Several PbZr 1−x Ti x O 3 (PZT) compositions in the proximity of the morphotropic phase boundary (MPB) were examined by means of Raman spectroscopy in the 15-800 K temperature range. Previous studies performed by other researchers using various techniques evidenced that, in the phase diagram of PZT, areas with rhombohedral/monoclinic and tetragonal/monoclinic phases coexist across the MPB. For these compositions, either long-range or short-range symmetry ordering of the monoclinic phase should be considered, so that no true rhombohedral-monoclinic-tetragonal phase boundary exists. In addition, the onset of antiferrodistortive phase transitions between high-T and low-T perovskite phases has been predicted by ab initio calculations and experimentally reported. In the present work, low-T and high-T Raman scattering spectra were collected on undoped PbZr 1−x Ti x O 3 with compositions x = 0.42, 0.45, 0.465, 0.48 and 0.53 in an attempt to clarify the current open issues on the phase diagram of PZT. Spectra clearly belonging to the respective phases were observed in the rhombohedral, monoclinic and tetragonal areas, thus confirming that monoclinic ordering is long-range only for a narrow range of compositions. Raman measurements at cryogenic temperatures allowed detecting all predicted low-T phases, including the tetragonal one. These results are in good agreement with both ab initio calculations and experimental results obtained by other authors on the same compositions.

ZnO layers doped simultaneously with Ga and N (codoping), and magnetic elements (V, Co) were characterized by Raman scattering to study their structural stability. Five impurity modes were observed in range 200-900 cm −1 in the doped samples, and showed characteristic variation with the doping level. It is shown that these modes can be used as a good measure of lattice defects induced by doping. The Raman spectra showed that the magnetic elements were incorporated up to 5 mol% without serious deterioration in crystallinity.

Ultra-shallow boron implanted ͑B + 1 keV 1.0 ϫ 10 15 cm −2 ͒ n-type Si wafers were prepared and characterized by multiwavelength Raman and photoluminescence ͑PL͒ spectroscopy before and after rapid thermal annealing ͑RTA͒. The Raman and PL characterization results were compared with sheet resistance from four point probe measurements and boron depth profiles from secondary ion mass spectroscopy. We have found a very strong correlation between the rapid, non-contact optical characterization results and important parameters of ultra-shallow junctions ͑USJs͒ obtained from conventional invasive techniques. Ultraviolet Raman was very sensitive to subsurface ͑ ϳ5 nm͒ B profiles near or above the solid solubility ͑ Ͼ 1 ϫ 10 20 cm −3 ͒ of B in Si. Visible wavelength excitation PL indicated the presence of significant levels of nonradiative recombination centers beyond the USJ depth and implant end-of-range damage even after RTA. Multi-wavelength Raman and PL are found to be very promising as complementary and/or alternative diagnostic metrology tools for implant process control and in-line device performance screening.For high performance and low power consumption, miniaturization of devices is essential. Physical dimensions and all design parameters have to be scaled down while keeping the dopant concentration of the source/drain region higher than ever, often higher than the solid solubility of dopants in thermal equilibrium. 1 The ultrashallow junction ͑USJ͒ fabrication process is one of the most critical, yet extremely challenging, areas in advanced device research and development ͑R&D͒ and manufacturing beyond 45 nm technology nodes. 1-9 Various types of millisecond annealing techniques, including flash annealing 2,6,7 and laser spike anneal, 10 have been proposed and implemented in production. The quality of USJs, including the degree of electrical activation and dopant profiles of USJ implanted Si, after implant activation and rapid thermal annealing ͑RTA͒ has been monitored by four point probes and secondary ion mass spectroscopy ͑SIMS͒. 1-9 These traditional USJ characterization techniques require either physical contact or destructive analysis. The existence of electrically active defects, dopants in excess of solid solubility, interstitial dopants around USJs, and junction leakage often lead to unrealistic conclusions. No easy, reliable, and practical USJ characterization methods are available at present, even though several novel characterization techniques, such as micro-four point probes and non-contact sheet resistance estimation using carrier spreading measurements, have been proposed. 7,11 For proper characterization of USJs, the development of alternative, complementary, subsurface characterization techniques to augment traditional techniques, and their introduction to advanced device R&D and the manufacturing community, is essential. Noncontact and non-destructive in-line characterization and/or monitoring methods are strongly desired for fast feedback of characterization results and the reduction of m...

This paper reports on a systematic investigation of nitrogen (N) doping in single-crystalline TiO2 films possessing an anatase phase. TiO2 films heavily doped with N were grown with high crystallinity by employing a pulsed laser ablation technique using a close lattice-matched LaAlO3 (100) substrate and NO as the source gases for N doping. N15 and O18 isotope tracing by secondary-ion-mass spectroscopy confirmed that N and O atoms were simultaneously incorporated into the films as a consequence of the gas phase reactions between Ti-related chemical species ablated by the laser and NO free radicals. The films yielded an absorption band at around 3.0 eV, as expected from the yellowish color, with band tailing becoming stronger with increasing N concentration. It is suggested that N-related complex defects in TiO2 acted as carrier compensation centers. Micro-Raman spectroscopy with a spatial resolution of 1μm2 revealed host-lattice defects and generation of secondary phases at the microscopic scale by N doping. This work showed that the visible absorption band in N-doped TiO2 films can be attributed to small structural modifications consisting of N-related complex defects and secondary phases formed at the microscopic scale. These structural modifications were associated with a concomitant enhancement in photocatalytic activity.

We have measured the Raman and cathodoluminescence (CL) spectra of ZnO nanoparticles with different crystallite sizes. The Raman spectra show that the frequency of the E2 (high) phonon in these nanoparticles, which is initially high, decreases with the crystallite size, while its linewidth increases. This result is explained by the size effect. The CL spectra show that the relative intensity ratio of the CL peak at around 500–600nm to the band-edge CL peak at approximately 360nm drastically increases as the crystallite size decreases. We use the surface recombination model to explain this result. According to this model, the relative intensity ratio increases because of an increase in the concentration of deep levels on the surface of the crystallites and/or an increase in the free-carrier concentration.

We have studied the epitaxial growth and photoluminescent (PL) properties of Eu3+-doped ZnO layers in correlation with structural analyses. Incorporation of Eu3+ ions into a ZnO host resulted in deterioration in crystal quality and lattice distortion. The spectral structure of Eu3+ emission revealed that Eu3+ ions were located at site symmetries lower than the original C3v of the Zn2+ ion sites in a hexagonal wurtzite structure of ZnO, which allowed for efficient red luminescence based on the electric dipole transitions. Moreover, we have found an anticorrelation of PL intensity between the excitonic and Eu3+ emissions, related to energy transfer from the ZnO host to the Eu3+ ions. The excitonic structure at the band edge was obscured upon doping with Eu3+ ions due to the formation of a band tail around 3.2 eV. This correlated with a reduction in excitonic emissions, leading to enhancement of Eu3+ emission. Strong PL emission from Eu3+ ions was only observed at low temperatures, and was remarkably suppressed with increasing temperature due to two types of nonradiative energy transfer paths. For the energy transfer process to Eu3+ ions, we suggest that the recombination energy of an electron–hole pair at the band tail near the band edge is close to that of high-lying excited levels in the Eu3+ 4f shell, providing an efficient energy pathway for the excitation of Eu3+ ions in the ZnO system.

We present in this work advanced results concerning heat shielding based on assembled sheets of In 2 O 3 :Sn nanoparticles (ITO-NP sheets) in terms of particle size and interparticle gap. We demonstrate that the oxide semiconductor nanoparticles are crucial to achieve required optical properties relevant to energy-saving applications. In the infrared (IR) range, strong electric-field (E-field) interactions between NPs are formed locally at narrow interparticle gaps. Changes in thickness and particle size greatly increase the magnitude and peak separation of the resonant reflectance, which widely covers the IR range. As a consequence, the size-dependent plasmonic properties contribute to high heat-shielding efficiency. As confirmed by electrodynamic simulations, plasmonic coupling results in these spectral changes due to three-dimensional E-field interactions along the in-plane and out-of-plane directions. Moreover, the resonant reflectance is tuned by mechanical stretchable strains, indicating one of the important factors for determining the resonant reflectance in addition to the control of particle size. From another perspective, the interparticle gap markedly affects the mechanism of electron transport in the NP sheets. The high electromagnetic transmission in the microwave range was due to the low electrical conductance caused by the spatial confinement of free carriers into the NPs. These results promoted development of flexible heat shielding in which optical and electromagnetic control is feasible for a wide range of wavelengths from ultraviolet to microwaves. Control of particle size and interparticle gap revealed important aspects that should be considered in structural design when fabricating heat-shielding materials.

The heteroepitaxy of Mg-rich Mg0.37Zn0.63O layers on ZnO (0001) substrates was carried out using laser molecular-beam epitaxy. Mg0.37Zn0.63O layers changed from a two-dimensional (2D) to three-dimensional growth mode at a layer thickness (tc) between 38 and 100 nm through lattice-strain relaxation. For tc>100nm, hexagonal nanodots with a density in the order of 109cm−2 formed naturally by the Stranski-Krastanov mode. The individual nanodots possessed pyramidal hillocks with lateral sizes raging from 100 to 200 nm, and phase separation to Mg-rich and Mg-poor regions in the Mg0.37Zn0.63O alloys was found from the results of atomic force microscopy and microphotoluminescence spectroscopy. A suitable layer thickness of Mg0.37Zn0.63O concerning quantum barriers was speculated as being 38 nm from a theoretical calculation based on the Matthew and Blakeslee model [J. Cryst. Growth 27, 118 (1974)]. For tc≦38nm, the top surface of the Mg0.37Zn0.63O layer was very flat due to the curtailment of 2D growth. This contributed to the coherent growth of Mg-rich Mg0.37Zn0.63O∕ZnO multi-quantum-well structure (MQWS) with high crystallinity, as characterized from structural analyses using high-resolution x-ray diffraction. The two-dimensional properties of the MQWS were confirmed from the anisotropic optical property and electrical conductivity with 2D electron transport at low temperatures.