PUBLIKASI - LEMBAGA ILMU PENGETAHUAN INDONESIA

Origin of coherent G -band phonon spectra in single-wall carbon nanotubes

Coherent phonons in single-wall carbon nanotubes (SWNTs) are observed as oscillations of the differential absorption coefficient as a function of time by means of pump-probe spectroscopy. For the radial breathing mode (RBM) of a SWNT, the coherent phonon signal is understood to be a result of the modulated diameter-dependent energy gaps due to the coherent RBM phonon oscillations. However, this mechanism might not be the dominant contribution to other phonon modes in the SWNT. In particular, for the G-band phonons, which correspond to bond-stretching motions, we find that the modulation of the interatomic optical dipole (electron-photon) matrix element gives rise… Selengkapnya

Deep-ultraviolet Raman scattering studies of monolayer graphene thin films

We present joint experimental and theoretical investigations of the deep-ultraviolet Raman scattering spectra of monolayer graphene thin films. We found that upon a 266 nm laser excitation, while the G mode remains pronounced, the G′ mode is not observed. The G′ mode exhibits distinctive linewidth broadening towards the ultraviolet frequency region. The peak intensity ratio of the G′ and G modes increases dramatically excited at 355, 532, and 785 nm wavelengths. All of the experimental findings are in good agreement with the theory calculated by the tight-binding method. We theoretically show that the integrated intensity of the G′ mode is… Selengkapnya

Breit-Wigner-Fano line shapes in Raman spectra of graphene

Excitation of electron-hole pairs in the vicinity of the Dirac cone by the Coulomb interaction gives rise to an asymmetric Breit-Wigner-Fano line shape in the phonon Raman spectra in graphene. This asymmetric line shape appears due to the interference effect between the phonon spectra and the electron-hole pair excitation spectra. The calculated Breit-Wigner-Fano asymmetric factor 1/qBWF as a function of the Fermi energy shows a V-shaped curve with a minimum value at the charge neutrality point and gives good agreement with the experimental results. Selengkapnya

Electronic Raman scattering and the Fano resonance in metallic carbon nanotubes

The Fano resonance spectra for the G band in metallic carbon nanotubes are calculated as a function of laser excitation energy, in which the origin of the resonance is given by an interference between the continuous electronic Raman spectra and the discrete phonon spectra. We found that the second-order scattering process of theq ≠ 0 electron-electron interaction is more relevant to the continuous spectra rather than the q = 0 first-order process because the q = 0 direct Coulomb interaction vanishes due to the symmetry of the two sublattices of a carbon nanotube. Selengkapnya

Excitonic effects on coherent phonon dynamics in single-wall carbon nanotubes

We discuss how excitons can affect the generation of coherent radial breathing modes in the ultrafast spectroscopy of single-wall carbon nanotubes. Photoexcited excitons can be localized spatially and give rise to a spatially distributed driving force in real space which involves many phonon wave vectors of the exciton-phonon interaction. The equation of motion for the coherent phonons is modeled phenomenologically by the Klein-Gordon equation, which we solve for the oscillation amplitudes as a function of space and time. By averaging the calculated amplitudes per nanotube length, we obtain time-dependent coherent phonon amplitudes that resemble the homogeneous oscillations that are observed… Selengkapnya

Electronic Raman spectroscopy of metallic carbon nanotubes

A single wall carbon nanotube (SWNT) is a single-layer graphite sheet rolled up into a cylinder, with diameter ∼1 nm and length ∼1 μm. In comparison with its length, a SWNT diameter is small enough, thus a SWNT can be regarded as a quasi one-dimensional (1D) material. Depending on how we roll up the graphene sheet, the geometry of SWNT is defined by a chirality index (n, m). The (n, m) value determines whether a SWNT is metallic (m-SWNT) or semiconducting (s-SWNT). In m-SWNTs, the existence of the gapless linear energy band in m-SWNT provides an interesting phenomenon of a… Selengkapnya

The Optical Low-Pass Filter Gain of a Ring Cavity

We have developed the equations describing the interaction of light and matter. The Maxwell-Schrödinger equations were modified to be The Maxwell-Bloch equations by means of homogeneity and slowly varying wave approximation. The boundary conditions of a unidirectional ring cavity were performed to complete the analytical calculation. From this study, we observed the existence of a low-pass filter gain, parallel with the phenomenon which exists in op-amp circuit. Selengkapnya

Metode Perbanyakan talas Beneng (Xanthosoma undipes K. Koch) secara in vitro

Invensi ini berhubungan dengan suatu proses perbanyakan tanaman talas Beneng Xanthosoma undipes K.Koch secara in vitro yang berasal dari bonggol. Hasil yang diperoleh dari proses ini berupa bibit tanaman yang seragam, bebas penyakit dan dapat diproduksi sepanjang musim. Tahapan proses dari invensi ini meliputi sterilisasi bonggol untuk menghasilkan kultur tunas talas Beneng, dilanjutkan dengan perlakuan perbanyakan tunas dengan berbagai konsentrasi BAP, dan melakukan aklimatisasi planlet. Hasil yang diperoleh melalui proses ini didapatkan tanaman talas Beneng yang mempunyai ketegaran tinggi di lapangan. Selengkapnya

MO.SS1.4. The Lignocellulolytic Activity and Ability to Produce Indole Acetic Acid Hormone of Fungal Inoculant Isolated From Spent Mushroom (Agaricus sp.) Substrate

The main problem in soil conservation is the lack of carbon source from organic material. Rice straw from spent mushroom substrate (SMS) can be used as organic fertilizer to supply organic carbon for soil. It can also improve soil structure and increase macro-elements and micro-elements required by plants. This research focused on analyzing lignocellulolytic activity and Indole Acetic Acid (IAA) concentration produced by 14 fungal strains isolated from rice straw that had previously been used as the substrate for champignon (Agaricus sp.). Four fungal strains were isolated (JPF 2, JPF 5, JPF 13, and JPF 14) and then characterized. JPF… Selengkapnya

MO.SS1.4. PENINGKATAN KADAR PATI RESISTEN TIPE III TEPUNG SINGKONG TERMODIFIKASI MELALUI FERMENTASI DAN PEMANASAN BERTEKANAN-PENDINGINAN

Modified Cassava flour (Mocaf) is a product derived from cassava flour that uses principles of cassava cell modification through fermentation for 12-72 hours. This study aims to improve the levels of resistant starch in cassava flour using lactic acid bacteria fermentation and autoclaving-cooling. Cassava slices fermented with mixed cultures of lactic acid bacteria (Lactobacillus plantarum B-307:Leuconostoc mesenteroides SU-LS 67=1:1) for 18 hours at 37oC. The fermented cassava then autoclaved (121oC, 15 min) and cooled (4oC, 24 hours) for 1-3 cycles. Cassava slices was dried (70oC, 16 hours), grounded and sieved (80 mesh) to obtain modified cassava flour. Combination of autoclaving-cooling… Selengkapnya