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Light Emission from Silicon Nanocrystals - Size Does Matter !
Robert G. Elliman,Andrew R. Wilkinson,Barry Luther-Davies,Marc G. Spooner,Marek Samoc,Max J. Lederer,Nathanael Smith,Tessica D.M. Weijers 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
A brief overview of two recent Si nanocrystal studies undertaken at the Australian National University is presented: recent work on hydrogen passivation of non-radiative defects and attempts to measure optical gain in waveguide structures. In the rst study, a generalized treatment of hydrogen passivation and desorption is employed to model the in uence of hydrogen on silicon nanocrystal luminescence. Values for reaction-rate parameters are determined from the model and found to be in excellent agreement with values previously determined for paramagnetic Si danglingbond defects (Pb-type centers) found at planar Si/SiO2 interfaces. In the second study, an attempt is made to measure optical gain in silicon nanocrystals by monitoring the intensity of a probe beam propagating in a waveguide structure containing silicon nanocrystals during photo-excitation of the nanocrystals. The probe beam is shown to be attenuated by the excitation demonstrating the dominance of absorptive processes. No gain was observed.
Saturation of Photoluminescence Intensity from Si Nanocrystals Exposed to Atomic Hydrogen
조현지,R. G. Elliman,A. R. Wilkinson,윤종환 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.2
Si nanocrystals embedded in silicon dioxide films are exposed to an atomic hydrogen plasma at different temperatures in the range from 100 to 350 . The photoluminescence (PL) from the nanocrystals is shown to increase in intensity with increasing exposure time before saturating at a level that depends on the exposure temperature. The saturation level depends on the final exposure temperature and shows no dependence on the thermal history of exposure. This behavior is shown to be consistent with a model in which the steady-state passivation level is determined by a balance between defect passivation and depassivation by hydrogen. Modelling suggests that the difference in activation energies for the passivation and depassivation reactions is eV, with the activation energy for the passivation reaction being larger than that for the depassivation reaction.
Luminescence study of Si- and Ge- implanted (1102) sapphires
Sung KIM,Suk-Ho CHOI,C. J PARK,H. Y CHO,R.G. ELLIMAN 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
Implantation with 30 keV Siက or Geက and subsequent annealing at 1100 C create nanocrystalline Si or Ge (nc-Si or nc-Ge) in host materials such as (1102) sapphire and fused silica. Photoluminescence (PL) and cathodluminescence (CL) have been used to investigate luminescence properties of nc-Si or nc-Ge embedded in the host materials. Light emissions from Siက- or Geက- implanted samples are compared with those from Oက- and Alက- implanted ones in order to investigate whether they are from nc-Si (or nc-Ge) or defect-related. The CL band at 574 nm and the PL band at 1380 nm are interpreted as Si- and Ge-nanocrystal-related, respectively, and the CL bands at 328 and 411 nm as defect-related. Especially, the 411-nm band is found after annealing as well as before annealing and sharply increases on increasing the implant dose. This indicates that even high-temperature annealing cannot completely rule out implantation-induced defect luminescence.
Sung Kim,Suk-Ho Choi,C. J. Park,H. Y. Cho,K. H. Cho,R. G. Elliman 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.3
The structural and the optical properties of Ge nanocrystals (NCs) showing large capacitancevoltage hysteresis have been studied by using infrared photoluminescence (PL), high-resolution transmission electron microscopy (HRTEM), high-resolution X-ray diraction (HRXRD). The memory eect strongly depends on the implant dose, the oxide thickness, and the annealing temperature in metal-oxide-semiconductor devices containing Ge NCs. Well-defined C-V characteristics with large hysteresis are found only for annealing temperatures 950 C where Ge NCs are known to form. HRTEM demonstrates the existence of Ge NCs which are almost aligned at an average distance of about 6.7 nm from the SiO2/Si interface. This suggests that the memory eect can be enhanced by accurately controlling the distribution of Ge NCs with respect to the Si/SiO2 interface, although it is also influenced by implantation-induced deep-level defects and SiGe complexes formed at the interface, as confirmed by PL and HRXRD.
Graphene synthesis by C implantation into Cu foils
Lee, J.S.,Jang, C.W.,Kim, J.M.,Shin, D.H.,Kim, S.,Choi, S.H.,Belay, K.,Elliman, R.G. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.66 No.-
Cu foils of 2x2cm<SUP>2</SUP> have been implanted with 70keV C<SUP>-</SUP> ions to nominal fluences of (2-10)x10<SUP>15</SUP>cm<SUP>-2</SUP> at room temperature (RT) and subsequently annealed at 900-1100<SUP>o</SUP>C for 15min, before being cooled to RT to form graphene layers on the Cu surfaces. Analyses with Raman spectroscopy and atomic force microscopy demonstrate that a continuous film of bi-layer graphene (BG) is produced for implant fluences as low as 2x10<SUP>15</SUP>cm<SUP>-2</SUP>, much less than the carbon content of the BG films. This suggests that the implanted carbon facilitates the nucleation and growth of graphene, with additional carbon supplied by the Cu substrate (0.515ppm carbon content). No graphene was observed on unimplanted Cu foils subjected to the same thermal treatment. This implantation method provides a novel technique for the selective growth of graphene on Cu surfaces.
Jang, Chan Wook,Kim, Ju Hwan,Lee, Dae Hun,Shin, Dong Hee,Kim, Sung,Choi, Suk-Ho,Hwang, Euyheon,Elliman, R.G. Elsevier 2017 Carbon Vol.118 No.-
<P>We report a new method of ion implantation for hole doping of graphene in which a layer of polymethyl methacrylate (PMMA) is used as a stopping layer to control the B-ion distribution in the graphene layer. This method is very useful for graphene doping in many aspects because it employs the ion energy comparable to what is commercially used in the semiconductor processes and strongly enhances the doping effect in contrast to the previous studies, resulting from B-ions-induced gating effect. PMMA/graphene/ Cu-foil stacks were implanted with 35 keV B- ions to nominal fluences (phi(B)) of 0.5 -50 x 10(10) cm(-2) at room temperature. The electron/hole mobilities are sharply reduced by doping at phi(B) = 0.5 x 10(10) cm(-2), but above this, they increase with increasing phi(B), as estimated from the Dirac curves. The Raman data and theoretical considerations suggest that the electrical properties of the B-doped graphene are governed by strain effect at low phi(B), but by charge-doping effect at high phi(B). (C) 2017 Elsevier Ltd. All rights reserved.</P>
Self-assembled growth and luminescence of crystalline Si/SiO<sub><i>x</i></sub> core–shell nanowires
Kim, S,Kim, C O,Shin, D H,Hong, S H,Kim, M C,Kim, J,Choi, S-H,Kim, T,Elliman, R G,Kim, Y-M IOP Pub 2010 Nanotechnology Vol.21 No.20
<P>Crystalline Si/SiO<SUB><I>x</I></SUB> core/shell nanowires (NWs) are self-assembled by annealing Ni-coated hydrogenated Si-rich SiO<SUB><I>x</I></SUB> (SRO:H) films at 1100 °C in the presence of Si powder. Plasma-enhanced chemical vapor deposition is used to grow 100 nm SRO:H thin films with varying silicon concentration (<I>n</I><SUB>Si</SUB>). The NWs vary from SiO<SUB><I>x</I></SUB> nanowires to Si/SiO<SUB><I>x</I></SUB> core/shell structures depending on the composition of the SRO:H substrate, with the fraction of core/shell structures increasing with increasing Si concentration. As <I>n</I><SUB>Si</SUB> increases from 37 to 43 at.%, the average diameter of the NWs also increases from 48 to 157 nm. A growth model based on the diffusion-assisted vapor–liquid–solid mechanism is proposed to explain how the core/shell structures are self-assembled. Photoluminescence (PL) spectra of the individual NWs have two major emission bands in the near UV (381 nm) and blue (423 nm) ranges at <I>n</I><SUB>Si</SUB> = 43 at.%, named as UV and BL PL bands, respectively. In contrast, only the BL PL band is observed at <I>n</I><SUB>Si</SUB> ≤ 39 at.%. These results suggest that the BL and UV PL bands can be attributed to the defect states in the SiO<SUB><I>x</I></SUB> shell and at the Si core/SiO<SUB><I>x</I></SUB> shell interface, respectively, and that the BL band is closely related to the growth process of the NWs. </P>