Optical and Structural Properties of Si Nanocrystals in SiO2 Films.

PubMed

Nikitin, Timur; Khriachtchev, Leonid

2015-04-22

Optical and structural properties of Si nanocrystals (Si-nc) in silica films are described. For the SiOx (x < 2) films annealed above 1000 °C, the Raman signal of Si-nc and the absorption coefficient are proportional to the amount of elemental Si detected by X-ray photoelectron spectroscopy. A good agreement is found between the measured refractive index and the value estimated by using the effective-medium approximation. The extinction coefficient of elemental Si is found to be between the values of crystalline and amorphous Si. Thermal annealing increases the degree of Si crystallization; however, the crystallization and the Si-SiO2 phase separation are not complete after annealing at 1200 °C. The 1.5-eV PL quantum yield increases as the amount of elemental Si decreases; thus, this PL is probably not directly from Si-nc responsible for absorption and detected by Raman spectroscopy. Continuous-wave laser light can produce very high temperatures in the free-standing films, which changes their structural and optical properties. For relatively large laser spots, the center of the laser-annealed area is very transparent and consists of amorphous SiO2. Large Si-nc (up to ∼300 nm in diameter) are observed in the ring around the central region. These Si-nc lead to high absorption and they are typically under compressive stress, which is connected with their formation from the liquid phase. By using strongly focused laser beams, the structural changes in the free-standing films can be made in submicron areas.

Optical and Structural Properties of Si Nanocrystals in SiO2 Films

PubMed Central

Nikitin, Timur; Khriachtchev, Leonid

2015-01-01

Optical and structural properties of Si nanocrystals (Si-nc) in silica films are described. For the SiOx (x < 2) films annealed above 1000 °C, the Raman signal of Si-nc and the absorption coefficient are proportional to the amount of elemental Si detected by X-ray photoelectron spectroscopy. A good agreement is found between the measured refractive index and the value estimated by using the effective-medium approximation. The extinction coefficient of elemental Si is found to be between the values of crystalline and amorphous Si. Thermal annealing increases the degree of Si crystallization; however, the crystallization and the Si–SiO2 phase separation are not complete after annealing at 1200 °C. The 1.5-eV PL quantum yield increases as the amount of elemental Si decreases; thus, this PL is probably not directly from Si-nc responsible for absorption and detected by Raman spectroscopy. Continuous-wave laser light can produce very high temperatures in the free-standing films, which changes their structural and optical properties. For relatively large laser spots, the center of the laser-annealed area is very transparent and consists of amorphous SiO2. Large Si-nc (up to ~300 nm in diameter) are observed in the ring around the central region. These Si-nc lead to high absorption and they are typically under compressive stress, which is connected with their formation from the liquid phase. By using strongly focused laser beams, the structural changes in the free-standing films can be made in submicron areas. PMID:28347028

Synthesis of SiC nanoparticles by SHG 532 nm Nd:YAG laser ablation of silicon in ethanol

NASA Astrophysics Data System (ADS)

Khashan, Khawla S.; Ismail, Raid A.; Mahdi, Rana O.

2018-06-01

In this work, colloidal spherical nanoparticles NPs of silicon carbide SiC have been synthesized using second harmonic generation 532 nm Nd:YAG laser ablation of silicon target dipped in ethanol solution at various laser fluences (1.5-5) J/cm2. X-Ray diffraction XRD, scanning electron microscopy SEM, transmission electron microscope TEM, Fourier transformed infrared spectroscopy FT-IR, Raman spectroscopy, photoluminescence PL spectroscopy, and UV-Vis absorption were employed to examine the structural, chemical and optical properties of SiC NPs. XRD results showed that all synthesised SiC nanoparticles are crystalline in nature and have hexagonal structure with preferred orientation along (103) plane. Raman investigation showed three characteristic peaks 764,786 and 954 cm-1, which are indexing to transverse optic TO phonon mode and longitudinal optic LO phonon mode of 4H-SiC structure. The optical absorption data showed that the values of optical energy gap of SiC nanoparticles prepared at 1.5 J/cm2 was 3.6 eV and was 3.85 eV for SiC synthesised at 5 J/cm2. SEM investigations confirmed that the nanoparticles synthesised at 5 J/cm2 are agglomerated to form larger particles. TEM measurements showed that SiC particles prepared at 1.5 J/cm2 have spherical shape with average size of 25 nm, while the particles prepared at 5 J/cm2 have an average size of 55 nm.

Effect of etching parameters on antireflection properties of Si subwavelength grating structures for solar cell applications

NASA Astrophysics Data System (ADS)

Leem, J. W.; Song, Y. M.; Lee, Y. T.; Yu, J. S.

2010-09-01

Silicon (Si) subwavelength grating (SWG) structures were fabricated on Si substrates by holographic lithography and subsequent inductively coupled plasma (ICP) etching process using SiCl4 with or without Ar addition for solar cell applications. To ensure a good nanosized pattern transfer into the underlying Si layer, the etch selectivity of Si over the photoresist mask is optimized by varying the etching parameters, thus improving antireflection characteristics. For antireflection analysis of Si SWG surfaces, the optical reflectivity is measured experimentally and it is also calculated theoretically by a rigorous coupled-wave analysis. The reflectance depends on the height, period, and shape of two-dimensional periodic Si subwavelength structures, correlated with ICP etching parameters. The optimized Si SWG structure exhibits a dramatic decrease in optical reflection of the Si surface over a wide angle of incident light ( θ i ), i.e. less than 5% at wavelengths of 300-1100 nm, leading to good wide-angle antireflection characteristics (i.e. solar-weighted reflection of 1.7-4.9% at θ i <50°) of Si solar cells.

Analysis of buried interfaces in multilayer mirrors using grazing incidence extreme ultraviolet reflectometry near resonance edges.

PubMed

Sertsu, M G; Nardello, M; Giglia, A; Corso, A J; Maurizio, C; Juschkin, L; Nicolosi, P

2015-12-10

Accurate measurements of optical properties of multilayer (ML) mirrors and chemical compositions of interdiffusion layers are particularly challenging to date. In this work, an innovative and nondestructive experimental characterization method for multilayers is discussed. The method is based on extreme ultraviolet (EUV) reflectivity measurements performed on a wide grazing incidence angular range at an energy near the absorption resonance edge of low-Z elements in the ML components. This experimental method combined with the underlying physical phenomenon of abrupt changes of optical constants near EUV resonance edges enables us to characterize optical and structural properties of multilayers with high sensitivity. A major advantage of the method is to perform detailed quantitative analysis of buried interfaces of multilayer structures in a nondestructive and nonimaging setup. Coatings of Si/Mo multilayers on a Si substrate with period d=16.4  nm, number of bilayers N=25, and different capping structures are investigated. Stoichiometric compositions of Si-on-Mo and Mo-on-Si interface diffusion layers are derived. Effects of surface oxidation reactions and carbon contaminations on the optical constants of capping layers and the impact of neighboring atoms' interactions on optical responses of Si and Mo layers are discussed.

Real-space study of the optical absorption in alternative phases of silicon

NASA Astrophysics Data System (ADS)

Ong, Chin Shen; Coh, Sinisa; Cohen, Marvin L.; Louie, Steven G.

2017-12-01

We introduce a real-space approach to understand the relationship between optical absorption and crystal structure. We apply this approach to alternative phases of silicon, with a focus on the Si20 crystal phase as a case study. We find that about 83% of the changes in the calculated low-energy absorption in Si20 as compared to Si in the diamond structure can be attributed to reducing the differences between the on-site energies of the bonding and antibonding orbitals as well as increasing the hopping integrals for specific Si-Si bonds.

Electronic and optical properties of Fe2SiO4 under pressure effect: ab initio study

NASA Astrophysics Data System (ADS)

Xiao, Lingping; Li, Xiaobin; Yang, Xue

2018-05-01

We report first-principles studies the structural, electronic, and optical properties of the Fe2SiO4 fayalite in orthorhombic structure, including pressure dependence of structural parameters, band structures, density of states, and optical constants up to 30 GPa. The calculated results indicate that the linear compressibility along b axis is significantly higher than a and c axes, which is in agreement with earlier work. Meanwhile, the pressure dependence of the electronic band structure, density of states and partial density of states of Fe2SiO4 fayalite up to 30 GPa were presented. Moreover, the evolution of the dielectric function, absorption coefficient (α(ω)), reflectivity (R(ω)), and the real part of the refractive index (n(ω)) at high pressure are also presented.

Anneal-induced enhancement of refractive index and hardness of silicophosphate glasses containing six-fold coordinated silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeng, Huidan, E-mail: hdzeng@ecust.edu.cn; Jiang, Qi; Li, Xiang

2015-01-12

A considerable number of optical devices have significantly benefited from the development of phosphate glasses as substrate materials. Introducing silica into sodium phosphate is an effective method to enhance its mechanical and optical properties. Through annealing treatment, the tetrahedral silicon oxide network structure (Si{sup (4)}) can be transformed into an octahedral structure (Si{sup (6)}) with more constraints. Here, we use high-temperature Raman and Nuclear Magnetic Resonance to reveal the mechanism of transformation between the Si{sup (4)} and Si{sup (6)} silicon oxide structures. The increase of the Si{sup (6)} content results in the phosphate glasses having higher refractive index and hardness.more » Based on this, the refractive index contribution of SiO{sub 6} is obtained.« less

Optical properties of Si+ implanted PMMA

NASA Astrophysics Data System (ADS)

Balabanov, S.; Tsvetkova, T.; Borisova, E.; Avramov, L.; Bischoff, L.; Zuk, J.

2010-04-01

In the present work, low energy ion beam irradiation was used for surface modification of polymethyl-methacrylate (PMMA) using silicon (Si+) as the ion species. After high doses ion implantation of Si+ in the polymer material, a characterization of the optical properties was performed using optical transmission measurements in the visible and near infra-red (IR) wavelength range. The optical absorption increase observed with the ion dose was attributed to ion beam induced structural changes in the modified material.

Investigation of the electronic, magnetic and optical properties of {\\sf Co}_{\\sf 2}{\\sf CrZ} (Z = Si, Ge) under pressure—a density functional theory study

NASA Astrophysics Data System (ADS)

Seema, K.; Kumar, Ranjan

2014-01-01

The structural, electronic, magnetic and optical properties of Co-based Heusler compounds, Co2CrZ (Z = Si, Ge), are studied using first-principle density functional theory. The calculations are performed within the generalized gradient approximation. Our calculated structural parameters at 0 GPa agree well with previous available results. The calculated magnetic moment agrees well with the Slater-Pauling (SP) rule. We have studied the effect of pressure on the electronic and magnetic properties of Co2CrSi and Co2CrGe. With an increase in applied pressure, a decrease in cell volume is observed. Under application of external pressure, the valence band and conduction band are shifted downward which leads to a modification of electronic structure. There exists an indirect band gap along Γ-X for both the alloys. Co2CrSi and Co2CrGe retain 100% spin polarization up to 60 and 50 GPa, respectively. The local magnetic moments of the Co and Si (Ge) atoms increase with an increase in pressure whereas the local magnetic moment of the Cr atom decreases. In addition, the optical properties such as dielectric function, absorption spectra, optical conductivity and energy loss function of these alloys have also been investigated. To our knowledge this is the first theoretical prediction of the pressure dependence of the structural, electronic, magnetic and optical properties of Co2CrSi and Co2CrGe.

Theoretical study of optical properties of anti phase domains in GaP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tea, E., E-mail: etea.contact@gmail.com; FOTON INSA-Rennes; Vidal, J.

III-V/Si heterostructures are currently investigated for silicon photonics and solar energy conversion. In particular, dilute nitride alloy GaAsPN grown on a GaP/Si platform exhibits lattice match with Si and an optimal band gap configuration for tandem solar cell devices. However, monolithic “coherent” growth of the GaP thin layer on Si suffers from the nucleation of extended structural defects, which can hamper device operation as well as the GaP/Si interface level and through their propagation inside the overall heterostructure. However, the effect of such structural defects on optical and transport properties is actually not well understood in details. In this letter,more » we investigate the anti phase domains defect (also called inversion domains) by means of ab initio calculations giving insights into the alteration of optical and transport properties of GaP due to the defective GaP/Si interface.« less

Three-dimensional photonic crystals as intermediate filter for thin-film tandem solar cells

NASA Astrophysics Data System (ADS)

Bielawny, Andreas; Miclea, Paul T.; Wehrspohn, Ralf B.; Lee, Seung-Mo; Knez, Mato; Rockstuhl, Carsten; Lisca, Marian; Lederer, Falk L.; Carius, Reinhard

2008-04-01

The concept of a 3D photonic crystal structure as diffractive and spectrally selective intermediate filter within 'micromorphous' (a-Si/μc-Si) tandem solar cells has been investigated numerically and experimentally. Our device aims for the enhancement of the optical pathway of incident light within the amorphous silicon top cell in its spectral region of low absorption. From our previous simulations, we expect a significant improvement of the tandem cell efficiency of about absolutely 1.3%. This increases the efficiency for a typical a-Si / μc-Si tandem cell from 11.1% to 12.4%, as a result of the optical current-matching of the two junctions. We suggest as wavelength-selective optical element a 3D-structured optical thin-film, prepared by self-organized artificial opal templates and replicated with atomic layer deposition. The resulting samples are highly periodic thin-film inverted opals made of conducting and transparent zinc-oxide. We describe the fabrication processes and compare experimental data on the optical properties in reflection and transmission with our simulations and photonic band structure calculations.

Correlation between structural and opto-electronic characteristics of crystalline Si microhole arrays for photonic light management

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sontheimer, Tobias, E-mail: tobias.sontheimer@helmholtz-berlin.de; Schnegg, Alexander; Lips, Klaus

2013-11-07

By employing electron paramagnetic resonance spectroscopy, transmission electron microscopy, and optical measurements, we systematically correlate the structural and optical properties with the deep-level defect characteristics of various tailored periodic Si microhole arrays, which are manufactured in an easily scalable and versatile process on nanoimprinted sol-gel coated glass. While tapered microhole arrays in a structured base layer are characterized by partly nanocrystalline features, poor electronic quality with a defect concentration of 10{sup 17} cm{sup −3} and a high optical sub-band gap absorption, planar polycrystalline Si layers perforated with periodic arrays of tapered microholes are composed of a compact crystalline structure and amore » defect concentration in the low 10{sup 16} cm{sup −3} regime. The low defect concentration is equivalent to the one in planar state-of-the-art solid phase crystallized Si films and correlates with a low optical sub-band gap absorption. By complementing the experimental characterization with 3-dimensional finite element simulations, we provide the basis for a computer-aided approach for the low-cost fabrication of novel high-quality structures on large areas featuring tailored opto-electronic properties.« less

Analysis of the structural, electronic and optic properties of Ni doped MgSiP{sub 2} semiconductor chalcopyrite compound

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocak, Belgin, E-mail: koakbelgin@gmail.com; Ciftci, Yasemin Oztekin, E-mail: yasemin@gazi.edu.tr

2016-03-25

The structural, electronic band structure and optic properties of the Ni doped MgSiP{sub 2} chalcopyrite compound have been performed by using first-principles method in the density functional theory (DFT) as implemented in Vienna Ab-initio Simulation Package (VASP). The generalized gradient approximation (GGA) in the scheme of Perdew, Burke and Ernzerhof (PBE) is used for the exchange and correlation functional. The present lattice constant (a) follows generally the Vegard’s law. The electronic band structure, total and partial density of states (DOS and PDOS) are calculated. We present data for the frequency dependence of imaginary and real parts of dielectric functions ofmore » Ni doped MgSiP{sub 2}. For further investigation of the optical properties the reflectivity, refractive index, extinction coefficient and electron energy loss function are also predicted. Our obtained results indicate that the lattice constants, electronic band structure and optical properties of this compound are dependent on the substitution concentration of Ni.« less

First principle study of electronic structures and optical properties of Ce-doped SiO2

NASA Astrophysics Data System (ADS)

Cong, Wei-Yan; Lu, Ying-Bo; Zhang, Peng; Guan, Cheng-Bo

2018-05-01

Electronic structures and optical properties of Silicon dioxide (SiO2) systems with and without cerium(Ce) dopant were calculated using the density functional theory. We find that after the Ce incorporation, a new localized impurity band appears between the valance band maximum (VBM) and the conduction band minimum (CBM) of SiO2 system, which is induced mainly by the Ce-4f orbitals. The localized impurity band constructs a bridge between the valence band and the conduction band, making the electronic transition much easier. The calculated optical properties show that in contrast from the pure SiO2 sample, absorption in the visible-light region is found in Ce-doped SiO2 system, which originates from the transition between the valence band and Ce-4f dominated impurity band, as well as the electronic transition from Ce-4f states to Ce-5d states. All calculated results indicate that Ce doping is an effective strategy to improve the optical performance of SiO2 sample, which is in agreement with the experimental results.

Structural and optical properties of axial silicon-germanium nanowire heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, X.; Tsybeskov, L., E-mail: tsybesko@njit.edu; Kamins, T. I.

2015-12-21

Detailed studies of the structural and optical properties of axial silicon-germanium nanowire heterojunctions show that despite the 4.2% lattice mismatch between Si and Ge they can be grown without a significant density of structural defects. The lattice mismatch induced strain is partially relieved due to spontaneous SiGe intermixing at the heterointerface during growth and lateral expansion of the Ge segment of the nanowire. The mismatch in Ge and Si coefficients of thermal expansion and low thermal conductivity of Si/Ge nanowire heterojunctions are proposed to be responsible for the thermally induced stress detected under intense laser radiation in photoluminescence and Ramanmore » scattering measurements.« less

Quasi-periodic photonic crystal Fabry–Perot optical filter based on Si/SiO2 for visible-laser spectral selectivity

NASA Astrophysics Data System (ADS)

Qi, Dong; Wang, Xian; Cheng, Yongzhi; Chen, Fu; Liu, Lei; Gong, Rongzhou

2018-06-01

We report on a 1D quasi-periodic photonic crystal Fabry–Perot optical filter Cs(Si/SiO2)3(SiO2/Si)3 for spectral selectivity of visible light and 1.55 µm laser. A material transparency interval of 1.03–2.06 µm makes Si a unique choice of high refractive index material. Owing to the CIE 1931 standard and equal inclination interference, the designed structure can be successfully fabricated with a certain color (brown, khaki, or blue) corresponding to the different Cs physical thickness d and response R(λ). In addition, the peak transmittance T max of the proposed structure can reach as high as 92.56% (Cs  =  20 nm), 90.83% (Cs  =  40 nm), and 88.85% (Cs  =  60 nm) with a relatively narrow full width at half maximum of 4.4, 4.6, and 4.8 nm at 1.55 µm. The as-prepared structure indicates that it is feasible for a photonic crystal Fabry–Perot optical filter to achieve visible-laser (1.55 µm) spectral selectivity.

Fabrication and characterization study of ZnTe/n-Si heterojunction solar cell application

NASA Astrophysics Data System (ADS)

AlMaiyaly, BushraK H.; Hussein, Bushra H.; Shaban, Auday H.

2018-05-01

Different thicknesses (150 250 and 350) ±20 nm has been deposited on the glass substrate and nSi wafer to fabricate ZnTe/n-Si heterojunction solar cell by vacuum evaporation technique Structural optical electrical and photovoltaic properties are investigated for the samples. The structural characteristics studied via X ray analyses indicated that the films are polycrystalline besides having a cubic (zinc blende) structure also average diameter and surface roughness calculated from AFM images The optical measurements of the deposited films were performed in different thicknesses to determine the transmission spectrum as a function of incident wavelength in the range of wavelength (4001000) nm and the optical energy gap calculated from the optical absorption spectra was found to reduse with thickness The IV characteristic at (dark and illuminated) and CV measurement for ZnTe/n-Si heterojunction shows the good rectifying behaviour under dark condition. The measurements of opencircuit voltage (VOC) short-circuit current density (JSC) fill factor (FF) and quantum fficiencies of the ZnTe/n-Si heterojunction are calculated for all samples The results of these studies are presented and discussed in this paper.

Si3 AlP: A New Promising Material for Solar Cell Absorber

NASA Astrophysics Data System (ADS)

Yang, Jihui; Zhai, Yingteng; Liu, Hengrui; Xiang, Hongjun; Gong, Xingao; Wei, Suhuai

2014-03-01

First-principles calculations are performed to study the structural and optoelectronic properties of the newly synthesized nonisovalent and lattice-matched (Si2)0.6(AlP)0.4 alloy [T. Watkins et al., J. Am. Chem. Soc. 2011, 133, 16212.] The most stable structure of Si3AlP is a superlattice along the <111>direction with separated AlP and Si layers, which has a similar optical absorption spectrum to silicon. The ordered C1c1-Si3AlP is found to be the most stable one among all the structures with -AlPSi3- motifs, in agreement with the experimental suggestions. We predict that C1c1-Si3AlP has good optical properties, i.e., it has a larger fundamental band gap and a smaller direct band gap than Si, thus it has much higher absorption in the visible light region, making it a promising candidate for improving the performance of the existing Si-based solar cells.

Periodically structured Si pillars for high-performing heterojunction photodetectors

NASA Astrophysics Data System (ADS)

Melvin David Kumar, M.; Yun, Ju-Hyung; Kim, Joondong

2015-03-01

A periodical array of silicon (Si) micro pillar structures was fabricated on Si substrates using PR etching process. Indium tin oxide (ITO) layer of 80 nm thickness was deposited over patterned Si substrates so as to make ITO/n-Si heterojunction devices. The influences of width and period of pillars on the optical and electrical properties of prepared devices were investigated. The surface morphology of the Si substrates revealed the uniform array of pillar structures. The 5/10 (width/period) Si pillar pattern reduced the optical reflectance to 6.5% from 17% which is of 5/7 pillar pattern. The current rectifying ratio was found higher for the device in which the pillars are situated in optimum periods. At both visible (600 nm) and near infrared (900 nm) range of wavelengths, the 5/7 and 5/10 pillar patterned device exhibited the better photoresponses which are suitable for making advanced photodetectors. This highly transmittance and photoresponsive pillar patterned Si substrates with an ITO layer would be a promising device for various photoelectric applications.

Optically detected cyclotron resonance investigations on 4H and 6H SiC: Band-structure and transport properties

NASA Astrophysics Data System (ADS)

Meyer, B. K.; Hofmann, D. M.; Volm, D.; Chen, W. M.; Son, N. T.; Janzén, E.

2000-02-01

We present experimental data on the band-structure and high-mobility transport properties of 6H and 4H-SiC epitaxial films based on optically detected cyclotron resonance investigations. From the orientational dependence of the electron effective mass in 6H-SiC we obtain direct evidence for the camels back nature of the conduction band between the M and L points. The broadening of the resonance signal in 4H-SiC as a function of temperature is used to extract information on electron mobilities and to conclude on the role of the different scattering mechanisms. Under high microwave powers an enhancement of the electron effective mass is found which is explained by a coupling of the electrons with longitudinal optical phonons.

Effect of oxygen on the optical, electrical and structural properties of mixed-phase boron doped nanocrystalline silicon oxide thin films

NASA Astrophysics Data System (ADS)

Das, Debajyoti; Mondal, Praloy

2017-11-01

Systematic investigation on the optoelectronic and structural changes occurring in the p-nc-Si network due to the inclusion of oxygen into the initial crystalline-like matrix has been done. The incorporation of O into the Si network occurs via the Si-O-Si bond which is effectively responsible for the widening of optical band gap. B incorporation takes place via the B-Si bonds as well as the B-O bonds which increases at enhanced CO2 dilution to the plasma. The continuously increased intensity of (SiH2)n wagging and Si-H2 bending mode in p-nc-SiOx films indicates poly-hydrogenation as inherent to the increasing oxygen alloying of the network. Two stage activation energies across around 340 K in the temperature dependent dark conductivity identify prominent two phase structure of the p-nc-SiOx material, the Si-ncs being embedded within amorphous p-SiOx matrix. The p-nc-SiOx film grown by typical 13.56 MHz PE-CVD at a low growth temperature ∼170 °C and optimized with a convincingly good combination of the electrical conductivity (σD ∼6.8 × 10-2 S cm-1), optical band gap (Eg ∼1.91 eV) and volume fraction (XC ∼54%) of the Si crystallinity containing CH <6 at% and CO < 1 at%, emerges highly competent for effective utilization in the window layer of nc-Si p-i-n solar cells with superstrate configuration.

Growth of periodic nano-layers of nano-crystals of Au, Ag, Cu by ion beam

NASA Technical Reports Server (NTRS)

Smith, Cydale C.; Zheng, B.; Muntele, C. I.; Muntele, I. C.; Ila, D.

2005-01-01

Multilayered thin films of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/, were grown by deposition. We have previously shown that MeV ion Bombardment of multi-nano-layers of SiO2/AU+ SiO2/ produces Au nanocrystals in the AU+ SiO2 layers. An increased number of nano-layers followed by MeV ion bombardment produces a wide optical absorption band, of which its FWHM depends on the number of nano-layers of SiO2/AU+ SiO2/. We have successfully repeated this process for nano-layers of SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/. In this work we used 5 MeV Si as the post deposition bombardment ion and monitored the location as well as the optical absorption's FWHM for each layered structure using Optical Absorption Photospectrometry. The concentration and location of the metal nano-crystals were measured by Rutherford Backscattering Spectrometry. We will report on the results obtained for nano-layered structures produced by post deposition bombardment of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/ layered systems as well as the results obtained from a system containing a periodic combination of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/.

SiC lightweight telescopes for advanced space applications. II - Structures technology

NASA Technical Reports Server (NTRS)

Anapol, Michael I.; Hadfield, Peter; Tucker, Theodore

1992-01-01

A critical technology area for lightweight SiC-based telescope systems is the structural integrity and thermal stability over spaceborne environmental launch and thermal operating conditions. Note, it is highly desirable to have an inherently athermal design of both SiC mirrors and structure. SSG has developed an 8 inch diameter SiC telescope system for brassboard level optical and thermal testing. The brassboard telescope has demonstrated less than 0.2 waves P-V in the visible wavefront change over +50 C to -200 C temperature range. SSG has also fabricated a SiC truss structural assembly and successfully qualified this hardware at environmental levels greater than 3 times higher than normal Delta, Titan, and ARIES launch loads. SSG is currently developing two SiC telescopes; an 20 cm diameter off-axis 3 mirror re-imaging and a 60 cm aperture on-axis 3 mirror re-imager. Both hardware developments will be tested to flight level environmental, optical, and thermal specifications.

First-Principles Study of Structural, Electronic, Optical, and Thermal Properties of BeSiSb2 and MgSiSb2

NASA Astrophysics Data System (ADS)

Benlamari, S.; Boukhtouta, M.; Taïri, L.; Meradji, H.; Amirouche, L.; Ghemid, S.

2018-03-01

Structural, electronic, optical, and thermal properties of ternary II-IV-V2 (BeSiSb2 and MgSiSb2) chalcopyrite semiconductors have been calculated using the full-potential linearized augmented plane wave scheme␣in the generalized gradient approximation. The optimized equilibrium structural parameters ( a, c, and u) are in good agreement with theoretical results obtained using other methods. The band structure and density of states reveal that BeSiSb2 has an indirect (Γ-Z) bandgap of about 0.61 eV, whereas MgSiSb2 has a direct (Γ-Γ) bandgap of 0.80 eV. The dielectric function, refractive index, and extinction coefficient were calculated to investigate the optical properties, revealing that BeSiSb2 and MgSiSb2 present very weak birefringence. The temperature dependence of the volume, bulk modulus, Debye temperature, and heat capacities ( C v and C p) was predicted using the quasiharmonic Debye model at different pressures. Significant differences in properties are observed at high pressure and high temperature. We predict that, at 300 K and 0 GPa, the heat capacity at constant volume C v, heat capacity at constant pressure C P, Debye temperature θ D, and Grüneisen parameter γ will be about 94.91 J/mol K, 98.52 J/mol K, 301.30 K, and 2.11 for BeSiSb2 and about 96.08 J/mol K, 100.47 J/mol K, 261.38 K, and 2.20 for MgSiSb2, respectively.

Subsurface Growth Of Silicide Structures In Silicon

NASA Technical Reports Server (NTRS)

Fathauer, Robert W.; George, Thomas; Pike, William T.; Schowalter, Leo

1993-01-01

Technique shows promise for fabrication of novel electronic, optoelectronic, and electro-optical devices. Experiments demonstrated feasibility of growing microscopic single-crystal CoSi2 structures beneath surfaces of Si substrates.

Theoretical Prediction of Si 2–Si 33 Absorption Spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Li -Zhen; Lu, Wen -Cai; Qin, Wei

Here, the optical absorption spectra of Si 2–Si 33 clusters were systematically studied by a time-dependent density functional theory approach. The calculations revealed that the absorption spectrum becomes significantly broad with increasing cluster size, stretching from ultraviolet to the infrared region. The absorption spectra are closely related to the structural motifs. With increasing cluster size, the absorption intensity of cage structures gradually increases, but the absorption curves of the prolate and the Y-shaped structures are very sensitive to cluster size. If the transition energy reaches ~12 eV, it is noted that all the clusters have remarkable absorption in deep ultravioletmore » region of 100–200 nm, and the maximum absorption intensity is ~100 times that in the visible region. Further, the optical responses to doping in the Si clusters were studied.« less

Theoretical Prediction of Si 2–Si 33 Absorption Spectra

DOE PAGES

Zhao, Li -Zhen; Lu, Wen -Cai; Qin, Wei; ...

2017-07-07

Here, the optical absorption spectra of Si 2–Si 33 clusters were systematically studied by a time-dependent density functional theory approach. The calculations revealed that the absorption spectrum becomes significantly broad with increasing cluster size, stretching from ultraviolet to the infrared region. The absorption spectra are closely related to the structural motifs. With increasing cluster size, the absorption intensity of cage structures gradually increases, but the absorption curves of the prolate and the Y-shaped structures are very sensitive to cluster size. If the transition energy reaches ~12 eV, it is noted that all the clusters have remarkable absorption in deep ultravioletmore » region of 100–200 nm, and the maximum absorption intensity is ~100 times that in the visible region. Further, the optical responses to doping in the Si clusters were studied.« less

SiC formation for a solar cell passivation layer using an RF magnetron co-sputtering system

PubMed Central

2012-01-01

In this paper, we describe a method of amorphous silicon carbide film formation for a solar cell passivation layer. The film was deposited on p-type silicon (100) and glass substrates by an RF magnetron co-sputtering system using a Si target and a C target at a room-temperature condition. Several different SiC [Si1-xCx] film compositions were achieved by controlling the Si target power with a fixed C target power at 150 W. Then, structural, optical, and electrical properties of the Si1-xCx films were studied. The structural properties were investigated by transmission electron microscopy and secondary ion mass spectrometry. The optical properties were achieved by UV-visible spectroscopy and ellipsometry. The performance of Si1-xCx passivation was explored by carrier lifetime measurement. PMID:22221730

Electronic and optical properties of Si and Ge nanocrystals: An ab initio study

NASA Astrophysics Data System (ADS)

Pulci, Olivia; Degoli, Elena; Iori, Federico; Marsili, Margherita; Palummo, Maurizia; Del Sole, Rodolfo; Ossicini, Stefano

2010-01-01

First-principles calculations within density functional theory and many-body perturbation theory have been carried out in order to investigate the structural, electronic and optical properties of undoped and doped silicon nanostructures. We consider Si nanoclusters co-doped with B and P. We find that the electronic band gap is reduced with respect to that of the undoped crystals, suggesting the possibility of impurity based engineering of electronic and optical properties of Si nanocrystals. Finally, motivated by recent suggestions concerning the chance of exploiting Ge dots for photovoltaic nanodevices, we present calculations of the electronic and optical properties of a Ge 35H 36 nanocrystal, and compare the results with those for the corresponding Si 35H 36 nanocrystals and the co-doped Si 33BPH 36.

Development and Ground-Test Validation of Fiber Optic Sensor Attachment Techniques for Hot Structures Applications

NASA Technical Reports Server (NTRS)

Piazza, Anthony; Hudson, Larry D.; Richards, W. Lance

2005-01-01

Fiber Optic Strain Measurements: a) Successfully attached silica fiber optic sensors to both metallics and composites; b) Accomplished valid EFPI strain measurements to 1850 F; c) Successfully attached EFPI sensors to large scale hot-structures; and d) Attached and thermally validated FBG bond and epsilon(sub app). Future Development a) Improve characterization of sensors on C-C and C-SiC substrates; b) Apply application to other composites such as SiC-SiC; c) Assist development of interferometer based Sapphire sensor currently being conducted under a Phase II SBIR; and d) Complete combined thermal/mechanical testing of FBG on composite substrates in controlled laboratory environment.

Transparent SiON/Ag/SiON multilayer passivation grown on a flexible polyethersulfone substrate using a continuous roll-to-roll sputtering system

PubMed Central

2012-01-01

We have investigated the characteristics of a silicon oxynitride/silver/silicon oxynitride [SiON/Ag/SiON] multilayer passivation grown using a specially designed roll-to-roll [R2R] sputtering system on a flexible polyethersulfone substrate. Optical, structural, and surface properties of the R2R grown SiON/Ag/SiON multilayer were investigated as a function of the SiON thickness at a constant Ag thickness of 12 nm. The flexible SiON/Ag/SiON multilayer has a high optical transmittance of 87.7% at optimized conditions due to the antireflection and surface plasmon effects in the oxide-metal-oxide structure. The water vapor transmission rate of the SiON/Ag/SiON multilayer is 0.031 g/m2 day at an optimized SiON thickness of 110 nm. This indicates that R2R grown SiON/Ag/SiON is a promising thin-film passivation for flexible organic light-emitting diodes and flexible organic photovoltaics due to its simple and low-temperature process. PMID:22221400

Study of the structural and optical properties of GaP(N) layers synthesized by molecular-beam epitaxy on Si(100) 4° substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kryzhanovskaya, N. V., E-mail: NataliaKryzh@gmail.com; Polubavkina, Yu. S.; Nevedomskiy, V. N.

The structural and optical properties of GaP and GaPN layers synthesized by molecular-beam epitaxy on Si(100) substrates misoriented by 4° are studied. The possibility of producing GaP buffer layers that exhibit a high degree of heterointerface planarity and an outcropping dislocation density of no higher than ~2 × 10{sup 8} cm{sup –2} is shown. Emission from the Si/GaP/GaPN structure in the spectral range of 630–640 nm at room temperature is observed. Annealing during growth of the Si/GaP/GaPN structure makes it possible to enhance the room-temperature photoluminescence intensity by a factor of 2.6, with no shift of the maximum of themore » emission line.« less

Theoretical investigation of stabilities and optical properties of Si12C12 clusters

NASA Astrophysics Data System (ADS)

Duan, Xiaofeng F.; Burggraf, Larry W.

2015-01-01

By sorting through hundreds of globally stable Si12C12 isomers using a potential surface search and using simulated annealing, we have identified low-energy structures. Unlike isomers knit together by Si-C bonds, the lowest energy isomers have segregated carbon and silicon regions that maximize stronger C-C bonding. Positing that charge separation between the carbon and silicon regions would produce interesting optical absorption in these cluster molecules, we used time-dependent density functional theory to compare the calculated optical properties of four isomers representing structural classes having different types of silicon and carbon segregation regions. Absorptions involving charge transfer between segregated carbon and silicon regions produce lower excitation energies than do structures having alternating Si-C bonding for which frontier orbital charge transfer is exclusively from separated carbon atoms to silicon atoms. The most stable Si12C12 isomer at temperatures below 1100 K is unique as regards its high symmetry and large optical oscillator strength in the visible blue. Its high-energy and low-energy visible transitions (1.15 eV and 2.56 eV) are nearly pure one-electron silicon-to-carbon transitions, while an intermediate energy transition (1.28 eV) is a nearly pure carbon-to-silicon one-electron charge transfer.

Electro-Optical Properties of Hydrogenated Si-Doped CdO

NASA Astrophysics Data System (ADS)

Dakhel, A. A.

2018-01-01

The optoelectronic properties of CdO films could be controlled and improved for transparent conducting (TC) purposes by means of doping. In the present work, several sets of CdO thin films hydrogenated and doped with different amounts of silicon were prepared on glass substrates by a thermal deposition technique in order to improve their TC properties. The x-ray diffraction method was used to study the crystal structural variations in CdO films as a consequence of Si(H) doping. Optical properties were studied by means of optical absorption and reflection spectroscopy. The observed blue-shifting in the optical bandgap by Si(H) doping was attributed to the Moss-Burstein effect with reduced structural bandgap by point defects created during the process of doping. The mechanism of the hydrogenation process was explained by the dissociation of hydrogen molecules into atoms/ions, which in turn interacted with structural oxygen ions leading to the creation of oxygen vacancies. The creation of oxygen vacancies caused increases in electron concentration ( N el) and electrical conductivity ( σ). The results showed that Si(H) doping of host CdO films significantly increased their conductivity, mobility, and carrier concentration by ˜ 69, 5.6, and 12.3 times, respectively. The results confirm that Si(H) doping is effective for using CdO films in transparent conducting oxide applications.

Investigations of nanodimensional Al{sup 2}O{sup 3} films deposited by ion-plasma sputtering onto porous silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seredin, P. V., E-mail: paul@phys.vsu.ru; Lenshin, A. S.; Goloshchapov, D. L.

2015-07-15

The purpose of this study is the deposition of nanodimensional Al{sup 2}O{sup 3} films on the surface of nanoporous silicon and also fundamental investigations of the structural, optical, and morphological properties of these materials. Analyzing the results obtained here, it is possible to state that ultrathin nanostructured Al{sup 2}O{sup 3} films can be obtained in the form of threads oriented in one direction and located at a distance of 300–500 nm from each other using ion-plasma sputtering on a layer of porous silicon. Such a mechanism of aluminum-oxide growth is conditioned by the crystallographic orientation of the initial single-crystalline siliconmore » wafer used to fabricate the porous layer. The results of optical spectroscopy show that the Al{sup 2}O{sup 3}/por-Si/Si(111) heterophase structure perfectly transmits electromagnetic radiation in the range of 190–900 nm. The maximum in the dispersion of the refractive index obtained for the Al{sup 2}O{sup 3} film grown on por-Si coincides with the optical-absorption edge for aluminum oxide and is located in the region of ∼5.60 eV. This fact is confirmed by the results of calculations of the optical-absorption spectrum of the Al{sup 2}O{sup 3}/por-Si/Si(lll) heterophase structure. The Al{sup 2}O{sup 3} films formed on the heterophase-structure surface in the form of nanodimensional structured threads can serve as channels of optical conduction and can be rather efficiently introduced into conventional technologies, which are of great importance in microelectronics and optoelectronics.« less

Nanoscale assembly of silicon-like [Al(As1-xNx)]ySi5-2y alloys: Fundamental theoretical and experimental studies of structural and optical properties

NASA Astrophysics Data System (ADS)

Jiang, L.; Sims, P. E.; Grzybowski, G.; Beeler, R. T.; Chizmeshya, A. V. G.; Smith, D. J.; Kouvetakis, J.; Menéndez, J.

2013-07-01

Ab initio theoretical simulations of Al(As1-xNx)Si3 alloys, a new class of optoelectronic materials, confirm that these compounds are likely to be disordered via a mechanism that preserves the integrity of the constituent III-V-Si3 tetrahedra but randomizes their orientation in the average diamond lattice of the compound. This type of disorder is consistent with experimental structural data and with the proposed growth mechanism for such alloys, according to which “III:V(SiH3)3” intermediate complexes are formed in the gas phase from reactions between group-III atomic beams and V(SiH3)3 molecules, delivering the entire III-V-Si3 tetrahedra to the growing film. Experimental optical studies of these Al(As1-xNx)Si3 alloys as well as more general [Al(As1-xNx)]ySi5-2y compounds grown on Si substrates were carried out using spectroscopic ellipsometry. The resulting dielectric functions are found to be similar to broadened versions of their counterparts in pure Si. This broadening may have important practical applications, particularly in photovoltaics, because it dramatically enhances the optical absorption of Si in the visible range of the electromagnetic spectrum. A critical point analysis reveals the existence of direct optical transitions at energies as low as 2.5 eV, well below the lowest direct absorption edge of Si at 3.3 eV. Such transitions are predicted theoretically for perfectly ordered III-V-Si3 compounds, and the experimental results suggest that they are robust against tetrahedra orientational disorder.

Optical, mechanical and structural properties of PMMA/SiO2 nanocomposite thin films

NASA Astrophysics Data System (ADS)

Soni, Gyanesh; Srivastava, Subodh; Soni, Purushottam; Kalotra, Pankaj; Vijay, Y. K.

2018-01-01

We have fabricated PMMA/SiO2 nanocomposite flexible thin films of 60 μm thicknesses by using solution casting method in the presence of transverse electric field. In this paper, we have investigated the effect of SiO2 nanoparticle (NP) loading on optical and mechanical properties of the composite thin film. The SEM images show that nanocomposite thin films have a smoother and uniform morphology. The transmittance peak near 1103 cm-1 in FT-IR spectrum confirms the presence of SiO2 NPs in the composite thin film. It is observed that optical bandgap decreases with an increase in the SiO2 NP concentration. Dynamic mechanical analysis shows that presence of SiO2 NP enhances the mechanical strength of the composite thin film.

Very low-refractive-index optical thin films consisting of an array of SiO2 nanorods

NASA Astrophysics Data System (ADS)

Xi, J.-Q.; Kim, Jong Kyu; Schubert, E. F.; Ye, Dexian; Lu, T.-M.; Lin, Shawn-Yu; Juneja, Jasbir S.

2006-03-01

The refractive-index contrast in dielectric multilayer structures, optical resonators, and photonic crystals is an important figure of merit that creates a strong demand for high-quality thin films with a low refractive index. A SiO2 nanorod layer with low refractive index of n=1.08, to our knowledge the lowest ever reported in thin-film materials, is grown by oblique-angle electron-beam deposition of SiO2. A single-pair distributed Bragg reflector employing a SiO2 nanorod layer is demonstrated to have enhanced reflectivity, showing the great potential of low-refractive-index films for applications in photonic structures and devices.

Exciton-polariton state in nanocrystalline SiC films

NASA Astrophysics Data System (ADS)

Semenov, A. V.; Lopin, A. V.

2016-05-01

We studied the features of optical absorption in the films of nanocrystalline SiC (nc-SiC) obtained on the sapphire substrates by the method of direct ion deposition. The optical absorption spectra of the films with a thickness less than ~500 nm contain a maximum which position and intensity depend on the structure and thickness of the nc-SiC films. The most intense peak at 2.36 eV is observed in the nc-SiC film with predominant 3C-SiC polytype structure and a thickness of 392 nm. Proposed is a resonance absorption model based on excitation of exciton polaritons in a microcavity. In the latter, under the conditions of resonance, there occurs strong interaction between photon modes of light with λph=521 nm and exciton of the 3С polytype with an excitation energy of 2.36 eV that results in the formation of polariton. A mismatch of the frequencies of photon modes of the cavity and exciton explains the dependence of the maximum of the optical absorption on the film thickness.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Joongoo; Park, Ji -Sang; Stradins, Pauls

In this paper, nonequilibrium growth of Si-III-V or Si-II-VI alloys is a promising approach to obtaining optically more active Si-based materials. We propose a new class of nonisovalent Si 2AlP (or Si 2ZnS) alloys in which the Al-P (or Zn-S) atomic chains are as densely packed as possible in the host Si matrix. As a hybrid of the lattice-matched parent phases, Si2AlP (or Si2ZnS) provides an ideal material system with tunable local chemical orders around Si atoms within the same composition and structural motif. Here, using first-principles hybrid functional calculations, we discuss how the local chemical orders affect the electronicmore » and optical properties of the nonisovalent alloys.« less

Si/Ge elatform for lasers, amplifiers, and nonlinear optical devices based on the Raman Effect

NASA Astrophysics Data System (ADS)

Claps, Ricardo; Dimitropoulos, Dimitrios; Raghunathan, Varun; Fathpour, Sasan; Jalali, Bahram; Jusserand, Bernard

2007-02-01

The use of a silicon-germanium platform for the development of optically active devices will be discussed in this paper, from the perspective of Raman and Brillouin scattering phenomena. Silicon-Germanium is becoming a prevalent technology for the development of high speed CMOS transistors, with advances in several key parameters as high carrier mobility, low cost, and reduced manufacturing logistics. Traditionally, Si-Ge structures have been used in the optoelectronics arena as photodetectors, due to the enhanced absorption of Ge in the telecommunications band. Recent developments in Raman-based nonlinearities for devices based on a silicon-on-insulator platform have shed light on the possibility of using these effects in Si-Ge architectures. Lasing and amplification have been demonstrated using a SiGe alloy structure, and Brillouin/Raman activity from acoustic phonon modes in SiGe superlattices has been predicted. Moreover, new Raman-active branches and inhomogeneously broadened spectra result from optical phonon modes, offering new perspectives for optical device applications. The possibilities for an electrically-pumped Raman laser will be outlined, and the potential for design and development of silicon-based, Tera-Hertz wave emitters and/or receivers.

Photoisomerization-induced manipulation of single-electron tunneling for novel Si-based optical memory.

PubMed

Hayakawa, Ryoma; Higashiguchi, Kenji; Matsuda, Kenji; Chikyow, Toyohiro; Wakayama, Yutaka

2013-11-13

We demonstrated optical manipulation of single-electron tunneling (SET) by photoisomerization of diarylethene molecules in a metal-insulator-semiconductor (MIS) structure. Stress is placed on the fact that device operation is realized in the practical device configuration of MIS structure and that it is not achieved in structures based on nanogap electrodes and scanning probe techniques. Namely, this is a basic memory device configuration that has the potential for large-scale integration. In our device, the threshold voltage of SET was clearly modulated as a reversible change in the molecular orbital induced by photoisomerization, indicating that diarylethene molecules worked as optically controllable quantum dots. These findings will allow the integration of photonic functionality into current Si-based memory devices, which is a unique feature of organic molecules that is unobtainable with inorganic materials. Our proposed device therefore has enormous potential for providing a breakthrough in Si technology.

About the optical properties of oxidized black silicon structures

NASA Astrophysics Data System (ADS)

Pincik, E.; Brunner, R.; Kobayashi, H.; Mikula, M.; Kučera, M.; Švec, P.; Greguš, J.; Vojtek, P.; Zábudlá, Z.; Imamura, K.; Zahoran, M.

2017-02-01

The paper deals with the optical and morphological properties of thermally oxidized black silicon (OBSi) nano-crystalline specimens produced by the surface structure chemical transfer method (SSCT). This method can produce a nano-crystalline Si black color layer on c-Si with a range of thickness of ∼50 nm to ∼300 nm by the contact of c-Si immersed in chemical solutions HF + H2O2 with a catalytic mesh. We present and discuss mainly the photoluminescence properties of both polished c-Si and OBSi structures, respectively. The similar photoluminescence (PL) behaviors recorded at liquid helium (6 K) and room temperatures on both polished crystalline Si and OBSi samples, respectively, indicate the similar origin of recorded luminescence light. As the positions of PL maxima of OBSi structures are mainly related to the size of Si nanocrystallites and SiO(x), we therefore suppose that the size of the dominant parts of the luminated OBSi nanostructure is pre-determined by the used polishing Si procedure, and/or the distribution function of the number of formed crystallites on their size is very similar. The blue shift of both PL spectra reaching almost value of 0.40 eV observed after the decrease of the sample temperature to 6 K we relate also with the change of the semiconductor band gap width.

Structural and optical characterization of pure Si-rich nitride thin films

PubMed Central

2013-01-01

The specific dependence of the Si content on the structural and optical properties of O- and H-free Si-rich nitride (SiNx>1.33) thin films deposited by magnetron sputtering is investigated. A semiempirical relation between the composition and the refractive index was found. In the absence of Si-H, N-H, and Si-O vibration modes in the FTIR spectra, the transverse and longitudinal optical (TO-LO) Si-N stretching pair modes could be unambiguously identified using the Berreman effect. With increasing Si content, the LO and the TO bands shifted to lower wavenumbers, and the LO band intensity dropped suggesting that the films became more disordered. Besides, the LO and the TO bands shifted to higher wavenumbers with increasing annealing temperature which may result from the phase separation between Si nanoparticles (Si-np) and the host medium. Indeed, XRD and Raman measurements showed that crystalline Si-np formed upon 1100°C annealing but only for SiNx<0.8. Besides, quantum confinement effects on the Raman peaks of crystalline Si-np, which were observed by HRTEM, were evidenced for Si-np average sizes between 3 and 6 nm. A contrario, visible photoluminescence (PL) was only observed for SiNx>0.9, demonstrating that this PL is not originating from confined states in crystalline Si-np. As an additional proof, the PL was quenched while crystalline Si-np could be formed by laser annealing. Besides, the PL cannot be explained neither by defect states in the bandgap nor by tail to tail recombination. The PL properties of SiNx>0.9 could be then due to a size effect of Si-np but having an amorphous phase. PMID:23324447

Structural and optical characterization of pure Si-rich nitride thin films

NASA Astrophysics Data System (ADS)

Debieu, Olivier; Nalini, Ramesh Pratibha; Cardin, Julien; Portier, Xavier; Perrière, Jacques; Gourbilleau, Fabrice

2013-01-01

The specific dependence of the Si content on the structural and optical properties of O- and H-free Si-rich nitride (SiN x>1.33) thin films deposited by magnetron sputtering is investigated. A semiempirical relation between the composition and the refractive index was found. In the absence of Si-H, N-H, and Si-O vibration modes in the FTIR spectra, the transverse and longitudinal optical (TO-LO) Si-N stretching pair modes could be unambiguously identified using the Berreman effect. With increasing Si content, the LO and the TO bands shifted to lower wavenumbers, and the LO band intensity dropped suggesting that the films became more disordered. Besides, the LO and the TO bands shifted to higher wavenumbers with increasing annealing temperature which may result from the phase separation between Si nanoparticles (Si-np) and the host medium. Indeed, XRD and Raman measurements showed that crystalline Si-np formed upon 1100°C annealing but only for SiN x<0.8. Besides, quantum confinement effects on the Raman peaks of crystalline Si-np, which were observed by HRTEM, were evidenced for Si-np average sizes between 3 and 6 nm. A contrario, visible photoluminescence (PL) was only observed for SiN x>0.9, demonstrating that this PL is not originating from confined states in crystalline Si-np. As an additional proof, the PL was quenched while crystalline Si-np could be formed by laser annealing. Besides, the PL cannot be explained neither by defect states in the bandgap nor by tail to tail recombination. The PL properties of SiN x>0.9 could be then due to a size effect of Si-np but having an amorphous phase.

SiGe layer thickness effect on the structural and optical properties of well-organized SiGe/SiO2 multilayers

NASA Astrophysics Data System (ADS)

Vieira, E. M. F.; Toudert, J.; Rolo, A. G.; Parisini, A.; Leitão, J. P.; Correia, M. R.; Franco, N.; Alves, E.; Chahboun, A.; Martín-Sánchez, J.; Serna, R.; Gomes, M. J. M.

2017-08-01

In this work, we report on the production of regular (SiGe/SiO2)20 multilayer structures by conventional RF-magnetron sputtering, at 350 °C. Transmission electron microscopy, scanning transmission electron microscopy, raman spectroscopy, and x-ray reflectometry measurements revealed that annealing at a temperature of 1000 °C leads to the formation of SiGe nanocrystals between SiO2 thin layers with good multilayer stability. Reducing the nominal SiGe layer thickness (t SiGe) from 3.5-2 nm results in a transition from continuous SiGe crystalline layer (t SiGe ˜ 3.5 nm) to layers consisting of isolated nanocrystals (t SiGe ˜ 2 nm). Namely, in the latter case, the presence of SiGe nanocrystals ˜3-8 nm in size, is observed. Spectroscopic ellipsometry was applied to determine the evolution of the onset in the effective optical absorption, as well as the dielectric function, in SiGe multilayers as a function of the SiGe thickness. A clear blue-shift in the optical absorption is observed for t SiGe ˜ 2 nm multilayer, as a consequence of the presence of isolated nanocrystals. Furthermore, the observed near infrared values of n = 2.8 and k = 1.5 are lower than those of bulk SiGe compounds, suggesting the presence of electronic confinement effects in the nanocrystals. The low temperature (70 K) photoluminescence measurements performed on annealed SiGe/SiO2 nanostructures show an emission band located between 0.7-0.9 eV associated with the development of interface states between the formed nanocrystals and surrounding amorphous matrix.

High-performance silicon nanowire bipolar phototransistors

NASA Astrophysics Data System (ADS)

Tan, Siew Li; Zhao, Xingyan; Chen, Kaixiang; Crozier, Kenneth B.; Dan, Yaping

2016-07-01

Silicon nanowires (SiNWs) have emerged as sensitive absorbing materials for photodetection at wavelengths ranging from ultraviolet (UV) to the near infrared. Most of the reports on SiNW photodetectors are based on photoconductor, photodiode, or field-effect transistor device structures. These SiNW devices each have their own advantages and trade-offs in optical gain, response time, operating voltage, and dark current noise. Here, we report on the experimental realization of single SiNW bipolar phototransistors on silicon-on-insulator substrates. Our SiNW devices are based on bipolar transistor structures with an optically injected base region and are fabricated using CMOS-compatible processes. The experimentally measured optoelectronic characteristics of the SiNW phototransistors are in good agreement with simulation results. The SiNW phototransistors exhibit significantly enhanced response to UV and visible light, compared with typical Si p-i-n photodiodes. The near infrared responsivities of the SiNW phototransistors are comparable to those of Si avalanche photodiodes but are achieved at much lower operating voltages. Compared with other reported SiNW photodetectors as well as conventional bulk Si photodiodes and phototransistors, the SiNW phototransistors in this work demonstrate the combined advantages of high gain, high photoresponse, low dark current, and low operating voltage.

Structural and optical characteristics of in-situ sputtered highly oriented 15R-SiC thin films on different substrates

NASA Astrophysics Data System (ADS)

Mourya, Satyendra; Jaiswal, Jyoti; Malik, Gaurav; Kumar, Brijesh; Chandra, Ramesh

2018-01-01

In this work, we have reported the in-situ fabrication of nanocrystalline rhombohedral silicon carbide (15R-SiC) thin films by RF-magnetron sputtering at 800 °C substrate temperature. The structural and optical properties were investigated for the films grown on four different substrates (ZrO2, MgO, SiC, and Si). The contact angle measurement was performed on all the substrates to investigate the role of interfacial surface energy in nucleation and growth of the films. The XRD measurement revealed the growth of (1 0 10) orientation for all the samples and demonstrated better crystallinity on Si substrate, which was further corroborated by the TEM results. The Raman spectroscopy confirmed the growth of rhombohedral phase with 15R polytype. Surface characteristics of the films have been investigated by energy dispersive x-ray spectroscopy, FTIR, and atomic force microscope (AFM) to account for chemical composition, bonding, and root mean square surface roughness (δrms). The optical dispersion behavior of 15R-SiC thin films was examined by variable angle spectroscopic ellipsometry in the wide spectral range (246-1688 nm), including the surface characteristics in the optical model. The non-linear optical parameters (χ3 and n2) of the samples have been calculated by the Tichy and Ticha relation using a single effective oscillator model of Wemple and Didomenico. Additionally, our optical results provided an alternative way to measure the ratio of carrier concentration to the effective mass (N/m*). These investigated optical parameters allow one to design and fabricate optoelectronic, photonic, and telecommunication devices for deployment in extreme environment.

Effect of AZO deposition on antireflective property of Si subwavelength grating structures

NASA Astrophysics Data System (ADS)

Leem, J. W.; Song, Y. M.; Lee, Y. T.; Yu, J. S.

2011-12-01

We investigate the effect of the aluminum-doped zinc oxide (AZO) deposition on the fabricated Si SWG structure on its antireflection characteristics for solar cell applications. The Si SWGs with the two-dimensional periodic nanostructure are fabricated by using holographic lithography and subsequent ICP etching process in SiCl4 plasma. For the antireflection analysis of AZO thin-film on the Si SWG structure, the optical reflectivity is measured experimentally. The maxima reflectance and its oscillation of the structure are significantly decreased on average than those of AZO thin-film on Si substrate over a wide wavelength range of 300-1100 nm, indicating average reflectance less than 4.5% with the maxima of <10%.

Structural and optical properties of SiC-SiO2 nanocomposite thin films

NASA Astrophysics Data System (ADS)

Bozetine, I.; Keffous, A.; Kaci, S.; Menari, H.; Manseri, A.

2018-03-01

This study deals with the deposition of thin films of a SiC-SiO2nanocomposite deposited on silicon substrates. The deposition is carried out by a co-sputtering RF magnetron 13.56 MHz, using two targets a polycristallin 6H-SiC and sprigs of SiO2. In order to study the influence of the deposition time on the morphology, the structural and optical properties of the thin films produced, two series of samples were prepared, namely a series A with a 30 min deposition time and a series B of one hour duration. The samples were investigated using different characterization techniques such as Scanning Electron Microscope (SEM), X-ray Diffraction (DRX), Fourier Transform Infrared Spectroscopy (FTIR), Secondary Ion Mass Spectrometry (SIMS) and photoluminescence. The results obtained, reveal an optical gap varies between 1.4 and 2.4 eV depending on the thickness of the film; thus depending on the deposition time. The SIMS profile recorded the presence of oxygen (16O) on the surface, which the signal beneath the silicon signal (28Si) and carbon (12C) signals, which confirms that the oxide (SiO2) is the first material deposited at the interface film - substrate with an a-OSiC structure. The photoluminescence (PL) measurement exhibits two peaks, centred at 390 nm due to the oxide and at 416 nm due probably to the nanocrystals of SiC crystals, note that when the deposition time increases, the intensity of the PL drops drastically, result in agreement with dense and smooth film.

Platinum Assisted Vapor–Liquid–Solid Growth of Er–Si Nanowires and Their Optical Properties

PubMed Central

2010-01-01

We report the optical activation of erbium coated silicon nanowires (Er–SiNWs) grown with the assist of platinum (Pt) and gold (Au), respectively. The NWs were grown on Si substrates by using a chemical vapor transport process using SiCl4 and ErCl4 as precursors. Pt as well as Au worked successfully as vapor–liquid–solid (VLS) catalysts for growing SiNWs with diameters of ~100 nm and length of several micrometers, respectively. The SiNWs have core–shell structures where the Er-crystalline layer is sandwiched between silica layers. Photoluminescence spectra analyses showed the optical activity of SiNWs from both Pt and Au. A stronger Er3+ luminescence of 1,534 nm was observed from the SiNWs with Pt at room- and low-temperature (25 K) using the 488- and/or 477-nm line of an Ar laser that may be due to the uniform incorporation of more Er ions into NWs with the exclusion of the formation of catalyst-induced deep levels in the band-gap. Pt would be used as a VLS catalyst for high performance optically active Er–SiNWs. PMID:20672113

Platinum assisted vapor-liquid-solid growth of er-si nanowires and their optical properties.

PubMed

Kim, Myoung-Ha; Kim, Il-Soo; Park, Yong-Hee; Park, Tae-Eon; Shin, Jung H; Choi, Heon-Jin

2009-11-14

We report the optical activation of erbium coated silicon nanowires (Er-SiNWs) grown with the assist of platinum (Pt) and gold (Au), respectively. The NWs were grown on Si substrates by using a chemical vapor transport process using SiCl4 and ErCl4 as precursors. Pt as well as Au worked successfully as vapor-liquid-solid (VLS) catalysts for growing SiNWs with diameters of ~100 nm and length of several micrometers, respectively. The SiNWs have core-shell structures where the Er-crystalline layer is sandwiched between silica layers. Photoluminescence spectra analyses showed the optical activity of SiNWs from both Pt and Au. A stronger Er3+ luminescence of 1,534 nm was observed from the SiNWs with Pt at room- and low-temperature (25 K) using the 488- and/or 477-nm line of an Ar laser that may be due to the uniform incorporation of more Er ions into NWs with the exclusion of the formation of catalyst-induced deep levels in the band-gap. Pt would be used as a VLS catalyst for high performance optically active Er-SiNWs.

Platinum Assisted Vapor-Liquid-Solid Growth of Er-Si Nanowires and Their Optical Properties

NASA Astrophysics Data System (ADS)

Kim, Myoung-Ha; Kim, Il-Soo; Park, Yong-Hee; Park, Tae-Eon; Shin, Jung H.; Choi, Heon-Jin

2010-02-01

We report the optical activation of erbium coated silicon nanowires (Er-SiNWs) grown with the assist of platinum (Pt) and gold (Au), respectively. The NWs were grown on Si substrates by using a chemical vapor transport process using SiCl4 and ErCl4 as precursors. Pt as well as Au worked successfully as vapor-liquid-solid (VLS) catalysts for growing SiNWs with diameters of ~100 nm and length of several micrometers, respectively. The SiNWs have core-shell structures where the Er-crystalline layer is sandwiched between silica layers. Photoluminescence spectra analyses showed the optical activity of SiNWs from both Pt and Au. A stronger Er3+ luminescence of 1,534 nm was observed from the SiNWs with Pt at room- and low-temperature (25 K) using the 488- and/or 477-nm line of an Ar laser that may be due to the uniform incorporation of more Er ions into NWs with the exclusion of the formation of catalyst-induced deep levels in the band-gap. Pt would be used as a VLS catalyst for high performance optically active Er-SiNWs.

Optical properties of amorphous Ba0.7Sr0.3TiO3 thin films obtained by metal organic decomposition technique

NASA Astrophysics Data System (ADS)

Qiu, Fei; Xu, Zhimou

2009-08-01

In this study, the amorphous Ba0.7Sr0.3TiO3 (BST0.7) thin films were grown onto fused quartz and silicon substrates at low temperature by using a metal organic decomposition (MOD)-spin-coating procedure. The optical transmittance spectrum of amorphous BST0.7 thin films on fused quartz substrates has been recorded in the wavelength range 190~900 nm. The films were highly transparent for wavelengths longer than 330 nm; the transmission drops rapidly at 330 nm, and the cutoff wavelength occurs at about 260 nm. In addition, we also report the amorphous BST0.7 thin film groove-buried type waveguides with 90° bent structure fabricated on Si substrates with 1.65 μm thick SiO2 thermal oxide layer. The design, fabrication and optical losses of amorphous BST0.7 optical waveguides were presented. The amorphous BST0.7 thin films were grown onto the SiO2/Si substrates by using a metal organic decomposition (MOD)-spin-coating procedure. The optical propagation losses were about 12.8 and 9.4 dB/cm respectively for the 5 and 10 μm wide waveguides at the wavelength of 632.8 nm. The 90° bent structures with a small curvature of micrometers were designed on the basis of a double corner mirror structure. The bend losses were about 1.2 and 0.9 dB respectively for 5 and 10 μm wide waveguides at the wavelength of 632.8 nm. It is expected for amorphous BST0.7 thin films to be used not only in the passive optical interconnection in monolithic OEICs but also in active waveguide devices on the Si chip.

Linear and Non-Linear Optical Imaging of Cancer Cells with Silicon Nanoparticles

PubMed Central

Tolstik, Elen; Osminkina, Liubov A.; Akimov, Denis; Gongalsky, Maksim B.; Kudryavtsev, Andrew A.; Timoshenko, Victor Yu.; Heintzmann, Rainer; Sivakov, Vladimir; Popp, Jürgen

2016-01-01

New approaches for visualisation of silicon nanoparticles (SiNPs) in cancer cells are realised by means of the linear and nonlinear optics in vitro. Aqueous colloidal solutions of SiNPs with sizes of about 10–40 nm obtained by ultrasound grinding of silicon nanowires were introduced into breast cancer cells (MCF-7 cell line). Further, the time-varying nanoparticles enclosed in cell structures were visualised by high-resolution structured illumination microscopy (HR-SIM) and micro-Raman spectroscopy. Additionally, the nonlinear optical methods of two-photon excited fluorescence (TPEF) and coherent anti-Stokes Raman scattering (CARS) with infrared laser excitation were applied to study the localisation of SiNPs in cells. Advantages of the nonlinear methods, such as rapid imaging, which prevents cells from overheating and larger penetration depth compared to the single-photon excited HR-SIM, are discussed. The obtained results reveal new perspectives of the multimodal visualisation and precise detection of the uptake of biodegradable non-toxic SiNPs by cancer cells and they are discussed in view of future applications for the optical diagnostics of cancer tumours. PMID:27626408

Impact of one-dimensional photonic crystal back reflector in thin-film c-Si solar cells on efficiency

NASA Astrophysics Data System (ADS)

Jalali, Tahmineh

2018-05-01

In this work, the effect of one-dimensional photonic crystal on optical absorption, which is implemented at the back side of thin-film crystalline silicon (c-Si) solar cells, is extensively discussed. The proposed structure acts as a Bragg reflector which reflects back light to the active layer as well as nanograting which couples the incident light to enhance optical absorption. To understand the optical mechanisms responsible for the enhancement of optical absorption, quantum efficiency and current density for all structures are calculated and the effect of influential parameters, such as grating period is investigated. The results confirm that our proposed structure have a great deal for substantial efficiency enhancement in a broad range from 400 to 1100 nm.

Theoretical exploration of structural, electro-optical and magnetic properties of gallium-doped silicon carbide nanotubes

NASA Astrophysics Data System (ADS)

Behzad, Somayeh; Chegel, Raad; Moradian, Rostam; Shahrokhi, Masoud

2014-09-01

The effects of gallium doping on the structural, electro-optical and magnetic properties of (8,0) silicon carbide nanotube (SiCNT) are investigated by using spin-polarized density functional theory. It is found from the calculation of the formation energies that gallium substitution for silicon atom is preferred. Our results show that gallium substitution at either single carbon or silicon atom site in SiCNT could induce spontaneous magnetization. The optical studies based on dielectric function indicate that new transition peaks and a blue shift are observed after gallium doping.

Nonisovalent Si-III-V and Si-II-VI alloys: Covalent, ionic, and mixed phases

DOE PAGES

Kang, Joongoo; Park, Ji -Sang; Stradins, Pauls; ...

2017-07-13

In this paper, nonequilibrium growth of Si-III-V or Si-II-VI alloys is a promising approach to obtaining optically more active Si-based materials. We propose a new class of nonisovalent Si 2AlP (or Si 2ZnS) alloys in which the Al-P (or Zn-S) atomic chains are as densely packed as possible in the host Si matrix. As a hybrid of the lattice-matched parent phases, Si2AlP (or Si2ZnS) provides an ideal material system with tunable local chemical orders around Si atoms within the same composition and structural motif. Here, using first-principles hybrid functional calculations, we discuss how the local chemical orders affect the electronicmore » and optical properties of the nonisovalent alloys.« less

Reflectance modulation using SiO2/TiO2 multilayer structures prepared by sol-gel spin coating process for optical applications

NASA Astrophysics Data System (ADS)

Dubey, R. S.; Ganesan, V.

2017-11-01

Passive devices made of SiO2/TiO2 bilayers have been demanded for the molding of electromagnetic waves in optical waveguides, microcavities, solar cells, sensors and so on. Here, we present the fabrication and characterization of SiO2/TiO2 multilayer structures as reflectors. The refractive indices were found to be 1.43 & 2.0 with thicknesses 230 & 70 nm corresponding to the SiO2 and TiO2 films respectively. AFM surface topography study showed little bit large surface roughness of the TiO2 as compared to SiO2 film due to its large grain size. The corresponding reflectance enhancement was noticed with the increased number of bilayers of SiO2/TiO2 films. Furthermore, six alternate layers of SiO2/TiO2 demonstrated the as much as 78% reflectance in the near-infrared wavelength range.

Fabrication of Transparent Protective Diamond-Like Carbon Films on Polymer

NASA Astrophysics Data System (ADS)

Baek, Sang-min; Shirafuji, Tatsuru; Saito, Nagahiro; Takai, Osamu

2011-08-01

Si doped hydrogenated amorphous carbon (Si-DLC) films as a candidate protection coating for polycarbonate (PC) were prepared using a pulse-biased inductively coupled plasma chemical vapor deposition (ICP-CVD) system with a gas mixture of acetylene (C2H2) and tetramethylsilane [Si(CH3)4]. The effects of Si incorporation on the structure and optical properties of the Si-DLC films were investigated. In addition, plasma pretreatments with O2, N2, and Ar gases were carried out to enhance the adhesion strength of Si-DLC films on polycarbonate. Structural characterization through Raman and X-ray photoelectron spectroscopy (XPS) analyses showed that the incorporation of Si atoms in DLC films leads to an increase in the optical band gap (Eopt) with the formation of sp3 C-Si bonds. O2 plasma pretreatment improved the strength of adhesion of the Si-DLC films to polycarbonate, while Ar and N2 plasma treatments did not. This can be explained by the formation of an activated dense interfacial layer by O2 plasma pretreatment.

A systematic optimization of design parameters in strained silicon waveguides to further enhance the linear electro-optic effect

NASA Astrophysics Data System (ADS)

Olivares, Irene; Angelova, Todora I.; Pinilla-Cienfuegos, Elena; Sanchis, Pablo

2016-05-01

The electro-optic Pockels effect may be generated in silicon photonics structures by breaking the crystal symmetry by means of a highly stressing cladding layer (typically silicon nitride, SiN) deposited on top of the silicon waveguide. In this work, the influence of the waveguide parameters on the strain distribution and its overlap with the optical mode to enhance the Pockels effect has been analyzed. The optimum waveguide structure have been designed based on the definition and quantification of a figure of merit. The fabrication of highly stressing SiN layers by PECVD has also been optimized to characterize the designed structures. The residual stress has been controlled during the growth process by analyzing the influence of the main deposition parameters. Therefore, two identical samples with low and high stress conditions were fabricated and electro-optically characterized to test the induced Pockels effect and the influence of carrier effects. Electro-optical modulation was only measured in the sample with the high stressing SiN layer that could be attributed to the Pockels effect. Nevertheless, the influence of carriers were also observed thus making necessary additional experiments to decouple both effects.

Ti Impurity Effect on the Optical Coefficients in 2D Cu2Si: A DFT Study

NASA Astrophysics Data System (ADS)

Nourozi, Bromand; Boochani, Arash; Abdolmaleki, Ahmad; Sartpi, Elmira; Darabi, Pezhman; Naderi, Sirvan

2018-01-01

The electronic and optical properties of 2D Cu2Si and Cu2Si:Ti are investigated based on the density functional theory (DFT) using the FP-LAPW method and GGA approximation. The 2D Cu2Si has metallic and non magnetic properties, whereas adding Ti impurity to its structure changes the electronic behavior to the half-metallic with 3.256μB magnetic moment. The optical transition is not occurred in the infrared and visible area for the 2D Cu2Si in x-direction and by adding Ti atom, the real part of dielectric function in the x-direction, Re (ε(ω))x is reached to a Dirac peak at this energy range. Moreover, the absorption gap tends to zero in x-direction of the 2D Cu2Si:Ti. Supported by Islamic Azad University, Kermanshah branch, Kermanshah, Iran

Structural studies of n-type nc-Si-QD thin films for nc-Si solar cells

NASA Astrophysics Data System (ADS)

Das, Debajyoti; Kar, Debjit

2017-12-01

A wide optical gap nanocrystalline silicon (nc-Si) dielectric material is a basic requirement at the n-type window layer of nc-Si solar cells in thin film n-i-p structure on glass substrates. Taking advantage of the high atomic-H density inherent to the planar inductively coupled low-pressure (SiH4 + CH4)-plasma, development of an analogous material in P-doped nc-Si-QD/a-SiC:H network has been tried. Incorporation of C in the Si-network extracted from the CH4 widens the optical band gap; however, at enhanced PH3-dilution of the plasma spontaneous miniaturization of the nc-Si-QDs below the dimension of Bohr radius (∼4.5 nm) further enhances the band gap by virtue of the quantum size effect. At increased flow rate of PH3, dopant induced continuous amorphization of the intrinsic crystalline network is counterbalanced by the further crystallization promoted by the supplementary atomic-H extracted from PH3 (1% in H2) in the plasma, eventually holding a moderately high degree of crystallinity. The n-type wide band gap (∼1.93 eV) window layer with nc-Si-QDs in adequate volume fraction (∼52%) could furthermore be instrumental as an effective seed layer for advancing sequential crystallization in the i-layer of nc-Si solar cells with n-i-p structure in superstrate configuration.

Effects of inter-tube coupling on the electro-optical properties of silicon carbide nanotube bundles studied by density functional theory

NASA Astrophysics Data System (ADS)

Behzad, Somayeh

2015-09-01

The electronic and optical properties of bundled armchair and zigzag silicon carbide nanotubes (SiCNTs) are investigated by using density functional theory. The effects of inter-tube coupling on the electronic dispersions of SiCNT bundles are demonstrated. It was found that the band structure of (6, 0) SiCNT bundle shows metallic feature. The calculated dielectric functions of the armchair and zigzag bundles are similar to that of the isolated tubes, except for the appearance of broadened peaks, small shifts of peak positions about 0.1 eV and increasing of peak intensities. For (6, 0) SiCNT with smaller radius, by considering interband and interaband transitions, the band structure coupling causes an extra peak at low energies.

Electrical and optical properties of Si-doped Ga2O3

NASA Astrophysics Data System (ADS)

Li, Yin; Yang, Chuanghua; Wu, Liyuan; Zhang, Ru

2017-05-01

The charge densities, band structure, density of states, dielectric functions of Si-doped β-Ga2O3 have been investigated based on the density functional theory (DFT) within the hybrid functional HSE06. The heavy doping makes conduction band split out more bands and further influences the band structure. It decreases the band gap and changes from a direct gap to an indirect gap. After doping, the top of the valence bands is mainly composed by the O-2p states, Si-3p states and Ga-4p states and the bottom of the conduction bands is almost formed by the Si-3s, Si-3p and Ga-4s orbits. The anisotropic optical properties have been investigated by means of the complex dielectric function. After the heavy Si doping, the position of absorption band edges did not change much. The slope of the absorption curve descends and indicates that the absorption became more slow for Si-doped β-Ga2O3 than undoped one due to the indirect gap of Si-doped β-Ga2O3.

Preparation, characterization, and infrared emissivity property of optically active polyurethane/TiO{sub 2}/SiO{sub 2} multilayered microspheres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang Yong; Zhou Yuming, E-mail: ymzhou@seu.edu.cn; Ge Jianhua

Optically active polyurethane/titania/silica (LPU/TiO{sub 2}/SiO{sub 2}) multilayered core-shell composite microspheres were prepared by the combination of titania deposition on the surface of silica spheres and subsequent polymer grafting. LPU/TiO{sub 2}/SiO{sub 2} was characterized by FT-IR, UV-vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), SEM and TEM, and the infrared emissivity value (8-14 {mu}m) was investigated in addition. The results indicated that titania and polyurethane had been successfully coated onto the surfaces of silica microspheres. LPU/TiO{sub 2}/SiO{sub 2} exhibited clearly multilayered core-shell construction. The infrared emissivity values reduced along with the increase of covering layers thus provedmore » that the interfacial interactions had direct influence on the infrared emissivity. Besides, LPU/TiO{sub 2}/SiO{sub 2} multilayered microspheres based on the optically active polyurethane took advantages of the orderly secondary structure and strengthened interfacial synergistic actions. Consequently, it possessed the lowest infrared emissivity value. - Graphical Abstract: Optically active polyurethane/titania/silica (LPU/TiO{sub 2}/SiO{sub 2}) multilayered core-shell composite microspheres were prepared by the combination of titania deposition on the surface of silica spheres and subsequent polymer grafting. Highlights: > Optically active polyurethane based on tyrosine was used for the modification of nanoparticles. > LPU/TiO{sub 2}/SiO{sub 2} multilayered core-shell microspheres were prepared and characterized. > Interfacial interactions and secondary structure affected the infrared emissivity of composite.« less

First-principles calculation on electronic structure and optical property of BaSi{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} phosphor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tong, Zhi-Fang, E-mail: tongzhifang1998@126.com; Wei, Zhan-Long; Xiao, Cheng

The crystal structure, electronic structure and optical properties of BaSi{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} with varying Eu doping concentrations are computed by the density functional theory (DFT) and compared with experimental results. The results show that the lattice parameters of primitive cells of Ba{sub 1−x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sub x} become smaller and Eu–N bond length shortens as Eu concentration increases. The band structure of Ba{sub 1−x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sub x} exhibits a direct optical band gap and it's propitious to luminescence. The energy differences from the lowest Eu 5d state to the lowest Eu 4f state decrease with increasing Eumore » concentrations. The analysis of simulative absorption spectra indicates that the electron transition from Eu 4f states to 5d states of both Eu and Ba atoms contributes to the absorption of Ba{sub 1−x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sub x}. Under the coupling effect between Eu and Ba, Ba in BaSi{sub 2}O{sub 2}N{sub 2} exhibits longer wavelength absorption and increases absorption efficiency. The emission wavelength is deduced by measuring energy differences from the lowest Eu 5d state to the lowest Eu 4f state, and the result is in good agreement with experimental value within experimental Eu{sup 2+} doping range. - Graphical abstract: The structure and optical property of BaSi{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} are computed by DFT and its absorption mechanism is analysed. Results show that absorption peak α is from the host lattice absorption. The absorption peaks β, γ and δ are from Eu 4f to Eu 5d and Ba 6s 5d states. The absorption is attributed to the coupling effect of Eu and Ba atom. - Highlights: • The crystal, electronic structure and optical properties of BaSi{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} are computed by DFT. • The lattice parameters of primitive cells reduces and Eu–N bond length shortens as Eu{sup 2+} increases. • The energy gap from Eu 5d state to Eu 4f state decrease with increasing Eu concentrations. • Both Eu and Ba atoms contributes to the absorption of Ba{sub 1−x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sub x}. • The deduced emission wavelength is in good agreement with experimental value.« less

Design of compact surface optical coupler based on vertically curved silicon waveguide for high-numerical-aperture single-mode optical fiber

NASA Astrophysics Data System (ADS)

Atsumi, Yuki; Yoshida, Tomoya; Omoda, Emiko; Sakakibara, Youichi

2017-09-01

A surface optical coupler based on a vertically curved Si waveguide was designed for coupling with high-numerical aperture single-mode optical fibers with a mode-field diameter of 5 µm. This coupler has a quite small device size, with a height of approximately 12 µm, achieved by introducing an effective spot-size converter configured with the combination of an extremely short Si exponential-inverse taper and a dome-structured SiO2 lens formed on the coupler top. The designed coupler shows high-efficiency optical coupling, with a loss of 0.8 dB for TE polarized light, as well as broad-band coupling with a 0.5-dB-loss band of 420 nm.

High-sensitivity silicon nanowire phototransistors

NASA Astrophysics Data System (ADS)

Tan, Siew Li; Zhao, Xingyan; Dan, Yaping

2014-08-01

Silicon nanowires (SiNWs) have emerged as a promising material for high-sensitivity photodetection in the UV, visible and near-infrared spectral ranges. In this work, we demonstrate novel planar SiNW phototransistors on silicon-oninsulator (SOI) substrate using CMOS-compatible processes. The device consists of a bipolar transistor structure with an optically-injected base region. The electronic and optical properties of the SiNW phototransistors are investigated. Preliminary simulation and experimental results show that nanowire geometry, doping densities and surface states have considerable effects on the device performance, and that a device with optimized parameters can potentially outperform conventional Si photodetectors.

Tunable Resonance Coupling in Single Si Nanoparticle-Monolayer WS2 Structures.

PubMed

Lepeshov, Sergey; Wang, Mingsong; Krasnok, Alex; Kotov, Oleg; Zhang, Tianyi; Liu, He; Jiang, Taizhi; Korgel, Brian; Terrones, Mauricio; Zheng, Yuebing; Alú, Andrea

2018-05-16

Two-dimensional semiconducting transition metal dichalcogenides (TMDCs) are extremely attractive materials for optoelectronic applications in the visible and near-infrared range. Coupling these materials to optical nanocavities enables advanced quantum optics and nanophotonic devices. Here, we address the issue of resonance coupling in hybrid exciton-polariton structures based on single Si nanoparticles (NPs) coupled to monolayer (1L)-WS 2 . We predict a strong coupling regime with a Rabi splitting energy exceeding 110 meV for a Si NP covered by 1L-WS 2 at the magnetic optical Mie resonance because of the symmetry of the mode. Further, we achieve a large enhancement in the Rabi splitting energy up to 208 meV by changing the surrounding dielectric material from air to water. The prediction is based on the experimental estimation of TMDC dipole moment variation obtained from the measured photoluminescence spectra of 1L-WS 2 in different solvents. An ability of such a system to tune the resonance coupling is realized experimentally for optically resonant spherical Si NPs placed on 1L-WS 2 . The Rabi splitting energy obtained for this scenario increases from 49.6 to 86.6 meV after replacing air by water. Our findings pave the way to develop high-efficiency optoelectronic, nanophotonic, and quantum optical devices.

Porous Silicon Gradient Refractive Index Micro-Optics.

PubMed

Krueger, Neil A; Holsteen, Aaron L; Kang, Seung-Kyun; Ocier, Christian R; Zhou, Weijun; Mensing, Glennys; Rogers, John A; Brongersma, Mark L; Braun, Paul V

2016-12-14

The emergence and growth of transformation optics over the past decade has revitalized interest in how a gradient refractive index (GRIN) can be used to control light propagation. Two-dimensional demonstrations with lithographically defined silicon (Si) have displayed the power of GRIN optics and also represent a promising opportunity for integrating compact optical elements within Si photonic integrated circuits. Here, we demonstrate the fabrication of three-dimensional Si-based GRIN micro-optics through the shape-defined formation of porous Si (PSi). Conventional microfabrication creates Si square microcolumns (SMCs) that can be electrochemically etched into PSi elements with nanoscale porosity along the shape-defined etching pathway, which imparts the geometry with structural birefringence. Free-space characterization of the transmitted intensity distribution through a homogeneously etched PSi SMC exhibits polarization splitting behavior resembling that of dielectric metasurfaces that require considerably more laborious fabrication. Coupled birefringence/GRIN effects are studied by way of PSi SMCs etched with a linear (increasing from edge to center) GRIN profile. The transmitted intensity distribution shows polarization-selective focusing behavior with one polarization focused to a diffraction-limited spot and the orthogonal polarization focused into two laterally displaced foci. Optical thickness-based analysis readily predicts the experimentally observed phenomena, which strongly match finite-element electromagnetic simulations.

Controlled waveguide coupling for photon emission from colloidal PbS quantum dot using tunable microcavity made of optical polymer and silicon

NASA Astrophysics Data System (ADS)

Nozaka, Takahiro; Mukai, Kohki

2016-04-01

A tunable microcavity device composed of optical polymer and Si with a colloidal quantum dot (QD) is proposed as a single-photon source for planar optical circuit. Cavity size is controlled by electrostatic micromachine behavior with the air bridge structure to tune timing of photon injection into optical waveguide from QD. Three-dimensional positioning of a QD in the cavity structure is available using a nanohole on Si processed by scanning probe microscope lithography. We fabricated the prototype microcavity with PbS-QD-mixed polymenthyl methacrylate on a SOI (semiconductor-on-insulator) substrate to show the tunability of cavity size as the shift of emission peak wavelength of QD ensemble.

First-principle calculations of structural, electronic, optical, elastic and thermal properties of MgXAs2 (X=Si, Ge) compounds

NASA Astrophysics Data System (ADS)

Cheddadi, S.; Boubendira, K.; Meradji, H.; Ghemid, S.; Hassan, F. El Haj; Lakel, S.; Khenata, R.

2017-12-01

First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite MgXAs2 (X=Si, Ge) have been performed within the density functional theory (DFT) using the full-potential linearized augmented plane wave (FP-LAPW) method. The obtained equilibrium structural parameters are in good agreement with the available experimental data and theoretical results. The calculated band structures reveal a direct energy band gap for the interested compounds. The predicted band gaps using the modified Becke-Johnson (mBJ) exchange approximation are in fairly good agreement with the experimental data. The optical constants such as the dielectric function, refractive index, and the extinction coefficient are calculated and analysed. The independent elastic parameters namely, C_{11}, C_{12}, C_{13}, C_{33}, C_{44} and C_{66 } are evaluated. The effects of temperature and pressure on some macroscopic properties of MgSiAs2 and MgGeAs2 are predicted using the quasiharmonic Debye model in which the lattice vibrations are taken into account.

Nanoscale Phase-Separated Structure in Core-Shell Nanoparticles of SiO2-Si1-xGexO2 Glass Revealed by Electron Microscopy.

PubMed

Kubo, Yugo; Yonezawa, Kazuhiro

2017-09-05

SiO 2 -based optical fibers are indispensable components of modern information communication technologies. It has recently become increasingly important to establish a technique for visualizing the nanoscale phase-separated structure inside SiO 2 -GeO 2 glass nanoparticles during the manufacturing of SiO 2 -GeO 2 fibers. This is because the rapidly increasing price of Ge has made it necessary to improve the Ge yield by clarifying the detailed mechanism of Ge diffusion into SiO 2 . However, direct observation of the internal nanostructure of glass particles has been extremely difficult, mainly due to electrostatic charging and the damage induced by electron and X-ray irradiation. In the present study, we used state-of-the-art scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDX) to examine cross-sectional samples of SiO 2 -GeO 2 particles embedded in an epoxy resin, which were fabricated using a broad Ar ion beam and a focused Ga ion beam. These advanced techniques enabled us to observe the internal phase-separated structure of the nanoparticles. We have for the first time clearly determined the SiO 2 -Si 1-x Ge x O 2 core-shell structure of such particles, the element distribution, the degree of crystallinity, and the quantitative chemical composition of microscopic regions, and we discuss the formation mechanism for the observed structure. The proposed imaging protocol is highly promising for studying the internal structure of various core-shell nanoparticles, which affects their catalytic, optical, and electronic properties.

Nonisovalent Si-III-V and Si-II-VI alloys: Covalent, ionic, and mixed phases

NASA Astrophysics Data System (ADS)

Kang, Joongoo; Park, Ji-Sang; Stradins, Pauls; Wei, Su-Huai

2017-07-01

Nonequilibrium growth of Si-III-V or Si-II-VI alloys is a promising approach to obtaining optically more active Si-based materials. We propose a new class of nonisovalent S i2AlP (or S i2ZnS ) alloys in which the Al-P (or Zn-S) atomic chains are as densely packed as possible in the host Si matrix. As a hybrid of the lattice-matched parent phases, S i2AlP (or S i2ZnS ) provides an ideal material system with tunable local chemical orders around Si atoms within the same composition and structural motif. Here, using first-principles hybrid functional calculations, we discuss how the local chemical orders affect the electronic and optical properties of the nonisovalent alloys.

Effect of doping on structural, optical and electrical properties of nanostructure ZnO films deposited onto a-Si:H/Si heterojunction

NASA Astrophysics Data System (ADS)

Sali, S.; Boumaour, M.; Kermadi, S.; Keffous, A.; Kechouane, M.

2012-09-01

We investigated the structural; optical and electrical properties of ZnO thin films as the n-type semiconductor for silicon a-Si:H/Si heterojunction photodiodes. The ZnO film forms the front contact of the super-strata solar cell and has to exhibit good electrical (high conductivity) and optical (high transmittance) properties. In this paper we focused our attention on the influence of doping on device performance. The results show that the X-ray diffraction (XRD) spectra revealed a preferred orientation of the crystallites along c-axis. SEM images show that all films display a granular, polycrystalline morphology and the ZnO:Al exhibits a better grain uniformity. The transmittance of the doped films was found to be higher when compared to undoped ZnO. A low resistivity of the order of 2.8 × 10-4 Ω cm is obtained for ZnO:Al using 0.4 M concentration of zinc acetate. The photoluminescence (PL) spectra exhibit a blue band with two peaks centered at 442 nm (2.80 eV) and 490 nm (2.53 eV). It is noted that after doping the ZnO films a shift of the band by 22 nm (0.15 eV) is recorded and a high luminescence occurs when using Al as a dopant. Dark I-V curves of ZnO/a-Si:H/Si structure showed large difference, which means there is a kind of barrier to current flow between ZnO and a-Si:H layer. Doping films was applied and the turn-on voltages are around 0.6 V. Under reverse bias, the current of the ZnO/a-Si:H/Si heterojunction is larger than that of ZnO:Al/a-Si:H/Si. The improvement with ZnO:Al is attributed to a higher number of generated carriers in the nanostructure (due to the higher transmittance and a higher luminescence) that increases the probability of collisions.

An Antibody-Immobilized Silica Inverse Opal Nanostructure for Label-Free Optical Biosensors.

PubMed

Lee, Wang Sik; Kang, Taejoon; Kim, Shin-Hyun; Jeong, Jinyoung

2018-01-20

Three-dimensional SiO₂-based inverse opal (SiO₂-IO) nanostructures were prepared for use as biosensors. SiO₂-IO was fabricated by vertical deposition and calcination processes. Antibodies were immobilized on the surface of SiO₂-IO using 3-aminopropyl trimethoxysilane (APTMS), a succinimidyl-[(N-maleimidopropionamido)-tetraethyleneglycol] ester (NHS-PEG₄-maleimide) cross-linker, and protein G. The highly accessible surface and porous structure of SiO₂-IO were beneficial for capturing influenza viruses on the antibody-immobilized surfaces. Moreover, as the binding leads to the redshift of the reflectance peak, the influenza virus could be detected by simply monitoring the change in the reflectance spectrum without labeling. SiO₂-IO showed high sensitivity in the range of 10³-10⁵ plaque forming unit (PFU) and high specificity to the influenza A (H1N1) virus. Due to its structural and optical properties, SiO₂-IO is a promising material for the detection of the influenza virus. Our study provides a generalized sensing platform for biohazards as various sensing strategies can be employed through the surface functionalization of three-dimensional nanostructures.

Integration of a UV curable polymer lens and MUMPs structures on a SOI optical bench

NASA Astrophysics Data System (ADS)

Hsieh, Jerwei; Hsiao, Sheng-Yi; Lai, Chun-Feng; Fang, Weileun

2007-08-01

This work presents the design concept of integrating a polymer lens, poly-Si MUMPs and single-crystal-silicon HARM structures on a SOI wafer to form a silicon optical bench. This approach enables the monolithic integration of various optical components on the wafer so as to improve the design flexibility of the silicon optical bench. Fabrication processes, including surface and bulk micromachining on the SOI wafer, have been established to realize bi-convex spherical polymer lenses with in-plane as well as out-of-plane optical axes. In addition, a micro device consisting of an in-plane polymer lens, a thick fiber holder and a mechanical shutter driven by an electrothermal actuator is also demonstrated using the present approach. In summary, this study significantly improves the design flexibility as well as the functions of SiOBs.

Additivity of the coefficient of thermal expansion in silicate optical fibers.

PubMed

Cavillon, M; Dragic, P D; Ballato, J

2017-09-15

A model that predicts the material additivity of the thermal expansion coefficient in the binary silicate glasses most commonly used for present (GeO 2 -SiO 2 , P 2 O 5 -SiO 2 , B 2 O 3 -SiO 2 , and Al 2 O 3 -SiO 2 ) and emerging (BaO-SiO 2 ) optical fibers is proposed. This model is based on a derivation of the expression for the coefficient of thermal expansion in isotropic solids, and gives direct insight on the parameters that govern its additivity in silicate glasses. Furthermore, a consideration of the local structural environment of the glass system is necessary to fully describe its additivity behavior in the investigated systems. This Letter is important for better characterizing and understanding of the impact of temperature and internal stresses on the behavior of optical fibers.

Optical properties of diamond like carbon nanocomposite thin films

NASA Astrophysics Data System (ADS)

Alam, Md Shahbaz; Mukherjee, Nillohit; Ahmed, Sk. Faruque

2018-05-01

The optical properties of silicon incorporated diamond like carbon (Si-DLC) nanocomposite thin films have been reported. The Si-DLC nanocomposite thin film deposited on glass and silicon substrate by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process. Fourier transformed infrared spectroscopic analysis revealed the presence of different bonding within the deposited films and deconvolution of FTIR spectra gives the chemical composition i.e., sp3/sp2 ratio in the films. Optical band gap calculated from transmittance spectra increased from 0.98 to 2.21 eV with a variation of silicon concentration from 0 to 15.4 at. %. Due to change in electronic structure by Si incorporation, the Si-DLC film showed a broad photoluminescence (PL) peak centered at 467 nm, i.e., in the visible range and its intensity was found to increase monotonically with at. % of Si.

A room-temperature-operated Si LED with β-FeSi2 nanocrystals in the active layer: μW emission power at 1.5 μm

NASA Astrophysics Data System (ADS)

Shevlyagin, A. V.; Goroshko, D. L.; Chusovitin, E. A.; Balagan, S. A.; Dotsenko, S. A.; Galkin, K. N.; Galkin, N. G.; Shamirzaev, T. S.; Gutakovskii, A. K.; Latyshev, A. V.; Iinuma, M.; Terai, Y.

2017-03-01

This article describes the development of an Si-based light-emitting diode with β-FeSi2 nanocrystals embedded in the active layer. Favorable epitaxial conditions allow us to obtain a direct band gap type-I band alignment Si/β-FeSi2 nanocrystals/Si heterostructure with optical transition at a wavelength range of 1500-1550 nm at room temperature. Transmission electron microscopy data reveal strained, defect-free β-FeSi2 nanocrystals of diameter 6 and 25 nm embedded in the Si matrix. Intense electroluminescence was observed at a pumping current density as low as 0.7 A/cm2. The device reached an optical emission power of up to 25 μW at 9 A/cm2 with an external quantum efficiency of 0.009%. Watt-Ampere characteristic linearity suggests that the optical power margin of the light-emitting diode has not been exhausted. Band structure calculations explain the luminescence as being mainly due to radiative recombination in the large β-FeSi2 nanocrystals resulting from the realization of an indirect-to-direct band gap electronic configuration transformation arising from a favorable deformation of nanocrystals. The direct band gap structure and the measured short decay time of the luminescence of several tens of ns give rise to a fast operation speed for the device. Thus a method for developing a silicon-based photonic integrated circuit, combining complementary metal-oxide-semiconductor technology functionality and near-infrared light emission, is reported here.

Transparent conductor-embedding nanocones for selective emitters: optical and electrical improvements of Si solar cells

PubMed Central

Kim, Joondong; Yun, Ju-Hyung; Kim, Hyunyub; Cho, Yunae; Park, Hyeong-Ho; Kumar, M. Melvin David; Yi, Junsin; Anderson, Wayne A.; Kim, Dong-Wook

2015-01-01

Periodical nanocone-arrays were employed in an emitter region for high efficient Si solar cells. Conventional wet-etching process was performed to form the nanocone-arrays for a large area, which spontaneously provides the graded doping features for a selective emitter. This enables to lower the electrical contact resistance and enhances the carrier collection due to the high electric field distribution through a nanocone. Optically, the convex-shaped nanocones efficiently reduce light-reflection and the incident light is effectively focused into Si via nanocone structure, resulting in an extremely improved the carrier collection performances. This nanocone-arrayed selective emitter simultaneously satisfies optical and electrical improvement. We report the record high efficiency of 16.3% for the periodically nanoscale patterned emitter Si solar cell. PMID:25787933

Transparent conductor-embedding nanocones for selective emitters: optical and electrical improvements of Si solar cells.

PubMed

Kim, Joondong; Yun, Ju-Hyung; Kim, Hyunyub; Cho, Yunae; Park, Hyeong-Ho; Kumar, M Melvin David; Yi, Junsin; Anderson, Wayne A; Kim, Dong-Wook

2015-03-19

Periodical nanocone-arrays were employed in an emitter region for high efficient Si solar cells. Conventional wet-etching process was performed to form the nanocone-arrays for a large area, which spontaneously provides the graded doping features for a selective emitter. This enables to lower the electrical contact resistance and enhances the carrier collection due to the high electric field distribution through a nanocone. Optically, the convex-shaped nanocones efficiently reduce light-reflection and the incident light is effectively focused into Si via nanocone structure, resulting in an extremely improved the carrier collection performances. This nanocone-arrayed selective emitter simultaneously satisfies optical and electrical improvement. We report the record high efficiency of 16.3% for the periodically nanoscale patterned emitter Si solar cell.

Structured illumination multimodal 3D-resolved quantitative phase and fluorescence sub-diffraction microscopy

PubMed Central

Chowdhury, Shwetadwip; Eldridge, Will J.; Wax, Adam; Izatt, Joseph A.

2017-01-01

Sub-diffraction resolution imaging has played a pivotal role in biological research by visualizing key, but previously unresolvable, sub-cellular structures. Unfortunately, applications of far-field sub-diffraction resolution are currently divided between fluorescent and coherent-diffraction regimes, and a multimodal sub-diffraction technique that bridges this gap has not yet been demonstrated. Here we report that structured illumination (SI) allows multimodal sub-diffraction imaging of both coherent quantitative-phase (QP) and fluorescence. Due to SI’s conventionally fluorescent applications, we first demonstrate the principle of SI-enabled three-dimensional (3D) QP sub-diffraction imaging with calibration microspheres. Image analysis confirmed enhanced lateral and axial resolutions over diffraction-limited QP imaging, and established striking parallels between coherent SI and conventional optical diffraction tomography. We next introduce an optical system utilizing SI to achieve 3D sub-diffraction, multimodal QP/fluorescent visualization of A549 biological cells fluorescently tagged for F-actin. Our results suggest that SI has a unique utility in studying biological phenomena with significant molecular, biophysical, and biochemical components. PMID:28663887

Photoactivated processes in optical fibers: generation and conversion mechanisms of twofold coordinated Si and Ge atoms

NASA Astrophysics Data System (ADS)

Giacomazzi, Luigi; Martin-Samos, L.; Boukenter, A.; Ouerdane, Y.; Girard, S.; Alessi, A.; de Gironcoli, S.; Richard, N.

2017-05-01

In this work we present an extensive investigation of nanoscale physical phenomena related to oxygen-deficient centers (ODCs) in silica and Ge-doped silica by means of first-principles calculations, including nudged-elastic band, electron paramagnetic resonance parameters calculations, and many-body perturbation theory (GW and Bethe-Salpeter equation) techniques. We show that by neutralizing positively charged oxygen monovacancies we can obtain model structures of twofold Si and Ge defects of which the calculated absorption spectra and singlet-to-triplet transitions are in excellent agreement with the experimental optical absorption and photo-luminescence data. In particular we provide an exhaustive analysis of the main exciton peaks related to the presence of twofold defects including long-range correlation effects. By calculating the reaction pathways and energy barriers necessary for the interconversion, we advance a double precursory origin of the {E}α \\prime and Ge(2) centers as due to the ionization of neutral oxygen monovacancies (Si-Si and Ge-Si dimers) and as due to the ionization of twofold Si and Ge defects. Furthermore two distinct structural conversion mechanisms are found to occur between the neutral oxygen monovacancy and the twofold Si (and Ge) atom configurations. Such conversion mechanisms allow to explain the radiation induced generation of the ODC(II) centers, their photobleaching, and also their generation during the drawing of optical fibers.

The effect of oxide shell thickness on the structural, electronic, and optical properties of Si-SiO{sub 2} core-shell nano-crystals: A (time dependent)density functional theory study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nazemi, Sanaz, E-mail: s.nazemi@ut.ac.ir, E-mail: pourfath@ut.ac.ir; Soleimani, Ebrahim Asl; Pourfath, Mahdi, E-mail: s.nazemi@ut.ac.ir, E-mail: pourfath@ut.ac.ir

2016-04-14

Due to their tunable properties, silicon nano-crystals (NC) are currently being investigated. Quantum confinement can generally be employed for size-dependent band-gap tuning at dimensions smaller than the Bohr radius (∼5 nm for silicon). At the nano-meter scale, however, increased surface-to-volume ratio makes the surface effects dominant. Specifically, in Si-SiO{sub 2} core-shell semiconductor NCs the interfacial transition layer causes peculiar electronic and optical properties, because of the co-existence of intermediate oxidation states of silicon (Si{sup n+}, n = 0–4). Due to the presence of the many factors involved, a comprehensive understanding of the optical properties of these NCs has not yet been achieved. Inmore » this work, Si-SiO{sub 2} NCs with a diameter of 1.1 nm and covered by amorphous oxide shells with thicknesses between 2.5 and 4.75 Å are comprehensively studied, employing density functional theory calculations. It is shown that with increased oxide shell thickness, the low-energy part of the optical transition spectrum of the NC is red shifted and attenuated. Moreover, the absorption coefficient is increased in the high-energy part of the spectrum which corresponds to SiO{sub 2} transitions. Structural examinations indicate a larger compressive stress on the central silicon cluster with a thicker oxide shell. Examination of the local density of states reveals the migration of frontier molecular orbitals from the oxide shell into the silicon core with the increase of silica shell thickness. The optical and electrical properties are explained through the analysis of the density of states and the spatial distribution of silicon sub-oxide species.« less

Determining the confined optical length of high index vertical Si nanoforest arrays for photonic applications

NASA Astrophysics Data System (ADS)

Chaliyawala, Harsh A.; Purohit, Zeel; Khanna, Sakshum; Ray, Abhijit; Pati, Ranjan K.; Mukhopadhyay, Indrajit

2018-06-01

The structural and the optical properties of different Si nanostructures have been compared. Detailed optical properties of Si nanowires arrays of different optical lengths, fabricated by facile electroless etching technique, have been reported. The theoretical calculation of exponential sine profile at constant λ = 600 nm shows a better explanation in terms of gradient index with optical length for vertical nanowires. The observations signify the possibility of strong light trapping due to an exponential gradient towards the high index along the nanowires and the existence of dense subwavelength features. The optical admittance (Ƶ) shows a strong impact on optical distance (Z) for Z < H, owing to the electromagnetic wave interaction with the nanowires that perceive a different Ƶ at the oblique angle of incidence (AOI). In addition, the experimental reflectance data and the theoretical model for transverse electric and transverse magnetic modes predict that an optical length of 5 μm can exhibit a very low reflectance value. This indicates that the Si nanowires are polarization insensitive over a wide range of AOI (0°-80°). Moreover, Raman spectra showed a very strong light confinement effect in the first order transverse optical band with increasing etching depths. The morphological dependent resonance theory predicts a strong localized light field confinement in the lower wavelength regime for SiNWs. The effect on the strong resonant absorption modes was further correlated with the simulation results obtained by using COMSOL. The obtained results are likely to enhance the maximum absorption of SiNWs for various photonic applications.

Strain gauge using Si-based optical microring resonator.

PubMed

Lei, Longhai; Tang, Jun; Zhang, Tianen; Guo, Hao; Li, Yanna; Xie, Chengfeng; Shang, Chenglong; Bi, Yu; Zhang, Wendong; Xue, Chenyang; Liu, Jun

2014-12-20

This paper presents a strain gauge using the mechanical-optical coupling method. The Si-based optical microring resonator was employed as the sensing element, which was embedded on the microcantilevers. The experimental results show that applying external strain triggers a clear redshift of the output resonant spectrum of the structure. The sensitivity of 93.72  pm/MPa was achieved, which also was verified using theoretical simulations. This paper provides what we believe is a new method to develop micro-opto-electromechanical system (MOEMS) sensors.

Correction of a Space Telescope Active Primary Mirror Using Adaptive Optics in a Woofer-Tweeter Configuration

DTIC Science & Technology

2015-09-01

shows the elements of an AHM. The substrate is a rib-stiffened silicon carbide ( SiC ) structure cast to meet the required optical figure. The...right) 2. SMT Three Point Linearity Test The active mirror under study is a 1-meter hexagonal SiC AHM mirror with 156 face sheet actuators. The...CORRECTION OF A SPACE TELESCOPE ACTIVE PRIMARY MIRROR USING ADAPTIVE OPTICS IN A WOOFER-TWEETER CONFIGURATION by Matthew R. Allen September 2015

Electrical interface characteristics (I-V), optical time of flight measurements, and the x-ray (20 keV) signal response of amorphous-selenium/crystalline-silicon heterojunction structures

NASA Astrophysics Data System (ADS)

Hunter, David M.; Ho, Chu An; Belev, George; De Crescenzo, Giovanni; Kasap, Safa O.; Yaffe, Martin J.

2011-03-01

We have investigated the dark current, optical TOF (time of flight) properties, and the X-ray response of amorphousselenium (a-Se)/crystalline-silicon (c-Si) heterostructures for application in digital radiography. The structures have been studied to determine if an x-ray generated electron signal, created in an a-Se layer, could be directly transferred to a c-Si based readout device such as a back-thinned CCD (charge coupled device). A simple first order band-theory of the structure indicates that x-ray generated electrons should transfer from the a-Se to the c-Si, while hole transfer from p-doped c-Si to the a-Se should be blocked, permitting a low dark signal as required. The structures we have tested have a thin metal bias electrode on the x-ray facing side of the a-Se which is deposited on the c-Si substrate. The heterostructures made with pure a-Se deposited on epitaxial p-doped (5×10 14 cm-3) c-Si exhibited very low dark current of 15 pA cm-2 at a negative bias field of 10 V μm-1 applied to the a-Se. The optical TOF (time of flight) measurements show that the applied bias drops almost entirely across the a-Se layer and that the a-Se hole and electron mobilities are within the range of commonly accepted values. The x-ray signal measurements demonstrate the structure has the expected x-ray quantum efficiency. We have made a back-thinned CCD coated with a-Se and although most areas of the device show a poor x-ray response, it does contain small regions which do work properly with the expected x-ray sensitivity. Improved understanding of the a-Se/c-Si interface and preparation methods should lead to properly functioning devices.

Structural and optical characterization of self-assembled Ge nanocrystal layers grown by plasma-enhanced chemical vapor deposition.

PubMed

Saeed, Saba; Buters, Frank; Dohnalova, Katerina; Wosinski, Lech; Gregorkiewicz, Tom

2014-10-10

We present a structural and optical study of solid-state dispersions of Ge nanocrystals prepared by plasma-enhanced chemical vapor deposition. Structural analysis shows the presence of nanocrystalline germanium inclusions embedded in an amorphous matrix of Si-rich SiO(2).Optical characterization reveals two prominent emission bands centered around 2.6 eV and 3.4 eV, and tunable by excitation energy. In addition, the lower energy band shows an excitation power-dependent blue shift of up to 0.3 eV. Decay dynamics of the observed emission contains fast (nanosecond) and slow (microseconds) components, indicating contributions of several relaxation channels. Based on these material characteristics, a possible microscopic origin of the individual emission bands is discussed.

Enhancement of optical and structural quality of semipolar (11-22) GaN by introducing nanoporous SiNx interlayers

NASA Astrophysics Data System (ADS)

Monavarian, Morteza; Metzner, Sebastian; Izyumskaya, Natalia; Müller, Marcus; Okur, Serdal; Zhang, Fan; Can, Nuri; Das, Saikat; Avrutin, Vitaliy; Özgür, Ümit; Bertram, Frank; Christen, Juergen; Morkoç, Hadis

2015-03-01

Enhancement of optical and structural quality of semipolar (11‾22) GaN grown by metal-organic chemical vapor deposition on planar m-sapphire substrates was achieved by using an in-situ epitaxial lateral overgrowth (ELO) technique with nanoporous SiNx layers employed as masks. In order to optimize the procedure, the effect of SiNx deposition time was studied by steady-state photoluminescence (PL), and X-ray diffraction. The intensity of room temperature PL for the (11‾22) GaN layers grown under optimized conditions was about three times higher compared to those for the reference samples having the same thickness but no SiNx interlayers. This finding is attributed to the blockage of extended defect propagation toward the surface by the SiNx interlayers as evidenced from the suppression of emissions associated with basal-plane and prismatic stacking faults with regard to the intensity of donor bound excitons (D0X) in lowtemperature PL spectra. In agreement with the optical data, full width at half maximum values of (11‾22) X-ray rocking curves measured for two different in-plane rotational orientations of [1‾100] and [11‾23] reduced from 0.33º and 0.26º for the reference samples to 0.2º and 0.16º for the nano-ELO structures grown under optimized conditions, respectively.

Structural and optical characterization of ZnO/Mg(x)Zn(1-x)O multiple quantum wells based random laser diodes.

PubMed

Jiang, Qike; Zheng, He; Wang, Jianbo; Long, Hao; Fang, Guojia

2012-12-01

Two kinds of laser diodes (LDs) comprised of ZnO/Mg(x)Zn(1-x)O (ZnO/MZO) multiple quantum wells (MQWs) grown on GaN (MQWs/GaN) and Si (MQWs/Si) substrates, respectively, have been constructed. The LD with MQWs/GaN exhibits ultraviolet random lasing under electrical excitation, while that with MQWs/Si does not. In the MQWs/Si, ZnO/MZO MQWs consist of nanoscaled crystallites, and the MZO layers undergo a phase separation of cubic MgO and hexagonal ZnO. Moreover, the Mg atom predominantly locates in the MZO layers along with a significant aggregation at the ZnO/MZO interfaces; in sharp contrast, the ZnO/MZO MQWs in the MQWs/GaN show a well-crystallized structure with epitaxial relationships among GaN, MZO, and ZnO. Notably, Mg is observed to diffuse into the ZnO well layers. The structure-optical property relationship of these two LDs is further discussed.

Improving the opto-microwave performance of SiGe/Si phototransistor through edge-illuminated structure

NASA Astrophysics Data System (ADS)

Tegegne, Z. G.; Viana, C.; Polleux, J. L.; Grzeskowiak, M.; Richalot, E.

2016-03-01

This paper demonstrates the experimental study of edge and top illuminated SiGe phototransistors (HPT) implemented using the existing industrial SiGe2RF Telefunken GmbH BiCMOS technology for opto-microwave (OM) applications using 850nm Multi-Mode Fibers (MMF). Its technology and structure are described. Two different optical window size HPTs with top illumination (5x5μm2, 10x10μm2) and an edge illuminated HPTs having 5μm x5μm size are presented and compared. A two-step post fabrication process was used to create an optical access on the edge of the HPT for lateral illumination with a lensed MMF through simple polishing and dicing techniques. We perform Opto-microwave Scanning Near-field Optical Microscopy (OM-SNOM) analysis on edge and top illuminated HPTs in order to observe the fastest and the highest sensitive regions of the HPTs. This analysis also allows understanding the parasitic effect from the substrate, and thus draws a conclusion on the design aspect of SiGe/Si HPT. A low frequency OM responsivity of 0.45A/W and a cutoff frequency, f-3dB, of 890MHz were measured for edge illuminated HPT. Compared to the top illuminated HPT of the same size, the edge illuminated HPT improves the f-3dB by a factor of more than two and also improves the low frequency responsivity by a factor of more than four. These results demonstrate that a simple etched HPT is still enough to achieve performance improvements compared to the top illuminated HPT without requiring a complex coupling structure. Indeed, it also proves the potential of edge coupled SiGe HPT in the ultra-low-cost silicon based optoelectronics circuits with a new approach of the optical packaging and system integration to 850nm MMF.

Magneto-transport phenomena in metal/SiO2/n(p)-Si hybrid structures

NASA Astrophysics Data System (ADS)

Volkov, N. V.; Tarasov, A. S.; Rautskii, M. V.; Lukyanenko, A. V.; Bondarev, I. A.; Varnakov, S. N.; Ovchinnikov, S. G.

2018-04-01

Present review touches upon a subject of magnetotransport phenomena in hybrid structures which consist of ferromagnetic or nonmagnetic metal layer, layer of silicon oxide and silicon substrate with n- or p-type conductivity. Main attention will be paid to a number gigantic magnetotransport effects discovered in the devices fabricated on the base of the M/SiO2/n(p)-Si (M is ferromagnetic or paramagnetic metal) hybrid structures. These effects include bias induced dc magnetoresistance, gigantic magnetoimpedance, dc magnetoresistance induced by an optical irradiation and lateral magneto-photo-voltaic effect. The magnetoresistance ratio in ac and dc modes for some of our devices can exceed 106% in a magnetic field below 1 T. For lateral magneto-photo-voltaic effect, the relative change of photo-voltage in magnetic field can reach 103% at low temperature. Two types of mechanisms are responsible for sensitivity of the transport properties of the silicon based hybrid structures to magnetic field. One is related to transformation of the energy structure of the (donor) acceptor states including states near SiO2/n(p)-Si interface in magnetic field. Other mechanism is caused by the Lorentz force action. The features in behaviour of magnetotransport effects in concrete device depend on composition of the used structure, device topology and experimental conditions (bias voltage, optical radiation and others). Obtained results can be base for design of some electronic devices driven by a magnetic field. They can also provide an enhancement of the functionality for existing sensors.

Prediction of direct band gap silicon superlattices with dipole-allowed optical transition

NASA Astrophysics Data System (ADS)

Kim, Sunghyun; Oh, Young Jun; Lee, In-Ho; Lee, Jooyoung; Chang, K. J.

While cubic diamond silicon (c-Si) is an important element in electronic devices, it has poor optical properties owing to its indirect gap nature, thereby limiting its applications to optoelectronic devices. Here, we report Si superlattice structures which are computationally designed to possess direct band gaps and excellent optical properties. The computational approach adopts density functional calculations and conformational space annealing for global optimization. The Si superlattices, which consist of alternating stacks of Si(111) layers and a defective layer with Seiwatz chains, have either direct or quasi-direct band gaps depending on the details of attacking layers. The photovoltaic efficiencies are calculated by solving Bethe-Salpeter equation together with quasiparticle G0W0 calculations. The strong direct optical transition is attributed to the overlap of the valence and conduction band edge states in the interface region. Our Si superlattices exhibit high thermal stability, with the energies lower by an order of magnitude than those of the previously reported Si allotropes. We discuss a possible route to the synthesis of the superlattices through wafer bonding. This work is supported by Samsung Science and Technology Foundation under Grant No. SSTF-BA1401-08.

Theoretical Prediction of an Antimony-Silicon Monolayer (penta-Sb2Si): Band Gap Engineering by Strain Effect

NASA Astrophysics Data System (ADS)

Morshedi, Hosein; Naseri, Mosayeb; Hantehzadeh, Mohammad Reza; Elahi, Seyed Mohammad

2018-04-01

In this paper, using a first principles calculation, a two-dimensional structure of silicon-antimony named penta-Sb2Si is predicted. The structural, kinetic, and thermal stabilities of the predicted monolayer are confirmed by the cohesive energy calculation, phonon dispersion analysis, and first principles molecular dynamic simulation, respectively. The electronic properties investigation shows that the pentagonal Sb2Si monolayer is a semiconductor with an indirect band gap of about 1.53 eV (2.1 eV) from GGA-PBE (PBE0 hybrid functional) calculations which can be effectively engineered by employing external biaxial compressive and tensile strain. Furthermore, the optical characteristics calculation indicates that the predicted monolayer has considerable optical absorption and reflectivity in the ultraviolet region. The results suggest that a Sb2Si monolayer has very good potential applications in new nano-optoelectronic devices.

Opto-electronic properties of P-doped nc-Si-QD/a-SiC:H thin films as foundation layer for all-Si solar cells in superstrate configuration

NASA Astrophysics Data System (ADS)

Kar, Debjit; Das, Debajyoti

2016-07-01

With the advent of nc-Si solar cells having improved stability, the efficient growth of nc-Si i-layer of the top cell of an efficient all-Si solar cell in the superstrate configuration prefers nc-Si n-layer as its substrate. Accordingly, a wide band gap and high conducting nc-Si alloy material is a basic requirement at the n-layer. Present investigation deals with the development of phosphorous doped n-type nanocrystalline silicon quantum dots embedded in hydrogenated amorphous silicon carbide (nc-Si-QD/a-SiC:H) hetero-structure films, wherein the optical band gap can be widened by the presence of Si-C bonds in the amorphous matrix and the embedded high density tiny nc-Si-QDs could provide high electrical conductivity, particularly in P-doped condition. The nc-Si-QDs simultaneously facilitate further widening of the optical band gap by virtue of the associated quantum confinement effect. A complete investigation has been made on the electrical transport phenomena involving charge transfer by tunneling and thermionic emission prevailing in n-type nc-Si-QD/a-SiC:H thin films. Their correlation with different phases of the specific heterostructure has been carried out for detailed understanding of the material, in order to improve its device applicability. The n-type nc-Si-QD/a-SiC:H films exhibit a thermally activated electrical transport above room temperature and multi-phonon hopping (MPH) below room temperature, involving defects in the amorphous phase and the grain-boundary region. The n-type nc-Si-QD/a-SiC:H films grown at ˜300 °C, demonstrating wide optical gap ˜1.86-1.96 eV and corresponding high electrical conductivity ˜4.5 × 10-1-1.4 × 10-2 S cm-1, deserve to be an effective foundation layer for the top nc-Si sub-cell of all-Si solar cells in n-i-p structure with superstrate configuration.

Synthesis, structural, electronic and linear electro-optical features of new quaternary Ag{sub 2}Ga{sub 2}SiS{sub 6} compound

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piasecki, M., E-mail: m.piasecki@ajd.czest.pl; Myronchuk, G.L.; Parasyuk, O.V.

For the first time phase equilibria and phase diagram of the AgGaS{sub 2}–SiS{sub 2} system were successfully explored by differential thermal and X-ray phase analysis methods. Crystal structure of low-temperature (LT) modification of Ag{sub 2}Ga{sub 2}SiS{sub 6} (LРў- Ag{sub 2}Ga{sub 2}SiS{sub 6}) was studied by X-ray powder method and it belongs to tetragonal space group I-42d, with unit cell parameters a=5.7164(4) Å, c=9.8023(7) Å, V=320.32(7) Å{sup 3}. Additional details regarding the crystal structure exploration are available at the web page Fachinformationszentrum Karlsruhe. X-ray photoelectron core-level and valence-band spectra were measured for pristine LРў- Ag{sub 2}Ga{sub 2}SiS{sub 6} crystal surface. Inmore » addition, the X-ray photoelectron valence-band spectrum of LРў-Ag{sub 2}Ga{sub 2}SiS{sub 6} was matched on a common energy scale with the X-ray emission S Kβ{sub 1,3} and Ga Kβ{sub 2} bands, which give information on the energy distribution of the S 3p and Ga 4p states, respectively. The presented X-ray spectroscopy results indicate that the valence S p and Ga p atomic states contribute mainly to the upper and central parts of the valence band of LРў-Ag{sub 2}Ga{sub 2}SiS{sub 6}, respectively, with a less significant contribution also to other valence-band regions. Band gap energy was estimated by measuring the quantum energy in the spectral range of the fundamental absorption. We have found that energy gap Eg is equal to 2.35 eV at 300 K. LT-Ag{sub 2}Ga{sub 2}SiS{sub 6} is a photosensitive material and reveals two spectral maxima on the curve of spectral photoconductivity spectra at λ{sub max1} =590 nm and λ{sub max2} =860 nm. Additionally, linear electro-optical effect of LT-Ag{sub 2}Ga{sub 2}SiS{sub 6} for the wavelengths of a cw He-Ne laser at 1150 nm was explored. - Graphical abstract: Manuscript present the technology of growth and investigation of properties a new quaternary compound Ag{sub 2}Ga{sub 2}SiS{sub 6} including the detailed study of the phase equilibria in the AgGaS{sub 2}–SiS{sub 2} system to determine the physico-chemical conditions of its formation. We examined crystal structure of the compound by X-ray powder method, its electronic structure by XPS method. Finally we have found these crystals like promising material for nonlinear optical, electrooptical and piezoelectric applications. - Highlights: • Phase diagram of the AgGaS{sub 2}–SiS{sub 2} system was successfully described at first time. • Crystal Ag{sub 2}Ga{sub 2}SiS{sub 6} was grown and its structure was determined. • Electronic structure and chemical bonding of the Ag{sub 2}Ga{sub 2}SiS{sub 6} crystal were examined by. • X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) methods. • Optical and photoelectrical properties were investigated.« less

Broadband High Efficiency Fractal-Like and Diverse Geometry Silicon Nanowire Arrays for Photovoltaic Applications

NASA Astrophysics Data System (ADS)

AL-Zoubi, Omar H.

Solar energy has many advantages over conventional sources of energy. It is abundant, clean and sustainable. One way to convert solar energy directly into electrical energy is by using the photovoltaic solar cells (PVSC). Despite PVSC are becoming economically competitive, they still have high cost and low light to electricity conversion efficiency. Therefore, increasing the efficiency and reducing the cost are key elements for producing economically more competitive PVSC that would have significant impact on energy market and saving environment. A significant percentage of the PVSC cost is due to the materials cost. For that, thin films PVSC have been proposed which offer the benefits of the low amount of material and fabrication costs. Regrettably, thin film PVSC show poor light to electricity conversion efficiency because of many factors especially the high optical losses. To enhance conversion efficiency, numerous techniques have been proposed to reduce the optical losses and to enhance the absorption of light in thin film PVSC. One promising technique is the nanowire (NW) arrays in general and the silicon nanowire (SiNW) arrays in particular. The purpose of this research is to introduce vertically aligned SiNW arrays with enhanced and broadband absorption covering the entire solar spectrum while simultaneously reducing the amount of material used. To this end, we apply new concept for designing SiNW arrays based on employing diversity of physical dimensions, especially radial diversity within certain lattice configurations. In order to study the interaction of light with SiNW arrays and compute their optical properties, electromagnetic numerical modeling is used. A commercial numerical electromagnetic solver software package, high frequency structure simulation (HFSS), is utilized to model the SiNW arrays and to study their optical properties. We studied different geometries factors that affect the optical properties of SiNW arrays. Based on this study, we found that the optical properties of SiNW arrays are strongly affected by the radial diversity, the arrangement of SiNW in a lattice, and the configuration of such lattice. The proper selection of these parameters leads to broaden and enhance the light absorption of the SiNW arrays. Inspired by natural configurations, fractal geometry and diamond lattice structures, we introduced two lattice configurations: fractal-like array (FLA) that is inspired by fractal geometry, and diamond-like array (DLA) that is inspired by diamond crystal lattice structure. Optimization, using parametric analysis, of the introduced arrays parameters for the light absorption level and the amount of used material has been performed. Both of the introduced SiNW arrays show broadband, strong light absorption coupled with reduction of the amount of the used material. DLA in specific showed significantly enhanced absorption covering the entire solar spectrum of interest, where near-unity absorption spectrum could be achieved. We studied the optical properties of complete PVSC devices that are based on SiNW array. Moreover, the performance of PVSC device that is based on SiNW has been investigated by using numerical modeling. SILVACO software package is used for performing the numerical simulation of the PVSC device performance, which can simultaneously handle the different coupled physical mechanisms contributing to the photovoltaic effect. The effect of the geometry of PVSC device that is based on SiNW is investigated, which shows that the geometry of such PVSC has a role in enhancing its electrical properties. The outcome of this study introduces new SiNW array configurations that have enhanced optical properties using a low amount of material that can be utilized for producing higher efficiency thin film PVCS. The overall conclusion of this work is that a weak absorption indirect band gap material, silicon, in the form of properly designed SiNW and SiNC arrays has the potentials to achieve near-unity ideal absorption spectrum using reduced amount of material, which can lead to produce new generation of lower cost and enhanced efficiency thin film PVSC.

Jwst from Below: An Overview of the Construction of the James Webb Space Telescope, Interesting Metrology, and Cryogenic-Vacuum Testing

NASA Technical Reports Server (NTRS)

Ohl, R.

2016-01-01

NASA's James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy (40K). The JWST Observatory includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) that contains four science instruments (SI) and the guider. The SIs are mounted to a composite metering structure. The SI and guider units are integrated to the ISIM structure and optically tested at NASA Goddard Space Flight Center as a suite using a telescope simulator (Optical Telescope Element SIMulator; OSIM). OSIM is a full field, cryogenic JWST telescope simulator. SI performance, including alignment and wavefront error, is evaluated using OSIM. This is an overview presentation to undergraduate students and other personnel at the University of Richmond, planned for 12 Oct, 2016. It uses material previously released by NASA on the Internet (e.g., via Flickr) or at engineering conferences (e.g., SPIE). This presentation provides an overview of the status of the project, with an emphasis on optics and measurement.

Annealing temperature and barrier thickness effect on the structural and optical properties of silicon nanocrystals/SiO₂ superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

López-Vidrier, J., E-mail: jlopezv@el.ub.edu; Hernández, S.; López-Conesa, L.

2014-10-07

The effect of the annealing temperature and the SiO₂ barrier thickness of silicon nanocrystal (NC)/SiO₂ superlattices (SLs) on their structural and optical properties is investigated. Energy-filtered transmission electron microscopy (TEM) revealed that the SL structure is maintained for annealing temperatures up to 1150 °C, with no variation on the nanostructure morphology for different SiO₂ barrier thicknesses. Nevertheless, annealing temperatures as high as 1250 °C promote diffusion of Si atoms into the SiO₂ barrier layers, which produces larger Si NCs and the loss of the NC size control expected from the SL approach. Complementary Raman scattering measurements corroborated these results formore » all the SiO₂ and Si-rich oxynitride layer thicknesses. In addition, we observed an increasing crystalline fraction up to 1250 °C, which is related to a decreasing contribution of the suboxide transition layer between Si NCs and the SiO₂ matrix due to the formation of larger NCs. Finally, photoluminescence measurements revealed that the emission of the superlattices exhibits a Gaussian-like lineshape with a maximum intensity after annealing at 1150 °C, indicating a high crystalline degree in good agreement with Raman results. Samples submitted to higher annealing temperatures display a progressive emission broadening, together with an increase in the central emission wavelength. Both effects are related to a progressive broadening of the size distribution with a larger mean size, in agreement with TEM observations. On the other hand, whereas the morphology of the Si NCs is unaffected by the SiO₂ barrier thickness, the emission properties are slightly modified. These observed modifications in the emission lineshape allow monitoring the precipitation process of Si NCs in a direct non-destructive way. All these experimental results evidence that an annealing temperature of 1150 °C and 1-nm SiO₂ barrier can be reached whilst preserving the SL structure, being thus the optimal structural SL parameters for their use in optoelectronics.« less

Self-assembly of cadmium metasilicate nanowires as a broadband optical limiter

NASA Astrophysics Data System (ADS)

Zheng, Chan; Dai, Chongchong; Huang, Li; Li, Wei; Chen, Wenzhe

2016-04-01

Cadmium metasilicate nanowires (CdSiO3 NWs) have been synthesized through a facile, eco-friendly, low-cost water-ethanol mixed-solution hydrothermal route. The transmission electron microscopy measurements of as-prepared samples indicate that the CdSiO3 NWs with diameters in the range of 10-60 nm and lengths of more than 1 μm were constructed by self-assembly of 5-10-nm CdSiO3 nanoparticles with good crystallinity. The monoclinic phase formation of the sample is studied in detail by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermo gravimetric analysis. The results indicate that a pure monoclinic phase of CdSiO3 can be obtained by a hydrothermal route without further calcinations and SiO4 tetrahedra were the main constituents of the CdSiO3 NWs. The nanosecond optical limiting (OL) effects were characterized by using an open-aperture (OA) Z-scan technique with 4-ns laser pulses at both 532 and 1064 nm. Theses CdSiO3 NWs displayed an excellent OL performance at 532 and 1064 nm, which was better than carbon nanotubes, a benchmark optical limiter. Input-fluence dependent scattering measurements suggested than nonlinear scattering played an important role in the observed optical limiting behavior in CdSiO3 NWs at 532 and 1064 nm. More significantly, the NLO performance in CdSiO3 NWs incorporated solid silica gel glass has been improved in comparison to those dispersed in water. The unique structure and excellent OL property render these CdSiO3 NWs competitors in the realms of optical limiting applications.

Acousto-optical and SAW propagation characteristics of temperature stable multilayered structures based on LiNbO3 and diamond

NASA Astrophysics Data System (ADS)

Shandilya, Swati; Sreenivas, K.; Gupta, Vinay

2008-01-01

Theoretical studies on the surface acoustic wave (SAW) properties of c-axis oriented LiNbO3/IDT/diamond and diamond/IDT/128° rotated Y-X cut LiNbO3 multilayered structures have been considered. Both layered structures exhibit a positive temperature coefficient of delay (TCD) characteristic, and a zero TCD device is obtained after integrating with an over-layer of either tellurium dioxide (TeO2) or silicon dioxide (SiO2). The presence of a TeO2 over-layer enhanced the electromechanical coupling coefficients of both multilayered structures, which acts as a better temperature compensation layer than SiO2. The temperature stable TeO2/LiNbO3/IDT/diamond layered structure exhibits good electromechanical coefficient and higher phase velocity for SAW device applications. On the other hand, a high acousto-optical (AO) figure of merit (30-37) × 10-15 s3 kg-1 has been obtained for the temperature stable SiO2/diamond/IDT/LiNbO3 layered structure indicating a promising device structure for AO applications.

Bismuth Oxide Nanoparticles Partially Substituted with EuIII, MnIV, and SiIV: Structural, Spectroscopic, and Optical Findings.

PubMed

Ortiz-Quiñonez, José-Luis; Zumeta-Dubé, Inti; Díaz, David; Nava-Etzana, Noel; Cruz-Zaragoza, Epifanio; Santiago-Jacinto, Patricia

2017-03-20

Interest in nanostructured partially substituted bismuth oxides has been increasing over the last years. Research on new synthesis methods, properties, and possible uses for these oxides is needed. The objective of this paper is to synthesize β-Bi 2 O 3 , β-Bi 2 O 3 :Eu 3+ , β-Bi 2 O 3 :Mn 4+ , Bi 12 Bi 0.8 O 19.2 , Bi 12 Bi 0.8 O 19.2 /Li + , Bi 12 MnO 20 , and Bi 12 SiO 20 nanoparticles and to investigate their structural, spectroscopic, and optical changes. Some of the causes that generated their properties are also discussed. These materials are important because the doping or partial substitution of bismuth oxide with these cations (Eu 3+ , Mn 4+ , and Si 4+ ) modifies some properties such as optical absorption, reactivity toward CO 2 , among others. X-ray diffraction (in powders), high-resolution transmission electron microscopy, Fourier transform infrared (FTIR), resonance Raman scattering, diffuse reflectance, and solid-state magic-angle-spinning 29 Si NMR were used for the characterization of the synthesized materials. We found that partial substitution of yellow Bi 12 Bi 0.8 O 19.2 with Mn 4+ and Si 4+ changed the color to green and whitish, respectively. New bands in the Raman scattering and FTIR spectra of these oxides are deeply discussed. Raman scattering spectroscopy was a valuable and reliable technique to detect the Eu 3+ and Mn 4+ cations as dopants in the bismuth oxides. The 29 Si chemical shift (δ) in Bi 12 SiO 20 was -78.16 ppm, whereas in SiO 2 , it was around -110 ppm. This considerable shift in Bi 12 SiO 20 occurred because of an increased shielding of the Si nucleus in the Si(O) 4 tetrahedron. This shielding was provided by the low-electronegativity and highly polarizable Bi cations. The isovalent doping of β-Bi 2 O 3 nanoparticles with Eu 3+ enhanced their thermal stability over 400 °C. Variation in the optical absorption and reactivity toward the acidic CO 2 molecule of the partially substituted bismuth oxides was explained on the basis of the optical basicity and ionic-covalent parameter concepts. Some possible uses for the synthesized oxides are suggested.

An Antibody-Immobilized Silica Inverse Opal Nanostructure for Label-Free Optical Biosensors

PubMed Central

Lee, Wang Sik; Kim, Shin-Hyun

2018-01-01

Three-dimensional SiO2-based inverse opal (SiO2-IO) nanostructures were prepared for use as biosensors. SiO2-IO was fabricated by vertical deposition and calcination processes. Antibodies were immobilized on the surface of SiO2-IO using 3-aminopropyl trimethoxysilane (APTMS), a succinimidyl-[(N-maleimidopropionamido)-tetraethyleneglycol] ester (NHS-PEG4-maleimide) cross-linker, and protein G. The highly accessible surface and porous structure of SiO2-IO were beneficial for capturing influenza viruses on the antibody-immobilized surfaces. Moreover, as the binding leads to the redshift of the reflectance peak, the influenza virus could be detected by simply monitoring the change in the reflectance spectrum without labeling. SiO2-IO showed high sensitivity in the range of 103–105 plaque forming unit (PFU) and high specificity to the influenza A (H1N1) virus. Due to its structural and optical properties, SiO2-IO is a promising material for the detection of the influenza virus. Our study provides a generalized sensing platform for biohazards as various sensing strategies can be employed through the surface functionalization of three-dimensional nanostructures. PMID:29361683

Colloidal PbS nanocrystals integrated to Si-based photonics for applications at telecom wavelengths

NASA Astrophysics Data System (ADS)

Humer, M.; Guider, R.; Jantsch, W.; Fromherz, T.

2013-05-01

In the last decade, Si based photonics has made major advances in terms of design, fabrication, and device implementation. But due to Silicon's indirect bandgap, it still remains a challenge to create efficient Si-based light emitting devices. In order to overcome this problem, an approach is to develop hybrid systems integrating light-emitting materials into Si. A promising class of materials for this purpose is the class of semiconducting nanocrystal quantum dots (NCs) that are synthesized by colloidal chemistry. As their absorption and emission wavelength depends on the dot size, which can easily be controlled during synthesis, they are extremely attractive as building blocks for nanophotonic applications. For applications in telecom wavelength, Lead chalcogenide colloidal NCs are optimum materials due to their unique optical, electronic and nonlinear properties. In this work, we experimentally demonstrate the integration of PbS nanocrystals into Si-based photonic structures like slot waveguides and ring resonators as optically pumped emitters for room temperature applications. In order to create such hybrid structures, the NCs were dissolved into polymer resists and drop cast on top of the device. Upon optical pumping, intense photoluminescence emission from the resonating modes is recorded at the output of the waveguide with transmission quality factors up to 14000. The polymer host material was investigated with respect to its ability to stabilize the NC's photoluminescence emission against degradation under ambient conditions. The waveguide-ring coupling efficiency was also investigated as function of the NCs concentrations blended into the polymer matrix. The integration of colloidal quantum dots into Silicon photonic structures as demonstrated in this work is a very versatile technique and thus opens a large range of applications utilizing the linear and nonlinear optical properties of PbS NCs at telecom wavelengths.

Near-infrared emitting In-rich InGaN layers grown directly on Si: Towards the whole composition range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aseev, Pavel, E-mail: pavel.aseev@upm.es; Rodriguez, Paul E. D. Soto; Gómez, Víctor J.

The authors report compact and chemically homogeneous In-rich InGaN layers directly grown on Si (111) by plasma-assisted molecular beam epitaxy. High structural and optical quality is evidenced by transmission electron microscopy, near-field scanning optical microscopy, and X-ray diffraction. Photoluminescence emission in the near-infrared is observed up to room temperature covering the important 1.3 and 1.55 μm telecom wavelength bands. The n-InGaN/p-Si interface is ohmic due to the absence of any insulating buffer layers. This qualitatively extends the application fields of III-nitrides and allows their integration with established Si technology.

SiP monolayers: New 2D structures of group IV-V compounds for visible-light photohydrolytic catalysts

NASA Astrophysics Data System (ADS)

Ma, Zhinan; Zhuang, Jibin; Zhang, Xu; Zhou, Zhen

2018-06-01

Because of graphene and phosphorene, two-dimensional (2D) layered materials of group IV and group V elements arouse great interest. However, group IV-V monolayers have not received due attention. In this work, three types of SiP monolayers were computationally designed to explore their electronic structure and optical properties. Computations confirm the stability of these monolayers, which are all indirect-bandgap semiconductors with bandgaps in the range 1.38-2.21 eV. The bandgaps straddle the redox potentials of water at pH = 0, indicating the potential of the monolayers for use as watersplitting photocatalysts. The computed optical properties demonstrate that certain monolayers of SiP 2D materials are absorbers of visible light and would serve as good candidates for optoelectronic devices.

A Photonic 1 × 4 Power Splitter Based on Multimode Interference in Silicon-Gallium-Nitride Slot Waveguide Structures.

PubMed

Malka, Dror; Danan, Yossef; Ramon, Yehonatan; Zalevsky, Zeev

2016-06-25

In this paper, a design for a 1 × 4 optical power splitter based on the multimode interference (MMI) coupler in a silicon (Si)-gallium nitride (GaN) slot waveguide structure is presented-to our knowledge, for the first time. Si and GaN were found as suitable materials for the slot waveguide structure. Numerical optimizations were carried out on the device parameters using the full vectorial-beam propagation method (FV-BPM). Simulation results show that the proposed device can be useful to divide optical signal energy uniformly in the C-band range (1530-1565 nm) into four output ports with low insertion losses (0.07 dB).

High photon-to-heat conversion efficiency in the wavelength region of 250–1200 nm based on a thermoelectric Bi2Te3 film structure

PubMed Central

Hu, Er-Tao; Yao, Yuan; Zang, Kai-Yan; Liu, Xin-Xing; Jiang, An-Qing; Zheng, Jia-Jin; Yu, Ke-Han; Wei, Wei; Zheng, Yu-Xiang; Zhang, Rong-Jun; Wang, Song-You; Zhao, Hai-Bin; Yoshie, Osamu; Lee, Young-Pak; Wang, Cai-Zhuang; Lynch, David W.; Guo, Jun-Peng; Chen, Liang-Yao

2017-01-01

In this work, 4-layered SiO2/Bi2Te3/SiO2/Cu film structures were designed and fabricated and the optical properties investigated in the wavelength region of 250–1200 nm for their promising applications for direct solar-thermal-electric conversion. A typical 4-layered film sample with the structure SiO2 (66.6 nm)/Bi2Te3 (7.0 nm)/SiO2 (67.0 nm)/Cu (>100.0 nm) was deposited on a Si or K9-glass substrate by magnetron sputtering. The experimental results agree well with the simulated ones showing an average optical absorption of 96.5%, except in the shorter wavelength region, 250–500 nm, which demonstrates the superior absorption property of the 4-layered film due to the randomly rough surface of the Cu layer resulting from the higher deposition power. The high reflectance of the film structure in the long wavelength region of 2–20 μm will result in a low thermal emittance, 0.064 at 600 K. The simpler 4-layered structure with the thermoelectric Bi2Te3 used as the absorption layer may provide a straightforward way to obtain solar-thermal-electric conversion more efficiently through future study. PMID:28300178

Stress engineering in GaN structures grown on Si(111) substrates by SiN masking layer application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szymański, Tomasz, E-mail: tomasz.szymanski@pwr.edu.pl; Wośko, Mateusz; Paszkiewicz, Bogdan

2015-07-15

GaN layers without and with an in-situ SiN mask were grown by using metal organic vapor phase epitaxy for three different approaches used in GaN on silicon(111) growth, and the physical and optical properties of the GaN layers were studied. For each approach applied, GaN layers of 1.4 μm total thickness were grown, using silan SiH{sub 4} as Si source in order to grow Si{sub x}N{sub x} masking layer. The optical micrographs, scanning electron microscope images, and atomic force microscope images of the grown samples revealed cracks for samples without SiN mask, and micropits, which were characteristic for the samples grownmore » with SiN mask. In situ reflectance signal traces were studied showing a decrease of layer coalescence time and higher degree of 3D growth mode for samples with SiN masking layer. Stress measurements were conducted by two methods—by recording micro-Raman spectra and ex-situ curvature radius measurement—additionally PLs spectra were obtained revealing blueshift of PL peak positions with increasing stress. The authors have shown that a SiN mask significantly improves physical and optical properties of GaN multilayer systems reducing stress in comparison to samples grown applying the same approaches but without SiN masking layer.« less

Strain analysis of SiGe microbridges

NASA Astrophysics Data System (ADS)

Anthony, Ross; Gilbank, Ashley; Crowe, Iain; Knights, Andrew

2018-02-01

We present the analysis of UV (325 nm) Raman scattering spectra from silicon-germanium (SiGe) microbridges where the SiGe has been formed using the so-called "condensation technique". As opposed to the conventional condensation technique in which SiGe is grown epitaxially, we use high-dose ion implantation of Ge ions into SOI as a means to introduce the initial Ge profile. The subsequent oxidation both repairs implantation induced damage, and forms epitaxial Ge. Using Si-Si and Si-Ge optical phonon modes, as well as the ratio of integrated intensities for Ge-Ge and Si-Si, we can determine both the composition and strain of the material. We show that although the material is compressively strained following condensation, by fabricating microbridge structures we can create strain relaxed or tensile strained structures, with subsequent interest for photonic applications.

The optical properties of β-FeSi 2 fabricated by ion beam assisted sputtering

NASA Astrophysics Data System (ADS)

McKinty, C. N.; Kewell, A. K.; Sharpe, J. S.; Lourenço, M. A.; Butler, T. M.; Valizadeh, R.; Colligon, J. S.; Reeson Kirkby, K. J.; Homewood, K. P.

2000-03-01

β-FeSi 2 has been shown to have a minimum direct band gap of 0.87 eV [T.D. Hunt, K.J. Reeson, K.P. Homewood, S.W. Teon, R.M. Gwilliam, B.J. Sealy, Nucl. Instr. and Meth. B 84 (1994) 168-171] which leads to the opportunity for Si based opto-electronics, optical communications and optical interconnects. Electroluminescence has been reported from structures containing β-FeSi 2, which were produced by high dose ion implantation and annealing [D. Leong, M.A. Harry, K.J. Reeson, K.P. Homewood, Nature 387 (12 June 1987) 686]. In this paper we report the formation of β-FeSi 2 by ion beam assisted co-sputtering of Fe and Si in varying percentages. The layers were deposited with a varying Fe/Si ratio, with a Si capping layer applied to prevent oxidation. Separate regions of the sample were investigated at room temperature using optical absorption, to measure the band gap values. Absorption under the fundamental edge was also analysed at room temperature. Further investigations looked at the temperature dependence of the band gap and the absorption under the fundamental edge. The results showed that a variety of Fe/Si ratios produced β-FeSi 2, the formation of which was ascertained by the presence of a suitable band gap value [0.83-0.88 eV]. Absorption under the fundamental edge was shown to follow an exponential Urbach tail [C.H. Grein, S. John, Phys. Rev. B 39 (1989) 1140]. The temperature measurements are in good agreement with the Einstein model.

Near-field nano-Raman imaging of Si device structures

NASA Astrophysics Data System (ADS)

Atesang, Jacob; Geer, Robert

2005-05-01

Apertureless-based, near-field Raman imaging holds the potential for nanoscale stress metrology in emerging Si devices. Preliminary application of near-field Raman imaging on Si device structures has demonstrated the potential for stress measurements. However, detailed investigations have not been published regarding the effect of tip radius on observed near-field enhancement. Such investigations are important to understand the fundamental limits regarding the signal-to-noise ratio of the measurement and the spatial resolution that can potentially be achieved before wide application to semiconductor metrology can be considered. Investigations are presented into near-field enhancement of Raman scattering from Si device structures using a modified near-field optical microscope (NSOM). The nano-Raman system utilizes an off-axis (45°) backscattering NSOM geometry with free-space collection optics. The spectroscopic configuration utilizes a single-bounce spectrometer incorporating a holographic notch filter assembly utilized as a secondary beam-splitter for an apertureless backscattering collection geometry. Near-field enhancement is observed for both Al- and Ag-coated probes. An inverse square power-law relationship is observed between near-field enhancement factor and tip radius.

Bioinspired Omnidirectional Self-Stable Reflectors with Multiscale Hierarchical Structures.

PubMed

Han, Zhiwu; Mu, Zhengzhi; Li, Bo; Feng, Xiaoming; Wang, Ze; Zhang, Junqiu; Niu, Shichao; Ren, Luquan

2017-08-30

Structured surfaces, demonstrating various wondrous physicochemical performances, are ubiquitous phenomena in nature. Butterfly wings with impressive structural colors are an interesting example for multiscale hierarchical structures (MHSs). However, most natural structural colors are relatively unstable and highly sensitive to incident angles, which limit their potential practical applications to a certain extent. Here, we reported a bioinspired color reflector with omnidirectional reflective self-stable (ORS) properties, which is inspired by the wing scales of Papilio palinurus butterfly. Through experimental exploration and theoretical analysis, it was found that the vivid colors of such butterfly wings are structure-based and possess novel ORS properties, which attributes to the multiple optical actions between light and the complex structures coupling the inverse opal-like structures (IOSs) and stacked lamellar ridges (SLRs). On the basis of this, we designed and successfully fabricated the SiO 2 -based bioinspired color reflectors (BCRs) through a facile and effective biotemplate method. It was confirmed that the MHSs in biotemplate are inherited by the obtained SiO 2 -based BCRs. More importantly, the SiO 2 -based BCRs also demonstrated the similar ORS properties in a wide wavelength range. We forcefully anticipate that the reported MHS-based ORS performance discovered in butterfly wing scales here could offer new thoughts for scientists to solve unstable reflection issues in particular optical field. The involved biotemplate fabrication method offers a facile and effective strategy for fabricating functional nanomaterials or bioinspired nanodevices with 3D complex nanostructures, such as structured optical devices, displays, and optoelectronic equipment.

Near-Infrared and Optical Beam Steering and Frequency Splitting in Air-Holes-in-Silicon Inverse Photonic Crystals.

PubMed

Tasolamprou, Anna C; Koschny, Thomas; Kafesaki, Maria; Soukoulis, Costas M

2017-11-15

We present the design of a dielectric inverse photonic crystal structure that couples line-defect waveguide propagating modes into highly directional beams of controllable directionality. The structure utilizes a triangular lattice made of air holes drilled in an infinitely thick Si slab, and it is designed for operation in the near-infrared and optical regime. The structure operation is based on the excitation and manipulation of dark dielectric surface states, in particular on the tailoring of the dark states' coupling to outgoing radiation. This coupling is achieved with the use of properly designed external corrugations. The structure adapts and matches modes that travel through the photonic crystal and the free space. Moreover it facilitates the steering of the outgoing waves, is found to generate well-defined, spatially and spectrally isolated beams, and may serve as a frequency splitting component designed for operation in the near-infrared regime and in particular the telecom optical wavelength band. The design complies with the state-of-the-art Si nanofabrication technology and can be directly scaled for operation in the optical regime.

Near-Infrared and Optical Beam Steering and Frequency Splitting in Air-Holes-in-Silicon Inverse Photonic Crystals

PubMed Central

2017-01-01

We present the design of a dielectric inverse photonic crystal structure that couples line-defect waveguide propagating modes into highly directional beams of controllable directionality. The structure utilizes a triangular lattice made of air holes drilled in an infinitely thick Si slab, and it is designed for operation in the near-infrared and optical regime. The structure operation is based on the excitation and manipulation of dark dielectric surface states, in particular on the tailoring of the dark states’ coupling to outgoing radiation. This coupling is achieved with the use of properly designed external corrugations. The structure adapts and matches modes that travel through the photonic crystal and the free space. Moreover it facilitates the steering of the outgoing waves, is found to generate well-defined, spatially and spectrally isolated beams, and may serve as a frequency splitting component designed for operation in the near-infrared regime and in particular the telecom optical wavelength band. The design complies with the state-of-the-art Si nanofabrication technology and can be directly scaled for operation in the optical regime. PMID:29541653

Spectroscopic Ellipsometry Studies of Thin Film a-Si:H/nc-Si:H Micromorph Solar Cell Fabrication in the p-i-n Superstrate Configuration

NASA Astrophysics Data System (ADS)

Huang, Zhiquan

Spectroscopic ellipsometry (SE) is a non-invasive optical probe that is capable of accurately and precisely measuring the structure of thin films, such as their thicknesses and void volume fractions, and in addition their optical properties, typically defined by the index of refraction and extinction coefficient spectra. Because multichannel detection systems integrated into SE instrumentation have been available for some time now, the data acquisition time possible for complete SE spectra has been reduced significantly. As a result, real time spectroscopic ellipsometry (RTSE) has become feasible for monitoring thin film nucleation and growth during the deposition of thin films as well as during their removal in processes of thin film etching. Also because of the reduced acquisition time, mapping SE is possible by mounting an SE instrument with a multichannel detector onto a mechanical translation stage. Such an SE system is capable of mapping the thin film structure and its optical properties over the substrate area, and thereby evaluating the spatial uniformity of the component layers. In thin film photovoltaics, such structural and optical property measurements mapped over the substrate area can be applied to guide device optimization by correlating small area device performance with the associated local properties. In this thesis, a detailed ex-situ SE study of hydrogenated amorphous silicon (a-Si:H) thin films and solar cells prepared by plasma enhanced chemical vapor deposition (PECVD) has been presented. An SE analysis procedure with step-by-step error minimization has been applied to obtain accurate measures of the structural and optical properties of the component layers of the solar cells. Growth evolution diagrams were developed as functions of the deposition parameters in PECVD for both p-type and n-type layers to characterize the regimes of accumulated thickness over which a-Si:H, hydrogenated nanocrystalline silicon (nc-Si:H) and mixed phase (a+nc)-Si:H thin films are obtained. The underlying materials for these depositions were newly-deposited intrinsic a-Si:H layers on thermal oxide coated crystalline silicon wafers, designed to simulate specific device configurations. As a result, these growth evolution diagrams can be applied to both p-i-n and n-i-p solar cell optimization. In this thesis, the n-layer growth evolution diagram expressed in terms of hydrogen dilution ratio was applied in correlations with the performance of p-i-n single junction devices in order to optimize these devices. Moreover, ex-situ mapping SE was also employed over the area of multilayer structures in order to achieve better statistics for solar cell optimization by correlating structural parameters locally with small area solar cell performance parameters. In the study of (a-Si:H p-i-n)/(nc-Si:H p-i-n) tandem solar cells, RTSE was successfully applied to monitor the fabrication of the top cell, and efforts to optimize the nanocrystalline p-layer and i-layer of the bottom cell were initiated.

Electrically driven hybrid Si/III-V Fabry-Pérot lasers based on adiabatic mode transformers.

PubMed

Ben Bakir, B; Descos, A; Olivier, N; Bordel, D; Grosse, P; Augendre, E; Fulbert, L; Fedeli, J M

2011-05-23

We report the first demonstration of an electrically driven hybrid silicon/III-V laser based on adiabatic mode transformers. The hybrid structure is formed by two vertically superimposed waveguides separated by a 100-nm-thick SiO2 layer. The top waveguide, fabricated in an InP/InGaAsP-based heterostructure, serves to provide optical gain. The bottom Si-waveguides system, which supports all optical functions, is constituted by two tapered rib-waveguides (mode transformers), two distributed Bragg reflectors (DBRs) and a surface-grating coupler. The supermodes of this hybrid structure are controlled by an appropriate design of the tapers located at the edges of the gain region. In the middle part of the device almost all the field resides in the III-V waveguide so that the optical mode experiences maximal gain, while in regions near the III-V facets, mode transformers ensure an efficient transfer of the power flow towards Si-waveguides. The investigated device operates under quasi-continuous wave regime. The room temperature threshold current is 100 mA, the side-mode suppression ratio is as high as 20 dB, and the fiber-coupled output power is ~7 mW.

Planar location of the simulative acoustic source based on fiber optic sensor array

NASA Astrophysics Data System (ADS)

Liang, Yi-Jun; Liu, Jun-feng; Zhang, Qiao-ping; Mu, Lin-lin

2010-06-01

A fiber optic sensor array which is structured by four Sagnac fiber optic sensors is proposed to detect and locate a simulative source of acoustic emission (AE). The sensing loops of Sagnac interferometer (SI) are regarded as point sensors as their small size. Based on the derived output light intensity expression of SI, the optimum work condition of the Sagnac fiber optic sensor is discussed through the simulation of MATLAB. Four sensors are respectively placed on a steel plate to structure the sensor array and the location algorithms are expatiated. When an impact is generated by an artificial AE source at any position of the plate, the AE signal will be detected by four sensors at different times. With the help of a single chip microcomputer (SCM) which can calculate the position of the AE source and display it on LED, we have implemented an intelligent detection and location.

Highly conducting and wide band gap phosphorous doped nc-Si–QD/a-SiC films as n-type window layers for solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kar, Debjit; Das, Debajyoti, E-mail: erdd@iacs.res.in

2016-05-23

Nano-crystalline silicon quantum dots (Si-QDs) embedded in the phosphorous doped amorphous silicon carbide (a-SiC) matrix has been successfully prepared at a low temperature (300 °C) by inductively coupled plasma assisted chemical vapor deposition (ICP-CVD) system from (SiH{sub 4} + CH{sub 4})-plasma with PH{sub 3} as the doping gas. The effect of PH{sub 3} flow rate on structural, optical and electrical properties of the films has been studied. Phosphorous doped nc-Si–QD/a-SiC films with high optical band gap (>1.9 eV) and superior conductivity (~10{sup −2} S cm{sup −1}) are obtained, which could be appropriately used as n-type window layers for nc-Si solarmore » cells in n-i-p configuration.« less

Growth of boron doped hydrogenated nanocrystalline cubic silicon carbide (3C-SiC) films by Hot Wire-CVD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pawbake, Amit; Tata Institute of Fundamental Research, Colaba, Mumbai 400 005; Mayabadi, Azam

Highlights: • Boron doped nc-3C-SiC films prepared by HW-CVD using SiH{sub 4}/CH{sub 4}/B{sub 2}H{sub 6}. • 3C-Si-C films have preferred orientation in (1 1 1) direction. • Introduction of boron into SiC matrix retard the crystallanity in the film structure. • Film large number of SiC nanocrystallites embedded in the a-Si matrix. • Band gap values, E{sub Tauc} and E{sub 04} (E{sub 04} > E{sub Tauc}) decreases with increase in B{sub 2}H{sub 6} flow rate. - Abstract: Boron doped nanocrystalline cubic silicon carbide (3C-SiC) films have been prepared by HW-CVD using silane (SiH{sub 4})/methane (CH{sub 4})/diborane (B{sub 2}H{sub 6}) gasmore » mixture. The influence of boron doping on structural, optical, morphological and electrical properties have been investigated. The formation of 3C-SiC films have been confirmed by low angle XRD, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FTIR) spectroscopy and high resolution-transmission electron microscopy (HR-TEM) analysis whereas effective boron doping in nc-3C-SiC have been confirmed by conductivity, charge carrier activation energy, and Hall measurements. Raman spectroscopy and HR-TEM analysis revealed that introduction of boron into the SiC matrix retards the crystallanity in the film structure. The field emission scanning electron microscopy (FE-SEM) and non contact atomic force microscopy (NC-AFM) results signify that 3C-SiC film contain well resolved, large number of silicon carbide (SiC) nanocrystallites embedded in the a-Si matrix having rms surface roughness ∼1.64 nm. Hydrogen content in doped films are found smaller than that of un-doped films. Optical band gap values, E{sub Tauc} and E{sub 04} decreases with increase in B{sub 2}H{sub 6} flow rate.« less

Phosphorus Doping in Si Nanocrystals/SiO2 msultilayers and Light Emission with Wavelength compatible for Optical Telecommunication

PubMed Central

Lu, Peng; Mu, Weiwei; Xu, Jun; Zhang, Xiaowei; Zhang, Wenping; Li, Wei; Xu, Ling; Chen, Kunji

2016-01-01

Doping in semiconductors is a fundamental issue for developing high performance devices. However, the doping behavior in Si nanocrystals (Si NCs) has not been fully understood so far. In the present work, P-doped Si NCs/SiO2 multilayers are fabricated. As revealed by XPS and ESR measurements, P dopants will preferentially passivate the surface states of Si NCs. Meanwhile, low temperature ESR spectra indicate that some P dopants are incorporated into Si NCs substitutionally and the incorporated P impurities increase with the P doping concentration or annealing temperature increasing. Furthermore, a kind of defect states will be generated with high doping concentration or annealing temperature due to the damage of Si crystalline lattice. More interestingly, the incorporated P dopants can generate deep levels in the ultra-small sized (~2 nm) Si NCs, which will cause a new subband light emission with the wavelength compatible with the requirement of the optical telecommunication. The studies of P-doped Si NCs/SiO2 multilayers suggest that P doping plays an important role in the electronic structures and optoelectronic characteristics of Si NCs. PMID:26956425

Measuring single-shot, picosecond optical damage threshold in Ge, Si, and sapphire with a 5.1-μm laser

DOE PAGES

Agustsson, R.; Pogorelsky, I.; Arab, E.; ...

2015-11-18

Optical photonic structures driven by picosecond, GW-class lasers are emerging as promising novel sources of electron beams and high quality X-rays. Due to quadratic dependence on wavelength of the laser ponderomotive potential, the performance of such sources scales very favorably towards longer drive laser wavelengths. However, to take full advantage of photonic structures at mid-IR spectral region, it is important to determine optical breakdown limits of common optical materials. To this end, an experimental study was carried out at a wavelength of 5 µm, using a frequency-doubled CO 2 laser source, with 5 ps pulse length. Single-shot optical breakdowns weremore » detected and characterized at different laser intensities, and damage threshold values of 0.2, 0.3, and 7.0 J/cm 2, were established for Ge, Si, and sapphire, respectively. As a result, the measured damage threshold values were stable and repeatable within individual data sets, and across varying experimental conditions.« less

Measuring single-shot, picosecond optical damage threshold in Ge, Si, and sapphire with a 5.1-μm laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agustsson, R.; Pogorelsky, I.; Arab, E.

Optical photonic structures driven by picosecond, GW-class lasers are emerging as promising novel sources of electron beams and high quality X-rays. Due to quadratic dependence on wavelength of the laser ponderomotive potential, the performance of such sources scales very favorably towards longer drive laser wavelengths. However, to take full advantage of photonic structures at mid-IR spectral region, it is important to determine optical breakdown limits of common optical materials. To this end, an experimental study was carried out at a wavelength of 5 µm, using a frequency-doubled CO 2 laser source, with 5 ps pulse length. Single-shot optical breakdowns weremore » detected and characterized at different laser intensities, and damage threshold values of 0.2, 0.3, and 7.0 J/cm 2, were established for Ge, Si, and sapphire, respectively. As a result, the measured damage threshold values were stable and repeatable within individual data sets, and across varying experimental conditions.« less

Structural and optical characteristics of GaAs films grown on Si/Ge substrates

NASA Astrophysics Data System (ADS)

Rykov, A. V.; Dorokhin, M. V.; Vergeles, P. S.; Baidus, N. V.; Kovalskiy, V. A.; Yakimov, E. B.; Soltanovich, O. A.

2018-03-01

A GaAs/AlAs heterostructure and a GaAs film grown on Si/Ge substrates have been fabricated and studied. A Ge buffer on a silicon substrate was fabricated using the MBE process. A3B5 films were grown by MOCVD at low pressures. Photoluminescence spectroscopy was used to define the optical quality of A3B5 films. Structural properties were investigated using the electron beam induced current method. It was established that despite a rather high density of dislocations on the epitaxial layers, the detected photoluminescence radiation of layers indicates the acceptable crystalline quality of the top GaAs layer.

An Overview of Integration and Test of the James Webb Space Telescope Integrated Science Instrument Module

NASA Technical Reports Server (NTRS)

Drury, Michael; Becker, Neil; Bos, Brent; Davila, Pamela; Frey, Bradley; Hylan, Jason; Marsh, James; McGuffey, Douglas; Novak, Maria; Ohl, Raymond;

Deposition of undoped and Al doped ZnO thin films using RF magnetron sputtering and study of their structural, optical and electrical properties

NASA Astrophysics Data System (ADS)

Parvathy Venu, M.; Shrisha B., V.; Balakrishna, K. M.; Naik, K. Gopalakrishna

2017-05-01

Undoped ZnO and Al doped ZnO thin films were deposited on glass and p-Si(100) substrates by RF magnetron sputtering technique at room temperature using homemade targets. ZnO target containing 5 at% of Al2O3 as doping source was used for the growth of Al doped ZnO thin films. XRD revealed that the films have hexagonal wurtzite structure with high crystallinity. Morphology and chemical composition of the films have been indicated by FESEM and EDAX studies. A blue shift of the band gap energy and higher optical transmittance has been observed in the case of Al doped ZnO (ZnO:Al) thin films with respect to the ZnO thin films. The as deposited films on p-Si were used to fabricate n-ZnO/p-Si(100) and n-ZnO:Al/p-Si(100) heterojunction diodes and their room temperature current-voltage characteristics were studied.

Preparation of low cost n-ZnO/MgO/p-Si heterojunction photodetector by laser ablation in liquid and spray pyrolysis

NASA Astrophysics Data System (ADS)

Ismail, Raid A.; Khashan, Khawla S.; Jawad, Muslim F.; Mousa, Ali M.; Mahdi, Farah

2018-05-01

In this study, low cost ZnO/Si and ZnO/MgO/Si heterojunction (HJ) photodetectors were fabricated using laser ablation and spray Pyrolysis techniques. MgO nanofibers were synthesized by laser ablation of Mg target in distilled water. Also; the ZnO films were prepared by spray pyrolysis technique. The optical and structural properties of nanostructured MgO were investigated using XRD, SEM and FT-IR. The XRD results showed that the MgO was polycrystalline with cubic structure. SEM investigation confirmed the formation of MgO nanofibers and sub-microparticles. The optical energy gaps of MgO and ZnO were calculated and found to be 5.7 eV and 3.3 eV, respectively. For the electrical properties; responsivity, quantum efficiency, specific detectivity, and speed of response of the photodetector were measured and found to enhance after the insertion of nanostructured MgO film. The Photoresponse results at 3 V reverse bias showed that the maximum responsivity of ZnO/Si and ZnO/MgO/Si photodetectors were 185 and 331 mAW‑1 at 500 nm, respectively. The specific detectivity of ZnO/MgO/Si Photodetector was higher than that of ZnO/Si.

A Photonic 1 × 4 Power Splitter Based on Multimode Interference in Silicon–Gallium-Nitride Slot Waveguide Structures

PubMed Central

Malka, Dror; Danan, Yossef; Ramon, Yehonatan; Zalevsky, Zeev

2016-01-01

In this paper, a design for a 1 × 4 optical power splitter based on the multimode interference (MMI) coupler in a silicon (Si)–gallium nitride (GaN) slot waveguide structure is presented—to our knowledge, for the first time. Si and GaN were found as suitable materials for the slot waveguide structure. Numerical optimizations were carried out on the device parameters using the full vectorial-beam propagation method (FV-BPM). Simulation results show that the proposed device can be useful to divide optical signal energy uniformly in the C-band range (1530–1565 nm) into four output ports with low insertion losses (0.07 dB). PMID:28773638

Optoelectronics Research Center

DTIC Science & Technology

1992-05-16

dot structures in Si and related materials. External cavity operation of diode lasers has provided a wealth of information on internal device physics...new class of optical information processing. A major feature of the AFOSR OERC has been interactions with the Air Force Phillips Laboratory and with...structures in Si and related materials. External cavity operation of diode lasers has provided a wealth of information on internal device physics and

Optical characteristics of sol-gel derived M3SiO5:Eu3+ (M = Sr, Ca and Mg) nanophosphors for display device technology

NASA Astrophysics Data System (ADS)

Singh, Devender; Sheoran, Suman; Bhagwan, Shri; Kadyan, Sonika

2016-12-01

A series of trivalent europium-doped M3SiO5 (M = Sr, Ca and Mg) phosphors were synthesized using sol-gel process at 950°C. Samples were further reheated at high temperature to study the effect of reheating on crystal structure and optical characteristics. X-ray diffraction measurement of these materials was carried out to know the crystal structure. Diffraction pattern showed monoclinic structure having space group Cm for Ca3SiO5 materials. However, tetragonal phase with space group P4/ncc was observed for Sr3SiO5 materials. Mg3SiO5 material show mixed diffraction peaks at 950 and 1,150°C. Transmission electron microscopic analysis was used to estimate the particle size of silicates. Photoluminescence emission spectra were recorded to check the luminescence properties of prepared materials. These phosphors exhibited a strong orange-red light under excitation at 395 nm. The prepared phosphors exhibited most intense peak in 610-620 nm region due to the 5D0→7F2 transition of europium (III) ion available in lattice. To overcome the deficiency of red silicates, M3SiO5 materials were explored and they might be integrated with ultraviolet LEDs to generate light which may be suitable for display applications.

All-optical coherent population trapping with defect spin ensembles in silicon carbide.

PubMed

Zwier, Olger V; O'Shea, Danny; Onur, Alexander R; van der Wal, Caspar H

2015-06-05

Divacancy defects in silicon carbide have long-lived electronic spin states and sharp optical transitions. Because of the various polytypes of SiC, hundreds of unique divacancies exist, many with spin properties comparable to the nitrogen-vacancy center in diamond. If ensembles of such spins can be all-optically manipulated, they make compelling candidate systems for quantum-enhanced memory, communication, and sensing applications. We report here direct all-optical addressing of basal plane-oriented divacancy spins in 4H-SiC. By means of magneto-spectroscopy, we fully identify the spin triplet structure of both the ground and the excited state, and use this for tuning of transition dipole moments between particular spin levels. We also identify a role for relaxation via intersystem crossing. Building on these results, we demonstrate coherent population trapping -a key effect for quantum state transfer between spins and photons- for divacancy sub-ensembles along particular crystal axes. These results, combined with the flexibility of SiC polytypes and device processing, put SiC at the forefront of quantum information science in the solid state.

Combining experiment and optical simulation in coherent X-ray nanobeam characterization of Si/SiGe semiconductor heterostructures

DOE PAGES

Tilka, J. A.; Park, J.; Ahn, Y.; ...

2016-07-06

Here, the highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale characterization of the structure of electronic materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. X-ray nanobeams exhibit optical coherence combined with a large angular divergence introduced by the x-ray focusing optics. The scattering of nanofocused x-ray beams from intricate semiconductor heterostructures produces a complex distribution of scattered intensity. We report here an extension of coherent xray optical simulations of convergent x-ray beam diffraction patterns to arbitrary x-ray incident angles to allow the nanobeam diffraction patternsmore » of complex heterostructures to be simulated faithfully. These methods are used to extract the misorientation of lattice planes and the strain of individual layers from synchrotron x-ray nanobeam diffraction patterns of Si/SiGe heterostructures relevant to applications in quantum electronic devices. The systematic interpretation of nanobeam diffraction patterns from semiconductor heterostructures presents a new opportunity in characterizing and ultimately designing electronic materials.« less

Effect of Aluminum on Characterization of ZnTe/n-Si Heterojunction Photo detector

NASA Astrophysics Data System (ADS)

Maki, Samir A.; Hassun, Hanan K.

2018-05-01

Aluminum doped zinc telluride ZnTenSi thin films of (400nm) thickness with (005 01 015 and 02) wt % were deposited on the glass substrate and nSi wafer to fabricate ZnTenSi heterojunction Photodetector by using thermal vacuum evaporation technique Structural optical electrical and photovoltaic properties are investigated for the samples XRD analysis shows that all the deposited ZnTenSi films show polycrystalline structure with cubic phases and highest sharp peak corresponding to (111) planes and from AFM images shows the surface roughness increase with increase Al percentage ratio The optical absorption measurement of the films was find from transmittance ranges in the variety of wavelength (400 1000) nm and the optical energy band gap decrease from 224 eV to 186 eV dependent upon the Aluminum ratio in the films moreover our studies contain the calculation of the electrical properties of hetero junction were obtained via IV (dark and light condition) and C V measurement The photoelectric properties indicated rise illumination current of heterojunctions through increasing both of incident lighting intensity and Aluminum dopant The values of specific detectivity and quantum efficiency are calculated for all samples also the best spectral response occurs when Al doping ratio 02% The high photo sensitivity and comparatively fast response haste are attributable to in height crystal quality of the [ZnTe ] thin films.

Magnetic field-driven lateral photovoltaic effect in the Fe/SiO2/p-Si hybrid structure with the Schottky barrier

NASA Astrophysics Data System (ADS)

Volkov, N. V.; Rautskii, M. V.; Tarasov, A. S.; Yakovlev, I. A.; Bondarev, I. A.; Lukyanenko, A. V.; Varnakov, S. N.; Ovchinnikov, S. G.

2018-07-01

We demonstrate that the lateral photovoltaic effect in the Fe/SiO2/p-Si structure not only strongly depends on the optical radiation wavelength and temperature, but is also sensitive to external magnetic fields. The magnetic field lowers the absolute value of photovoltage regardless of the wavelength and temperature; however, the relative photovoltage variation significantly depends on these parameters. The lateral photovoltage is observed both on the Fe film and Si substrate sides and results from separation of photoinduced electrons and holes in a built-in electric field of the Schottky barrier with their subsequent diffusion to the structure in the lateral direction from the illuminated area. The observed features in the behavior of the lateral photovoltaic effect originate from the variation in the light absorption coefficient of the semiconductor and the related quantum efficiency upon light wavelength variation. In addition, an important role is played by the change in the characteristics of the Schottky barrier at the redistribution of optically generated carriers and temperature variation. The effect of the magnetic field is attributed to the Lorentz force, which bends trajectories of carriers drifting under the action of the Schottky barrier field and, consequently, suppresses the lateral photovoltaic effect.

Structural and optical properties of silicon-carbide nanowires produced by the high-temperature carbonization of silicon nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavlikov, A. V., E-mail: pavlikov@physics.msu.ru; Latukhina, N. V.; Chepurnov, V. I.

Silicon-carbide (SiC) nanowire structures 40–50 nm in diameter are produced by the high-temperature carbonization of porous silicon and silicon nanowires. The SiC nanowires are studied by scanning electron microscopy, X-ray diffraction analysis, Raman spectroscopy, and infrared reflectance spectroscopy. The X-ray structural and Raman data suggest that the cubic 3C-SiC polytype is dominant in the samples under study. The shape of the infrared reflectance spectrum in the region of the reststrahlen band 800–900 cm{sup –1} is indicative of the presence of free charge carriers. The possibility of using SiC nanowires in microelectronic, photonic, and gas-sensing devices is discussed.

Influence of interface layer on optical properties of sub-20 nm-thick TiO2 films

NASA Astrophysics Data System (ADS)

Shi, Yue-Jie; Zhang, Rong-Jun; Li, Da-Hai; Zhan, Yi-Qiang; Lu, Hong-Liang; Jiang, An-Quan; Chen, Xin; Liu, Juan; Zheng, Yu-Xiang; Wang, Song-You; Chen, Liang-Yao

2018-02-01

The sub-20 nm ultrathin titanium dioxide (TiO2) films with tunable thickness were deposited on Si substrates by atomic layer deposition (ALD). The structural and optical properties were acquired by transmission electron microscopy, atomic force microscopy and spectroscopic ellipsometry. Afterwards, a constructive and effective method of analyzing interfaces by applying two different optical models consisting of air/TiO2/Ti x Si y O2/Si and air/effective TiO2 layer/Si, respectively, was proposed to investigate the influence of interface layer (IL) on the analysis of optical constants and the determination of band gap of TiO2 ultrathin films. It was found that two factors including optical constants and changing components of the nonstoichiometric IL could contribute to the extent of the influence. Furthermore, the investigated TiO2 ultrathin films of 600 ALD cycles were selected and then annealed at the temperature range of 400-900 °C by rapid thermal annealing. Thicker IL and phase transition cause the variation of optical properties of TiO2 films after annealing and a shorter electron relaxation time reveals the strengthened electron-electron and electron-phonon interactions in the TiO2 ultrathin films at high temperature. The as-obtained results in this paper will play a role in other studies of high dielectric constants materials grown on Si substrates and in the applications of next generation metal-oxide-semiconductor devices.

SIC material and technology for space optics

NASA Astrophysics Data System (ADS)

Bougoin, Michel

2017-11-01

Taking benefit from its very high specific stiffness and its exclusive thermal stability, the SiCSPACE material is now used for the fabrication of scientific and commercial lightweight space telescopes. This paper gives a review of the characteristics of this sintered silicon carbide. The BOOSTEC facilities and the technology described here allow to manufacture large structural components or mirrors (up to several meters) at cost effective condition, from a single part to mass production. Several examples of SiC space optical components are presented.

Valence and charge-transfer optical properties for some SinCm (m, n ≤ 12) clusters: Comparing TD-DFT, complete-basis-limit EOMCC, and benchmarks from spectroscopy.

PubMed

Lutz, Jesse J; Duan, Xiaofeng F; Ranasinghe, Duminda S; Jin, Yifan; Margraf, Johannes T; Perera, Ajith; Burggraf, Larry W; Bartlett, Rodney J

2018-05-07

Accurate optical characterization of the closo-Si 12 C 12 molecule is important to guide experimental efforts toward the synthesis of nano-wires, cyclic nano-arrays, and related array structures, which are anticipated to be robust and efficient exciton materials for opto-electronic devices. Working toward calibrated methods for the description of closo-Si 12 C 12 oligomers, various electronic structure approaches are evaluated for their ability to reproduce measured optical transitions of the SiC 2 , Si 2 C n (n = 1-3), and Si 3 C n (n = 1, 2) clusters reported earlier by Steglich and Maier [Astrophys. J. 801, 119 (2015)]. Complete-basis-limit equation-of-motion coupled-cluster (EOMCC) results are presented and a comparison is made between perturbative and renormalized non-iterative triples corrections. The effect of adding a renormalized correction for quadruples is also tested. Benchmark test sets derived from both measurement and high-level EOMCC calculations are then used to evaluate the performance of a variety of density functionals within the time-dependent density functional theory (TD-DFT) framework. The best-performing functionals are subsequently applied to predict valence TD-DFT excitation energies for the lowest-energy isomers of Si n C and Si n-1 C 7-n (n = 4-6). TD-DFT approaches are then applied to the Si n C n (n = 4-12) clusters and unique spectroscopic signatures of closo-Si 12 C 12 are discussed. Finally, various long-range corrected density functionals, including those from the CAM-QTP family, are applied to a charge-transfer excitation in a cyclic (Si 4 C 4 ) 4 oligomer. Approaches for gauging the extent of charge-transfer character are also tested and EOMCC results are used to benchmark functionals and make recommendations.

Enhanced Visible Transmittance of Thermochromic VO₂ Thin Films by SiO₂ Passivation Layer and Their Optical Characterization.

PubMed

Yu, Jung-Hoon; Nam, Sang-Hun; Lee, Ji Won; Boo, Jin-Hyo

2016-07-09

This paper presents the preparation of high-quality vanadium dioxide (VO₂) thermochromic thin films with enhanced visible transmittance (T vis ) via radio frequency (RF) sputtering and plasma enhanced chemical vapor deposition (PECVD). VO₂ thin films with high T vis and excellent optical switching efficiency (E os ) were successfully prepared by employing SiO₂ as a passivation layer. After SiO₂ deposition, the roughness of the films was decreased 2-fold and a denser structure was formed. These morphological changes corresponded to the results of optical characterization including the haze, reflectance and absorption spectra. In spite of SiO₂ coating, the phase transition temperature (T c ) of the prepared films was not affected. Compared with pristine VO₂, the total layer thickness after SiO₂ coating was 160 nm, which is an increase of 80 nm. Despite the thickness change, the VO₂ thin films showed a higher T vis value (λ 650 nm, 58%) compared with the pristine samples (λ 650 nm, 43%). This enhancement of T vis while maintaining high E os is meaningful for VO₂-based smart window applications.

Broadband optical absorption by tunable Mie resonances in silicon nanocone arrays

DOE PAGES

Wang, Z. Y.; Zhang, R. J.; Wang, S. Y.; ...

2015-01-15

Nanostructure arrays such as nanowire, nanopillar, and nanocone arrays have been proposed to be promising antireflection structures for photovoltaic applications due to their great light trapping ability. In this paper, the optical properties of Si nanopillar and nanocone arrays in visible and infrared region were studied by both theoretical calculations and experiments. The results show that the Mie resonance can be continuously tuned across a wide range of wavelength by varying the diameter of the nanopillars. However, Si nanopillar array with uniform diameter exhibits only discrete resonance mode, thus can't achieve a high broadband absorption. On the other hand, themore » Mie resonance wavelength in a Si nanocone array can vary continuously as the diameters of the cross sections increase from the apex to the base. Therefore Si nanocone arrays can strongly interact with the incident light in the broadband spectrum and the absorbance by Si nanocone arrays is higher than 95% over the wavelength from 300 to 2000 nm. In addition to the Mie resonance, the broadband optical absorption of Si nanocone arrays is also affected by Wood-Rayleigh anomaly effect and metal impurities introduced in the fabrication process.« less

Broadband optical absorption by tunable Mie resonances in silicon nanocone arrays

PubMed Central

Wang, Z. Y.; Zhang, R. J.; Wang, S. Y.; Lu, M.; Chen, X.; Zheng, Y. X.; Chen, L. Y.; Ye, Z.; Wang, C. Z.; Ho, K. M.

2015-01-01

Nanostructure arrays such as nanowire, nanopillar, and nanocone arrays have been proposed to be promising antireflection structures for photovoltaic applications due to their great light trapping ability. In this paper, the optical properties of Si nanopillar and nanocone arrays in visible and infrared region were studied by both theoretical calculations and experiments. The results show that the Mie resonance can be continuously tuned across a wide range of wavelength by varying the diameter of the nanopillars. However, Si nanopillar array with uniform diameter exhibits only discrete resonance mode, thus can't achieve a high broadband absorption. On the other hand, the Mie resonance wavelength in a Si nanocone array can vary continuously as the diameters of the cross sections increase from the apex to the base. Therefore Si nanocone arrays can strongly interact with the incident light in the broadband spectrum and the absorbance by Si nanocone arrays is higher than 95% over the wavelength from 300 to 2000 nm. In addition to the Mie resonance, the broadband optical absorption of Si nanocone arrays is also affected by Wood-Rayleigh anomaly effect and metal impurities introduced in the fabrication process. PMID:25589290

Optical gradients in a-Si:H thin films detected using real-time spectroscopic ellipsometry with virtual interface analysis

NASA Astrophysics Data System (ADS)

Junda, Maxwell M.; Karki Gautam, Laxmi; Collins, Robert W.; Podraza, Nikolas J.

2018-04-01

Virtual interface analysis (VIA) is applied to real time spectroscopic ellipsometry measurements taken during the growth of hydrogenated amorphous silicon (a-Si:H) thin films using various hydrogen dilutions of precursor gases and on different substrates during plasma enhanced chemical vapor deposition. A procedure is developed for optimizing VIA model configurations by adjusting sampling depth into the film and the analyzed spectral range such that model fits with the lowest possible error function are achieved. The optimal VIA configurations are found to be different depending on hydrogen dilution, substrate composition, and instantaneous film thickness. A depth profile in the optical properties of the films is then extracted that results from a variation in an optical absorption broadening parameter in a parametric a-Si:H model as a function of film thickness during deposition. Previously identified relationships are used linking this broadening parameter to the overall shape of the optical properties. This parameter is observed to converge after about 2000-3000 Å of accumulated thickness in all layers, implying that similar order in the a-Si:H network can be reached after sufficient thicknesses. In the early stages of growth, however, significant variations in broadening resulting from substrate- and processing-induced order are detected and tracked as a function of bulk layer thickness yielding an optical property depth profile in the final film. The best results are achieved with the simplest film-on-substrate structures while limitations are identified in cases where films have been deposited on more complex substrate structures.

Study of low dimensional SiGe island on Si for potential visible Metal-Semiconductor-Metal photodetector

NASA Astrophysics Data System (ADS)

Rahim, Alhan Farhanah Abd; Zainal Badri, Nur'Amirah; Radzali, Rosfariza; Mahmood, Ainorkhilah

2017-11-01

In this paper, an investigation of design and simulation of silicon germanium (SiGe) islands on silicon (Si) was presented for potential visible metal semiconductor metal (MSM) photodetector. The characterization of the performances in term of the structural, optical and electrical properties of the structures was analyzed from the simulation results. The project involves simulation using SILVACO Technology Computer Aided Design (TCAD) tools. The different structures of the silicon germanium (SiGe) island on silicon substrate were created, which were large SiGe, small SiGe, combination SiGe and bulk Ge. All the structures were tested for potential Metal Semiconductor Metal (MSM) photodetector. The extracted data such as current versus voltage characteristic, current gain and spectral response were obtained using ATLAS SILVACO tools. The performance of SiGe island structures and bulk Ge on Si substrate as (MSM) photodetector was evaluated by photo and dark current-voltage (I-V) characteristics. It was found that SiGe islands exhibited higher energy band gap compared to bulk Ge. The SiGe islands current-voltage characteristics showed improved current gain compared to bulk Ge. Specifically the enhancement of the islands gain was contributed by the enhanced photo currents and lower dark currents. The spectral responses of the SiGe islands showed peak response at 590 nm (yellow) which is at the visible wavelength. This shows the feasibility of the SiGe islands to be utilized for visible photodetections.

Ion beam figuring of CVD silicon carbide mirrors

NASA Astrophysics Data System (ADS)

Gailly, P.; Collette, J.-P.; Fleury Frenette, K.; Jamar, C.

2017-11-01

Optical and structural elements made of silicon carbide are increasingly found in space instruments. Chemical vapor deposited silicon carbide (CVD-SiC) is used as a reflective coating on SiC optics in reason of its good behavior under polishing. The advantage of applying ion beam figuring (IBF) to CVD-SiC over other surface figure-improving techniques is discussed herein. The results of an IBF sequence performed at the Centre Spatial de Liège on a 100 mm CVD-SiC mirror are reported. The process allowed to reduce the mirror surface errors from 243 nm to 13 nm rms . Beside the surface figure, roughness is another critical feature to consider in order to preserve the optical quality of CVD-SiC . Thus, experiments focusing on the evolution of roughness were performed in various ion beam etching conditions. The roughness of samples etched at different depths down to 3 ≠m was determined with an optical profilometer. These measurements emphasize the importance of selecting the right combination of gas and beam energy to keep roughness at a low level. Kaufman-type ion sources are generally used to perform IBF but the performance of an end-Hall ion source in figuring CVD-SiC mirrors was also evaluated in this study. In order to do so, ion beam etching profiles obtained with the end-Hall source on CVD-SiC were measured and used as a basis for IBF simulations.

A molded surface-micromachining and bulk etching release (MOSBE) fabrication platform on (1 1 1) Si for MOEMS

NASA Astrophysics Data System (ADS)

Wu, Mingching; Fang, Weileun

2006-02-01

This work attempts to integrate poly-Si thin film and single-crystal-silicon (SCS) structures in a monolithic process. The process integrated multi-depth DRIE (deep reactive ion etching), trench-refilled molding, a two poly-Si MUMPs process and (1 1 1) Si bulk micromachining to accomplish multi-thickness and multi-depth structures for superior micro-optical devices. In application, a SCS scanning mirror driven by self-aligned vertical comb-drive actuators was demonstrated. The stiffness of the mirror was significantly increased by thick SCS structures. The thin poly-Si film served as flexible torsional springs and electrical routings. The depth difference of the vertical comb electrodes was tuned by DRIE to increase the devices' stroke. Finally, a large moving space was available after the bulk Si etching. In summary, the present fabrication process, named (1 1 1) MOSBE (molded surface-micromachining and bulk etching release on (1 1 1) Si substrate), can further integrate with the MUMPs devices to establish a more powerful platform.

Opto-electronic properties of P-doped nc-Si–QD/a-SiC:H thin films as foundation layer for all-Si solar cells in superstrate configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kar, Debjit; Das, Debajyoti, E-mail: erdd@iacs.res.in

2016-07-14

With the advent of nc-Si solar cells having improved stability, the efficient growth of nc-Si i-layer of the top cell of an efficient all-Si solar cell in the superstrate configuration prefers nc-Si n-layer as its substrate. Accordingly, a wide band gap and high conducting nc-Si alloy material is a basic requirement at the n-layer. Present investigation deals with the development of phosphorous doped n-type nanocrystalline silicon quantum dots embedded in hydrogenated amorphous silicon carbide (nc-Si–QD/a-SiC:H) hetero-structure films, wherein the optical band gap can be widened by the presence of Si–C bonds in the amorphous matrix and the embedded high densitymore » tiny nc-Si–QDs could provide high electrical conductivity, particularly in P-doped condition. The nc-Si–QDs simultaneously facilitate further widening of the optical band gap by virtue of the associated quantum confinement effect. A complete investigation has been made on the electrical transport phenomena involving charge transfer by tunneling and thermionic emission prevailing in n-type nc-Si–QD/a-SiC:H thin films. Their correlation with different phases of the specific heterostructure has been carried out for detailed understanding of the material, in order to improve its device applicability. The n-type nc-Si–QD/a-SiC:H films exhibit a thermally activated electrical transport above room temperature and multi-phonon hopping (MPH) below room temperature, involving defects in the amorphous phase and the grain-boundary region. The n-type nc-Si–QD/a-SiC:H films grown at ∼300 °C, demonstrating wide optical gap ∼1.86–1.96 eV and corresponding high electrical conductivity ∼4.5 × 10{sup −1}–1.4 × 10{sup −2} S cm{sup −1}, deserve to be an effective foundation layer for the top nc-Si sub-cell of all-Si solar cells in n-i-p structure with superstrate configuration.« less

Physical, structural and optical characterizations of borate modified bismuth-silicate-tellurite glasses

NASA Astrophysics Data System (ADS)

Berwal, Neelam; Kundu, R. S.; Nanda, Kirti; Punia, R.; Kishore, N.

2015-10-01

Quaternary bismuthate glasses with compositions xB2O3-(80 - x) Bi2O3-15SiO2-5TeO2 have been prepared by melt-quench technique. X-ray diffraction studies were performed to ascertain the amorphous nature of samples. The density, molar volume and crystalline volume decrease with increase in B2O3 content whereas the glass transition temperature shows the reverse trend. The Raman and FTIR spectra of the studied glasses indicate that B2O3 has been found to exist in the form of BO3 trigonal and BO4 tetrahedral structural units and vibrations corresponding to these structural units increase with increase in B2O3 content. SiO2 is present in the form of SiO4 tetrahedral structural units and TeO2 in the form of TeO3 structural units. Bismuth plays the role of network modifier [BiO6 octahedra] as well as network former [BiO3 pyramids] for all the glass compositions. The optical band gap energy has been calculated from the fitting of both Mott and Davis's model and Hydrogenic excitonic model with the experimentally observed absorption spectra. A good fitting of experimental data with HEM indicates the excitonic formation in the studies glass system. The values of optical band gap energy show nonlinear behavior due to the structural changes that take place in the present glass samples. The Urbach energy calculated using Urbach empirical formula for studied glass samples suggest the possibility of reduction in defect concentrations. The metallization criterion of the presently studied samples suggests that the prepared glasses may be potential candidates for nonlinear optical applications.

Multipulse nanosecond laser irradiation of silicon for the investigation of surface morphology and photoelectric properties

NASA Astrophysics Data System (ADS)

Sardar, Maryam; Chen, Jun; Ullah, Zaka; Jelani, Mohsan; Tabassum, Aasma; Cheng, Ju; Sun, Yuxiang; Lu, Jian

2017-12-01

We irradiate the single crystal boron-doped silicon (Si) with different number of laser pulses at constant fluence (7.5 J cm-2) in ambient air using Nd:YAG laser and examine its surface morphology and photoelectric properties in details. The results obtained from optical micrographs reveal the increase in heat affected zone (HAZ) and melted area of laser irradiated Si with increasing number of laser pulses. The SEM micrographs evidence the formation of various surface morphologies like laser induced periodic surface structures, crater, microcracks, clusters, cavities, pores, trapped bubbles, nucleation sites, micro-bumps, redeposited material and micro- and nano-particles on the surface of irradiated Si. The surface profilometry analysis informs that the depth of crater is increased with increase in number of incident laser pulses. The spectroscopic ellipsometry reveals that the multipulse irradiation of Si changes its optical properties (refractive index and extinction coefficient). The current-voltage (I-V) characteristic curves of laser irradiated Si show that although the multipulse laser irradiation produces considerable number of surface defects and damages, the electrical properties of Si are well sustained after the multipulse irradiation. The current findings suggest that the multipulse irradiation can be an effective way to tune the optical properties of Si for the fabrication of wide range of optoelectronic devices.

Magnetic and optical properties of carbon and silicon decorated free standing buckled germanene: A DFT approach

NASA Astrophysics Data System (ADS)

Dhar, Namrata; Jana, Debnarayan

2018-04-01

Ab initio magnetic and optical properties of group IV elements (carbon (C) and silicon (Si)) decorated free standing (FS) buckled germanene systems have been employed theoretically. Our study elucidates that, decoration of these elements in proper sites with suitable concentrations form dynamically stable configurations. Band structure is modified due to decoration of these atoms in Ge-nanosheet and pristine semi-metallic germanene undergoes to semiconductors with a finite amount of bandgap. Interestingly, this bandgap value meets closely the requirement of gap for field effect transistor (FET) applications. Moreover, significant magnetic moment is induced in non-magnetic germanene for C decorated structure and ground state in anti-ferromagnetic in nature for this structure. Along with magnetic property, optical properties like dielectric functions, optical absorption, electron energy loss spectra (EELS), refractive index and reflectivity of these systems have also been investigated. Maximum number of plasma frequencies appear for Si decorated configuration considering both parallel and perpendicular polarizations. In addition, birefringence characteristics of these configurations have also been studied as it is an important parameter in various applications of optical devices, liquid crystal displays, light modulators etc.

Optical Enhancement in Optoelectronic Devices Using Refractive Index Grading Layers.

PubMed

Lee, Illhwan; Park, Jae Yong; Gim, Seungo; Kim, Kisoo; Cho, Sang-Hwan; Choi, Chung Sock; Song, Seung-Yong; Lee, Jong-Lam

2016-02-10

We enhanced the optical transmittance of a multilayer barrier film by inserting a refractive index grading layer (RIGL). The result indicates that the Fresnel reflection, induced by the difference of refractive indices between Si(x)N(y) and SiO2, is reduced by the RIGL. To eliminate the Fresnel reflection while maintaining high transmittance, the optimized design of grading structures with the RIGL was conducted using an optical simulator. With the RIGL, we achieved averaged transmittance in the visible wavelength region by 89.6%. It is found that the optimized grading structure inserting the multilayer barrier film has a higher optical transmittance (89.6%) in the visible region than that of a no grading sample (82.6%). Furthermore, luminance is enhanced by 14.5% (from 10,190 to 11,670 cd m(-2) at 30 mA cm(-2)) when the grading structure is applied to organic light-emitting diodes. Finally, the results offer new opportunities in development of multilayer barrier films, which assist industrialization of very cost-effective flexible organic electronic devices.

Effect of the tetrahedral groups on the optical properties of LaBRO{sub 5} (R = Si and Ge): A first-principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Linping; School of Physics Science and Technology, Xinjiang University, Urumqi 830046; Jing, Qun

2015-09-21

As potential candidates for deep-UV nonlinear optical (NLO) crystals, borosilicates and borogermanates, which contain NLO-active groups such as B-O, Si-O, and Ge-O groups, have fascinated many material scientists' research enthusiasm. In this paper, the electronic structures and optical properties of two isostructural noncentrosymmetric crystals LaBRO{sub 5} (R = Si and Ge) have been studied by the first-principles method. Combined with the analyses of the SHG-density and the localized electron-density difference, contributions of the constituent tetrahedra to the total NLO responses are investigated. Eventually, BO{sub 4} and GeO{sub 4} groups give nearly equal contributions to the SHG effect of LaBGeO{sub 5}, but formore » LaBSiO{sub 5}, SiO{sub 4} groups express stronger SHG response than that of BO{sub 4}. Such interesting conclusion is consistent with the distortion index analyses and dipole moment.« less

Optical and electrical characterization methods of plasma-induced damage in silicon nitride films

NASA Astrophysics Data System (ADS)

Kuyama, Tomohiro; Eriguchi, Koji

2018-06-01

We proposed evaluation methods of plasma-induced damage (PID) in silicon nitride (SiN) films. The formation of an oxide layer by air exposure was identified for damaged SiN films by X-ray photoelectron spectroscopy (XPS). Bruggeman’s effective medium approximation was employed for an optical model consisting of damaged and undamaged layers, which is applicable to an in-line monitoring by spectroscopic ellipsometry (SE). The optical thickness of the damaged layer — an oxidized layer — extended after plasma exposure, which was consistent with the results obtained by a diluted hydrofluoric acid (DHF) wet etching. The change in the conduction band edge of the damaged SiN films was presumed from two electrical techniques, i.e., current–voltage (I–V) measurement and time-dependent dielectric breakdown (TDDB) test with a constant voltage stress. The proposed techniques can be used for assigning the plasma-induced structural change in an SiN film widely used as an etch-protecting layer.

Optical absorption of suspended graphene based metal plasmonic grating in the visible range

NASA Astrophysics Data System (ADS)

Han, Y. X.; Chen, B. B.; Yang, J. B.; He, X.; Huang, J.; Zhang, J. J.; Zhang, Z. J.

2018-05-01

We employ finite-difference time-domain ( FDTD) method and Raman spectroscopy to study the properties of graphene, which is suspended on a gold/SiO2/Si grating structure with different trench depth of SiO2 layer. The absorption enhancement of suspended graphene and plasmonic resonance of metal grating are investigated in the visible range using 2D FDTD method. Moreover, it is found that the intensity of the Raman features depends very sensitively on the trench depth of SiO2 layer. Raman enhancement in our experiments is attributed to the enhanced optical absorption of graphene by near-field coupling based metal plasmonic grating. The enhanced absorption of suspended graphene modulated by localized surface plasmon resonance (LSPR) offers a potential application for opto-electromechanical devices.

Extreme IR absorption in group IV-SiGeSn core-shell nanowires

NASA Astrophysics Data System (ADS)

Attiaoui, Anis; Wirth, Stephan; Blanchard-Dionne, André-Pierre; Meunier, Michel; Hartmann, J. M.; Buca, Dan; Moutanabbir, Oussama

2018-06-01

Sn-containing Si and Ge (Ge1-y-xSixSny) alloys are an emerging family of semiconductors with the potential to impact group IV material-based devices. These semiconductors provide the ability to independently engineer both the lattice parameter and bandgap, which holds the premise to develop enhanced or novel photonic and electronic devices. With this perspective, we present detailed investigations of the influence of Ge1-y-xSixSny layers on the optical properties of Si and Ge based heterostructures and nanowires. We found that by adding a thin Ge1-y-xSixSny capping layer on Si or Ge greatly enhances light absorption especially in the near infrared range, leading to an increase in short-circuit current density. For the Ge1-y-xSixSny structure at thicknesses below 30 nm, a 14-fold increase in the short-circuit current is observed with respect to bare Si. This enhancement decreases by reducing the capping layer thickness. Conversely, decreasing the shell thickness was found to improve the short-circuit current in Si/Ge1-y-xSixSny and Ge/Ge1-y-xSixSny core/shell nanowires. The optical absorption becomes very important by increasing the Sn content. Moreover, by exploiting an optical antenna effect, these nanowires show extreme light absorption, reaching an enhancement factor, with respect to Si or Ge nanowires, on the order of 104 in Si/Ge0.84Si0.04Sn0.12 and 12 in Ge/Ge0.84Si0.04Sn0.12. Furthermore, we analyzed the optical response after the addition of a dielectric layer of Si3N4 to the Si/Ge1-y-xSixSny core-shell nanowire and found approximatively a 50% increase in the short-circuit current density for a dielectric layer of thickness equal to 45 nm and both a core radius and a shell thickness greater than 40 nm. The core-shell optical antenna benefits from a multiplication of enhancements contributed by leaky mode resonances in the semiconductor part and antireflection effects in the dielectric part.

Near-Infrared and Optical Beam Steering and Frequency Splitting in Air-Holes-in-Silicon Inverse Photonic Crystals

DOE PAGES

Tasolamprou, Anna C.; Koschny, Thomas; Kafesaki, Maria; ...

2017-09-28

Here, we present the design of a dielectric inverse photonic crystal structure that couples line-defect waveguide propagating modes into highly directional beams of controllable directionality. The structure utilizes a triangular lattice made of air holes drilled in an infinitely thick Si slab, and it is designed for operation in the near-infrared and optical regime. The structure operation is based on the excitation and manipulation of dark dielectric surface states, in particular on the tailoring of the dark states’ coupling to outgoing radiation. This coupling is achieved with the use of properly designed external corrugations. The structure adapts and matches modesmore » that travel through the photonic crystal and the free space. Moreover it facilitates the steering of the outgoing waves, is found to generate well-defined, spatially and spectrally isolated beams, and may serve as a frequency splitting component designed for operation in the near-infrared regime and in particular the telecom optical wavelength band. The design complies with the state-of-the-art Si nanofabrication technology and can be directly scaled for operation in the optical regime.« less

Determination of a refractive index and an extinction coefficient of standard production of CVD-graphene.

PubMed

Ochoa-Martínez, Efraín; Gabás, Mercedes; Barrutia, Laura; Pesquera, Amaia; Centeno, Alba; Palanco, Santiago; Zurutuza, Amaia; Algora, Carlos

2015-01-28

The refractive index and extinction coefficient of chemical vapour deposition grown graphene are determined by ellipsometry analysis. Graphene films were grown on copper substrates and transferred as both monolayers and bilayers onto SiO2/Si substrates by using standard manufacturing procedures. The chemical nature and thickness of residual debris formed after the transfer process were elucidated using photoelectron spectroscopy. The real layered structure so deduced has been used instead of the nominal one as the input in the ellipsometry analysis of monolayer and bilayer graphene, transferred onto both native and thermal silicon oxide. The effect of these contamination layers on the optical properties of the stacked structure is noticeable both in the visible and the ultraviolet spectral regions, thus masking the graphene optical response. Finally, the use of heat treatment under a nitrogen atmosphere of the graphene-based stacked structures, as a method to reduce the water content of the sample, and its effect on the optical response of both graphene and the residual debris layer are presented. The Lorentz-Drude model proposed for the optical response of graphene fits fairly well the experimental ellipsometric data for all the analysed graphene-based stacked structures.

Near-Infrared and Optical Beam Steering and Frequency Splitting in Air-Holes-in-Silicon Inverse Photonic Crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tasolamprou, Anna C.; Koschny, Thomas; Kafesaki, Maria

Here, we present the design of a dielectric inverse photonic crystal structure that couples line-defect waveguide propagating modes into highly directional beams of controllable directionality. The structure utilizes a triangular lattice made of air holes drilled in an infinitely thick Si slab, and it is designed for operation in the near-infrared and optical regime. The structure operation is based on the excitation and manipulation of dark dielectric surface states, in particular on the tailoring of the dark states’ coupling to outgoing radiation. This coupling is achieved with the use of properly designed external corrugations. The structure adapts and matches modesmore » that travel through the photonic crystal and the free space. Moreover it facilitates the steering of the outgoing waves, is found to generate well-defined, spatially and spectrally isolated beams, and may serve as a frequency splitting component designed for operation in the near-infrared regime and in particular the telecom optical wavelength band. The design complies with the state-of-the-art Si nanofabrication technology and can be directly scaled for operation in the optical regime.« less

Structural and optical properties of glancing angle deposited In2O3 columnar arrays and Si/In2O3 photodetector

NASA Astrophysics Data System (ADS)

Mondal, A.; Shougaijam, B.; Goswami, T.; Dhar, J. C.; Singh, N. K.; Choudhury, S.; Chattopadhay, K. K.

2014-04-01

Ordered and perpendicular columnar arrays of In2O3 were synthesized on conducting ITO electrode by a simple glancing angle deposition (GLAD) technique. The as-deposited In2O3 columns were investigated by field emission gun-scanning electron microscope (FEG-SEM). The average length and diameter of the columns were estimated ˜400 nm and ˜100 nm, respectively. The morphology of the structure was examined by transmission electron microscopy (TEM). X-ray diffraction (XRD) analysis shows the polycrystalline nature of the sample which was verified by selective area electron diffraction (SAED) analysis. The growth mechanism and optical properties of the columns were also discussed. Optical absorption shows that In2O3 columns have a high band to band transition at ˜3.75 eV. The ultraviolet and green emissions were obtained from the In2O3 columnar arrays. The P-N junction was formed between In2O3 and P-type Si substrate. The GLAD synthesized In2O3 film exhibits low current conduction compared to In2O3 TF. However, the Si/GLAD-In2O3 detector shows ˜1.5 times enhanced photoresponsivity than that of Si/In2O3 TF.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petkov, Valeri; Hessel, Colin M.; Ovtchinnikoff, Justine

High-energy synchrotron X-ray diffraction coupled to atomic pair distribution function analysis and computer simulations is used to determine the atomic-scale structure of silicon (Si) nanoparticles obtained by two different synthetic routes. Results show that Si nanoparticles may have significant structural differences depending on the synthesis route and surface chemistry. In this case, one method produced Si nanoparticles that are highly crystalline but surface oxidized, whereas a different method yields organic ligand-passivated nanoparticles without surface oxide but that are structurally distorted at the atomic scale. Particular structural features of the oxide-free Si nanoparticles such as average first coordination numbers, length ofmore » structural coherence, and degree of local distortions are compared to their optical properties such as photoluminescence emission energy, quantum yield, and Raman spectra. A clear structure–properties correlation is observed indicating that the former may need to be taken into account when considering the latter.« less

Structural and optical properties of silicon layers with InSb and InAs nanocrystals formed by ion-beam synthesis

NASA Astrophysics Data System (ADS)

Komarov, F.; Vlasukova, L.; Greben, M.; Milchanin, O.; Zuk, J.; Wesch, W.; Wendler, E.; Togambaeva, A.

2013-07-01

We have studied the formation of InSb and InAs precipitates with sizes of several nanometers in Si and SiO2/Si by means of implantation of (Sb + In) or (As + In) ions with energies from 170 to 350 keV and fluencies from 2.8 to 3.5 × 1016 cm-2 at 500 °C and subsequent annealing at 1050-1100 °C for 3-30 min. RBS, TEM/TED, RS and PL techniques were employed to characterize the implanted layers. A broad band in the region of 1.2-1.6 μm has been registered in the low-temperature PL spectra of both (Sb + In) and (As + In) implanted and annealed silicon crystals. It was shown that structural and optical properties of oxidized silicon crystals strongly depend on type of implanted species in silicon crystals.

β-FeSi II as a Kankyo (environmentally friendly) semiconductor for solar cells in the space application

NASA Astrophysics Data System (ADS)

Makita, Yunosuke; Ootsuka, Teruhisa; Fukuzawa, Yasuhiro; Otogawa, Naotaka; Abe, Hironori; Liu, Zhengxin; Nakayama, Yasuhiko

2006-04-01

β-FeSi II defined as a Kankyo (Environmentally Friendly) semiconductor is regarded as one of the 3-rd generation semiconductors after Si and GaAs. Versatile features about β-FeSi II are, i) high optical absorption coefficient (>10 5cm -1), ii) chemical stability at temperatures as high as 937°C, iii) high thermoelectric power (Seebeck coefficient of k ~ 10 -4/K), iv) a direct energy band-gap of 0.85 eV, corresponding to 1.5μm of quartz optical fiber communication, v) lattice constant nearly well-matched to Si substrate, vi) high resistance against the humidity, chemical attacks and oxidization. Using β-FeSi II films, one can fabricate various devices such as Si photosensors, solar cells and thermoelectric generators that can be integrated basically on Si-LSI circuits. β-FeSi II has high resistance against the exposition of cosmic rays and radioactive rays owing to the large electron-empty space existing in the electron cloud pertinent to β-FeSi II. Further, the specific gravity of β-FeSi II (4.93) is placed between Si (2.33) and GaAs ((5.33). These features together with the aforementioned high optical absorption coefficient are ideal for the fabrication of solar cells to be used in the space. To demonstrate fascinating capabilities of β-FeSi II, one has to prepare high quality β-FeSi II films. We in this report summarize the current status of β-FeSi II film preparation technologies. Modified MBE and facing-target sputtering (FTS) methods are principally discussed. High quality β-FeSi II films have been formed on Si substrates by these methods. Preliminary structures of n-β-FeSi II /p-Si and p-β-FeSi II /n-Si solar cells indicated an energy conversion efficiency of 3.7%, implying that β-FeSi II is practically a promising semiconductor for a photovoltaic device.

Magneto-optical properties of cerium substituted yttrium iron garnet films with reduced thermal budget for monolithic photonic integrated circuits.

PubMed

Goto, Taichi; Onbaşlı, Mehmet C; Ross, C A

2012-12-17

Thin films of polycrystalline cerium substituted yttrium iron garnet (CeYIG) were grown on an yttrium iron garnet (YIG) seed layer on Si and Si-on-insulator substrates by pulsed laser deposition, and their optical and magneto-optical properties in the near-IR region were measured. A YIG seed layer of ~30 nm thick processed by rapid thermal anneal at 800°C provided a virtual substrate to promote crystallization of the CeYIG. The effect of the thermal budget of the YIG/CeYIG growth process on the film structure, magnetic and magnetooptical properties was determined.

Study of the composition, structure, and optical properties of a-Si{sub 1-x}C{sub x}:H Left-Pointing-Angle-Bracket Er Right-Pointing-Angle-Bracket films erbium doped from the Er(pd){sub 3} complex compound

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kudoyarova, V. Kh., E-mail: kudoyarova@mail.ioffe.ru; Tolmachev, V. A.; Gushchina, E. V.

2013-03-15

Rutherford backscattering, IR spectroscopy, ellipsometry, and atomic-force microscopy are used to perform an integrated study of the composition, structure and optical properties of a-Si{sub 1-x}C{sub x}:H Left-Pointing-Angle-Bracket Er Right-Pointing-Angle-Bracket amorphous films. The technique employed to obtain the a-Si{sub 1-x}C{sub x}:H Left-Pointing-Angle-Bracket Er Right-Pointing-Angle-Bracket amorphous films includes the high-frequency decomposition of a mixture of gases, (SiH{sub 4}){sub a} + (CH{sub 4}){sub b}, and the simultaneous thermal evaporation of a complex compound, Er(pd){sub 3}. It is demonstrated that raising the amount of CH{sub 4} in the gas mixture results in an increase in the carbon content of the films under study andmore » an increase in the optical gap E{sub g}{sup opt} from 1.75 to 2.2 eV. Changes in the composition of a-Si{sub 1-x}C{sub x}:H Left-Pointing-Angle-Bracket Er Right-Pointing-Angle-Bracket amorphous films, accompanied, in turn, by changes in the optical constants, are observed in the IR spectra. The ellipsometric spectra obtained are analyzed in terms of multiple-parameter models. The conclusion is made on the basis of this analysis that the experimental and calculated spectra coincide well when variation in the composition of the amorphous films with that of the gas mixture is taken into account. The existence of a thin (6-8 nm) silicon-oxide layer on the surface of the films under study and the validity of using the double-layer model in ellipsometric calculations is confirmed by the results of structural analyses by atomic-force microscopy.« less

Valence and charge-transfer optical properties for some SinCm (m, n ≤ 12) clusters: Comparing TD-DFT, complete-basis-limit EOMCC, and benchmarks from spectroscopy

NASA Astrophysics Data System (ADS)

Lutz, Jesse J.; Duan, Xiaofeng F.; Ranasinghe, Duminda S.; Jin, Yifan; Margraf, Johannes T.; Perera, Ajith; Burggraf, Larry W.; Bartlett, Rodney J.

2018-05-01

Accurate optical characterization of the closo-Si12C12 molecule is important to guide experimental efforts toward the synthesis of nano-wires, cyclic nano-arrays, and related array structures, which are anticipated to be robust and efficient exciton materials for opto-electronic devices. Working toward calibrated methods for the description of closo-Si12C12 oligomers, various electronic structure approaches are evaluated for their ability to reproduce measured optical transitions of the SiC2, Si2Cn (n = 1-3), and Si3Cn (n = 1, 2) clusters reported earlier by Steglich and Maier [Astrophys. J. 801, 119 (2015)]. Complete-basis-limit equation-of-motion coupled-cluster (EOMCC) results are presented and a comparison is made between perturbative and renormalized non-iterative triples corrections. The effect of adding a renormalized correction for quadruples is also tested. Benchmark test sets derived from both measurement and high-level EOMCC calculations are then used to evaluate the performance of a variety of density functionals within the time-dependent density functional theory (TD-DFT) framework. The best-performing functionals are subsequently applied to predict valence TD-DFT excitation energies for the lowest-energy isomers of SinC and Sin-1C7-n (n = 4-6). TD-DFT approaches are then applied to the SinCn (n = 4-12) clusters and unique spectroscopic signatures of closo-Si12C12 are discussed. Finally, various long-range corrected density functionals, including those from the CAM-QTP family, are applied to a charge-transfer excitation in a cyclic (Si4C4)4 oligomer. Approaches for gauging the extent of charge-transfer character are also tested and EOMCC results are used to benchmark functionals and make recommendations.

Ultrafast photocarrier dynamics related to defect states of Si1-xGex nanowires measured by optical pump-THz probe spectroscopy.

PubMed

Bae, Jung Min; Lee, Woo-Jung; Jung, Seonghoon; Ma, Jin Won; Jeong, Kwang-Sik; Oh, Seung Hoon; Kim, Seongsin M; Suh, Dongchan; Song, Woobin; Kim, Sunjung; Park, Jaehun; Cho, Mann-Ho

2017-06-14

Slightly tapered Si 1-x Ge x nanowires (NWs) (x = 0.29-0.84) were synthesized via a vapor-liquid-solid procedure using Au as a catalyst. We measured the optically excited carrier dynamics of Si 1-x Ge x NWs as a function of Ge content using optical pump-THz probe spectroscopy. The measured -ΔT/T 0 signals of Si 1-x Ge x NWs were converted into conductivity in the THz region. We developed a fitting formula to apply to indirect semiconductors such as Si 1-x Ge x , which explains the temporal population of photo-excited carriers in the band structure and the relationship between the trapping time and the defect states on an ultrafast time scale. From the fitting results, we extracted intra- and inter-valley transition times and trapping times of electrons and holes of Si 1-x Ge x NWs as a function of Ge content. On the basis of theoretical reports, we suggest a physical model to interpret the trapping times related to the species of interface defect states located at the oxide/NW: substoichiometric oxide states of Si(Ge) 0+,1+,2+ , but not Si(Ge) 3+ , could function as defect states capturing photo-excited electrons or holes and could determine the different trapping times of electrons and holes depending on negatively or neutrally charged states.

Structural, optical and Carrier dynamics of self-assembled InGaN nanocolumns on Si(111)

NASA Astrophysics Data System (ADS)

Kumar, Praveen; Devi, Pooja; Soto Rodriguez, P. E. D.; Jain, Rishabh; Jaggi, Neena; Sinha, R. K.; Kumar, Mahesh

2018-05-01

We investigated the morphological, structural, optical, electrical and carrier relaxation dynamic changes on the self-assembled grown InGaN nanocolumns (NCs) directly on p-Si(111) substrate at two different substrate temperature, namely 580 °C (A) and 500 °C (B). The emission wavelength of comparably low temperature (LT) grown NCs was red-shifted from 3.2eV to 2.4eV. First observations on the charge carrier dynamics of these directly grown NCs show comparable broad excited state absorption (ESA) for LT gown NCs, which manifest bi-exponential decay due to the radiative defects generated during the coalescence of these NCs.

Characterization and enhanced nonlinear optical limiting response in carbon nanodots dispersed in solid-state hybrid organically modified silica gel glasses

NASA Astrophysics Data System (ADS)

Huang, Li; Zheng, Chan; Guo, Qiaohang; Huang, Dongdong; Wu, Xiukai; Chen, Ling

2018-02-01

Freely dispersed carbon nanodots (CNDs) were introduced into a 3-glycidoxy-propyltrimethoxysilane modified silicate gel glass (i.e. an organically modified silica or ORMOSIL) by a highly efficient and simple sol-gel process, which could be easily extended to prepare functional molecules/nanoparticles solid state optoelectronic devices. Scanning electron microscope imaging, Fourier transform infrared spectroscopy, pore structure measurements, ultraviolet-visible spectroscopy, and fluorescence spectroscopy were used to investigate the surface characteristics, structure, texture, and linear optical properties of the CND/SiO2 ORMOSIL gel glasses. Images and UV/Vis spectra confirmed the successful dispersion of CNDs in the ORMOSIL gel glass. The surface characteristics and pore structure of the host SiO2 matrix were markedly changed through the introduction of the CNDs. The linear optical properties of the guest CNDs were also affected by the sol-gel procedure. The nonlinear optical (NLO) properties of the CNDs were investigated by a nanosecond open-aperture Z-scan technique at 532 nm both in liquid and solid matrices. We found that the NLO response of the CNDs was considerably improved after their incorporation into the ORMOSIL gel glasses. Possible enhancement mechanisms were also explored. The nonlinear extinction coefficient gradually increased while the optical limiting (OL) threshold decreased as the CND doping level was increased. This result suggests that the NLO and OL properties of the composite gel glasses can be optimized by tuning the concentration of CNDs in the gel glass matrix. Our findings show that CND/SiO2 ORMOSIL gel glasses are promising candidates for optical limiters to protect sensitive instruments and human eyes from damage caused by high power lasers.

Hybrid silicon honeycomb/organic solar cells with enhanced efficiency using surface etching.

PubMed

Liu, Ruiyuan; Sun, Teng; Liu, Jiawei; Wu, Shan; Sun, Baoquan

2016-06-24

Silicon (Si) nanostructure-based photovoltaic devices are attractive for their excellent optical and electrical performance, but show lower efficiency than their planar counterparts due to the increased surface recombination associated with the high surface area and roughness. Here, we demonstrate an efficiency enhancement for hybrid nanostructured Si/polymer solar cells based on a novel Si honeycomb (SiHC) structure using a simple etching method. SiHC structures are fabricated using a combination of nanosphere lithography and plasma treatment followed by a wet chemical post-etching. SiHC has shown superior light-trapping ability in comparison with the other Si nanostructures, along with a robust structure. Anisotropic tetramethylammonium hydroxide etching not only tunes the final surface morphologies of the nanostructures, but also reduces the surface roughness leading to a lower recombination rate in the hybrid solar cells. The suppressed recombination loss, benefiting from the reduced surface-to-volume ratio and roughness, has resulted in a high open-circuit voltage of 600 mV, a short-circuit current of 31.46 mA cm(-2) due to the light-trapping ability of the SiHCs, and yields a power conversion efficiency of 12.79% without any other device structure optimization.

Realization of GaInP/Si dual-junction solar cells with 29.8% 1-sun efficiency

DOE PAGES

Essig, Stephanie; Steiner, Myles A.; Allebe, Christophe; ...

2016-04-27

Combining a Si solar cell with a high-bandgap top cell reduces the thermalization losses in the short wavelength and enables theoretical 1-sun efficiencies far over 30%. We have investigated the fabrication and optimization of Si-based tandem solar cells with 1.8-eV rear-heterojunction GaInP top cells. The III-V and Si heterojunction subcells were fabricated separately and joined by mechanical stacking using electrically insulating optically transparent interlayers. Our GaInP/Si dual-junction solar cells have achieved a certified cumulative 1-sun efficiency of 29.8% ± 0.6% (AM1.5g) in four-terminal operation conditions, which exceeds the record 1-sun efficiencies achieved with both III-V and Si single-junction solar cells.more » Furthermore, the effect of luminescent coupling between the subcells has been investigated, and optical losses in the solar cell structure have been addressed.« less

Excellent Brightness with Shortening Lifetime of Textured Zn2SiO4:Mn2+ Phosphor Films on Quartz Glass

NASA Astrophysics Data System (ADS)

Park, Jehong; Park, Kwangwon; Lee, Jaebum; Kim, Jongsu; Kim, Seongsin Margaret; Kung, Patrick

2010-04-01

Green-emissive textured Zn2SiO4:Mn2+ phosphor films were fabricated by the thermal diffusion of ZnO:Mn on quartz glass. The Zn2SiO4:Mn2+ phosphor films became textured along several hexagonal directions and their chemical composition was continuously graded at the interface. The decay time of Mn2+ was as short as 4.4 ms, and the optical transition probability of the films defined as the inverse of decay time showed a strong correlation with film texture degree as a function of annealing temperature. The brightest Zn2SiO4:Mn2+ film showed a photoluminescent brightness as high as 65% compared with a commercial Zn2SiO4:Mn2+ phosphor powder screen and a maximum absolute transparency of 70%. These excellent optical properties are explained by the combination of the unique textured structure and continuous grading of the Zn2SiO4:Mn2+ chemical composition at the interface.

Effect of 3C-SiC intermediate layer in GaN—based light emitting diodes grown on Si(111) substrate

NASA Astrophysics Data System (ADS)

Zhu, Youhua; Wang, Meiyu; Li, Yi; Tan, Shuxin; Deng, Honghai; Guo, Xinglong; Yin, Haihong; Egawa, Takashi

2017-03-01

GaN-based light emitting diodes (LEDs) have been grown by metalorganic chemical vapor deposition on Si(111) substrate with and without 3C-SiC intermediate layer (IL). Structural property has been characterized by means of atomic force microscope, X-ray diffraction, and transmission electron microscope measurements. It has been revealed that a significant improvement in crystalline quality of GaN and superlattice epitaxial layers can be achieved by using 3C-SiC as IL. Regarding of electrical and optical characteristics, it is clearly observed that the LEDs with its IL have a smaller leakage current and higher light output power comparing with the LEDs without IL. The better performance of LEDs using 3C-SiC IL can be contributed to both of the improvements in epitaxial layers quality and light extraction efficiency. As a consequence, in terms of optical property, a double enhancement of the light output power and external quantum efficiency has been realized.

Realization of GaInP/Si dual-junction solar cells with 29.8% 1-sun efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Essig, Stephanie; Steiner, Myles A.; Allebe, Christophe

Combining a Si solar cell with a high-bandgap top cell reduces the thermalization losses in the short wavelength and enables theoretical 1-sun efficiencies far over 30%. We have investigated the fabrication and optimization of Si-based tandem solar cells with 1.8-eV rear-heterojunction GaInP top cells. The III-V and Si heterojunction subcells were fabricated separately and joined by mechanical stacking using electrically insulating optically transparent interlayers. Our GaInP/Si dual-junction solar cells have achieved a certified cumulative 1-sun efficiency of 29.8% ± 0.6% (AM1.5g) in four-terminal operation conditions, which exceeds the record 1-sun efficiencies achieved with both III-V and Si single-junction solar cells.more » Furthermore, the effect of luminescent coupling between the subcells has been investigated, and optical losses in the solar cell structure have been addressed.« less

Fabrication of 3D SiO x structures using patterned PMMA sacrificial layer

NASA Astrophysics Data System (ADS)

Li, Zhiqin; Xiang, Quan; Zheng, Mengjie; Bi, Kaixi; Chen, Yiqin; Chen, Keqiu; Duan, Huigao

2018-02-01

Three-dimensional (3D) nanofabrication based on electron-beam lithography (EBL) has drawn wide attention for various applications with its high patterning resolution and design flexibility. In this work, we present a bilayer EBL process to obtain 3D freestanding SiO x structures via the release of the bottom sacrificial layer. This new kind of bilayer process enables us to define various 3D freestanding SiO x structures with high resolution and low edge roughness. As a proof of concept for applications, metal-coated freestanding SiO x microplates with an underlying air gap were fabricated to form asymmetric Fabry-Perot resonators, which can be utilized for colorimetric refractive index sensing and thus also have application potential for biochemical detection, anti-counterfeiting and smart active nano-optical devices.

Si light-emitting device in integrated photonic CMOS ICs

NASA Astrophysics Data System (ADS)

Xu, Kaikai; Snyman, Lukas W.; Aharoni, Herzl

2017-07-01

The motivation for integrated Si optoelectronics is the creation of low-cost photonics for mass-market applications. Especially, the growing demand for sensitive biochemical sensors in the environmental control or medicine leads to the development of integrated high resolution sensors. Here CMOS-compatible Si light-emitting device structures are presented for investigating the effect of various depletion layer profiles and defect engineering on the photonic transition in the 1.4-2.8 eV. A novel Si device is proposed to realize both a two-terminal Si-diode light-emitting device and a three-terminal Si gate-controlled diode light-emitting device in the same device structure. In addition to the spectral analysis, differences between two-terminal and three-terminal devices are discussed, showing the light emission efficiency change. The proposed Si optical source may find potential applications in micro-photonic systems and micro-optoelectro-mechanical systems (MOEMS) in CMOS integrated circuitry.

Laser characterization of the depth profile of complex refractive index of PMMA implanted with 50 keV silicon ions

NASA Astrophysics Data System (ADS)

Stefanov, Ivan L.; Stoyanov, Hristiyan Y.; Petrova, Elitza; Russev, Stoyan C.; Tsutsumanova, Gichka G.; Hadjichristov, Georgi B.

2013-03-01

The depth profile of the complex refractive index of silicon ion (Si+) implanted polymethylmethacrylate (PMMA) is studied, in particular PMMA implanted with Si+ ions accelerated to a relatively low energy of 50 keV and at a fluence of 3.2 × 1015 cm-2. The ion-modified material with nano-clustered structure formed in the near(sub)surface layer of a thickness of about 100 nm is optically characterized by simulation based on reflection ellipsometry measurements at a wavelength of 632.8 nm (He-Ne laser). Being of importance for applications of ion-implanted PMMA in integrated optics, optoelectronics and optical communications, the effect of the index depth profile of Si+-implanted PMMA on the profile of the reflected laser beam due to laser-induced thermo-lensing in reflection is also analyzed upon illumination with a low power cw laser (wavelength 532 nm, optical power 10 - 50 mW).

Surface plasmon effect in electrodeposited diamond-like carbon films for photovoltaic application

NASA Astrophysics Data System (ADS)

Ghosh, B.; Ray, Sekhar C.; Espinoza-González, Rodrigo; Villarroel, Roberto; Hevia, Samuel A.; Alvarez-Vega, Pedro

2018-04-01

Diamond-like carbon (DLC) films and nanocrystalline silver particles containing diamond-like carbon (DLC:Ag) films were electrodeposited on n-type silicon substrate (n-Si) to prepare n-Si/DLC and n-Si/DLC:Ag heterostructures for photovoltaic (PV) applications. Surface plasmon resonance (SPR) effect in this cell structure and its overall performance have been studied in terms of morphology, optical absorption, current-voltage characteristics, capacitance-voltage characteristics, band diagram and external quantum efficiency measurements. Localized surface plasmon resonance effect of silver nanoparticles (Ag NPs) in n-Si/DLC:Ag PV structure exhibited an enhancement of ∼28% in short circuit current density (JSC), which improved the overall efficiency of the heterostructures.

Band-gap tuning and optical response of two-dimensional Si x C 1 - x : A first-principles real-space study of disordered two-dimensional materials

DOE PAGES

Sadhukhan, Banasree; Singh, Prashant; Nayak, Arabinda; ...

2017-08-09

We present a real-space formulation for calculating the electronic structure and optical conductivity of random alloys based on Kubo-Greenwood formalism interfaced with augmented space recursion technique formulated with the tight-binding linear muffin-tin orbital basis with the van Leeuwen–Baerends corrected exchange potential. This approach has been used to quantitatively analyze the effect of chemical disorder on the configuration averaged electronic properties and optical response of two-dimensional honeycomb siliphene Si xC 1–x beyond the usual Dirac-cone approximation. We predicted the quantitative effect of disorder on both the electronic structure and optical response over a wide energy range, and the results are discussedmore » in the light of the available experimental and other theoretical data. As a result, our proposed formalism may open up a facile way for planned band-gap engineering in optoelectronic applications.« less

Effects of boron addition on a-Si(90)Ge(10):H films obtained by low frequency plasma enhanced chemical vapour deposition.

PubMed

Pérez, Arllene M; Renero, Francisco J; Zúñiga, Carlos; Torres, Alfonso; Santiago, César

2005-06-29

Optical, structural and electric properties of (a-(Si(90)Ge(10))(1-y)B(y):H) thin film alloys, deposited by low frequency plasma enhanced chemical vapour deposition, are presented. The chemical bonding structure has been studied by IR spectroscopy, while the composition was investigated by Raman spectroscopy. A discussion about boron doping effects, in the composition and bonding of samples, is presented. Transport of carriers has been studied by measurement of the conductivity dependence on temperature, which increases from 10(-3) to 10(1) Ω(-1) cm(-1) when the boron content varies from 0 to 50%. Similarly, the activation energy is between 0.62 and 0.19 eV when the doping increases from 0 to 83%. The optical properties have been determined from the film's optical transmission, using Swanepoel's method. It is shown that the optical gap varies from 1.3 to 0.99 eV.

Band-gap tuning and optical response of two-dimensional Si x C 1 - x : A first-principles real-space study of disordered two-dimensional materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadhukhan, Banasree; Singh, Prashant; Nayak, Arabinda

We present a real-space formulation for calculating the electronic structure and optical conductivity of random alloys based on Kubo-Greenwood formalism interfaced with augmented space recursion technique formulated with the tight-binding linear muffin-tin orbital basis with the van Leeuwen–Baerends corrected exchange potential. This approach has been used to quantitatively analyze the effect of chemical disorder on the configuration averaged electronic properties and optical response of two-dimensional honeycomb siliphene Si xC 1–x beyond the usual Dirac-cone approximation. We predicted the quantitative effect of disorder on both the electronic structure and optical response over a wide energy range, and the results are discussedmore » in the light of the available experimental and other theoretical data. As a result, our proposed formalism may open up a facile way for planned band-gap engineering in optoelectronic applications.« less

First principles calculation of material properties of group IV elements and III-V compounds

NASA Astrophysics Data System (ADS)

Malone, Brad Dean

This thesis presents first principles calculations on the properties of group IV elements and group III-V compounds. It includes investigations into what structure a material is likely to form in, and given that structure, what are its electronic, optical, and lattice dynamical properties as well as what are the properties of defects that might be introduced into the sample. The thesis is divided as follows: • Chapter 1 contains some of the conceptual foundations used in the present work. These involve the major approximations which allow us to approach the problem of systems with huge numbers of interacting electrons and atomic cores. • Then, in Chapter 2, we discuss one of the major limitations to the DFT formalism introduced in Chapter 1, namely its inability to predict the quasiparticle spectra of materials and in particular the band gap of a semiconductor. We introduce a Green's function approach to the electron self-energy Sigma known as the GW approximation and use it to compute the quasiparticle band structures of a number of group IV and III-V semiconductors. • In Chapter 3 we present a first-principles study of a number of high-pressure metastable phases of Si with tetrahedral bonding. The phases studied include all experimentally determined phases that result from decompression from the metallic beta-Sn phase, specifically the BC8 (Si-III), hexagonal diamond (Si-IV), and R8 (Si-XII). In addition to these, we also study the hypothetical ST12 structure found upon decompression from beta-Sn in germanium. • Our attention is then turned to the first principles calculations of optical properties in Chapter 4. The Bethe-Salpeter equation is then solved to obtain the optical spectrum of this material including electron-hole interactions. The calculated optical spectrum is compared with experimental data for other forms of silicon commonly used in photovoltaic devices, namely the cubic, polycrystalline, and amorphous forms. • In Chapter 5 we present first principles calculations of the quasiparticle and optical excitation spectra of recently predicted silicon and germanium polytypes in the body-centered-tetragonal (bct) structure. The quasiparticle spectra calculated within the GW approximation predict that both silicon and germanium in the bct structure are small band gap materials. The optical spectra are then evaluated by solving the Bethe-Salpeter equation taking into account. • We examine the low-pressure phases of Ge in Chapter 6 by performing first principles calculations of the electronic structure and lattice dynamics of the R8, BC8, ST12, and hexagonal diamond structures of Ge. To aid future experimental investigation, we include predictions of the Raman-active frequencies of these phases as well as present the full phonon dispersion throughout the zone. • In Chapter 7 we demonstrate how first principles calculations can be used to predict new structures. In a study aimed at finding new useful forms of silicon, we use an ab initio random structure searching (AIRSS) method to identify a new phase of silicon in the Ibamstructure. The Ibam phase is found to be semimetallic within density functional theory with a small band overlap, and it is expected that quasiparticle corrections using the GW approximation would yield a semiconducting state with a small band gap. • We present a first-principles study of boron and phosphorus substitutional defects in Si-XII in Chapter 8. Recent result from nanoindentation experiments reveal that the Si-XII phase is semiconducting and has the interesting property that it can be doped n- and p-type at room temperature without an annealing step. Using the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we examine the formation energies of the B and P defects at the two distinct atomic sites in Si-XII to find on which site the substitutional defects are more easily accommodated. We also estimate the thermodynamic transition levels of each defect in its relevant charge states. (Abstract shortened by UMI.).

Dielectric response of crystalline tris(acetylacetonato)cobalt(III) films grown on Si substrate for low- k dielectric applications

NASA Astrophysics Data System (ADS)

Dakhel, A. A.; Ali-Mohamed, A. Y.

2008-01-01

Thin films of the complex tris(acetylacetonato)cobalt(III) [abb. Co(acac) 3] were deposited in vacuum on glass and p-Si substrates for optical and dielectric studies. The samples were characterised by X-ray diffraction and fluorescence methods as well as optical absorption spectroscopy. The prepared films show a polycrystalline of monoclinic P2 1/ c structure. The optical absorption spectrum of the prepared film was not exactly fit to that of the molecular one. The energy of the optical absorption onset of the Co(acac) 3 film was calculated by using usual solid-state methods. For electrical measurements on the complex as insulator, samples in the form of metal-insulator-semiconductor (MIS) structure were prepared and characterised by measurement of the capacitance as a function of gate voltage at 1 MHz. The frequency dependence of the complex dielectric constant of the complex was studied in the frequency range (1-1000 kHz) in the temperature range (294-323 K). The experimental results were analysed in the framework of Debye single relaxation model. Generally, the present study shows that a film of complex Co(acac) 3 grown on Si substrate is a promising candidate for low- k dielectric applications, it displays low- k value around 1.7 at high frequencies.

Gallium Arsenide Monolithic Optoelectronic Circuits

NASA Astrophysics Data System (ADS)

Bar-Chaim, N.; Katz, J.; Margalit, S.; Ury, I.; Wilt, D.; Yariv, A.

1981-07-01

The optical properties of GaAs make it a very useful material for the fabrication of optical emitters and detectors. GaAs also possesses electronic properties which allow the fabrication of high speed electronic devices which are superior to conventional silicon devices. Monolithic optoelectronic circuits are formed by the integration of optical and electronic devices on a single GaAs substrate. Integration of many devices is most easily accomplished on a semi-insulating (SI) sub-strate. Several laser structures have been fabricated on SI GaAs substrates. Some of these lasers have been integrated with Gunn diodes and with metal semiconductor field effect transistors (MESFETs). An integrated optical repeater has been demonstrated in which MESFETs are used for optical detection and electronic amplification, and a laser is used to regenerate the optical signal. Monolithic optoelectronic circuits have also been constructed on conducting substrates. A heterojunction bipolar transistor driver has been integrated with a laser on an n-type GaAs substrate.

Interfacial effect on the structural and optical properties of pure SnO2 and dual shells (ZnO; SiO2) coated SnO2 core-shell nanospheres for optoelectronic applications

NASA Astrophysics Data System (ADS)

Selvi, N.; Sankar, S.; Dinakaran, K.

2014-12-01

Nanocrystallites of SnO2 core and dual shells (ZnO, SiO2) coated SnO2 core-shell nanospheres were successfully synthesized by co-precipitation method. The as prepared and annealed samples were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), High resolution transmission electron microscopy (HRTEM) and UV-Vis analysis. XRD pattern confirms the obtained SnO2 core with tetragonal rutile crystalline structure and the shell ZnO with hexagonal structure. FTIR result shows the functional groups present in the samples. The spherical morphology and the formation of the core-shell structures have been confirmed by HRTEM measurements. The UV-Vis showed that band gap is red shifted for as-prepared and the shells coated core-shell samples. From this investigation it can be concluded that the surface modification with different metal and insulating oxides strongly influences the optical properties of the core-shell materials which enhance their potential applications towards optical devices fabrication.

Unique sodium phosphosilicate glasses designed through extended topological constraint theory.

PubMed

Zeng, Huidan; Jiang, Qi; Liu, Zhao; Li, Xiang; Ren, Jing; Chen, Guorong; Liu, Fude; Peng, Shou

2014-05-15

Sodium phosphosilicate glasses exhibit unique properties with mixed network formers, and have various potential applications. However, proper understanding on the network structures and property-oriented methodology based on compositional changes are lacking. In this study, we have developed an extended topological constraint theory and applied it successfully to analyze the composition dependence of glass transition temperature (Tg) and hardness of sodium phosphosilicate glasses. It was found that the hardness and Tg of glasses do not always increase with the content of SiO2, and there exist maximum hardness and Tg at a certain content of SiO2. In particular, a unique glass (20Na2O-17SiO2-63P2O5) exhibits a low glass transition temperature (589 K) but still has relatively high hardness (4.42 GPa) mainly due to the high fraction of highly coordinated network former Si((6)). Because of its convenient forming and manufacturing, such kind of phosphosilicate glasses has a lot of valuable applications in optical fibers, optical amplifiers, biomaterials, and fuel cells. Also, such methodology can be applied to other types of phosphosilicate glasses with similar structures.

Growth and characterization of PbSe and Pb{sub 1{minus}x}Sn{sub x}Se layers on Si (100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sachar, H.K.; Chao, I.; Fang, X.M.

1998-12-31

Crack-free layers of PbSe were grown on Si (100) by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. The PbSe layer was grown by LPE on Si(100) using a MBE-grown PbSe/BaF{sub 2}/CaF{sub 2} buffer layer structure. Pb{sub 1{minus}x}Sn{sub x}Se layers with tin contents in the liquid growth solution equal to 3%, 5%, 6%, 7%, and 10%, respectively, were also grown by LPE on Si(100) substrates using similar buffer layer structures. The LPE-grown PbSe and Pb{sub 1{minus}x}Sn{sub x}Se layers were characterized by optical Nomarski microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electronmore » microscopy (SEM). Optical Nomarski characterization of the layers revealed their excellent surface morphologies and good growth solution wipe-offs. FTIR transmission experiments showed that the absorption edge of the Pb{sub 1{minus}x}Sn{sub x}Se layers shifted to lower energies with increasing tin contents. The PbSe epilayers were also lifted-off from the Si substrate by dissolving the MBE-grown BaF{sub 2} buffer layer. SEM micrographs of the cleaved edges revealed that the lifted-off layers formed structures suitable for laser fabrication.« less

Effect of rapid oxidation on optical and electrical properties of silicon nanowires obtained by chemical etching

NASA Astrophysics Data System (ADS)

Karyaoui, M.; Bardaoui, A.; Ben Rabha, M.; Harmand, J. C.; Amlouk, M.

2012-05-01

In the present work, we report the investigation of passivated silicon nanowires (SiNWs) having an average radius of 3.7 μm, obtained by chemical etching of p-type silicon (p-Si). The surface passivation of the SiNWs was performed through a rapid oxidation conducted under a controlled atmosphere at different temperatures and durations. The morphology of the SiNWs was examined using a scanning electron microscope (SEM) that revealed a wave-like structure of dense and vertically aligned one-dimensional silicon nanostructures. On the other hand, optical and electrical characterizations of the SiNWs were studied using a UV-Vis-NIR spectrometer, the Fourier transform infrared spectroscopy (FTIR) and I-V measurements. The reflectance of SiNWs has been dropped to approximately 2% in comparison to that of bare p-Si. This low reflectance slightly increased after carrying out the rapid thermal annealing. The observed behavior was attributed to the formation of a SiO2 layer, as confirmed by FTIR measurements. Finally, the electrical measurements have shown that the rapid oxidation, at certain conditions, contributes to the improvement of the electrical responses of the SiNWs, which can be of great interest for photovoltaic applications.

Bio-inspired, subwavelength surface structures to control reflectivity, transmission, and scattering in the infrared

NASA Astrophysics Data System (ADS)

Lora Gonzalez, Federico

Controlling the reflection of visible and infrared (IR) light at interfaces is extremely important to increase the power efficiency and performance of optics, electro-optical and (thermo)photovoltaic systems. The eye of the moth has evolved subwavelength protuberances that increase light transmission into the eye tissue and prevent reflection. The subwavelength protuberances effectively grade the refractive index from that of air (n=1) to that of the tissue (n=1.4), making the interface gradual, suppressing reflection. In theory, the moth-eye (ME) structures can be implemented with any material platform to achieve an antireflectance effect by scaling the pitch and size of protuberances for the wavelength range of interest. In this work, a bio-inspired, scalable and substrate-independent surface modification protocol was developed to realize broadband antireflective structures based on the moth-eye principle. Quasi-ordered ME arrays were fabricated in IR relevant materials using a colloidal lithography method to achieve highly efficient, omni-directional transmission of mid and far infrared (IR) radiation. The effect of structure height and aspect ratio on transmittance and scattering is explored, with discussion on experimental techniques and effective medium theory (EMT). The highest aspect ratio structures (AR = 9.4) achieved peak single-side transmittance of 98%, with >85% transmission for lambda = 7--30 microns. A detailed photon balance constructed by transmission, forward scattering, specular reflection and diffuse reflection measurements to quantify optical losses due to near-field effects will be discussed. In addition, angle-dependent transmission measurements showed that moth-eye structures provide superior antireflective properties compared to unstructured interfaces over a wide angular range (0--60° incidence). Finally, subwavelength ME structures are incorporated on a Si substrate to enhance the absorption of near infrared (NIR) light in PtSi films to increase Schottky-barrier detector efficiency. Absorbance enhancement of 70--200% in the lambda =1--2.5 micron range is demonstrated in crystalline PtSi films grown via electron beam evaporation of Pt and subsequent vacuum annealing. Low total reflectance (<10%) was measured in ME films, demonstrating the efficacy of the moth eye effect. Effective medium theory and transfer matrix calculations show that the large absorption enhancement at short wavelengths is partly due to light trapping, which increases the effective optical path length in PtSi. The demonstrated structures are promising candidates for efficient PtSi/p-Si Schottky barrier diode detectors in the NIR. Results further suggest a general method for relatively low-cost absorption enhancement of backside-illuminated detectors based on a wide variety of infrared absorptive materials. The methods presented here to fabricate quasi-ordered ME structures provide a general platform for creating antireflective structures in many different materials, devices, and bandwidths. Furthermore, understanding the relationship between protuberance shape, height, aspect ratio, etc. and performance (antireflection, scattering loss, etc.) can guide the design of antireflective surfaces for different applications (for example, in certain applications, large amounts of forward scattering is desired, e.g. photovoltaics).

Decalin-assisted light emitting porous Si formation and its optical, surface and morphological properties

NASA Astrophysics Data System (ADS)

Karatutlu, Ali; Istengir, Sumeyra; Cosgun, Sedat; Seker, Isa; Unal, Bayram

2017-11-01

In this research paper, light emitting porous silicon (Lep-Si) samples were fabricated by a surfactant-mediated chemical stain etching solution in order to form homogenous luminescent nanostructures at room temperature. As an industrially important solvent, decalin (decahydronaphtalene) was used as a surfactant in the HF/HNO3 solutions in order to control the etching process. Morphological, surface and optical properties of the Lep-Si samples were examined using atomic force microscopy, X-ray photoelectron spectroscopy, photoluminescence (PL) spectroscopy, and laser scanning confocal microscopy (LSCM) techniques. These characterization techniques were correlated with the various etching times including depth dependent luminescence profiles for the first time. We report the optimum conditions for production of the most efficient Lep-Si using decalin (decahydronaphtalene) and possible structural origins of light emission using the depth dependent luminescence measurements.

Potential of SiO2/ZrO2 matrix doped with CoFe2O4 magnetic nanoparticles in achieving integrated magneto-optical isolators

NASA Astrophysics Data System (ADS)

Zamani, Mehdi; Hocini, Abdesselam

2017-05-01

We have investigated the potential of the SiO2/ZrO2 matrix doped with CoFe2O4 magnetic nanoparticles in order to overcome the problem of integration of the magneto-optical isolators (MOIs). In this way, we have performed a theoretical study for the case of designing perfect and adjustable MOIs based on magnetophotonic crystals (MPCs) containing SiO2/ZrO2 matrix doped with CoFe2O4 magnetic nanoparticles as a magnetic medium. Despite the existence the attenuation coefficient for SiO2/ZrO2 matrix at wavelength 1550 nm that leads to a non-perfect transmittance, we could introduce an MPC structure having no reflectance; therefore, an ideal MOI for eliminating unwanted back-reflection could be achieved.

Strong green fluorescent hydrogels with Ba2 MgSi2 O7 :Eu2+ phosphor embedded in cellulose.

PubMed

Zhang, Xinguo; Qin, Xingzhen; Chen, Hailan

2017-06-01

Non-cytotoxic and green-emitting fluorescent hydrogels were constructed from a cellulose solution containing Ba 2 MgSi 2 O 7 :Eu 2 + green phosphor in a NaOH/urea aqueous system. The structure, optical properties and cytotoxicity of these hydrogels were studied. The Ba 2 MgSi 2 O 7 :Eu 2 + phosphor particles were dispersed evenly in the cellulose hydrogel matrix. Good luminescent properties of Ba 2 MgSi 2 O 7 :Eu 2 + phosphor were maintained in the hydrogels, leading to strong green emission under ultraviolet excitation. Fluorescent hydrogels have no obvious cytotoxicity in a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) proliferation test, and have potential use in in vivo applications like optical imaging and drug delivery. Copyright © 2016 John Wiley & Sons, Ltd.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, K.M.; Al-Jassim, M.M.; Williamson, D.L.

Over the last two decades extensive studies on the optical and electrical properties of hydrogenated amorphous Si (a-Si:H) have been reported. However, less attention was given to the structural characterization of this material partly due to the insensitivity to hydrogen of structural probes such as x-rays and electron diffraction. From a recent set of experiments, results on the solubility limit of hydrogen in a special type of a-Si:H and the characterization of hydrogen induced complexes or nanobubbles has been reported. In this study, we report TEM observations of the structural morphology of hydrogen related defects that support these recent measurementsmore » obtained by secondary ion mass spectrometry (SIMS) and small-angle x-ray scattering (SAXS).« less

Tailoring single-cycle electromagnetic pulses in the 2-9 THz frequency range using DAST/SiO₂ multilayer structures pumped at Ti:sapphire wavelength.

PubMed

Stepanov, Andrei G; Rogov, Andrii; Bonacina, Luigi; Wolf, Jean-Pierre; Hauri, Christoph P

2014-09-08

We present a numerical parametric study of single-cycle electromagnetic pulse generation in a DAST/SiO₂multilayer structure via collinear optical rectification of 800 nm femtosecond laser pulses. It is shown that modifications of the thicknesses of the DAST and SiO₂layers allow tuning of the average frequency of the generated THz pulses in the frequency range from 3 to 6 THz. The laser-to-THz energy conversion efficiency in the proposed structures is compared with that in a bulk DAST crystal and a quasi-phase-matching periodically poled DAST crystal and shows significant enhancement.

Enhancement of broadband optical absorption in photovoltaic devices by band-edge effect of photonic crystals.

PubMed

Tanaka, Yoshinori; Kawamoto, Yosuke; Fujita, Masayuki; Noda, Susumu

2013-08-26

We numerically investigate broadband optical absorption enhancement in thin, 400-nm thick microcrystalline silicon (µc-Si) photovoltaic devices by photonic crystals (PCs). We realize absorption enhancement by coupling the light from the free space to the large area resonant modes at the photonic band-edge induced by the photonic crystals. We show that multiple photonic band-edge modes can be produced by higher order modes in the vertical direction of the Si photovoltaic layer, which can enhance the absorption on multiple wavelengths. Moreover, we reveal that the photonic superlattice structure can produce more photonic band-edge modes that lead to further optical absorption. The absorption average in wavelengths of 500-1000 nm weighted to the solar spectrum (AM 1.5) increases almost twice: from 33% without photonic crystal to 58% with a 4 × 4 period superlattice photonic crystal; our result outperforms the Lambertian textured structure.

Effect of ammonia and methane adsorption on the electronic structure of undoped and Fe-doped 2D silica: a first-principles calculation

NASA Astrophysics Data System (ADS)

Chibisov, A. N.; Chibisova, M. A.

2018-05-01

Two-dimensional silicon oxide (2D SiO2) is a unique surface phase with interesting optical, structural and electronic properties. In this study, important novel results on the effect of Fe on the structural and electronic properties of 2D SiO2 during adsorption of CH4 and NH3 molecules are presented. Density functional theory calculations are used to investigate the interaction of CH4 and NH3 molecules with silica. The electronic structure and molecules adsorption energy are studied in detail for undoped and Fe-doped surfaces. The results show that adsorption of CH4 and NH3 molecules on the surface decreases the spin polarization of Fe/SiO2. The results are relevant to understanding the adsorption physics of 2D SiO2 for practical usage in modern nanoelectronic sensors for nanotechnology and optoelectronics.

Folic acid-conjugated GdPO4:Tb3+@SiO2 Nanoprobe for folate receptor-targeted optical and magnetic resonance bi-modal imaging

NASA Astrophysics Data System (ADS)

Xu, Xianzhu; Zhang, Xiaoying; Wu, Yanli

2016-11-01

Both fluorescent and magnetic nanoprobes have great potential applications for diagnostics and therapy. In the present work, a folic acid-conjugated and silica-modified GdPO4:Tb3+ (GdPO4:Tb3+@SiO2-FA) dual nanoprobe was strategically designed and synthesized for the targeted dual-modality optical and magnetic resonance (MR) imaging via a facile aqueous method. Their structural, optical, and magnetic properties were determined using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), ultraviolet-visible spectra (UV-Vis), photoluminescence (PL), and superconducting quantum interference device (SQUID). These results indicated that GdPO4:Tb3+@SiO2-FA were uniform monodisperse core-shell structured nanorods (NRs) with an average length of 200 nm and an average width of 25 nm. The paramagnetic property of the synthesized GdPO4:Tb3+@SiO2-FA NRs was confirmed with its linear hysteresis plot (M-H). In addition, the NRs displayed an obvious T1-weighted effect and thus it could potentially serve as a T1-positive contrast agent. The NRs emitted green lights due to the 5D4 → 7F5 transition of the Tb3+. The in vitro assays with NCI-H460 lung cancer cells and human embryonic kidney cell line 293T cells indicated that the GdPO4:Tb3+@SiO2-FA nanoprobe could specifically bind the cells bearing folate receptors (FR). The MTT assay of the NRs revealed that its cytotoxicity was very low. Further in vivo MRI experiments distinctively depict enhanced anatomical features in a xenograft tumor. These results suggest that the GdPO4:Tb3+@SiO2-FA NPs have excellent imaging and cell-targeting abilities for the folate receptor-targeted dual-modality optical and MR imaging and can be potentially used as the nanoprobe for bioimaging.

Towards Resonant-State THz Laser Based on Strained p-Ge and SiGe QW Structures

DTIC Science & Technology

2006-07-01

used. The relaxed compositionally graded Si1-xGex/Si(001) buffer layer with low threading dislocations density have been grown by chemical vapour ...observe in absorption experiments. 5. Intracenter optical transitions between hydrogenic levels in doped silicon, germanium, and gallium arsenid [P...34, b. Critical magnetic field Hc vs valence band splitting Δ. Lines show the calculated Hc(Δ) dependence. 14. The gallium -doped Ge crystals with

Bamboo-like 3C-SiC nanowires with periodical fluctuating diameter: Homogeneous synthesis, synergistic growth mechanism, and their luminescence properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Meng; Zhao, Jian; Li, Zhenjiang, E-mail: zhenjiangli@qust.edu.cn

Herein, bamboo-like 3C-SiC nanowires have been successfully fabricated on homogeneous 6H-SiC substrate by a simple chemical vapor reaction (CVR) approach. The obtained 3C-SiC nanostructure with periodical fluctuating diameter, is composed of two alternating structure units, the typical normal-sized stem segment with perfect crystallinity and obvious projecting nodes segment having high-density stacking faults. The formation of the interesting morphology is significantly subjected to the peculiar growth condition provided by the homogeneous substrate as well as the varying growth elastic energy. Furthermore, the photoluminescence (PL) performance measured on the bamboo-like SiC nanowire shows an intensive emission peaks centered at 451 nm andmore » 467 nm, which has been expected to make a positive progress toward the optical application of the SiC-based one-dimensional (1D) nanostructures, such as light emission diode (LED). - Graphical abstract: Based on the synergistic growth mechanism from homogeneous substrate and elastic energy, bamboo-like 3C-SiC nanowires with periodically fluctuating diameter have been synthesized on 6H-SiC. The blue-violet light emission properties of the bamboo-like nanowires have also been investigated for exploring their peculiar optical application. - Highlights: • Bamboo-like 3C-SiC nanowires with periodically fluctuating diameter have been synthesized on 6H-SiC. • A synergistic growth mechanism from homogeneous substrate and elastic energy has been proposed firstly. • The blue-violet light emission properties of the products displayed peculiar optical application.« less

Nanostructured germanium deposited on heated substrates with enhanced photoelectric properties.

PubMed

Stavarache, Ionel; Maraloiu, Valentin Adrian; Prepelita, Petronela; Iordache, Gheorghe

2016-01-01

Obtaining high-quality materials, based on nanocrystals, at low temperatures is one of the current challenges for opening new paths in improving and developing functional devices in nanoscale electronics and optoelectronics. Here we report a detailed investigation of the optimization of parameters for the in situ synthesis of thin films with high Ge content (50 %) into SiO 2 . Crystalline Ge nanoparticles were directly formed during co-deposition of SiO 2 and Ge on substrates at 300, 400 and 500 °C. Using this approach, effects related to Ge-Ge spacing are emphasized through a significant improvement of the spatial distribution of the Ge nanoparticles and by avoiding multi-step fabrication processes or Ge loss. The influence of the preparation conditions on structural, electrical and optical properties of the fabricated nanostructures was studied by X-ray diffraction, transmission electron microscopy, electrical measurements in dark or under illumination and response time investigations. Finally, we demonstrate the feasibility of the procedure by the means of an Al/n-Si/Ge:SiO 2 /ITO photodetector test structure. The structures, investigated at room temperature, show superior performance, high photoresponse gain, high responsivity (about 7 AW -1 ), fast response time (0.5 µs at 4 kHz) and great optoelectronic conversion efficiency of 900% in a wide operation bandwidth, from 450 to 1300 nm. The obtained photoresponse gain and the spectral width are attributed mainly to the high Ge content packed into a SiO 2 matrix showing the direct connection between synthesis and optical properties of the tested nanostructures. Our deposition approach put in evidence the great potential of Ge nanoparticles embedded in a SiO 2 matrix for hybrid integration, as they may be employed in structures and devices individually or with other materials, hence the possibility of fabricating various heterojunctions on Si, glass or flexible substrates for future development of Si-based integrated optoelectronics.

Enhanced Visible Transmittance of Thermochromic VO2 Thin Films by SiO2 Passivation Layer and Their Optical Characterization

PubMed Central

Yu, Jung-Hoon; Nam, Sang-Hun; Lee, Ji Won; Boo, Jin-Hyo

2016-01-01

This paper presents the preparation of high-quality vanadium dioxide (VO2) thermochromic thin films with enhanced visible transmittance (Tvis) via radio frequency (RF) sputtering and plasma enhanced chemical vapor deposition (PECVD). VO2 thin films with high Tvis and excellent optical switching efficiency (Eos) were successfully prepared by employing SiO2 as a passivation layer. After SiO2 deposition, the roughness of the films was decreased 2-fold and a denser structure was formed. These morphological changes corresponded to the results of optical characterization including the haze, reflectance and absorption spectra. In spite of SiO2 coating, the phase transition temperature (Tc) of the prepared films was not affected. Compared with pristine VO2, the total layer thickness after SiO2 coating was 160 nm, which is an increase of 80 nm. Despite the thickness change, the VO2 thin films showed a higher Tvis value (λ 650 nm, 58%) compared with the pristine samples (λ 650 nm, 43%). This enhancement of Tvis while maintaining high Eos is meaningful for VO2-based smart window applications. PMID:28773679

Near zero reflection by nanostructured anti-reflection coating design for Si substrates

NASA Astrophysics Data System (ADS)

Al-Fandi, Mohamed; Makableh, Yahia F.; Khasawneh, Mohammad; Rabady, Rabi

2018-05-01

The nanostructure design of near zero reflection coating for Si substrates by using ZnO Nanoneedles (ZnONN) is performed and optimized for the visible spectral range. The design investigates the ZnONN tip to body ratio effect on the anti-reflection coating properties. Different tip to body ratios are used on Si substrates. Around zero reflection is achieved by the Nanoneedles structure design presented in this work, leading to minimal reflection losses from the Si surface. The current design evolves a solution to optical losses and surface contamination effects associated with Si solar cells.

Effect of substrates on structural and optical properties of tin oxide (SnO2) nanostructures.

PubMed

Johari, Anima; Bhatnagar, M C; Rana, Vikas

2012-10-01

We report on controlling the morphology of tin oxide (SnO2) nanostructures and the study of the effect of surface morphology on structural and optical properties of SnO2 nanostuctures. In present work, Tin oxide (SnO2) nanostructures such as nanowires and nanorods have been grown by thermal evaporation of SnO2 powder. To demonstrate the effect of different substrates on the morphology of grown SnO2 nanostructures, the thermal evaporation of SnO2 powder was carried out on Si and gold catalyzed Si (Au/Si) substrates. The scanning-electron-microscopic analysis shows the growth of SnO2 nanowires on Au/Si substrate and growth of SnO2 nanorods on Si substrate. The scanning-and transmission-electron-microscopic analysis shows that the diameter of SnO2 nanowires and nanorods are about 70 nm and 95 nm respectively and their length is about 80 microm and 30 microm respectively. The vapor-liquid-solid (VLS) growth of SnO2 nanowires and vapor-solid (VS) growth of SnO2 nanorods is also confirmed with the help of TEM and EDX spectra. The synthesized SnO2 nanowires show tetragonal rutile structure of SnO2, whereas SnO2 nanorods show tetragonal rutile as well as cassiterite structure of SnO2. UV-Vis absorption spectra showed the optical band gaps of 4.1 eV and 3.8 eV for the SnO2 nanowires and the nanorods, respectively. The SnO2 nanowires and nanorods show photoluminescence with broad emission peaks centred at around 600 nm and 580 nm respectively. Raman spectra of SnO2 nanowires shows three Raman shifts (478, 632, 773 cm(-1)) corresponding to Eg, A1g and B2g vibration modes, whereas in Raman spectra of SnO2 nanorods, A1g peak is dramatically reduced and the B2g mode is totally quenched.

Characterisation and optimisation of PECVD SiNx as an antireflection coating and passivation layer for silicon solar cells

NASA Astrophysics Data System (ADS)

Wan, Yimao; McIntosh, Keith R.; Thomson, Andrew F.

2013-03-01

In this work, we investigate how the film properties of silicon nitride (SiNx) depend on its deposition conditions when formed by plasma enhanced chemical vapour deposition (PECVD). The examination is conducted with a Roth & Rau AK400 PECVD reactor, where the varied parameters are deposition temperature, pressure, gas flow ratio, total gas flow, microwave plasma power and radio-frequency bias voltage. The films are evaluated by Fourier transform infrared spectroscopy to determine structural properties, by spectrophotometry to determine optical properties, and by capacitance-voltage and photoconductance measurements to determine electronic properties. After reporting on the dependence of SiNx properties on deposition parameters, we determine the optimized deposition conditions that attain low absorption and low recombination. On the basis of SiNx growth models proposed in the literature and of our experimental results, we discuss how each process parameter affects the deposition rate and chemical bond density. We then focus on the effective surface recombination velocity Seff, which is of primary importance to solar cells. We find that for the SiNx prepared in this work, 1) Seff does not correlate universally with the bulk structural and optical properties such as chemical bond densities and refractive index, and 2) Seff depends primarily on the defect density at the SiNx-Si interface rather than the insulator charge. Finally, employing the optimized deposition condition, we achieve a relatively constant and low Seff,UL on low-resistivity (≤1.1 Ωcm) p- and n-type c-Si substrates over a broad range of n = 1.85-4.07. The results of this study demonstrate that the trade-off between optical transmission and surface passivation can be circumvented. Although we focus on photovoltaic applications, this study may be useful for any device for which it is desirable to maximize light transmission and surface passivation.

Antireflection coatings with SiOx-TiO2 multilayer structures

NASA Astrophysics Data System (ADS)

Lu, Jong-Hong; Luo, Jen-Wei; Chuang, Shiou-Ruei; Chen, Bo-Ying

2014-11-01

In this study, we used SiOx-TiO2 multilayer antireflective coatings to achieve optical average transmittances of 94.93 and 98.07% for one-sided and double-sided coatings on a glass substrate, respectively. A SiOx film was employed as the material with a low refractive index and a TiO2 film as the material with a high refractive index. Results showed that when any layer thickness of the SiOx-TiO2 nano-multilayer (NML) structure is much less than the wavelength of visible light, the SiOx-TiO2 thickness ratio can be used to adjust the optical refractive index of the entire NML film. In this study, we produced dense antireflective coatings of three layers (SiOx, TiO2, and SiOx-TiO2 NML/glass substrate) and four layers (SiOx, TiO2, SiOx, and TiO2/glass substrate) with film thicknesses and refractive indices controlled by reactive magnetron sputtering. Thermal treatment at 600 °C in an air atmosphere was also shown to reduce the absorption of visible light, resolving the issue of degraded transparency caused by increasing sputtering speed. The microhardness of the antireflective film was 8.44 GPa, similar to that of the glass substrate. Process window analysis demonstrated the feasibility of the antireflective coating process window from an engineering standpoint. The thickness of the film deviated by less than 10% from the ideal thickness, corresponding to a 98% transmittance range, and the simulation and experimental results were relatively consistent.

Octoxy capped Si nanoparticles synthesized by homogeneous reduction of SiCl4 with crown ether alkalide.

PubMed

Sletnes, M; Maria, J; Grande, T; Lindgren, M; Einarsrud, M-A

2014-02-07

Blue-green luminescent octoxy capped Si nanoparticles were synthesized via homogeneous reduction of SiCl4 with the crown ether alkalide K(+)(15-crown-5)2K(-) in tetrahydrofuran. The Si nanoparticles were characterized with respect to size, crystal structure, morphology, surface termination, optical properties and stability. Si diamond structure nanoparticles with narrow size distributions, and average diameters ranging from 3 to 7 nm were obtained. A finite-size effect on the lattice dimensions was observed, in the form of an expansion of the [220] lattice planes of smaller Si nanoparticles. The concentration of SiCl4 was found to be the most important parameter governing the particle size and size distribution. The octoxy capped particles were stable under an ambient atmosphere for at least one month, but exposure to water made them prone to oxidation. An average radiative recombination lifetime of 8.8 ns was measured for the blue-green luminescence. The luminescence appears to originate from surface defects, rather than from quantum confinement.

Ultra-lightweight optics for laser communications

NASA Astrophysics Data System (ADS)

Vukobratovich, Daniel

1990-07-01

Recent applications of the very light Al/SiC metal-matrix composite SXA in the construction of telescopes for use as receiver antennas in optical intersatellite communication systems are reviewed and illustrated with drawings and diagrams. Data on the mechanical properties (specific stiffness, fundamental frequency, dynamic response, and fracture toughness) and the thermal expansion, distortion, and diffusivity of SXA are compared with those for Al 6016-T6, Be I-70A, SiC, and Zerodur in tables, and the advantages of SXA structural foams of density 250-500 kg/cu m are indicated. The criteria evaluated for optimization of the mirror shape and the overall telescope design are discussed, and four prototype Cassegrain telescopes (with Meinel or Dall truss structures) are described in detail.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Hua-Jun, E-mail: cszzl772002@yeah.net; State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002

Two quaternary sulfides RE{sub 3}Sb{sub 0.33}SiS{sub 7} (RE=La, Pr) have been prepared from stoichiometric mixtures of elements at 1223 K in an evacuated silica tube. They are the first examples of chalcogenides in the quaternary RE/Si/Sb/Q (RE=rare earth metal; Q=S, Se, Te) system. These two isostructural materials crystallize in the Ce{sub 3}Al{sub 1.67}S{sub 7} structure type in the hexagonal space group P6{sub 3}. Their structure features one-dimensional chains of face-sharing SbS{sub 6} octahedra running parallel to the c direction surrounded by the discrete SiS{sub 4} tetrahedra and RE cations. The La{sub 3}Sb{sub 0.33}SiS{sub 7} exhibits a SHG signal about 0.5more » times that of the commercially used IR NLO material AgGaS{sub 2} at 2.05 μm laser. The optical gap of 1.92 eV for La{sub 3}Sb{sub 0.33}SiS{sub 7} was deduced from UV/Vis reflectance spectroscopy. - Graphical abstract: The RE{sub 3}Sb{sub 0.33}SiS{sub 7} (RE=La, Pr), crystalling in the Ce{sub 3}Al{sub 1.67}S{sub 7} structure type, have been prepared. The La{sub 3}Sb{sub 0.33}SiS{sub 7} exhibits a SHG signal about 0.5 times that of the IR NLO material AgGaS{sub 2}. - Highlights: • The RE{sub 3}Sb{sub 0.33}SiS{sub 7} (RE=La, Pr), crystalling in the Ce{sub 3}Al{sub 1.67}S{sub 7} structure type, have been prepared. • The La{sub 3}Sb{sub 0.33}SiS{sub 7} exhibits a SHG signal about 0.5 times that of the IR NLO material AgGaS{sub 2}. • The optical gap of 1.92 eV for La{sub 3}Sb{sub 0.33}SiS{sub 7} was deduced from UV/Vis reflectance spectroscopy.« less

Microstructure and ferroelectricity of BaTiO3 thin films on Si for integrated photonics

NASA Astrophysics Data System (ADS)

Kormondy, Kristy J.; Popoff, Youri; Sousa, Marilyne; Eltes, Felix; Caimi, Daniele; Rossell, Marta D.; Fiebig, Manfred; Hoffmann, Patrik; Marchiori, Chiara; Reinke, Michael; Trassin, Morgan; Demkov, Alexander A.; Fompeyrine, Jean; Abe, Stefan

2017-02-01

Significant progress has been made in integrating novel materials into silicon photonic structures in order to extend the functionality of photonic circuits. One of these promising optical materials is BaTiO3 or barium titanate (BTO) that exhibits a very large Pockels coefficient as required for high-speed light modulators. However, all previous demonstrations show a noticable reduction of the Pockels effect in BTO thin films deposited on silicon substrates compared to BTO bulk crystals. Here, we report on the strong dependence of the Pockels effect in BTO thin films on their microstructure, and provide guidelines on how to engineer thin films with strong electro-optic response. We employ several deposition methods such as molecular beam epitaxy and chemical vapor deposition to realize BTO thin films with different morphology and crystalline structure. While a linear electro-optic response is present even in porous, polycrystalline BTO thin films with an effective Pockels coefficient r eff = 6 pm V-1, it is maximized for dense, tetragonal, epitaxial BTO films (r eff = 140 pm V-1). By identifying the key structural predictors of electro-optic response in BTO/Si, we provide a roadmap to fully exploit the linear electro-optic effect in novel hybrid oxide/semiconductor nanophotonic devices.

Preparation of magnetron sputtered ZrO2 films on Si for gate dielectric application

NASA Astrophysics Data System (ADS)

Kondaiah, P.; Mohan Rao, G.; Uthanna, S.

2012-11-01

Zirconium oxide (ZrO2) thin films were deposited on to p - Si and quartz substrates by sputtering of zirconium target at an oxygen partial pressure of 4x10-2 Pa and sputter pressure of 0.4 Pa by using DC reactive magnetron sputtering technique. The effect of annealing temperature on structural, optical, electrical and dielectric properties of the ZrO2 films was systematically studied. The as-deposited films were mixed phases of monoclinic and orthorhombic ZrO2. As the annealing temperature increased to 1073 K, the films were transformed in to single phase orthorhombic ZrO2. Fourier transform infrared studies conform the presence of interfacial layer between Si and ZrO2. The optical band gap and refractive index of the as-deposited films were 5.82 eV and 1.81. As the annealing temperature increased to 1073 K the optical band gap and refractive index increased to 5.92 eV and 2.10 respectively. The structural changes were influenced the capacitance-voltage and current-voltage characteristics of Al/ZrO2/p-Si capacitors. The dielectric constant was increased from 11.6 to 24.5 and the leakage current was decreased from 1.65×10-7 to 3.30×10-9 A/ cm2 for the as-deposited and annealed at 1073 K respectively.

Betavoltaic device in por-SiC/Si C-Nuclear Energy Converter

NASA Astrophysics Data System (ADS)

Akimchenko, Alina; Chepurnov, Victor; Dolgopolov, Mikhail; Gurskaya, Albina; Kuznetsov, Oleg; Mashnin, Alikhan; Radenko, Vitaliy; Radenko, Alexander; Surnin, Oleg; Zanin, George

2017-10-01

The miniature and low-power devices with long service life in hard operating conditions like the Carbon-14 beta-decay energy converters indeed as eternal resource for integrated MEMS and NEMS are considered. Authors discuss how to create the power supply for MEMS/NEMS devices, based on porous SiC/Si structure, which are tested to be used as the beta-decay energy converters of radioactive C-14 into electrical energy. This is based on the silicon carbide obtaining by self-organizing mono 3C-SiC endotaxy on the Si substrate. The new idea is the C-14 atoms including in molecules in the silicon carbide porous structure by this technology, which will increase the efficiency of the converter due to the greater intensity of electron-hole pairs generation rate in the space charge region. The synthesis of C-14 can be also performed by using the electronically controlled magneto-optic chamber.

2D materials integrated in Si3N4 photonics platform

NASA Astrophysics Data System (ADS)

Faneca, Joaquin; Hogan, Benjamin T.; Torres Alonso, E.; Craciun, Monica; Baldycheva, Anna

2018-02-01

In this paper, we discuss a back-end CMOS fabrication process for the large-scale integration of 2D materials on SOI (siliconon-insulator) platform and present a complete theoretical study of the change in the effective refractive index of 2D materialsenabled silicon nitride waveguide structures. The chemical vapour deposition (CVD) and liquid exfoliation fabrication methods are described for the fabrication of graphene, WS2 and MoS2 thin films. Finite-difference frequency-domain (FDFD) approach and the Transfer Matrix Method were used in order to mathematically describe these structures. The introduction of thin films of 2D material onto Si3N4 waveguide structures allows manipulation of the optical characteristics to a high degree of precision by varying the Fermi-level through the engineering of the number of atomically thin layers or by electrical tuning, for example. Based on the proposed tuning approach, designs of graphene, WS2 and MoS2 enabled Si3N4 micro-ring structures are presented for the visible and NIR range, which demonstrate versatility and desirable properties for a wide range of applications, such as bio-chemical sensing and optical communications.

Optical reflectivity study of silicon ion implanted poly(methyl methacrylate)

NASA Astrophysics Data System (ADS)

Hadjichristov, Georgi B.; Stefanov, Ivan L.; Florian, Bojana I.; Blaskova, Gergana D.; Ivanov, Victor G.; Faulques, Eric

2009-11-01

The optical reflectivity (both specular and off-specular) of poly(methyl methacrylate) (PMMA) implanted with silicon ions (Si +) at energy of 50 keV, is studied in the spectral range 0.25-25 μm. The effect from the Si + implantation on the reflectivity of two PMMA materials is examined in the dose range from 10 14 to 10 17 ions/cm 2 and is linked to the structure formed in this ion implanted plastic. As compared to the pristine PMMA, an enhancement of the reflectivity of Si + implanted PMMA is observed, that is attributed to the modification of the subsurface region of PMMA upon the ion implantation. The ion-produced subsurface organic interface is also probed by laser-induced thermo-lens.

Materials, structures, and devices for high-speed electronics

NASA Technical Reports Server (NTRS)

Woollam, John A.; Snyder, Paul G.

1992-01-01

Advances in materials, devices, and instrumentation made under this grant began with ex-situ null ellipsometric measurements of simple dielectric films on bulk substrates. Today highly automated and rapid spectroscopic ellipsometers are used for ex-situ characterization of very complex multilayer epitaxial structures. Even more impressive is the in-situ capability, not only for characterization but also for the actual control of the growth and etching of epitaxial layers. Spectroscopic ellipsometry has expanded from the research lab to become an integral part of the production of materials and structures for state of the art high speed devices. Along the way, it has contributed much to our understanding of the growth characteristics and material properties. The following areas of research are summarized: Si3N4 on GaAs, null ellipsometry; diamondlike carbon films; variable angle spectroscopic ellipsometry (VASE) development; GaAs-AlGaAs heterostructures; Ta-Cu diffusion barrier films on GaAs; GaAs-AlGaAs superlattices and multiple quantum wells; superconductivity; in situ elevated temperature measurements of III-V's; optical constants of thermodynamically stable InGaAs; doping dependence of optical constants of GaAs; in situ ellipsometric studies of III-V epitaxial growth; photothermal spectroscopy; microellipsometry; and Si passivation and Si/SiGe strained-layer superlattices.

Improving optical properties of silicon nitride films to be applied in the middle infrared optics by a combined high-power impulse/unbalanced magnetron sputtering deposition technique.

PubMed

Liao, Bo-Huei; Hsiao, Chien-Nan

2014-02-01

Silicon nitride films are prepared by a combined high-power impulse/unbalanced magnetron sputtering (HIPIMS/UBMS) deposition technique. Different unbalance coefficients and pulse on/off ratios are applied to improve the optical properties of the silicon nitride films. The refractive indices of the Si3N4 films vary from 2.17 to 2.02 in the wavelength ranges of 400-700 nm, and all the extinction coefficients are smaller than 1×10(-4). The Fourier transform infrared spectroscopy and x-ray diffractometry measurements reveal the amorphous structure of the Si3N4 films with extremely low hydrogen content and very low absorption between the near IR and middle IR ranges. Compared to other deposition techniques, Si3N4 films deposited by the combined HIPIMS/UBMS deposition technique possess the highest refractive index, the lowest extinction coefficient, and excellent structural properties. Finally a four-layer coating is deposited on both sides of a silicon substrate. The average transmittance from 3200 to 4800 nm is 99.0%, and the highest transmittance is 99.97% around 4200 nm.

Structural evolution and electronic properties of n-type doped hydrogenated amorphous silicon thin films

NASA Astrophysics Data System (ADS)

He, Jian; Li, Wei; Xu, Rui; Qi, Kang-Cheng; Jiang, Ya-Dong

2011-12-01

The relationship between structure and electronic properties of n-type doped hydrogenated amorphous silicon (a-Si:H) thin films was investigated. Samples with different features were prepared by plasma enhanced chemical vapor deposition (PECVD) at various substrate temperatures. Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy were used to evaluate the structural evolution, meanwhile, electronic-spin resonance (ESR) and optical measurement were applied to explore the electronic properties of P-doped a-Si:H thin films. Results reveal that the changes in materials structure affect directly the electronic properties and the doping efficiency of dopant.

The Stellar Imager (SI) Project: A Deep Space UV/Optical Interferometer (UVOI) to Observe the Universe at 0.1 Milli-Arcsec Angular Resolution

NASA Technical Reports Server (NTRS)

Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

2008-01-01

The Stellar Imager (SI) is a space-based, UV/ Optical Interferometer (UVOI) designed to enable 0.1 milliarcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding, of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes, such as accretion, in the Universe. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI is a "Flagship and Landmark Discovery Mission" in the 2005 Heliophysics Roadmap and a potential implementation of the UVOI in the 2006 Science Program for NASA's Astronomy and Physics Division. We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this missin. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

Laser marking on microcrystalline silicon film.

PubMed

Park, Min Gyu; Choi, Se-Bum; Ruh, Hyun; Hwang, Hae-Sook; Yu, Hyunung

2012-07-01

We present a compact dot marker using a CW laser on a microcrystalline silicon (Si) thin film. A laser annealing shows a continuous crystallization transformation from nano to a large domain (> 200 nm) of Si nanocrystals. This microscale patterning is quite useful since we can manipulate a two-dimentional (2-D) process of Si structural forms for better and efficient thin-film transistor (TFT) devices as well as for photovoltaic application with uniform electron mobility. A Raman scattering microscope is adopted to draw a 2-D mapping of crystal Si film with the intensity of optical-phonon mode at 520 cm(-1). At a 300-nm spatial resolution, the position resolved the Raman scattering spectra measurements carried out to observe distribution of various Si species (e.g., large crystalline, polycrystalline and amorphous phase). The population of polycrystalline (poly-Si) species in the thin film can be analyzed with the frequency shift (delta omega) from the optical-phonon line since poly-Si distribution varies widely with conditions, such as an irradiated-laser power. Solid-phase crystallization with CW laser irradiation improves conductivity of poly-Si with micropatterning to develop the potential of the device application.

Large-Scale Fabrication of Silicon Nanowires for Solar Energy Applications.

PubMed

Zhang, Bingchang; Jie, Jiansheng; Zhang, Xiujuan; Ou, Xuemei; Zhang, Xiaohong

2017-10-11

The development of silicon (Si) materials during past decades has boosted up the prosperity of the modern semiconductor industry. In comparison with the bulk-Si materials, Si nanowires (SiNWs) possess superior structural, optical, and electrical properties and have attracted increasing attention in solar energy applications. To achieve the practical applications of SiNWs, both large-scale synthesis of SiNWs at low cost and rational design of energy conversion devices with high efficiency are the prerequisite. This review focuses on the recent progresses in large-scale production of SiNWs, as well as the construction of high-efficiency SiNW-based solar energy conversion devices, including photovoltaic devices and photo-electrochemical cells. Finally, the outlook and challenges in this emerging field are presented.

Hollow waveguides with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films

NASA Astrophysics Data System (ADS)

Zhao, Y.; Jenkins, M.; Measor, P.; Leake, K.; Liu, S.; Schmidt, H.; Hawkins, A. R.

2011-02-01

A type of integrated hollow core waveguide with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films is demonstrated. Hollow core waveguides made with a combination of plasma-enhanced chemical vapor deposition SiO2 and sputtered Ta2O5 provide a nearly optimal structure for optofluidic biofluorescence measurements with low optical loss, high fabrication yield, and low background photoluminescence. Compared to earlier structures made using Si3N4, the photoluminescence background of Ta2O5 based hollow core waveguides is decreased by a factor of 10 and the signal-to-noise ratio for fluorescent nanobead detection is improved by a factor of 12.

Polarization and angle independent magneto-electric Fano resonance in multilayer hetero-nanoshells

NASA Astrophysics Data System (ADS)

Wang, Wudeng; Xiong, Li; Zheng, Li; Li, Wei; Shi, Ying; Qi, Jianguang

2018-05-01

In this work, we have demonstrated that the Si-SiO2 -Au multilayer hetero-nanoshells can support the polarization and angle independent magneto-electric Fano resonance. Such Fano resonance arises from the direct destructive interference between the orthogonal electric dipole mode of Au core and magnetic dipole mode of the Si shell and is independent of the angle due to the high structural symmetry. In contrast to metal particle arrays, here is a possibility to generate controllable interaction between the electric and magnetic dipole resonances of individual nanoshell with the structural features. The discrete magnetic responses provided directly by the Si shell pave the groundwork for designing the magnetic responses at optical frequencies and enable many fascinating applications in nanophotonics.

Ge/graded-SiGe multiplication layers for low-voltage and low-noise Ge avalanche photodiodes on Si

NASA Astrophysics Data System (ADS)

Miyasaka, Yuji; Hiraki, Tatsurou; Okazaki, Kota; Takeda, Kotaro; Tsuchizawa, Tai; Yamada, Koji; Wada, Kazumi; Ishikawa, Yasuhiko

2016-04-01

A new structure is examined for low-voltage and low-noise Ge-based avalanche photodiodes (APDs) on Si, where a Ge/graded-SiGe heterostructure is used as the multiplication layer of a separate-absorption-carrier-multiplication structure. The Ge/SiGe heterojunction multiplication layer is theoretically shown to be useful for preferentially enhancing impact ionization for photogenerated holes injected from the Ge optical-absorption layer via the graded SiGe, reflecting the valence band discontinuity at the Ge/SiGe interface. This property is effective not only for the reduction of operation voltage/electric field strength in Ge-based APDs but also for the reduction of excess noise resulting from the ratio of the ionization coefficients between electrons and holes being far from unity. Such Ge/graded-SiGe heterostructures are successfully fabricated by ultrahigh-vacuum chemical vapor deposition. Preliminary pin diodes having a Ge/graded-SiGe multiplication layer act reasonably as photodetectors, showing a multiplication gain larger than those for diodes without the Ge/SiGe heterojunction.

Optical modulation in silicon-vanadium dioxide photonic structures

NASA Astrophysics Data System (ADS)

Miller, Kevin J.; Hallman, Kent A.; Haglund, Richard F.; Weiss, Sharon M.

2017-08-01

All-optical modulators are likely to play an important role in future chip-scale information processing systems. In this work, through simulations, we investigate the potential of a recently reported vanadium dioxide (VO2) embedded silicon waveguide structure for ultrafast all-optical signal modulation. With a VO2 length of only 200 nm, finite-differencetime- domain simulations suggest broadband (200 nm) operation with a modulation greater than 12 dB and an insertion loss of less than 3 dB. Predicted performance metrics, including modulation speed, modulation depth, optical bandwidth, insertion loss, device footprint, and energy consumption of the proposed Si-VO2 all-optical modulator are benchmarked against those of current state-of-the-art all-optical modulators with in-plane optical excitation.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: A super junction SiGe low-loss fast switching power diode

NASA Astrophysics Data System (ADS)

Ma, Li; Gao, Yong

2009-01-01

This paper proposes a novel super junction (SJ) SiGe switching power diode which has a columnar structure of alternating p- and n- doped pillar substituting conventional n- base region and has far thinner strained SiGe p+ layer to overcome the drawbacks of existing Si switching power diode. The SJ SiGe diode can achieve low specific on-resistance, high breakdown voltages and fast switching speed. The results indicate that the forward voltage drop of SJ SiGe diode is much lower than that of conventional Si power diode when the operating current densities do not exceed 1000 A/cm2, which is very good for getting lower operating loss. The forward voltage drop of the Si diode is 0.66 V whereas that of the SJ SiGe diode is only 0.52 V at operating current density of 10 A/cm2. The breakdown voltages are 203 V for the former and 235 V for the latter. Compared with the conventional Si power diode, the reverse recovery time of SJ SiGe diode with 20 per cent Ge content is shortened by above a half and the peak reverse current is reduced by over 15%. The SJ SiGe diode can remarkably improve the characteristics of power diode by combining the merits of both SJ structure and SiGe material.

Effect of strain on the Curie temperature and band structure of low-dimensional SbSI

NASA Astrophysics Data System (ADS)

Wang, Yiping; Hu, Yang; Chen, Zhizhong; Guo, Yuwei; Wang, Dong; Wertz, Esther A.; Shi, Jian

2018-04-01

Photoferroelectric materials show great promise for developing alternative photovoltaics and photovoltaic-type non-volatile memories. However, the localized nature of the d orbital and large bandgap of most natural photoferroelectric materials lead to low electron/hole mobility and limit the realization of technologically practical devices. Antimony sulpho-iodide (SbSI) is a photoferroelectric material which is expected to have high electron/hole mobility in the ferroelectric state due to its non-local band dispersion and narrow bandgap. However, SbSI exhibits the paraelectric state close to room temperature. In this report, as a proof of concept, we explore the possibility to stabilize the SbSI ferroelectric phase above room temperature via mechanical strain engineering. We synthesized thin low-dimensional crystals of SbSI by chemical vapor deposition, confirmed its crystal structure with electron diffraction, studied its optical properties via photoluminescence spectroscopy and time-resolved photoluminescence spectroscopy, and probed its phase transition using temperature-dependent steady-state photoluminescence spectroscopy. We found that introducing external mechanical strain to these low-dimensional crystals may lead to an increase in their Curie temperature (by ˜60 K), derived by the strain-modified optical phase transition in SbSI and quantified by Kern formulation and Landau theory. The study suggests that strain engineering could be an effective way to stabilize the ferroelectric phase of SbSI at above room temperature, providing a solution enabling its application for technologically useful photoferroelectric devices.

Direct measurement of Dirac point energy at the graphene/oxide interface.

PubMed

Xu, Kun; Zeng, Caifu; Zhang, Qin; Yan, Rusen; Ye, Peide; Wang, Kang; Seabaugh, Alan C; Xing, Huili Grace; Suehle, John S; Richter, Curt A; Gundlach, David J; Nguyen, N V

2013-01-09

We report the direct measurement of the Dirac point, the Fermi level, and the work function of graphene by performing internal photoemission measurements on a graphene/SiO(2)/Si structure with a unique optical-cavity enhanced test structure. A complete electronic band alignment at the graphene/SiO(2)/Si interfaces is accurately established. The observation of enhanced photoemission from a one-atom thick graphene layer was possible by taking advantage of the constructive optical interference in the SiO(2) cavity. The photoemission yield was found to follow the well-known linear density-of-states dispersion in the vicinity of the Dirac point. At the flat band condition, the Fermi level was extracted and found to reside 3.3 eV ± 0.05 eV below the bottom of the SiO(2) conduction band. When combined with the shift of the Fermi level from the Dirac point, we are able to ascertain the position of the Dirac point at 3.6 eV ± 0.05 eV with respect to the bottom of the SiO(2) conduction band edge, yielding a work function of 4.5 eV ± 0.05 eV which is in an excellent agreement with theory. The accurate determination of the work function of graphene is of significant importance to the engineering of graphene-based devices, and the measurement technique we have advanced in this Letter will have significant impact on numerous applications for emerging graphene-like 2-dimensional material systems.

Amorphous Ge quantum dots embedded in crystalline Si: ab initio results.

PubMed

Laubscher, M; Küfner, S; Kroll, P; Bechstedt, F

2015-10-14

We study amorphous Ge quantum dots embedded in a crystalline Si matrix through structure modeling and simulation using ab initio density functional theory including spin-orbit interaction and quasiparticle effects. Three models are generated by replacing a spherical region within diamond Si by Ge atoms and creating a disordered bond network with appropriate density inside the Ge quantum dot. After total-energy optimisations of the atomic geometry we compute the electronic and optical properties. We find three major effects: (i) the resulting nanostructures adopt a type-I heterostructure character; (ii) the lowest optical transitions occur only within the Ge quantum dots, and do not involve or cross the Ge-Si interface. (iii) for larger amorphous Ge quantum dots, with diameters of about 2.0 and 2.7 nm, absorption peaks appear in the mid-infrared spectral region. These are promising candidates for intense luminescence at photon energies below the gap energy of bulk Ge.

Multifunctional, angle dependent antireflection, and hydrophilic properties of SiO2 inspired by nano-scale structures of cicada wings

NASA Astrophysics Data System (ADS)

Zada, Imran; Zhang, Wang; Sun, Peng; Imtiaz, Muhammad; Abbas, Waseem; Zhang, Di

2017-10-01

Inspired by the multifunctional properties of cicada wings, we have precisely replicated biomorphic SiO2 with antireflective structures (ARSs) using a simple, inexpensive, and highly effective sol-gel ultrasonic method. The biomorphic replica of SiO2 was directly achieved from a cicada template at high calcination. The biomorphic SiO2 not only inherited the ARS effectively but also exhibited the excellent angle dependent antireflective properties over a wide range of incident angles (10°-60°). The change in reflectance spectra (visible wavelength) of biomorphic SiO2 was observed from 0.3% to 3.3% with the increasing incident angles. The smooth surface of the SiO2 crystal without nanostructures showed a high reflection of 9.2% compared to the biomorphic SiO2 with ARS. These excellent antireflective properties of biomorphic SiO2 can be attributed to the nanoscale structures which introduce a gradient in the refractive index between air and the material surface via ARS. In the meantime, biomorphic SiO2 demonstrates high hydrophilic properties due to the existence of nanostructures on its surface. These multifunctional properties of biomorphic SiO2, angle dependent antireflective properties, and hydrophilicity with high thermal stability may have potential applications in solar cells and antifogging optical materials.

3D structured illumination microscopy using an incoherent illumination system based on a Fresnel biprism

NASA Astrophysics Data System (ADS)

Shabani, H.; Doblas, A.; Saavedra, G.; Preza, C.

2018-02-01

Three-dimensional (3D) structured illumination (SI) patterns that include lateral and axial variations have attracted more attention recently as their use in fluorescence microscope enhances the 3D resolution of the native imaging system. 3D SI patterns have already been created by interfering three mutually-coherent waves using a diffraction grating or some electro-optical devices such as spatial light modulators. Here, an interesting approach to generate a 3D SI pattern of tunable modulation frequency is shown. Our proposed illumination system is based on the incoherent illumination of a Fresnel biprism using several equidistant linear sources (i.e., slits). Previously, we investigated and compared numerically this tunable SI microscopy (SIM) system with the one achieved with three-wave interference. In this contribution, we implement our proposed incoherent 3D SIM system of tunable-frequency in an open-setup. We evaluate the axial confinement of the illumination pattern obtained with this system by recording the SI pattern using a mirror sample and different number of slits and compare these data with simulation results. Moreover, we verify that with a higher number of slits used, the axial confinement of the pattern increases, and consequently, the system's optical sectioning capability improves.

Nanoscale plasmonic phenomena in CVD-grown MoS 2 monolayer revealed by ultra-broadband synchrotron radiation based nano-FTIR spectroscopy and near-field microscopy

DOE PAGES

Patoka, Piotr; Ulrich, Georg; Nguyen, Ariana E.; ...

2016-01-13

Here, nanoscale plasmonic phenomena observed in single and bi-layers of molybdenum disulfide (MoS 2) on silicon dioxide (SiO 2) are reported. A scattering type scanning near-field optical microscope (s-SNOM) with a broadband synchrotron radiation (SR) infrared source was used. We also present complementary optical mapping using tunable CO 2-laser radiation. Specifically, there is a correlation of the topography of well-defined MoS 2 islands grown by chemical vapor deposition, as determined by atomic force microscopy, with the infrared (IR) signature of MoS 2. The influence of MoS 2 islands on the SiO 2 phonon resonance is discussed. The results reveal themore » plasmonic character of the MoS 2 structures and their interaction with the SiO 2 phonons leading to an enhancement of the hybridized surface plasmon-phonon mode. A theoretical analysis shows that, in the case of monolayer islands, the coupling of the MoS 2 optical plasmon mode to the SiO 2 surface phonons does not affect the infrared spectrum significantly. For two-layer MoS 2, the coupling of the extra inter-plane acoustic plasmon mode with the SiO 2 surface transverse phonon leads to a remarkable increase of the surface phonon peak at 794 cm -1. This is in agreement with the experimental data. These results show the capability of the s-SNOM technique to study local multiple excitations in complex non-homogeneous structures.« less

Extracting the Density of States of Copper Phthalocyanine at the SiO2 Interface with Electronic Sum Frequency Generation.

PubMed

Pandey, Ravindra; Moon, Aaron P; Bender, Jon A; Roberts, Sean T

2016-03-17

Organic semiconductors (OSCs) constitute an attractive platform for optoelectronics design due to the ease of their processability and chemically tunable properties. Incorporating OSCs into electrical circuits requires forming junctions between them and other materials, yet the change in dielectric properties about these junctions can strongly perturb the electronic structure of the OSC. Here we adapt an interface-selective optical technique, electronic sum frequency generation (ESFG), to the study of a model OSC thin-film system, copper phthalocyanine (CuPc) deposited on SiO2. We find that by modeling the thickness dependence of our measured spectra, we can identify changes in CuPc's electronic density of states at both its buried interface with SiO2 and air-exposed surface. Our work demonstrates that ESFG can be used to noninvasively probe the interfacial electronic structure of optically thick OSC films, indicating that it can be used for the study of OSC-based optoelectronics in situ.

Controlling the opto-electronic properties of nc-SiOx:H films by promotion of 〈220〉 orientation in the growth of ultra-nanocrystallites at the grain boundary

NASA Astrophysics Data System (ADS)

Das, Debajyoti; Samanta, Subhashis

2018-01-01

A systematic development of undoped nc-SiOx:H thin films from (SiH4 + CO2) plasma diluted by a combination of H2 and He has been investigated through structural, optical and electrical characterization and correlation. Gradual inclusion of O into a highly crystalline silicon network progressively produces a two-phase structure where Si-nanocrystals (Si-nc) are embedded into the a-SiOx:H matrix. However, at the intermediate grain boundary region the growth of ultra-nanocrystallites controls the effectiveness of the material. The ultra-nanocrystallites are the part and portion of crystallinity accommodating the dominant fraction of thermodynamically preferred 〈220〉 crystallographic orientation, most favourable for stacked layer device performance. Atomic H plays a dominant role in maintaining an improved nanocrystalliny in the network even during O inclusion, while He in its excited state (He*) maintains a good energy balance at the grain boundary and produces a significant fraction of ultra-nanocrystalline component which has been demonstrated to organize the energetically favourable 〈220〉 crystallographic orientation in the network. The nc-SiOx:H films, maintaining proportionally good electrical conductivity over an wide range of optical band gap, remarkably low microstructure factor and simultaneous high crystalline volume fraction dominantly populated by ultra-nanocrystallites of 〈220〉 crystallographic orientation mostly at the grain boundary, have been obtained in technologically most popular 13.56 MHz PECVD SiH4 plasma even at a low substrate temperature ∼250 °C, convenient for device fabrication.

Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

DOE PAGES

Subedi, Indra; Silverman, Timothy J.; Deceglie, Michael G.; ...

2017-10-18

Al is a commonly used material for rear side metallization in commercial silicon (Si) wafer solar cells. In this study, through-the-silicon spectroscopic ellipsometry is used in a test sample to measure Al+Si interface optical properties like those in Si wafer solar cells. Two different spectroscopic ellipsometers are used for measurement of Al+Si interface optical properties over the 1128-2500 nm wavelength range. For validation, the measured interface optical properties are used in a ray tracing simulation over the 300-2500 nm wavelength range for an encapsulated Si solar cell having random pyramidal texture. The ray tracing model matches well with the measuredmore » total reflectance at normal incidence of a commercially available Si module. The Al+Si optical properties presented here enable quantitative assessment of major irradiance/current flux losses arising from reflection and parasitic absorption in encapsulated Si solar cells.« less

Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Subedi, Indra; Silverman, Timothy J.; Deceglie, Michael G.

Al is a commonly used material for rear side metallization in commercial silicon (Si) wafer solar cells. In this study, through-the-silicon spectroscopic ellipsometry is used in a test sample to measure Al+Si interface optical properties like those in Si wafer solar cells. Two different spectroscopic ellipsometers are used for measurement of Al+Si interface optical properties over the 1128-2500 nm wavelength range. For validation, the measured interface optical properties are used in a ray tracing simulation over the 300-2500 nm wavelength range for an encapsulated Si solar cell having random pyramidal texture. The ray tracing model matches well with the measuredmore » total reflectance at normal incidence of a commercially available Si module. The Al+Si optical properties presented here enable quantitative assessment of major irradiance/current flux losses arising from reflection and parasitic absorption in encapsulated Si solar cells.« less

Light-emitting diodes based on colloidal silicon quantum dots

NASA Astrophysics Data System (ADS)

Zhao, Shuangyi; Liu, Xiangkai; Pi, Xiaodong; Yang, Deren

2018-06-01

Colloidal silicon quantum dots (Si QDs) hold great promise for the development of printed Si electronics. Given their novel electronic and optical properties, colloidal Si QDs have been intensively investigated for optoelectronic applications. Among all kinds of optoelectronic devices based on colloidal Si QDs, QD light-emitting diodes (LEDs) play an important role. It is encouraging that the performance of LEDs based on colloidal Si QDs has been significantly increasing in the past decade. In this review, we discuss the effects of the QD size, QD surface and device structure on the performance of colloidal Si-QD LEDs. The outlook on the further optimization of the device performance is presented at the end.

Synthesis and Characterization of Monodisperse Core-shell Lanthanide Upconversion Nanoparticles NaYF4: Yb,Tm/SiO2

NASA Astrophysics Data System (ADS)

Manurung, R. V.; Wiranto, G.; Hermida, I. D. P.

2018-05-01

Lanthanide up-converting luminescent nanoparticles (UCNPs) are exciting and promising materials for optical bioimaging, biosensor and theranostic due to their unique and advantageous optical and chemical properties. The UCNPs absorb low energy near-infrared (NIR) light and emit high-energy shorter wavelength photons (visible light). Their unique features allow them to overcome various problems associated with conventional imaging probes such as photostability, lack of toxicity, and to provide versatility for creating nanoplatforms with both imaging and therapeutic modalities. This paper reports synthesis and characterization of core-shell structured of NaYF4:Yb,Tm/SiO2 microspheres. The synthesis of lanthanide upconversion nanoparticles NaYF4:Yb,Tm was prepared by thermal decomposition process which involves dissolving organic precursors in high-boiling-point solvents oleic acid (OA) and octadecene (ODE). After that, the NaYF4:Yb,Tm phosphors was coated by silica via reverse microemulsion process to obtain core-shell structured NaYF4:Yb,Tm/SiO2. Scanning electron microscopy, transmission electron microscopy, specific area electron diffraction, and photoluminescence were applied to characterize these samples. The obtained core-shell structured NaYF4:Yb,Tm/SiO2 phosphors exhibit a perfect cubic morphology with narrow size distribution and smooth surface. Upon IR excitation at 980 nm, the NaYF4:Yb,Tm/SiO2 samples exhibit whitish blue upconversion (UC) luminescence, respectively. These phosphors show potential applications in the displaying on biological fields and biosensing.

Laser-induced thermo-lens in ion-implanted optically-transparent polymer

NASA Astrophysics Data System (ADS)

Stefanov, Ivan L.; Ivanov, Victor G.; Hadjichristov, Georgi B.

2009-10-01

A strong laser-induced thermo-lens (LITL) effect is found in optically-transparent ion-implanted polymer upon irradiation by a cw laser with a power up to 100 mW (λ = 532 nm). The effect is observed in bulk polymethylmethacrylate (PMMA) implanted with silicon ions (Si+). A series of PMMA specimens is examined, subjected to low-energy (50 keV) Si+ implantation at various dosages in the range from 1014 to 1017 ions/cm2. The thermo-lensing is unambiguously attributed to the modification of the subsurface region of the polymer upon the ion implantation. Having a gradient refractive-index in-depth profile, the subsurface organic-carbonaceous layer produced in the polymer by ion implantation, is responsible for the LITL effect observed in reflection geometry. The LITL occurs due to optical absorption of the ion-implanted layer of a thickness of about 100 nm buried in a depth ~ 100 nm, and subsequent laser-induced change in the refractive index of the Si+-implanted PMMA. Being of importance as considering photonic applications of ion-implanted optically-transparent polymers, the LITL effect in Si+-implanted PMMA is studied as a function of the implant dose, the incident laser power and incidence angle, and is linked to the structure formed in this ion-implanted plastic.

Porous silicon formation during Au-catalyzed etching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Algasinger, Michael; Bernt, Maximilian; Koynov, Svetoslav

2014-04-28

The formation of “black” nano-textured Si during the Au-catalyzed wet-chemical etch process was investigated with respect to photovoltaic applications. Cross-sectional scanning electron microscopy (SEM) images recorded at different stages of the etch process exhibit an evolution of a two-layer structure, consisting of cone-like Si hillocks covered with a nano-porous Si (np-Si) layer. Optical measurements confirm the presence of a np-Si phase which appears after the first ∼10 s of the etch process and continuously increases with the etch time. Furthermore, the etch process was investigated on Si substrates with different doping levels (∼0.01–100 Ω cm). SEM images show a transition frommore » the two-layer morphology to a structure consisting entirely of np-Si for higher doping levels (<0.1 Ω cm). The experimental results are discussed on the basis of the model of a local electrochemical etch process. A better understanding of the metal-catalyzed etch process facilitates the fabrication of “black” Si on various Si substrates, which is of significant interest for photovoltaic applications.« less

Buffer layer between a planar optical concentrator and a solar cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solano, Manuel E.; Barber, Greg D.; Department of Chemistry, Pennsylvania State University, University Park, PA 16802

2015-09-15

The effect of inserting a buffer layer between a periodically multilayered isotropic dielectric (PMLID) material acting as a planar optical concentrator and a photovoltaic solar cell was theoretically investigated. The substitution of the photovoltaic material by a cheaper dielectric material in a large area of the structure could reduce the fabrication costs without significantly reducing the efficiency of the solar cell. Both crystalline silicon (c-Si) and gallium arsenide (GaAs) were considered as the photovoltaic material. We found that the buffer layer can act as an antireflection coating at the interface of the PMLID and the photovoltaic materials, and the structuremore » increases the spectrally averaged electron-hole pair density by 36% for c-Si and 38% for GaAs compared to the structure without buffer layer. Numerical evidence indicates that the optimal structure is robust with respect to small changes in the grating profile.« less

Growth of low temperature silicon nano-structures for electronic and electrical energy generation applications.

PubMed

Gabrielyan, Nare; Saranti, Konstantina; Manjunatha, Krishna Nama; Paul, Shashi

2013-02-15

This paper represents the lowest growth temperature for silicon nano-wires (SiNWs) via a vapour-liquid-solid method, which has ever been reported in the literature. The nano-wires were grown using plasma-enhanced chemical vapour deposition technique at temperatures as low as 150°C using gallium as the catalyst. This study investigates the structure and the size of the grown silicon nano-structure as functions of growth temperature and catalyst layer thickness. Moreover, the choice of the growth temperature determines the thickness of the catalyst layer to be used.The electrical and optical characteristics of the nano-wires were tested by incorporating them in photovoltaic solar cells, two terminal bistable memory devices and Schottky diode. With further optimisation of the growth parameters, SiNWs, grown by our method, have promising future for incorporation into high performance electronic and optical devices.

Growth of low temperature silicon nano-structures for electronic and electrical energy generation applications

PubMed Central

2013-01-01

This paper represents the lowest growth temperature for silicon nano-wires (SiNWs) via a vapour-liquid–solid method, which has ever been reported in the literature. The nano-wires were grown using plasma-enhanced chemical vapour deposition technique at temperatures as low as 150°C using gallium as the catalyst. This study investigates the structure and the size of the grown silicon nano-structure as functions of growth temperature and catalyst layer thickness. Moreover, the choice of the growth temperature determines the thickness of the catalyst layer to be used. The electrical and optical characteristics of the nano-wires were tested by incorporating them in photovoltaic solar cells, two terminal bistable memory devices and Schottky diode. With further optimisation of the growth parameters, SiNWs, grown by our method, have promising future for incorporation into high performance electronic and optical devices. PMID:23413969

Nano-Bio Quantum Technology for Device-Specific Materials

NASA Technical Reports Server (NTRS)

Choi, Sang H.

2009-01-01

The areas discussed are still under development: I. Nano structured materials for TE applications a) SiGe and Be.Te; b) Nano particles and nanoshells. II. Quantum technology for optical devices: a) Quantum apertures; b) Smart optical materials; c) Micro spectrometer. III. Bio-template oriented materials: a) Bionanobattery; b) Bio-fuel cells; c) Energetic materials.

Dipole-allowed direct band gap silicon superlattices

PubMed Central

Oh, Young Jun; Lee, In-Ho; Kim, Sunghyun; Lee, Jooyoung; Chang, Kee Joo

2015-01-01

Silicon is the most popular material used in electronic devices. However, its poor optical properties owing to its indirect band gap nature limit its usage in optoelectronic devices. Here we present the discovery of super-stable pure-silicon superlattice structures that can serve as promising materials for solar cell applications and can lead to the realization of pure Si-based optoelectronic devices. The structures are almost identical to that of bulk Si except that defective layers are intercalated in the diamond lattice. The superlattices exhibit dipole-allowed direct band gaps as well as indirect band gaps, providing ideal conditions for the investigation of a direct-to-indirect band gap transition. The fact that almost all structural portions of the superlattices originate from bulk Si warrants their stability and good lattice matching with bulk Si. Through first-principles molecular dynamics simulations, we confirmed their thermal stability and propose a possible method to synthesize the defective layer through wafer bonding. PMID:26656482

Al{sub 4}SiC{sub 4} wurtzite crystal: Structural, optoelectronic, elastic, and piezoelectric properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pedesseau, L., E-mail: laurent.pedesseau@insa-rennes.fr, E-mail: jacky.even@insa-rennes.fr; Even, J., E-mail: laurent.pedesseau@insa-rennes.fr, E-mail: jacky.even@insa-rennes.fr; Durand, O.

New experimental results supported by theoretical analyses are proposed for aluminum silicon carbide (Al{sub 4}SiC{sub 4}). A state of the art implementation of the density functional theory is used to analyze the experimental crystal structure, the Born charges, the elastic properties, and the piezoelectric properties. The Born charge tensor is correlated to the local bonding environment for each atom. The electronic band structure is computed including self-consistent many-body corrections. Al{sub 4}SiC{sub 4} material properties are compared to other wide band gap wurtzite materials. From a comparison between an ellipsometry study of the optical properties and theoretical results, we conclude thatmore » the Al{sub 4}SiC{sub 4} material has indirect and direct band gap energies of about 2.5 eV and 3.2 eV, respectively.« less

Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands.

PubMed

Carroll, Gerard M; Limpens, Rens; Neale, Nathan R

2018-05-09

The optical properties of silicon nanocrystals (Si NCs) are a subject of intense study and continued debate. In particular, Si NC photoluminescence (PL) properties are known to depend strongly on the surface chemistry, resulting in electron-hole recombination pathways derived from the Si NC band-edge, surface-state defects, or combined NC-conjugated ligand hybrid states. In this Letter, we perform a comparison of three different saturated surface functional groups-alkyls, amides, and alkoxides-on nonthermal plasma-synthesized Si NCs. We find a systematic and size-dependent high-energy (blue) shift in the PL spectrum of Si NCs with amide and alkoxy functionalization relative to alkyl. Time-resolved photoluminescence and transient absorption spectroscopies reveal no change in the excited-state dynamics between Si NCs functionalized with alkyl, amide, or alkoxide ligands, showing for the first time that saturated ligands-not only surface-derived charge-transfer states or hybridization between NC and low-lying ligand orbitals-are responsible for tuning the Si NC optical properties. To explain these PL shifts we propose that the atom bound to the Si NC surface strongly interacts with the Si NC electronic wave function and modulates the Si NC quantum confinement. These results reveal a potentially broadly applicable correlation between the optoelectronic properties of Si NCs and related quantum-confined structures based on the interaction between NC surfaces and the ligand binding group.

Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands

DOE PAGES

Carroll, Gerard M.; Limpens, Rens; Neale, Nathan R.

2018-04-16

The optical properties of silicon nanocrystals (Si NCs) are a subject of intense study and continued debate. In particular, Si NC photoluminescence (PL) properties are known to depend strongly on the surface chemistry, resulting in electron-hole recombination pathways derived from the Si NC band-edge, surface-state defects, or combined NC-conjugated ligand hybrid states. In this Letter, we perform a comparison of three different saturated surface functional groups - alkyls, amides, and alkoxides - on nonthermal plasma-synthesized Si NCs. We find a systematic and size-dependent high-energy (blue) shift in the PL spectrum of Si NCs with amide and alkoxy functionalization relative tomore » alkyl. Time-resolved photoluminescence and transient absorption spectroscopies reveal no change in the excited-state dynamics between Si NCs functionalized with alkyl, amide, or alkoxide ligands, showing for the first time that saturated ligands - not only surface-derived charge-transfer states or hybridization between NC and low-lying ligand orbitals - are responsible for tuning the Si NC optical properties. To explain these PL shifts we propose that the atom bound to the Si NC surface strongly interacts with the Si NC electronic wave function and modulates the Si NC quantum confinement. Furthermore, these results reveal a potentially broadly applicable correlation between the optoelectronic properties of Si NCs and related quantum-confined structures based on the interaction between NC surfaces and the ligand binding group.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neale, Nathan R; Carroll, Gerard; Limpens, Rens

The optical properties of silicon nanocrystals (Si NCs) are a subject of intense study and continued debate. In particular, Si NC photoluminescence (PL) properties are known to depend strongly on the surface chemistry, resulting in electron-hole recombination pathways derived from the Si NC band-edge, surface-state defects, or combined NC-conjugated ligand hybrid states. In this Letter, we perform a comparison of three different saturated surface functional groups - alkyls, amides, and alkoxides - on nonthermal plasma-synthesized Si NCs. We find a systematic and size-dependent high-energy (blue) shift in the PL spectrum of Si NCs with amide and alkoxy functionalization relative tomore » alkyl. Time-resolved photoluminescence and transient absorption spectroscopies reveal no change in the excited-state dynamics between Si NCs functionalized with alkyl, amide, or alkoxide ligands, showing for the first time that saturated ligands - not only surface-derived charge-transfer states or hybridization between NC and low-lying ligand orbitals - are responsible for tuning the Si NC optical properties. To explain these PL shifts we propose that the atom bound to the Si NC surface strongly interacts with the Si NC electronic wave function and modulates the Si NC quantum confinement. These results reveal a potentially broadly applicable correlation between the optoelectronic properties of Si NCs and related quantum-confined structures based on the interaction between NC surfaces and the ligand binding group.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahlawat, Navneet; Aghamkar, Praveen; Ahlawat, Neetu

Lithium lead silicate glasses with composition 30Li{sub 2}O{center_dot}(70-x)PbO{center_dot}xSiO{sub 2}(where, x = 10, 20, 30, 40, 50 mol %)(LPS glasses) were prepared by normal melt quench technique at 1373 K for half an hour in air to understand their structure. Compositional dependence of density, molar volume and glass transition temperature of these glasses indicates more compactness of the glass structure with increasing SiO{sub 2} content. Fourier transform infrared (FTIR) spectroscopic data obtained for these glasses was used to investigate the changes induced in the local structure of samples as the ratio between PbO and SiO{sub 2} content changes from 6.0 tomore » 0.4. The observed absorption band around 450-510 cm{sup -1} in IR spectra of these glasses indicates the presence of network forming PbO{sub 4} tetrahedral units in glass structure. The increase in intensity with increasing SiO{sub 2} content (upto x = 30 mol %) suggests superposition of Pb-O and Si-O bond vibrations in absorption band around 450-510 cm{sup -1}. The values of optical basicity in these glasses were found to be dependent directly on PbO/SiO{sub 2} ratio.« less

Recent achievements using chemical vapor composite silicon carbide (CVC SiC)

NASA Astrophysics Data System (ADS)

Goodman, William A.; Tanaka, Clifford

2009-08-01

This annual review documents our progress towards inexpensive mass production of silicon carbide mirrors and optical structures. Results are provided for a NASA Small Business Technology Transfer (STTR) X-Ray Mirror project. Trex partnered with the University of Alabama-Huntsville Center for Advanced Optics (UAH-CAO) to develop fabrication methods for polished cylindrical and conical chemical vapor composite (CVCTM) SiC mandrels. These mandrels are envisioned as pre-forms for the replication of fused silica x-ray optics to be eventually used in the International X-Ray Observatory (IXO). CVC SiCTM offers superior high temperature stability, thermal and mechanical performance and polishability required for this precision replication process. In this program, Trex fabricated prototype mandrels with design diameters of 10.5cm, 20cm and 45cm. UAH-CAO was Trex's university partner in this effort and worked on polishing and metrology of the unusual x-ray mandrel geometries. UAH-CAO successfully developed an innovative interferometric method for measuring the CVC SiCTM x-ray mandrels based on a precision cylindrical lens system. UAH-CAO also developed finishing and polishing methods for CVC SiCTM that utilized a Zeeko IRP200 computer controlled polishing tool. The three technologies key technologies demonstrated in this program (near net shape forming of CVC SiCTM mandrels, the x-ray mandrel metrology and free-form polishing capability on CVC SiCTM) could enable cost-effective manufacture of the x-ray mandrels required for the International X-Ray Observatory (IXO).

The Stellar Imager (SI) project: a deep space UV/Optical Interferometer (UVOI) to observe the Universe at 0.1 milli-arcsec angular resolution

NASA Astrophysics Data System (ADS)

Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

2009-04-01

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI’s science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes, such as accretion, in the Universe. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI is a “Flagship and Landmark Discovery Mission” in the 2005 Heliophysics Roadmap and a potential implementation of the UVOI in the 2006 Science Program for NASA’s Astronomy and Physics Division. We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/

Thermo-mechanical performance of precision C/SiC mounts

NASA Astrophysics Data System (ADS)

Goodman, William A.; Mueller, Claus E.; Jacoby, Marc T.; Wells, Jim D.

2001-12-01

For complex shaped, lightweight, high precision opto- mechanical structures that must operate in adverse environments and over wide ranges of temperature, we consider IABG's optical grade silicon carbide composite ceramic (C/SiC) as the material of choice. C/SiC employs conventional NC machining/milling equipment to rapidly fabricate near-net shape parts, providing substantial schedule, cost, and risk savings for high precision components. Unlike powder based SiC ceramics, C/SiC does not experience significant shrinkage during processing, nor does it suffer from incomplete densification. If required, e.g. for large-size components, a fully-monolithic ceramic joining technique can be applied. Generally, the thermal and mechanical properties of C/SiC are tunable in certain ranges by modifying certain process steps. This paper focuses on the thermo-mechanical performance of new, high precision mounts designed by Schafer Corporation and manufactured by IABG. The mounts were manufactured using standard optical grade C/SiC (formulation internally called A-3). The A-3 formulation has a near-perfect CTE match with silicon, making it the ideal material to athermally support Schafer produced Silicon Lightweight Mirrors (SLMs) that will operate in a cryogenic environment. Corresponding thermo- mechanical testing and analysis is presented in this manuscript.

Thin SiGe virtual substrates for Ge heterostructures integration on silicon

NASA Astrophysics Data System (ADS)

Cecchi, S.; Gatti, E.; Chrastina, D.; Frigerio, J.; Müller Gubler, E.; Paul, D. J.; Guzzi, M.; Isella, G.

2014-03-01

The possibility to reduce the thickness of the SiGe virtual substrate, required for the integration of Ge heterostructures on Si, without heavily affecting the crystal quality is becoming fundamental in several applications. In this work, we present 1 μm thick Si1-xGex buffers (with x > 0.7) having different designs which could be suitable for applications requiring a thin virtual substrate. The rationale is to reduce the lattice mismatch at the interface with the Si substrate by introducing composition steps and/or partial grading. The relatively low growth temperature (475 °C) makes this approach appealing for complementary metal-oxide-semiconductor integration. For all the investigated designs, a reduction of the threading dislocation density compared to constant composition Si1-xGex layers was observed. The best buffer in terms of defects reduction was used as a virtual substrate for the deposition of a Ge/SiGe multiple quantum well structure. Room temperature optical absorption and photoluminescence analysis performed on nominally identical quantum wells grown on both a thick graded virtual substrate and the selected thin buffer demonstrates a comparable optical quality, confirming the effectiveness of the proposed approach.

The effect of thermal oxidation on the luminescence properties of nanostructured silicon.

PubMed

Liu, Lijia; Sham, Tsun-Kong

2012-08-06

Herein is reported a detailed study of the luminescence properties of nanostructured Si using X-ray excited optical luminescence (XEOL) in combination with X-ray absorption near-edge structures (XANES). P-type Si nanowires synthesized via electroless chemical etching from Si wafers of different doping levels and porous Si synthesized using electrochemical method are examined under X-ray excitation across the Si K-, L(3,2) -, and O K-edges. It is found that while as-prepared Si nanostructures are weak light emitters, intense visible luminescence is observed from thermally oxidized Si nanowires and porous Si. The luminescence mechanism of Si upon oxidation is investigated by oxidizing nanostructured Si at different temperatures. Interestingly, the two luminescence bands observed show different response with the variation of absorption coefficient upon Si and O core-electron excitation in elemental silicon and silicon oxide. A correlation between luminescence properties and electronic structures is thus established. The implications of the finding are discussed in terms of the behavior of the oxygen deficient center (OCD) and non-bridging oxygen hole center (NBOHC). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Comparative Study of Structural Stability and Mechanical and Optical Properties of Fluorapatite (Ca5(PO4)3F) and Lithium Disilicate (Li2Si2O5) Components Forming Dental Glass-Ceramics: First Principles Study

NASA Astrophysics Data System (ADS)

Biskri, Z. E.; Rached, H.; Bouchear, M.; Rached, D.; Aida, M. S.

2016-10-01

The aim of this paper is a comparative study of structural stability and mechanical and optical properties of fluorapatite (FA) (Ca5(PO4)3F) and lithium disilicate (LD) (Li2Si2O5), using the first principles pseudopotential method based on density functional theory (DFT) within the generalized gradient approximation (GGA). The stability of fluorapatite and lithium disilicate compounds has been evaluated on the basis of their formation enthalpies. The results show that fluorapatite is more energetically stable than lithium disilicate. The independent elastic constants and related mechanical properties, including bulk modulus ( B), shear modulus ( G), Young's modulus ( E) and Poisson's ratio ( ν) as well as the Vickers hardness ( H v), have been calculated for fluorapatite compound and compared with other theoretical and experimental results. The obtained values of the shear modulus, Young's modulus and Vickers hardness are smaller in comparison with those of lithium disilicate compound, implying that lithium disilicate is more rigid than fluorapatite. The brittle and ductile properties were also discussed using B/ G ratio and Poisson's ratio. Optical properties such as refractive index n( ω), extinction coefficient k( ω), absorption coefficient α( ω) and optical reflectivity R( ω) have been determined from the calculations of the complex dielectric function ɛ( ω), and interpreted on the basis of the electronic structures of both compounds. The calculated values of static dielectric constant ɛ 1(0) and static refractive index n(0) show that the Li2Si2O5 compound has larger values compared to those of the Ca5(PO4)3F compound. The results of the extinction coefficient show that Li2Si2O5 compound exhibits a much stronger ultraviolet absorption. According to the absorption and reflectivity spectra, we inferred that both compounds are theoretically the best visible and infrared transparent materials.

Optical sensor in planar configuration based on multimode interference

NASA Astrophysics Data System (ADS)

Blahut, Marek

2017-08-01

In the paper a numerical analysis of optical sensors based on multimode interference in planar one-dimensional step-index configuration is presented. The structure consists in single-mode input and output waveguides and multimode waveguide which guide only few modes. Material parameters discussed refer to a SU8 polymer waveguide on SiO2 substrate. The optical system described will be designed to the analysis of biological substances.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xin, Yunzi; Nishio, Kazuyuki; Saitow, Ken-ichi, E-mail: saitow@hiroshima-u.ac.jp

A silicon (Si) quantum dot (QD)-based hybrid inorganic/organic light-emitting diode (LED) was fabricated via solution processing. This device exhibited white-blue electroluminescence at a low applied voltage of 6 V, with 78% of the effective emission obtained from the Si QDs. This hybrid LED produced current and optical power densities 280 and 350 times greater than those previously reported for such device. The superior performance of this hybrid device was obtained by both the prepared Si QDs and the optimized layer structure and thereby improving carrier migration through the hybrid LED and carrier recombination in the homogeneous Si QD layer.

Polymer sol-gel composite inverse opal structures.

PubMed

Zhang, Xiaoran; Blanchard, G J

2015-03-25

We report on the formation of composite inverse opal structures where the matrix used to form the inverse opal contains both silica, formed using sol-gel chemistry, and poly(ethylene glycol), PEG. We find that the morphology of the inverse opal structure depends on both the amount of PEG incorporated into the matrix and its molecular weight. The extent of organization in the inverse opal structure, which is characterized by scanning electron microscopy and optical reflectance data, is mediated by the chemical bonding interactions between the silica and PEG constituents in the hybrid matrix. Both polymer chain terminus Si-O-C bonding and hydrogen bonding between the polymer backbone oxygens and silanol functionalities can contribute, with the polymer mediating the extent to which Si-O-Si bonds can form within the silica regions of the matrix due to hydrogen-bonding interactions.

Fabrication and characterization of Al{sub 2}O{sub 3} /Si composite nanodome structures for high efficiency crystalline Si thin film solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Ruiying, E-mail: ryzhang2008@sinano.ac.cn; State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 China; Zhu, Jian

2015-12-15

We report on our fabrication and characterization of Al{sub 2}O{sub 3}/Si composite nanodome (CND) structures, which is composed of Si nanodome structures with a conformal cladding Al{sub 2}O{sub 3} layer to evaluate its optical and electrical performance when it is applied to thin film solar cells. It has been observed that by application of Al{sub 2}O{sub 3}thin film coating using atomic layer deposition (ALD) to the Si nanodome structures, both optical and electrical performances are greatly improved. The reflectivity of less than 3% over the wavelength range of from 200 nm to 2000 nm at an incident angle from 0°more » to 45° is achieved when the Al{sub 2}O{sub 3} film is 90 nm thick. The ultimate efficiency of around 27% is obtained on the CND textured 2 μm-thick Si solar cells, which is compared to the efficiency of around 25.75% and 15% for the 2 μm-thick Si nanodome surface-decorated and planar samples respectively. Electrical characterization was made by using CND-decorated MOS devices to measure device’s leakage current and capacitance dispersion. It is found the electrical performance is sensitive to the thickness of the Al{sub 2}O{sub 3} film, and the performance is remarkably improved when the dielectric layer thickness is 90 nm thick. The leakage current, which is less than 4x10{sup −9} A/cm{sup 2} over voltage range of from -3 V to 3 V, is reduced by several orders of magnitude. C-V measurements also shows as small as 0.3% of variation in the capacitance over the frequency range from 10 kHz to 500 kHz, which is a strong indication of surface states being fully passivated. TEM examination of CND-decorated samples also reveals the occurrence of SiO{sub x} layer formed between the interface of Si and the Al{sub 2}O{sub 3} film, which is thin enough that ensures the presence of field-effect passivation, From our theoretical and experimental study, we believe Al{sub 2}O{sub 3} coated CND structures is a truly viable approach to achieving higher device efficiency.« less

Spectroscopic Ellipsometry Studies of n-i-p Hydrogenated Amorphous Silicon Based Photovoltaic Devices

PubMed Central

Karki Gautam, Laxmi; Junda, Maxwell M.; Haneef, Hamna F.; Collins, Robert W.; Podraza, Nikolas J.

2016-01-01

Optimization of thin film photovoltaics (PV) relies on characterizing the optoelectronic and structural properties of each layer and correlating these properties with device performance. Growth evolution diagrams have been used to guide production of materials with good optoelectronic properties in the full hydrogenated amorphous silicon (a-Si:H) PV device configuration. The nucleation and evolution of crystallites forming from the amorphous phase were studied using in situ near-infrared to ultraviolet spectroscopic ellipsometry during growth of films prepared as a function of hydrogen to reactive gas flow ratio R = [H2]/[SiH4]. In conjunction with higher photon energy measurements, the presence and relative absorption strength of silicon-hydrogen infrared modes were measured by infrared extended ellipsometry measurements to gain insight into chemical bonding. Structural and optical models have been developed for the back reflector (BR) structure consisting of sputtered undoped zinc oxide (ZnO) on top of silver (Ag) coated glass substrates. Characterization of the free-carrier absorption properties in Ag and the ZnO + Ag interface as well as phonon modes in ZnO were also studied by spectroscopic ellipsometry. Measurements ranging from 0.04 to 5 eV were used to extract layer thicknesses, composition, and optical response in the form of complex dielectric function spectra (ε = ε1 + iε2) for Ag, ZnO, the ZnO + Ag interface, and undoped a-Si:H layer in a substrate n-i-p a-Si:H based PV device structure. PMID:28773255

Effect of post annealing on structural, optical and dielectric properties of MgTiO3 thin films deposited by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Santhosh Kumar, T.; Bhuyan, R. K.; Pamu, D.

2013-01-01

MgTiO3 (MTO) thin films have been deposited on to quartz and platinized silicon (Pt/TiO2/SiO2/Si) substrates by RF magnetron sputtering. The metal-MTO-metal (Ag-MTO-Pt/TiO2/SiO2/Si) thin film capacitors have been fabricated at different oxygen mixing percentage (OMP). The effects of OMP and post annealing on the structural, microstructural, optical and dielectric properties of MTO films were studied. The MTO target has been synthesized by mechanochemical synthesis method. The phase purity of the sputtering target was confirmed from X-ray diffraction pattern and refined to R3bar space group with lattice parameters a = b = 5.0557(12) Å, c = 13.9003(9) Å. The chemical composition of the deposited films was confirmed from EDS spectra and all the films exhibited the composition of the sputtering target. The XRD patterns of the as-deposited films are amorphous and annealing at 700 °C for 1 h induced nanocrystallinity with the improved optical and dielectric properties. The annealed films exhibit refractive index in the range of 2.12-2.19 at 600 nm with an optical bandgap value in between 4.11 and 4.19 eV. The increase in the refractive index and bandgap upon annealing can be attributed to the improvement in packing density, crystallinity, and decrease in porosity ratio. Both the dielectric constant and tan δ decrease with the increase in frequency and were in the range of 13.7-31.11 and 0.006-0.124, respectively. The improvement in dielectric properties with the increase in OMP has been correlated to the reduction in oxygen vacancies, increase in crystallinity and grain size of the films.

Synthesis and characterization study of n-Bi2O3/p-Si heterojunction dependence on thickness

NASA Astrophysics Data System (ADS)

Al-Maiyaly, Bushra K. H.; Hussein, Bushra H.; Salih, Ayad A.; Shaban, Auday H.; Mahdi, Shatha H.; Khudayer, Iman H.

2018-05-01

In this work, Bi2O3 was deposited as a thin film of different thickness (400, 500, and 600 ±20 nm) by using thermal oxidation at 573 K with ambient oxygen of evaporated bismuth (Bi) thin films in a vacuum on glass substrate and on Si wafer to produce n-Bi2O3/p-Si heterojunction. The effect of thickness on the structural, electrical, surface and optical properties of Bi2O3 thin films was studied. XRD analysis reveals that all the as deposited Bi2O3 films show polycrystalline tetragonal structure, with preferential orientation in the (201) direction, without any change in structure due to increase of film thickness. AFM and SEM images are used to investigate the influences of film thickness on surface properties. The optical measurement were taken for the wave length range (400-1100) nm showed that the nature of the optical transition has been direct allowed with average band gap energies varies in the range of (2.9-2.25) eV with change thickness parameter. The extent and nature of transmittance, absorbance, reflectance and optimized band gap of the material assure to utilize it for photovoltaic applications. Hall measurements showed that all the films are n-type. The electrical properties of n-Bi2O3/p-Si heterojunction (HJ) were obtained by I-V (dark and illuminated) and C-V measurement at frequency (10 MHz) at different thickness. The ideality factor saturation current density, depletion width, built-in potential and carrier concentration are characterized under different thickness. The results show these HJ were of abrupt type. The photovoltaic measurements short-circuit current density, open-circuit voltage, fill factor and efficiencies are determined for all samples. Finally thermal oxidation allowed fabrication n-Bi2O3/p-Si heterojunction with different thickness for solar cell application.

Formation, optical properties, and electronic structure of thin Yb silicide films on Si(111)

NASA Astrophysics Data System (ADS)

Galkin, N. G.; Maslov, A. M.; Polyarnyi, V. O.

2005-06-01

Continuous very thin (2.5-3.0 nm) and thin (16-18 nm) ytterbium suicide films with some pinhole density (3×107- 1×108 cm-2) have been formed on Si(111) by solid phase epitaxy (SPE) and reactive deposition epitaxy (RDE) growth methods on templates. The stoichiometric ytterbium suicide (YbSi2) formation has shown in SPE grown films by AES and EELS data. Very thin Yb suicide films grown by RDE method had the silicon enrichment in YbSi2 suicide composition. The analysis of LEED data and AFM imaging has shown that ytterbium suicide films had non-oriented blocks with the polycrystalline structure. The analysis of scanning region length dependencies of the root mean square roughness deviation (σR(L)) for grown suicide films has shown that the formation of ytterbium suicide in SPE and RDE growth methods is determined by the surface diffusion of Yb atoms during the three-dimensional growth process. Optical functions (n, k, α, ɛ1, ɛ2, Im ɛ1-1, neff, ɛeff) of ytterbium silicide films grown on Si(1 1 1) have been calculated from transmittance and reflectance spectra in the energy range of 0.1-6.2 eV. Two nearly discrete absorption bands have been observed in the electronic structure of Yb silicide films with different composition, which connected with interband transitions on divalent and trivalent Yb states. It was established that the reflection coefficient minimum in R-spectra at energies higher 4.2 eV corresponds to the state density minimum in Yb suicide between divalent and trivalent Yb states. It was shown from optical data that Yb silicide films have the semi-metallic properties with low state densities at energies less 0.4 eV and high state densities at 0.5-2.5 eV.

Vapor sensors using porous silicon-based optical interferometers

NASA Astrophysics Data System (ADS)

Gao, Ting

The ability to detect or monitor various gases is important for many applications. Smaller, more portable, lower power, and less expensive gas sensors are needed. Porous silicon (PS) has attracted attention for use in such devices due to its unique optical and electronic properties and its large surface area. This thesis describes the preparation and characteristics of vapor sensors using thin PS Fabry-Perot films. The average refractive index of the PS layer increases when the PS film is exposed to analyte vapors, causing the optical fringes to shift to longer wavelengths. Two methods for monitoring the shifts in these optical fringes are explored in this thesis. The first technique measures the reflection spectrum using a white light source, and the second measures the intensity of reflected light using a low-power red diode laser source. The latter method offers a simple, low-cost and reliable transduction mechanism for vapor sensing. A vapor sensor with a detection limit of 250 ppb and a wide dynamic range (five orders of magnitude) is demonstrated. The effect of the PS film thickness and porosity on sensitivity are systematically studied. A model based on the Bruggeman approximation and capillary condensation is proposed to explain this sensing behavior. Two approaches to improve the sensitivity of the PS sensors are explored. In the first, porous Si is chemically modified and the investigation shows that the sensing response varies with different surface properties. In a second study, thin polymer layers are coated on the porous Si substrate to selectively filter solvent vapors. This bi-layer approach is also applied to porous Si layers that have luminescent quantum structures. These latter structures sense adsorbates based on quenching of luminescence from the quantum-confined silicon nanostructures. In the course of this thesis, an anomalous response of ozone-oxidized PS films to water vapor was discovered. The effect was studied by optical interferometry, isotope studies, and in-situ Fourier transform infrared spectroscopy. It is concluded that in some porous Si films, water forms a strongly hydrogen bonded network that results in compression of the porous Si layer.

Room temperature photoluminescence properties of ZnO nanorods grown by hydrothermal reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iwan, S., E-mail: iwan-sugihartono@unj.ac.id; Prodi Ilmu Material, Departemen Fisika, FMIPA, Universitas Indonesia, Kampus UI Depok; Fauzia, Vivi

Zinc oxide (ZnO) nanorods were fabricated by a hydrothermal reaction on silicon (Si) substrate at 95 °C for 6 hours. The ZnO seed layer was fabricated by depositing ZnO thin films on Si substrates by ultrasonic spray pyrolisis (USP). The annealing effects on crystal structure and optical properties of ZnO nanorods were investigated. The post-annealing treatment was performed at 800 °C with different environments. The annealed of ZnO nanorods were characterized by X-ray diffraction (XRD) and photoluminescence (PL) in order to analyze crystal structure and optical properties, respectively. The results show the orientations of [002], [101], [102], and [103] diffractionmore » peaks were observed and hexagonal wurtzite structure of ZnO nanorods were vertically grown on Si substrates. The room temperature PL spectra show ultra-violet (UV) and visible emissions. The annealed of ZnO nanorods in vacuum condition (3.8 × 10{sup −3} Torr) has dominant UV emission. Meanwhile, non-annealed of ZnO nanorods has dominant visible emission. It was expected that the annealed of ZnO in vacuum condition suppresses the existence of native defects in ZnO nanorods.« less

Optical Testing and Verification Methods for the James Webb Space Telescope Integrated Science Instrument Module Element

NASA Technical Reports Server (NTRS)

Antonille, Scott R.; Miskey, Cherie L.; Ohl, Raymond G.; Rohrbach, Scott O.; Aronstein, David L.; Bartoszyk, Andrew E.; Bowers, Charles W.; Cofie, Emmanuel; Collins, Nicholas R.; Comber, Brian J.;

Structural, optical, and spin properties of hydrogenated amorphous silicon-germanium alloys

NASA Astrophysics Data System (ADS)

Stutzmann, M.; Street, R. A.; Tsai, C. C.; Boyce, J. B.; Ready, S. E.

1989-07-01

We report on a detailed study of structural and electronic properties of hydrogenated amorphous silicon-germanium alloys deposited by rf glow discharge from SiH4 and GeH4 in a diode reactor. The chemical composition of the alloys is related to the deposition conditions, with special emphasis on preferential incorporation of Ge into the solid phase and on the role of inert dilutant gases. Hydrogen bonding in the alloys is investigated with nuclear magnetic resonance and vibrational (Raman and infrared) spectroscopy. The optical properties of a-SiGe:H samples deposited under optimal conditions are analyzed with the help of subgap absorption measurements and band-tail luminescence for the entire range of alloy composi-tions. A large part of the article describes an investigation of the electron-spin-resonance response of undoped alloys. The spin density associated with dangling bond defects localized on Si and Ge atoms has been measured as a function of alloy composition for optimized material. In addition, the dependence of the two defect densities on the detailed deposition conditions (rf power, substrate temperature, and dilution) has been determined in a systematic way for alloys deposited from a plasma with a fixed SiH4/GeH4ratio. The results of this study, especially the preferential creation of Ge dangling bonds, are discussed in the context of our structural data. Furthermore, spin resonance is employed to investigate the light-induced degradation (Staebler-Wronski effect) of a-SiGe:H. Finally, the changes of the spin-resonance spectra of a-Si0.7 Ge0.3 :H upon substitutional doping with phosphorus and boron have been obtained experimentally, and are used to construct a model for the electronic density of states in this material.

Observation of the strain field near the Si(111) 7 x 7 surface with a new X-ray diffraction technique.

PubMed

Emoto, T; Akimoto, K; Ichimiya, A

1998-05-01

A new X-ray diffraction technique has been developed in order to measure the strain field near a solid surface under ultrahigh vacuum (UHV) conditions. The X-ray optics use an extremely asymmetric Bragg-case bulk reflection. The glancing angle of the X-rays can be set near the critical angle of total reflection by tuning the X-ray energy. Using this technique, rocking curves for Si surfaces with different surface structures, i.e. a native oxide surface, a slightly oxide surface and an Si(111) 7 x 7 surface, were measured. It was found that the widths of the rocking curves depend on the surface structures. This technique is efficient in distinguishing the strain field corresponding to each surface structure.

Role of surface energy on the morphology and optical properties of GaP micro & nano structures grown on polar and non-polar substrates

NASA Astrophysics Data System (ADS)

Roychowdhury, R.; Kumar, Shailendra; Wadikar, A.; Mukherjee, C.; Rajiv, K.; Sharma, T. K.; Dixit, V. K.

2017-10-01

Role of surface energy on the morphology, crystalline quality, electronic structure and optical properties of GaP layer grown on Si (001), Si (111), Ge (111) and GaAs (001) is investigated. GaP layers are grown on four different substrates under identical growth kinetics by metal organic vapour phase epitaxy. The atomic force microscopy images show that GaP layer completely covers the surface of GaAs substrate. On the other hand, the surfaces of Si (001), Si (111), Ge (111) substrates are partially covered with crystallographically morphed GaP island type micro and nano-structures. Origin of these crystallographically morphed GaP island is explained by the theoretical calculation of surface energy of the layer and corresponding substrates respectively. The nature of GaP island type micro and nano-structures and layers are single crystalline with existence of rotational twins on Si and Ge (111) substrates which is confirmed by the phi, omega and omega/2theta scans of high resolution x-ray diffraction. The electronic valence band offsets between the GaP and substrates have been determined from the valence band spectra of ultraviolet photoelectron spectroscopy. The valence electron plasmon of GaP are investigated by studying the energy values of Ga (3d) core level along with loss peaks in the energy dependent photoelectron spectra. The peak observed within the range of 3-6 eV from the Ga (3d) core level in the photoelectron spectra are associated to inter band transitions as their energy values are estimated from the pseudo dielectric function by the spectroscopic ellipsometry.

Optical properties of amorphous SiO2-TiO2 multi-nanolayered coatings for 1064-nm mirror technology

NASA Astrophysics Data System (ADS)

Magnozzi, M.; Terreni, S.; Anghinolfi, L.; Uttiya, S.; Carnasciali, M. M.; Gemme, G.; Neri, M.; Principe, M.; Pinto, I.; Kuo, L.-C.; Chao, S.; Canepa, M.

2018-01-01

The use of amorphous, SiO2-TiO2 nanolayered coatings has been proposed recently for the mirrors of 3rd-generation interferometric detectors of gravitational waves, to be operated at low temperature. Coatings with a high number of low-high index sub-units pairs with nanoscale thickness were found to preserve the amorphous structure for high annealing temperatures, a key factor to improve the mechanical quality of the mirrors. The optimization of mirror designs based on such coatings requires a detailed knowledge of the optical properties of sub-units at the nm-thick scale. To this aim we have performed a Spectroscopic Ellipsometry (SE) study of amorphous SiO2-TiO2 nanolayered films deposited on Si wafers by Ion Beam Sputtering (IBS). We have analyzed films that are composed of 5 and 19 nanolayers (NL5 and NL19 samples) and have total optical thickness nominally equivalent to a quarter of wavelength at 1064 nm. A set of reference optical properties for the constituent materials was obtained by the analysis of thicker SiO2 and TiO2 homogeneous films (∼ 120 nm) deposited by the same IBS facility. By flanking SE with ancillary techniques, such as TEM and AFM, we built optical models that allowed us to retrieve the broad-band (250-1700 nm) optical properties of the nanolayers in the NL5 and NL19 composite films. In the models which provided the best agreement between simulation and data, the thickness of each sub-unit was fitted within rather narrow bounds determined by the analysis of TEM measurements on witness samples. Regarding the NL5 sample, with thickness of 19.9 nm and 27.1 nm for SiO2 and TiO2 sub-units, respectively, the optical properties presented limited variations with respect to the thin film counterparts. For the NL19 sample, which is composed of ultrathin sub-units (4.4 nm and 8.4 nm for SiO2 and TiO2, respectively) we observed a significant decrease of the IR refraction index for both types of sub-units; this points to a lesser mass density with respect to the thin film reference. The results are discussed in the light of the existing literature on nanofilms of amorphous oxides.

Back scattering involving embedded silicon nitride (SiN) nanoparticles for c-Si solar cells

NASA Astrophysics Data System (ADS)

Ghosh, Hemanta; Mitra, Suchismita; Siddiqui, M. S.; Saxena, A. K.; Chaudhuri, Partha; Saha, Hiranmay; Banerjee, Chandan

2018-04-01

A novel material, structure and method of synthesis for dielectric light trapping have been presented in this paper. First, the light scattering behaviour of silicon nitride nanoparticles have been theoretically studied in order to find the optimized size for dielectric back scattering by FDTD simulations from Lumerical Inc. The optical results have been used in electrical analysis and thereby, estimate the effect of nanoparticles on efficiency of the solar cells depending on substrate thickness. Experimentally, silicon nitride (SiN) nanoparticles have been formed using hydrogen plasma treatment on SiN layer deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD). The size and area coverage of the nanoparticles were controlled by varying the working pressure, power density and treatment duration. The nanoparticles were integrated with partial rear contact c-Si solar cells as dielectric back reflector structures for the light trapping in thin silicon solar cells. Experimental results revealed the increases of current density by 2.7% in presence of SiN nanoparticles.

Si-rich SiNx based Kerr switch enables optical data conversion up to 12 Gbit/s

PubMed Central

Lin, Gong-Ru; Su, Sheng-Pin; Wu, Chung-Lun; Lin, Yung-Hsiang; Huang, Bo-Ji; Wang, Huai-Yung; Tsai, Cheng-Ting; Wu, Chih-I; Chi, Yu-Chieh

2015-01-01

Silicon photonic interconnection on chip is the emerging issue for next-generation integrated circuits. With the Si-rich SiNx micro-ring based optical Kerr switch, we demonstrate for the first time the wavelength and format conversion of optical on-off-keying data with a bit-rate of 12 Gbit/s. The field-resonant nonlinear Kerr effect enhances the transient refractive index change when coupling the optical data-stream into the micro-ring through the bus waveguide. This effectively red-shifts the notched dip wavelength to cause the format preserved or inversed conversion of data carried by the on-resonant or off-resonant probe, respectively. The Si quantum dots doped Si-rich SiNx strengthens its nonlinear Kerr coefficient by two-orders of magnitude higher than that of bulk Si or Si3N4. The wavelength-converted and cross-amplitude-modulated probe data-stream at up to 12-Gbit/s through the Si-rich SiNx micro-ring with penalty of −7 dB on transmission has shown very promising applicability to all-optical communication networks. PMID:25923653

Si-rich SiNx based Kerr switch enables optical data conversion up to 12 Gbit/s.

PubMed

Lin, Gong-Ru; Su, Sheng-Pin; Wu, Chung-Lun; Lin, Yung-Hsiang; Huang, Bo-Ji; Wang, Huai-Yung; Tsai, Cheng-Ting; Wu, Chih-I; Chi, Yu-Chieh

2015-04-29

Silicon photonic interconnection on chip is the emerging issue for next-generation integrated circuits. With the Si-rich SiNx micro-ring based optical Kerr switch, we demonstrate for the first time the wavelength and format conversion of optical on-off-keying data with a bit-rate of 12 Gbit/s. The field-resonant nonlinear Kerr effect enhances the transient refractive index change when coupling the optical data-stream into the micro-ring through the bus waveguide. This effectively red-shifts the notched dip wavelength to cause the format preserved or inversed conversion of data carried by the on-resonant or off-resonant probe, respectively. The Si quantum dots doped Si-rich SiNx strengthens its nonlinear Kerr coefficient by two-orders of magnitude higher than that of bulk Si or Si3N4. The wavelength-converted and cross-amplitude-modulated probe data-stream at up to 12-Gbit/s through the Si-rich SiNx micro-ring with penalty of -7 dB on transmission has shown very promising applicability to all-optical communication networks.

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

NASA Astrophysics Data System (ADS)

Christensen-Dalsgaard, Jørgen; Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita; Si Team

2011-01-01

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is a "Landmark/Discovery Mission" in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

BACKWARD ANGLE STRUCTURE IN THE 20Ne+28Si QUASIELASTIC SCATTERING

NASA Astrophysics Data System (ADS)

Sgouros, O.; Soukeras, V.; Pakou, A.; Patronis, N.; Zerva, K.; Keeley, N.; Strojek, I.; Trzcińska, A.; Piasecki, E.; Rusek, K.; Stiliaris, E.; Mazzocco, M.

2013-10-01

New data for the quasielastic scattering of 20Ne from a 28Si target at incident energies of 42.5 MeV and 52.3 MeV and for the 28Si(20Ne, 24Mg)24Mg, 28Si(20Ne, 16O)32S and 28Si(20Ne, 12C)36Ar transfer reactions at 52.3 MeV are reported. Oscillations are observed in the backward angle quasielastic scattering data at 52.3 MeV and the 28Si(20Ne, 12C)36Ar transfer cross-sections are of the same magnitude as those for single-α stripping. Coupled reaction channels (CRC) calculations are unable to describe either the quasielastic or the 28Si(20Ne, 12C)36Ar transfer data assuming a sequential α transfer process with α-particle form factors from the literature. The addition of direct 8Be cluster transfer can provide a reasonable description of both data sets, but only with much larger spectroscopic factors than suggested by simple structure calculations or the large 8Be emission thresholds of 20Ne, 28Si and 36Ar, suggesting that the observed structure is of resonance-like origin. An optical model analysis of the quasielastic scattering data is also reported.

Photoluminescence Properties of Ca3Si2O7: Pr3+ Orange-Red Phosphors Prepared by High-Temperature Solid-State Method

NASA Astrophysics Data System (ADS)

Peng, Zhi-Qing; Chen, Rong; Feng, Wen-Lin

2018-06-01

Novel luminescent materials Ca3-xSi2O7: xPr3+ were successfully prepared by the high-temperature solid-state method. The crystal structure, morphology, and optical spectrum were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopy, respectively. The XRD patterns of the samples indicate that the crystal structure is monoclinic symmetry. The SEM shows that the selected sample has good crystallinity although its appearance is irregular and scalelike. The peak of the excitation spectrum of the sample is located at around 449 nm, corresponding to 3H4→3P2 transition of Pr3+. The peak of the emission spectrum of the sample is situated at around 612 nm which is attributed to 3P0→3H6 transition of Pr3+, and the colour is orange-red. The optimum concentration for Pr3+ replaced Ca2+ sites in Ca3Si2O7: Pr3+ is 0.75 mol%. The lifetime (8.48 μs) of a typical sample (Ca2.9925Pr0.0075)Si2O7 is obtained. It reveals that orange-red phosphors Ca3-xSi2O7: xPr3+ possess remarkable optical properties and can be used in white light emitting devices.

2D photonic crystal layer assisted thiosilicate ceramic plate with red-emitting film for high quality w -LEDs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dai, Wubin; Lei, Yifeng; Zhou, Jia

In this work, we have succeeded in obtaining high quality warm w-light-emitting-diodes (LEDs) by adopting hybrid two-dimensional (2D) structure of SiNx photonic crystal layer (PCL) assisted cyan-emitting ceramic-plate thiosilicate SrLa2Si2S8:Ce3+ with red-emitting film SrLiAl3N4:Eu2+ phosphor on a 430 nm blue LED chip at 350 mA. 2D SiNx PCL was capped with thiosilicate is because it can enhance the luminous efficacy and maintain the low correlated color temperature (CCT) and high color-rendering index (CRI). High luminous efficacy (82.3 lm/W), high special CRI (R9=75) as well as the low CCT (5431 K) of the optimal w-LED was obtained due to the assistancesmore » of 2D SiNx PCL and narrow-band red-emitting phosphor with the doping percentage at 10 wt%. The synthesis processes, structural analysis, optical properties and LED device performances were detailed investigated to find out the relationship between the optimum composition and good optical properties. Based on intriguing luminescence properties by the 2D SiNx PCL and red-emitting film phosphor introducing, we proclaim this method could also have high potential application in other phosphor-converted w-LEDs.« less

Effect of sintering temperature on physical, structural and optical properties of wollastonite based glass-ceramic derived from waste soda lime silica glasses

NASA Astrophysics Data System (ADS)

Almasri, Karima Amer; Sidek, Hj. Ab Aziz; Matori, Khamirul Amin; Zaid, Mohd Hafiz Mohd

The impact of different sintering temperatures on physical, optical and structural properties of wollastonite (CaSiO3) based glass-ceramics were investigated for its potential application as a building material. Wollastonite based glass-ceramics was provided by a conventional melt-quenching method and followed by a controlled sintering process. In this work, soda lime silica glass waste was utilized as a source of silicon. The chemical composition and physical properties of glass were characterized by using Energy Dispersive X-ray Fluorescence (EDXRF) and Archimedes principle. The Archimedes measurement results show that the density increased with the increasing of sintering temperature. The generation of CaSiO3, morphology, size and crystal phase with increasing the heat-treatment temperature were examined by field emission scanning electron microscopy (FESEM), Fourier transforms infrared reflection spectroscopy (FTIR), and X-ray diffraction (XRD). The average calculated crystal size gained from XRD was found to be in the range 60 nm. The FESEM results show a uniform distribution of particles and the morphology of the wollastonite crystal is in relict shapes. The appearance of CaO, SiO2, and Ca-O-Si bands disclosed from FTIR which showed the formation of CaSiO3 crystal phase. In addition to the calculation of the energy band gap which found to be increased with increasing sintering temperature.

T- and Y-splitters based on an Au/SiO2 nanoring chain at an optical communication band.

PubMed

Ahmadivand, A; Golmohammadi, S; Rostami, A

2012-05-20

In this paper, we have utilized Au nanoring chains in an SiO2 host to design certain T-and Y-structures, and expanded it to transport and split the electromagnetic energy in integrated nanophotonic devices operating at an optical communication band (λ≈1550 nm). We compared two structures and tried to choose the best one, with lower losses and higher efficiency at the output branches, in order to split and transport the optical energy. Comparing the different types of nanoparticles corroborates that nanorings have an extra degree of tunability in their geometrical components. Meanwhile, nanorings show strong confinement in near-field coupling, less extinction coefficient, and also lower scattering into the far field during energy transportation at the C-band spectrum. Due to the nanoring's particular properties, transportation losses would be lower than in other nanoparticle-based structures like nanospheres, nanorods, and nanodisks. We demonstrate that Au nanorings surrounded by an SiO2 host yield suitable conditions to excite surface Plasmons inside the metal. Comparison between Y-and T-splitters shows that the Y-splitter is a more suitable alternative than the T-splitter, with higher transmission efficiency and lower losses. In the Y-structure, the power ratio (time-averaged power across the surface) is 24.7%, and electromagnetic energy transportation takes place at group velocities in the vicinity of 30% of the velocity of light; transmission losses are γT=3 dB/655 nm and γT=3 dB/443 nm. In this work, we have applied the finite-difference time-domain method (FDTD) to simulate and indicate the properties of structures.

Damage mechanisms of MoN/SiN multilayer optics for next-generation pulsed XUV light sources.

PubMed

Sobierajski, R; Bruijn, S; Khorsand, A R; Louis, E; van de Kruijs, R W E; Burian, T; Chalupsky, J; Cihelka, J; Gleeson, A; Grzonka, J; Gullikson, E M; Hajkova, V; Hau-Riege, S; Juha, L; Jurek, M; Klinger, D; Krzywinski, J; London, R; Pelka, J B; Płociński, T; Rasiński, M; Tiedtke, K; Toleikis, S; Vysin, L; Wabnitz, H; Bijkerk, F

2011-01-03

We investigated the damage mechanism of MoN/SiN multilayer XUV optics under two extreme conditions: thermal annealing and irradiation with single shot intense XUV pulses from the free-electron laser facility in Hamburg - FLASH. The damage was studied "post-mortem" by means of X-ray diffraction, interference-polarizing optical microscopy, atomic force microscopy, and scanning transmission electron microscopy. Although the timescale of the damage processes and the damage threshold temperatures were different (in the case of annealing it was the dissociation temperature of Mo2N and in the case of XUV irradiation it was the melting temperature of MoN) the main damage mechanism is very similar: molecular dissociation and the formation of N2, leading to bubbles inside the multilayer structure.

Enhancement of Fluorescence and Raman Scattering in Cyanine-Dye Molecules on the Surface of Silicon-Coated Silver Nanoparticles

NASA Astrophysics Data System (ADS)

Kamalieva, A. N.; Toropov, N. A.; Bogdanov, K. V.; Vartanyan, T. A.

2018-03-01

A method of formation of a composite structure based on silver nanoparticles and a thin protective silicon film (Ag NPs/Si) is developed. Enhancement of the fluorescence and Raman scattering in cyaninedye molecules deposited onto the formed nanostructure is observed. The optical properties and morphology stability of particles that are in contact with cyanine-dye solutions in organic solvents are studied. It is shown that the Ag NPs/Si composite structure can be multiply used as an SERS-active surface.

Two-dimensional Ag/SiO2 and Cu/SiO2 nanocomposite surface-relief grating couplers and their vertical input coupling properties

NASA Astrophysics Data System (ADS)

Wang, Jun; Mu, Xiaoyu; Wang, Gang; Liu, Changlong

2017-11-01

By etching two SiO2 optical waveguide slabs separately implanted with 90 keV Ag ions and 60 keV Cu ions at the same dose of 6 × 1016 cm-2, two-dimensional Ag/SiO2 and Cu/SiO2 nanocomposite surface-relief grating couplers with 600-nm periodicity and 100-nm thickness were fabricated, and their structural and vertical input coupling properties were investigated. Experimental results revealed that the two couplers could convert light beams at wavelengths of 620-880 nm into guided waves with different efficiencies, highlighting the special importance of metal nanoparticles (NPs). Further discussions also revealed that owing to the introduction of periodically distributed metal NPs, the periodical phase modification of the transmitted beam was enhanced drastically, and the nanocomposite veins could behave as efficient light scatterers. As a result, the two couplers were much larger in coupling efficiency than the NP-free one with identical morphological parameters. The above findings may be useful to construct thin and short but efficient surface-relief grating couplers on glass optical waveguides.

Computational assessment of promising mid-infrared nonlinear optical materials Mg–IV–V2 (IV = Si, Ge, Sn; V = P, As): a first-principles study

NASA Astrophysics Data System (ADS)

Xiao, Jianping; Zhu, Shifu; Zhao, Beijun; Chen, Baojun; Liu, Hui; He, Zhiyu

2018-03-01

The mid-infrared (mid-IR) nonlinear optical (NLO) capabilities of Mg–IV–V2 (IV = Si, Ge, Sn; V = P, As) are systematically assessed by the first-principles calculation. The results show that the compounds in this group except MgSiP2 and MgSnP2 have moderate birefringence values to fulfill the phase-matching conditions. In particular, MgGeP2 and MgSiAs2 possess relatively large band gaps and almost three to four times larger static SHG coefficients than the benchmark material AgGaSe2, exhibiting good potential for mid-IR NLO application. According to the detailed analysis of the electronic structures, it is found that the dominant SHG contributions are from the orbitals of the asymmetry anionic unit [IV–V2]2‑. Moreover, the further evaluation reveals that MgSiAs2, MgGeAs2, MgSnP2 and MgSnAs2 are not thermodynamically stable and the new synthesis strategy (i.e. synthesis under non-equilibrium conditions) should be considered.

TOPICAL REVIEW: The doping process and dopant characteristics of GaN

NASA Astrophysics Data System (ADS)

Sheu, J. K.; Chi, G. C.

2002-06-01

The characteristic effects of doping with impurities such as Si, Ge, Se, O, Mg, Be, and Zn on the electrical and optical properties of GaN-based materials are reviewed. In addition, the roles of unintentionally introduced impurities, such as C, H, and O, and grown-in defects, such as vacancy and antisite point defects, are also discussed. The doping process during epitaxial growth of GaN, AlGaN, InGaN, and their superlattice structures is described. Doping using the diffusion process and ion implantation techniques is also discussed. A p-n junction formed by Si implantation into p-type GaN is successfully fabricated. The results on crystal structure, electrical resistivity, carrier mobility, and optical spectra obtained by means of x-rays, low-temperature Hall measurements, and photoluminescence are also discussed.

The James Webb Space Telescope

NASA Technical Reports Server (NTRS)

Nowak, Maria; Eichorn, William; Hill, Michael; Hylan, Jason; Marsh, James; Ohl, Raymond; Sampler, Henry; Wright, Geraldine; Crane, Allen; Herrera, Acey;

Strained-layer epitaxy of germanium-silicon alloys

NASA Astrophysics Data System (ADS)

Bean, J. C.

1985-10-01

Strained-layer epitaxy is presented as a developing technique for combining Si with other materials in order to obtain semiconductors with enhanced electronic properties. The method involves applying layers sufficiently thin so that the atoms deposited match the bonding configurations of the substrate crystal. When deposited on Si, a four-fold bonding pattern is retained, with a lowered interfacial energy and augmented stored strain energy in the epitaxial layer. The main problem which remains is building an epitaxial layer thick enough to yield desired epitaxial properties while avoiding a reversion to an unstrained structure. The application of a Ge layer to Si using MBE is described, along with the formation of heterojunction multi-layer superlattices, which can reduce the dislocation effects in some homojunctions. The technique shows promise for developing materials of use as bipolar transistors, optical detectors and fiber optic transmission devices.

Optimization of figure of merit in magnetoplasmonic waveguides with Fe/Au multilayer for optical isolator based on nonreciprocal coupling on Si waveguides

NASA Astrophysics Data System (ADS)

Shimizu, Hiromasa; Shimodaira, Takahiro

2018-04-01

We report on magnetoplasmonic Si waveguides with a ferromagnetic Fe/conductive metal Au multilayer for realizing a sizable magnetooptic effect with a low propagation loss for integrated optical isolators. By combining the ferromagnetic metal Fe with a highly conductive Au layer, the largest nonreciprocal differences in effective index were estimated for propagation lengths of 1-20 µm. Mode analysis with and without a Au layer clarified that the insertion of a Au layer on an Fe layer improves the optical confinement in the Fe layer with reduced propagation loss and is effective in enlarging the magnetooptic effect for the same propagation length. On the basis of the optimized Fe/Au multilayer structure, we designed waveguide optical isolators based on nonreciprocal coupling by the finite difference time domain (FDTD) method. We estimated an optical isolation of 10.8 dB with a forward insertion loss of 13.4 dB in a 34-µm-long nonreciprocal directional coupler.

The transformation of ZnO submicron dumbbells into perfect hexagonal tubular structures using CBD: a post treatment route.

PubMed

Borade, P; Joshi, K U; Gokarna, A; Lerondel, G; Jejurikar, S M

2016-01-15

In this paper, we report the synthesis of dumbbell-shaped ZnO structures and their subsequent transformation into perfect hexagonal tubes by the extended chemical bath deposition (CBD) method, retaining all advantages such as reproducibility, simplicity, quickness and economical aspect. Well-dispersed sub-micron-sized dumbbell-shaped ZnO structures were synthesized on a SiO2/Si substrate by the CBD method. As an extension of the CBD process the synthesized ZnO dumbbells were exposed to the evaporate coming out of the chemical bath for a few minutes (simply by adjusting the height of the deposit so that it remained just above the solution) to convert them into hexagonal tubes via the dissolution process. The possible dissolution mechanism responsible for the observed conversion is discussed. The optical properties (photo-luminescence) recorded at low temperature on both the structures showed an intense, sharp excitonic peak located at ∼370 nm. The improved intensity and low FWHM of the UV peak observed in the hexagonal tubular structures assures high optical quality, and hence can be used for optoelectronic applications.

Formation of silicides in annealed periodic multilayers

NASA Astrophysics Data System (ADS)

Maury, H.; Jonnard, P.; Le Guen, K.; André, J.-M.

2009-05-01

Periodic multilayers of nanometric period are widely used as optical components for the X-ray and extreme UV (EUV) ranges, in X-ray space telescopes, X-ray microscopes, EUV photolithography or synchrotron beamlines for example. Their optical performances depend on the quality of the interfaces between the various layers: chemical interdiffusion or mechanical roughness shifts the application wavelength and can drastically decrease the reflectance. Since under high thermal charge interdiffusion is known to get enhanced, the study of the thermal stability of such structures is essential to understand how interfacial compounds develop. We have characterized X-ray and EUV siliconcontaining multilayers (Mo/Si, Sc/Si and Mg/SiC) as a function of the annealing temperature (up to 600°C) using two non-destructive methods. X-ray emission from the silicon atoms, describing the Si valence states, is used to determine the chemical nature of the compounds present in the interphases while X-ray reflectivity in the hard and soft X-ray ranges can be related to the optical properties. In the three cases, interfacial metallic (Mo, Sc, Mg) silicides are evidenced and the thickness of the interphase increases with the annealing temperature. For Mo/Si and Sc/Si multilayers, silicides are even present in the as-prepared multilayers. Characteristic parameters of the stacks are determined: composition of the interphases, thickness and roughness of the layers and interphases if any. Finally, we have evidenced the maximum temperature of application of these multilayers to minimize interdiffusion.

Strong spin-lattice coupling in CrSiTe 3

DOE PAGES

Casto, L. D.; Clune, A. J.; Yokosuk, M. O.; ...

2015-03-19

CrSiTe 3 has attracted recent interest as a candidate single-layer ferromagnetic semiconductor, but relatively little is known about the bulk properties of this material. Here, we report single-crystal X-ray diffraction, magnetic properties, thermal conductivity, vibrational, and optical spectroscopies and compare our findings with complementary electronic structure and lattice dynamics principles calculations. The high temperature paramagnetic phase is characterized by strong spin-lattice interactions that give rise to glassy behavior, negative thermal expansion, and an optical response that reveals that CrSiTe 3 is an indirect gap semiconductor with indirect and direct band gaps at 0.4 and 1.2 eV, respectively. Measurements of themore » phonons across the 33 K ferromagnetic transition provide additional evidence for strong coupling between the magnetic and lattice degrees of freedom. In conclusion, the Si-Te stretching and Te displacement modes are sensitive to the magnetic ordering transition, a finding that we discuss in terms of the superexchange mechanism. Lastly, spin-lattice coupling constants are also extracted.« less

Goos-Hänchen effect on Si thin films with spherical and cylindrical pores

NASA Astrophysics Data System (ADS)

Olaya, Cherrie May; Garcia, Wilson O.; Hermosa, Nathaniel

2018-02-01

We examine the effects on the spatial and angular Goos-Hanchen (GH) beam shifts of spherical and cylindrical pores in a thin film. In our calculations, a p-polarized light is incident on a 1-μm thick porous silicon (Si) thin film on a Si substrate. The beam shifts are within the measurement range of usual optical detectors. Our results show that a technique based on GH shift can be used to determine the porosity and pore structure of thin films at a given thickness.

Microstructures of BN/SiC coatings on nicalon fibers

NASA Technical Reports Server (NTRS)

Dickerson, R. M.; Singh, M.

1995-01-01

The microstructures of Nicalon silicon carbide (SiC) fibers and layered coatings of boron nitride (BN) followed by chemical vapor infiltrated silicon carbide (CVI-SiC) were characterized using optical and electron microscopy. Two different precursors and reactions were used to produce the BN layers while the deposition of CVI silicon carbide was nearly identical. Coated tows were examined in cross-section to characterize the chemistry and structures of the constituents and the interfaces. One BN precursor yielded three sublayers while the other gave a relatively homogeneous nanocrystalline layer.

Preparation and Optoelectrical Properties of p-CuO/n-Si Heterojunction by a Simple Sol-Gel Method

NASA Astrophysics Data System (ADS)

He, Bo; Xu, Jing; Ning, Huanpo; Zhao, Lei; Xing, Huaizhong; Chang, Chien-Cheng; Qin, Yuming; Zhang, Lei

The Cuprous oxide (CuO) thin film was prepared on texturized Si wafer by a simple sol-gel method to fabricate p-CuO/n-Si heterojunction photoelectric device. The novel sol-gel method is very cheap and convenient. The structural, optical and electrical properties of the CuO film were studied by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), X-ray photoelectron spectroscopy (XPS), UV-Vis spectrophotometer and Hall effect measurement. A good nonlinear rectifying behavior is obtained for the p-CuO/n-Si heterojunction. Under reverse bias, good photoelectric behavior is obtained.

Solidification of Magnesium (AM50A) / vol%. SiCp composite

NASA Astrophysics Data System (ADS)

Zhang, X.; Hu, H.

2012-01-01

Magnesium matrix composite is one of the advanced lightweight materials with high potential to be used in automotive and aircraft industries due to its low density and high specific mechanical properties. The magnesium composites can be fabricated by adding the reinforcements of fibers or/and particles. In the previous literature, extensive studies have been performed on the development of matrix grain structure of aluminum-based metal matrix composites. However, there is limited information available on the development of grain structure during the solidification of particulate-reinforced magnesium. In this work, a 5 vol.% SiCp particulate-reinforced magnesium (AM50A) matrix composite (AM50A/SiCp) was prepared by stir casting. The solidification behavior of the cast AM50A/SiCp composite was investigated by computer-based thermal analysis. Optical and scanning electron microscopies (SEM) were employed to examine the occurrence of nucleation and grain refinement involved. The results indicate that the addition of SiCp particulates leads to a finer grain structure in the composite compared with the matrix alloy. The refinement of grain structure should be attributed to both the heterogeneous nucleation and the restricted primary crystal growth.

Structural defects in cubic semiconductors characterized by aberration-corrected scanning transmission electron microscopy.

PubMed

Arroyo Rojas Dasilva, Yadira; Kozak, Roksolana; Erni, Rolf; Rossell, Marta D

2017-05-01

The development of new electro-optical devices and the realization of novel types of transistors require a profound understanding of the structural characteristics of new semiconductor heterostructures. This article provides a concise review about structural defects which occur in semiconductor heterostructures on the basis of micro-patterned Si substrates. In particular, one- and two-dimensional crystal defects are being discussed which are due to the plastic relaxation of epitaxial strain caused by the misfit of crystal lattices. Besides a few selected examples from literature, we treat in particular crystal defects occurring in GaAs/Si, Ge/Si and β-SiC/Si structures which are studied by high-resolution annular dark-field scanning transmission electron microscopy. The relevance of this article is twofold; firstly, it should provide a collection of data which are of help for the identification and characterization of defects in cubic semiconductors by means of atomic-resolution imaging, and secondly, the experimental data shall provide a basis for advancing the understanding of device characteristics with the aid of theoretical modelling by considering the defective nature of strained semiconductor heterostructures. Copyright © 2016 Elsevier B.V. All rights reserved.

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

NASA Technical Reports Server (NTRS)

Christensen-Dalsgaard, Jorgen; Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

2012-01-01

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled processes in the Universe. SI is a "LandmarklDiscovery Mission" in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission

Optical spectra of composite silver-porous silicon (Ag-pSi) nanostructure based periodical lattice

NASA Astrophysics Data System (ADS)

Amedome Min-Dianey, Kossi Aniya; Zhang, Hao-Chun; Brohi, Ali Anwar; Yu, Haiyan; Xia, Xinlin

2018-03-01

Numerical finite differential time domain (FDTD) tools were used in this study for predicting the optical characteristics through the nanostructure of composite silver-porous silicon (Ag-pSi) based periodical lattice. This is aimed at providing an interpretation of the optical spectra at known porosity in improvement of the light manipulating efficiency through a proposed structure. With boundary conditions correctly chosen, the numerical simulation was achieved using FDTD Lumerical solutions. This was used to investigate the effect of porosity and the number of layers on the reflection, transmission and absorption characteristics through a proposed structure in a visible wavelength range of 400-750 nm. The results revealed that the higher the number of layers, the lower the reflection. Also, the reflection increases with porosity increase. The transmission characteristics were the inverse to those found in the case of reflection spectra and optimum transmission was attained at high number of layers. Also, increase in porosity results in reduced transmission. Increase in porosity as well as in the number of layers led to an increase in absorption. Therefore, absorption into such structure can be enhanced by elevating the number of layers and the degree of porosity.

Synthesis, structural, electronic and linear electro-optical features of new quaternary Ag2Ga2SiS6 compound

NASA Astrophysics Data System (ADS)

Piasecki, M.; Myronchuk, G. L.; Parasyuk, O. V.; Khyzhun, O. Y.; Fedorchuk, A. O.; Pavlyuk, V. V.; Kozer, V. R.; Sachanyuk, V. P.; El-Naggar, A. M.; Albassam, A. A.; Jedryka, J.; Kityk, I. V.

2017-02-01

For the first time phase equilibria and phase diagram of the AgGaS2-SiS2 system were successfully explored by differential thermal and X-ray phase analysis methods. Crystal structure of low-temperature (LT) modification of Ag2Ga2SiS6 (LT- Ag2Ga2SiS6) was studied by X-ray powder method and it belongs to tetragonal space group I-42d, with unit cell parameters a=5.7164(4) Å, c=9.8023(7) Å, V=320.32(7) Å3. Additional details regarding the crystal structure exploration are available at the web page Fachinformationszentrum Karlsruhe. X-ray photoelectron core-level and valence-band spectra were measured for pristine LT- Ag2Ga2SiS6 crystal surface. In addition, the X-ray photoelectron valence-band spectrum of LT-Ag2Ga2SiS6 was matched on a common energy scale with the X-ray emission S Kβ1,3 and Ga Kβ2 bands, which give information on the energy distribution of the S 3p and Ga 4p states, respectively. The presented X-ray spectroscopy results indicate that the valence S p and Ga p atomic states contribute mainly to the upper and central parts of the valence band of LT-Ag2Ga2SiS6, respectively, with a less significant contribution also to other valence-band regions. Band gap energy was estimated by measuring the quantum energy in the spectral range of the fundamental absorption. We have found that energy gap Eg is equal to 2.35 eV at 300 K. LT-Ag2Ga2SiS6 is a photosensitive material and reveals two spectral maxima on the curve of spectral photoconductivity spectra at λmax1 =590 nm and λmax2 =860 nm. Additionally, linear electro-optical effect of LT-Ag2Ga2SiS6 for the wavelengths of a cw He-Ne laser at 1150 nm was explored.

Si/SiGe heterointerfaces in one-, two-, and three-dimensional nanostructures: their impact on SiGe light emission

NASA Astrophysics Data System (ADS)

Lockwood, David; Wu, Xiaohua; Baribeau, Jean-Marc; Mala, Selina; Wang, Xialou; Tsybeskov, Leonid

2016-03-01

Fast optical interconnects together with an associated light emitter that are both compatible with conventional Si-based complementary metal-oxide- semiconductor (CMOS) integrated circuit technology is an unavoidable requirement for the next-generation microprocessors and computers. Self-assembled Si/Si1-xGex nanostructures, which can emit light at wavelengths within the important optical communication wavelength range of 1.3 - 1.55 μm, are already compatible with standard CMOS practices. However, the expected long carrier radiative lifetimes observed to date in Si and Si/Si1-xGex nanostructures have prevented the attainment of efficient light-emitting devices including the desired lasers. Thus, the engineering of Si/Si1-xGex heterostructures having a controlled composition and sharp interfaces is crucial for producing the requisite fast and efficient photoluminescence (PL) at energies in the range 0.8-0.9 eV. In this paper we assess how the nature of the interfaces between SiGe nanostructures and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in three dimensions (corresponding to the case of quantum dots), two dimensions (corresponding to quantum wires), and one dimension (corresponding to quantum wells). The interface sharpness is influenced by many factors such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for nanostructure confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW) heterojunctions (HJs) with a Si/Ge NW diameter in the range 50 - 120 nm produce a clear PL signal associated with band-to-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1-xGex nanostructures incorporated into a Si0.6Ge0.4 wavy superlattice structure display PL of high intensity while exhibiting a characteristic decay time that is up to 1000 times shorter than that found in conventional Si/SiGe nanostructures. The non-exponential PL decay found experimentally in Si/SiGe nanostructures can be interpreted as resulting from variations in the separation distance between electrons and holes at the Si/SiGe heterointerface. The results demonstrate that a sharp Si/SiGe heterointerface acts to reduce the carrier radiative recombination lifetime and increase the PL quantum

Crystal structure of laser-induced subsurface modifications in Si

NASA Astrophysics Data System (ADS)

Verburg, P. C.; Smillie, L. A.; Römer, G. R. B. E.; Haberl, B.; Bradby, J. E.; Williams, J. S.; Huis in't Veld, A. J.

2015-08-01

Laser-induced subsurface modification of dielectric materials is a well-known technology. Applications include the production of optical components and selective etching. In addition to dielectric materials, the subsurface modification technology can be applied to silicon, by employing near to mid-infrared radiation. An application of subsurface modifications in silicon is laser-induced subsurface separation, which is a method to separate wafers into individual dies. Other applications for which proofs of concept exist are the formation of waveguides and resistivity tuning. However, limited knowledge is available about the crystal structure of subsurface modifications in silicon. In this work, we investigate the geometry and crystal structure of laser-induced subsurface modifications in monocrystalline silicon wafers. In addition to the generation of lattice defects, we found that transformations to amorphous silicon and Si -iii/Si -xii occur as a result of the laser irradiation.

Realization of 10 GHz minus 30dB on-chip micro-optical links with Si-Ge RF bi-polar technology

NASA Astrophysics Data System (ADS)

Ogudo, Kingsley A.; Snyman, Lukas W.; Polleux, Jean-Luc; Viana, Carlos; Tegegne, Zerihun

2014-06-01

Si Avalanche based LEDs technology has been developed in the 650 -850nm wavelength regime [1, 2]. Correspondingly, small micro-dimensioned detectors with pW/μm2 sensitivity have been developed for the same wavelength range utilizing Si-Ge detector technology with detection efficiencies of up to 0.85, and with a transition frequencies of up to 80 GHz [3] A series of on-chip optical links of 50 micron length, utilizing 650 - 850 nm propagation wavelength have been designed and realized, utilizing a Si Ge radio frequency bipolar process. Micron dimensioned optical sources, waveguides and detectors were all integrated on the same chip to form a complete optical link on-chip. Avalanche based Si LEDs (Si Av LEDs), Schottky contacting, TEOS densification strategies, silicon nitride based waveguides, and state of the art Si-Ge bipolar detector technologies were used as key design strategies. Best performances show optical coupling from source to detector of up to 10GHz and - 40dBm total optical link budget loss with a potential transition frequency coupling of up to 40GHz utilizing Si Ge based LEDs. The technology is particularly suitable for application as on-chip optical links, optical MEMS and MOEMS, as well as for optical interconnects utilizing low loss, side surface, waveguide- to-optical fiber coupling. Most particularly is one of our designed waveguide which have a good core axis alignment with the optical source and yield 10GHz -30dB on-chip micro-optical links as shown in Fig 9 (c). The technology as developed has been appropriately IP protected.

PECVD based silicon oxynitride thin films for nano photonic on chip interconnects applications.

PubMed

Sharma, Satinder K; Barthwal, Sumit; Singh, Vikram; Kumar, Anuj; Dwivedi, Prabhat K; Prasad, B; Kumar, Dinesh

2013-01-01

Thin silicon oxynitride (SiO(x)N(y)) films were deposited by low temperature (~300°C) plasma enhanced chemical vapour deposition (PECVD), using SiH(4), N(2)O, NH(3) precursor of the flow rate 25, 100, 30 sccm and subjected to the post deposition annealing (PDA) treatment at 400°C and 600°C for nano optical/photonics on chip interconnects applications. AFM result reveals the variation of roughness from 60.9 Å to 23.4 Å after PDA treatment with respect to the as-deposited films, favourable surface topography for integrated waveguide applications. A model of decrease in island height with the effect of PDA treatment is proposed in support of AFM results. Raman spectroscopy and FTIR measurements are performed in order to define the change in crystallite and chemical bonding of as-deposited as well as PDA treated samples. These outcomes endorsed to the densification of SiO(x)N(y) thin films, due to decrease in Si-N and Si-O bonds strain, as well the O-H, N-H bonds with in oxynitride network. The increase in refractive index and PL intensity of as deposited SiO(x)N(y) thin films to the PDA treated films at 400°C and 600°C are observed. The significant shift of PL spectra peak positions indicate the change in cluster size as the result of PDA treatment, which influence the optical properties of thin films. It might be due to out diffusion of hydrogen containing species from silicon oxynitride films after PDA treatment. In this way, the structural and optical, feasibility of SiO(x)N(y) films are demonstrated in order to obtain high quality thin films for nano optical/photonics on chip interconnects applications. Copyright © 2012 Elsevier Ltd. All rights reserved.

4 channel × 10 Gb/s bidirectional optical subassembly using silicon optical bench with precise passive optical alignment.

PubMed

Kang, Eun Kyu; Lee, Yong Woo; Ravindran, Sooraj; Lee, Jun Ki; Choi, Hee Ju; Ju, Gun Wu; Min, Jung Wook; Song, Young Min; Sohn, Ik-Bu; Lee, Yong Tak

2016-05-16

We demonstrate an advanced structure for optical interconnect consisting of 4 channel × 10 Gb/s bidirectional optical subassembly (BOSA) formed using silicon optical bench (SiOB) with tapered fiber guiding holes (TFGHs) for precise and passive optical alignment of vertical-cavity surface-emitting laser (VCSEL)-to-multi mode fiber (MMF) and MMF-to-photodiode (PD). The co-planar waveguide (CPW) transmission line (Tline) was formed on the backside of silicon substrate to reduce the insertion loss of electrical data signal. The 4 channel VCSEL and PD array are attached at the end of CPW Tline using a flip-chip bonder and solder pad. The 12-channel ribbon fiber is simply inserted into the TFGHs of SiOB and is passively aligned to the VCSEL and PD in which no additional coupling optics are required. The fabricated BOSA shows high coupling efficiency and good performance with the clearly open eye patterns and a very low bit error rate of less than 10^-12 order at a data rate of 10 Gb/s with a PRBS pattern of 2³¹-1.

Electronic structure, magnetism, and optical properties of Fe2SiO4 fayalite at ambient and high pressures: A GGA+U study

NASA Astrophysics Data System (ADS)

Jiang, Xuefan; Guo, G. Y.

2004-04-01

The electronic structure, magnetism, and optical properties of Fe2SiO4 fayalite, the iron-rich end member of the olivine-type silicate, one of the most abundant minerals in Earth’s upper mantle, have been studied by density-functional theory within the generalized gradient approximation (GGA) with the on-site Coulomb energy U=4.5 eV taken into account (GGA+U). The stable insulating antiferromagnetic solution with an energy gap ˜1.49 eV and a spin magnetic moment of 3.65μB and an orbital magnetic moment of 0.044μB per iron atom is obtained. It is found that the gap opening in this fayalite results mainly from the strong on-site Coulomb interaction on the iron atoms. In this band structure, the top of valence bands consists mainly of the 3d orbitals of Fe2 atoms, and the bottom of the conduction bands is mainly composed of the 3d orbitals of Fe1 atoms. Therefore, since the electronic transition from the Fe2 3d to Fe1 3d states is weak, significant electronic transitions would appear only about 1 eV above the absorption edge when Fe-O orbitals are involved in the final states. In addition, our band-structure calculations can explain the observed phenomena including redshift near the absorption edge and the decrease of the electrical resistivity of Fe2SiO4 upon compression. The calculated Fe p partial density of states agree well with Fe K-edge x-ray absorption spectrum. The calculated lattice constants and atomic coordinates for Fe2SiO4 fayalite in orthorhombic structure are in good agreement with experiments.

Towards a subcutaneous optical biosensor based on thermally hydrocarbonised porous silicon.

PubMed

Tong, Wing Yin; Sweetman, Martin J; Marzouk, Ezzat R; Fraser, Cara; Kuchel, Tim; Voelcker, Nicolas H

2016-01-01

Advanced biosensors in future medicine hinge on the evolvement of biomaterials. Porous silicon (pSi), a generally biodegradable and biocompatible material that can be fabricated to include environment-responsive optical characteristics, is an excellent candidate for in vivo biosensors. However, the feasibility of using this material as a subcutaneously implanted optical biosensor has never been demonstrated. Here, we investigated the stability and biocompatibility of a thermally-hydrocarbonised (THC) pSi optical rugate filter, and demonstrated its optical functionality in vitro and in vivo. We first compared pSi films with different surface chemistries and observed that the material was cytotoxic despite the outstanding stability of the THC pSi films. We then showed that the cytotoxicity correlates with reactive oxygen species levels, which could be mitigated by pre-incubation of THC pSi (PITHC pSi). PITHC pSi facilitates normal cellular phenotypes and is biocompatible in vivo. Importantly, the material also possesses optical properties capable of responding to microenvironmental changes that are readable non-invasively in cell culture and subcutaneous settings. Collectively, we demonstrate, for the first time, that PITHC pSi rugate filters are both biocompatible and optically functional for lab-on-a-chip and subcutaneous biosensing scenarios. We believe that this study will deepen our understanding of cell-pSi interactions and foster the development of implantable biosensors. Copyright © 2015 Elsevier Ltd. All rights reserved.

Characterization of the dimensional stability of advanced metallic materials using an optical test bench structure

NASA Technical Reports Server (NTRS)

Hsieh, Cheng; O'Donnell, Timothy P.

1991-01-01

The dimensional stability of low-density high specific-strength metal-matrix composites (including 30 vol pct SiC(p)/SXA 24-T6 Al, 25 vol pct SiC(p)/6061-T6 Al, 40 vol pct graphite P100 fiber/6061 Al, 50 vol pct graphite P100 fiber/6061 Al, and 40 vol pct P100 graphite fiber/AZ91D Mg composites) and an Al-Li-Mg metal alloy was evaluated using a specially designed five-strut optical test bench structure. The structure had 30 thermocouple locations, one retroreflector, one linear interferometer multilayer insulation, and various strip heaters. It was placed in a 10 exp -7 torr capability vacuum chamber with a laser head positioned at a window port, and a laser interferometer system for collecting dimensional change data. It was found that composite materials have greater 40-C temporal dimensional stability than the AL-Li-Mg alloy. Aluminum-based composites demonstrated better 40-C temporal stability than Mg-based composites.

Investigation on nonlinear optical properties of MoS2 nanoflake, grown on silicon and quartz substrates

NASA Astrophysics Data System (ADS)

Bayesteh, S.; Mortazavi, S. Z.; Reyhani, A.

2018-03-01

In this study, MoS2 was directly synthesized by one-step thermal chemical vapour deposition (TCVD), on different substrates including Si/SiO2 and quartz, using MoO3 and sulfide powders as precursor. The XRD patterns demonstrate the high crystallinity of MoS2 on Si/SiO2 and quartz substrates. SEM confirmed the formation of MoS2 grown on both substrates. According to line width and frequency difference between the E1 2g and A1g in Raman spectroscopy, it is inferred that the MoS2 grown on Si/SiO2 substrate is monolayer and the MoS2 grown on quartz substrate is multilayer. Moreover, by assessment of MoS2 nanoflake band gap via UV-visible analysis, it verified the formation of few layer structures. In addition, the open-aperture and close-aperture Z-scan techniques were employed to study the nonlinear optical properties including nonlinear absorption and nonlinear refraction of the synthesized MoS2. All experiments were performed using a diode laser with a wavelength of 532 nm as light source. The monolayer MoS2 synthesized on Si/SiO2, display considerable two-photon absorption. However, the multilayer MoS2 synthesized on quartz displayed saturable absorption (SA). It is noticeable that both samples demonstrate obvious self-defocusing behaviour.

Preparation and Anodizing of SiCp/Al Composites with Relatively High Fraction of SiCp

PubMed Central

2018-01-01

By properly proportioned SiC particles with different sizes and using squeeze infiltration process, SiCp/Al composites with high volume fraction of SiC content (Vp = 60.0%, 61.2%, 63.5%, 67.4%, and 68.0%) were achieved for optical application. The flexural strength of the prepared SiCp/Al composites was higher than 483 MPa and the elastic modulus was increased from 174.2 to 206.2 GPa. With an increase in SiC volume fraction, the flexural strength and Poisson's ratio decreased with the increase in elastic modulus. After the anodic oxidation treatment, an oxidation film with porous structure was prepared on the surface of the composite and the oxidation film was uniformly distributed. The anodic oxide growth rate of composite decreased with SiC content increased and linearly increased with anodizing time. PMID:29682145

Preparation and Anodizing of SiCp/Al Composites with Relatively High Fraction of SiCp.

PubMed

Wang, Bin; Qu, Shengguan; Li, Xiaoqiang

2018-01-01

By properly proportioned SiC particles with different sizes and using squeeze infiltration process, SiCp/Al composites with high volume fraction of SiC content (Vp = 60.0%, 61.2%, 63.5%, 67.4%, and 68.0%) were achieved for optical application. The flexural strength of the prepared SiC p /Al composites was higher than 483 MPa and the elastic modulus was increased from 174.2 to 206.2 GPa. With an increase in SiC volume fraction, the flexural strength and Poisson's ratio decreased with the increase in elastic modulus. After the anodic oxidation treatment, an oxidation film with porous structure was prepared on the surface of the composite and the oxidation film was uniformly distributed. The anodic oxide growth rate of composite decreased with SiC content increased and linearly increased with anodizing time.

Thousands of Stellar SiO masers in the Galactic center: The Bulge Asymmetries and Dynamic Evolution (BAaDE) survey

NASA Astrophysics Data System (ADS)

Sjouwerman, Loránt O.; Pihlström, Ylva M.; Rich, R. Michael; Morris, Mark R.; Claussen, Mark J.

2017-01-01

A radio survey of red giant SiO sources in the inner Galaxy and bulge is not hindered by extinction. Accurate stellar velocities (<1 km/s) are obtained with minimal observing time (<1 min) per source. Detecting over 20,000 SiO maser sources yields data comparable to optical surveys with the additional strength of a much more thorough coverage of the highly obscured inner Galaxy. Modeling of such a large sample would reveal dynamical structures and minority populations; the velocity structure can be compared to kinematic structures seen in molecular gas, complex orbit structure in the bar, or stellar streams resulting from recently infallen systems. Our Bulge Asymmetries and Dynamic Evolution (BAaDE) survey yields bright SiO masers suitable for follow-up Galactic orbit and parallax determination using VLBI. Here we outline our early VLA observations at 43 GHz in the northern bulge and Galactic plane (0

Structural and optical characterization of GaAs nano-crystals selectively grown on Si nano-tips by MOVPE.

PubMed

Skibitzki, Oliver; Prieto, Ivan; Kozak, Roksolana; Capellini, Giovanni; Zaumseil, Peter; Arroyo Rojas Dasilva, Yadira; Rossell, Marta D; Erni, Rolf; von Känel, Hans; Schroeder, Thomas

2017-03-01

We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (Si) (001) substrates fabricated using a CMOS technology compatible process. The selective growth of GaAs nano-crystals (NCs) was achieved at 570 °C by MOVPE. A detailed structure and defect characterization study of the grown nano-heterostructures was performed using scanning transmission electron microscopy, x-ray diffraction, micro-Raman, and micro-photoluminescence (μ-PL) spectroscopy. The results show single-crystalline, nearly relaxed GaAs NCs on top of slightly, by the SiO 2 -mask compressively strained Si nano-tips (NTs). Given the limited contact area, GaAs/Si nanostructures benefit from limited intermixing in contrast to planar GaAs films on Si. Even though a few growth defects (e.g. stacking faults, micro/nano-twins, etc) especially located at the GaAs/Si interface region were detected, the nanoheterostructures show intensive light emission, as investigated by μ-PL spectroscopy. Achieving well-ordered high quality GaAs NCs on Si NTs may provide opportunities for superior electronic, photonic, or photovoltaic device performances integrated on the silicon technology platform.

Liquid phase epitaxy of binary III–V nanocrystals in thin Si layers triggered by ion implantation and flash lamp annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wutzler, Rene, E-mail: r.wutzler@hzdr.de; Rebohle, Lars; Prucnal, Slawomir

2015-05-07

The integration of III–V compound semiconductors in Si is a crucial step towards faster and smaller devices in future technologies. In this work, we investigate the formation process of III–V compound semiconductor nanocrystals, namely, GaAs, GaSb, and InP, by ion implantation and sub-second flash lamp annealing in a SiO{sub 2}/Si/SiO{sub 2} layer stack on Si grown by plasma-enhanced chemical vapor deposition. Raman spectroscopy, Rutherford Backscattering spectrometry, and transmission electron microscopy were performed to identify the structural and optical properties of these structures. Raman spectra of the nanocomposites show typical phonon modes of the compound semiconductors. The formation process of themore » III–V compounds is found to be based on liquid phase epitaxy, and the model is extended to the case of an amorphous matrix without an epitaxial template from a Si substrate. It is shown that the particular segregation and diffusion coefficients of the implanted group-III and group-V ions in molten Si significantly determine the final appearance of the nanostructure and thus their suitability for potential applications.« less

Structure-Dependent Spectroscopic Properties of Yb3+-Doped Phosphosilicate Glasses Modified by SiO₂.

PubMed

Wang, Ling; Zeng, Huidan; Yang, Bin; Ye, Feng; Chen, Jianding; Chen, Guorong; Smith, Andew T; Sun, Luyi

2017-02-28

Yb 3+ -doped phosphate glasses containing different amounts of SiO₂ were successfully synthesized by the conventional melt-quenching method. The influence mechanism of SiO₂ on the structural and spectroscopic properties was investigated systematically using the micro-Raman technique. It was worth noting that the glass with 26.7 mol % SiO₂ possessed the longest fluorescence lifetime (1.51 ms), the highest gain coefficient (1.10 ms·pm²), the maximum Stark splitting manifold of ²F 7/2 level (781 cm -1 ), and the largest scalar crystal-field N J and Yb 3+ asymmetry degree. Micro-Raman spectra revealed that introducing SiO₂ promoted the formation of P=O linkages, but broke the P=O linkages when the SiO₂ content was greater than 26.7 mol %. Based on the previous 29 Si MAS NMR experimental results, these findings further demonstrated that the formation of [SiO₆] may significantly affect the formation of P=O linkages, and thus influences the spectroscopic properties of the glass. These results indicate that phosphosilicate glasses may have potential applications as a Yb 3+ -doped gain medium for solid-state lasers and optical fiber amplifiers.

Structure-Dependent Spectroscopic Properties of Yb3+-Doped Phosphosilicate Glasses Modified by SiO2

PubMed Central

Wang, Ling; Zeng, Huidan; Yang, Bin; Ye, Feng; Chen, Jianding; Chen, Guorong; Smith, Andew T.; Sun, Luyi

2017-01-01

Yb3+-doped phosphate glasses containing different amounts of SiO2 were successfully synthesized by the conventional melt-quenching method. The influence mechanism of SiO2 on the structural and spectroscopic properties was investigated systematically using the micro-Raman technique. It was worth noting that the glass with 26.7 mol % SiO2 possessed the longest fluorescence lifetime (1.51 ms), the highest gain coefficient (1.10 ms·pm2), the maximum Stark splitting manifold of 2F7/2 level (781 cm−1), and the largest scalar crystal-field NJ and Yb3+ asymmetry degree. Micro-Raman spectra revealed that introducing SiO2 promoted the formation of P=O linkages, but broke the P=O linkages when the SiO2 content was greater than 26.7 mol %. Based on the previous 29Si MAS NMR experimental results, these findings further demonstrated that the formation of [SiO6] may significantly affect the formation of P=O linkages, and thus influences the spectroscopic properties of the glass. These results indicate that phosphosilicate glasses may have potential applications as a Yb3+-doped gain medium for solid-state lasers and optical fiber amplifiers. PMID:28772601

Structural, electrical, and optical characterization of coalescent p-n GaN nanowires grown by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kolkovsky, Vl.; Zytkiewicz, Z. R.; Sobanska, M.

2015-12-14

The electrical, structural, and optical properties of coalescent p-n GaN nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrate are investigated. From photoluminescence measurements the full width at half maximum of bound exciton peaks AX and DA is found as 1.3 and 1.2 meV, respectively. These values are lower than those reported previously in the literature. The current-voltage characteristics show the rectification ratio of about 10{sup 2} and the leakage current of about 10{sup −4} A/cm{sup 2} at room temperature. We demonstrate that the thermionic mechanism is not dominant in these samples and spatial inhomogeneties and tunneling processes through amore » ∼2 nm thick SiN{sub x} layer between GaN and Si could be responsible for deviation from the ideal diode behavior. The free carrier concentration in GaN NWs determined by capacitance-voltage measurements is about 4 × 10{sup 15 }cm{sup −3}. Two deep levels (H190 and E250) are found in the structures. We attribute H190 to an extended defect located at the interface between the substrate and the SiN{sub x} interlayer or near the sidewalls at the bottom of the NWs, whereas E250 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.« less

Integrated optical isolators using magnetic surface plasmon (Presentation Recording)

NASA Astrophysics Data System (ADS)

Shimizu, Hiromasa; Kaihara, Terunori; Umetsu, Saori; Hosoda, Masashi

2015-09-01

Optical isolators are one of the essential components to protect semiconductor laser diodes (LDs) from backward reflected light in integrated optics. In order to realize optical isolators, nonreciprocal propagation of light is necessary, which can be realized by magnetic materials. Semiconductor optical isolators have been strongly desired on Si and III/V waveguides. We have developed semiconductor optical isolators based on nonreciprocal loss owing to transverse magneto-optic Kerr effect, where the ferromagnetic metals are deposited on semiconductor optical waveguides1). Use of surface plasmon polariton at the interface of ferromagnetic metal and insulator leads to stronger optical confinement and magneto-optic effect. It is possible to modulate the optical confinement by changing the magnetic field direction, thus optical isolator operation is proposed2, 3). We have investigated surface plasmons at the interfaces between ferrimagnetic garnet/gold film, and applications to waveguide optical isolators. We assumed waveguides composed of Au/Si(38.63nm)/Ce:YIG(1700nm)/Si(220nm)/Si , and calculated the coupling lengths between Au/Si(38.63nm)/Ce:YIG plasmonic waveguide and Ce:YIG/Si(220nm)/Si waveguide for transversely magnetized Ce:YIG with forward and backward directions. The coupling length was calculated to 232.1um for backward propagating light. On the other hand, the coupling was not complete, and the length was calculated to 175.5um. The optical isolation by using the nonreciprocal coupling and propagation loss was calculated to be 43.7dB when the length of plasmonic waveguide is 700um. 1) H. Shimizu et al., J. Lightwave Technol. 24, 38 (2006). 2) V. Zayets et al., Materials, 5, 857-871 (2012). 3) J. Montoya, et al, J. Appl. Phys. 106, 023108, (2009).

Carbon-carbon mirrors for exoatmospheric and space applications

NASA Astrophysics Data System (ADS)

Krumweide, Duane E.; Wonacott, Gary D.; Woida, Patrick M.; Woida, Rigel Q.; Shih, Wei

2007-09-01

The cost and leadtime associated with beryllium has forced the MDA and other defense agencies to look for alternative materials with similar structural and thermal properties. The use of carbon-carbon material, specifically in optical components has been demonstrated analytically in prior SBIR work at San Diego Composites. Carbon-carbon material was chosen for its low in-plane and through-thickness CTE (athermal design), high specific stiffness, near-zero coefficient of moisture expansion, availability of material (specifically c-c honeycomb for lightweight substrates), and compatibility with silicon monoxide (SiO) and silicon dioxide (SiO II) coatings. Subsequent development work has produced shaped carbon-carbon sandwich substrates which have been ground, polished, coated and figured using traditional optical processing. Further development has also been done on machined monolithic carbon-carbon mirror substrates which have also been processed using standard optical finishing techniques.

Theory for n-type doped, tensile-strained Ge-Si(x)Ge(y)Sn1-x-y quantum-well lasers at telecom wavelength.

PubMed

Chang, Guo-En; Chang, Shu-Wei; Chuang, Shun Lien

2009-07-06

We propose and develop a theoretical gain model for an n-doped, tensile-strained Ge-Si(x)Ge(y)Sn(1-x-y) quantum-well laser. Tensile strain and n doping in Ge active layers can help achieve population inversion in the direct conduction band and provide optical gain. We show our theoretical model for the bandgap structure, the polarization-dependent optical gain spectrum, and the free-carrier absorption of the n-type doped, tensile-strained Ge quantum-well laser. Despite the free-carrier absorption due to the n-type doping, a significant net gain can be obtained from the direct transition. We also present our waveguide design and calculate the optical confinement factors to estimate the modal gain and predict the threshold carrier density.

Magneto-photonic crystal microcavities based on magnetic nanoparticles embedded in Silica matrix

NASA Astrophysics Data System (ADS)

Hocini, Abdesselam; Moukhtari, Riad; Khedrouche, Djamel; Kahlouche, Ahmed; Zamani, Mehdi

2017-02-01

Using the three-dimensional finite difference time domain method (3D FDTD) with perfectly matched layers (PML), optical and magneto-optical properties of two-dimensional magneto-photonic crystals micro-cavity is studied. This micro-cavity is fabricated by SiO2/ZrO2 or SiO2/TiO2 matrix doped with magnetic nanoparticles, in which the refractive index varied in the range of 1.51-1.58. We demonstrate that the Q factor for the designed cavity increases as the refractive index increases, and we find that the Q factor decreases as the volume fraction VF% due to off-diagonal elements increases. These magnetic microcavities may serve as a fundamental structure in a variety of ultra compact magneto photonic devices such as optical isolators, circulators and modulators in the future.

Investigation of isochronal annealing on the optical properties of HWCVD amorphous silicon nitride deposited at low temperatures and low gas flow rates

NASA Astrophysics Data System (ADS)

Muller, T. F. G.; Jacobs, S.; Cummings, F. R.; Oliphant, C. J.; Malgas, G. F.; Arendse, C. J.

2015-06-01

Hydrogenated amorphous silicon nitride (a-SiNx:H) is used as anti-reflection coatings in commercial solar cells. A final firing step in the production of micro-crystalline silicon solar cells allows hydrogen effusion from the a-SiNx:H into the solar cell, and contributes to bulk passivation of the grain boundaries. In this study a-SiNx:H deposited in a hot-wire chemical vapour deposition (HWCVD) chamber with reduced gas flow rates and filament temperature compared to traditional deposition regimes, were annealed isochronally. The UV-visible reflection spectra of the annealed material were subjected to the Bruggeman Effective Medium Approximation (BEMA) treatment, in which a theoretical amorphous semiconductor was combined with particle inclusions due to the structural complexities of the material. The extraction of the optical functions and ensuing Wemple-DeDomenici analysis of the wavelength-dependent refractive index allowed for the correlation of the macroscopic optical properties with the changes in the local atomic bonding configuration, involving silicon, nitrogen and hydrogen.

Barrier height enhancement of metal/semiconductor contact by an enzyme biofilm interlayer

NASA Astrophysics Data System (ADS)

Ocak, Yusuf Selim; Gul Guven, Reyhan; Tombak, Ahmet; Kilicoglu, Tahsin; Guven, Kemal; Dogru, Mehmet

2013-06-01

A metal/interlayer/semiconductor (Al/enzyme/p-Si) MIS device was fabricated using α-amylase enzyme as a thin biofilm interlayer. It was observed that the device showed an excellent rectifying behavior and the barrier height value of 0.78 eV for Al/α-amylase/p-Si was meaningfully larger than the one of 0.58 eV for conventional Al/p-Si metal/semiconductor (MS) contact. Enhancement of the interfacial potential barrier of Al/p-Si MS diode was realized using enzyme interlayer by influencing the space charge region of Si semiconductor. The electrical properties of the structure were executed by the help of current-voltage and capacitance-voltage measurements. The photovoltaic properties of the structure were executed under a solar simulator with AM1.5 global filter between 40 and 100 mW/cm2 illumination conditions. It was also reported that the α-amylase enzyme produced from Bacillus licheniformis had a 3.65 eV band gap value obtained from optical method.

Fabrication of GaAs/Al0.3Ga0.7As multiple quantum well nanostructures on (100) si substrate using a 1-nm InAs relief layer.

PubMed

Oh, H J; Park, S J; Lim, J Y; Cho, N K; Song, J D; Lee, W; Lee, Y J; Myoung, J M; Choi, W J

2014-04-01

Nanometer scale thin InAs layer has been incorporated between Si (100) substrate and GaAs/Al0.3Ga0.7As multiple quantum well (MQW) nanostructure in order to reduce the defects generation during the growth of GaAs buffer layer on Si substrate. Observations based on atomic force microscopy (AFM) and transmission electron microscopy (TEM) suggest that initiation and propagation of defect at the Si/GaAs interface could be suppressed by incorporating thin (1 nm in thickness) InAs layer. Consequently, the microstructure and resulting optical properties improved as compared to the MQW structure formed directly on Si substrate without the InAs layer. It was also observed that there exists some limit to the desirable thickness of the InAs layer since the MQW structure having thicker InAs layer (4 nm-thick) showed deteriorated properties.

Dark field photoelectron emission microscopy of micron scale few layer graphene

NASA Astrophysics Data System (ADS)

Barrett, N.; Conrad, E.; Winkler, K.; Krömker, B.

2012-08-01

We demonstrate dark field imaging in photoelectron emission microscopy (PEEM) of heterogeneous few layer graphene (FLG) furnace grown on SiC(000-1). Energy-filtered, threshold PEEM is used to locate distinct zones of FLG graphene. In each region, selected by a field aperture, the k-space information is imaged using appropriate transfer optics. By selecting the photoelectron intensity at a given wave vector and using the inverse transfer optics, dark field PEEM gives a spatial distribution of the angular photoelectron emission. In the results presented here, the wave vector coordinates of the Dirac cones characteristic of commensurate rotations of FLG on SiC(000-1) are selected providing a map of the commensurate rotations across the surface. This special type of contrast is therefore a method to map the spatial distribution of the local band structure and offers a new laboratory tool for the characterisation of technically relevant, microscopically structured matter.

Bluish-green color emitting Ba2Si3O8:Eu2+ ceramic phosphors for white light-emitting diodes.

PubMed

Xiao, F; Xue, Y N; Zhang, Q Y

2009-10-15

This paper reports on the structural and optical properties of Eu(2+) activated Ba(2)Si(3)O(8) ceramic phosphors synthesized by a sol-gel method. The ceramic phosphors have been characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and fluorescence measurements. The structural characterization results suggest that the as-prepared phosphors are of single phase monoclinic Ba(2)Si(3)O(8) with rod-like morphology. A broad excitation band ranging from 300 to 410 nm matches well with the ultraviolet (UV) radiation of light-emitting diodes (LEDs). Upon 380 nm UV light excitation, these phosphors emit bluish-green emission centered at 500 nm with color coordination (x=0.25, y=0.40). All the obtained results indicate that the Ba(2)Si(3)O(8):Eu(2+) ceramic phosphors are promising bluish-green candidates for the phosphor-converted white LEDs.

Penta-P2X (X=C, Si) monolayers as wide-bandgap semiconductors: A first principles prediction

NASA Astrophysics Data System (ADS)

Naseri, Mosayeb; Lin, Shiru; Jalilian, Jaafar; Gu, Jinxing; Chen, Zhongfang

2018-06-01

By means of density functional theory computations, we predicted two novel two-dimensional (2D) nanomaterials, namely P2X (X=C, Si) monolayers with pentagonal configurations. Their structures, stabilities, intrinsic electronic, and optical properties as well as the effect of external strain to the electronic properties have been systematically examined. Our computations showed that these P2C and P2Si monolayers have rather high thermodynamic, kinetic, and thermal stabilities, and are indirect semiconductors with wide bandgaps (2.76 eV and 2.69 eV, respectively) which can be tuned by an external strain. These monolayers exhibit high absorptions in the UV region, but behave as almost transparent layers for visible light in the electromagnetic spectrum. Their high stabilities and exceptional electronic and optical properties suggest them as promising candidates for future applications in UV-light shielding and antireflection layers in solar cells.

BC8 Silicon (Si-III) is a Narrow-Gap Semiconductor

NASA Astrophysics Data System (ADS)

Zhang, Haidong; Liu, Hanyu; Wei, Kaya; Kurakevych, Oleksandr O.; Le Godec, Yann; Liu, Zhenxian; Martin, Joshua; Guerrette, Michael; Nolas, George S.; Strobel, Timothy A.

2017-04-01

Large-volume, phase-pure synthesis of BC8 silicon (I a 3 ¯ , c I 16 ) has enabled bulk measurements of optical, electronic, and thermal properties. Unlike previous reports that conclude BC8-Si is semimetallic, we demonstrate that this phase is a direct band gap semiconductor with a very small energy gap and moderate carrier concentration and mobility at room temperature, based on far- and midinfrared optical spectroscopy, temperature-dependent electrical conductivity, Seebeck and heat capacity measurements. Samples exhibit a plasma wavelength near 11 μ m , indicating potential for infrared plasmonic applications. Thermal conductivity is reduced by 1-2 orders of magnitude depending on temperature as compared with the diamond cubic (DC-Si) phase. The electronic structure and dielectric properties can be reproduced by first-principles calculations with hybrid functionals after adjusting the level of exact Hartree-Fock (HF) exchange mixing. These results clarify existing limited and controversial experimental data sets and ab initio calculations.

Characterization of semiconductor materials using synchrotron radiation-based near-field infrared microscopy and nano-FTIR spectroscopy.

PubMed

Hermann, Peter; Hoehl, Arne; Ulrich, Georg; Fleischmann, Claudia; Hermelink, Antje; Kästner, Bernd; Patoka, Piotr; Hornemann, Andrea; Beckhoff, Burkhard; Rühl, Eckart; Ulm, Gerhard

2014-07-28

We describe the application of scattering-type near-field optical microscopy to characterize various semiconducting materials using the electron storage ring Metrology Light Source (MLS) as a broadband synchrotron radiation source. For verifying high-resolution imaging and nano-FTIR spectroscopy we performed scans across nanoscale Si-based surface structures. The obtained results demonstrate that a spatial resolution below 40 nm can be achieved, despite the use of a radiation source with an extremely broad emission spectrum. This approach allows not only for the collection of optical information but also enables the acquisition of near-field spectral data in the mid-infrared range. The high sensitivity for spectroscopic material discrimination using synchrotron radiation is presented by recording near-field spectra from thin films composed of different materials used in semiconductor technology, such as SiO2, SiC, SixNy, and TiO2.

Transient absorption phenomena and related structural transformations in femtosecond laser-excited Si

NASA Astrophysics Data System (ADS)

Kudryashov, Sergey I.

2004-09-01

Analysis of processes affecting transient optical absorption and photogeneration of electron-hole plasma in silicon pumped by an intense NIR or visible femtosecond laser pulse has been performed taking into account the most important electron-photon, electron-electron and electron-phonon interactions and, as a result, two main regimes of such laser-matter interaction have been revealed. The first regime is concerned with indirect interband optical absorption in Si, enhanced by a coherent shrinkage of its smallest indirect bandgap due to dynamic Franz-Keldysh effect (DFKE). The second regime takes place due to the critical renormalization of the Si direct bandgap along Λ-axis of its first Brillouin zone because of DFKE and the deformation potential electron-phonon interaction and occurs as intense direct single-photon excitation of electrons into one of the quadruplet of equivalent Λ-valleys in the lowest conduction band, which is split down due to the electron-phonon interaction.

Soft X-Ray Optics by Pulsed Laser Deposition

NASA Technical Reports Server (NTRS)

Fernandez, Felix E.

1996-01-01

Mo/Si and C/Co multilayers for soft x-ray optics were designed for spectral regions of interest in possible applications. Fabrication was effected by Pulsed Laser Deposition using Nd:YAG (355 nm) or excimer (248 nm) lasers in order to evaluate the suitability of this technique. Results for Mo/Si structures were not considered satisfactory due mainly to problems with particulate production and target surface modification during Si ablation. These problems may be alleviated by a two-wavelength approach, using separate lasers for each target. Results for C/Co multilayers are much more encouraging, since indication of good layering was observed for extremely thin layers. We expect to continue investigating this possibility. In order to compete with traditional PVD techniques, it is necessary to achieve film coverage uniformity over large enough areas. It was shown that this is feasible, and novel means of achieving it were devised.

Giant Phonon Anharmonicity and Anomalous Pressure Dependence of Lattice Thermal Conductivity in Y2Si2O7 silicate

PubMed Central

Luo, Yixiu; Wang, Jiemin; Li, Yiran; Wang, Jingyang

2016-01-01

Modification of lattice thermal conductivity (κL) of a solid by means of hydrostatic pressure (P) has been a crucially interesting approach that targets a broad range of advanced materials from thermoelectrics and thermal insulators to minerals in mantle. Although it is well documented knowledge that thermal conductivity of bulk materials normally increase upon hydrostatic pressure, such positive relationship is seriously challenged when it comes to ceramics with complex crystal structure and heterogeneous chemical bonds. In this paper, we predict an abnormally negative trend dκL/dP < 0 in Y2Si2O7 silicate using density functional theoretical calculations. The mechanism is disclosed as combined effects of slightly decreased group velocity and significantly augmented scattering of heat-carrying acoustic phonons in pressured lattice, which is originated from pressure-induced downward shift of low-lying optic and acoustic phonons. The structural origin of low-lying optic phonons as well as the induced phonon anharmonicity is also qualitatively elucidated with respect to intrinsic bonding heterogeneity of Y2Si2O7. The present results are expected to bring deeper insights for phonon engineering and modulation of thermal conductivity in complex solids with diverging structural flexibility, enormous bonding heterogeneity, and giant phonon anharmonicity. PMID:27430670

Design Approaches for Enhancing Photovoltaic Performance of Silicon Solar Cells Sensitized by Proximal Nanocrystalline Quantum Dots

NASA Astrophysics Data System (ADS)

Shafiq, Natis

Energy transfer (ET) based sensitization of silicon (Si) using proximal nanocrystal quantum dots (NQDs) has been studied extensively in recent years as a means to develop thin and flexible Si based solar cells. The driving force for this research activity is a reduction in materials cost. To date, the main method for determining the role of ET in sensitizing Si has been optical spectroscopic studies. The quantitative contribution from two modes of ET (namely, nonradiative and radiative) has been reported using time-resolved photoluminescence (TRPL) spectroscopy coupled with extensive theoretical modelling. Thus, optical techniques have established the potential for utilizing ET based sensitization of Si as a feasible way to develop novel NQD-Si hybrid solar cells. However, the ultimate measure of the efficiency of ET-based mechanisms is the generation of electron-hole pairs by the impinging photons. It is therefore important to perform electrical measurements. However, only a couple of studies have attempted electrical quantification of ET modes. A few studies have focused on photocurrent measurements, without considering industrially relevant photovoltaic (PV) systems. Therefore, there is a need to develop a systematic approach for the electrical quantification of ET-generated charges and to help engineer new PV architectures optimized for harnessing the full advantages of ET mechanisms. Within this context, the work presented in this dissertation aims to develop an experimental testing protocol that can be applied to different PV structures for quantifying ET contributions from electrical measurements. We fabricated bulk Si solar cells (SCs) as a test structure and utilized CdSe/ZnS NQDs for ET based sensitization. The NQD-bulk Si hybrid devices showed ˜30% PV enhancement after NQD deposition. We measured external quantum efficiency (EQE) of these devices to quantify ET-generated charges. Reflectance measurements were also performed to decouple contributions of intrinsic optical effects (i.e., anti-reflection) from NQD mediated ET processes. Our analysis indicates that the contribution of ET-generated charges cannot be detected by EQE measurements. Instead, changes in the optical properties (i.e., anti-reflection property) due to the NQD layer are found to be the primary source of the photocurrent enhancement. Based on this finding, we propose to minimize bulk Si absorption by using an ultrathin (˜300 nm) Si PV architecture which should enable measurements of ET-generated charges. We describe an optimized process flow for fabricating such ultrathin Si devices. The devices fabricated by this method behave like photo-detectors and show enhanced sensitivity under 1 Sun AM1.5G illumination. The geometry and process flow of these devices make it possible to incorporate NQDs for sensitization. Overall, this dissertation provides a protocol for the quantification of ET-generated charges and documents an optimized process flow for the development of an ultrathin Si solar cells.

Structural and optical study on antimony-silicate glasses doped with thulium ions.

PubMed

Dorosz, D; Zmojda, J; Kochanowicz, M; Miluski, P; Jelen, P; Sitarz, M

2015-01-05

Structural, spectroscopic and thermal properties of SiO₂-Al₂O₃-Sb₂O₃-Na₂O glass system doped with 0.2 mol% Tm₂O₃ have been presented. Synthesis of antimony-silicate glasses with relatively low phonon energy (600 cm(-1), which implicates a small non-radiative decay rate) was performed by conventional high-temperature melt-quenching methods. The effect of SiO₂/Sb₂O₃ ratio in fabricated Tm(3+) doped glass on thermal, structural and luminescence properties was investigated. On the basis of structural investigations decomposition of absorption bands in the infrared FTIR region was performed, thus determining that antimony ions are the only glass-forming ions, setting up the lattice of fabricated glasses. Luminescence band at the wavelength of 1.8 μm corresponding to (3)F₄→(3)H₆ transition in thulium ions was obtained under 795 nm laser pumping. It was observed that combination of relatively low phonon energy and greater separation of optically active centers in the fabricated glasses influenced in decreasing the luminescence intensity at 1800 nm. Copyright © 2014 Elsevier B.V. All rights reserved.

Improvement of optical quality of semipolar (11 2 ¯ 2 ) GaN on m-plane sapphire by in-situ epitaxial lateral overgrowth

NASA Astrophysics Data System (ADS)

Monavarian, Morteza; Izyumskaya, Natalia; Müller, Marcus; Metzner, Sebastian; Veit, Peter; Can, Nuri; Das, Saikat; Özgür, Ümit; Bertram, Frank; Christen, Jürgen; Morkoç, Hadis; Avrutin, Vitaliy

2016-04-01

Among the major obstacles for development of non-polar and semipolar GaN structures on foreign substrates are stacking faults which deteriorate the structural and optical quality of the material. In this work, an in-situ SiNx nano-network has been employed to achieve high quality heteroepitaxial semipolar (11 2 ¯ 2 ) GaN on m-plane sapphire with reduced stacking fault density. This approach involves in-situ deposition of a porous SiNx interlayer on GaN that serves as a nano-mask for the subsequent growth, which starts in the nanometer-sized pores (window regions) and then progresses laterally as well, as in the case of conventional epitaxial lateral overgrowth (ELO). The inserted SiNx nano-mask effectively prevents the propagation of defects, such as dislocations and stacking faults, in the growth direction and thus reduces their density in the overgrown layers. The resulting semipolar (11 2 ¯ 2 ) GaN layers exhibit relatively smooth surface morphology and improved optical properties (PL intensity enhanced by a factor of 5 and carrier lifetimes by 35% to 85% compared to the reference semipolar (11 2 ¯ 2 ) GaN layer) which approach to those of the c-plane in-situ nano-ELO GaN reference and, therefore, holds promise for light emitting and detecting devices.

Optical and structural characterization of Nb, Zr, Nb/Zr, Zr/Nb thin films on Si3N4 membranes windows

NASA Astrophysics Data System (ADS)

Jimenez, K.; Gaballah, A. E. H.; Ahmed, Nadeem; Zuppella, P.; Nicolosi, P.

2017-05-01

High brilliance sources in the EUV spectral range such as Synchrotron and Free Electron Lasers (FEL) are widely used in multiple scientific and technological applications thanks to their peculiar characteristics. One main technical problem of FEL is related to the rejection of high harmonics, seed laser, first stage photons, and diffuse light; in order to improve the quality of the beam delivered by these sources, a suitable optical system acting as band-pass filters is necessary. In this paper we discuss the optical and structure characterization of Nb/Zr and Zr/Nb self-stand transmittance filters, designed for 4.5 nm-20 nm wavelength ranges. In order to understand the properties of these bilayers filters, a campaign of measurements has been planned to be performed on Zr and Nb films on Si3N4 membrane windows and silicon substrates, deposited with e- beam deposition technique. Comparison of the results has been planned too. IMD transmittance and reflectance simulations, together with preliminary AFM and reflectance measurements will be shown in this work.

Optical and structural investigation of Dy3+-Nd3+ co-doped in magnesium lead borosilicate glasses.

PubMed

Rao, T G V M; Rupesh Kumar, A; Neeraja, K; Veeraiah, N; Rami Reddy, M

2014-01-24

MgO-PbO-B2O3-SiO2-Nd2O3-Dy2O3 glasses are prepared by melt-quenching technique. The samples are characterized by X-ray diffraction (XRD), optical absorption, luminescence and Fourier transform infrared (FT-IR) spectral studied. XRD analysis evidently indicates that the prepared samples are fully amorphous nature. From the optical absorption spectra, the bonding environment surrounding the Dy(3+) and their energy level scheme in glass network is analyzed. Enhancement of Dy(3+) emission by non-radiative energy transfers from Nd(3+) has been observed here. The samples emits intensive bluish yellow color from the (4)F9/2→(6)H15/2, (6)H13/2 transition of Dy(3+) ions in these glasses which are nearer to white light and it is also supported by the chromaticity color coordinates. The FT-IR spectra reveal that network connectivity is increased with replacement of bonds B-O-B, Si-O-Si by more resistant B-O-Si bonds with gradually increasing the content of Dy(3+) ions in the glass network. Along with spectroscopic parameters some physical parameters like density, refractive index etc. are measured for the glasses. Copyright © 2013 Elsevier B.V. All rights reserved.

Stabilization of flat aromatic Si6 rings analogous to benzene: ab initio theoretical prediction.

PubMed

Zdetsis, Aristides D

2007-12-07

It is shown by ab initio calculations, based on density functional (DFT/B3LYP), and high level coupled-cluster [CCSD(T)] and quadratic CI [QCISD(T)] methods, that flat aromatic silicon structures analogous to benzene (C6H6) can be stabilized in the presence of lithium. The resulting planar Si6Li6 structure is both stable and aromatic, sharing many key characteristics with benzene. To facilitate possible synthesis and characterization of these species, routes of formation with high exothermicity are suggested and several spectral properties (including optical absorption, infrared, and Raman) are calculated.

Silicon carbide optics for space and ground based astronomical telescopes

NASA Astrophysics Data System (ADS)

Robichaud, Joseph; Sampath, Deepak; Wainer, Chris; Schwartz, Jay; Peton, Craig; Mix, Steve; Heller, Court

2012-09-01

Silicon Carbide (SiC) optical materials are being applied widely for both space based and ground based optical telescopes. The material provides a superior weight to stiffness ratio, which is an important metric for the design and fabrication of lightweight space telescopes. The material also has superior thermal properties with a low coefficient of thermal expansion, and a high thermal conductivity. The thermal properties advantages are important for both space based and ground based systems, which typically need to operate under stressing thermal conditions. The paper will review L-3 Integrated Optical Systems - SSG’s (L-3 SSG) work in developing SiC optics and SiC optical systems for astronomical observing systems. L-3 SSG has been fielding SiC optical components and systems for over 25 years. Space systems described will emphasize the recently launched Long Range Reconnaissance Imager (LORRI) developed for JHU-APL and NASA-GSFC. Review of ground based applications of SiC will include supporting L-3 IOS-Brashear’s current contract to provide the 0.65 meter diameter, aspheric SiC secondary mirror for the Advanced Technology Solar Telescope (ATST).

Micromirror structure based on TiNi shape memory thin films

NASA Astrophysics Data System (ADS)

Fu, Yong Qing; Hu, Min; Du, Hejun; Luo, Jack; Flewitt, Andrew J.; Milne, William I.

2005-02-01

TiNi films were deposited on silicon by co-sputtering TiNi target and a separate Ti target at a temperature of 450°C. Results from differential scanning calorimeter, in-situ X-ray diffraction and curvature measurement revealed clearly martensitic transformation upon heating and cooling. Two types of TiNi/Si optical micromirror structures with a Si mirror cap (20 micron thick) and TiNi/Si actuation beams were designed and fabricated. For the first design, three elbow shaped Si beams with TiNi electrodes were used as the arms to actuate the mirror. In the second design, a V-shaped cantilever based on TiNi/Si bimorph beams was used as the actuation mechanism for micromirror. TiNi electrodes were patterned and wet-etched in a solutions of HF:HNO3:H2O (1:1:20) with an etch rate of 0.6 μm/min. The TiNi/Si microbeams were flat at room temperature, and bent up with applying voltage in TiNi electrodes (due to phase transformation and shape memory effect), thus causing the changes in angles of micromirror.

Grism manufacturing by low temperature mineral bonding

NASA Astrophysics Data System (ADS)

Kalkowski, G.; Grabowski, K.; Harnisch, G.; Flügel-Paul, T.; Zeitner, U.; Risse, S.

2017-09-01

By uniting a grating with a prism to a GRISM compound, the optical characteristics of diffractive and refractive elements can be favorably combined to achieve outstanding spectral resolution features. Ruling the grating structure into the prism surface is common for wavelengths around 1 μm and beyond, while adhesive bonding of two separate parts is generally used for shorter wavelengths and finer structures. We report on a manufacturing approach for joining the corresponding glass elements by the technology of hydrophilic direct bonding. This allows to manufacture the individual parts separately and subsequently combine them quasimonolithically by generating stiff and durable bonds of vanishing thickness, high strength and excellent transmission. With this approach for GRISM bonding, standard direct-write- or mask-lithography equipment may be used for the fabrication of the grating structure and the drawbacks of adhesive bonding (thermal mismatch, creep, aging) are avoided. The technology of hydrophilic bonding originates from "classical" optical contacting [1], but has been much improved and perfected during the last decades in the context of 3-dimensinal stacking Si-wafers for microelectronic applications [2]. It provides joins through covalent bonds of the Si-O-Si type at the nanometer scale, i.e. the elementary bond type in many minerals and glasses. The mineral nature of the bond is perfectly adapted to most optical materials and the extremely thin bonding layers generated with this technology are well suited for transmission optics. Creeping under mechanical load, as commonly observed with adhesive bonding, is not an issue. With respect to diffusion bonding, which operates at rather high temperatures close to the glass transition or crystal melting point, hydrophilic bonding is a low temperature process that needs only moderate heating. This facilitates provision of handling and alignment means for the individual parts during the set-up stages and greatly eases joining optical materials of different thermal expansion. The technology has been successfully used in the past for bonding various glasses as well as crystalline optical materials [3, 4]. Here we will focus on bonding prisms elements and binary gratings of fused silica with and without coatings at the bonding interface. Further, preliminary results on bonding prism-grating-prism (PGP) combinations will be presented.

Studies on linear, nonlinear optical and excited state dynamics of silicon nanoparticles prepared by picosecond laser ablation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamad, Syed; Nageswara Rao, S. V. S.; Pathak, A. P.

2015-12-15

We report results from our studies on the fabrication and characterization of silicon (Si) nanoparticles (NPs) and nanostructures (NSs) achieved through the ablation of Si target in four different liquids using ∼2 picosecond (ps) pulses. The consequence of using different liquid media on the ablation of Si target was investigated by studying the surface morphology along with material composition of Si based NPs. The recorded mean sizes of these NPs were ∼9.5 nm, ∼37 nm, ∼45 nm and ∼42 nm obtained in acetone, water, dichloromethane (DCM) and chloroform, respectively. The generated NPs were characterized by selected area electron diffraction (SAED),more » high resolution transmission microscopy (HRTEM), Raman spectroscopic techniques and Photoluminescence (PL) studies. SAED, HRTEM and Raman spectroscopy data confirmed that the material composition was Si NPs in acetone, Si/SiO{sub 2} NPs in water, Si-C NPs in DCM and Si-C NPs in chloroform and all of them were confirmed to be polycrystalline in nature. Surface morphological information of the fabricated Si substrates was obtained using the field emission scanning electron microscopic (FESEM) technique. FESEM data revealed the formation of laser induced periodic surface structures (LIPSS) for the case of ablation in acetone and water while random NSs were observed for the case of ablation in DCM and chloroform. Femtosecond (fs) nonlinear optical properties and excited state dynamics of these colloidal Si NPs were investigated using the Z-scan and pump-probe techniques with ∼150 fs (100 MHz) and ∼70 fs (1 kHz) laser pulses, respectively. The fs pump-probe data obtained at 600 nm consisted of single and double exponential decays which were tentatively assigned to electron-electron collisional relaxation (<1 ps) and non-radiative transitions (>1 ps). Large third order optical nonlinearities (∼10{sup −14} e.s.u.) for these colloids have been estimated from Z-scan data at an excitation wavelength of 680 nm suggesting that the colloidal Si NPs find potential applications in photonic devices.« less

Electroluminescence and transport properties in amorphous silicon nanostructures

NASA Astrophysics Data System (ADS)

Irrera, Alessia; Iacona, Fabio; Crupi, Isodiana; Presti, Calogero D.; Franzò, Giorgia; Bongiorno, Corrado; Sanfilippo, Delfo; Di Stefano, Gianfranco; Piana, Angelo; Fallica, Pier Giorgio; Canino, Andrea; Priolo, Francesco

2006-03-01

We report the results of a detailed study on the structural, electrical and optical properties of light emitting devices based on amorphous Si nanostructures. Amorphous nanostructures may constitute an interesting system for the monolithic integration of optical and electrical functions in Si ULSI technology. In fact, they exhibit an intense room temperature electroluminescence (EL), with the advantage of being formed at a temperature of 900 °C, while at least 1100 °C is needed for the formation of Si nanocrystals. Optical and electrical properties of amorphous Si nanocluster devices have been studied in the temperature range between 30 and 300 K. The EL is seen to have a bell-shaped trend as a function of temperature with a maximum at around 60 K. The efficiency of these devices is comparable to that found in devices based on Si nanocrystals, although amorphous nanostructures exhibit peculiar working conditions (very high current densities and low applied voltages). Time resolved EL measurements demonstrate the presence of a short lifetime, only partially due to the occurrence of non-radiative phenomena, since the very small amorphous clusters formed at 900 °C are characterized by a short radiative lifetime. By forcing a current through the device a phenomenon of charge trapping in the Si nanostructures has been observed. Trapped charges affect luminescence through an Auger-type non-radiative recombination of excitons. Indeed, it is shown that unbalanced injection of carriers (electrons versus holes) is one of the main processes limiting luminescence efficiency. These data will be reported and the advantages and limitations of this approach will be discussed.

High index glass thin film processing for photonics and photovoltaic (PV) applications

NASA Astrophysics Data System (ADS)

Ogbuu, Okechukwu Anthony

To favorably compete with fossil-fuel technology, the greatest challenge for thin film solar-cells is to improve efficiency and reduce material cost. Thickness scaling to thin film reduces material cost but affects the light absorption in the cells; therefore a concept that traps incident photons and increases its optical path length is needed to boost absorption in thin film solar cells. One approach is the integration of low symmetric gratings (LSG), using high index material, on either the front-side or backside of 30 um thin c-Si cells. In this study, Multicomponent TeO2--Bi2O 3--ZnO (TBZ) glass thin films were prepared using RF magnetron sputtering under different oxygen flow rates. The influences of oxygen flow rate on the structural and optical properties of the resulting thin films were investigated. The structural origin of the optical property variation was studied using X-ray diffraction, X-ray photoelectron spectroscopy, Raman Spectroscopy, and transmission electron microscopy. The results indicate that TBZ glass thin film is a suitable material for front side LSG material photovoltaic and photonics applications due to their amorphous nature, high refractive index (n > 2), broad band optical transparency window, low processing temperature. We developed a simple maskless method to pattern sputtered tellurite based glass thin films using unconventional agarose hydrogel mediated wet etching. Conventional wet etching process, while claiming low cost and high throughput, suffers from reproducibility and pattern fidelity issues due to the isotropic nature of wet chemical etching when applied to glasses and polymers. This method overcomes these challenges by using an agarose hydrogel stamp to mediate a conformal etching process. In our maskless method, agarose hydrogel stamps are patterned following a standard soft lithography and replica molding process from micropatterned masters and soaked in a chemical etchant. The micro-scale features on the stamp are subsequently transferred into glass and polymer thin films via conformal wet etching. High refractive index chalcogenide glass (n = 2.6) thin films with composition As20Se80 was selected for backside LSG material due to their attractive properties. We developed an optimized integration protocol for LSG integration and successfully integrated these LSG structures at the back side of both 30 microm c-Si solar cells and standalone 30 microm c-Si wafers. Optical and electrical characterization of LSG on thin c-Si cells shows that LSG structures create higher absorption enhancement and external quantum efficiency at long wavelengths.

Electrically pumped 1.3 microm room-temperature InAs/GaAs quantum dot lasers on Si substrates by metal-mediated wafer bonding and layer transfer.

PubMed

Tanabe, Katsuaki; Guimard, Denis; Bordel, Damien; Iwamoto, Satoshi; Arakawa, Yasuhiko

2010-05-10

An electrically pumped InAs/GaAs quantum dot laser on a Si substrate has been demonstrated. The double-hetero laser structure was grown on a GaAs substrate by metal-organic chemical vapor deposition and layer-transferred onto a Si substrate by GaAs/Si wafer bonding mediated by a 380-nm-thick Au-Ge-Ni alloy layer. This broad-area Fabry-Perot laser exhibits InAs quantum dot ground state lasing at 1.31 microm at room temperature with a threshold current density of 600 A/cm(2). (c) 2010 Optical Society of America.

Strain engineering of the silicon-vacancy center in diamond

NASA Astrophysics Data System (ADS)

Meesala, Srujan; Sohn, Young-Ik; Pingault, Benjamin; Shao, Linbo; Atikian, Haig A.; Holzgrafe, Jeffrey; Gündoǧan, Mustafa; Stavrakas, Camille; Sipahigil, Alp; Chia, Cleaven; Evans, Ruffin; Burek, Michael J.; Zhang, Mian; Wu, Lue; Pacheco, Jose L.; Abraham, John; Bielejec, Edward; Lukin, Mikhail D.; Atatüre, Mete; Lončar, Marko

2018-05-01

We control the electronic structure of the silicon-vacancy (SiV) color-center in diamond by changing its static strain environment with a nano-electro-mechanical system. This allows deterministic and local tuning of SiV optical and spin transition frequencies over a wide range, an essential step towards multiqubit networks. In the process, we infer the strain Hamiltonian of the SiV revealing large strain susceptibilities of order 1 PHz/strain for the electronic orbital states. We identify regimes where the spin-orbit interaction results in a large strain susceptibility of order 100 THz/strain for spin transitions, and propose an experiment where the SiV spin is strongly coupled to a nanomechanical resonator.

Combinatorial study of low-refractive Mg-F-Si-O nano-composites deposited by magnetron co-sputtering from compound targets

NASA Astrophysics Data System (ADS)

Mertin, Stefan; Länzlinger, Tony; Sandu, Cosmin S.; Scartezzini, Jean-Louis; Muralt, Paul

2018-03-01

Deposition of nano-composite Mg-F-Si-O films on optical grade silica glass was studied employing RF magnetron co-sputtering from magnesium fluoride (MgF2) and fused silica (SiO2) targets. The aim was to obtain a stable and reliable sputtering process for optical coatings exhibiting a refractive index lower than the one of quartz glass (1.46 at 550 nm) without adding gaseous fluorine to the deposition process. The two magnetrons were installed in a confocal way at 45° off-axis with respect to a static substrate, thus creating a lateral gradient in the thin-film composition. The deposited Mg-F-Si-O coatings were structurally analysed by electron dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The obtained films consist of MgF2 nanocrystals embedded in a SiO2-rich amorphous matrix. Spectroscopic ellipsometry and spectrophotometry measurements showed that they are highly transparent exhibiting a very-low extinction coefficient k and a refractive index n in the desired range between the one of MgF2 (1.38) and SiO2 (1.46). Films with n = 1.424 and 1.435 at 550 nm were accomplished with absorption below the detection threshold.

Optimized piranha etching process for SU8-based MEMS and MOEMS construction

PubMed Central

Holmes, Matthew; Keeley, Jared; Hurd, Katherine; Schmidt, Holger; Hawkins, Aaron

2011-01-01

We demonstrate the optimization of the concentration, temperature and cycling of a piranha (H2O2:H2SO4) mixture that produces high yields while quickly etching hollow structures made using a highly crosslinked SU8 polymer sacrificial core. The effects of the piranha mixture on the thickness, refractive index and roughness of common micro-electromechanical systems and micro-opto-electromechanical systems fabrication materials (SiN, SiO2 and Si) were determined. The effectiveness of the optimal piranha mixture was demonstrated in the construction of hollow anti-resonant reflecting optical waveguides. PMID:21423840

Optimized piranha etching process for SU8-based MEMS and MOEMS construction.

PubMed

Holmes, Matthew; Keeley, Jared; Hurd, Katherine; Schmidt, Holger; Hawkins, Aaron

2010-11-01

We demonstrate the optimization of the concentration, temperature and cycling of a piranha (H(2)O(2):H(2)SO(4)) mixture that produces high yields while quickly etching hollow structures made using a highly crosslinked SU8 polymer sacrificial core. The effects of the piranha mixture on the thickness, refractive index and roughness of common micro-electromechanical systems and micro-opto-electromechanical systems fabrication materials (SiN, SiO(2) and Si) were determined. The effectiveness of the optimal piranha mixture was demonstrated in the construction of hollow anti-resonant reflecting optical waveguides.

Optimized piranha etching process for SU8-based MEMS and MOEMS construction

NASA Astrophysics Data System (ADS)

Holmes, Matthew; Keeley, Jared; Hurd, Katherine; Schmidt, Holger; Hawkins, Aaron

2010-11-01

We demonstrate the optimization of the concentration, temperature and cycling of a piranha (H2O2:H2SO4) mixture that produces high yields while quickly etching hollow structures made using a highly crosslinked SU8 polymer sacrificial core. The effects of the piranha mixture on the thickness, refractive index and roughness of common micro-electromechanical systems and micro-opto-electromechanical systems fabrication materials (SiN, SiO2 and Si) were determined. The effectiveness of the optimal piranha mixture was demonstrated in the construction of hollow anti-resonant reflecting optical waveguides.

Excitonic and band-band transitions of Cu2ZnSiS4 determined from reflectivity spectra

NASA Astrophysics Data System (ADS)

Guc, M.; Levcenko, S.; Dermenji, L.; Gurieva, G.; Schorr, S.; Syrbu, N. N.; Arushanov, E.

2014-07-01

Exciton spectra of Cu2ZnSiS4 single crystals are investigated by reflection spectroscopy at 10 and 300 K for light polarized perpendicular (E⊥c) and parallel (E∥c) to the optical axis. The parameters of the excitons and dielectric constant are determined. The free carriers effective masses have been estimated. The room temperature reflectivity spectra at photon energies higher than the fundamental band gap in the polarization Е⊥с and E∥с were measured and related to the electronic band structure of Cu2ZnSiS4.

Heterojunction between the delafossite TCO n-copper indium oxide and p-Si for solar cell applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keerthi, K.; Nair, B. G.; Philip, R. R., E-mail: reenatara@rediffmail.com

2016-05-23

Junction formation of n-copper indium oxide (CIO) (extrinsically undoped) with p-Si leading to conversion of photons in the UV-Vis range is being reported for the first time. I-V and temporal photoconductivity data confirm positively the carrier generation in CIO under irradiation while optical absorbance data furnish its band gap to be ~ 3.1 eV. Ultraviolet photoelectron spectroscopy is used to study the electronic band structure of CIO on Si and to construct a schematic diagram of the hetero-junction to explain the observed photovoltaic phenomena.

Multi-scale silica structures for improved point of care detection

NASA Astrophysics Data System (ADS)

Lin, Sophia; Lin, Lancy; Cho, Eunbyul; Pezzani, Gaston A. O.; Khine, Michelle

2017-03-01

The need for sensitive, portable diagnostic tests at the point of care persists. We report on a simple method to obtain improved detection of biomolecules by a two-fold mechanism. Silica (SiO2) is coated on pre-stressed thermoplastic shrink-wrap film. When the film retracts, the resulting micro- and nanostructures yield far-field fluorescence signal enhancements over their planar or wrinkled counterparts. Because the film shrinks by 95% in surface area, there is also a 20x concentration effect. The SiO2 structured substrate is therefore used for improved detection of labeled proteins and DNA hybridization via both fluorescent and bright field. Through optical characterization studies, we attribute the fluorescence signal enhancements of 100x to increased surface density and light scattering from the rough SiO2 structures. Combining with our open channel self-wicking microfluidics, we can achieve extremely low cost yet sensitive point of care diagnostics.

Crystal structure of laser-induced subsurface modifications in Si

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verburg, P. C.; Smillie, L. A.; Römer, G. R. B. E.

2015-06-04

Laser-induced subsurface modification of dielectric materials is a well-known technology. Applications include the production of optical components and selective etching. In addition to dielectric materials, the subsurface modification technology can be applied to silicon, by employing near to mid-infrared radiation. An application of subsurface modifications in silicon is laser-induced subsurface separation, which is a method to separate wafers into individual dies. Other applications for which proofs of concept exist are the formation of waveguides and resistivity tuning. However, limited knowledge is available about the crystal structure of subsurface modifications in silicon. In this paper, we investigate the geometry and crystalmore » structure of laser-induced subsurface modifications in monocrystalline silicon wafers. Finally, in addition to the generation of lattice defects, we found that transformations to amorphous silicon and Si-iii/Si-xii occur as a result of the laser irradiation.« less

Wafer-scale epitaxial graphene on SiC for sensing applications

NASA Astrophysics Data System (ADS)

Karlsson, Mikael; Wang, Qin; Zhao, Yichen; Zhao, Wei; Toprak, Muhammet S.; Iakimov, Tihomir; Ali, Amer; Yakimova, Rositza; Syväjärvi, Mikael; Ivanov, Ivan G.

2015-12-01

The epitaxial graphene-on-silicon carbide (SiC-G) has advantages of high quality and large area coverage owing to a natural interface between graphene and SiC substrate with dimension up to 100 mm. It enables cost effective and reliable solutions for bridging the graphene-based sensors/devices from lab to industrial applications and commercialization. In this work, the structural, optical and electrical properties of wafer-scale graphene grown on 2'' 4H semi-insulating (SI) SiC utilizing sublimation process were systemically investigated with focus on evaluation of the graphene's uniformity across the wafer. As proof of concept, two types of glucose sensors based on SiC-G/Nafion/Glucose-oxidase (GOx) and SiC-G/Nafion/Chitosan/GOx were fabricated and their electrochemical properties were characterized by cyclic voltammetry (CV) measurements. In addition, a few similar glucose sensors based on graphene by chemical synthesis using modified Hummer's method were also fabricated for comparison.

Thin film characterization by laser interferometry combined with SIMS

NASA Astrophysics Data System (ADS)

Kempf, J.; Nonnenmacher, M.; Wagner, H. H.

1988-10-01

Thin film properties of technologically important materials (Si, GaAs, SiO2, WSix) have been measured by using a novel technique that combines secondary ion mass spectrometry (SIMS) and laser interferometry. The simultaneous measurement of optical phase and reflectance as well as SIMS species during ion sputtering yielded optical constants, sputtering rates and composition of thin films with high depth resolution. A model based on the principle of multiple reflection within a multilayer structure, which considered also transformation of the film composition in depth and time during sputtering, was fitted to the reflectance and phase data. This model was applied to reveal the transformation of silicon by sputtering with O{2/+} ions. Special attention was paid to the preequilibrium phase of the sputter process (amorphization, oxidation, and volume expansion). To demonstrate the analytical potential of our method the multilayer system WSix/poly-Si/SiO2/Si was investigated. The physical parameters and the stoichiometry of tungsten suicide were determined for annealed as well as deposited films. A highly sensitive technique that makes use of a Fabry-Perot etalon integrated with a Michelson type interferometer is proposed. This two-stage interferometer has the potential to profile a sample surface with subangstroem resolution.

New silicate-germanate Cs2Pb2[(Si0.6Ge0.4)2O7] from the series A2Pb2[B2O7], A = K, Cs, B = Si, Ge with the umbrella-like [PbO3]4- group

NASA Astrophysics Data System (ADS)

Belokoneva, Elena L.; Morozov, Ivan A.; Volkov, Anatoly S.; Dimitrova, Olga V.; Stefanovich, Sergey Yu.

2018-04-01

New silicate-germanate Cs2Pb2[(Si0.6Ge0.4)2O7] was synthesized in multi-components hydrothermal solution with 20 w.% concentration of Cs2CO3 mineralizer, pH = 10. Novel mixed compound belongs to the structure type A2Pb2[B2O7] previously indicated for powders with A = K, B=Si or Ge. Singe crystal structure determination of Cs2Pb2[(Si0.6Ge0.4)2O7] revealed the need for the correction of the space group of the earlier suggested structural model from P-3 to P-3m1, as well as for the splitting of the Pb-atom position. Umbrella-like groups [PbO3]4- are located between [(Si,Ge)O4]4- tetrahedra in mica-like honeycomb layers and play the role of tetrahedra with the Pb-lone-pair as the forth apex. Crystal chemical comparison revealed similarities and differences with the classical structure type of α-celsian Ba[Al2Si2O8] with the tetrahedral double layer. Recently investigated nonlinear optical acentric borates Pb2(BO3)(NO3) and Pb2(BO3)Cl are both related to this structural type, possessing umbrella-like groups [PbO3]4- and honeycomb layers [Pb2(BO3)]+ with the BO3-triangles on the tetrahedral positions.

Controlling the optical properties of monocrystalline 3C-SiC heteroepitaxially grown on silicon at low temperatures

NASA Astrophysics Data System (ADS)

Colston, Gerard; Myronov, Maksym

2017-11-01

Cubic silicon carbide (3C-SiC) offers an alternative wide bandgap semiconductor to conventional materials such as hexagonal silicon carbide (4H-SiC) or gallium nitride (GaN) for the detection of UV light and can offer a closely lattice matched virtual substrate for subsequent GaN heteroepitaxy. As 3C-SiC can be heteroepitaxially grown on silicon (Si) substrates its optical properties can be manipulated by controlling the thickness and doping concentrations. The optical properties of 3C-SiC epilayers have been characterized by measuring the transmission of light through suspended membranes. Decreasing the thickness of the 3C-SiC epilayers is shown to shift the absorbance edge to lower wavelengths, a result of the indirect bandgap nature of silicon carbide. This property, among others, can be exploited to fabricate very low-cost, tuneable 3C-SiC based UV photodetectors. This study investigates the effect of thickness and doping concentration on the optical properties of 3C-SiC epilayers grown at low temperatures by a standard Si based growth process. The results demonstrate the potential photonic applications of 3C-SiC and its heterogeneous integration into the Si industry.

Recent Advances on Luminescent Enhancement-Based Porous Silicon Biosensors.

PubMed

Jenie, S N Aisyiyah; Plush, Sally E; Voelcker, Nicolas H

2016-10-01

Luminescence-based detection paradigms have key advantages over other optical platforms such as absorbance, reflectance or interferometric based detection. However, autofluorescence, low quantum yield and lack of photostability of the fluorophore or emitting molecule are still performance-limiting factors. Recent research has shown the need for enhanced luminescence-based detection to overcome these drawbacks while at the same time improving the sensitivity, selectivity and reducing the detection limits of optical sensors and biosensors. Nanostructures have been reported to significantly improve the spectral properties of the emitting molecules. These structures offer unique electrical, optic and magnetic properties which may be used to tailor the surrounding electrical field of the emitter. Here, the main principles behind luminescence and luminescence enhancement-based detections are reviewed, with an emphasis on europium complexes as the emitting molecule. An overview of the optical porous silicon microcavity (pSiMC) as a biosensing platform and recent proof-of-concept examples on enhanced luminescence-based detection using pSiMCs are provided and discussed.

Above room temperature ferromagnetism in Si:Mn and TiO(2-delta)Co.

PubMed

Granovsky, A; Orlov, A; Perov, N; Gan'shina, E; Semisalova, A; Balagurov, L; Kulemanov, I; Sapelkin, A; Rogalev, A; Smekhova, A

2012-09-01

We present recent experimental results on the structural, electrical, magnetic, and magneto-optical properties of Mn-implanted Si and Co-doped TiO(2-delta) magnetic oxides. Si wafers, both n- and p-type, with high and low resistivity, were used as the starting materials for implantation with Mn ions at the fluencies up to 5 x 10(16) cm(-2). The saturation magnetization was found to show the lack of any regular dependence on the Si conductivity type, type of impurity and the short post-implantation annealing. According to XMCD Mn impurity in Si does not bear any appreciable magnetic moment at room temperature. The obtained results indicate that above room temperature ferromagnetism in Mn-implanted Si originates not from Mn impurity but rather from structural defects in Si. The TiO(2-delta):Co thin films were deposited on LaAlO3 (001) substrates by magnetron sputtering in the argon-oxygen atmosphere at oxygen partial pressure of 2 x 10(-6)-2 x 10(-4) Torr. The obtained transverse Kerr effect spectra at the visible and XMCD spectra indicate on intrinsic room temperature ferromagnetism in TiO(2-delta):Co thin films at low (< 1%) volume fraction of Co.

Enhanced optical properties of Si nanocrystals in planar microcavity

NASA Astrophysics Data System (ADS)

Toshikiyo, Kimiaki; Fujii, Minoru; Hayashi, Shinji

2003-04-01

The emission property of Si nanocrystals (nc-Si) in an optical microcavity was studied by photoluminescence (PL) and time resolved PL measurements. The PL from the microcavity was narrowed to the line width of 17 meV, enhanced by a factor of 20 compared to the same film without microcavity. The lifetime for nc-Si became shorter by putting the film in microcavity. This results could be well-explained by the redistribution of the optical modes in the cavity due to the presence of the optical resonator.

Highly stable porous silicon-carbon composites as label-free optical biosensors.

PubMed

Tsang, Chun Kwan; Kelly, Timothy L; Sailor, Michael J; Li, Yang Yang

2012-12-21

A stable, label-free optical biosensor based on a porous silicon-carbon (pSi-C) composite is demonstrated. The material is prepared by electrochemical anodization of crystalline Si in an HF-containing electrolyte to generate a porous Si template, followed by infiltration of poly(furfuryl) alcohol (PFA) and subsequent carbonization to generate the pSi-C composite as an optically smooth thin film. The pSi-C sensor is significantly more stable toward aqueous buffer solutions (pH 7.4 or 12) compared to thermally oxidized (in air, 800 °C), hydrosilylated (with undecylenic acid), or hydrocarbonized (with acetylene, 700 °C) porous Si samples prepared and tested under similar conditions. Aqueous stability of the pSi-C sensor is comparable to related optical biosensors based on porous TiO(2) or porous Al(2)O(3). Label-free optical interferometric biosensing with the pSi-C composite is demonstrated by detection of rabbit IgG on a protein-A-modified chip and confirmed with control experiments using chicken IgG (which shows no affinity for protein A). The pSi-C sensor binds significantly more of the protein A capture probe than porous TiO(2) or porous Al(2)O(3), and the sensitivity of the protein-A-modified pSi-C sensor to rabbit IgG is found to be ~2× greater than label-free optical biosensors constructed from these other two materials.

The optical characterization of organometallic complex thin films by spectroscopic ellipsometry and photovoltaic diode application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Özaydın, C.; Güllü, Ö., E-mail: omergullu@gmail.com; Pakma, O.

2016-05-15

Highlights: • Optical properties and thickness of the A novel organometallic complex (OMC) film were investigated by spectroscopic ellipsometry (SE). • Au/OMC/n-Si metal/interlayer/semiconductor (MIS) diode has been fabricated • This paper presents the I–V analysis of Au/OMC/n-Si MIS diode. • Current–voltage and photovoltaic properties of the diode were investigated. - Abstract: In this work, organometallic complex (OMC) films have been deposited onto glass or silicon substrates by spin coating technique and their photovoltaic application potential has been investigated. Optical properties and thickness of the film have been investigated by spectroscopic ellipsometry (SE). Also, transmittance spectrum has been taken by UV/vismore » spectrophotometer. The optical method has been used to determine the band gap value of the films. Also, Au/OMC/n-Si metal/interlayer/semiconductor (MIS) diode has been fabricated. Current–voltage and photovoltaic properties of the structure were investigated. The ideality factor (n) and barrier height (Φ{sub b}) values of the diode were found to be 2.89 and 0.79 eV, respectively. The device shows photovoltaic behavior with a maximum open-circuit voltage of 396 mV and a short circuit current of 33.8 μA under 300 W light.« less

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Research on reverse recovery characteristics of SiGeC p-i-n diodes

NASA Astrophysics Data System (ADS)

Gao, Yong; Liu, Jing; Yang, Yuan

2008-12-01

This paper analyses the reverse recovery characteristics and mechanism of SiGeC p-i-n diodes. Based on the integrated systems engineering (ISE) data, the critical physical models of SiGeC diodes are proposed. Based on hetero-junction band gap engineering, the softness factor increases over six times, reverse recovery time is over 30% short and there is a 20% decrease in peak reverse recovery current for SiGeC diodes with 20% of germanium and 0.5% of carbon, compared to Si diodes. Those advantages of SiGeC p-i-n diodes are more obvious at high temperature. Compared to lifetime control, SiGeC technique is more suitable for improving diode properties and the tradeoff between reverse recovery time and forward voltage drop can be easily achieved in SiGeC diodes. Furthermore, the high thermal-stability of SiGeC diodes reduces the costs of further process steps and offers more freedoms to device design.

Erbium-doped borosilicate glasses containing various amounts of P{sub 2}O{sub 5} and Al{sub 2}O{sub 3}: Influence of the silica content on the structure and thermal, physical, optical and luminescence properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bourhis, Kevin; Massera, Jonathan; BioMediTech, Tampere

2015-10-15

Highlights: • Er{sup 3+} doped borosilicate glasses were processed with different compositions and characterizations. • An increase in the SiO{sub 2} content leads to a silicate-rich environment around the Er{sup 3+} site. • An increase in the SiO{sub 2} content decreases the Er{sup 3+} absorption cross-section at 980 nm. • Glasses with 60 mol% of SiO{sub 2} exhibit a stronger emission intensity at 1530 nm than glasses with x = 50. • Highest 1.5 μm emission intensity was achieved for the Al and P containing glass with 60 mol% of SiO{sub 2}. - Abstract: The influence of the silica contentmore » on several properties of Er-doped borosilicate glasses in the presence of various amounts of P{sub 2}O{sub 5} and Al{sub 2}O{sub 3} has been investigated. The introduction of P{sub 2}O{sub 5} and/or Al{sub 2}O{sub 3} are responsible for structural modifications in the glass network through a charge-compensation mechanism related to the formation of negatively-charged PO{sub 4} and AlO{sub 4} groups or through the formation of AlPO{sub 4}-like structural units. In this paper, we show that an increase in the SiO{sub 2} content leads to a silicate-rich environment around the Er{sup 3+} site, resulting in an increased dependence of the Er{sup 3+} ions optical and luminescence properties on the P{sub 2}O{sub 5} and/or Al{sub 2}O{sub 3} concentration. The highest emission intensity at 1.5 μm was achieved for the glass with an equal proportion of P and Al in the glass system with 60 mol% of SiO{sub 2}.« less

A hybrid density functional study of silicon and phosphorus doped hexagonal boron nitride monolayer

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Igumbor, E.; Chetty, N.

2016-10-01

We present a hybrid density functional study of silicon (Si) and phosphorus (P) doped hexagonal boron nitride (h-BN). The local geometry, electronic structure and thermodynamic stability of Si B , Si N , P B and P N are examined using hybrid Heyd-Scuseria- Ernzerhof (HSE) functional. The defect induced buckling and the local bond distances around the defect are sensitive to charge state modulation q = -2, -1, 0, +1 and +2. The +1 charge state is found to be the most energetically stable state and significantly reduces the buckling. Based on the charge state thermodynamic transition levels, we noted that the Si N , Si N and P B defects are too deep to be ionized, and can alter the optical properties of h-BN material.

Practical routes to (SiH₃)₃P: applications in group IV semiconductor activation and in group III-V molecular synthesis.

PubMed

Tice, Jesse B; Chizmeshya, A V G; Tolle, J; D' Costa, V R; Menendez, J; Kouvetakis, J

2010-05-21

The (SiH₃)₃P hydride is introduced as a practical source for n-doping of group IV semiconductors and as a highly-reactive delivery agent of -(SiH₃)₂P functionalities in exploratory synthesis. In contrast to earlier methods, the compound is produced here in high purity quantitative yields via a new single-step method based on reactions of SiH₃Br and (Me₃Sn)₃P, circumventing the need for toxic and unstable starting materials. As an initial demonstration of its utility we synthesized monosubstituted Me₂M-P(SiH₃)₂ (M = Al, Ga, In) derivatives of Me₃M containing the (SiH₃)₂P ligand for the first time, in analogy to the known Me₂M-P(SiMe₃)₂ counterparts. A dimeric structure of Me₂M-P(SiH₃)₂ is proposed on the basis of spectroscopic characterizations and quantum chemical simulations. Next, in the context of materials synthesis, the (SiH₃)₃P compound was used to dope germanium for the first time by building a prototype p(++)Si(100)/i-Ge/n-Ge photodiode structure. The resultant n-type Ge layers contained active carrier concentrations of 3-4 × 10¹⁹ atoms cm⁻³ as determined by spectroscopic ellipsometry and confirmed by SIMS. Strain analysis using high resolution XRD yielded a Si content of 4 × 10²⁰ atoms cm⁻³ in agreement with SIMS and within the range expected for incorporating Si₃P type units into the diamond cubic Ge matrix. Extensive characterizations for structure, morphology and crystallinity indicate that the Si co-dopant plays essentially a passive role and does not compromise the device quality of the host material nor does it fundamentally alter its optical properties.

Interaction transfer of silicon atoms forming Co silicide for Co/√(3)×√(3)R30°-Ag/Si(111) and related magnetic properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Cheng-Hsun-Tony; Fu, Tsu-Yi; Tsay, Jyh-Shen, E-mail: jstsay@phy.ntnu.edu.tw

Combined scanning tunneling microscopy, Auger electron spectroscopy, and surface magneto-optic Kerr effect studies were employed to study the microscopic structures and magnetic properties for ultrathin Co/√(3)×√(3)R30°-Ag/Si(111). As the annealing temperature increases, the upward diffusion of Si atoms and formation of Co silicides occurs at temperature above 400 K. Below 600 K, the √(3)×√(3)R30°-Ag/Si(111) surface structure persists. We propose an interaction transferring mechanism of Si atoms across the √(3)×√(3)R30°-Ag layer. The upward transferred Si atoms react with Co atoms to form Co silicide. The step height across the edge of the island, a separation of 0.75 nm from the analysis of the 2 × 2 structure,more » and the calculations of the normalized Auger signal serve as strong evidences for the formation of CoSi{sub 2} at the interface. The interaction transferring mechanism for Si atoms enhances the possibility of interactions between Co and Si atoms. The smoothness of the surface is advantage for that the easy axis of magnetization for Co/√(3)×√(3)R30°-Ag/Si(111) is in the surface plane. This provides a possible way of growing flat magnetic layers on silicon substrate with controllable silicide formation and shows potential applications in spintronics devices.« less

Fully Tunable Silicon Nanowire Arrays Fabricated by Soft Nanoparticle Templating.

PubMed

Rey, By Marcel; Elnathan, Roey; Ditcovski, Ran; Geisel, Karen; Zanini, Michele; Fernandez-Rodriguez, Miguel-Angel; Naik, Vikrant V; Frutiger, Andreas; Richtering, Walter; Ellenbogen, Tal; Voelcker, Nicolas H; Isa, Lucio

2016-01-13

We demonstrate a fabrication breakthrough to produce large-area arrays of vertically aligned silicon nanowires (VA-SiNWs) with full tunability of the geometry of the single nanowires and of the whole array, paving the way toward advanced programmable designs of nanowire platforms. At the core of our fabrication route, termed "Soft Nanoparticle Templating", is the conversion of gradually compressed self-assembled monolayers of soft nanoparticles (microgels) at a water-oil interface into customized lithographical masks to create VA-SiNW arrays by means of metal-assisted chemical etching (MACE). This combination of bottom-up and top-down techniques affords excellent control of nanowire etching site locations, enabling independent control of nanowire spacing, diameter and height in a single fabrication route. We demonstrate the fabrication of centimeter-scale two-dimensional gradient photonic crystals exhibiting continuously varying structural colors across the entire visible spectrum on a single silicon substrate, and the formation of tunable optical cavities supported by the VA-SiNWs, as unambiguously demonstrated through numerical simulations. Finally, Soft Nanoparticle Templating is combined with optical lithography to create hierarchical and programmable VA-SiNW patterns.

Farbrication of diffractive optical elements on a Si chip by an imprint lithography using nonsymmetrical silicon mold

NASA Astrophysics Data System (ADS)

Hirai, Yoshihiko; Okano, Masato; Okuno, Takayuki; Toyota, Hiroshi; Yotsuya, Tsutomu; Kikuta, Hisao; Tanaka, Yoshio

2001-11-01

Fabrication of a fine diffractive optical element on a Si chip is demonstrated using imprint lithography. A chirped diffraction grating, which has modulated pitched pattern with curved cross section is fabricated by an electron beam lithography, where the exposure dose profile is automatically optimized by computer aided system. Using the resist pattern as an etching mask, anisotropic dry etching is performed to transfer the resist pattern profile to the Si chip. The etched Si substrate is used as a mold in the imprint lithography. The Si mold is pressed to a thin polymer (poly methyl methacrylate) on a Si chip. After releasing the mold, a fine diffractive optical pattern is successfully transferred to the thin polymer. This method is exceedingly useful for fabrication of integrated diffractive optical elements with electric circuits on a Si chip.

ZrO2 film interfaces with Si and SiO2

NASA Astrophysics Data System (ADS)

Lopez, C. M.; Suvorova, N. A.; Irene, E. A.; Suvorova, A. A.; Saunders, M.

2005-08-01

The interface formed by the thermal oxidation of sputter-deposited Zr metal onto Si(100)- and SiO2-coated Si(100) wafers was studied in situ and in real time using spectroscopic ellipsometry (SE) in the 1.5-4.5 photon energy range and mass spectrometry of recoiled ions (MSRI). SE yielded optical properties for the film and interface and MSRI yielded film and interface composition. An optical model was developed and verified using transmission electron microscopy. Interfacial reaction of the ZrO2 was observed for both substrates, with more interaction for Si substrates. Equivalent oxide thicknesses and interface trap levels were determined on capacitors with lower trap levels found on samples with a thicker SiO2 underlayer. In addition to the optical properties for the intermixed interface layer, the optical properties for Zr metal and unreacted ZrO2 are also reported.

Fabrication & Characterization of AIAS/pSi Heterojunction Solar Cell

NASA Astrophysics Data System (ADS)

Hassun, Hanan K.; Shaban, Auday H.; Salman, Ebtisam M. T.

2018-05-01

Silver Indium Aluminum Selenium AgIn1xAlxSe2 AIAS for x=01 thin films was deposited by thermal evaporation at RT and different thickness 100, 150 and 200 nm on the glass substrate and p2Si wafer to produce AIAS/p3Si heterojunction solar cell 4. Structural optical electrical and photovoltaic properties 6 are investigated for the samples XRD analysis reveals that all the deposited AIAS films show polycrystalline structure without any change due to increase of thickness. Average diameter and roughness calculated from AFM images shows an increase in its value with increasing thickness. The optical absorbance and transmittance for samples are measured using a spectrometer type UV Visible 1800 spectrophotometer to study the energy 6 gap. The electrical properties 7 of heterojunction were obtained by IV8 dark and illuminated 9 and C10V measurement. The ideality 1 factor and the saturation 2 current density were calculated. Under illuminated 3 the open circuit voltage Voc4 short circuit current density Jsc6 fill factor 6FF and quantum efficiencies were calculated. The built in potential 7Vbi carrier concentration and depletion width are measured with different 9 thickness.

Second harmonic generation spectroscopy in the Reststrahl band of SiC using an infrared free-electron laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paarmann, Alexander, E-mail: alexander.paarmann@fhi-berlin.mpg.de; Razdolski, Ilya; Melnikov, Alexey

2015-08-24

The Reststrahl spectral region of silicon carbide has recently attracted much attention owing to its potential for mid-infrared nanophotonic applications based on surface phonon polaritons (SPhPs). Studies of optical phonon resonances responsible for surface polariton formation, however, have so far been limited to linear optics. In this Letter, we report the first nonlinear optical investigation of the Reststrahl region of SiC, employing an infrared free-electron laser to perform second harmonic generation (SHG) spectroscopy. We observe two distinct resonance features in the SHG spectra, one attributed to resonant enhancement of the nonlinear susceptibility χ{sup (2)} and the other due to amore » resonance in the Fresnel transmission. Our work clearly demonstrates high sensitivity of mid-infrared SHG to phonon-driven phenomena and opens a route to studying nonlinear effects in nanophotonic structures based on SPhPs.« less

The optical properties of transferred graphene and the dielectrics grown on it obtained by ellipsometry

NASA Astrophysics Data System (ADS)

Kasikov, Aarne; Kahro, Tauno; Matisen, Leonard; Kodu, Margus; Tarre, Aivar; Seemen, Helina; Alles, Harry

2018-04-01

Graphene layers grown by chemical vapour deposition (CVD) method and transferred from Cu-foils to the oxidized Si-substrates were investigated by spectroscopic ellipsometry (SE), Raman and X-Ray Photoelectron Spectroscopy (XPS) methods. The optical properties of transferred CVD graphene layers do not always correspond to the ones of the exfoliated graphene due to the contamination from the chemicals used in the transfer process. However, the real thickness and the mean properties of the transferred CVD graphene layers can be found using ellipsometry if a real thickness of the SiO2 layer is taken into account. The pulsed laser deposition (PLD) and atomic layer deposition (ALD) methods were used to grow dielectric layers on the transferred graphene and the obtained structures were characterized using optical methods. The approach demonstrated in this work could be useful for the characterization of various materials grown on graphene.

One-dimensional dielectric bi-periodic photonic structures based on ternary photonic crystals

NASA Astrophysics Data System (ADS)

Dadoenkova, Nataliya N.; Dadoenkova, Yuliya S.; Panyaev, Ivan S.; Sannikov, Dmitry G.; Lyubchanskii, Igor L.

2018-01-01

We investigate the transmittivity spectra, fields, and energy distribution of the electromagnetic eigenwaves propagating in a one-dimensional (1D) dielectric photonic crystal [(TiO2/SiO2)NAl2O3]M with two periods formed by unit cells TiO2/SiO2 and (TiO2/SiO2)NAl2O3. Spectra of TE- and TM-modes depend on the geometric parameters of the structure and undergo modifications with the change in the period numbers, layer thicknesses, and incidence angle. Special attention is paid to the applicability of the hybrid effective medium approximation comprising the long-wave approximation and two-dimensional (2 × 2) transfer matrix method. We demonstrate spectral peculiarities of the bi-periodic structure and also show the differences between the band gap spectra of the bi-periodic and ternary 1D dielectric photonic crystals. The presented photonic crystal structure can find its applications in optoelectronics and nanophotonics areas as omnidirectional reflectors, optical ultra-narrow bandpass filters, and antireflection coatings.

Suspended mid-infrared fiber-to-chip grating couplers for SiGe waveguides

NASA Astrophysics Data System (ADS)

Favreau, Julien; Durantin, Cédric; Fédéli, Jean-Marc; Boutami, Salim; Duan, Guang-Hua

2016-03-01

Silicon photonics has taken great importance owing to the applications in optical communications, ranging from short reach to long haul. Originally dedicated to telecom wavelengths, silicon photonics is heading toward circuits handling with a broader spectrum, especially in the short and mid-infrared (MIR) range. This trend is due to potential applications in chemical sensing, spectroscopy and defense in the 2-10 μm range. We previously reported the development of a MIR photonic platform based on buried SiGe/Si waveguide with propagation losses between 1 and 2 dB/cm. However the low index contrast of the platform makes the design of efficient grating couplers very challenging. In order to achieve a high fiber-to-chip efficiency, we propose a novel grating coupler structure, in which the grating is locally suspended in air. The grating has been designed with a FDTD software. To achieve high efficiency, suspended structure thicknesses have been jointly optimized with the grating parameters, namely the fill factor, the period and the grating etch depth. Using the Efficient Global Optimization (EGO) method we obtained a configuration where the fiber-to-waveguide efficiency is above 57 %. Moreover the optical transition between the suspended and the buried SiGe waveguide has been carefully designed by using an Eigenmode Expansion software. Transition efficiency as high as 86 % is achieved.

Study by molecular dynamics of the influence of temperature and pressure on the optical properties of undoped 3C-SiC structures

NASA Astrophysics Data System (ADS)

Domingues, Gilberto; Monthe, Aubin Mekeze; Guévelou, Simon; Rousseau, Benoit

2018-01-01

Silicon carbide (SiC)-based open-cell foams appear to be promising porous materials for designing high-temperature energy conversion systems such as volumetric solar receivers. In these media, heat transfers and fluid flows occur simultaneously. The numerical models developed for computing the thermal efficiencies of SiC foams must take into account the energy contribution of thermal radiation. In particular, the thermal radiative properties of these foams must be accurately known. This explains why knowledge of the pressure and temperature dependences of the optical properties of the crystalline parts, which compose the foams, is of primary concern for computing the latter properties correctly. However, the data available in the literature provide the evolution laws of the dielectric functions, needed to calculate the optical properties, as dependent on one thermodynamic parameter at a time. To deal with this issue, a study of the temperature/pressure influence on the dielectric functions of a silicon carbide structure by simulation with molecular dynamics (MD) is presented in this paper. The Vashishta interaction potential, based on the sum of two- and three-body terms, is used in this study. The simulations are carried out on undoped 3C-SiC at pressures ranging from 0.2 to 20 GPa and temperatures ranging from 300 K to 1500 K. The dielectric functions are obtained by applying the linear response theory and comparing them with values provided in the literature, using a Lorentz model. The simulated results, in good agreement with the experimental ones, make it possible to establish the evolution laws of the dielectric functions with both parameters, temperature and pressure, applicable to any field requiring the use of undoped silicon carbide.

Light Absorption Enhancement of Silicon-Based Photovoltaic Devices with Multiple Bandgap Structures of Porous Silicon

PubMed Central

Wu, Kuen-Hsien; Li, Chong-Wei

2015-01-01

Porous-silicon (PS) multi-layered structures with three stacked PS layers of different porosity were prepared on silicon (Si) substrates by successively tuning the electrochemical-etching parameters in an anodization process. The three PS layers have different optical bandgap energy and construct a triple-layered PS (TLPS) structure with multiple bandgap energy. Photovoltaic devices were fabricated by depositing aluminum electrodes of Schottky contacts on the surfaces of the developed TLPS structures. The TLPS-based devices exhibit broadband photoresponses within the spectrum of the solar irradiation and get high photocurrent for the incident light of a tungsten lamp. The improved spectral responses of devices are owing to the multi-bandgap structures of TLPS, which are designed with a layered configuration analog to a tandem cell for absorbing a wider energy range of the incidental sun light. The large photocurrent is mainly ascribed to an enhanced light-absorption ability as a result of applying nanoporous-Si thin films as the surface layers to absorb the short-wavelength light and to improve the Schottky contacts of devices. Experimental results reveal that the multi-bandgap PS structures produced from electrochemical-etching of Si wafers are potentially promising for development of highly efficient Si-based solar cells. PMID:28793542

Optical Waveguides Written in Silicon with Femtosecond Laser

NASA Astrophysics Data System (ADS)

Pavlov, Ihor; Tokel, Onur; Pavlova, Svitlana; Kadan, Viktor; Makey, Ghaith; Turnali, Ahmed; Ilday, Omer

Silicon is one of the most widely used materials in modern technology, ranging from electronics and Si-photonics to microfluidic and sensor applications. Despite the long history of Si-based devices, and the strong demand for opto-electronical integration, 3D Si laser processing technology is still challenging. Recently, nanosecond-pulsed laser was used to fabricate embedded holographic elements in Si. However, until now, there was no demonstration of femtosecond-laser-written optical elements inside Si. In this paper, we present optical waveguides written deep inside Si with 1.5 um femtosecond laser. The laser beam, with 2 uJ pulse energy and 350 fs pulse duration focused inside Si sample, produces permanent modification of Si. By moving the lens along the beam direction we were able to produce optical waveguides up to 5 mm long. The diameter of the waveguide is measured to be 10 um. The waveguides were characterized with both optical shadowgraphy and far field imaging after CW light coupling. We observed nearly single mode propagation of light inside of the waveguide. The obtained difference of refractive index inside of the waveguide, is 2.5*10-4. TUBITAK Grant 113M930, TUBITAK Grant 114F256.

Experimental investigations of quantum confined silicon nanoparticle light emitting devices

NASA Astrophysics Data System (ADS)

Ligman, Rebekah Kristine

2007-12-01

As the demands on our world's energy resources continue to grow, alternative high efficiency materials such as quantum confined silicon nanoparticles (Si nps) are desirable for their potential low cost application in white light illumination, in optical displays, and in on-chip optical interconnects. Many fabrication and passivation techniques exist that produce Si nps with high photogenerated quantum yield. However, high electrically generated Si np quantum efficiency has eluded our society. Predominantly due to the lack of a stable surface passivation and a device fabrication technique that preserves the Si np optical properties. To amend these deficiencies, the passivation of nonthermal plasma fabricated Si nps with a surface oxide grown under UV exposure was first investigated. Control over the surface oxidized Si np (Si/SiO2) passivation growth was demonstrated and the optical stability of Si/SiO2 nps was suitable for demonstrating Si np electroluminescence (EL). Two approaches for constructing hybrid organic light emitting diode (OLED) devices around nonthermal plasma fabricated Si nps were then investigated. Multilayer devices, composed of a nonthermal plasma fabricated Si np layer embedded within an OLED, were first studied. However, no EL from Si nps was obtained using the multilayer device architecture due to poor control over the Si np film thickness. Single layer polymer(Si/SiO2) hybrid devices, composed of nps randomly dispersed within an extrinsic conductive polymer, were then studied and EL from Si/SiO2 nps was obtained. The hybrid device optical and electrical response was enhanced over the control devices, possibly due to morphology changes induced by the Si/SiO2 nps. The energy transfer (ET) processes in single layer polymer(Si/SiO 2) hybrid devices were then investigated by imposing known spatial separations between the intrinsic conductive polymers and Si/SiO2 nps. No measurable Si/SiO2 np emission was observed from the intrinsic hybrid devices independent of the spatial separation, implying no ET occurs between the intrinsic polymers and Si/SiO2 nps. These results suggest the observed Si/SiO 2 np emission from extrinsic polymer(Si/SiO2) hybrid devices may be produced by direct carrier injection, Forster or Dexter ET mechanisms.

Characterization of Si (sub X)Ge (sub 1-x)/Si Heterostructures for Device Applications Using Spectroscopic Ellipsometry

NASA Technical Reports Server (NTRS)

Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.; Tanner, M.; Wang, K. L.; Mena, R. A.; Young, P. G.

1993-01-01

Spectroscopic ellipsometry (SE) characterization of several complex Si (sub X)Ge (sub 1-x)/Si heterostructures prepared for device fabrication, including structures for heterojunction bipolar transistors (HBT), p-type and n-type heterostructure modulation doped field effect transistors, has been performed. We have shown that SE can simultaneously determine all active layer thicknesses, Si (sub X)Ge (sub 1-x) compositions, and the oxide overlayer thickness, with only a general knowledge of the structure topology needed a priori. The characterization of HBT material included the SE analysis of a Si (sub X)Ge (sub 1-x) layer deeply buried (600 nanometers) under the silicon emitter and cap layers. In the SE analysis of n-type heterostructures, we examined for the first time a silicon layer under tensile strain. We found that an excellent fit can be obtained using optical constants of unstrained silicon to represent the strained silicon conduction layer. We also used SE to measure lateral sample homogeneity, providing quantitative identification of the inhomogeneous layer. Surface overlayers resulting from prior sample processing were also detected and measured quantitatively. These results should allow SE to be used extensively as a non-destructive means of characterizing Si (sub X)Ge (sub 1-x)/Si heterostructures prior to device fabrication and testing.

Effect of temperature on optical properties of PMMA/SiO2 composite thin film

NASA Astrophysics Data System (ADS)

Soni, Gyanesh; Srivastava, Subodh; Soni, Purushottam; Kalotra, Pankaj; Vijay, Y. K.

2018-05-01

Effect of temperature on PMMA/SiO2 composites thin films were investigated. Nanocomposite flexible thin films of 60 µm thicknesses with different loading of SiO2 nanoparticles were prepared using solution casting method. SEM images show that SiO2 nanoparticles are distributed uniformly in PMMA matrix without any lumps on the surface, and PMMA/SiO2 nano composite thin films had a smoother and regular morphology. UV-Vis and optical band gap measurements revealed that both the concentration of SiO2 nanoparticles and temperature affect the optical properties of the composite thin film in comparison to the pure PMMA film.

Canadian Semiconductor Technology Conference, 6th, Ottawa, Canada, Aug. 11-13, 1992, Proceedings

NASA Astrophysics Data System (ADS)

Baribeau, Jean-Marc

1992-11-01

This volume contains papers on the growth efficiency and distribution coefficient of GaInP-InP epilayers and heterostructures, X-ray photoelectron spectroscopy studies of Ge epilayers on Si(100), and mechanical properties of silicon carbide films for X-ray lithography application. Attention is also given to fine structure in Raman spectroscopy and X-ray reflectometry and its uses for the characterization of superlattices, phase formation in Fe-Si thin-film diffusion couples, process optimization for a micromachined silicon nonreverse valve, and a numerical study of heat transport in thermally isolated flow-rate microsensors. Particular consideration is given to a versatile 2D model for InGaAsP quantum-well semiconductor lasers, gallium arsenide electronics in the marketplace, and optical channel grading in p-type Si/SiGe MOSFETs. Other papers are on ultrafast electron tunneling in a reverse-biased high-efficiency quantum well laser structure, excess currents as a result of trap-assisted tunneling in double-barrier resonant tunneling diodes, and carrier lifetimes in strained InGaAsP multiple quantum-well laser structures.

Optical, Electrical, and Crystal Properties of TiO2 Thin Films Grown by Atomic Layer Deposition on Silicon and Glass Substrates

NASA Astrophysics Data System (ADS)

Kupa, I.; Unal, Y.; Cetin, S. S.; Durna, L.; Topalli, K.; Okyay, A. K.; Ates, H.

2018-05-01

TiO2 thin films have been deposited on glass and Si(100) by atomic layer deposition (ALD) technique using tetrakis(diethylamido)titanium(IV) and water vapor as reactants. Thorough investigation of the properties of the TiO2/glass and TiO2/Si thin films was carried out, varying the deposition temperature in the range from 100°C to 250°C while keeping the number of reaction cycles fixed at 1000. Physical and material property analyses were performed to investigate optical and electrical properties, composition, structure, and morphology. TiO2 films grown by ALD may represent promising materials for future applications in optoelectronic devices.

Annealing Temperature Dependent Structural and Optical Properties of RF Sputtered ZnO Thin Films.

PubMed

Sharma, Shashikant; Varma, Tarun; Asokan, K; Periasamy, C; Boolchandani, Dharmendar

2017-01-01

This work investigates the effect of annealing temperature on structural and optical properties of ZnO thin films grown over Si 100 and glass substrates using RF sputtering technique. Annealing temperature has been varied from 300 °C to 600 °C in steps of 100, and different microstructural parameters such as grain size, dislocation density, lattice constant, stress and strain have been evaluated. The structural and surface morphological characterization has been done using X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM). XRD analysis reveals that the peak intensity of 002 crystallographic orientation increases with increased annealing temperature. Optical characterization of deposited films have been done using UV-Vis-NIR spectroscopy and photoluminescence spectrometer. An increase in optical bandgap of deposited ZnO thin films with increasing annealing temperature has been observed. The average optical transmittance was found to be more than 85% for all deposited films. Photoluminiscense spectra (PL) suggest that the crystalline quality of deposited film has increased at higher annealing temperature.

Characterization of Si3N4/SiO2 optical channel waveguides by photon scanning tunneling microscopy

NASA Technical Reports Server (NTRS)

Wang, Yan; Chudgar, Mona H.; Jackson, Howard E.; Miller, Jeffrey S.; De Brabander, Gregory N.; Boyd, Joseph T.

1993-01-01

Photon scanning tunneling microscopy (PSTM) is used to characterize Si3N4/Si02 optical channel waveguides being used for integrated optical-micromechanical sensors. PSTM utilizes an optical fiber tapered to a fine point which is piezoelectrically positioned to measure the decay of the evanescent field intensity associated with the waveguide propagating mode. Evanescent field decays are recorded for both ridge channel waveguides and planar waveguide regions. Values for the local effective refractive index are calculated from the data for both polarizations and compared to model calculations.

Si-based optical I/O for optical memory interface

NASA Astrophysics Data System (ADS)

Ha, Kyoungho; Shin, Dongjae; Byun, Hyunil; Cho, Kwansik; Na, Kyoungwon; Ji, Hochul; Pyo, Junghyung; Hong, Seokyong; Lee, Kwanghyun; Lee, Beomseok; Shin, Yong-hwack; Kim, Junghye; Kim, Seong-gu; Joe, Insung; Suh, Sungdong; Choi, Sanghoon; Han, Sangdeok; Park, Yoondong; Choi, Hanmei; Kuh, Bongjin; Kim, Kichul; Choi, Jinwoo; Park, Sujin; Kim, Hyeunsu; Kim, Kiho; Choi, Jinyong; Lee, Hyunjoo; Yang, Sujin; Park, Sungho; Lee, Minwoo; Cho, Minchang; Kim, Saebyeol; Jeong, Taejin; Hyun, Seokhun; Cho, Cheongryong; Kim, Jeong-kyoum; Yoon, Hong-gu; Nam, Jeongsik; Kwon, Hyukjoon; Lee, Hocheol; Choi, Junghwan; Jang, Sungjin; Choi, Joosun; Chung, Chilhee

2012-01-01

Optical interconnects may provide solutions to the capacity-bandwidth trade-off of recent memory interface systems. For cost-effective optical memory interfaces, Samsung Electronics has been developing silicon photonics platforms on memory-compatible bulk-Si 300-mm wafers. The waveguide of 0.6 dB/mm propagation loss, vertical grating coupler of 2.7 dB coupling loss, modulator of 10 Gbps speed, and Ge/Si photodiode of 12.5 Gbps bandwidth have been achieved on the bulk-Si platform. 2x6.4 Gbps electrical driver circuits have been also fabricated using a CMOS process.

Bulk magnetic domain structures visualized by neutron dark-field imaging

NASA Astrophysics Data System (ADS)

Grünzweig, C.; David, C.; Bunk, O.; Dierolf, M.; Frei, G.; Kühne, G.; Schäfer, R.; Pofahl, S.; Rønnow, H. M. R.; Pfeiffer, F.

2008-09-01

We report on how a neutron grating interferometer can yield projection images of the internal domain structure in bulk ferromagnetic samples. The image contrast relies on the ultrasmall angle scattering of unpolarized neutrons at domain wall structures in the specimen. The results show the basic domains of (110)-oriented sheets in an FeSi test sample. The obtained domain structures could be correlated with surface sensitive magneto-optical Kerr effect micrographs.

Development of reaction-sintered SiC mirror for space-borne optics

NASA Astrophysics Data System (ADS)

Yui, Yukari Y.; Kimura, Toshiyoshi; Tange, Yoshio

2017-11-01

We are developing high-strength reaction-sintered silicon carbide (RS-SiC) mirror as one of the new promising candidates for large-diameter space-borne optics. In order to observe earth surface or atmosphere with high spatial resolution from geostationary orbit, larger diameter primary mirrors of 1-2 m are required. One of the difficult problems to be solved to realize such optical system is to obtain as flat mirror surface as possible that ensures imaging performance in infrared - visible - ultraviolet wavelength region. This means that homogeneous nano-order surface flatness/roughness is required for the mirror. The high-strength RS-SiC developed and manufactured by TOSHIBA is one of the most excellent and feasible candidates for such purpose. Small RS-SiC plane sample mirrors have been manufactured and basic physical parameters and optical performances of them have been measured. We show the current state of the art of the RS-SiC mirror and the feasibility of a large-diameter RS-SiC mirror for space-borne optics.

Ultrafast spontaneous emission of copper-doped silicon enhanced by an optical nanocavity.

PubMed

Sumikura, Hisashi; Kuramochi, Eiichi; Taniyama, Hideaki; Notomi, Masaya

2014-05-23

Dopants in silicon (Si) have attracted attention in the fields of photonics and quantum optics. However, the optical characteristics are limited by the small spontaneous emission rate of dopants in Si. This study demonstrates a large increase in the spontaneous emission rate of copper isoelectronic centres (Cu-IECs) doped into Si photonic crystal nanocavities. In a cavity with a quality factor (Q) of ~16,000, the photoluminescence (PL) lifetime of the Cu-IECs is 1.1 ns, which is 30 times shorter than the lifetime of a sample without a cavity. The PL decay rate is increased in proportion to Q/Vc (Vc is the cavity mode volume), which indicates the Purcell effect. This is the first demonstration of a cavity-enhanced ultrafast spontaneous emission from dopants in Si, and it may lead to the development of fast and efficient Si light emitters and Si quantum optical devices based on dopants with efficient optical access.

Ultrafast spontaneous emission of copper-doped silicon enhanced by an optical nanocavity

PubMed Central

SUMIKURA, HISASHI; KURAMOCHI, EIICHI; TANIYAMA, HIDEAKI; NOTOMI, MASAYA

2014-01-01

Dopants in silicon (Si) have attracted attention in the fields of photonics and quantum optics. However, the optical characteristics are limited by the small spontaneous emission rate of dopants in Si. This study demonstrates a large increase in the spontaneous emission rate of copper isoelectronic centres (Cu-IECs) doped into Si photonic crystal nanocavities. In a cavity with a quality factor (Q) of ~16,000, the photoluminescence (PL) lifetime of the Cu-IECs is 1.1 ns, which is 30 times shorter than the lifetime of a sample without a cavity. The PL decay rate is increased in proportion to Q/Vc (Vc is the cavity mode volume), which indicates the Purcell effect. This is the first demonstration of a cavity-enhanced ultrafast spontaneous emission from dopants in Si, and it may lead to the development of fast and efficient Si light emitters and Si quantum optical devices based on dopants with efficient optical access. PMID:24853336

Structure and properties of ZrB2, ZrSiB and ZrAlSiB cathode materials and coatings obtained by their magnetron sputtering

NASA Astrophysics Data System (ADS)

Iatsyuk, I. V.; Lemesheva, M. V.; Kiryukhantsev-Korneev, Ph V.; Levashov, E. A.

2018-04-01

The ceramic ZrB2, ZrSiB, and ZrAlSiB cathodes were manufactured by means of self-propagating high-temperature synthesis (SHS). The parameters of SHS process including dependence of the combustion temperature and rate on the initial temperature of the reaction mixtures, as well as values of effective activation energy were estimated. Cathodes were subjected to the magnetron sputtering in the argon atmosphere. The structure and properties of cathodes and coatings were studied by means of X-ray diffraction, scanning electron microscopy, energy-dispersive and glow discharge optical emission spectroscopy. Bulk ceramic samples and coatings were characterised in terms of their hardness, elastic modulus, elastic recovery, density, and residual porosity. Results obtained shows that cathodes posses homogeneous structure with low porosity level in range 2-6% and hardness between 10 and 17 GPa. Coatings demonstrate dense defect-free structure and contain nanocrystallites of h-ZrB2 phase. The grain size and hardness decrease from 8 down to 2 nm and from 37 down to 16 GPa with the addition of the silicon and aluminum dopes.

Discrete impurity band from surface danging bonds in nitrogen and phosphorus doped SiC nanowires

NASA Astrophysics Data System (ADS)

Li, Yan-Jing; Li, Shu-Long; Gong, Pei; Li, Ya-Lin; Cao, Mao-Sheng; Fang, Xiao-Yong

2018-04-01

The electronic structure and optical properties of the nitrogen and phosphorus doped silicon carbide nanowires (SiCNWs) are investigated using first-principle calculations based on density functional theory. The results show doping can change the type of the band gap and improve the conductivity. However, the doped SiCNWs form a discrete impurity levels at the Fermi energy, and the dispersion degree decreases with the diameter increasing. In order to reveal the root of this phenomenon, we hydrogenated the doped SiCNWs, found that the surface dangling bonds were saturated, and the discrete impurity levels are degeneracy, which indicates that the discrete impurity band of the doped SiCNWs is derived from the dangling bonds. The surface passivation can degenerate the impurity levels. Therefore, both doping and surface passivation can better improve the photoelectric properties of the SiCNWs. The result can provide additional candidates in producing nano-optoelectronic devices.

Structural and optical characterization of p-type highly Fe-doped SnO2 thin films and tunneling transport on SnO2:Fe/p-Si heterojunction

NASA Astrophysics Data System (ADS)

Ben Haj Othmen, Walid; Ben Hamed, Zied; Sieber, Brigitte; Addad, Ahmed; Elhouichet, Habib; Boukherroub, Rabah

2018-03-01

Nanocrystalline highly Fe-doped SnO2 thin films were prepared using a new simple sol-gel method with iron amounts of 5, 10, 15 and 20%. The obtained gel offers a long durability and high quality allowing to reach a sub-5 nm nanocrystalline size with a good crystallinity. The films were structurally characterized through X-ray diffraction (XRD) that confirms the formation of rutile SnO2. High Resolution Transmission Electron Microscopy (HRTEM) images reveals the good crystallinity of the nanoparticles. Raman spectroscopy shows that the SnO2 rutile structure is maintained even for high iron concentration. The variation of the PL intensity with Fe concentration reveals that iron influences the distribution of oxygen vacancies in tin oxide. The optical transmittance results indicate a redshift of the SnO2 band gap when iron concentration increases. The above optical results lead us to assume the presence of a compensation phenomenon between oxygen vacancies and introduced holes following Fe doping. From current-voltage measurements, an inversion of the conduction type from n to p is strongly predicted to follow the iron addition. Electrical characterizations of SnO2:Fe/p-Si and SnO2:Fe/n-Si heterojunctions seem to be in accordance with this deduction. The quantum tunneling mechanism is expected to be important at high Fe doping level, which was confirmed by current-voltage measurements at different temperatures. Both optical and electrical properties of the elaborated films present a particularity for the same iron concentration and adopt similar tendencies with Fe amount, which strongly correlate the experimental observations. In order to evaluate the applicability of the elaborated films, we proceed to the fabrication of the SnO2:Fe/SnO2 homojunction for which we note a good rectifying behavior.

Silicon nanostructure arrays prepared by single step metal assisted chemical etching from single crystal wafer

NASA Astrophysics Data System (ADS)

Sarkar, Kalyan; Das, Debajyoti

2018-04-01

Arrays of silicon nanostructures have been produced by single step Metal Assisted Chemical Etching (MACE) of single crystal Si-wafers at room temp and normal atmospheric condition. By studying optical and structural properties of the silicon nanowire like structures synthesized by Ag catalyst assisted chemical etching, a significant change in the reflectance spectra has been obtained leading to a gross reduction in reflectance from ˜31% to less than 1%. In comparison with bulk c-Si, the surface areas of the nanostructured samples have been increased significantly with the etching time, leading to an efficient absorption of light, favorable for photovoltaic applications.

Testing and Characterization of CMC Combustor Liners

NASA Technical Reports Server (NTRS)

Robinson, R. Craig; Verrilli, Michael J.

2003-01-01

Multiple combustor liner applications, both segmented and fully annular designs, have been configured for exposure in NASA's High Pressure Burner Rig (HPBR). The segmented liners were attached to the rig structure with SiC/SiC fasteners and exposed to simulated gas turbine conditions for nearly 200 hours. Test conditions included pressures of 6 atm., gas velocity of 42 m/s, and gas temperatures near 1450 C. The temperatures of both the cooled and combustion flow sides of the liners were measured using optical and contact measurement techniques. Minor weight loss was observed, but the liners remained structural sound, although damage was noted in some fasteners.

Tunable dual-channel filter based on the photonic crystal with air defects.

PubMed

Zhao, Xiaodan; Yang, Yibiao; Wen, Jianhua; Chen, Zhihui; Zhang, Mingda; Fei, Hongming; Hao, Yuying

2017-07-01

We propose a tuning filter containing two channels by inserting a defect layer (Air/Si/Air/Si/Air) into a one-dimensional photonic crystal of Si/SiO 2 , which is on the symmetry of the defect. Two transmission peaks (1528.98 and 1564.74 nm) appear in the optical communication S-band and C-band, and the transmittance of these two channels is up to 100%. In addition, this design realizes multi-channel filtering to process large dynamic range or multiple independent signals in the near-infrared band by changing the structure. The tuning range will be enlarged, and the channels can be moved in this range through the easy control of air thickness and incident angle.

Cathodoluminescence study of one-dimensional free-standing widegap-semiconductor nanostructures: GaN nanotubes, Si3N4 nanobelts and ZnS/Si nanowires.

PubMed

Sekiguchi, Takashi; Hu, Junqing; Bando, Yoshio

2004-01-01

Luminescence properties of one-dimensional free-standing widegap-semiconductor nanostructures were characterized by means of cathodoluminescence (CL). GaN nanopipes, alpha-Si3N4 nanobelts and ZnS/Si nanowires were fabricated by a catalyst-free method, namely grown in an induction furnace from powders. After the observation of morphology by scanning electron microscopy as well as the confirmation of their crystal structures by transmission electron microscopy, their CL spectra and images were observed. The CL spectra mapping as well as the monochromatic CL imaging revealed the variation of the luminescence spectra of different nanowires as well as that along a single wire. These results revealed the optical features of nanostructures.

Recovery of Multilayer-Coated Zerodur and ULE Optics for Extreme-Ultraviolet Lithography by Recoating, Reactive-Ion Etching, and Wet-Chemical Processes.

PubMed

Mirkarimi, P B; Baker, S L; Montcalm, C; Folta, J A

2001-01-01

Extreme-ultraviolet lithography requires expensive multilayer-coated Zerodur or ULE optics with extremely tight figure and finish specifications. Therefore it is desirable to develop methods to recover these optics if they are coated with a nonoptimum multilayer films or in the event that the coating deteriorates over time owing to long-term exposure to radiation, corrosion, or surface contamination. We evaluate recoating, reactive-ion etching, and wet-chemical techniques for the recovery of Mo/Si and Mo/Be multilayer films upon Zerodur and ULE test optics. The recoating technique was successfully employed in the recovery of Mo/Si-coated optics but has the drawback of limited applicability. A chlorine-based reactive-ion etch process was successfully used to recover Mo/Si-coated optics, and a particularly large process window was observed when ULE optics were employed; this is an advantageous for large, curved optics. Dilute HCl wet-chemical techniques were developed and successfully demonstrated for the recovery of Mo/Be-coated optics as well as for Mo/Si-coated optics when Mo/Be release layers were employed; however, there are questions about the extendability of the HCl process to large optics and multiple coat and strip cycles. The technique of using carbon barrier layers to protect the optic during removal of Mo/Si in HF:HNO(3) also showed promise.

Realization of optical multimode TSV waveguides for Si-Interposer in 3D-chip-stacks

NASA Astrophysics Data System (ADS)

Killge, S.; Charania, S.; Richter, K.; Neumann, N.; Al-Husseini, Z.; Plettemeier, D.; Bartha, J. W.

2017-05-01

Optical connectivity has the potential to outperform copper-based TSVs in terms of bandwidth at the cost of more complexity due to the required electro-optical and opto-electrical conversion. The continuously increasing demand for higher bandwidth pushes the breakeven point for a profitable operation to shorter distances. To integrate an optical communication network in a 3D-chip-stack optical through-silicon vertical VIAs (TSV) are required. While the necessary effort for the electrical/optical and vice versa conversion makes it hard to envision an on-chip optical interconnect, a chip-to-chip optical link appears practicable. In general, the interposer offers the potential advantage to realize electro-optical transceivers on affordable expense by specific, but not necessarily CMOS technology. We investigated the realization and characterization of optical interconnects as a polymer based waveguide in high aspect ratio (HAR) TSVs proved on waferlevel. To guide the optical field inside a TSV as optical-waveguide or fiber, its core has to have a higher refractive index than the surrounding material. Comparing different material / technology options it turned out that thermal grown silicon dioxide (SiO2) is a perfect candidate for the cladding (nSiO2 = 1.4525 at 850 nm). In combination with SiO2 as the adjacent polymer layer, the negative resist SU-8 is very well suited as waveguide material (nSU-8 = 1.56) for the core. Here, we present the fabrication of an optical polymer based multimode waveguide in TSVs proved on waferlevel using SU-8 as core and SiO2 as cladding. The process resulted in a defect-free filling of waveguide TSVs with SU-8 core and SiO2 cladding up to aspect ratio (AR) 20:1 and losses less than 3 dB.

The properties of RE-TM magneto-optical films

NASA Astrophysics Data System (ADS)

Lee, Z. Y.; Miao, X. S.; Zhu, P.; Hu, Y. S.; Wan, D. F.; Dai, D. W.; Chen, S. B.; Lin, G. Q.

1992-09-01

In this paper, the magnetic, magneto-optical and galvonomagnetic properties, and their temperature dependence for LRE-TM SmCo, SmCoDy and HRE-TM TbFeCo magneto-optical films as high density recording media prepared by rf magnetron sputtering or evaporation are reported. By adding Dy to SmCo thin film, the SmCoDy thin film is more suitable for magneto-optical recording, its domain size being below 0.63 μm. The Kerr enhancement and corrosion protective effects of AIN and AlSiN for optimum design of the multi-layer structure of magneto-optical disk are described. The instruments of measuring the magneto-optical Kerr effect and magneto-optical recording domain characteristics of thin films are reviewed.

Structural and optical properties of p-quaterphenyl thin films and application in organic/inorganic photodiodes

NASA Astrophysics Data System (ADS)

Attia, A. A.; Saadeldin, M. M.; Soliman, H. S.; Gadallah, A.-S.; Sawaby, K.

2016-12-01

Para-quaterpheny1 (p-4pheny1) thin films were deposited by the thermal evaporation method on glass/quartz substrates for structural and optical investigations. The XRD of p-4phenyl thin films showed that the as-deposited films have a monoclinic structure. The surface morphology of p-4phenyl thin film was studied using scanning electron microscope. The absorption spectrum of p-4phenyl thin film recorded in the wavelength range 200-2500 nm. Photoluminescence measurements revealed two emission peaks at 435 and 444 nm using N2-laser (337.8 nm). The energy gap obtained from the absorption and photoluminescence data was found to be 2.87 and 2.74 eV respectively with Stokes shift value of 0.13 eV. The current-voltage characteristics of p-4phenyl/p-Si heterojunction have been recorded in the dark and under illumination of laser (337.8 nm). Responsivity, Detectivity, External quantum efficiency and Response speed of (Au/p-4pheny1/p-Si/Al) photodetector have been determined using different laser sources at -1 V bias.

Pressure-induced structural transition in chalcopyrite ZnSiP2

NASA Astrophysics Data System (ADS)

Bhadram, Venkata S.; Krishna, Lakshmi; Toberer, Eric S.; Hrubiak, Rostislav; Greenberg, Eran; Prakapenka, Vitali B.; Strobel, Timothy A.

2017-05-01

The pressure-dependent phase behavior of semiconducting chalcopyrite ZnSiP2 was studied up to 30 GPa using in situ X-ray diffraction and Raman spectroscopy in a diamond-anvil cell. A structural phase transition to the rock salt type structure was observed between 27 and 30 GPa, which is accompanied by soft phonon mode behavior and simultaneous loss of Raman signal and optical transmission through the sample. The high-pressure rock salt type phase possesses cationic disorder as evident from broad features in the X-ray diffraction patterns. The behavior of the low-frequency Raman modes during compression establishes a two-stage, order-disorder phase transition mechanism. The phase transition is partially reversible, and the parent chalcopyrite structure coexists with an amorphous phase upon slow decompression to ambient conditions.

Large Block Copolymer Self-Assembly for Fabrication of Subwavelength Nanostructures for Applications in Optics.

PubMed

Mokarian-Tabari, Parvaneh; Senthamaraikannan, Ramsankar; Glynn, Colm; Collins, Timothy W; Cummins, Cian; Nugent, David; O'Dwyer, Colm; Morris, Michael A

2017-05-10

Nanostructured surfaces are common in nature and exhibit properties such as antireflectivity (moth eyes), self-cleaning (lotus leaf), iridescent colors (butterfly wings), and water harvesting (desert beetles). We now understand such properties and can mimic some of these natural structures in the laboratory. However, these synthetic structures are limited since they are not easily mass produced over large areas due to the limited scalability of current technologies such as UV-lithography, the high cost of infrastructure, and the difficulty in nonplanar surfaces. Here, we report a solution process based on block copolymer (BCP) self-assembly to fabricate subwavelength structures on large areas of optical and curved surfaces with feature sizes and spacings designed to efficiently scatter visible light. Si nanopillars (SiNPs) with diameters of ∼115 ± 19 nm, periodicity of 180 ± 18 nm, and aspect ratio of 2-15 show a reduction in reflectivity by a factor of 100, <0.16% between 400 and 900 nm at an angle of incidence of 30°. Significantly, the reflectivity remains below 1.75% up to incident angles of 75°. Modeling the efficiency of a SiNP PV suggests a 24.6% increase in efficiency, representing a 3.52% (absolute) or 16.7% (relative) increase in electrical energy output from the PV system compared to AR-coated device.

The structural and optical properties of Y (Y  =  Al, B, Si and Ti)-doped ZnO nano thin films from the first principles calculations

NASA Astrophysics Data System (ADS)

Zhang, Wenshu; Hu, Huijun; Zhang, Caili; Li, Jianguo; Li, Yuping; Ling, Lixia; Han, Peide

2017-12-01

Based on the density functional theory, the structural stability and optical properties of undoped and Y (Y  =  Al, B, Si and Ti)-doped ZnO nano thin films are investigated. The good stability of the films based on the ZnO (0 0 0 1) can be obtained when the layer is larger than 12. Moreover, the dielectric function, refractive index, absorption, and reflectivity of doped ZnO nano thin films have been analyzed in detail. In the visible light range, the values of ZnO films from 12 to 24 layers are all smaller than those of the bulk. And with the augment of the layers, the values keep increasing. All the results signify that the nano film of 12 layers possesses the lowest reflectivity and weakest absorption. In addition, there is an evident impact of some doped element on the properties of nano films. The absorption and reflectivity of Ti, Si-doped ZnO nano thin films are higher than those of the clean films, while Al, B-doped are lower, especially B-doped. Moreover, the conductivity of the doped structure is better than that of the bulk. Thus, the B-doped ZnO nano thin films could be potential candidate materials of transparent conductive films.

Some aspects of pulsed laser deposition of Si nanocrystalline films

NASA Astrophysics Data System (ADS)

Polyakov, B.; Petruhins, A.; Butikova, J.; Kuzmin, A.; Tale, I.

2009-11-01

Nanocrystalline silicon films were deposited by a picosecond laser ablation on different substrates in vacuum at room temperature. A nanocrystalline structure of the films was evidenced by atomic force microscopy (AFM), optical and Raman spectroscopies. A blue shift of the absorption edge was observed in optical absorption spectra, and a decrease of the optical phonon energy at the Brillouin zone centre was detected by Raman scattering. Early stages of nanocrystalline film formation on mica and HOPG substrates were studied by AFM. Mechanism of nanocrystal growth on substrate is discussed. in here

Time-resolved photoluminescence of SiOx encapsulated Si

NASA Astrophysics Data System (ADS)

Kalem, Seref; Hannas, Amal; Österman, Tomas; Sundström, Villy

Silicon and its oxide SiOx offer a number of exciting electrical and optical properties originating from defects and size reduction enabling engineering new electronic devices including resistive switching memories. Here we present the results of photoluminescence dynamics relevant to defects and quantum confinement effects. Time-resolved luminescence at room temperature exhibits an ultrafast decay component of less than 10 ps at around 480 nm and a slower component of around 60 ps as measured by streak camera. Red shift at the initial stages of the blue luminescence decay confirms the presence of a charge transfer to long lived states. Time-correlated single photon counting measurements revealed a life-time of about 5 ns for these states. The same quantum structures emit in near infrared close to optical communication wavelengths. Nature of the emission is described and modeling is provided for the luminescence dynamics. The electrical characteristics of metal-oxide-semiconductor devices were correlated with the optical and vibrational measurement results in order to have better insight into the switching mechanisms in such resistive devices as possible next generation RAM memory elements. ``This work was supported by ENIAC Joint Undertaking and Laser-Lab Europe''.

An Evaluation of Structural, Topographic, Optical, and Temperature-Dependent Electrical Features of Sol-Gel Spin-Coated p-NiO/n-Si Heterojunction

NASA Astrophysics Data System (ADS)

Turgut, Güven; Duman, Songül; Özcelik, Fikriye Şeyma

2017-06-01

p-NiO/n-Si heterodiode was deposited with an easy and cheap sol-gel route using a spin coater. The XRD results revealed that NiO film had polycrystalline cubic bunsenite structure with (200) preferential direction. The AFM and SEM micrographs indicated that the film was composed of homogenously distributed nanoparticles on n-Si surface. The uniform scattering of Ni and O elements was also seen from EDX mapping pictures. The band gap value for NiO sample was found to be 3.74 eV. The current-voltage ( I- V) properties of Ag/p-NiO/n-Si heterojunction were inquired in the temperature range of 80 K to 300 K (-193 °C to 27 °C). The temperature coefficient of barrier height of the Ag/p-NiO/n-Si heterojunction was determined to be 2.6 meV/K. The I- V measurements showed that the barrier height of the heterojunction increased with an increment in the temperature.

Synthesis of hybrid cellulose nanocomposite bonded with dopamine SiO2/TiO2 and its antimicrobial activity

NASA Astrophysics Data System (ADS)

Ramesh, Sivalingam; Kim, Gwang-Hoon; Kim, Jaehwan; Kim, Joo-Hyung

2015-04-01

Organic-inorganic hybrid material based cellulose was synthesized by the sol-gel approach. The explosion of activity in this area in the past decade has made tremendous progress in industry or academic both fundamental understanding of sol-gel process and applications of new functionalized hybrid materials. In this present research work, we focused on cellulose-dopamine functionalized SiO2/TiO2 hybrid nanocomposite by sol-gel process. The cellulose-dopamine hybrid nanocomposite was synthesized via γ-aminopropyltriethoxysilane (γ-APTES) coupling agent by in-situ sol-gel process. The chemical structure of cellulose-amine functionalized dopamine bonding to cellulose structure with covalent cross linking hybrids was confirmed by FTIR spectral analysis. The morphological analysis of cellulose-dopamine nanoSiO2/TiO2 hybrid nanocomposite materials was characterized by XRD, SEM and TEM. From this different analysis results indicate that the optical transparency, thermal stability, control morphology of cellulose-dopamine-SiO2/TiO2 hybrid nanocomposite. Furthermore cellulose-dopamine-SiO2/TiO2 hybrid nanocomposite was tested against pathogenic bacteria for antimicrobial activity.

Ion-implanted Si-nanostructures buried in a SiO{sub 2} substrate studied with soft-x-ray spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, R.; Rubensson, J.E.; Eisebitt, S.

1997-04-01

In recent years silicon nanostructures have gained great interest because of their optical luminescence, which immediately suggests several applications, e.g., in optoelectronic devices. Nanostructures are also investigated because of the fundamental physics involved in the underlying luminescence mechanism, especially attention has been drawn to the influence of the reduced dimensions on the electronic structure. The forming of stable and well-defined nanostructured materials is one goal of cluster physics. For silicon nanostructures this goal has so far not been reached, but various indirect methods have been established, all having the problem of producing less well defined and/or unstable nanostructures. Ion implantationmore » and subsequent annealing is a promising new technique to overcome some of these difficulties. In this experiment the authors investigate the electronic structure of ion-implanted silicon nanoparticles buried in a stabilizing SiO{sub 2} substrate. Soft X-ray emission (SXE) spectroscopy features the appropriate information depth to investigate such buried structures. SXE spectra to a good approximation map the local partial density of occupied states (LPDOS) in broad band materials like Si. The use of monochromatized synchrotron radiation (MSR) allows for selective excitation of silicon atoms in different chemical environments. Thus, the emission from Si atom sites in the buried structure can be separated from contributions from the SiO{sub 2} substrate. In this preliminary study strong size dependent effects are found, and the electronic structure of the ion-implanted nanoparticles is shown to be qualitatively different from porous silicon. The results can be interpreted in terms of quantum confinement and chemical shifts due to neighboring oxygen atoms at the interface to SiO{sub 2}.« less

Driving force of stacking-fault formation in SiC p-i-n diodes.

PubMed

Ha, S; Skowronski, M; Sumakeris, J J; Paisley, M J; Das, M K

2004-04-30

The driving force of stacking-fault expansion in SiC p-i-n diodes was investigated using optical emission microscopy and transmission electron microscopy. The stacking-fault expansion and properties of the partial dislocations were inconsistent with any stress as the driving force. A thermodynamic free energy difference between the perfect and a faulted structure is suggested as a plausible driving force in the tested diodes, indicating that hexagonal polytypes of silicon carbide are metastable at room temperature.

The Interplay of Quantum Confinement and Hydrogenation in Amorphous Silicon Quantum Dots.

PubMed

Askari, Sadegh; Svrcek, Vladmir; Maguire, Paul; Mariotti, Davide

2015-12-22

Hydrogenation in amorphous silicon quantum dots (QDs) has a dramatic impact on the corresponding optical properties and band energy structure, leading to a quantum-confined composite material with unique characteristics. The synthesis of a-Si:H QDs is demonstrated with an atmospheric-pressure plasma process, which allows for accurate control of a highly chemically reactive non-equilibrium environment with temperatures well below the crystallization temperature of Si QDs. © 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Band gap tuning of epitaxial SrTiO{sub 3-δ}/Si(001) thin films through strain engineering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cottier, Ryan J.; Steinle, Nathan A.; Currie, Daniel A.

2015-11-30

We investigate the effect of strain and oxygen vacancies (V{sub O}) on the crystal and optical properties of oxygen deficient, ultra-thin (4–30 nm) films of SrTiO{sub 3-δ} (STO) grown heteroepitaxially on p-Si(001) substrates by molecular beam epitaxy. We demonstrate that STO band gap tuning can be achieved through strain engineering and show that the energy shift of the direct energy gap transition of SrTiO{sub 3-δ}/Si films has a quantifiable dimensional and doping dependence that correlates well with the changes in crystal structure.

Synthesis, characterization and chemical stability of silicon dichalcogenides, Si(Se xS 1₋x) 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Chen; Zhang, Xiaotian; Krishna, Lakshmi

Silicon dichalcogenides have an intriguing crystal structure consisting of long tetrahedral chains held together by van der Waals forces but the electronic and optical properties have been less explored. In the present work, bulk SiSe 2, SiS 2, and Si(Se xS 1-x) 2 were synthesized by the congruent melt growth method and characterized by Raman spectroscopy, X-ray Diffraction and UV/visible/IR transmission measurements supported by first-principles calculations. First-principles calculations reveal a nearly linear decrease of band gap energy in Si(Se xS 1-x) 2 with increasing Se content, i.e., from SiS 2 to SiSe 2 which corresponds with a blue-shift in themore » transmission spectra from bulk SiSe 2 to Si(Se 0.6S 0.4) 2, and to SiS 2. Air stability tests demonstrate the formation of toxic H 2Se/H 2S gas from sample oxidation at room temperature upon exposure to ambient air, and great care should be paid when handling these materials.« less

Precursor Routes to Complex Ternary Intermetallics: Single-Crystal and Microcrystalline Preparation of Clathrate-I Na8Al8Si38 from NaSi + NaAlSi.

PubMed

Dong, Yongkwan; Chai, Ping; Beekman, Matt; Zeng, Xiaoyu; Tritt, Terry M; Nolas, George S

2015-06-01

Single crystals of the ternary clathrate-I Na8Al8Si38 were synthesized by kinetically controlled thermal decomposition (KCTD), and microcrystalline Na8Al8Si38 was synthesized by spark plasma sintering (SPS) using a NaSi + NaAlSi mixture as the precursor. Na8AlxSi46-x compositions with x ≤ 8 were also synthesized by SPS from precursor mixtures of different ratios. The crystal structure of Na8Al8Si38 was investigated using both Rietveld and single-crystal refinements. Temperature-dependent transport and UV/vis measurements were employed in the characterization of Na8Al8Si38, with diffuse-reflectance measurement indicating an indirect optical gap of 0.64 eV. Our results indicate that, when more than one precursor is used, both SPS and KCTD are effective methods for the synthesis of multinary inorganic phases that are not easily accessible by traditional solid-state synthesis or crystal growth techniques.

Synthesis, characterization and chemical stability of silicon dichalcogenides, Si(SexS1-x)2

NASA Astrophysics Data System (ADS)

Chen, Chen; Zhang, Xiaotian; Krishna, Lakshmi; Kendrick, Chito; Shang, Shun-Li; Toberer, Eric; Liu, Zi-Kui; Tamboli, Adele; Redwing, Joan M.

2016-10-01

Silicon dichalcogenides have an intriguing crystal structure consisting of long tetrahedral chains held together by van der Waals forces but the electronic and optical properties have been less explored. In the present work, bulk SiSe2, SiS2, and Si(SexS1-x)2 were synthesized by the congruent melt growth method and characterized by Raman spectroscopy, X-ray Diffraction and UV/visible/IR transmission measurements supported by first-principles calculations. First-principles calculations reveal a nearly linear decrease of band gap energy in Si(SexS1-x)2 with increasing Se content, i.e., from SiS2 to SiSe2 which corresponds with a blue-shift in the transmission spectra from bulk SiSe2 to Si(Se0.6S0.4)2, and to SiS2. Air stability tests demonstrate the formation of toxic H2Se/H2S gas from sample oxidation at room temperature upon exposure to ambient air, and great care should be paid when handling these materials.

Casimir forces from conductive silicon carbide surfaces

NASA Astrophysics Data System (ADS)

Sedighi, M.; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.

2014-05-01

Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of frequencies. The samples show significant far-infrared absorption due to concentration of charge carriers and a sharp surface phonon-polariton peak. The Casimir interaction of SiC with different materials is calculated and discussed. As a result of the infrared structure and beyond to low frequencies, the Casimir force for SiC-SiC and SiC-Au approaches very slowly the limit of ideal metals, while it saturates significantly below this limit if interaction with insulators takes place (SiC-SiO2). At short separations (<10 nm) analysis of the van der Waals force yielded Hamaker constants for SiC-SiC interactions lower but comparable to those of metals, which is of significance to adhesion and surface assembly processes. Finally, bifurcation analysis of microelectromechanical system actuation indicated that SiC can enhance the regime of stable equilibria against stiction.

Improved Optical Transmittance and Crystal Characteristics of ZnS:TbOF Thin Film on Bi4Ti3O12/Indium Tin Oxide/Glass Substrate by Using a SiO2 Buffer Layer

NASA Astrophysics Data System (ADS)

Chia, Wei‑Kuo; Yokoyama, Meiso; Yang, Cheng‑Fu; Chiang, Wang‑Ta; Chen, Ying‑Chung

2006-07-01

Bi4Ti3O12 thin films are deposited on indium tin oxide (ITO)/glass substrates using RF magnetron sputtering technology and are annealed at 675 °C in a rapid thermal annealing furnace in an oxygen atmosphere. The resulting films have high optical transmittances and good crystalline characteristics. ZnS:TbOF films are then deposited on the Bi4Ti3O12 films, causing the originally highly transparent specimens to blacken and to resemble a glass surface coated with carbon powder. The optical transmittance of the specimen is less than 15% under the visible wavelength range, and neither a crystalline phase nor a distinct ZnS grain structure is evident in X-ray diffractometer (XRD) and scanning electronic microscope (SEM). Secondary ion mass spectrometer (SIMS) analysis reveals the occurrence of interdiffusion between the ZnS and Bi4Ti3O12 layers. This suggests that one or more unknown chemical reactions take place among the elements Bi, S, and O at the interface during the deposition of ZnS:TbOF film on a Bi4Ti3O12/ITO/glass substrate. These reactions cause the visible transmittance of the specimens to deteriorate dramatically. To prevent interdiffusion, a silicon dioxide (SiO2) buffer layer 100 nm thick was grown on the Bi4Ti3O12/ITO/glass substrate using plasma-enhanced chemical vapor deposition (PECVD), then the ZnS:TbOF film was grown on the SiO2 buffer layer. The transmittance of the resulting specimen is enhanced approximately 8-fold in the visible region. XRD patterns reveal the ZnS(111)-oriented phase is dominant. Furthermore, dense, crack-free ZnS:TbOF grains are observed by SEM. The results imply that the SiO2 buffer layer sandwiched between the ZnS:TbOF and Bi4Ti3O2 layers effectively separates the two layers. Therefore, interdiffusion and chemical reactions are prevented at the interface of the two layers, and the crystalline characteristics of the ZnS:TbOF layer and the optical transmittance of the specimen are improved as a result. Finally, the dielectric constant of the stacked structure is lower than that of the single layer structure without SiO2, but the dielectric breakdown strength is enhanced.

High resolution photolithography using arrays of polystyrene and SiO2 micro- and nano-sized spherical lenses

NASA Astrophysics Data System (ADS)

Dvoretckaia, L. N.; Mozharov, A. M.; Mukhin, I. S.

2017-11-01

Photolithography mask made of close-packed array of micro- and nano-sized spherical lenses allows to obtain the ordered structures and provides highest “optical resolution/cost” ratio between all existing photolithography and laser direct writing methods. In this letter, we present results of modeling the propagation of a plane wave falling on the array of quartz (SiO2) microspherical lenses and focusing in the image reverse photoresist layer. We present here experimental results on fabrication of ordered arrays of submicron wells and columns and substrate preparation for growth of monocrystalline nanowires on metal surface using photolithography with mask of SiO2 microspheres. Such ordered nano-sized arrays of wells and columns can be used in fabrication of further growth of monocrystalline nanowires, quantum dots and production of plasmon structures.

Structure and magnetic properties of mono- and bi-layer graphene films on ultraprecision figured 4H-SiC(0001) surfaces.

PubMed

Hattori, Azusa N; Okamoto, Takeshi; Sadakuni, Shun; Murata, Junji; Oi, Hideo; Arima, Kenta; Sano, Yasuhisa; Hattori, Ken; Daimon, Hiroshi; Endo, Katsuyoshi; Yamauchi, Kazuto

2011-04-01

Monolayer and bilayer graphene films with a few hundred nm domain size were grown on ultraprecision figured 4H-SiC(0001) on-axis and 8 degrees -off surfaces by annealing in ultra-high vacuum. Using X-ray photoelectron spectroscopy (XPS), atomic force microscopy, reflection high-energy electron diffraction, low-energy electron diffraction (LEED), Raman spectroscopy, and scanning tunneling microscopy, we investigated the structure, number of graphene layers, and chemical bonding of the graphene surfaces. Moreover, the magnetic property of the monolayer graphene was studied using in-situ surface magneto-optic Kerr effect at 40 K. LEED spots intensity distribution and XPS spectra for monolayer and bilayer graphene films could become an obvious and accurate fingerprint for the determination of graphene film thickness on SiC surface.

Enhanced Broadband Electromagnetic Absorption in Silicon Film with Photonic Crystal Surface and Random Gold Grooves Reflector

PubMed Central

Chen, Zhi-Hui; Qiao, Na; Yang, Yibiao; Ye, Han; Liu, Shaoding; Wang, Wenjie; Wang, Yuncai

2015-01-01

We show a hybrid structure consisting of Si film with photonic crystal surface and random triangular gold grooves reflector at the bottom, which is capable of realizing efficient, broad-band, wide-angle optical absorption. It is numerically demonstrated that the enhanced absorption in a broad wavelength range (0.3–9.9 μm) due to the scattering effect of both sides of the structure and the created resonance modes. Larger thickness and period are favored to enhance the absorption in broader wavelength range. Substantial electric field concentrates in the grooves of surface photonic crystal and in the Si film. Our structure is versatile for solar cells, broadband photodetection and stealth coating. PMID:26238270

Optical transmission larger than 1 (T>1) through ZnS -SiO2/AgOx/ZnS-SiO2 sandwiched thin films

NASA Astrophysics Data System (ADS)

Wei, Jingsong; Xiao, Mufei

2006-09-01

Optical transmission through flat media should be smaller than 1. However, we have observed optical transmission up to T =1.18. The samples were ZnS -SiO2/AgOx/ZnS-SiO2 sandwiched thin films on glass substrate. The supertransmission could only be observed in the near field. We attribute the supertransmission to the lateral propagation relayed by the laser activated and decomposed Ag nanoparticles.

Optical study of Tm-doped solid solution (Sc0.5Y0.5)2SiO5 crystal

NASA Astrophysics Data System (ADS)

Shi, Jiaojiao; Liu, Bin; Zheng, Lihe; Wang, Qingguo; Tang, Huili; Liu, Junfang; Su, Liangbi; Wu, Feng; Zhao, Hengyu; He, Nuotian; Li, Na; Li, Qiu; Guo, Chao; Xu, Jun; Yang, Kejian; Xu, Xiaodong; Ryba-Romanowski, Witold; Lisiecki, Radosław; Solarz, Piotr

2018-04-01

Tm-doped (Sc0.5Y0.5)2SiO5 (SYSO) crystals were grown by Czochralski method. The UV-VIR-NIR absorption spectra and the near-infrared emission spectra were measured and analysed by the Judd-Ofelt approach. Temperature influence on both absorption and emission spectra has been determined from the data recorded at room temperature and 10 K. It has been found that the structural disorder resulting from dissimilar ionic radii of Sc3+ and Y3+ in the solid solution (Sc0.5Y0.5)2SiO5 crystal brings about a strong inhomogeneous broadening of Tm3+ ions spectra. However, it affects the excited state relaxation dynamics inherent to thulium-doped Y2SiO5 and Sc2SiO5 hosts weakly.

Fabrication and electrical characterization of silicon nanowires based resistors

NASA Astrophysics Data System (ADS)

Ni, L.; Demami, F.; Rogel, R.; Salaün, A. C.; Pichon, L.

2009-11-01

Silicon nanowires (SiNWs) are synthesized via the Vapor-Liquid-Solid (VLS) mechanism using gold (Au) as metal catalyst and silane (SiH4) as precursor gas. Au nanoparticles are employed as liquid droplets catalysis during the SiNWs growth performed in a hot wall LPCVD reactor at 480°C and 40 Pa. SiNWs local synthesis at micron scale is demonstrated using classical optical photolithography process. SiNWs grow with high density anchored at the dedicated catalyst islands. This resulting network is used to interconnect two heavily doped polysilicon interdigitated electrodes leading to the formation of electrical resistors in a coplanar structure. Current-voltage (I-V) characteristics highlight a symmetric shape. The temperature dependence of the electrical resistance is activated, with activation energy of 0.47 eV at temperatures greater than 300K.

Effect of Trisodium Citrate Concentration on the Structural and Photodiode Performance of CdO Thin Films

NASA Astrophysics Data System (ADS)

Ravikumar, M.; Valanarasu, S.; Chandramohan, R.; Jacob, S. Santhosh Kumar; Kathalingam, A.

2015-08-01

CdO thin films were deposited on glass and silicon substrates by simple perfume atomizer at 350°C using cadmium acetate and trisodium citrate (TSC). The effect of the TSC concentration on the structural, morphological, optical, and photoconductive properties of the prepared CdO thin films was investigated. X-Ray diffraction (XRD) studies of the deposited films revealed improvement in crystalline nature with increase of TSC concentration. Films prepared without TSC showed porous nature, not fully covering the substrate, whereas films prepared using TSC exhibited full coverage of the substrate with uniform particles. Optical transmittance study of the films showed high transmittance (50% to 60%), and the absorption edge was found to shift towards the red region depending on the TSC concentration. The films exhibited a direct band-to-band transition with bandgap varying between 2.31 eV and 2.12 eV. Photoconductivity studies of the n-CdO/ p-Si structure for various TSC concentrations were also carried out. I- V characteristics of this n-CdO/ p-Si structure revealed the formation of rectifying junctions, and its photoconductivity was found to increase with the TSC concentration.

Calculation of optical band gaps of a-Si:H thin films by ellipsometry and UV-Vis spectrophotometry

NASA Astrophysics Data System (ADS)

Qiu, Yijiao; Li, Wei; Wu, Maoyang; Fu, Junwei; Jiang, Yadong

2010-10-01

Hydrogenated amorphous silicon (a-Si:H) thin films doped with Phosphorus (P) and Nitrogen (N) were deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). The optical band gaps of the thin films obtained through either changing the gas pressure (P-doped only) or adulterating nitrogen concentration (with fixed P content) were investigated by means of Ellipsometric and Ultraviolet-Visible (UV-Vis) spectroscopy, respectively. Tauc formula was used in calculating the optical band gaps of the thin films in both methods. The results show that Ellipsometry and UV-Vis spectrophotometry can be applied in the research of the optical properties of a-Si:H thin films experimentally. Both methods reflect the variation law of the optical band gaps caused by CVD process parameters, i.e., the optical band gap of the a-Si:H thin films is increased with the rise of the gas pressure or the nitrogen concentration respectively. The difference in optical band gaps of the doped a-Si:H thin films calculated by Ellipsometry or UV-Vis spectrophotometry are not so great that they both can be used to measure the optical band gaps of the thin films in practical applications.

UV Light-Driven Photodegradation of Methylene Blue by Using Mn0.5Zn0.5Fe2O4/SiO2 Nanocomposites

NASA Astrophysics Data System (ADS)

Indrayana, I. P. T.; Julian, T.; Suharyadi, E.

2018-04-01

The photodegradation activity of nanocomposites for 20 ppm methylene blue solution has been investigated in this work. Nanocomposites Mn0.5Zn0.5Fe2O4/SiO2 have been synthesized using coprecipitation method. The X-ray diffraction (XRD) pattern confirmed the formation of three phases in sample Mn0.5Zn0.5Fe2O4/SiO2 i.e., Mn0.5Zn0.5Fe2O4, Zn(OH)2, and SiO2. The appearance of SiO2 phase showed that the encapsulation process has been carried out. The calculated particles size of Mn0.5Zn0.5Fe2O4/SiO2 is greater than Mn0.5Zn0.5Fe2O4. Bonding analysis via vibrational spectra for Mn0.5Zn0.5Fe2O4/SiO2 confirmed the formation of bonds Me-O-Si stretching (2854.65 cm-1) and Si-O-Si asymmetric stretching (1026.13 cm-1). The optical gap energy of Mn0.5Zn0.5Fe2O4/SiO2 was smaller (2.70 eV) than Mn0.5Zn0.5Fe2O4 (3.04 eV) due to smaller lattice dislocation and microstrain that affect their electronic structure. The Mn0.5Zn0.5Fe2O4/SiO2 showed high photodegradation ability due to smaller optical gap energy and the appearance of SiO2 ligand that can easily attract dye molecules. The Mn0.5Zn0.5Fe2O4/SiO2 also showed high degradation activity even without UV light radiation. The result showed that photodegradation reaction doesn’t follow pseudo-first order kinetics.

The influence of conjugated alkynyl(aryl) surface groups on the optical properties of silicon nanocrystals: photoluminescence through in-gap states.

PubMed

Angı, Arzu; Sinelnikov, Regina; Heenen, Hendrik H; Meldrum, Al; Veinot, Jonathan G C; Scheurer, Christoph; Reuter, Karsten; Ashkenazy, Or; Azulay, Doron; Balberg, Isaac; Millo, Oded; Rieger, Bernhard

2018-08-31

Developing new methods, other than size and shape, for controlling the optoelectronic properties of semiconductor nanocrystals is a highly desired target. Here we demonstrate that the photoluminescence (PL) of silicon nanocrystals (SiNCs) can be tuned in the range 685-800 nm solely via surface functionalization with alkynyl(aryl) (phenylacetylene, 2-ethynylnaphthalene, 2-ethynyl-5-hexylthiophene) surface groups. Scanning tunneling microscopy/spectroscopy on single nanocrystals revealed the formation of new in-gap states adjacent to the conduction band edge of the functionalized SiNCs. PL red-shifts were attributed to emission through these in-gap states, which reduce the effective band gap for the electron-hole recombination process. The observed in-gap states can be associated with new interface states formed via (-Si-C≡C-) bonds in combination with conjugated molecules as indicated by ab initio calculations. In contrast to alkynyl(aryl)s, the formation of in-gap states and shifts in PL maximum of the SiNCs were not observed with aryl (phenyl, naphthalene, 2-hexylthiophene) and alkynyl (1-dodecyne) surface groups. These outcomes show that surface functionalization with alkynyl(aryl) molecules is a valuable tool to control the electronic structure and optical properties of SiNCs via tuneable interface states, which may enhance the performance of SiNCs in semiconductor devices.

Investigation on mechanical behavior and material characteristics of various weight composition of SiCp reinforced aluminium metal matrix composite

NASA Astrophysics Data System (ADS)

Pichumani, Sivachidambaram; Srinivasan, Raghuraman; Ramamoorthi, Venkatraman

2018-02-01

Aluminium - silicon carbide (Al - SiC) metal matrix composite is produced with following wt % of SiC reinforcement (4%, 8% & 12%) using stir casting method. Mechanical testing such as micro hardness, tensile testing and bend testing were performed. Characterizations, namely micro structure, X-ray diffraction (XRD) analysis, inductive coupled plasma - optical emission spectroscopy (ICP-OES) and scanning electron microscopy (SEM) analysis, were carried out on Al - SiC composites. The presence of SiC on Al - SiC composite is confirmed through XRD technique and microstructure. The percentage of SiC was confirmed through ICP-OES technique. Increase in weight percentage of SiC tends to increase micro hardness, ultimate strength & yield strength but it reduces the bend strength and elongation (%) of the material. SEM factrography of tensile tested fractured samples of Al - 8% SiC & Al - 12% SiC showed fine dimples on fractured surface & coarse dimples fractured surface respectively. This showed significant fracture differences between Al - 8% SiC & Al - 12% SiC. From the above experiment, Al - 8% SiC had good micro hardness, ultimate strength & yield strength without significant loss in elongation (%) & bend strength.

Optical metasurfaces for high angle steering at visible wavelengths

DOE PAGES

Lin, Dianmin; Melli, Mauro; Poliakov, Evgeni; ...

2017-05-23

Metasurfaces have facilitated the replacement of conventional optical elements with ultrathin and planar photonic structures. Previous designs of metasurfaces were limited to small deflection angles and small ranges of the angle of incidence. Here, we have created two types of Si-based metasurfaces to steer visible light to a large deflection angle. These structures exhibit high diffraction efficiencies over a broad range of angles of incidence. We have demonstrated metasurfaces working both in transmission and reflection modes based on conventional thin film silicon processes that are suitable for the large-scale fabrication of high-performance devices.

Time Resolved Digital PIV Measurements of Flow Field Cyclic Variation in an Optical IC Engine

NASA Astrophysics Data System (ADS)

Jarvis, S.; Justham, T.; Clarke, A.; Garner, C. P.; Hargrave, G. K.; Halliwell, N. A.

2006-07-01

Time resolved digital particle image velocimetry (DPIV) experimental data is presented for the in-cylinder flow field development of a motored four stroke spark ignition (SI) optical internal combustion (IC) engine. A high speed DPIV system was employed to quantify the velocity field development during the intake and compression stroke at an engine speed of 1500 rpm. The results map the spatial and temporal development of the in-cylinder flow field structure allowing comparison between traditional ensemble average and cycle average flow field structures. Conclusions are drawn with respect to engine flow field cyclic variations.

Nanohole Structuring for Improved Performance of Hydrogenated Amorphous Silicon Photovoltaics.

PubMed

Johlin, Eric; Al-Obeidi, Ahmed; Nogay, Gizem; Stuckelberger, Michael; Buonassisi, Tonio; Grossman, Jeffrey C

2016-06-22

While low hole mobilities limit the current collection and efficiency of hydrogenated amorphous silicon (a-Si:H) photovoltaic devices, attempts to improve mobility of the material directly have stagnated. Herein, we explore a method of utilizing nanostructuring of a-Si:H devices to allow for improved hole collection in thick absorber layers. This is achieved by etching an array of 150 nm diameter holes into intrinsic a-Si:H and then coating the structured material with p-type a-Si:H and a conformal zinc oxide transparent conducting layer. The inclusion of these nanoholes yields relative power conversion efficiency (PCE) increases of ∼45%, from 7.2 to 10.4% PCE for small area devices. Comparisons of optical properties, time-of-flight mobility measurements, and internal quantum efficiency spectra indicate this efficiency is indeed likely occurring from an improved collection pathway provided by the nanostructuring of the devices. Finally, we estimate that through modest optimizations of the design and fabrication, PCEs of beyond 13% should be obtainable for similar devices.

Optical and Nonlinear Optical Response of Light Sensor Thin Films

PubMed Central

Liu, Huimin; Rua, Armando; Vasquez, Omar; Vikhnin, Valentin S.; Fernandez, Felix E.; Fonseca, Luis F.; Resto, Oscar; Weisz, Svi Z.

2005-01-01

For potential ultrafast optical sensor application, both VO2 thin films and nanocomposite crystal-Si enriched SiO2 thin films grown on fused quartz substrates were successfully prepared using pulsed laser deposition (PLD) and RF co-sputtering techniques. In photoluminescence (PL) measurement c-Si/SiO2 film contains nanoparticles of crystal Si exhibits strong red emission with the band maximum ranging from 580 to 750 nm. With ultrashort pulsed laser excitation all films show extremely intense and ultrafast nonlinear optical (NLO) response. The recorded holography from all these thin films in a degenerate-four-wave-mixing configuration shows extremely large third-order response. For VO2 thin films, an optically induced semiconductor-to-metal phase transition (PT) immediately occurred upon laser excitation. it accompanied. It turns out that the fast excited state dynamics was responsible to the induced PT. For c-Si/SiO2 film, its NLO response comes from the contribution of charge carriers created by laser excitation in conduction band of the c-Si nanoparticles. It was verified by introducing Eu3+ which is often used as a probe sensing the environment variations. It turns out that the entire excited state dynamical process associated with the creation, movement and trapping of the charge carriers has a characteristic 500 ps duration.

Biotin-decorated silica coated PbS nanocrystals emitting in the second biological near infrared window for bioimaging

NASA Astrophysics Data System (ADS)

Corricelli, M.; Depalo, N.; di Carlo, E.; Fanizza, E.; Laquintana, V.; Denora, N.; Agostiano, A.; Striccoli, M.; Curri, M. L.

2014-06-01

Nanoparticles (NPs) emitting in the second biological near infrared (NIR) window of the electromagnetic spectrum have been successfully synthesized by growing a silica shell on the hydrophobic surface of OLEA/TOP PbS nanocrystals (NCs), by means of a reverse microemulsion approach, and subsequently decorated with biotin molecules. The fabrication of very uniform and monodisperse NPs, formed of SiO2 shell coated single core PbS NCs, has been demonstrated by means of a set of complementary optical and structural techniques (Vis-NIR absorption and photoluminescence spectroscopy, transmission electron microscopy) that have highlighted how experimental parameters, such as PbS NC and silica precursor concentration, are crucial to direct the morphology and optical properties of silica coated PbS NPs. Subsequently, the silica surface of the core-shell NPs has been grafted with amino groups, in order to achieve covalent binding of biotin to NIR emitting silica coated NPs. Finally the successful reaction with a green-fluorescent labelled streptavidin has verified the molecular recognition response of the biotin molecules decorating the PbS@SiO2 NP surface. Dynamic light scattering (DLS) and ζ-potential techniques have been used to monitor the hydrodynamic diameter and colloidal stability of both PbS@SiO2 and biotin decorated NPs, showing their high colloidal stability in physiological media, as needed for biomedical applications. Remarkably the obtained biotinylated PbS@SiO2 NPs have been found to retain emission properties in the `second optical window' of the NIR region of the electromagnetic spectrum, thus representing attractive receptor-targeted NIR fluorescent probes for in vivo tumour imaging.Nanoparticles (NPs) emitting in the second biological near infrared (NIR) window of the electromagnetic spectrum have been successfully synthesized by growing a silica shell on the hydrophobic surface of OLEA/TOP PbS nanocrystals (NCs), by means of a reverse microemulsion approach, and subsequently decorated with biotin molecules. The fabrication of very uniform and monodisperse NPs, formed of SiO2 shell coated single core PbS NCs, has been demonstrated by means of a set of complementary optical and structural techniques (Vis-NIR absorption and photoluminescence spectroscopy, transmission electron microscopy) that have highlighted how experimental parameters, such as PbS NC and silica precursor concentration, are crucial to direct the morphology and optical properties of silica coated PbS NPs. Subsequently, the silica surface of the core-shell NPs has been grafted with amino groups, in order to achieve covalent binding of biotin to NIR emitting silica coated NPs. Finally the successful reaction with a green-fluorescent labelled streptavidin has verified the molecular recognition response of the biotin molecules decorating the PbS@SiO2 NP surface. Dynamic light scattering (DLS) and ζ-potential techniques have been used to monitor the hydrodynamic diameter and colloidal stability of both PbS@SiO2 and biotin decorated NPs, showing their high colloidal stability in physiological media, as needed for biomedical applications. Remarkably the obtained biotinylated PbS@SiO2 NPs have been found to retain emission properties in the `second optical window' of the NIR region of the electromagnetic spectrum, thus representing attractive receptor-targeted NIR fluorescent probes for in vivo tumour imaging. Electronic supplementary information (ESI) available: Size statistical analysis of silanized PbS NPs, TLC plate showing the ninhydrin test results and a table summarizing the DH and ζ-potential values for the investigated samples. See DOI: 10.1039/c4nr01025f

Broadband sensitive pump-probe setup for ultrafast optical switching of photonic nanostructures and semiconductors.

PubMed

Euser, Tijmen G; Harding, Philip J; Vos, Willem L

2009-07-01

We describe an ultrafast time resolved pump-probe spectroscopy setup aimed at studying the switching of nanophotonic structures. Both femtosecond pump and probe pulses can be independently tuned over broad frequency range between 3850 and 21,050 cm(-1). A broad pump scan range allows a large optical penetration depth, while a broad probe scan range is crucial to study strongly photonic crystals. A new data acquisition method allows for sensitive pump-probe measurements, and corrects for fluctuations in probe intensity and pump stray light. We observe a tenfold improvement of the precision of the setup compared to laser fluctuations, allowing a measurement accuracy of better than DeltaR=0.07% in a 1 s measurement time. Demonstrations of the improved technique are presented for a bulk Si wafer, a three-dimensional Si inverse opal photonic bandgap crystal, and z-scan measurements of the two-photon absorption coefficient of Si, GaAs, and the three-photon absorption coefficient of GaP in the infrared wavelength range.

Fabrication Method for LOBSTER-Eye Optics in <110> Silicon

NASA Technical Reports Server (NTRS)

Chervenak, James; Collier, Michael; Mateo, Jennette

2013-01-01

Soft x-ray optics can use narrow slots to direct x-rays into a desirable pattern on a focal plane. While square-pack, square-pore, slumped optics exist for this purpose, they are costly. Silicon (Si) is being examined as a possible low-cost replacement. A fabrication method was developed for narrow slots in <110> Si demonstrating the feasibility of stacked slot optics to replace micropores. Current micropore optics exist that have 20-micron-square pores on 26-micron pitch in glass with a depth of 1 mm and an extent of several square centimeters. Among several proposals to emulate the square pore optics are stacked slot chips with etched vertical slots. When the slots in the stack are positioned orthogonally to each other, the component will approach the soft x-ray focusing observed in the micropore optics. A specific improvement Si provides is that it can have narrower sidewalls between slots to permit greater throughput of x-rays through the optics. In general, Si can have more variation in slot geometry (width, length). Further, the sidewalls can be coated with high-Z materials to enhance reflection and potentially reduce the surface roughness of the reflecting surface. Narrow, close-packed deep slots in <110> Si have been produced using potassium hydroxide (KOH) etching and a patterned silicon nitride (SiN) mask. The achieved slot geometries have sufficient wall smoothness, as observed through scanning electron microscope (SEM) imaging, to enable evaluation of these slot plates as an optical element for soft x-rays. Etches of different angles to the crystal plane of Si were evaluated to identify a specific range of etch angles that will enable low undercut slots in the Si <110> material. These slots with the narrow sidewalls are demonstrated to several hundred microns in depth, and a technical path to 500-micron deep slots in a precision geometry of narrow, closepacked slots is feasible. Although intrinsic stress in ultrathin wall Si is observed, slots with walls approaching 1.5 microns can be achieved (a significant improvement over the 6-micron walls in micro - pore optics). The major advantages of this technique are the potential for higher x-ray throughout (due to narrow slot walls) and lower cost over the existing slumped micropore glass plates. KOH etching of smooth sidewalls has been demonstrated for many applications, suggesting its feasibility for implementation in x-ray optics. Si cannot be slumped like the micropore optics, so the focusing will be achieved with millimeter-scale slot plates that populate a spherical dome. The possibility for large-scale production exists for Si parts that is more difficult to achieve in micropore parts.

Growth of rutile TiO2 nanorods in Ti and Cu ion sequentially implanted SiO2 and the involved mechanisms

NASA Astrophysics Data System (ADS)

Mu, Xiaoyu; Liu, Xiaoyu; Wang, Xiaohu; Dai, Haitao; Liu, Changlong

2018-01-01

TiO2 in nanoscale exhibits unique physicochemical and optoelectronic properties and has attracted much more interest of the researchers. In this work, TiO2 nanostructures are synthesized in amorphous SiO2 slices by implanting Ti ions, or sequentially implanting Ti and Cu ions combined with annealing at high temperature. The morphology, structure, spatial distribution and optical properties of the formed nanostructures have been investigated in detail. Our results clearly show that the thermal growth of TiO2 nanostructures in SiO2 substrate is significantly enhanced by presence of post Cu ion implantation, which depends strongly on the applied Cu ion fluence, as well as the annealing atmosphere. Due to the formation of Cu2O in the substrate, rutile TiO2 nanorods of large size have been well fabricated in the Ti and Cu sequentially implanted SiO2 after annealing in N2 atmosphere, in which Cu2O plays a role as a catalyst. Moreover, the sample with well-fabricated TiO2 nanorods exhibits a narrowed band gap, an enhanced optical absorption in visible region, and catalase-/peroxidase-like catalytic characteristics. Our findings provide an effective route to fabricate functional TiO2 nanorods in SiO2 via ion implantation.

Light-activated resistance switching in SiOx RRAM devices

NASA Astrophysics Data System (ADS)

Mehonic, A.; Gerard, T.; Kenyon, A. J.

2017-12-01

We report a study of light-activated resistance switching in silicon oxide (SiOx) resistive random access memory (RRAM) devices. Our devices had an indium tin oxide/SiOx/p-Si Metal/Oxide/Semiconductor structure, with resistance switching taking place in a 35 nm thick SiOx layer. The optical activity of the devices was investigated by characterising them in a range of voltage and light conditions. Devices respond to illumination at wavelengths in the range of 410-650 nm but are unresponsive at 1152 nm, suggesting that photons are absorbed by the bottom p-type silicon electrode and that generation of free carriers underpins optical activity. Applied light causes charging of devices in the high resistance state (HRS), photocurrent in the low resistance state (LRS), and lowering of the set voltage (required to go from the HRS to LRS) and can be used in conjunction with a voltage bias to trigger switching from the HRS to the LRS. We demonstrate negative correlation between set voltage and applied laser power using a 632.8 nm laser source. We propose that, under illumination, increased electron injection and hence a higher rate of creation of Frenkel pairs in the oxide—precursors for the formation of conductive oxygen vacancy filaments—reduce switching voltages. Our results open up the possibility of light-triggered RRAM devices.

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

NASA Astrophysics Data System (ADS)

Alireza, Samavati; Othaman, Z.; K. Ghoshal, S.; K. Mustafa, M.

2015-02-01

The influences of thermal annealing on the structural and optical features of radio frequency (rf) magnetron sputtered self-assembled Ge quantum dots (QDs) on Si (100) are investigated. Preferentially oriented structures of Ge along the (220) and (111) directions together with peak shift and reduced strain (4.9% to 2.7%) due to post-annealing at 650 °C are discerned from x-ray differaction (XRD) measurement. Atomic force microscopy (AFM) images for both pre-annealed and post-annealed (650 °C) samples reveal pyramidal-shaped QDs (density ˜ 0.26× 1011 cm-2) and dome-shape morphologies with relatively high density ˜ 0.92 × 1011 cm-2, respectively. This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity. The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role. The observed red-shift ˜ 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing, and is related to the effect of quantum confinement. Furthermore, the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO2 or GeOx and holes in the ground state of Ge dots. Raman spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart. An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes. A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established. Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated. Project supported by Ibnu Sina Institute for Fundamental Science Study, Universiti Teknologi Malaysia through Vote Q.J130000.2526.02H94, O5 and Postdoctoral Research Grant.

Fabrication of AgInSe2 heterojunction solar cell

NASA Astrophysics Data System (ADS)

Khudayer, Iman Hameed

2018-05-01

Silver, Indium Selenium thin film with a thickness (5001±30) nm, deposited by thermal evaporation methods at RT and annealing3temperature (Ta = 400, 500 and 600) K on a substrate of glass to study structural and optical properties of thin films and on p-Si wafer to fabricate the AgInSe2/p-Si heterojunction solar cell. XRD analysis shows that the AgInSe2 (AIS) deposited film at RT and annealing3temperature (Ta = 400, 500 and 600) K have polycrystalline structure. The average grain size has been estimated from AFM images. The energy gap was estimated from the optical transmittance using a spectrometer type (UV.-Visible 1800 spectra photometer). From I-V characterization, the photovoltaic parameters such as, open-circuit voltage, short-circuit current density, fill factor, ideality factor, and efficiencies, were computed. As well as the built-in potential, carrier concentration and depletion width were determined under RT and (Ta = 400, 500 and 600) K from C-V measurement.

First-principles calculations of phonons and Raman and infrared spectra in Cd-IV-N2 compounds

NASA Astrophysics Data System (ADS)

Lyu, Sai; Lambrecht, Walter R. L.

2018-05-01

A first-principles study of the phonons at the zone center in Cd-IV-N2 compounds is presented with IV = Si, Ge, Sn. The calculations are performed for the most likely Pbn21 crystal structure, after showing that it is indeed lower in total energy compared to the closely related Pmc21 structure. The normal mode frequencies are calculated using density functional perturbation theory and symmetry labeled. The longitudinal optical-transverse optical splittings are determined using the Born effective charges which are also reported. These are used to simulate polarized Raman spectra for different scattering configurations as well as the infrared absorption and reflection spectra. The mode frequencies are found to decrease from Si to Ge to Sn as group-IV cation. The spectra show a wide variety of number of prominent peaks and relative intensities in spite of the great similarities of these three materials. Phonon densities of states and their analysis in atom by atom contributions are also reported.

Effect of CoSi2 buffer layer on structure and magnetic properties of Co films grown on Si (001) substrate

NASA Astrophysics Data System (ADS)

Hu, Bo; He, Wei; Ye, Jun; Tang, Jin; Syed Sheraz, Ahmad; Zhang, Xiang-Qun; Cheng, Zhao-Hua

2015-01-01

Buffer layer provides an opportunity to enhance the quality of ultrathin magnetic films. In this paper, Co films with different thickness of CoSi2 buffer layers were grown on Si (001) substrates. In order to investigate morphology, structure, and magnetic properties of films, scanning tunneling microscope (STM), low energy electron diffraction (LEED), high resolution transmission electron microscopy (HRTEM), and surface magneto-optical Kerr effect (SMOKE) were used. The results show that the crystal quality and magnetic anisotropies of the Co films are strongly affected by the thickness of CoSi2 buffer layers. Few CoSi2 monolayers can prevent the interdiffusion of Si substrate and Co film and enhance the Co film quality. Furthermore, the in-plane magnetic anisotropy of Co film with optimal buffer layer shows four-fold symmetry and exhibits the two-jumps of magnetization reversal process, which is the typical phenomenon in cubic (001) films. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB921801 and 2012CB933102), the National Natural Science Foundation of China (Grant Nos. 11374350, 11034004, 11274361, and 11274033), and the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20131102130005).

Comprehensive photonics-electronics convergent simulation and its application to high-speed electronic circuit integration on a Si/Ge photonic chip

NASA Astrophysics Data System (ADS)

Takeda, Kotaro; Honda, Kentaro; Takeya, Tsutomu; Okazaki, Kota; Hiraki, Tatsurou; Tsuchizawa, Tai; Nishi, Hidetaka; Kou, Rai; Fukuda, Hiroshi; Usui, Mitsuo; Nosaka, Hideyuki; Yamamoto, Tsuyoshi; Yamada, Koji

2015-01-01

We developed a design technique for a photonics-electronics convergence system by using an equivalent circuit of optical devices in an electrical circuit simulator. We used the transfer matrix method to calculate the response of an optical device. This method used physical parameters and dimensions of optical devices as calculation parameters to design a device in the electrical circuit simulator. It also used an intermediate frequency to express the wavelength dependence of optical devices. By using both techniques, we simulated bit error rates and eye diagrams of optical and electrical integrated circuits and calculated influences of device structure change and wavelength shift penalty.

Structural properties of Al/Mo/SiC multilayers with high reflectivity for extreme ultraviolet light.

PubMed

Hu, Min-Hui; Le Guen, Karine; André, Jean-Michel; Jonnard, Philippe; Meltchakov, Evgueni; Delmotte, Franck; Galtayries, Anouk

2010-09-13

We present the results of an optical and chemical, depth and surface study of Al/Mo/SiC periodic multilayers, designed as high reflectivity coatings for the extreme ultra-violet (EUV) range. In comparison to the previously studied Al/SiC system, the introduction of Mo as a third material in the multilayer structure allows us to decrease In comparison to the previously studied Al/SiC system with a reflectance of 37% at near normal incidence around 17 nm, the introduction of Mo as a third material in the multilayer structure allows us to decrease the interfacial roughness and achieve an EUV reflectivity of 53.4%, measured with synchrotron radiation. This is the first report of a reflectivity higher than 50% around 17 nm. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS) measurements are performed on the Al/Mo/SiC system in order to analyze the individual layers within the stack. ToF-SIMS and XPS results give evidence that the first SiC layer is partially oxidized, but the O atoms do not reach the first Mo and Al layers. We use these results to properly describe the multilayer stack and discuss the possible reasons for the difference between the measured and simulated EUV reflectivity values.

Improved longitudinal magneto-optic Kerr effect signal contrast from nanomagnets with dielectric coatings

NASA Astrophysics Data System (ADS)

Holiday, L. F.; Gibson, U. J.

2006-12-01

We report on the use of dielectric coatings to improve the contrast of longitudinal magneto-optic Kerr effect signals from submicron magnetic structures. Electron-beam lithography was used to define disks in 22 nm thick Ni films deposited on Si substrates. The structures were measured in four configurations: as-deposited, through a fused silica prism using index-matching fluid, coated with ZnS, and using a prism on top of the ZnS layer. The modified samples show up to 20 times improvement in the MOKE contrast due to admittance matching to the magnetic material and suppression of the substrate reflectance. The behavior is successfully predicted by a model that includes the magneto-optic response of the nickel layer and accounts for the fraction of the beam intercepted by the magnetic structure.

Influence of bias voltage on structural and optical properties of TiN{sub x} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Omveer, E-mail: poonia.omveer@gmail.com; Dahiya, Raj P.; Deenbandhu Chhotu Ram University of Science and Technology, Murthal – 131039

In the present work, Ti thin films were deposited on Si substrate using DC sputtering technique. Indigenous hot cathode arc discharge plasma system was used for nitriding over these samples, where the plasma parameters and work piece can be controlled independently. A mixture of H{sub 2} and N{sub 2} gases (in the ratio of 80:20) was supplied into the plasma chamber. The effect of bias voltage on the crystal structure, morphology and optical properties was investigated by employing various physical techniques such as X-ray Diffraction, Atomic Force Microscopy and UV-Vis spectrometry. It was found that bias voltage affects largely themore » crystal structure and band gap which in turn is responsible for the modifications in optical properties of the deposited films.« less

Fabrication of poly-crystalline Si-based Mie resonators via amorphous Si on SiO2 dewetting.

PubMed

Naffouti, Meher; David, Thomas; Benkouider, Abdelmalek; Favre, Luc; Ronda, Antoine; Berbezier, Isabelle; Bidault, Sebastien; Bonod, Nicolas; Abbarchi, Marco

2016-02-07

We report the fabrication of Si-based dielectric Mie resonators via a low cost process based on solid-state dewetting of ultra-thin amorphous Si on SiO2. We investigate the dewetting dynamics of a few nanometer sized layers annealed at high temperature to form submicrometric Si-particles. Morphological and structural characterization reveal the polycrystalline nature of the semiconductor matrix as well as rather irregular morphologies of the dewetted islands. Optical dark field imaging and spectroscopy measurements of the single islands reveal pronounced resonant scattering at visible frequencies. The linewidth of the low-order modes can be ∼20 nm in full width at half maximum, leading to a quality factor Q exceeding 25. These values reach the state-of-the-art ones obtained for monocrystalline Mie resonators. The simplicity of the dewetting process and its cost-effectiveness opens the route to exploiting it over large scales for applications in silicon-based photonics.

Dynamic ultrasound modulated optical tomography by self-referenced photorefractive holography.

PubMed

Benoit a la Guillaume, Emilie; Bortolozzo, Umberto; Huignard, Jean-Pierre; Residori, Stefania; Ramaz, Francois

2013-02-01

Photorefractive Bi(12)SiO(20) single crystal is used for acousto-optic imaging in thick scattering media in the green part of the spectrum, in an adaptive speckle correlation configuration. Light fields at the output of the scattering sample exhibit typical speckle grains of 1 μm size within the volume of the nonlinear crystal. This heterogeneous illumination induces a complex refractive index structure without applying a reference beam on the crystal, leading to a self-referenced diffraction correlation scheme. We demonstrate that this simple and robust configuration is able to perform axially resolved ultrasound modulated optical tomography of thick scattering media with an improved optical etendue.

Measurement and Control of In-plane Surface Chemistry at the Silicon/Silicon Dioxide Interface

NASA Astrophysics Data System (ADS)

Gokce, Bilal

In-plane directional control of surface chemistry during interface formation can lead to new opportunities regarding device structures and applications. Control of this type requires techniques that can probe and hence provide feedback on the chemical reactivity of bonds not only in specific directions but also in real time. In this thesis work, I demonstrate both control and measurement of the oxidation of H-terminated Si(111). The nonlinear optical tool of Second-Harmonic-Generation (SHG) is used to show that Si oxidation in air is a two-stage process where the H of the "up" bonds of the outermost Si layer is replaced by OH, followed by O insertion into the "back" bonds. Detailed information about both stages is revealed by investigating the effect of uniaxial strain and carrier concentration on this chemical reaction. It is shown that even small amounts of strain manipulate the reaction kinetics of surface bonds significantly, with tensile strain enhancing oxidation and compressive strain retarding it. This dramatic change suggests a strain-driven charge transfer mechanism between Si--H up bonds and Si--Si back bonds in the outer layer of Si atoms. Data on differently doped samples reveal that high concentrations of electrons increase the chemical reactivity of the outer-layer Si--Si back bonds relative to the Si--H up bonds while high concentrations of holes cause a greater increase in the reactivity of the Si--H up bonds than that of the Si--Si back bonds. However, the thicknesses of the natural oxides of all samples follow the same path and stabilize near 1 nm at room temperature, regardless of the chemical kinetics of the different bonds, as determined by spectroscopic ellipsometry. Real-time measurement during SHG experiments is achieved by analyzing SHG anisotropy data with the anisotropic bond-charge model of nonlinear optics where peaks in the SHG spectrum are correlated with the near alignment of bonds to the direction of the excitation field.

Influence of 20 MeV electron irradiation on the optical properties and phase composition of SiOx thin films

NASA Astrophysics Data System (ADS)

Hristova-Vasileva, Temenuga; Petrik, Peter; Nesheva, Diana; Fogarassy, Zsolt; Lábár, János; Kaschieva, Sonia; Dmitriev, Sergei N.; Antonova, Krassimira

2018-05-01

Homogeneous films from SiO1.3 (250 nm thick) were deposited on crystalline Si substrates by thermal evaporation of silicon monoxide. A part of the films was further annealed at 700 °C to grow amorphous Si (a-Si) nanoclusters in an oxide matrix, thus producing composite a-Si-SiO1.8 films. Homogeneous as well as composite films were irradiated by 20-MeV electrons at fluences of 7.2 × 1014 and 1.44 × 1015 el/cm2. The film thicknesses and optical constants were explored by spectroscopic ellipsometry. The development of the phase composition of the films caused by the electron-beam irradiation was studied by transmission electron microscopy. The ellipsometric and electron microscopy results have shown that the SiOx films are optically homogeneous and the electron irradiation with a fluence of 7.2 × 1014 el/cm2 has led to small changes in the optical constants and the formation of very small a-Si nanoclusters. The irradiation of the a-Si-SiOx composite films caused a decrease in the effective refractive index and, at the same time, an increase in the refractive index of the oxide matrix. Irradiation induced increase in the optical band gap and decrease in the absorption coefficient of the thermally grown amorphous Si nanoclusters have also been observed. The obtained results are discussed in terms of the formation of small amorphous silicon nanoclusters in the homogeneous layers and electron irradiation induced reduction in the nanocluster size in the composite films. The conclusion for the nanoparticle size reduction is supported by infrared transmittance results.

Improved opto-electronic properties of silicon heterojunction solar cells with SiO x /Tungsten-doped indium oxide double anti-reflective coatings

NASA Astrophysics Data System (ADS)

Yu, Jian; Zhou, Jie; Bian, Jiantao; Zhang, Liping; Liu, Yucheng; Shi, Jianhua; Meng, Fanying; Liu, Jinning; Liu, Zhengxin

2017-08-01

Amorphous SiO x was prepared by plasma enhanced chemical vapor deposition (PECVD) to form SiO x /tungsten-doped indium oxide (IWO) double anti-reflective coatings for silicon heterojunction (SHJ) solar cell. The sheet resistance of SiO x /IWO stacks decreases due to plasma treatment during deposition process, which means thinner IWO film would be deposited for better optical response. However, the comparisons of three anti-reflective coating (ARC) structures reveal that SiO x film limits carier transport and the path of IWO-SiO x -Ag structure is non-conductive. The decrease of sheet resistance is defined as pseudo conductivity. IWO film capping with SiO x allows observably reduced reflectance and better response in 300-400 and 600-1200 nm wavelength ranges. Compared with IWO single ARC, the average reflection is reduced by 1.65% with 70 nm SiO x /80 nm IWO double anti-reflective coatings (DARCs) in 500-1200 nm wavelength range, leading to growing external quantum efficiency response, short circuit current density (J sc), and efficiency. After well optimization of SiO x /IWO stacks, an impressive efficiency of 23.08% is obtained with high J sc and without compromising open circuit voltage (V oc) and fill factor. SiO x /IWO DARCs provide better anti-reflective properties over a broad range of wavelength, showing promising application for SHJ solar cells.

Two-photon absorption in SiO{sub 2}- and (SiO{sub 2} + GeO{sub 2})-based fibres at a wavelength of 349 nm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chunaev, D S; Karasik, A Ya

2014-06-30

The nonlinear two-photon light absorption coefficients have been measured in an optical fibre with a quartz glass (SiO{sub 2}) core and in a fibre with a germanosilicate glass (SiO{sub 2} + GeO{sub 2}) core. The two-photon absorption coefficient β measured at a wavelength of 349 nm in the (SiO{sub 2} + GeO{sub 2})-based fibre (13.7 cm TW{sup -1}) multiply exceeds that for the pure quartz glass optical fibre (0.54 cm TW{sup -1}). (nonlinear optical phenomena)

Silicon waveguide optical switch with embedded phase change material.

PubMed

Miller, Kevin J; Hallman, Kent A; Haglund, Richard F; Weiss, Sharon M

2017-10-30

Phase-change materials (PCMs) have emerged as promising active elements in silicon (Si) photonic systems. In this work, we design, fabricate, and characterize a hybrid Si-PCM optical switch. By integrating vanadium dioxide (a PCM) within a Si photonic waveguide, in a non-resonant geometry, we achieve ~10 dB broadband optical contrast with a PCM length of 500 nm using thermal actuation.

High efficiency silicon solar cell based on asymmetric nanowire.

PubMed

Ko, Myung-Dong; Rim, Taiuk; Kim, Kihyun; Meyyappan, M; Baek, Chang-Ki

2015-07-08

Improving the efficiency of solar cells through novel materials and devices is critical to realize the full potential of solar energy to meet the growing worldwide energy demands. We present here a highly efficient radial p-n junction silicon solar cell using an asymmetric nanowire structure with a shorter bottom core diameter than at the top. A maximum short circuit current density of 27.5 mA/cm(2) and an efficiency of 7.53% were realized without anti-reflection coating. Changing the silicon nanowire (SiNW) structure from conventional symmetric to asymmetric nature improves the efficiency due to increased short circuit current density. From numerical simulation and measurement of the optical characteristics, the total reflection on the sidewalls is seen to increase the light trapping path and charge carrier generation in the radial junction of the asymmetric SiNW, yielding high external quantum efficiency and short circuit current density. The proposed asymmetric structure has great potential to effectively improve the efficiency of the SiNW solar cells.

Investigation of the dielectric function of solution-processed InGaZnO films using ellipsometry.

PubMed

Kim, Tae Jung; Yoon, Jae Jin; Hwang, Soo Min; Choi, Jun Hyuk; Hwang, Soon Yong; Ghong, Tae Ho; Barange, Nilesh; Kim, Jun Young; Kim, Young Dong; Joo, Jinho

2012-07-01

The optical properties of InGaZnO (IGZO) films grown through the sol-gel process as a function of sintering time were investigated with spectroscopic ellipsometry (SE). The IGZO precursor sol was prepared by mixing In nitrate, Ga nitrate, and Zn acetate at a molar ratio of In:Ga:Zn = 3:1:1. The solution was deposited on a SiO2/Si substrate via spin coating. Sintering was performed at 400 degrees C for 1-15 h in an ambient atmosphere. The optical properties were measured over the range 1.12-6.52 eV via variable angle SE, at room temperature. The angle of incidence was varied from 50 to 70 degrees in 5 degree steps. To extract the pure optical properties of IGZO, multilayer-structure calculation with Tauc-Lorentz dispersion relation for IGZO was performed. The changes in the dielectric function of the IGZO films with varying sintering time were observed. The resultant optical properties can be related to the concentration of oxygen vacancies in the material, which can be controlled by the sintering time.

Time-Resolved Diffuse Optical Spectroscopy and Imaging Using Solid-State Detectors: Characteristics, Present Status, and Research Challenges.

PubMed

Alayed, Mrwan; Deen, M Jamal

2017-09-14

Diffuse optical spectroscopy (DOS) and diffuse optical imaging (DOI) are emerging non-invasive imaging modalities that have wide spread potential applications in many fields, particularly for structural and functional imaging in medicine. In this article, we review time-resolved diffuse optical imaging (TR-DOI) systems using solid-state detectors with a special focus on Single-Photon Avalanche Diodes (SPADs) and Silicon Photomultipliers (SiPMs). These TR-DOI systems can be categorized into two types based on the operation mode of the detector (free-running or time-gated). For the TR-DOI prototypes, the physical concepts, main components, figures-of-merit of detectors, and evaluation parameters are described. The performance of TR-DOI prototypes is evaluated according to the parameters used in common protocols to test DOI systems particularly basic instrumental performance (BIP). In addition, the potential features of SPADs and SiPMs to improve TR-DOI systems and expand their applications in the foreseeable future are discussed. Lastly, research challenges and future developments for TR-DOI are discussed for each component in the prototype separately and also for the entire system.

Integration of GaN/AlN all-optical switch with SiN/AlN waveguide utilizing spot-size conversion.

PubMed

Iizuka, Norio; Yoshida, Haruhiko; Managaki, Nobuto; Shimizu, Toshimasa; Hassanet, Sodabanlu; Cumtornkittikul, Chiyasit; Sugiyama, Masakazu; Nakano, Yoshiaki

2009-12-07

Spot-size converters for an all-optical switch utilizing the intersubband transition in GaN/AlN multiple quantum wells are studied with the purpose of reducing operation power by improving the coupling efficiency between the input fiber and the switch. With a stair-like spot-size converter, the absorption saturation of 5 dB is achieved with a pulse energy of 25 pJ. The switch is integrated with a SiN/AlN waveguide and spot-size converters, and the structure provides the possibility of an integration of the switch with other functional devices. To further improve the coupling loss between the waveguide and the switch, triangular-shaped converters are investigated, demonstrating losses as low as 2 dB/facet.

Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadoh, Taizoh, E-mail: sadoh@ed.kyushu-u.ac.jp; Chikita, Hironori; Miyao, Masanobu

2015-09-07

Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%–26%) and annealing conditions (300–1000 °C, 1 s–48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (∼80%) SiGe layers with Sn concentrations of ∼2% are realized by ultra-low temperature annealingmore » (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.« less

Towards the development of new phosphors with reduced content of rare earth elements: Structural and optical characterization of Ce:Tb: Al{sub 2}SiO{sub 5}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chiriu, D.; Stagi, L.; Carbonaro, C.M.

2016-05-15

Highlights: • A new promising inert matrix as host of luminescent ions is proposed. • Al2SiO5 matrix is free from Rare earths (critical raw materials). • Doping the matrix with Ce and Tb we obtain an efficient green emitter. • Cerium acts as sensitizer for Terbium emission. - Abstract: A new promising inert matrix as host of luminescent ions is proposed. Al2SiO5 samples, doped with rare earths (Ce, Tb single doped and co-doped) are proposed as good prospect for the development of new UV–vis converter with reduced content of rare earths elements. Structural characterization by Raman, XRD spectroscopy and TEMmore » imaging reveals the sillimanite phase and nano sized dimension of the investigated powders. Optical characterization by steady time and time resolved emission spectroscopy for the single doped and co-doped samples allows to identify an efficient energy transfer from Ce to Tb ions under near UV excitation wavelength. The intense green emission observed in the Ce:Tb co-doped Al2SiO5 system suggests its potential application as efficient blue pumped green emitter phosphor to be exploited for white LED: to this purpose we tested the compound in combination with a red emitting doping ion recording for Ce:Tb:Cr:ASO system a correlated color temperature of 6720 K.« less

Electronic, Optical, and Thermal Properties of Reduced-Dimensional Semiconductors

NASA Astrophysics Data System (ADS)

Huang, Shouting

Reduced-dimensional materials have attracted tremendous attention because of their new physics and exotic properties, which are of great interests for fundamental science. More importantly, the manipulation and engineering of matter on an atomic scale yield promising applications for many fields including nanoelectronics, nanobiotechnology, environments, and renewable energy. Because of the unusual quantum confinement and enhanced surface effect of reduced-dimensional materials, traditional empirical models suffer from necessary but unreliable parameters extracted from previously-studied bulk materials. In this sense, quantitative, parameter-free approaches are highly useful for understanding properties of reduced-dimensional materials and, furthermore, predicting their novel applications. The first-principles density functional theory (DFT) is proven to be a reliable and convenient tool. In particular, recent progress in many-body perturbation theory (MBPT) makes it possible to calculate excited-state properties, e.g., quasiparticle (QP) band gap and optical excitations, by the first-principles approach based on DFT. Therefore, during my PhD study, I employed first-principles calculations based on DFT and MBPT to systematically study fundamental properties of typical reduced-dimensional semiconductors, i.e., the electronic structure, phonons, and optical excitations of core-shell nanowires (NWs) and graphene-like two-dimensional (2D) structures of current interests. First, I present first-principles studies on how to engineer band alignments of nano-sized radial heterojunctions, Si/Ge core-shell NWs. Our calculation reveals that band offsets in these one-dimensional (1D) nanostructures can be tailored by applying axial strain or varying core-shell sizes. In particular, the valence band offset can be efficiently tuned across a wide range and even be diminished via applied strain. Two mechanisms contribute to this tuning of band offsets. Furthermore, varying the size of Si/Ge core-shell NWs and corresponding quantum confinement is shown to be efficient for modifying both valence and conduction band offsets simultaneously. Our proposed approaches to control band offsets in nano-sized heterojunctions may be of practical interest for nanoelectronic and photovoltaic applications. Additionally, I also studied the lattice vibrational modes of Si/Ge core-shell N-Ws. Our calculations show that the internal strain induced by the lattice mismatch between core and shell plays an important role in significantly shifting the frequency of characteristic optical modes of core-shell NWs. In particular, our simulation demonstrates that these frequency shifts can be detected by Raman-scattering experiments, giving rise to a convenient and nondestructive way to obtain structural information of core-shell materials. Meanwhile, another type of collective modes, the radial breathing modes (RBM), is identified in Si-core/Ge-shell NWs and their frequency dependence is explained by an elastic media model. Our studied vibrational modes and their frequency evolution are useful for thermoelectric applications based on core-shell nanostructures. Then I studied optical properties and exciton spectra of 2D semiconducting carbon structures. The energy spectra and wavefunctions of excitons in the 2D graphene derivatives, i.e., graphyne and graphane, are found to be strongly modified by quantum confinement, making them qualitatively different from the usual Rydberg series. However, their parity and optical selection rules are preserved. Thus a one-parameter hydrogenic model is applied to quantitatively explain the ab initio exciton spectra, and allows one to extrapolate the electron-hole binding energy from optical spectroscopies of 2D semiconductors without costly simulations. Meanwhile, our calculated optical absorption spectrum and enhanced spin singlet-triplet splitting project graphyne, an allotrope of graphene, as a good candidate for intriguing energy and biomedical applications. Lastly, we report first-principles results on electronic structures of 2D graphene-like system, i.e., silicene. For planar and simply buckled silicene structures, we confirm their zero-gap nature and show a significant renormalization of their Fermi velocity by including many-electron effects. However, the other two recently proposed silicene structures exhibit a finite band gap, indicating that they are gapped semiconductors instead of expected Dirac-fermion semimetals. This finite band gap of the latter two structures is preserved even with the Ag substrate included. The gap opening is explained by the symmetry breaking of the buckled structures. Moreover, our GW calculation reveals enhanced many-electron effects in these 2D structures. Finally the band gap of the latter two structures can be tuned in a wide range by applying strain.

SiPM electro-optical detection system noise suppression method

NASA Astrophysics Data System (ADS)

Bi, Xiangli; Yang, Suhui; Hu, Tao; Song, Yiheng

2014-11-01

In this paper, the single photon detection principle of Silicon Photomultipliers (SiPM) device is introduced. The main noise factors that infect the sensitivity of the electro-optical detection system are analyzed, including background light noise, detector dark noise, preamplifier noise and signal light noise etc. The Optical, electrical and thermodynamic methods are used to suppress the SiPM electro-optical detection system noise, which improved the response sensitivity of the detector. Using SiPM optoelectronic detector with a even high sensitivity, together with small field large aperture optical system, high cutoff narrow bandwidth filters, low-noise operational amplifier circuit, the modular design of functional circuit, semiconductor refrigeration technology, greatly improved the sensitivity of optical detection system, reduced system noise and achieved long-range detection of weak laser radiation signal. Theoretical analysis and experimental results show that the proposed methods are reasonable and efficient.

229 nm UV LEDs on aluminum nitride single crystal substrates using p-type silicon for increased hole injection

NASA Astrophysics Data System (ADS)

Liu, Dong; Cho, Sang June; Park, Jeongpil; Seo, Jung-Hun; Dalmau, Rafael; Zhao, Deyin; Kim, Kwangeun; Gong, Jiarui; Kim, Munho; Lee, In-Kyu; Albrecht, John D.; Zhou, Weidong; Moody, Baxter; Ma, Zhenqiang

2018-02-01

AlGaN based 229 nm light emitting diodes (LEDs), employing p-type Si to significantly increase hole injection, were fabricated on single crystal bulk aluminum nitride (AlN) substrates. Nitride heterostructures were epitaxially deposited by organometallic vapor phase epitaxy and inherit the low dislocation density of the native substrate. Following epitaxy, a p-Si layer is bonded to the heterostructure. LEDs were characterized both electrically and optically. Owing to the low defect density films, large concentration of holes from p-Si, and efficient hole injection, no efficiency droop was observed up to a current density of 76 A/cm2 under continuous wave operation and without external thermal management. An optical output power of 160 μW was obtained with the corresponding external quantum efficiency of 0.03%. This study demonstrates that by adopting p-type Si nanomembrane contacts as a hole injector, practical levels of hole injection can be realized in UV light-emitting diodes with very high Al composition AlGaN quantum wells, enabling emission wavelengths and power levels that were previously inaccessible using traditional p-i-n structures with poor hole injection efficiency.

Blinking and spectral diffusion of CdSe/ZnS nanoparticles

NASA Astrophysics Data System (ADS)

Lorke, Axel; Braam, Daniel; Mölleken, Andreas; Offer, Matthias; Prinz, Günther; Geller, Martin

2012-02-01

Even though the tunable optical properties of colloidal nanoparticles have been studied extensively, their luminescent behaviour is still not fully understood. The random emission intermittency and the power-law of on- and off-times as well as shifts in the emission wavelength still lack a comprehensive understanding [1]. We investigate the excitonic structure of CdSe/ZnS core/shell nanoparticles using a micro-photoluminescence (PL) setup with confocal as well as imaging optics. The nanoparticles are dispersed in toluene with 1% PMMA and deposited by spin-coating on different substrates (bare Si/SiO2 as well as Si/SiO2 covered with different rough metallic layers). Depending on the substrate, we observe emission intermittency or nearly blinking-free emission with spectral jumps of 25 meV in the emission energy. Both can be assigned to excitonic transitions affected by additional charge inside or outside the nanoparticle [2]. Furthermore, we observe a phonon replica of 25 meV and smaller (<10 meV) energetic shifts of the emission lines, which are likely caused random charge variations in the environment of the nanoparticle. [4pt] [1] P. Frantsuzov et al., Nature 4, 519 (2008). [0pt] [2] A. Efros, Nature Mat. 7, 612 (2008)

Improvement in the electrical performance and bias-stress stability of dual-active-layered silicon zinc oxide/zinc oxide thin-film transistor

NASA Astrophysics Data System (ADS)

Liu, Yu-Rong; Zhao, Gao-Wei; Lai, Pai-To; Yao, Ruo-He

2016-08-01

Si-doped zinc oxide (SZO) thin films are deposited by using a co-sputtering method, and used as the channel active layers of ZnO-based TFTs with single and dual active layer structures. The effects of silicon content on the optical transmittance of the SZO thin film and electrical properties of the SZO TFT are investigated. Moreover, the electrical performances and bias-stress stabilities of the single- and dual-active-layer TFTs are investigated and compared to reveal the effects of the Si doping and dual-active-layer structure. The average transmittances of all the SZO films are about 90% in the visible light region of 400 nm-800 nm, and the optical band gap of the SZO film gradually increases with increasing Si content. The Si-doping can effectively suppress the grain growth of ZnO, revealed by atomic force microscope analysis. Compared with that of the undoped ZnO TFT, the off-state current of the SZO TFT is reduced by more than two orders of magnitude and it is 1.5 × 10-12 A, and thus the on/off current ratio is increased by more than two orders of magnitude. In summary, the SZO/ZnO TFT with dual-active-layer structure exhibits a high on/off current ratio of 4.0 × 106 and superior stability under gate-bias and drain-bias stress. Projected supported by the National Natural Science Foundation of China (Grant Nos. 61076113 and 61274085), the Natural Science Foundation of Guangdong Province (Grant No. 2016A030313474), and the University Development Fund (Nanotechnology Research Institute, Grant No. 00600009) of the University of Hong Kong, China.

Si K EDGE STRUCTURE AND VARIABILITY IN GALACTIC X-RAY BINARIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schulz, Norbert S.; Corrales, Lia; Canizares, Claude R.

2016-08-10

We survey the Si K edge structure in various absorbed Galactic low-mass X-ray binaries (LMXBs) to study states of silicon in the inter- and circum-stellar medium. The bulk of these LMXBs lie toward the Galactic bulge region and all have column densities above 10{sup 22} cm{sup −2}. The observations were performed using the Chandra High Energy Transmission Grating Spectrometer. The Si K edge in all sources appears at an energy value of 1844 ± 0.001 eV. The edge exhibits significant substructure that can be described by a near edge absorption feature at 1849 ± 0.002 eV and a far edgemore » absorption feature at 1865 ± 0.002 eV. Both of these absorption features appear variable with equivalent widths up to several mÅ. We can describe the edge structure using several components: multiple edge functions, near edge absorption excesses from silicates in dust form, signatures from X-ray scattering optical depths, and a variable warm absorber from ionized atomic silicon. The measured optical depths of the edges indicate much higher values than expected from atomic silicon cross sections and interstellar medium abundances, and they appear consistent with predictions from silicate X-ray absorption and scattering. A comparison with models also indicates a preference for larger dust grain sizes. In many cases, we identify Si xiii resonance absorption and determine ionization parameters between log ξ = 1.8 and 2.8 and turbulent velocities between 300 and 1000 km s{sup −1}. This places the warm absorber in close vicinity of the X-ray binaries. In some data, we observe a weak edge at 1.840 keV, potentially from a lesser contribution of neutral atomic silicon.« less

The effect of local atomic structure on the optical properties of GeSi self-assembled islands buried in silicon matrix

NASA Astrophysics Data System (ADS)

Demchenko, I. N.; Lawniczak-Jablonska, K.; Kret, S.; Novikov, A. V.; Laval, J.-Y.; Zak, M.; Szczepanska, A.; Yablonskiy, A. N.; Krasilnik, Z. F.

2007-03-01

The local atomic structure of GeSi self-assembled islands buried in a silicon matrix strongly influences the optical properties of such systems. In the present paper this structure was determined by x-ray absorption fine-structure (XAFS) spectroscopy and high resolution transmission electron microscopy (HRTEM) and used to build a schematic description of the band structure model. Quantitative analysis of the extended XAFS (EXAFS) spectrum was performed for three coordination shells around the Ge absorbing atom with multiple scattering taken into account. It was proved that the coordination number of elements in an alloy resulting from EXAFS analysis for all three coordination spheres (i.e. 'mixing degree' parameters) cannot be taken as the concentration of alloy but can be used together with a proper model of the alloy unit cell to calculate a realistic concentration. The fraction of Ge calculated in this way is consistent with HRTEM results. The found model of the unit cell was used to generate a x-ray absorption near edge structure spectrum by ab initio calculations. This approach yielded a spectrum in good agreement with the experimental one. The information gained from XAFS and HRTEM was then used for calculation of the band structure diagram. Results of the calculation are discussed and compared with the experimental photoluminescence spectrum.

Deposition of tetracene thin films on SiO2/Si substrates by rapid expansion of supercritical solutions using carbon dioxide

NASA Astrophysics Data System (ADS)

Fujii, Tatsuya; Takahashi, Yuta; Uchida, Hirohisa

2015-03-01

We report on a novel deposition technique of tetracene (naphthacene) thin films on SiO2/Si substrates by rapid expansion of supercritical solutions (RESS) using CO2. Optical microscopy and scanning electron microscopy show that the thin films consist of a high density of submicron-sized grains. The growth mode of the grains followed the Volmer-Weber mode. X-ray diffraction shows that the thin films have regularly arranged structures in both the horizontal and vertical directions of the substrate. A fabricated top-contacted organic thin-film transistor with the tetracene active layer showed p-type transistor characteristics with a field-effect mobility of 5.1 × 10-4 cm2 V-1 s-1.

Very high laser-damage threshold of polymer-derived Si(B)CN-carbon nanotube composite coatings.

PubMed

Bhandavat, R; Feldman, A; Cromer, C; Lehman, J; Singh, G

2013-04-10

We study the laser irradiance behavior and resulting structural evolution of polymer-derived silicon-boron-carbonitride (Si(B)CN) functionalized multiwall carbon nanotube (MWCNT) composite spray coatings on copper substrate. We report a damage threshold value of 15 kWcm(-2) and an optical absorbance of 0.97 after irradiation. This is an order of magnitude improvement over MWCNT (1.4 kWcm(-2), 0.76), SWCNT (0.8 kWcm(-2), 0.65) and carbon paint (0.1 kWcm(-2), 0.87) coatings previously tested at 10.6 μm (2.5 kW CO2 laser) exposure. Electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy suggests partial oxidation of Si(B)CN forming a stable protective SiO2 phase upon irradiation.

Integrating photonic crystals in thin film silicon photovoltaics

NASA Astrophysics Data System (ADS)

O'Brien, P. G.; Chutinan, A.; Ozin, G. A.; Kherani, N. P.; Zukotynski, S.

2010-06-01

Wave-optics analysis is performed to investigate the benefits of integrating photonic crystals into micromorph cells. Specifically, we theoretically investigate two novel micromorph cells which integrate photonic crystals and compare their optical performance with that of conventional micromorph cells. In the first innovative micromorph cell configuration the intermediate reflector is a selectively transparent and conducting photonic crystal (STCPC). In the second micromorph cell its bottom μc-Si:H cell is structured in the form of an inverted opal. Our results show that with the AM1.5 solar spectrum at normal incidence the current generated in a conventional micromorph cell is increased from 12.1 mA/cm2 to 13.0 mA/cm2 when the bottom μc-Si:H cell is structured in the form of an inverted opal. However, the current generated in the micromorph cell can be increased to as much as 13.7 mA/cm2 when an STCPC is utilized as the intermediate reflector. Furthermore, the thickness of the μc-Si:H opal must be relatively large in order to absorb a sufficient amount of the solar irradiance, which is expected to degrade the electrical performance of the device. In contrast, our results suggest that STCPC intermediate reflectors are a viable technology that could potentially enhance the performance of micromorph cells.

Micropore and nanopore fabrication in hollow antiresonant reflecting optical waveguides

PubMed Central

Holmes, Matthew R.; Shang, Tao; Hawkins, Aaron R.; Rudenko, Mikhail; Measor, Philip; Schmidt, Holger

2011-01-01

We demonstrate the fabrication of micropore and nanopore features in hollow antiresonant reflecting optical waveguides to create an electrical and optical analysis platform that can size select and detect a single nanoparticle. Micropores (4 μm diameter) are reactive-ion etched through the top SiO2 and SiN layers of the waveguides, leaving a thin SiN membrane above the hollow core. Nanopores are formed in the SiN membranes using a focused ion-beam etch process that provides control over the pore size. Openings as small as 20 nm in diameter are created. Optical loss measurements indicate that micropores did not significantly alter the loss along the waveguide. PMID:21922035

Micropore and nanopore fabrication in hollow antiresonant reflecting optical waveguides.

PubMed

Holmes, Matthew R; Shang, Tao; Hawkins, Aaron R; Rudenko, Mikhail; Measor, Philip; Schmidt, Holger

2010-01-01

We demonstrate the fabrication of micropore and nanopore features in hollow antiresonant reflecting optical waveguides to create an electrical and optical analysis platform that can size select and detect a single nanoparticle. Micropores (4 μm diameter) are reactive-ion etched through the top SiO(2) and SiN layers of the waveguides, leaving a thin SiN membrane above the hollow core. Nanopores are formed in the SiN membranes using a focused ion-beam etch process that provides control over the pore size. Openings as small as 20 nm in diameter are created. Optical loss measurements indicate that micropores did not significantly alter the loss along the waveguide.

Resonant inelastic light scattering and photoluminescence in isolated nc-Si/SiO{sub 2} quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bairamov, F. B., E-mail: Bairamov@mail.ioffe.ru; Toporov, V. V.; Poloskin, E. D.

2013-05-15

Observation at the room temperature the spectra of the resonant inelastic light scattering by the spatially confined optical phonons as well as the excitonic luminescence caused by confinement effects in the ensemble of isolated quantum dots (QDs) nc-Si/SiO{sub 2} is reported. It is shown that the samples investigated are high purity and high crystalline perfection quality nc-Si/SiO{sub 2} QDs without amorphous phase {alpha}-Si and contaminants. Comparison between the experimental data obtained and phenomenological model of the strong space confinement of optical phonons revealed the need of the more accurate form of the weighted function for the confinement of optical phonons.more » It is shown that simultaneous detection of the inelastic light scattering by the confinement of phonons and the excitonic luminescence spectra by the confined electron-hole pairs in the nc-Si/SiO{sub 2} QDs allows selfconsistently to determine more accurate values of the diameter of the nc-Si/SiO{sub 2} QDs.« less

Investigation on nonlinear optical properties of MoS2 nanoflakes grown on silicon and quartz substrates

NASA Astrophysics Data System (ADS)

Bayesteh, Samaneh; Zahra Mortazavi, Seyedeh; Reyhani, Ali

2018-05-01

In this study, MoS2 nanoflakes were directly grown on different substrates—Si/SiO2 and quartz—by one-step thermal chemical vapor deposition using MoO3 and sulfide powders as precursors. Scanning electron microscopy and x-ray diffraction patterns demonstrated the formation of MoS2 structures on both substrates. Moreover, UV-visible and photoluminescence analysis confirmed the formation of MoS2 few-layer structures. According to Raman spectroscopy, by assessment of the line width and frequency shift differences between the and A 1g, it was inferred that the MoS2 grown on the silicon substrate was monolayer and that grown on the quartz substrate was multilayer. In addition, open-aperture and close-aperture Z-scan techniques were employed to study the nonlinear optical properties including nonlinear absorption and nonlinear refraction of the grown MoS2. All experiments were performed using a diode laser with a wavelength of 532 nm as the light source. It is noticeable that both samples demonstrate obvious self-defocusing behavior. The monolayer MoS2 grown on the silicon substrate displayed considerable two-photon absorption while, the multilayer MoS2 synthesized on the quartz exhibited saturable absorption. In general, few-layered MoS2 would be useful for the development of nanophotonic devices like optical limiters, optical switchers, etc.

Pressure-induced structural transition in chalcopyrite ZnSiP 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhadram, Venkata S.; Krishna, Lakshmi; Toberer, Eric S.

The pressure-dependent phase behavior of semiconducting chalcopyrite ZnSiP 2 was studied up to 30 GPa using in situ X-ray diffraction and Raman spectroscopy in a diamond-anvil cell. A structural phase transition to the rock salt type structure was observed between 27 and 30 GPa, which is accompanied by soft phonon mode behavior and simultaneous loss of Raman signal and optical transmission through the sample. The high-pressure rock salt type phase possesses cationic disorder as evident from broad features in the X-ray diffraction patterns. The behavior of the low-frequency Raman modes during compression establishes a two-stage, order-disorder phase transition mechanism. Themore » phase transition is partially reversible, and the parent chalcopyrite structure coexists with an amorphous phase upon slow decompression to ambient conditions.« less

Development of a high-voltage waveguide photodetector comprised of Schottky diodes and based on the Ge-Si structure with Ge quantum dots for portable thermophotovoltaic converters

NASA Astrophysics Data System (ADS)

Pakhanov, N. A.; Pchelyakov, O. P.; Yakimov, A. I.; Voitsekhovskii, A. V.

2017-03-01

This paper demontstrates the possibility of developing a high-voltage waveguide photodetector comprised of Schottky diodes and based on a Au/Ge — Si structure with Ge quantum dots pseudomorphic to a silicon matrix, which ensures an increase in the external quantum yield and open-circuit voltage. It is shown on this photodetector that there is a great increase and broadening in sensitivity up to λ = 2.1 μm, which coincides with the main radiation range of a black (gray) body at the emitter temperatures from 1200 to 1700 °C, practically used in thermophotovoltaic converters. This state of the ensemble of Ge quantum dots by means of molecular beam epitaxy can be obtained only under the condition of low growth temperature (250-300 °C). It is established that, below the Si absorption edge, photoresponse on the photodetectors under consideration is determined by two main mechanisms: absorption on the ensemble of Ge quantum dots and Fowler emission. It is shown by the analysis of the Raman scattering spectra on the optical photons of Ge-Si structures that the quantum efficiency of photodetectors based on them in the first case is due to the degree of nonuniform stress relaxation in the array of Ge quantum dots. The photoresponse directly associated with the Ge quantum dots is manifested on Schottky diodes with a superthin intermediate oxide layer SiO2, which eliminates the second mechanism. In further development, the proposed photodetector architecture with pseudomorphic Ge quantum dots can be used both for portable thermophotovoltaic converters and fiber-optic data transmission systems at wavelengths corresponding to basic telecommunication standards (λ = 0.85, 1.3 and 1.55, 1.3, and 1.55 μm) on the basis of silicon technologies.

Giant (12 ×12 ) and (4 ×8 ) reconstructions of the 6 H -SiC(0001) surface obtained by progressive enrichment in Si atoms

NASA Astrophysics Data System (ADS)

Martrou, David; Leoni, Thomas; Chaumeton, Florian; Castanié, Fabien; Gauthier, Sébastien; Bouju, Xavier

2018-02-01

Silicon carbide (SiC) is nowadays a major material for applications in high power electronics, quantum optics, or nitride semiconductors growth. Mastering the surface of SiC substrate is crucial to obtain reproducible results. Previous studies on the 6 H -SiC(0001) surface have determined several reconstructions, including the (√{3 }×√{3 }) -R 30∘ and the (3 ×3 ) . Here, we introduce a process of progressive Si enrichment that leads to the formation of two reconstructions, the giant (12 ×12 ) and the (4 ×8 ) . From electron diffraction and tunneling microscopy completed by molecular dynamics simulations, we build models introducing a type of Si adatom bridging two Si surface atoms. Using these Si bridges, we also propose a structure for two other reconstructions, the (2 √{3 }×2 √{3 }) -R 30∘ and the (2 √{3 }×2 √{13 } ). We show that five reconstructions follow each other with Si coverage ranging from 1 and 1.444 monolayer. This result opens the way to greatly improve the control of 6 H -SiC(0001) at the atomic scale.

The role of the substrate in Graphene/Silicon photodiodes

NASA Astrophysics Data System (ADS)

Luongo, G.; Giubileo, F.; Iemmo, L.; Di Bartolomeo, A.

2018-01-01

The Graphene/Silicon (Gr/Si) junction can function as a Schottky diode with performances strictly related to the quality of the interface. Here, we focus on the substrate geometry and on its effects on Gr/Si junction physics. We fabricate and study the electrical and optical behaviour of two types of devices: one made of a Gr/Si planar junction, the second realized with graphene on an array of Si nanotips. We show that the Gr/Si flat device exhibits a reverse photocurrent higher than the forward current and achieves a photoresponsivity of 2.5 A/W. The high photoresponse is due to the charges photogenerated in Si below a parasitic graphene/SiO2/Si structure, which are injected into the Gr/Si junction region. The other device with graphene on Si-tips displays a reverse current that grows exponentially with the bias. We explain this behaviour by taking into account the tip geometry of the substrate, which magnifies the electric field and shifts the Fermi level of graphene, thus enabling fine-tuning of the Schottky barrier height. The Gr/Si-tip device achieves a higher photoresponsivity, up to 3 A/W, likely due to photocharge internal multiplication.

Effect of cell thickness on the electrical and optical properties of thin film silicon solar cell

NASA Astrophysics Data System (ADS)

Zaki, A. A.; El-Amin, A. A.

2017-12-01

In this work Electrical and optical properties of silicon thin films with different thickness were measured. The thickness of the Si films varied from 100 to 800 μm. The optical properties of the cell were studied at different thickness. A maximum achievable current density (MACD) generated by a planar solar cell, was measured for different values of the cell thickness which was performed by using photovoltaic (PV) optics method. It was found that reducing the values of the cell thickness improves the open-circuit voltage (VOC) and the fill factor (FF) of the solar cell. The optical properties were measured for thin film Si (TF-Si) at different thickness by using the double beam UV-vis-NIR spectrophotometer in the wavelength range of 300-2000 nm. Some of optical parameters such as refractive index with dispersion relation, the dispersion energy, the oscillator energy, optical band gap energy were calculated by using the spectra for the TF-Si with different thickness.

Thermal Annealing Effect on Optical Properties of Binary TiO₂-SiO₂ Sol-Gel Coatings.

PubMed

Wang, Xiaodong; Wu, Guangming; Zhou, Bin; Shen, Jun

2012-12-24

TiO₂-SiO₂ binary coatings were deposited by a sol-gel dip-coating method using tetrabutyl titanate and tetraethyl orthosilicate as precursors. The structure and chemical composition of the coatings annealed at different temperatures were analyzed by Raman spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. The refractive indices of the coatings were calculated from the measured transmittance and reflectance spectra. An increase in refractive index with the high temperature thermal annealing process was observed. The Raman and FTIR results indicate that the refractive index variation is due to changes in the removal of the organic component, phase separation and the crystal structure of the binary coatings.

Design and fabrication of MEMS devices using the integration of MUMPs, trench-refilled molding, DRIE and bulk silicon etching processes

NASA Astrophysics Data System (ADS)

Wu, Mingching; Fang, Weileun

2005-03-01

This work integrates multi-depth DRIE etching, trench-refilled molding, two poly-Si layers MUMPs and bulk releasing to improve the variety and performance of MEMS devices. In summary, the present fabrication process, named MOSBE II, has three merits. First, this process can monolithically fabricate and integrate poly-Si thin-film structures with different thicknesses and stiffnesses, such as the flexible spring and the stiff mirror plate. Second, multi-depth structures, such as vertical comb electrodes, are available from the DRIE processes. Third, a cavity under the micromachined device is provided by the bulk silicon etching process, so that a large out-of-plane motion is allowed. In application, an optical scanner driven by the self-aligned vertical comb actuator was demonstrated. The poly-Si micromachined components fabricated by MOSBE II can further integrate with the MUMPs devices to establish a more powerful MOEMS platform.

The controlled growth of GaN microrods on Si(111) substrates by MOCVD

NASA Astrophysics Data System (ADS)

Foltynski, Bartosz; Garro, Nuria; Vallo, Martin; Finken, Matthias; Giesen, Christoph; Kalisch, Holger; Vescan, Andrei; Cantarero, Andrés; Heuken, Michael

2015-03-01

In this paper, a selective area growth (SAG) approach for growing GaN microrods on patterned SiNx/Si(111) substrates by metal-organic chemical vapor deposition (MOCVD) is studied. The surface morphology, optical and structural properties of vertical GaN microrods terminated by pyramidal shaped facets (six { 10 1 bar 1} planes) were characterized using scanning electron microscopy (SEM), room temperature photoluminescence (PL) and Raman spectroscopy, respectively. Measurements revealed high-quality GaN microcolumns grown with silane support. Characterized structures were grown nearly strain-free (central frequency of Raman peak of 567±1 cm-1) with crystal quality comparable to bulk crystals (FWHM=4.2±1 cm-1). Such GaN microrods might be used as a next-generation device concept for solid-state lighting (SSL) applications by realizing core-shell InGaN/GaN multi-quantum wells (MQWs) on the n-GaN rod base.