Device Optimization of Tris-Aluminum (Alq3) Based Bilayer Organic Light Emitting Diode Structures

In this work we present detailed analysis of the emitted radiation spectrum from tris(8-hydroxyquinoline) aluminum (Alq3) based bilayer OLEDs as a function of: the choice of cathode, the thickness of organic layers, and the position of the hole transport layer/Alq3 interface. The calculations fully take into account dispersion in the glass substrate, the indium tin oxide anode, and in the organic layers, as well as the dispersion in the metal cathode. Influence of the incoherent transparent substrate (1 mm glass substrate) is also fully accounted for. Four cathode structures have been considered: Mg/Ag, Ca/Ag, LiF/Al, and Ag. For the hole transport layer, N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) and N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) were considered. As expected, emitted radiation is strongly dependent on the position of the emissive layer inside the cavity and its distance from the metal cathode. Although our optical model for an OLED does not explicitly include exciton quenching in vicinity of the metal cathode, designs placing the emissive layer near the cathode are excluded to avoid unrealistic results. Guidelines for designing devices with optimum emission efficiency are presented. Finally, several different devices were fabricated and characterized and experimental and calculated emission spectra were compared

DETERMINATION OF MOLECULAR CONSTANTS OF THE X~4Σg−(v=4−7)\tilde{X}^{4}\Sigma^{-}_{g}(v= 4-7) LEVELS OF C2+C_{2}^{+} USING STIMULATED EMISSION PUMPING SPECTROSCOPY

Author Institution: Code 6174, Naval Research Lab, 4555 Overlook Ave.; Institut f\""{u}r Physikalische Chemie, Universit\""at BaselUsing stimulated emission pumping (SEP) spectroscopy, vibrationally excited levels of the $\tilde{X}^{4}\Sigma^{-}_{g}$ ground electronic state of $C_{2}^{+}$ were characterized. Transitions were detected by decreased total fluorescence from laser-excited $\tilde{B}^{4}\Sigma^{-}_{u}$ levels. To obtain the 2-photon spectra, a modulation scheme which discriminated against one-photon fluorescence signals was successfully employed. Molecular constants determined for the $C^{+}_{2}\tilde{X}^{4}\Sigma^{-}_{g} (v=4-7)$ levels are presented

Open chromatin in grapevine marks candidate CREs and with other chromatin features correlates with gene expression

Vitis vinifera is an economically important crop and a useful model in which to study chromatin dynamics. In contrast to the small and relatively simple genome of Arabidopsis thaliana, grapevine contains a complex genome of 487 Mb that exhibits extensive colonization by transposable elements. We used Hi-C, ChIP-seq and ATAC-seq to measure how chromatin features correlate to the expression of 31 845 grapevine genes. ATAC-seq revealed the presence of more than 16 000 open chromatin regions, of which we characterize nearly 5000 as possible distal enhancer candidates that occur in intergenic space > 2 kb from the nearest transcription start site (TSS). A motif search identified more than 480 transcription factor (TF) binding sites in these regions, with those for TCP family proteins in greatest abundance. These open chromatin regions are typically within 15 kb from their nearest promoter, and a gene ontology analysis indicated that their nearest genes are significantly enriched for TF activity. The presence of a candidate cis-regulatory element (cCRE) > 2 kb upstream of the TSS, location in the active nuclear compartment as determined by Hi-C, and the enrichment of H3K4me3, H3K4me1 and H3K27ac at the gene are correlated with gene expression. Taken together, these results suggest that regions of intergenic open chromatin identified by ATAC-seq can be considered potential candidates for cis-regulatory regions in V. vinifera. Our findings enhance the characterization of a valuable agricultural crop, and help to clarify the understanding of unique plant biology

Studies of thin strained InAs, AlAs, and AlSb layers by spectroscopic ellipsometry

The optical constants for thin layers of strained InAs, AlAs, and AlSb have been investigated by spectroscopic ellipsometry and multi-sample analyses. These materials are important for high-speed resonant tunneling diodes in the AlAs/InAs/In0.53Ga0.47As and AlSb/InAs material systems. Understanding the optical properties for these thin layers is important for developing in situ growth control using spectroscopic ellipsometry. Ex situ room-temperature measurements were made on multiple samples. The resulting fitted optical constants are interpreted as apparent values because they are dependent on the fit model and sample structure. These apparent optical constants for very thin layers can be dependent on thickness and surrounding material, and are generally applicable only for layers found in a similar structural context. The critical point features of optical constants for the strained layers and for the thin unstrained cap layers were found to differ from bulk values, and three principle effects (strain, quantum confinement, and thin-barrier critical-point broadening) have been identified as responsible. Of these three, the broadening of the E1 and E1+ Δ 1 critical points for thin barrier material is the newest and most pronounced. This thin barrier effect is shown to be a separate effect from strain, and is also observable for the AlAs/GaAs system

Determination of AlAs optical constants by variable angle spectroscopic ellipsometry and a multisample analysis

Using variable angle spectroscopic ellipsometry, optical constants for AlAs (1.4-5.0 eV) are presented which are simultaneously compatible with measured data from four different samples. The below-gap index values are compatible with published prism measured values. The second derivative spectrum are compatible with published values above the direct band gap. The AlAs spectra is Kramers-Kronig self-consistent over the measured range and is compatible with published values from 0.6 to 1.4 eV. The optical constants for thin (\u3c50 \u3eÅ) GaAs caps on AlAs are shown to be different from bulk GaAs values and require special consideration when fitting ellipsometric data. For the thin GaAs caps, the E1 and E1+ Δ1 critical-point structure is shifted to higher energies as previously observed for GaAs quantum wells. Bulk AlAs optical constants are shown to be different from those of a thin (~20 Å) AlAs barrier layer embedded in GaAs. The thin barrier layer exhibits a highly broadened critical-point structure. This barrier broadening effect (AlAs) and the thin cap shifting effects (GaAs) have implications for in situ growth control schemes which make use of the E1 and E1+ Δ1, critical-point region