InP Quantum Dot-Organosilicon Nanocomposites

Dung, Mai Xuan,Mohapatra, Priyaranjan,Choi, Jin-Kyu,Kim, Jin-Hyeok,Jeong, So-Hee,Jeong, Hyun-Dam Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.5

InP quantum dot (QD)-organosilicon nanocomposites were synthesized and their photoluminescence quenching was mainly investigated because of their applicability to white LEDs (light emitting diodes). The as-synthesized InP QDs are capped with myristic acid (MA), which are incompatible with typical silicone encapsulants. We have introduced a new ligand, 3-aminopropyldimethylsilane (APDMS), which enables embedding the QDs into vinyl-functionalized silicones through direct chemical bonding. The exchange of ligand from MA to APDMS does not significantly affect the UV absorbance of the InP QDs, but quenches the PL to about 10% of its original value with the relative increase in surface related emission intensities, which is explained by stronger coordination of the APDMS ligands to the surface indium atoms. InP QD-organosilicon nanocomposites were synthesized by connecting the QDs using a short cross-linker such as 1,4-divinyltetramethylsilylethane (DVMSE) by the hydrosilylation reaction. The formation and changes in the optical properties of the InP QD-organosilicon nanocomposite were monitored by ultraviolet visible (UV-vis) absorbance and steady state photoluminescence (PL) spectroscopies. As the hydrosilylation reaction proceeds, the QD-organosilicon nanocomposite is formed and grows in size, causing an increase in the UV-vis absorbance due to the scattering effect. At the same time, the PL spectrum is red-shifted and, very interestingly, the PL is quenched gradually. Three PL quenching mechanisms are regarded as strong candidates for the PL quenching of the QD nanocomposites, namely the scattering effect, F$\ddot{o}$rster resonance energy transfer (FRET) and cross-linker tension preventing the QD's surface relaxation.

Ultralow-n SiO₂ Thin Films Synthesized Using Organic Nanoparticles Template

Dung, Mai Xuan,Lee, June-Key,Soun, Woo-Sik,Jeong, Hyun-Dam Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.12

In an original effort, this lab attempted to employ polystyrene nanoparticles as a template for the synthesis of ordered and highly porous macroporous $SiO_2$ thin films, utilizing their high combustion temperature and narrow size distribution. However, polystyrene nanoparticle thin films were not obtained due to the low interaction between individual particles and between the particle and silicon substrate. However, polystyrene-polyacrylic acid (PS-AA) colloidal particles of a core-shell structure were synthesized by a one-pot miniemulsion polymerization approach, with hydrophilic polyacrylic acid tails on the particle surface that improved interaction between individual particles and between the particle and silicon substrate. The PS-AA thin films were spin-coated in the thickness ranges from monolayer to approximately $1.0\;{\mu}m$. Using the PS-AA thin films as sacrificial templates, macroporous $SiO_2$ thin films were successfully synthesized by vapor deposition or conventional solution sol-gel infiltration methods. Inspection with field emission scanning electron microscopy (FE-SEM) showed that the macroporous $SiO_2$ thin films consist of interconnected air balls (~100 nm). Typical macroporous $SiO_2$ thin films showed ultralow refractive indices ranging from 1.098 to 1.138 at 633 nm, according to the infiltration conditions, which were confirmed by spectroscopy ellipsometry (SE) measurements. This research shows how the synthetic control of the macromolecule such as hydrophilic polystyrene nanopaticles and silicate sol precursors innovates the optical properties and processabilities for actual applications.

Synthesis of Styryl-Terminated Silicon Quantum Dots: Reconsidering the Use of Methanol

Dung, Mai Xuan,Jeong, Hyun-Dam Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.12

Newly Synthesized Silicon Quantum Dot–Polystyrene Nanocomposite Having Thermally Robust Positive Charge Trapping

Dung, Mai Xuan,Choi, Jin-Kyu,Jeong, Hyun-Dam American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.7

<P>Striving to replace the well known silicon nanocrystals embedded in oxides with solution-processable charge-trapping materials has been debated because of large scale and cost effective demands. Herein, a silicon quantum dot–polystyrene (SiQD–PS) nanocomposite (NC) was synthesized by post-functionalization of hydrogen-terminated silicon quantum dots (H-SiQDs) with styrene using a thermally induced surface-initiated polymerization approach. The NC contains two miscible components: PS and SiQD@PS which, respectively, are polystyrene and polystyrene chains-capped SiQDs. Spin-coated films of the nanocomposite on various substrate were thermally annealed at different temperatures and subsequently used to construct metal-insulator-semiconductor (MIS) devices and thin film field-effect transistors (TFTs) having a structure of p-Si<SUP>++</SUP>/SiO<SUB>2</SUB>/NC/pentacene/Au source-drain. Capacitance–voltage (<I>C</I>–<I>V</I>) curves obtained from the MIS devices exhibit a well-defined counterclockwise hysteresis with negative fat band shifts, which was stable over a wide range of curing temperatures (50–250 °C). The positive charge trapping capability of the NC originates from the spherical potential well structure of the SiQD@PS component while the strong chemical bonding between SiQDs and polystyrene chains accounts for the thermal stability of the charge trapping property. The transfer curve of the transistor was controllably shifted to the negative direction by varying applied gate voltage. Thereby, this newly synthesized and solution processable SiQD–PS nanocomposite is applicable as charge trapping materials for TFT based memory devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-7/am400356r/production/images/medium/am-2013-00356r_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am400356r'>ACS Electronic Supporting Info</A></P>

Tuning optical properties of Si quantum dots by π-conjugated capping molecules.

Dung, Mai Xuan,Tung, Dao Duy,Jeong, Sohee,Jeong, Hyun-Dam Wiley-VCH 2013 Chemistry, an Asian journal Vol.8 No.3

<P>The absorption and photoluminescence (PL) properties of silicon quantum dots (QDs) are greatly influenced by their size and surface chemistry. Herein, we examined the optical properties of three Si QDs with increasing σ-π conjugation length: octyl-, (trimethylsilyl)vinyl-, and 2-phenylvinyl-capped Si QDs. The PL photon energy obtained from as-prepared samples decreased by 0.1-0.3 eV, while the PL excitation (PLE) extended from 360 nm (octyl-capped Si QDs) to 400 nm (2-phenylvinyl-capped Si QDs). A vibrational PL feature was observed in all samples with an energy separation of about 0.1920.013 eV, which was explained based on electron-phonon coupling. After soft oxidization through drying, all samples showed blue PL with maxima at approximately 410 nm. A similar high-energy peak was observed with the bare Si QD sample. The changes in the optical properties of Si QDs were mainly explained by the formation of additional states arising from the strong σ-π conjugation and QD oxidation.</P>

Newly Synthesized Silicon Quantum Dot-Polystyrene Nanocomposite Having Thermally Robust Positive Charge Trapping

Mai Xuan Dung,Jin-Kyu Choi,Hyun-Dam Jeong 한국진공학회 2013 한국진공학회 학술발표회초록집 Vol.2013 No.2

Electrical Instabilities of Mesoporous Silica Thin Films

Mai Xuan Dung, Hyun-Dam Jeong 조선대학교 기초과학연구원 2010 조선자연과학논문집 Vol.3 No.4

On the surface of mesoporous silica thin films (MSTF) which were fabricated by sol-gel approach there are existences of water and three different silanol types including chained, germinal and isolated silanol. Their amounts changes as a function of aging time of used sol solution, as confirmed by FT-IR. The adsorbed water generates ionic carriers such as H+ and OH- and passivates the Si dangling bonds at the interface of silicon wafer-MSTF. The ionic carriers can not only transport across the thickness of thin film to enhance the leakage current but also diffuse toward the silicon wafer-MSTF interface to depassivate Si dangling bonds. On the other hand, chained silanols or germinal silanols promote the moisture adsorption of MSTF and tend to form strongly hydrogen bonded systems with adsorbed water molecules resulting in very high dielectric constant. Isolated silanol, on the contrary, affects less on electrical properties of thin film.

Ultralow-n SiO2 Thin Films Synthesized Using Organic Nanoparticles Template

Mai Xuan Dung,이준기,Woo-Sik Soun,정현담 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.12

In an original effort, this lab attempted to employ polystyrene nanoparticles as a template for the synthesis of ordered and highly porous macroporous SiO2 thin films, utilizing their high combustion temperature and narrow size distribution. However, polystyrene nanoparticle thin films were not obtained due to the low interaction between individual particles and between the particle and silicon substrate. However, polystyrene-polyacrylic acid (PS-AA) colloidal particles of a core-shell structure were synthesized by a one-pot miniemulsion polymerization approach, with hydrophilic polyacrylic acid tails on the particle surface that improved interaction between individual particles and between the particle and silicon substrate. The PS-AA thin films were spin-coated in the thickness ranges from monolayer to approximately 1.0 μm. Using the PS-AA thin films as sacrificial templates, macroporous SiO2 thin films were successfully synthesized by vapor deposition or conventional solution sol-gel infiltration methods. Inspection with field emission scanning electron microscopy (FE-SEM) showed that the macroporous SiO2 thin films consist of interconnected air balls (~100nm). Typical macroporous SiO2 thin films showed ultralow refractive indices ranging from 1.098 to 1.138 at 633 nm,according to the infiltration conditions, which were confirmed by spectroscopy ellipsometry (SE) measurements. This research shows how the synthetic control of the macromolecule such as hydrophilic polystyrene nanopaticles and silicate sol precursors innovates the optical properties and processabilities for actual applications.

Synthesis of Styryl-Terminated Silicon Quantum Dots: Reconsidering the Use of Methanol

Mai Xuan Dung,Hyun-Dam Jeong 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.12

InP Quantum Dot-Organosilicon Nanocomposites

Mai Xuan Dung,Priyaranjan Mohapatra,최진규,김진혁,정소희,정현담 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.5

InP quantum dot (QD)-organosilicon nanocomposites were synthesized and their photoluminescence quenching was mainly investigated because of their applicability to white LEDs (light emitting diodes). The as-synthesized InP QDs are capped with myristic acid (MA), which are incompatible with typical silicone encapsulants. We have introduced a new ligand, 3-aminopropyldimethylsilane (APDMS), which enables embedding the QDs into vinyl-functionalized silicones through direct chemical bonding. The exchange of ligand from MA to APDMS does not significantly affect the UV absorbance of the InP QDs, but quenches the PL to about 10% of its original value with the relative increase in surface related emission intensities, which is explained by stronger coordination of the APDMS ligands to the surface indium atoms. InP QD-organosilicon nanocomposites were synthesized by connecting the QDs using a short cross-linker such as 1,4-divinyltetramethylsilylethane (DVMSE) by the hydrosilylation reaction. The formation and changes in the optical properties of the InP QD-organosilicon nanocomposite were monitored by ultraviolet visible (UV-vis) absorbance and steady state photoluminescence (PL) spectroscopies. As the hydrosilylation reaction proceeds, the QD-organosilicon nanocomposite is formed and grows in size, causing an increase in the UV-vis absorbance due to the scattering effect. At the same time, the PL spectrum is red-shifted and, very interestingly, the PL is quenched gradually. Three PL quenching mechanisms are regarded as strong candidates for the PL quenching of the QD nanocomposites, namely the scattering effect, Förster resonance energy transfer (FRET) and cross-linker tension preventing the QD’s surface relaxation.