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1.
The accurate manipulation of strain in silicon nanowires can unveil new fundamental properties and enable novel or enhanced functionalities. To exploit these potentialities, it is essential to overcome major challenges at the fabrication and characterization levels. With this perspective, we have investigated the strain behavior in nanowires fabricated by patterning and etching of 15 nm thick tensile strained silicon (100) membranes. To this end, we have developed a method to excite the "forbidden" transverse-optical (TO) phonons in single tensile strained silicon nanowires using high-resolution polarized Raman spectroscopy. Detecting this phonon is critical for precise analysis of strain in nanoscale systems. The intensity of the measured Raman spectra is analyzed based on three-dimensional field distribution of radial, azimuthal, and linear polarizations focused by a high numerical aperture lens. The effects of sample geometry on the sensitivity of TO measurement are addressed. A significantly higher sensitivity is demonstrated for nanowires as compared to thin layers. In-plane and out-of-plane strain profiles in single nanowires are obtained through the simultaneous probe of local TO and longitudinal-optical (LO) phonons. New insights into strained nanowires mechanical properties are inferred from the measured strain profiles. 相似文献
2.
Here we report the influence of Sb doping on the structural and optical properties of Zn1−xSbxSe (0 ⩽ x ⩾ 0.15) thin films prepared by thermal evaporation technique on glass substrate. Various characterization techniques such as X-ray diffraction (XRD), EDS, Raman spectroscopy and spectroscopic ellipsometer are employed to assess the structural and optical properties of the deposited films. XRD analysis reveals the formation of polycrystalline cubic structure having preferred growth orientation along (1 1 1) plane without any evidence of secondary phases. Crystallographic parameters like grain size, micro strain, dislocation density, number of crystallites per unit area and texture coefficient point out the structural modification in ZnSe films with Sb inclusion. Raman analysis shows the existence of three 1LO, 2LO and 3LO phonon modes at 251, 511 and 745 cm−1 in pure ZnSe while 3LO mode disappears by the incorporation of Sb atoms in ZnSe matrix. Increase in FWHM of Raman peaks with Sb concentration also indicates the change in crystalline quality of ZnSe films which is in accordance with our XRD results. Spectroscopic ellipsometry results demonstrate a decreasing trend for the optical band gap energy (from 2.61 eV to 1.81 eV) with increasing Sb content. 相似文献
3.
Tian Z Xin K Wang M Han J Wang H Tian ZR Zhang W 《Journal of nanoscience and nanotechnology》2011,11(11):9636-9640
Far-infrared optical and dielectric properties of ferroelectric SrTiO3 and BaTiO3 nanofibers, prepared by hydrothermal syntheses, were studied using terahertz time-domain spectroscopy. The power absorption, refractive index, and complex dielectric function were characterized in the frequency range from 0.2 to 1.0 THz. The measured results are well reproduced by theoretical fittings based on the dielectric models and the effective medium model. The study reveals that the low-frequency dielectric properties of the ferroelectric SrTiO3 nanofibers are associated with the lowest transverse optical (TO) soft mode TO1 at 2.70 THz (90.0 cm(-1)), and that of the ferroelectric BaTiO3 nanofibers are related to the lowest pair of transverse optical (TO) and longitudinal optical (LO) modes near 5.35 THz, which are both consistent with their bulk single-crystal and thin-film counterparts. 相似文献
4.
The structural properties of GaN grown on AlGaN/AlN stress mitigating layers on 100-mm diameter Si (111) substrate by ammonia molecular beam epitaxy have been reported. High resolution X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy and secondary ion mass spectroscopy have been used to study the influence of AlN thickness and AlGaN growth temperature on the quality of GaN. GaN grown on thicker AlN showed reduced dislocation density and lesser tensile strain. Three-dimensional growth regime was observed for GaN grown at lower AlGaN growth temperature while higher AlGaN growth temperature resulted in two-dimensional growth mode. The dislocation bending and looping at the AlGaN/AlN interface was found to have significant influence on the dislocation density and strain in the GaN layer. The evolution and interaction of threading dislocations play a major role in determining the quality and the strain states of GaN. 相似文献
5.
An overview on microstructural and electronic properties of stoichiometric microcrystalline silicon carbide (μc-SiC) prepared by Hot-Wire Chemical Vapor Deposition (HWCVD) at low substrate temperatures will be given. The electronic properties are strongly dependent on crystalline phase, local bonding, strain, defects, impurities, etc. Therefore these quantities need to be carefully investigated in order to evaluate their influence and to develop strategies for material improvement. We will particularly address the validity of different experimental methods like Raman spectroscopy and IR spectroscopy to provide information on the crystalline volume fraction by comparing the results with Transmission Electron Microscopy (TEM) and X-Ray diffraction data. Finally the electronic properties as derived from optical absorption and transport measurements will be related to the microstructure. 相似文献
6.
Fracture of metal/ceramic interfaces 总被引:1,自引:0,他引:1
The present paper examines metal/ceramic interfaces. Energy release rates are calculated with the finite element method for different elastic–plastic material laws of the metal. The local strain field of the metal is measured during a four-point bending test with an optical method and compared with results from the simulations. The aim of the work is to understand the influence of interface strength and material properties on the energy release rate. 相似文献
7.
The transportable setup of the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS) is presented. Frequency tuneability over a wide range provided by the use of tuneable diode lasers as local oscillators (LO) allows a variety of molecules in the mid-infrared to be observed. Longtime integration, which is essential for astronomical observations, is possible owing to tight frequency control of the LO with optical feedback from an external cavity. THIS is developed to fly on the Stratospheric Observatory for Infrared Astronomy beginning in 2006 but can also be used on different types of ground-based telescopes. 相似文献
8.
We present the optical, electrical and mechanical properties of Ga-doped zinc oxide (GZO) thin films prepared by radio-frequency (RF) magnetron sputtering at room temperature under different RF powers (80–180 W). The thickness, electron concentration, and electron mobility of the GZO thin film were determined by fitting the visible-to-near-infrared transmittance spectrum of GZO film/glass using the transfer matrix method. The bending force per unit width was measured by a home-made Twyman–Green interferometer with the fast Fourier transform method. The obtained results show that the optical, electrical and mechanical properties of GZO thin film are subject to the RF power. At an RF power of 140 W, the local minimum of bending force per unit width corresponds to the highest electron mobility in GZO thin film. This study demonstrates that the optical, electrical and mechanical properties of GZO thin film can be fully resolved by non-contact optical methods. 相似文献
9.
Yoshikawa M Seki H Inoue K Matsuda K Tanahashi Y Sako H Nanen Y Kato M Kimoto T 《Applied spectroscopy》2011,65(5):543-548
We used Fourier transform infrared (FT-IR) spectroscopy to characterize silicon dioxide (SiO(2)) films on a 4H-SiC(0001) Si face. We found that the peak frequency of the transverse optical (TO) phonon in SiO(2) films grown on a 4H-SiC substrate agrees well with that in SiO(2) films grown on a Si substrate, whereas the peak frequency of the longitudinal optical (LO) phonon in SiO(2) films on a 4H-SiC substrate is red-shifted by approximately 50 cm(-1) relative to that in SiO(2) films on a Si substrate. We concluded that this red-shift of the LO phonon is mainly caused by a change in inhomogeneity due to a decrease in density in the SiO(2) films. Furthermore, cathodoluminescence (CL) spectroscopy results indicated that the channel mobility of the SiC metal-oxide-semiconductor field-effect transistor (MOSFET) decreases roughly in proportion to the increase in the intensity of the CL peak at 460 and 490 nm, which is attributed to the increase in the number of oxygen vacancy centers (OVCs). FT-IR and CL spectroscopies provide us with a large amount of data on OVCs in the SiO(2) films on a 4H-SiC substrate. 相似文献
10.
Three-dimensional (3-D) photonic crystals (PCs) have been studied as possible strain sensing materials, based on strain-induced stop band frequency shifting. Self-assembly of polystyrene microspheres, achieved by sedimentation over a flexible polyimide tape substrate whose surface hydrophilicity was optimized in order to achieve maximum wettability, led to an organized 3-D direct opal template. This was infiltrated with a silica sol-gel solution by dip-coating or by chemical vapour deposition and an inverse opal structure was ultimately obtained by chemical dissolution of the polymer template. The structural and optical properties of these PCs have been studied by scanning electron microscopy (FE-SEM) and UV/visible spectroscopy under variable degrees of strain. FE-SEM showed the presence of ordered domains up to ∼30 μm2. A mechano-optical effect was evidenced by strain-induced shifting of the photonic stop band peak wavelength of the direct, infiltrated and inverse opals up to 50 nm in transmission mode, due to changes in interplanar spacing upon bending the flexible PCs. Optical response strain cycles were studied, suggesting the possible use of these structures in reversible photonic strain sensors integrated in sensor/actuator devices. 相似文献
11.
12.
Jing-lin Xiao 《Journal of Low Temperature Physics》2014,174(5-6):284-291
We study a strong coupling bipolaron’s vibrational frequency, self-trapping energy and potential induced by the electron–longitudinal optical (LO) phonon interaction in an asymmetric quantum dot (AQD). The effects of the electron–phonon coupling strength, the transverse and longitudinal effective confinement lengths are taken into account by using linear combination operator and unitary transformation methods. It is found that the vibrational frequency is an increasing function of the electron–phonon coupling strength, whereas it is a decreasing one of the transverse and longitudinal effective confinement lengths. The absolute values of the self-trapping energy and the potential induced by the electron–LO phonon interaction will increase with increasing coupling strength or decreasing effective confinement lengths. 相似文献
13.
We report experiments evaluating the feasibility of quantum-cascade lasers (QCLs) at mid-infrared wavelengths for use as local oscillators (LOs) in a heterodyne receiver. Performance tests with continuous-wave (cw) lasers around 9.6 and 9.2 microm were carried out investigating optical output power, laser linewidth, and tunability. A direct comparison with a CO2 gas laser LO is presented as well. The achieved system sensitivity in a heterodyne spectrometer of only a factor of 2 above the quantum limit together with the measured linewidth of less than 1.5 MHz shows that QCLs are suitable laser sources for heterodyne spectroscopy with sufficient output power to replace gas lasers as LOs even in high-sensitivity astronomical heterodyne receivers. In addition, our experiments show that the tunability of the lasers can be greatly enhanced by use of an external cavity. 相似文献
14.
We have investigated metal-ferroelectric-insulator semiconductor (MFIS) structures with lanthanum substituted bismuth titanate
(BLT) as a ferroelectric layer and lanthanum oxide (LO) or zirconium silicate (ZSO) as an insulating buffer layer between
BLT and Si substrate. The morphology of BLT films deposited on LO or ZSO oxide was not changed due to the good thermal stability
of LO and ZSO films. But an interface reaction between BLT and buffer layer started at high annealing temperature (750 °C),
which was confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The maximum
memory window was 3.59 V at a sweep voltage of 7 V with the LO film annealed at 650 °C and a thickness of 5 nm. With BLT/LO
annealed at 750 °C, the window was decreased due to the reaction between the BLT film and LO. The memory window was about
1 V lower with a ZSO film because ZSO film has a lower dielectric constant than LO film. The MFIS structure annealed at 750 °C
had a lower leakage current density because the electrical properties of the buffer layer (La oxide or Zr silicate) were improved
by the thermal process. 相似文献
15.
16.
Crisman E.E. Derov J.S. Barchard G.J. Gregory O.J. Euler W.B. 《IEEE sensors journal》2005,5(6):1321-1326
An optical sensor is described which can be attached to a structure and used as a gage for measuring bending strain. This device can be adjusted to maximize the gage factor for predetermined strain ranges. The sensor consists of glass capillaries coated on the outer surfaces with an optical absorbing layer followed by a reflecting layer. A mechanical strengthening layer can be included to extend the range of strain response. A source laser beam from an optical fiber is injected into one end of the gage. The light remaining in the beam after traveling through the gage is collected via another optical fiber. The optically active layer is adjusted during manufacture to provide a predetermined gage factor. For a given thickness of the absorber layer, the detected light is proportional to the amount of bending. Thus, by rigidly affixing the sensor to a structural member, the strain experienced by the member can be monitored. 相似文献
17.
Paweena Sureeyatanapas Marek HejdaStephen J. Eichhorn Robert J. Young 《Composites Science and Technology》2010
The study of the interfacial stress transfer for glass fibres in polymer composites through the fragmentation test requires certain assumptions, such as a constant interfacial shear stress. In order to map the local interfacial properties of a composite, both Raman spectroscopy and luminescence spectroscopy have been independently used. Unlike other polymer fibre composites, the local strain state of a glass fibre cannot be obtained using Raman spectroscopy, since only very broad and weak peaks are obtainable. This study shows that when single-walled carbon nanotubes (SWNTs) are added to the silane sizing as a strain sensor, it becomes possible to map the local fibre strain in glass fibres using Raman spectroscopy. Moreover, if this model glass fibre contains a small amount of Sm2O3, as one of the components, luminescence spectroscopy can be simultaneously used to confirm this local fibre strain. A combined micromechanical properties study of stress transfer at the fibre–matrix interface using luminescence spectroscopy, together with Raman spectroscopy, is therefore reported. The local strain behaviour of both Sm3+ doped glass and SWNTs in the silane coating are shown to be consistent with a shear-lag model. This indicates that Sm3+ dopants and SWNTs are excellent sensors for the local deformation of glass fibre composites. 相似文献
18.
Yejin Kim Hyung Soon Im Kidong Park Jundong Kim Jae‐Pyoung Ahn Seung Jo Yoo Jin‐Gyu Kim Jeunghee Park 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(19)
Nanowires (NWs) have witnessed tremendous development over the past two decades owing to their varying potential applications. Semiconductor NWs often contain stacking faults due to the presence of coexisting phases, which frequently hampers their use. Herein, it is investigated how stacking faults affect the optical properties of bent ZnSe and CdSe NWs, which are synthesized using the vapor transport method. Polytypic zinc blende–wurtzite structures are produced for both these NWs by altering the growth conditions. The NWs are bent by the mechanical buckling of poly(dimethylsilioxane), and micro‐photoluminescence (PL) spectra were then collected for individual NWs with various bending strains (0–2%). The PL measurements show peak broadening and red shifts of the near‐band‐edge emission as the bending strain increases, indicating that the bandgap decreases with increasing the bending strain. Remarkably, the bandgap decrease is more significant for the polytypic NWs than for the single phase NWs. This work provides insights into flexible electronic devices of 1D nanostructures by engineering the polytypic structures. 相似文献
19.
Min Wei Junce Zhang David M. Fryauf Juan J. Diaz Leon Kate J. Norris Hong Deng Guangjun Wen Shih-Yuan Wang Nobuhiko P. Kobayashi 《Journal of Materials Science: Materials in Electronics》2014,25(10):4444-4449
The epitaxial growth of indium phosphide nanowires (InP NWs) on transparent conductive aluminum-doped zinc oxide (ZnO:Al) thin films is proposed and demonstrated. ZnO:Al thin films were prepared on quartz substrates by radio frequency magnetron sputtering, then InP NWs were grown on them by plasma enhanced metal organic chemical vapor deposition with gold catalyst. Microstructure and optical properties of InP nanowires on ZnO:Al thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectric spectroscopy (XPS), photoluminescence and Raman spectroscopy at room temperature. SEM shows that randomly oriented and intersecting InP nanowires were grown to form a network on ZnO:Al thin films. Both wurtzite (WZ) and zincblende (ZB) structures coexist in the random orientation InP NWs on ZnO:Al thin film had been proved by XRD analysis. XPS result indicates Zn diffusion exists in the InP NWs on ZnO:Al. The photoluminescence spectra of InP nanowires with Zn diffusion present an emission at 915 nm. Zn diffusion also bring effect on Raman spectra of InP NWs, leading to more Raman-shift and larger relative intensity ratio of TO/LO. 相似文献
20.
Photonic microwave frequency down-conversion based on carrier suppression single sideband (CS-SSB) modulation via an integrated dual-drive dual-parallel Mach-Zehnder modulator (DP-MZM) is proposed. The MZM on the up path of the DP-MZM is used to generate SSB modulation signal, while the MZM on the bottom path of the DP-MZM is unmodulated. By adjusting the amplitude and phase of the unmodulated optical carrier, two optical carriers are cancelled out, which improves the performance of the system with reduced local oscillator (LO) power and large suppression of mixing spurious sidebands. The frequency down-conversion approach is theoretically analyzed and verified by simulation. Simulation results show that the power of frequency down-conversion signal is at least 39?dB higher than that of the mixing spurious sidebands. Besides, 9.5?dB gain, 2.8?dB noise figure (NF) and 1.9?dB spurious-free dynamic range (SFDR) improvements can be obtained compared with the previous OCS modulation frequency down-conversion scheme while the required LO power is 10?dB, 5?dB and 5?dB lower than that of the OCS modulation scheme, respectively. 相似文献