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The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is a worldwide non-interventional study of stroke prevention in patients with non-valvular AF.52,080 patients with newly diagnosed AF were prospectively enrolled from 2010 to 2016. 4121 (7.9%) of these patients were recruited in DACH [Germany (n = 3567), Austria (n = 465) and Switzerland (n = 89) combined], and 47,959 patients were from 32 countries in other regions worldwide (ORW). Hypertension was most prevalent in DACH and ORW (85.3% and 75.6%, respectively). Diabetes, hypercholesterolaemia, carotid occlusive disease and vascular disease were more prevalent in DACH patients vs ORW (27.6%, 49.4%, 5.8% and 29.0% vs 21.7%, 40.9%, 2.8% and 24.5%). The use of non-vitamin K antagonist oral anticoagulants (NOACs) increased more in DACH over time. Management of vitamin K antagonists was suboptimal in DACH and ORW (time in therapeutic range of INR ≥ 65% in 44.6% and 44.4% of patients or ≥ 70% in 36.9% and 36.0% of patients, respectively). Adjusted rates of cardiovascular mortality and MI/ACS were higher in DACH while non-haemorrhagic stroke/systemic embolism was lower after 2-year follow-up.Similarities and dissimilarities in AF management and clinical outcomes are seen in DACH and ORW. The increased use of NOAC was associated with a mismatch of risk-adapted anticoagulation (over-and-undertreatment) in DACH. Suboptimal control of INR requires educational activities in both regional groups. Higher rates of cardiovascular death in DACH may reflect the higher risk profile of these patients and lower rates of non-haemorrhagic stroke could be associated with increased NOAC use.

An electron-transporting triazole (Tz) and hole transporting carbazole (Cz) moieties were introduced into the fluorene structure via a Suzuki coupling reaction. The resulting material, 9-(4'-(9-(4'-(4,5-diphenyl-4H-1,2,4-triazol-3-y)-[1,1'-biphenyl]-4-yl)-9H-fluoren-9-yl)-[1,1'-biphenyl]-4-yl)-9H-carbazole (Tz-FL-Cz), was synthesized and can be used as the host layer in phosphorescent OLEDs. The synthesized material exhibits wide energy gap (3.46 eV). The absorption and emission maximum of the Tz-FL-Cz was observed at 300 nm and 389 nm, respectively. Blue phosphorescent devices using Tz-FL-Cz as host material exhibited maximum current efficiency of 3.2 cd/A and power efficiency of 1.3 lm/W, respectively.

Polymer-capped silicon nanoparticles (Si NPs) were prepared using poly(vinylpyrrolidone) (PVP) as a protection layer to minimize the surface oxidation of the surface. The wet synthetic procedure were performed at room temperature via a one-pot synthesis. The PVP capped Si-NPs were characterized by thermo gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), high resolution transmission electron microscopy (HR-TEM) and field emission scanning electron microscopy (FE-SEM). HR-TEM micrograms confirm the presence of crystalline Si-NPs. The pattern by Selected Area Electron Diffraction (SAED) reveals (111), (220) lattice planes which are consistent with the cubic-structured crystalline silicon. The mean size of Si-NPs is estimated to be ca. 10 nm, which is larger than those from conventional wet synthetic methods for silicon quantum dots.

A series of fluorene-thiophene-based pi-conjugated copolymers, PFT2, PFT4, and PFT2BP, have been synthesized using the Suzuki coupling reaction. Compared to PFT2 and PFT2BP, PFT4 film showed clearly red-shifted UV-visible absorption and photoluminescence (PL) spectra with maxima at 474 and 597 nm, respectively. The optical and electrochemical properties of copolymers could be tuned by changing conjugation lengths of comonomer units from bithiophene (PFT2) to quaterthiophene (PFT4). Moreover, PFT4 containing quaterthiophene showed relatively lower optical band gap of 2.16 eV. The organic photovoltaic cells (OPVs) were fabricated using the copolymers as donor with a sandwich configuration of ITO/PEDOT:PSS/copolymer:PC71BM/LiF/Al. PFT4 showed the best device performance with the optimized power conversion efficiency (PCE) of 2.26% (J(SC) = 7.67 mA/cm2, V(OC) = 0.81 V, FF = 0.36). The higher OPV performance of PFT4 can be explained by its relatively low energy band gap and improved UV absorption property.

Two linear-type π -conjugated small molecules based on thiophene and benzothiadiazole, β -DH5TB(1) and β -DH5TB(2) , were synthesized using the Suzuki coupling reaction to have β -substituted solubilizing alkyl groups. The solubility of β -DH5TB s was significantly improved by changing the direction of the alkyl group compared to α -substituted oligothiophene ( α -DH5TB ). The relationship between the alkyl substitution pattern and the photovoltaic properties was investigated by measuring the optical and electrochemical properties and the film morphology. Among them, the 4-hexyl substituted β -DH5TB(2) showed the lowest optical band gap and HOMO level together with a red-shifted broad UV absorption. In addition, a high degree of molecular alignment was also observed in β -DH5TB(2) , indicative of good charge transport. The β -DH5TB(2) film showed higher field-effect mobility (μ FET ) of 6.28×10 −4 cm 2 V −1 s −1 than β -DH5TB(1) film. Owing to the improved solubility, two of the synthesized β -DH5TB s could be used as donor materials in solution-processed organic photovoltaic cells (OPVs), whereas the α -DH5TB :PC 71 BM blend film showed no photovoltaic properties due to the poor solubility of α -DH5TB . The improved absorption and molecular alignment of the β -DH5TB(2) yielded a device efficiency (0.98%) higher than that of β -DH5TB(1) .

This paper reports the synthesis and characterization of a new vinazene-based small molecule, 4,7-bis(2-(1-(2-ethylhexyl)-4,5-dicyanoimidazol-2-yl) vinyl)diketopyrrolopyrrole (EV-DPP). The known vinazene-based small molecule, 4,7-bis(2-(1-(2-ethylhexyl)-4,5-dicyanoimidazol-2-yl)vinyl)benzo[c][1,2,5]thiadizole (EV-BT), was also prepared for comparison. The benzothiadiazole unit in EV-BT was replaced with a DPP unit in EV-DPP because DPP units are strong absorbing chromospheres. The UV absorption maxima of EV-DPP film (λ max = 386, 573 nm) were greatly red shifted compared to the maxima of EV-BT film (λ max = 337, 444 nm). Our preliminary device work showed the possibility of the use of EV-DPP as an electron acceptor in OPVs. The P3HT: EV-DPP film showed a better power conversion efficiency of 0.02% compared to P3HT: EV-BT due to the preferable UV absorption characteristics of EV-DPP.

Poly(3,4-ethylenedioxythiophene) (PEDOT)-indium tin oxide (ITO) nanocomposites were synthesized via a solution route. The electrochromic behavior of the devices was investigated in terms of particle sizes, dispersibility and electrical conductivity of the nanocomposites. The electrical conductivity of PEDOT-ITO composite thin films were in the range of 0.1∼15 S/cm with transparency changes from 25% to 85%. The electrochromic properties of the nanocomposite as an active material for the devices (ECDs) are discussed in terms of conductivity and transparency. The electrochromic behavior was confirmed with colored state and blanched state at +3.1 V∼−2.9 V which transparency difference about 50∼60% at 600 nm. The switching speeds of the ECD are closely correlated with the changes in the electrical conductivity and the morphology of the nanocomposite.

New conjugated polymers based on benzo[1,2-b:4,5-b']dithiophene, poly(benzo[1,2-b:4,5-b'] dithiophene-alt-bithiophene) (PBT-2T) and poly(benzo[1,2-b:4,5-b']dithiophene-alt-terthiophene) (PBT-3T), have been synthesized via the Stille coupling reaction and their optical and electrochemical properties were characterized by UV-vis, photoluminescence (PL) and cyclic voltammetry (CV) measurements. Compared to PBT-2T, PBT-3T film showed clearly red-shifted UV-visible absorption and PL spectra with maxima at 511 and 653 nm, respectively. Especially, PBT-3T containing terthiophene showed very small optical band gap of 1.65 eV. The PBT-2T and PBT-3T showed the power conversion efficiencies of 0.25% and 0.34%, respectively, under AM 1.5 (100 m/cm2).

In this paper, we have synthesized a series of fluorene-thiophene-based copolymers by Suzuki coupling polymerization for the use of donor materials in organic photovoltaic cells (OPVs). New conjugated polymers have an electron-deficient moiety such as benzothiadiazole (BT), oxadiazole (OX) and triazole (TZ) or an electron-rich triphenylamine (TPA) moiety or both in the main chains as third or fourth comonomers. The photovoltaic properties of the polymers were varied by introduced electron- or hole-transporting units. The order in the efficiency of the photovoltaic cells was P1 (BT)

We introduced a benzothiadiazole unit into a small molecule conjugated system and determined the electronic features and organic photovoltaic cell (OPV) characteristics of the resulting material, 4,7-bis(5′-hexyl-2,2′-bithiophene-5-yl)benzothiadiazole ( DH5TB ). DH5TB showed remarkably red-shifted UV–vis absorption and photoluminescence (PL) emission spectra compared with α,α′-dihexyl-quinquethiophene ( DH5T ). The low energy band gap of 1.95 eV and good film morphology of DH5TB resulted in good OPV performance. We investigated the DH5TB :C 60 blend ratio dependence on OPV performance and further improved the efficiency by introducing a C 60 interlayer on top of the DH5TB :C 60 layer. In the present work, the best photovoltaic cells had a J SC of 4.75 mA/cm 2 , a V OC of 0.53 V, and a fill factor (FF) of 0.38, giving a power conversion efficiency of 0.97% under AM 1.5 (100 m/cm 2 ) without thermal annealing.

In this study, microwave annealing treatment was introduced into poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61butyric acid methyl ester (PCBM) and poly(9,9‘-dioctylfluorene-cobithiophene (PFT2):PCBM systems instead of thermal annealing treatment. In both systems, microwave annealing showed photovoltaic performane comparable to that of conventional thermal annealing. Through the UV-vis absorption, atomic force microscopy (AFM) and X-ray diffraction (XRD) studies, we were able to confirm that the microwave annealing increases the crystallization of the P3HT polymer chains.

The aromatic triazole is an interesting electron-injection/transport chromophore because it possesses high electron affinity and thermal stability. In organic lighting-emitting diodes (OLEDs), highly electron-deficient triazole (Tz) derivates have been demonstrated to have more efficient electron-transport and hole-blocking characteristics and have a higher stability to high current density than the oxadiazole derivates. In this study, we have successfully synthesized a star-shaped soluble oligomer,4-(4-butylphenyl)-3,5-bis(4-(5'-hexyl-2,2'-bithiophen-5-yl)phenyl)-4H-1,2,4-triazole(Tz-2T-Hex) via Suzuki coupling reaction. The Tz-2T-Hex shows a red-shifted UV-vis absorption spectrum than Tz-Br with a maximum at 380 nm, due to the introduction of two bithiophene units at both ends. As film, Tz-2T-Hex showed the PL maximum at 530 nm. Tz-2T-Hex emitted light of a white color with the CIE coordinates (0.32 and 0.34).

The ink-jet printing method is an important process in display industry due to the low-cost production of large-scale electronic devices. In this work, we prepared the nanoparticle indium tin oxide (ITO) solutions for ink-jet printing and characterized the electrical, structural and morphological properties of the film. The improvement of conductivity after reduction process was correlated with the sharpening of the diffraction peak as proved by X-ray diffraction measurement. The ITO inks was coated on a glass by spin-coating process and patterned by the ink-jet printing technique using a 50 μm diameter ink-jet nozzle. The sheet resistance and optical transmission of ITO thin film was ca. 50∼300Ω/sq and ca. 75∼95%, respectively. The electrical resistance of patterned ITO lines showed about 5∼30 ∗ 103Ω. The detailed relationship between microstructure and properties are discussed.

Graphene sheets were produced by chemical reduction of graphite oxides in the solution of ionic conductive polymer, Nafion. The obtained graphene, coated with Nafion, can be re-dispersed in water, and readily forms stable dispersed state. The polymer-coated graphene had been characterized by FT-IR spectroscopy, UV–vis and X-ray photoelectron spectroscopy (XPS). The PEDOT film with Nafion-coated graphene increased significantly from 0.25 S/cm for pure PEDOT film and reached 12 S/cm. Further, the films of PEDOT doped Nafion-coated graphene had also higher conductivities compared to films doped PSS-coated graphene.

The ionic materials were added to PEDOT/PSS solution as secondary dopants. The conductivity of PEDOT/PSS film improved with adding ionic materials. The film of PEDOT/PSS with 1% pyridinium p-toluene-sulfonate showed the conductivity of 23S/cm, which is increased about three orders than the film of origin PEDOT/PSS with 0.028S/cm. The surface morphology of films of PEDOT/PSS mixture is investigated by atomic force microscope. The AFM showed the increasing of grain size with the addition of pyridinium p-toluene-sulfonate.

Temperature effects on deposition rate of silicon nitride films were characterized by building a neural network prediction model. The silicon nitride films were deposited by using a plasma enhanced chemical vapor deposition system and process parameter effects were systematically characterized by 26−1 fractional factorial experiment. The process parameters involved include a radio frequency power, pressure, temperature, SiH4, N2, and NH3 flow rates. The prediction performance of generalized regression neural network was drastically improved by optimizing multi-valued training factors using a genetic algorithm. Several 3D plots were generated to investigate parameter effects at various temperatures. Predicted variations were experimentally validated. The temperature effect on the deposition rate was a complex function of parameters but N2 flow rate. Larger decreases in the deposition rate with the temperature were only noticed at lower SiH4 (or higher NH3) flow rates. Typical effects of SiH4 or NH3 flow rate were only observed at higher or lower temperatures. A comparison with the refractive index model facilitated a selective choice of either SiH4 or NH3 for process optimization.

Computer prediction models are crucial to control complex plasma processes. A new plasma model was constructed by using a radial basis function network (RBFN) and genetic algorithm (GA). The GA was used to search for an optimized set of training factors. This technique was evaluated with the plasma etching data. The etching of silica thin film was conducted in an inductively coupled plasma. The etch responses modelled include aluminum (Al) etch rate, silica etch rate, Al selectivity, silica profile angle, and silica sidewall roughness. For comparison, conventional RBFN models as well as four types of statistical regression models were constructed . Compared to conventional RBFN models, GA-RBFN models exhibited improved predictions of more than 20% for Al etch rate, Al selectivity, and silica sidewall roughness. For the remaining two etch responses, both GA-RBFN and RBFN models were almost comparable. Compared to statistical regression models, GA-RBFN demonstrated improved predictions for nearly all etch responses. The improvement was even more than 35% for the Al selectivity and silica sidewall roughness. The comparisons revealed that the presented method can be effectively used to construct improved prediction models for plasma control.

Using a wavelet, a profile nonuniformity was characterized and applied to a tungsten etching conducted in a SF 6 helicon plasma. The profile nonuniformity was examined as a function of process parameters, including radio frequency source power, bias power, SF 6 flow rate, and substrate temperature. It was correlated to the etch rate nonuniformity or the fluorine radical measured by an optical emission spectroscopy. The profile nonuniformity increased with increasing all parameters but the source power. Etch mechanisms were estimated by investigating the nonuniformity dependency on ion or radical density distribution.

The introduction of a low band-gap oligomer, oligo(benzo[1,2,5]thiadiazole-alt-3,3'''-dihexylquaterthiophene) (BT4T) improved the performance of P3HT:PCBM bulk heterojunction organic photovoltaic cells due to improved UV-vis absorption and increased P3HT crystallinity.

We present a comprehensive study of the electrical, optical, and structural properties of wurtzite GaN films grown under various initial growth conditions The GaN films were grown directly on sapphire substrates using GaN nucleation layers by a Riber 3200 system with a radio-frequency plasma source. In situ reflection high-energy electron diffraction (RHEED) reveals a strong correlation between nucleation conditions, including the nitridation step, and the final surface reconstruction of the GaN thin film. Well-defined reconstruction patterns, primarily (2 � 2) and(4 � 4), are observed for some of the nucleation conditions. Hall mobility, photoluminescence (PL), X-ray rocking curve data, and transmission electron microscopy (TEM) measurements are usedto interpret the observedrelationship. The results show that for the conditions investigated, an unreconstructed (1 � 1) surface after growth correlates with improved electrical, optical, andstructural properties. The surface reconstructedthin film exhibits a strong columnar growth with inversion domains (IDs). We attribute the degraded characteristics to the presence of a mixture of both polarities in the films with reconstruction. r 2001 Publishedby Elsevier Science B.V.

A new low-band gap polymer containing thiophene and cyclopentadiene, poly(5,2,2'-dioctyldithio-phenylcyclopentadiene) (PDTCP), has been synthesized via the FeCl3 oxidative polymerization. PDTCP showed a broad absorption band and a low energy band gap of 1.82 eV. The photoluminescence (PL) of PDTCP is completely quenched upon addition of PCBM indicative of efficient charge transfer. Bulk heterojunction organic photovoltaic cells (OPVs) fabricated from PDTCP as an electron donor showed an open-circuit voltage (V(OC)) of 0.50 V, a short-circuit current (J(SC)) of 1.24 mA/cm2, and the power conversion efficiency of up to 0.20% under AM 1.5 (100 mW/cm2).

A white light-emitting diode was fabricated by preparing multilayer emitting films with an inserted buffer layer. The device structures are ITO/PEDOT:PSS/Emissive layer/LiF/Al. The emissive layer comprises a yellow-emitting layer of Poly[9,9-dioctylfluorenyl-2,7-diyl]-co-1,4-benzo-(2,1,3)-thiadiazole (F8BT), a blue-emitting layer of Poly[9,9-di-(2'-ethylhexyl)fluorenyl-2,7-diyl] (BEHF) and PEDOT:PSS as a buffer layer between the emission layers. The solution processed multi-layer polymer light-emitting diodes (PLED) were prepared by introduction of a water-soluble buffer layer between organic solvent soluble layers. We present white organic light-emitting diodes (WOLEDs) that has bilayer emission zones. This device exhibits a brightness of 280 cd/m2 and emission efficiency of 1.18 cd/A at 12.6 V. The device with a doped PEDOT:PSS layer and a thicker blue-emission layer exhibits CIE color coordinates of (0.30, 0.34), which is close to the white coordinates of (0.33, 0.33) used by the standard CIE color coordinates.

An electron-transporting triazole (Tz) unit was introduced into the fluorene-thiophene-based copolymer backbone via a Suzuki coupling reaction. The resulting copolymer, poly[9,9'-dioctyl-fluorene-co-5, 5-(4', 7'-di-2-thienyl-2', 1',3'-benzothiadiazole)-co-(4-(4-butyl-phenyl)-3, 5-diphenyl-4H-1,2,4]triazole)] (PF3TBTz), was soluble in common organic solvents and can be easily used as the active layer in organic photovoltaic cells (OPVs). By the introduction of the triazole unit, the OPV performance was nearly doubled from 0.62% (PF3TB) to 1.25% (PF3TBTz) under the same conditions. The higher performance can be explained by the improved surface morphology, resulting in better charge photogeneration and higher short circuit current (J(sc)) value in PF3TBTz in comparison with PF3TB. The possibility of the use of triazole units in OPV applications are described herein.

The regioregular hexyl-substituted poly(3,4-ethylenedioxy-2-thiophenylthiophene) (PEDOTt), structurally alternating copolymer of EDOT and thiophene, was synthesized via the Grignard Metathesis (GRIM) using catalytic amounts of Ni(dppp)Cl2. The products were characterized by 1H NMR spectroscopy, UV-vis spectroscopy and XRD. The alkyl-substituted conjugated polymer showed an enhancement of solubility in common organic solvents. Based on XRD data, the regioregular hexyl-substituted poly(3,4-ethylenedioxy-2-thiophenylthiophene) (PEDOTt) shows better crystallinity than the regiorandom hexyl-substituted PEDOTt owing to self-ordering. In addition, regioregular hexyl-PEDOTt has a conductivity of 0.788 S/cm by iodine doping.

We report a low-temperature aqueous solution growth of uniformly aligned ZnO nanorod arrays on flexible substrates. The substrate is Indium Tin Oxide (ITO) film coated on polyethylene terephthalate (PET). Solutions with five different concentrations of the precursors with equimolar Zinc Nitrate and Hexamethylenetetramine (HMT) in distilled water were prepared to systematically study the effect of precursor solution concentration on the structural and optical properties of ZnO nanorods. It was concluded that the precursor concentration have great influence on the morphology, crystal quality, and optical property of ZnO nanorods. The diameter, density, and orientation of the nanorods are dependent on the precursor solution concentration. X-ray diffraction and micro-Raman spectroscopy showed that the ZnO nanorods with the highest concentration of 50 mM were highly aligned and have the highest level of surface coverage. It was also found that the diameter and length of the nanorods increases upon increasing precursor solution concentration. This is the first systematic investigation of studying the effect of precursor solution concentration on the quality of ZnO nanorods grown on ITO/PET substrates by low-temperature solution method. We believe that our work will contribute to the realization of flexible organic-inorganic hybrid solar cell based on ZnO nanorods and conjugated polymer.

Films of Ag nanoislands (NIs) were successfully grown on two different transparent conducting oxide coated substrates (indium tin oxide (ITO) coated glass and indium oxide (In2O3) coated polyethylene terephthalate (PET) flexible film) by direct current (DC) magnetron sputtering. The morphology of the Ag NIs was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Both SEM and TEM confirm the formation of silver NIs. To amplify the localised surface plasmon resonance (SPR) effect, post-deposition annealing was performed at 200°C for 30 minutes in a nitrogen atmosphere, resulting in tuning the shape and size of the NIs. Optical transmission spectroscopy was performed in the ultraviolet–visible–near-infrared spectral region to examine the SPR characteristics of the Ag NIs deposited on ITO-glass and In2O3-PET. Post-deposition annealing is found to tune the SPR wavelength and results in strong enhancement of the SPR of the Ag NIs on both ITO-glass and In2O3-PET. DC magnetron sputtering and the post-deposition annealing technique can be applied for the growth of size-controlled Ag NIs. The result can be applied to the enhancement of the efficiency of organic light emitting diodes and solar cells.

A promising possibility for the quantitative analysis of X-ray absorption near edge structure (XANES) spectra of nanosized electrode materials is demonstrated. We used a 2D map representation technique, which utilizes the values of the first derivatives of the absorbance with respect to the inserted Li + content plotted over the two-dimensional space defined by the inserted Li + content (mole) versus photon energy (eV) as a single map. The technique was applied to XANES spectra of the LiyCoO system in the first Li + insertion reaction for determining the structural and electronic variations associated with the change in Li + content. The obtained show that the intensities of two peaks at 7725 and 7711 eV increased with the Li + content and the difference of intensity change of these two peaks carried out for successive couples of spectra yielded the largest changes at 1.05 and 1.98 mol of Li content. This approach for quantitative analysis of XANES without using conventional simulation techniques enable us to interpret X-ray absorption spectroscopy (XAS) as a quantitative analytical technique with greater confidence. © 2007 Elsevier B.V. All rights reserved.

Critical interdependent effects have been observed in the growth of AlGaAs/InGaAs quantum-well structures by molecular beam epitaxy. It is shown that statistical experimental design is an effective method for quickly optimizing complex device structures. This technique is very useful for the optimization of processes with a large number of interdependent parameters, and allows for the clear visualization and separation of complex interwoven effects. In the present work, we show the importance of the oxide desorption process for the optimal growth of AlGaAs-containing structures.

This paper presents a statistically designed experiment for systematic characterization of the molecular beam epitaxy (MBE) process to quantitatively describe the effects of process conditions on the qualities of grown films. This methodology is applied to a five-layer, undoped AlGaAs and InGaAs single quantum well structure grown on a GaAs substrate. Six input factors (time and temperature for oxide removal, substrate temperatures for AlGaAs and InGaAs layer growth, beam equivalent pressure of the As source and quantum well interrupt time) are examined by means of a Resolution IV, 2/sup 6-2/ fractional factorial design requiring sixteen trials. Several responses are characterized, including defect density, X-ray diffraction, and photoluminescence. Results indicate that the manipulation of each of the six factors over the ranges examined are statistically significant and lead to considerable variation in the responses. Following characterization, backpropagation neural networks are trained to model the process responses. The neural process models exhibit very good agreement with experimental results.

This paper presents the systematic characterization of the molecular beam epitaxy (MBE) process to quantitatively model the effects of process conditions on film qualities. A five-layer, undoped AlGaAs and InGaAs single quantum well structure grown on a GaAs substrate is designed and fabricated. Six input factors (time and temperature for oxide removal, substrate temperatures for AlGaAs and InGaAs layer growth, beam equivalent pressure of the As source and quantum well interrupt time) are examined by means of a fractional factorial experiment. Defect density, x-ray diffraction, and photoluminescence are characterized by a static response model developed by training back-propagation neural networks. In addition, two novel approaches for characterizing reflection high-energy electron diffraction (RHEED) signals used in the real-time monitoring of MBE are developed. In the first technique, principal component analysis is used to reduce the dimensionality of the RHEED data set, and the reduced RHEED data set is used to train neural nets to model the process responses. A second technique uses neural nets to model RHEED intensity signals as time series, and matches specific RHEED patterns to ambient process conditions. In each case, the neural process models exhibit good agreement with experimental results.

This paper introduces a novel technique for constructing an empirical model which relates RHEED intensity patterns to the physical characteristics of MBE grown thin films. A fractional factorial experiment is used to systematically characterize the growth of a five-layer, undoped AlGaAs-InGaAs single quantum well structure on a GaAs substrate as a function of time and temperature for oxide removal, substrate temperatures for AlGaAs and InGaAs layer growth, beam equivalent pressure of the As source and quantum well interrupt time. MBE growth takes place in a Varian Gen-II MBE system using substrate rotation, and RHEED signals are monitored for each experimental trial. RHEED pattern variation is used as an indicator of defect density, X-ray diffraction, and photoluminescence of the grown films. Principal component analysis is used to reduce the dimensionality of the RHEED data set, while maintaining the integrity of the information contained within. The reduced RHEED data set is used to train back-propagation neural networks to model the process responses. These models are quite accurate (about 3% RMSE on training data and less than 10% RMSE for test data), implying that the principal components are a reliable source of input data. Continued development will lead to models which provide a platform upon which to build an automated process control system for MBE growth.