Joseph Shinar

Glucose biosensors based on organic light-emitting devices structurally integrated with a luminescent sensing element

A platform for photoluminescence (PL) based biosensing is demonstrated for glucose. The sensor is structurally integrated, i.e., individually addressable organic light-emitting device (OLED) pixels (serving as the light source) and the sensing element are fabricated on glass or plastic substrates attached back-to-back. This results in a very compact, potentially miniaturizable sensor, which should strongly impact PL-based biosensor technology. The sensing element is an oxygen-sensitive dye coembedded with glucose oxidase in a thin film or dissolved in solution. The glucose biosensor is demonstrated for two OLED∕dye pairs: [blue OLED]∕[Ru dye] and [green OLED]∕[Pt dye]. Both PL-intensity and PL-lifetime modes are demonstrated for each pair; the lifetime mode eliminates the need for frequent sensor calibration. The sensor performance is evaluated in terms of design, dynamic range, limit of detection, and stability. The use of the glucose biosensor in conjunction with an oxygen sensor is also discussed.

An IR, optical, and electron‐spin‐resonance study of as‐deposited and annealed a‐Ge1−xCx: H prepared by rf sputtering in Ar/H2/C3H8

Hydrogenated amorphous germanium carbide (a‐Ge1−xCx: H ) films were prepared by rf sputtering, at various rf power levels and mixtures of Ar, H2, and propane. As in the case of a‐Si:H rf sputtered under similar conditions, the concentration of Ge–H bond, as determined by the IR absorption spectra, and the Tauc determined optical gap, generally increase as the rf power is decreased. The optical gap of the a‐Ge1−xCx: H films range from 0.85–2.3 eV, and the electron‐spin‐resonance defect spin densities from 6.5×1017 to 3×1018 spins/cm3. Auger spectroscopy was used to determine the C/Ge ratio and indicated that in most of the samples, this ratio was ≲0.15. Isochronal annealing up to 400u2009°C indicated that (i) Ge‐C segregation effects already initiated at 100u2009°C are greatly enhanced above 300u2009°C, (ii) at 300u2009°C C–H bonds are formed at the expense of Ge–H ones, and (iii) all of the hydrogen bonded to Ge and most of that bonded to carbon evolve out of the sample at or slightly below 400u2009°C.

Raman study of the network disorder in sputtered and glow discharge a‐Si:H films

We have carried out a comprehensive study of the Raman spectra of a‐Si:H films produced by the glow discharge (GD) and radio frequency sputtering (RFS) deposition techniques. The results show that the short‐range disorder (bond‐angle deviation), as measured by the width of the TO band (ΓTO), is larger in RFS than in GD a‐Si:H films. The intermediate‐range disorder (dihedral angle deviation), as measured by the ratio of the intensity of the TA band to that of the TO band (ITA/ITO), is generally larger in RFS than in GD a‐Si:H films. However, while the ITA/ITO values of RFS films remain relatively close to those of GD films when the interior is probed, the near surface of RFS films shows much larger values evidencing the existence of a significant disorder gradient along the growth axis. Together, these results indicate that the network order and homogeneity of RFS amorphous silicon is lower than those of GD for substrate temperatures that produce the hydrogenated material. These structural differences are ...

Optical properties of nanocrystalline silicon within silica gel monoliths

Described herein is the incorporation of nanocrystalline silicon nc-Si from porous silicon (PSi) in a silica matrix fabricated by the sol-gel technique that yields highly photoluminescent (PL) and optically transparent monoliths with uniformly distributed nc-Si inclusions or nanoclusters. The sample monoliths were prepared with PSi-derived nanoclusters (PSi-n) with average diameters of 14–45nm. Concentrated samples of PSi-n-exhibited blueshifted orange emission bands with maximum peaks between 600 and 750nm with PL emission intensities ten times stronger than those of the original PSi, while diluted samples exhibited UV to blue (350–450nm) emission bands. The PL quantum yield of the typical PSi-n monoliths was 44% higher than the native PSi. Light absorption measurements showed a linear response to laser powers before the saturation threshold at 80mW. PL bleaching following 3h of constant laser power exposure resulted in 90% reduction of the maximum initial PL. Mechanical and thermal stability properties ...

A study of plasma‐film interactions in He/H2, Ar/H2, and Xe/H2 radio frequency sputtered a‐Si:H

A study of plasma‐film interactions present during the deposition process of a‐Si:H prepared by radio frequency (rf) sputtering in 10 mTorr of either He, Ar, or Xe and 0.5 mTorr H2, at rf power levels of 0.27–3.3 W/cm2 (50–600 W), on nominally unheated substrates, is presented. Measurement techniques included scanning electron microscopy (SEM), infrared (IR) and optical absorption, and electron‐spin resonance (ESR). The SEM images indicated that the films prepared in He/H2 at low power are morphologically porous and/or columnar; the evidence suggests that as the rf power is increased, the islands coalesce to form larger ones and the images appear glassy and cracked. IRabsorption spectra indicated that the porous films undergo post‐depositional oxidation. A comparison between the observed deposition rates and the rates expected from previously published sputtering yields indicated that resputtering of the growing film is a dominant feature in films deposited in Ar/H2 and Xe/H2 but a weaker one in those gro...

Combinatorial fabrication and studies of 4,4'-bis(9-carbazolyl) biphenyl (CBP)-based UV-violet OLED arrays

Arrays of UV-violet [indium tin oxide (ITO)]/[copper phthalocyanine (CuPc)]/[4,4-bis(9- carbazolyl)biphenyl(CBP)]/[2-(4-biphenylyl)-5-(4-tert- butylphenyl)-1,3,4-oxadiazole(Bu-PBD)]/CsF/Al organic light- emitting devices (OLEDs), fabricated combinatorially using a sliding shutter technique, are described. Comparison of the electroluminescence spectrum with the photoluminescence spectrum of CBP indicates that the emission originates from the bulk of that layer. However, due to the high gap of CBP and the strong hole capture cross section of perylene contaminants, it was difficult to completely eliminate the emission from the latter. In arrays of devices in which the thickness of the CuPc and Bu-PBD were varied, but that of CBP was fixed at 50 nm, the optimal radiance R was obtained at CuPc and Bu-PBD thicknesses of 15 and 18 nm, respectively. At 10 mA/Cm2, R was 0.38 mW/cm2, i.e., the external quantum efficiency was 1.25%; R increased to ~1.2 mW/cm2 at 100 mA/cm2.

Photoluminescence-detected magnetic resonance (PLDMR) study of rubrene and oxygen-doped rubrene films and powders

A comprehensive photoluminescence (PL)-detected magnetic resonance (PLDMR) study of various vacuum-sealed rubrene films and powders is described. Three PLDMR features are observed and analyzed: (i) A negative (PL-quenching) triplet exciton (TE) resonance at T > 50K, due to reduced spin-dependent fusion of geminate TE pairs to singlet excitons (SEs). (ii) A positive (PL-enhancing) triplet resonance at T < 50K. This resonance is suspected to result from reduced quenching of SEs by a reduced population of polarons and nongeminate TEs, the latter due to the spin-dependent annihilation of TEs by polarons. (iii) A negative spin 1/2 (polaron) resonance, believed to be due to enhanced formation of trions at oxygen centers. As single crystal thin films of oxygen-doped rubrene exhibit exceptionally high room-temperature carrier mobility, the relation of this positive resonance to these transport properties is also discussed.

Electroluminescence- and electrically-detected magnetic resonance studies of spin one-half-polaron and singlet-exciton dynamics in multilayer small molecular organic light-emitting devices

The electroluminescence (EL)- and electrically-detected magnetic resonance (ELDMR and EDMR, respectively) of tris- (8-hydroxyquinoline) Al (Alq3)]/[buffer]/Al-based organic light-emitting devices (OLEDs) are described. Positive spin ½ ELDMR and EDMR observed at T<60K are similar to the typical photoluminescence-detected magnetic resonance of (pi) -conjugated polymers, and consequently attributed to enhanced polaron recombination and consequent reduction of singlet exciton quenching by trapped and free polarons. A negative spin ½ EL- and current-quenching (negative) resonance is observed at T>=60 K. Its amplitude increases with T, and it is much stronger in devices with an AlOx buffer layer than in those with a CsF buffer. Its behavior is consistent with magnetic resonance enhancement of the spin-dependent formation of dianions at the organic/cathode interface.

Novel bright small molecular white OLEDs

Bright [indium tin oxide (ITO)]/[N,N-diphenyl-N,N-bis(1- naphthyl-phenyl)-1,1-biphenyl-4,4-diamine(NPB)]/[2 wt.% perylene-doped 4,4-bis(9-carbazolyl) biphenyl (CBP)]/[2-(4- biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (Bu- PBD)]/[2 wt.% 4-(dicyano-methylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran (DCM1)-doped tris-(8-hydroxy quinoline) Al(Alq3)]/CsF/Al OLEDS are described. The electroluminescence (EL) spectra consist of blue and green bands at 453, 487, and 524 nm due to perylene and a red band at 600 nm due to DCM1, i.e., the emission zones are completely separated by the Bu-PBD. As the thickness of the NPB and perylene: CBP layers increases and that of the DCM1:alq3 layer decreases the intensity of the perylene emission increases strongly relative to the DCM1 emission. For 350 A thick NPB, 350 A thick perylene: CBP, 100 A Bu- PBD, and 150 A DCM1:Alq3, the onset voltage is 6.5 V, the brightness reaches 3750 Cd/m2 at 20 V, the efficiency is 2.4 Cd/A at 19V, and the (x,y) CIE coordinates are well within the white region. However, as the bias is increased the intensity of the perylene emission increases relative to the DCM1 emission, so (x,y) evolves from (0.42, 0.35) at 14V to (0.29, 0.32) at 21V. Both the layer thickness- and bias-dependence are believed to result from changes in the recombination zone and in the field-and cathode-mirror- induced quenching of the DCM1 singlet excitons.

Long-lived polarons and triplet excitons in ladder-type poly(p-phenylenes) and poly(p-phenylene ethynylenes)

Recent x-band optically detected magnetic resonance studies of spin 1/2 polaron and spin 1 triplet exciton dynamics in ladder-type poly(p-phenylene) and poly(p-phenylene ethynylene) (PPE) films and solutions are described. The results suggest that the polaron resonance is due to interchain polaron pairs with lifetimes 10 microsecond(s) <EQ (tau) <EQ 4 ms range. The absence of delayed fluorescence at such times as well as other observations lead to the conclusion that the mechanism responsible for this resonance is the nonradiative quenching of singlet excitons by the polarons, whose population decreases at the field-for- resonance. The full-field triplet pattern is 700 - 1200 G wide, consistent with a triplet localized on a phenylene ring. In frozen toluene solutions of PPE, the amplitudes (Delta) I/I of both the polaron and half-field triplet resonances decrease similarly with concentration, and increase similarly with laser power P as P(alpha ), where 1/3 <EQ (alpha) <EQ 1/2. Hence, the triplet resonance is believed to be due to triplet intrinsically trapped and stabilized at similar interchain sites. Possible scenarios which link the processes yielding the resonances are also discussed.