Fabrication of Si Thermoelectric Nanomaterials Containing Ultrasmall Epitaxial Ge Nanodots with an Ultrahigh Density

Yamasaka, Shuto; Nakamura, Yoshiaki; Ueda, Tomohiro; Takeuchi, Shinichi; Yamamoto, Yuta; Arai, Shigeo; Tanji, Takayoshi; Tanaka, Nobuo; Sakai, Akira

doi:10.1007/s11664-015-3643-6

Cited by 15 publications

(20 citation statements)

References 36 publications

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“…The cross section of the NDs for the heat current is also an important factor for phonon transport, which corresponds to the projection of θ on the plane perpendicular to the heat current direction, that is the Si(001) plane ( θ p ). Although Ge NDs grew on rough Si layers in some cases, the structure factors of Ge NDs such as h , r , and projected widths of the ND lateral size on the Si(001) planes exhibited almost the same values in any n th cycle structure ( n = 1–8) within the error, which were confirmed by analysis of HAADF-STEM (high-angle annular dark-field-scanning transmission microscopy) images reported in our previous work 21 (see supplementary information ). Therefore, the θ and θ p in the first cycle structures were used as typical values in the sample, which were estimated from the STM images.…”

Section: Resultssupporting

confidence: 83%

“…The stacked structure of x -nm diameter Ge NDs/ y -ML Si layers is referred to as the “ x -nm NDs/ y -ML Si sample”. This technique for forming Si/Ge ND stacked structure was reported in our previous paper 21 .…”

Section: Methodsmentioning

confidence: 96%

“…In this structure, the size and shape of the NDs can be tuned for phonon scattering and the Si layers can be designed to have high carrier mobilities for carrier transport, independently. Ge is one of the promising candidates as a ND material because of its compatibility with conventional Si process technologies and recently we developed the formation technique of the new nanoarchitecture using the ultrathin SiO 2 film technique 21 . In this nanoarchitecture, ultrasmall Ge NDs were epitaxially grown with identical crystal orientations, which were completely different from the conventional nanostructured SiGe bulk alloys made by sintering.…”

mentioning

confidence: 99%

“…In addition, the Ge NDs in these structures are expected to effectively reduce κ because of the ultrasmall (nanoscale) ND size compared with the case of Ge NDs/Si superlattices that use the well-established Stranski-Krastanov (SK) growth mode, which have a typical ND size of ~30–100 nm 22 23 . Furthermore, unlike SK NDs, the interfaces between the ultrasmall Ge NDs and Si can be well-controlled; intermixing at the interfaces is suppressed and there are no strains and misfit dislocations in the Ge NDs 21 24 25 . Therefore, this nanoarchitecture is useful to control the phonon and carrier transport properties related to enhancing the TE performance and to clarify its mechanism.…”

mentioning

confidence: 99%

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Phonon transport control by nanoarchitecture including epitaxial Ge nanodots for Si-based thermoelectric materials

Yamasaka

Nakamura

Ueda

et al. 2015

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Phonon transport in Si films was controlled using epitaxially-grown ultrasmall Ge nanodots (NDs) with ultrahigh density for the purpose of developing Si-based thermoelectric materials. The Si/Ge ND stacked structures, which were formed by the ultrathin SiO2 film technique, exhibited lower thermal conductivities than those of the conventional nanostructured SiGe bulk alloys, despite the stacked structures having a smaller Ge fraction. This came from the large thermal resistance caused by phonon scattering at the Si/Ge ND interfaces. The phonon scattering can be controlled by the Ge ND structure, which was independent of Si layer structure for carrier transport. These results demonstrate the effectiveness of ultrasmall epitaxial Ge NDs as phonon scattering sources, opening up a route for the realisation of Si-based thermoelectric materials.

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Section: Resultssupporting

confidence: 83%

Section: Methodsmentioning

confidence: 96%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Phonon transport control by nanoarchitecture including epitaxial Ge nanodots for Si-based thermoelectric materials

Yamasaka

Nakamura

Ueda

et al. 2015

Sci Rep

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“…Silicon nanowires 312 , silicon nanotubes 313 , and Si-embedded graphite 314 are finding use in battery applications, most likely due to the versatile nature of synthetically controllable nanostructure shapes and motifs. These different structural motifs demonstrate tunable physical properties unique to the nanomaterial, such as nanonetworks to enhance electronic conduction 315 or tailorable core−shell structures to promote thermoelectric effects 316 , making it advantageous to use nanomaterials in an increasing variety of new ways.…”

Section: Bulk Fe3o4mentioning

confidence: 99%

Extending accurate density functional modeling for the study of interface reactivity and environmental applications

Xu¹

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To my parents, Fangyan and Xingcheniii ACKNOWLEDGEMENTS Seven years in the University of Iowa have become an amazing chapter in my life.I want to express my gratitude to all the people who have helped and encouraged me during this wonderful journey. And among them all, I would like to thank my advisor, Sara E.Mason, for taking a chance to accept me and opening the entire new world of computational chemistry for me. I could never imagine that I can work on so many challenging projects.Your patience, enthusiasm and trust are not just helping me in my academic progress, but also making me grow up through all the ups and downs. I greatly appreciate your guidance and all of the opportunities to reach out in my graduate career.are not just providing the opportunities for us to apply our computational expertise in solving problems in reality, but also letting us understand the structural and chemical complexity of materials under real conditions that pushed our theoretical models to new levels. Our collaborations have built up current and future directions for our projects, and also provided more prospects in bigger academic communities. I am also thankful for the previous members of the Mason group: Dr. Sai Kumar Ramadugu, Dr. Katie Corum, and Dr. Diane Neff, you were extremely helpful for teaching me the knowledge of quantum theory and computational skills, as well as our collaborations in many different projects. iv I would also like to thank our research specialist: Dr. Joseph W. Bennett, for your in-depth understanding of materials and computational chemistry, and your tireless support for the entire group in every aspect. I am not only making academic progress by learning from your knowledge and experience, but also learning how to become a responsible and competent collaborator in team work, and deal with all the obstacles and setbacks during research. I would further like to thank all the group members, Jennifer, Diamond, Irene, Sidney and Blake, for your support and encouragement. It was a great pleasure to work with all of you. Finally, I want to thank my parents, who were thousands miles away, living on the other side of the Pacific Ocean. I just briefly spent about a month with them during my graduate years, but they provided unconditional love and support to me all the time. You constantly believed in me and encouraged my pursuits. I am eternally grateful. v ABSTRACTDensity functional theory (DFT) has become the most widely used first-principles computational method to simulate different atomic, molecular, and solid phase systems based on the electron density assumptions. The complexity of describing a many-body system has been significantly reduced in DFT. However, it also brings in potential error when dealing with a system that involves the interactions between metallic and nonmetallic species. DFT tends to overly-delocalize the electrons in metallic species and sometimes results in the overestimation of reaction energy, metallic properties in insulators, and predicts relative surface stabilities incorre...

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Fabrication of Carrier-Doped Si Nanoarchitecture for Thermoelectric Material by Ultrathin SiO2 Film Technique

Ueda

Sakane

Ishibe

et al. 2015

Journal of Elec Materi

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Fabrication of Si Thermoelectric Nanomaterials Containing Ultrasmall Epitaxial Ge Nanodots with an Ultrahigh Density

Cited by 15 publications

References 36 publications

Phonon transport control by nanoarchitecture including epitaxial Ge nanodots for Si-based thermoelectric materials

Phonon transport control by nanoarchitecture including epitaxial Ge nanodots for Si-based thermoelectric materials

Extending accurate density functional modeling for the study of interface reactivity and environmental applications

Fabrication of Carrier-Doped Si Nanoarchitecture for Thermoelectric Material by Ultrathin SiO2 Film Technique

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