021, Science China Materials
Shiyang He, Yang Yang, Zhili Li, Jiye Zhang, Chenyang Wang, Wenqing Zhang, Jun Luo
High-throughput (HTP) experiments play key roles in accelerating the discovery of advanced materials, but the HTP preparation and characterization, especially for bulk samples, are extremely difficult. In this work, we developed a novel and general strategy for HTP screening of high-performance bulk thermoelectric materials. The performed full-chain HTP experiments cover rapid synthesis of the bulk sample with quasi-continuous composition, microarea phase identification and structure analysis, and measurement of the spatial distribution of the sample composition, electrical and thermal transport properties. According to our experiments, bulk Bi2−xSbxTe3 (x = 1−2) and Bi2Te3−xSex (x = 0−1.5) samples with quasi-continuous compositions have been rapidly fabricated by this HTP method. The target thermoelectric materials with the best Sb/Bi and Te/Se ratios are successfully screened out based on subsequent HTP characterization results, demonstrating that this HTP technique is effective in speeding up the exploration of novel high-performance thermoelectric materials.
Semiconductor glass with superior flexibility and high room temperature thermoelectric performance
Apr. 1, 2020, Science Advances
Shiyang He, Yongbo Li, Lu Liu, Ying Jiang, Jingjing Feng, Wei Zhu, Jiye Zhang, Zirui Dong, Yuan Deng, Jun Luo, Wenqing Zhang, Gang Chen
Most crystalline inorganic materials, except for metals and some layer materials, exhibit bad flexibility because of strong ionic or covalent bonds, while amorphous materials usually display poor electrical properties due to structural disorders. Here, we report the simultaneous realization of extraordinary room temperature flexibility and thermoelectric performance in Ag2Te1–xSx–based materials through amorphization. The coexistence of amorphous main phase and crystallites results in exceptional flexibility and ultralow lattice thermal conductivity. Furthermore, the flexible Ag2Te0.6S0.4 glass exhibits a degenerate semiconductor behavior with a room temperature Hall mobility of ~750 cm2 V−1 s−1 at a carrier concentration of 8.6 × 1018 cm−3, which is at least an order of magnitude higher than other amorphous materials, leading to a thermoelectric power factor also an order of magnitude higher than the best amorphous thermoelectric materials known. The in-plane prototype uni-leg thermoelectric generator made from this material demonstrates its potential for flexible thermoelectric device.
High thermoelectric performance of Cu-doped PbSe-PbS system enabled by high-throughput experimental screening
Mar. 7, 2020, Research
Li You, Zhili Li, Quanying Ma, Shiyang He, Qidong Zhang, Feng Wang, Guoqiang Wu, Qingyi Li, Pengfei Luo, Jiye Zhang, Jun Luo
Recent advances in high-throughput (HTP) computational power and machine learning have led to great achievements in exploration of new thermoelectric materials. However, experimental discovery and optimization of thermoelectric materials have long relied on the traditional Edisonian trial and error approach. Herein, we demonstrate that ultrahigh thermoelectric performance in a Cu-doped PbSe-PbS system can be realized by HTP experimental screening and precise property modulation. Combining the HTP experimental technique with transport model analysis, an optimal ratio showing high thermoelectric performance has been efficiently screened out. Subsequently, based on the screened ratio, the doping content of Cu has been subtly adjusted to reach the optimum carrier concentration. As a result, an outstanding peak is achieved at 873 K for a 1.8 at% Cu-doped PbSe0.6S0.4 sample, which is the superior value among the -type Te-free lead chalcogenides. We anticipate that current work will stimulate large-scale unitization of the HTP experimental technique in the thermoelectric field, which can greatly accelerate the research and development of new high-performance thermoelectric materials.
Thermal stability of Ag9GaSe6 and its potential as a functionally graded thermoelectric material
Oct. 15, 2019, Chemical Engineering Journal
Xingyue Qi, Jing Chen, Kai Guo, Shiyang He, Jiong Yang, Zhili Li, Juanjuan Xing, Jianfeng Hu, Hongjie Luo, Wenqing Zhang, Jun Luo
Even though Ag9GaSe6 shows competitive thermoelectric performance comparing with commercial thermoelectric materials, the thermal stability of this argyrodite-type superionic conductor limits its practical application. The present work investigates the electrical transport behavior of Ag9GaSe6 and validates Ag ions segregation as the instable source. Due to the temperature gradient during the measured process, Ag ions migrate, and thus resulting in a graded distribution of Ag ions in the sample. Therefore, the electrical transport properties vary essentially for the first and second measurements. However, the graded distribution of Ag ions can be maintained once it is constructed at a given temperature gradient, indicating that Ag9GaSe6 can be used as a functionally graded thermoelectric material. In addition, the thermoelectric performance of Ag9GaSe6 is further optimized by creating Ag vacancies and alloying Ag with Cu. As a result, a maximum zT value of ∼1.6 has been achieved in the Cu-doped sample. The samples show also good stability and repeatability, which can be considered as a good n-type candidate for matching p-type thermoelectrics.
Accelerating sample preparation of graded thermoelectric materials using an automatic powder feeding system
Sep. 1, 2019, Advances in Manufacturing
Huayan Pu, Rongqing Xie, Yan Peng, Yang Yang, Shiyang He, Jun Luo, Yi Sun, Shaorong Xie
In recent years, the development of techniques for the controlled preparation of functionally graded materials (FGMs) has become a vigorous research field. In this study, to improve the efficiency and accuracy of sample preparations, an automated feeding system based on gravimetric principles for dry powder with three dosing feeders is designed and realized. The feeding rate and accuracy can be regulated by coordinating the protruded length L (mm) and rotational speed V (r/min) of the feeder stirrer. To demonstrate this automatic sample preparation system, the well-known thermoelectric material BixSb2−xTe3 (x = 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) is selected and prepared by the developed system, and the composition distribution of the functional graded material is characterized. Experimental results show that the BixSb2−xTe3 (x = 0.3–0.8) functionally graded material crystalizes in the rhombohedral phase after hot-pressing sintering and annealing and the prepared sample has a good gradient composition distribution. This verifies the reliability and accuracy of the feeding system. The concept of samples with a gradient component and application of the automatic powder feeding system could considerably accelerate the research and development of new materials.
Progress on high-throughput synthesis and characterization methods for thermoelectric materials
Jan. 1, 2019, Journal of Inorganic Materials
Jun Luo, Shiyang He, Zhili Li, Yongbo Li, Feng Wang, Jiye Zhang
High-throughput experiments aimed to promptly obtain the relationship among composition-phase-structure- performance with fewer experiments and screen out optimal material systems with optimized compositions. Up to now, high-throughput experiments are successfully applied in superconducting materials, fluorescent materials and giant magnetoresistance materials. Thermoelectric materials are functional materials that can realize the direct conversion between thermal energy and electrical energy and can be potentially applied in the fields of thermoelectric power generation and waste heat utilization. However, traditional preparation and characterization methods for thermoelectric materials have disadvantages of time consuming and low efficiency. Therefore, it is of great theoretical and practical significance to introduce methods and concepts of high-throughput experiments into development and optimization of new thermoelectric materials. In this paper, we summarize and discuss the existing high-throughput experimental preparation and characterization techniques with great application prospects in thermoelectric materials, including high-throughput sample preparation, composition-structure, and electro-thermal transport properties characterization, and then analyze the advantages and limitations of these high-throughput techniques. We hope to provide a reference for future high-throughput optimization and screening of thermoelectric materials.
An experimental investigation and modeling of micro array replication with Zr-based bulk metallic glass using a hot embossing process
Jun.1, 2015, International Journal of Machine Tools and Manufacture
Xiang Zhang, Yongsheng Luo, Junfeng Li, Bowen Dun, Shiyang He, Shujie Yan, Qian Li
Zirconium-based bulk metallic glass (Zr-based BMG) is a potential material for micro/nano molds. In this study, we investigated the flow characteristics of Zr-based BMG in the supercooled liquid region (SLR) with a series of uniaxial compression tests. The Newtonian viscosity model of Zr-based BMG is constructed by fitting with the experimental results based on the Arrhenius equation. The hot embossing process which can be seen as a combination of two kinds of simultaneous flows is theoretically analyzed based on Navier-Stokes (N-S) equations. The velocity and pressure fields in a BMG sample have been evaluated. Two kinds of filling modes are proposed considering the interfacial tension and oxide layer that forms on the BMG surface. The exact solutions are obtained when the cavities of the micro arrays are circular, triangular and rectangular in shape based on N-S equations. The theoretical solutions, considered surface resistance, are in good agreement with our experimental results. These models can be used to describe the fillings of metallic glass in micro hot embossing process. Finally, we studied the effects of micro cavity size and shape on BMG filling, and found that the cavities of micro rectangular array are easier filling in same feature size, however, the cavities of micro circular array are easier filling in same area. The exact models developed in this paper can be used to calculate the BMG filling heights in the cavities of micro arrays and verify the reliability of simulation results in future mold designs.