Browsing by Author "Li, Guodong"
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- ItemDoping High-Mobility Donor : Acceptor Copolymer Semiconductors with an Organic Salt for High-Performance Thermoelectric Materials(Weinheim : Wiley-VCH Verlag GmbH & Co. KG, 2020) Guo, Jing; Li, Guodong; Reith, Heiko; Jiang, Lang; Wang, Ming; Li, Yuhao; Wang, Xinhao; Zeng, Zebing; Zhao, Huaizhou; Lu, Xinhui; Schierning, Gabi; Nielsch, Kornelius; Liao, Lei; Hu, YuanyuanOrganic semiconductors (OSCs) are attractive for fabrication of thermoelectric devices with low cost, large area, low toxicity, and high flexibility. In order to achieve high-performance organic thermoelectric devices (OTEs), it is essential to develop OSCs with high conductivity (σ), large Seebeck coefficient (S), and low thermal conductivity (κ). It is equally important to explore efficient dopants matching the need of thermoelectric devices. The thermoelectric performance of a high-mobility donor–acceptor (D–A) polymer semiconductor, which is doped by an organic salt, is studied. Both a high p-type electrical conductivity approaching 4 S cm−1 and an excellent power factor (PF) of 7 µW K−2 m−1 are obtained, which are among the highest reported values for polymer semiconductors. Temperature-dependent conductivity, Seebeck coefficient and power factor of the doped materials are systematically investigated. Detailed analysis on the results of thermoelectric measurements has revealed a hopping transport in the materials, which verifies the empirical relationship: S ∝ σ−1/4 and PF ∝ σ1/2. The results demonstrate that D–A copolymer semiconductors with proper combination of dopants have great potential for fabricating high-performance thermoelectric devices. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemEngineering interface-type resistive switching in BiFeO3 thin film switches by Ti implantation of bottom electrodes(London : Nature Publishing Group, 2015) You, Tiangui; Ou, Xin; Niu, Gang; Bärwolf, Florian; Li, Guodong; Du, Nan; Bürger, Danilo; Skorupa, Ilona; Jia, Qi; Yu, Wenjie; Wang, Xi; Schmidt, Oliver G.; Schmidt, HeidemarieBiFeO3 based MIM structures with Ti-implanted Pt bottom electrodes and Au top electrodes have been fabricated on Sapphire substrates. The resulting metal-insulator-metal (MIM) structures show bipolar resistive switching without an electroforming process. It is evidenced that during the BiFeO3 thin film growth Ti diffuses into the BiFeO3 layer. The diffused Ti effectively traps and releases oxygen vacancies and consequently stabilizes the resistive switching in BiFeO3 MIM structures. Therefore, using Ti implantation of the bottom electrode, the retention performance can be greatly improved with increasing Ti fluence. For the used raster-scanned Ti implantation the lateral Ti distribution is not homogeneous enough and endurance slightly degrades with Ti fluence. The local resistive switching investigated by current sensing atomic force microscopy suggests the capability of down-scaling the resistive switching cell to one BiFeO3 grain size by local Ti implantation of the bottom electrode.
- ItemHighly Symmetric and Extremely Compact Multiple Winding Microtubes by a Dry Rolling Mechanism(Weinheim : Wiley-VCH, 2020) Moradi, Somayeh; Naz, Ehsan Saei Ghareh; Li, Guodong; Bandari, Nooshin; Bandari, Vineeth Kumar; Zhu, Feng; Wendrock, Horst; Schmidt, Oliver G.Rolled-up nanotechnology has received significant attention to self-assemble planar nanomembranes into 3D micro and nanotubular architectures. These tubular structures have been well recognized as novel building blocks in a variety of applications ranging from microelectronics and nanophotonics to microbatteries and microrobotics. However, fabrication of multiwinding microtubes with precise control over the winding interfaces, which is crucial for many complex applications, is not easy to achieve by existing materials and technologies. Here, a dry rolling approach is introduced to tackle this challenge and create tight windings in compact and highly symmetric cylindrical microstructures. This technique exploits hydrophobicity of fluorocarbon polymers and the thermal expansion mismatch of polymers and inorganic films upon thermal treatment. Quality parameters for rolled-up microtubes, against which different fabrication technologies can be benchmarked are defined. The technique offers to fabricate long freestanding multiwinding microtubes as well as hierarchical architectures incorporating rolled-up wrinkled nanomembranes. This work presents an important step forward toward the fabrication of more complex but well-controlled microtubes for advanced high-quality device architectures. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemThermoelectric Characterization Platform for Electrochemically Deposited Materials(Weinheim : Wiley-VCH Verlag GmbH & Co. KG, 2020) Barati, Vida; Garcia Fernandez, Javier; Geishendorf, Kevin; Schnatmann, Lauritz Ule; Lammel, Michaela; Kunzmann, Alexander; Pérez, Nicolás; Li, Guodong; Schierning, Gabi; Nielsch, Kornelius; Reith, HeikoSuccessful optimization of the thermoelectric (TE) performance of materials, described by the figure of merit zT, is a key enabler for its application in energy harvesting or Peltier cooling devices. While the zT value of bulk materials is accessible by a variety of commercial measurement setups, precise determination of the zT value for thin and thick films remains a great challenge. This is particularly relevant for films synthesized by electrochemical deposition, where the TE material is deposited onto an electrically conductive seed layer causing an in-plane short circuit. Therefore, a platform for full in-plane zT characterization of electrochemically deposited TE materials is developed, eliminating the impact of the electrically conducting seed layer. The characterization is done using a suspended TE material within a transport device which was prepared by photolithography in combination with chemical etching steps. An analytical model to determine the thermal conductivity is developed and the results verified using finite element simulations. Taken together, the full in-plane zT characterization provides an inevitable milestone for material optimization under realistic conditions in TE devices. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim