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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.
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>
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>
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.
Condensable InP quantum dots solid
Mai Xuan Dung,Dao Duy Tung,Hyun-Dam Jeong 한국물리학회 2013 Current Applied Physics Vol.13 No.6
Colloidal thioacetic acid-capped InP quantum dots (InP-TAA QDs) and their spin coated-films have been examined in comparison with those of myristic acid-capped InP (InP-MA) QDs. While the QDs are far away from each other in the InP-MA QD films, even in a InP-MA QD film cured at 250 ℃, upon thermal annealing a film of InP-TAA QDs at 250 ℃, the indium thioacetate groups on the surfaces QDs likely condensed, thus resulting in the QD film that consists of individual and proximally packed InP QDs. The structures of the films of InP-MA QDs or InP-TAA QDs were characterized by means of TEM, XRD, and XPS. The current through the film of InP-TAA QDs cured at 250 ℃ was about 2-5 orders of magnitude higher than that of the film of InP-MA film annealed by the sample conditions. We, newly in this letter,define this kind of materials architecture as the condensable QDs solid concept.