Browsing by Author "Kherani, Nazir P."

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Erbium-Doped Amorphous Carbon-Based Thin Films: A Photonic Material Prepared by Low-Temperature RF-PEMOCVD
(2014-03-01)
Hsu, Hui-Lin
;
Leong, Keith R.
;
Teng, I-Ju
;
Halamicek, Michael
;
Juang, Jenh-Yih
The integration of photonic materials into CMOS processing involves the use of new materials. A simple one-step metal-organic radio frequency plasma enhanced chemical vapor deposition system (RF-PEMOCVD) was deployed to grow erbium-doped amorphous carbon thin films (a-C:(Er)) on Si substrates at low temperatures (<200 degrees C). A partially fluorinated metal-organic compound, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) Erbium(+III) or abbreviated Er(fod)(3), was incorporated in situ into a-C based host. Six-fold enhancement of Er room-temperature photoluminescence at 1.54 mu m was demonstrated by deuteration of the a-C host. Furthermore, the effect of RF power and substrate temperature on the photoluminescence of a-C:D(Er) films was investigated and analyzed in terms of the film structure. Photoluminescence signal increases with increasing RF power, which is the result of an increase in [O]/[Er] ratio and the respective erbium-oxygen coordination number. Moreover, photoluminescence intensity decreases with increasing substrate temperature, which is attributed to an increased desorption rate or a lower sticking coefficient of the fluorinated fragments during film growth and hence [Er] decreases. In addition, it is observed that Er concentration quenching begins at similar to 2.2 at% and continues to increase until 5.5 at% in the studied a-C: D(Er) matrix. This technique provides the capability of doping Er in a vertically uniform profile.
In-situ doping of erbium in hydrogenated amorphous carbon by low temperature metalorganic radio frequency plasma enhanced chemical vapor deposition
(2014-11-03)
Hsu, Hui-Lin
;
Leong, Keith R.
;
Halamicek, Michael
;
Teng, I-Ju
;
Mahtani, Pratish
A significant improvement in the photoluminescence of erbium doped amorphous carbon (a-C: H(Er)) is reported. The effects of the RF power on the anode and cathode a-C: H films were investigated in terms of the microstructural and local bonding features. It was determined that Er doped a-C: H films should be placed on the anode to obtain wider bandgap and lower percentage of sp(2) carbon bonding. The metalorganic compound, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) Erbium(+III) or Er(fod)(3), was incorporated in-situ into an a-C: H host by metalorganic rf plasma enhanced chemical vapor deposition. This technique provides the capability of doping Er in a vertically uniform profile. The high erbium concentration (3.9 at.%), partial fluorination of the surrounding ligands, and the large optical bandgap of the host a-C: H are the primary factors that enable enhancement of the photoluminescence. (C) 2014 Elsevier B. V. All rights reserved.
On the use of new oxidized Co-Cr-Pt-O catalysts for vertically-aligned few-walled carbon nanotube forest synthesis in electron cyclotron resonance chemical vapor deposition
(2014-12-01)
Teng, I-Ju
;
Huang, Chong-Sian
;
Hsu, Hui-Lin
;
Chung, I-Chuan
;
Jian, Sheng-Rui
A new class of the multi-element catalysis system, Co-Cr-Pt-O, is used for vertically-aligned few-walled carbon nanotube (CNT) forest synthesis by a sandwich-growth technology in electron cyclotron resonance chemical vapor deposition. The effect of catalyst compositions on the resulting particle sizes after pretreatment, and the influence of process parameters on the CNT forest heights and diameters are investigated. Results show that a plasma pretreatment step reduces the metal oxides present in the as-deposited Co-Cr-Pt-O catalyst to their metallic states or to mixed metallic/oxidic states, and the co-catalytic synergistic effect during the reduction process thus leads to the production of uniformly small particles with a size of 3.3-3.9 nm over the substrate. Moreover, with CH4 as the carbon source, vertically-aligned CNT forests of similar to 12 mu m in height are achieved, and further characterizations indicate that the forests consist of dominant triple-walled nanotubes with an average inner tube diameter of 3.2-3.7 nm mostly. Additionally, field emission measurements show that the turn-on field of the CNT-forest emitters is below 2.6 V/mu m, and the emission current density can reach 110 mA/cm(2) at 4.5 V/mu m. High reproducibility of field emission characteristics and Raman signals suggests the regularity of the CNT forests in structure and size. (C) 2014 Elsevier Ltd. All rights reserved.
Reduction of Photoluminescence Quenching by Deuteration of Ytterbium-Doped Amorphous Carbon-Based Photonic Materials
(2014-08-01)
Hsu, Hui-Lin
;
Leong, Keith R.
;
Teng, I-Ju
;
Halamicek, Michael
;
Juang, Jenh-Yih
In situ Yb-doped amorphous carbon thin films were grown on Si substrates at low temperatures (<200 degrees C) by a simple one-step RF-PEMOCVD system as a potential photonic material for direct integration with Si CMOS back end-of-line processing. Room temperature photoluminescence around 1 mu m was observed via direct incorporation of optically active Yb3+ ions from the selected Yb(fod)(3) metal-organic compound. The partially fluorinated Yb(fod)(3) compound assists the suppression of photoluminescence quenching by substitution of C-H with C-F bonds. A four-fold enhancement of Yb photoluminescence was demonstrated via deuteration of the a-C host. The substrate temperature greatly influences the relative deposition rate of the plasma dissociated metal-organic species, and hence the concentration of the various elements. Yb and F incorporation are promoted at lower substrate temperatures, and suppressed at higher substrate temperatures. O concentration is slightly elevated at higher substrate temperatures. Photoluminescence was limited by the concentration of Yb within the film, the concentration of Yb ions in the +3 state, and the relative amount of quenching due to the various de-excitation pathways associated with the vibrational modes of the host a-C network. The observed wide full-width-at-half-maximum photoluminescence signal is a result of the variety of local bonding environments due to the a-C matrix, and the bonding of the Yb3+ ions to O and/or F ions as observed in the X-ray photoelectron spectroscopy analyses.