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Synthesis and characterization of me...

Kang, Chris Byung-hwa.

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Synthesis and characterization of mesoporous semiconductors and their energy applications.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	Synthesis and characterization of mesoporous semiconductors and their energy applications./
Author:	Kang, Chris Byung-hwa.
Description:	184 p.
Notes:	Source: Dissertation Abstracts International, Volume: 75-02(E), Section: B.
Contained By:	Dissertation Abstracts International75-02B(E).
Subject:	Chemistry, General. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3599484
ISBN:	9781303487705

Synthesis and characterization of mesoporous semiconductors and their energy applications.
Kang, Chris Byung-hwa.

Synthesis and characterization of mesoporous semiconductors and their energy applications. - 184 p.

Source: Dissertation Abstracts International, Volume: 75-02(E), Section: B.

Thesis (Ph.D.)--University of California, Los Angeles, 2013.

In this dissertation, we examine the structure and physical properties of mesoporous group IV materials. Two different synthetic routes were developed to synthesize mesoporous germanium powder and thin film mesoporous silicon. The structural of these materials was confirmed by various analytical techniques. The electrochemical behavior of mesoporous silicon was further explored for applications as anodes in lithium ion batteries. The thermal conductivity was also measured and the electrical conductivity was tuned for potential applications as thermoelectrics. Ordered nanostructured germanium composite materials were produced using solution-phase surfactant templating methods. Anionic germanium/surfactand frameworks with a 2-D hexagonal structure were prepared and then condensed to form zero-valent porous germanium using oxidative coupling. The majority of the cationic surfactant inside the pores can be removed, resulting in mesoporous germanium with surface areas up to 500 m2/g. Thin film of mesoporous silicon was produced from polymer template porous silica films at relatively low temperature (<700 C) using magnesium vapor as reducing agent. The final porous silicon retains its ordered cubic mesoporosity. The lithium ion cycling performance of mesoporous silicon anodes was then examined. Mesoporous silicon films formed directly on a metal current collector showed stable cycling with excellent coulomb efficiency over 3000 cycles with capacities up to 3000 mAh/g at cycling rates between 1C to 20C. The results indicate porous silicon material in this size scale can accommodate the volume expansion associated with Li alloying without cracking or loosing contact with the current collector. The thermal conductivity of mesoporous silicon was also measured using the 3 omega method. Periodic pores and grain boundaries enhance phonon scattering to dissipate thermal energy throughout the material, resulting in a decrease in the thermal conductivity by 3-5 orders of magnitude (as low as 0.01 W/m*K) from the bulk value (150 W/m*K). As thermal conductivity of mesostructured silicon decreased, its electrical conductivity decreased as well. To overcome the high overall resistance, several dopoing methods were developed to decrease the internal resistance of silicon grains. The internal resistivity decreased from 25ohm&dot;cm for as-prepared mesoporous silicon to as low as 0.16 ohm&dot;cm for samples optimally doped with boron.

ISBN: 9781303487705Subjects--Topical Terms:

1021807
Chemistry, General.

Synthesis and characterization of mesoporous semiconductors and their energy applications.
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100 1 $a Kang, Chris Byung-hwa. $3 2096180
245 1 0 $a Synthesis and characterization of mesoporous semiconductors and their energy applications.
300 $a 184 p.
500 $a Source: Dissertation Abstracts International, Volume: 75-02(E), Section: B.
500 $a Adviser: Sarah H. Tolbert.
502 $a Thesis (Ph.D.)--University of California, Los Angeles, 2013.
520 $a In this dissertation, we examine the structure and physical properties of mesoporous group IV materials. Two different synthetic routes were developed to synthesize mesoporous germanium powder and thin film mesoporous silicon. The structural of these materials was confirmed by various analytical techniques. The electrochemical behavior of mesoporous silicon was further explored for applications as anodes in lithium ion batteries. The thermal conductivity was also measured and the electrical conductivity was tuned for potential applications as thermoelectrics. Ordered nanostructured germanium composite materials were produced using solution-phase surfactant templating methods. Anionic germanium/surfactand frameworks with a 2-D hexagonal structure were prepared and then condensed to form zero-valent porous germanium using oxidative coupling. The majority of the cationic surfactant inside the pores can be removed, resulting in mesoporous germanium with surface areas up to 500 m2/g. Thin film of mesoporous silicon was produced from polymer template porous silica films at relatively low temperature (<700 C) using magnesium vapor as reducing agent. The final porous silicon retains its ordered cubic mesoporosity. The lithium ion cycling performance of mesoporous silicon anodes was then examined. Mesoporous silicon films formed directly on a metal current collector showed stable cycling with excellent coulomb efficiency over 3000 cycles with capacities up to 3000 mAh/g at cycling rates between 1C to 20C. The results indicate porous silicon material in this size scale can accommodate the volume expansion associated with Li alloying without cracking or loosing contact with the current collector. The thermal conductivity of mesoporous silicon was also measured using the 3 omega method. Periodic pores and grain boundaries enhance phonon scattering to dissipate thermal energy throughout the material, resulting in a decrease in the thermal conductivity by 3-5 orders of magnitude (as low as 0.01 W/m*K) from the bulk value (150 W/m*K). As thermal conductivity of mesostructured silicon decreased, its electrical conductivity decreased as well. To overcome the high overall resistance, several dopoing methods were developed to decrease the internal resistance of silicon grains. The internal resistivity decreased from 25ohm&dot;cm for as-prepared mesoporous silicon to as low as 0.16 ohm&dot;cm for samples optimally doped with boron.
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650 4 $a Nanoscience. $3 587832
650 4 $a Chemistry, Inorganic. $3 517253
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710 2 $a University of California, Los Angeles. $b Chemistry 0153. $3 2096181
773 0 $t Dissertation Abstracts International $g 75-02B(E).
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