Ultra-thin single wall carbon nanotubes (SWNTs) with a diameter of only 0.3 nm were synthesized in the nano-channels
of AlPO4-11 porous single crystals. Raman spectra, with excitation wavelengths in the range from 457.9 to 647.1 nm,
show excellent agreement with the density functional calculations of the Raman-active vibration modes of the armchair
(2,2) SWCNTs. Calculated imaginary part of the dielectric function also displays qualitative agreement with the
resonant Raman data. Interestingly, the (2,2) nanotube has two metastable ground state corresponding two slightly
different lattice constants in axial direction, one state is metallic and the other is semiconducting. The polarizibility of the
Raman modes agrees well with the calculated intensities for non-resonant Raman scattering, although the resonant
Raman scattering plays a key role in the process. Both theory and experiment show the free-standing (2,2) SWNTs to be
unstable. Confinement of the SWNTs in the nano-channels stablilizes the structure.
Quantum wire is one of the central subjects of nano-electronics. Quantum wire shows unusual electronic and optical
properties attributed to the following effects: quantum confinement effect, surface effects, and quantum tunneling effect.
Many different kinds of techniques have been developed for researchers to produce quantum wires, such as laser ablation
technique, electrochemical processing, chemical vapor deposition technique, etc. However, controlling the sample size
and orientation distribution is a big challenge in these fabrication methods. One promising technique to prepare monosized
well-aligned quantum wires is using template technique, i.e., deposition of guests into porous matrices.
In this paper, several template synthesis processes for preparations of carbon nanotubes were investigated. The carbon
nanotubes produced by template technique have narrow size distributions and involve fragments of highly ordered
shapes which are due to the limitation of matrix size and channel direction. Because of the restricted dimension of the
matrix, the system shows peculiar properties such as polarization in spectra, strong quantum effects, and faster optical
response. These may be used in electric transport, optic switches, nonlinear optics and lasers.
Raman scattering is an inelastic process, in which we can obtain information about material lattice vibration frequencies. If the wavelength of the excitation laser is within the electronic spectrum of the material, the intensity of some Raman-active vibrations will increase enormously. This resonant Raman effect can be quite useful to explore the electron-phonon coupling in the substance. In this article, we report the investigations on the electron-phonon coupling effect in Se nanoclusters using resonant Raman technique. Up to 10 different laser lines are used in the experiment. The Raman intensity strongly depends on the energy of the laser lines used for excitation. The one-phonon symmetric A1 modes for Se single helix and Se8 rings are enhanced in the vicinity of their absorption bands. Detailed analysis shows that the Raman intensity in the high frequency range 450 - 550 cm-1 is a sum of individual second-order Raman scattering intensities for the confined Se species. These two-phonon Raman shifts occur at twice the frequency shift of the first-order Raman lines, and their intensities are also enhanced when the excitation laser energy matches an electronic transition in Se nanoclusters.
Aluminophosphate AlPO4-5 single crystal is a kind of nanoporous material. Its framework consists of alternative tetrahedra of AlO4 and PO4 which form an array of opened one-dimensional channels and pack in hexagonal structure as two-dimensional photonic crystal. The inner diameter of the channel is 0.73 nm. Since the AlPO4-5 single crystal is electrically insulated and thermally stable up to 900°C, it is an ideal host to incorporate nano-structured species. These guest-host materials are potentially new functional materials in electric transport, optic switches, nonlinear optics and lasers. We have synthesized two different types of guest-host systems, including selenium and carbon nanotube in the channels of AlPO4-5 crystals. Polarized absorption spectra and polarized Raman spectra have been investigated. Both crystals behave as good polarizers with high absorption for the light polarized parallel to the c-axis of the crystal. This anisotropic optical property implies that ordered species with a large aspect ratio are formed in the channel. The
polarization angle dependence of the Raman intensity indicates that the enclosed species are highly oriented in the channels with their dipole transition moment mostly along the channels. These guest-host systems are useful for applications of optical filters or polarizers.
Micro-cavity laser has attracted extensive attentions due to its potential applications in high-speed integrated opto-electronic device and system. In micro-cavity, spontaneous emission process is enhanced or prohibited, and lasing can occur without a visible threshold. In the past, micro-cavity was realized with semiconductors such as microdisks or vertical cavity surface emitting lasers, with organic dyes embedded in planar resonators as Langmuir-Blodgett films or in spheres, and with gain medium in photonic crystals. In this article, we report a new type of micro-cavity laser based on organic dye molecules incorporated in the channels of AlPO4-5 single crystals by physical diffusion method. The optical measurements reveal that the dipole transition moment of the enclosed organic dye molecules is highly oriented in the channels. Due to size confinement of the AlPO4-5 channels, there is a structure deformation of the dye molecules, which leads to a large blue shift in the absorption spectra for the dye/AlPO4-5 crystal. The micro-sized hexagonal AlPO4-5 single crystal serves as a good natural micro-cavity for the lasing action of the adsorbed dye molecules. The micro-cavity mode of the lasing action is demonstrated.
High quality ZnO/Zn1MgO multi-quantum wells (MQWs) have been prepared on lattice-matched ScAIMgO4 substrates by laser-MBE method. Nine pixels of MQWs having different well widths were integrated in the same substrate by means of combinatorial masking techniques, which provided excellent specimens to systematically study the dependence of physical properties of MQWs on well widths. Optically pumped stimulated emission spectra were measured in these ZnO/Zn1MgO multi-quantum wells by using a tunable pulsed dye laser as excitation source. We investigated the pump-intensity dependence of the stimulated emission spectra from 5 to 300 K. At low temperatures, only one peak in the stimulated emission was observed, which could be assigned to the emission induced by exciton-exciton inelastic scattering (P-band). When the temperature increases above 160 K, there appears an additional peak at the lower energy side of the P-band, which was assigned to electronhole plasma emission. However, the emission due to the exciton-exciton scattering still remains up to room temperature. The gain spectrum for a multi-quantum well sample has been obtained by variable stripe method at room temperature. At an excitation intensity of about 2 MW/cm2, the peak gains for the P-band and electron-hole plasma emission are 239 cm1 and 380 cm1, respectively. The exciton binding energy was deduced from the energy difference between the P-band and free exciton band. The exciton binding energies of these samples having different well widths were found to increase with decreasing the well widths due to the quantum confinement effect. This enhancement of exciton binding energy should be favorable for the stability of exciton states at higher temperatures.
We report high-throughput optimizations for various material parameters of Mg,Zn1-xO and Zn1-xCdxO alloy films, Al-doped ZnO films, MgxZn1-xO/ZnO single quantum wells and superlattice structures with using combinatorial laser MBE. Combinatorial chips including nine thin film pixels were grown on lattice-matched ScAlMgO4 (0001) substrates by switching the mask patterns and targets during pulsed laser deposition.
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