H1 Defects Research Articles

Dependence on hydrostatic pressure in two-dimensional triangular photonic crystals

Abstract The plane wave expansion method is used to calculate photonic band structures for transverse electric (TE) polarization, in a two-dimensional (2D) photonic crystal with a hexagonal lattice composed air holes with triangular cross sections embedded in a semiconductor (GaAs) background. This study focuses on the dependence of the GaAs dielectric constant on pressure and temperature. The air holes are isosceles triangles with fixed areas. We found that the width of the photonic band gap increases, when the internal angle of the triangle and the angle of rotation in the unit cell are increased at constant hydrostatic pressure values. The width of the photonic band gap remains unchanged when the hydrostatic pressure is increased at fixed internal and rotation angle values. In addition, when considering an H1 defect in the crystal, using the supercell technique, we find that the number of defective modes within the photonic band gap increases with the triangle rotation in the unit cell.

High figure of merit ultra-compact 3-channel parallel-connected photonic crystal mini-hexagonal-H1 defect microcavity sensor array

Abstract In this paper, a photonic crystal (PhC) butt-coupled mini-hexagonal-H1 defect (MHHD) microcavity sensor is proposed. The MHHD microcavity is designed by introducing six mini-holes into the initial H1 defect region. Further, based on a well-designed 1 ×3 PhC Beam Splitter and three optimal MHHD microcavity sensors with different lattice constants (a), a 3-channel parallel-connected PhC sensor array on monolithic silicon on insulator (SOI) is proposed. Finite-difference time-domain (FDTD) simulations method is performed to demonstrate the high performance of our structures. As statistics show, the quality factor (Q) of our optimal MHHD microcavity attains higher than 7×104, while the sensitivity (S) reaches up to 233 nm/RIU(RIU = refractive index unit). Thus, the figure of merit (FOM) >104 of the sensor is obtained, which is enhanced by two orders of magnitude compared to the previous butt-coupled sensors [1] , [2] , [3] , [4] . As for the 3-channel parallel-connected PhC MHHD microcavity sensor array, the FOMs of three independent MHHD microcavity sensors are 8071, 8250 and 8250, respectively. In addition, the total footprint of the proposed 3-channel parallel-connected PhC sensor array is ultra-compactness of 12.5 µm ×31 µm (width × length). Therefore, the proposed high FOM sensor array is an ideal platform for realizing ultra-compact highly parallel refractive index (RI) sensing.

Histone H1 defect in escort cells triggers germline tumor in Drosophila ovary

Drosophila ovary is recognized as one of the best model systems to study stem cell biology in vivo. We had previously identified an autonomous role of the histone H1 in germline stem cell (GSC) maintenance. Here, we found that histone H1 depletion in escort cells (ECs) resulted in an increase of spectrosome-containing cells (SCCs), an ovary tumor-like phenotype. Further analysis showed that the Dpp pathway is excessively activated in these SCC cells, while the expression of bam is attenuated. In the H1-depleted ECs, both transposon activity and DNA damage had increased dramatically, followed by EC apoptosis, which is consistent with the role of H1 in other somatic cells. Surprisingly, H1-depleted ECs acquired cap cell characteristics including dpp expression, and the resulting abnormal Dpp level inhibits SCC further differentiation. Most interestingly, double knockdown of H1 and dpp in ECs can reduce the number of SCCs to the normal level, indicating that the additional Dpp secreted by ECs contributes to the germline tumor. Taken together, our findings indicate that histone H1 is an important epigenetic factor in controlling EC characteristics and a key suppressor of germline tumor.

Automated optimization of photonic crystal slab cavities.

Thanks to their high quality factor, combined to the smallest modal volume, defect-cavities in photonic crystal slabs represent a promising, versatile tool for fundamental studies and applications in photonics. In paricular, the L3, H0, and H1 defects are the most popular and widespread cavity designs, due to their compactness, simplicity, and small mode volume. For these cavities, the current best optimal designs still result in Q-values of a few times 105 only, namely one order of magnitude below the bound set by fabrication imperfections and material absorption in silicon. Here, we use a genetic algorithm to find a global maximum of the quality factor of these designs, by varying the positions of few neighbouring holes. We consistently find Q-values above one million – one order of magnitude higher than previous designs. Furthermore, we study the effect of disorder on the optimal designs and conclude that a similar improvement is also expected experimentally in state-of-the-art systems.

A-SiO_x<Er> active photonic crystal resonator membrane fabricated by focused Ga^+ ion beam

We have fabricated thin erbium-doped amorphous silicon sub-oxide (a-SiOx<Er>) photonic crystal membrane using focused gallium ion beam (FIB). The photonic crystal is composed of a hexagonal lattice with a H1 defect supporting two quasi-doubly degenerate second order dipole states. 2-D simulation was used for the design of the structure and full 3-D FDTD (Finite-Difference Time-Domain) numerical simulations were performed for a complete analysis of the structure. The simulation predicted a quality factor for the structure of Q = 350 with a spontaneous emission enhancement of 7. Micro photoluminescence measurements showed an integrated emission intensity enhancement of ~2 times with a Q = 130. We show that the discrepancy between simulation and measurement is due to the conical shape of the photonic crystal holes and the optical losses induced by FIB milling.

Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy

In this study deep level transient spectroscopy has been performed on boron–nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration ( N A –N D )∼3×10 17 cm −3 . We observed a hole H 1 majority carrier and an electron E 1 minority carrier traps in the device having activation energies E v + 0.24 eV, E c −0.41 eV, respectively. The capture cross-section and trap concentration of H 1 and E 1 levels were found to be (5×10 −19 cm 2 , 2×10 15 cm −3 ) and (1.6×10 −16 cm 2 , 3×10 15 cm −3 ), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H 1 defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E 1 defect to a nitrogen donor.

Discussion of some “trap signatures” observed by admittance spectroscopy in CdTe thin-film solar cells

Considerable ambiguity and controversy exist concerning the defect signatures (H1, H2, and H3) frequently observed in admittance spectroscopy of thin-film CdTe solar cells. We prove that the commonly labeled H1 defects, observed in all devices in this study, are actually due to the freeze-out of the majority carriers in the neutral CdTe absorber. This freeze-out is evident in the temperature dependencies of capacitance, carrier concentration, and depletion region width. Contrary to intuitive expectation, the activation energy of freeze-out is less than, not identical to, that of the conductivity. In some other cases, H2 or H3 are observed and attributed to the back-contact potential barrier, rather than to the carrier emission from the traps. We extract the back-contact barrier height from the activation energy of the saturation current determined from the temperature-dependent current-voltage curves using the back-to-back diode model. The back-contact barrier height agrees well with the H2 or H3 energy determined by admittance spectroscopy. We present a more comprehensive and realistic equivalent circuit that includes the admittances from both the back-contact and the neutral absorber.

Impact of guided bone regeneration and defect dimension on wound healing at chemically modified hydrophilic titanium implant surfaces: an experimental study in dogs

The aim of the present study was to evaluate the impact of guided bone regeneration and defect dimension on wound healing at chemically modified titanium implant surfaces (modSLA). ModSLA implants were placed at chronic-type lateral ridge defects of different heights (H1-H4: 2, 4, 6 and 8 mm) and randomly allocated to either (a) GBR (polyethylene glycol membrane + biphasic calcium phosphate) or (b) untreated control. At 2 and 8 weeks (n=6 dogs each), dissected blocks were processed for histomorphometrical analysis [e.g., percentage linear fill (PLF), regenerated area (RA)]. At 8 weeks, both groups revealed comparable mean PLF (%) [ H1 (26.1 +/- 5.8)-H4 (60.4 +/- 11.8); GBR: H1 (8.3 +/- 5.3)-H4 (50.7 +/- 23.1)] and RA (mm(2)) [ H1 (2.5 +/- 0.4)-H4 (7.4 +/- 4.1); GBR: H1 (1.8 +/- 1.0)-H4 (10.8 +/- 5.9)] values. A significant difference was observed for the mean PLF values at H1 defects. It was concluded that (i) modSLA titanium implants supported bone regeneration and osseointegration at H1-H4 defects and (ii) the present GBR procedure did not seem to improve the outcome of vertical bone regeneration, but tended to increase the mean RA values.

The Influence of the Cylindrical Shape of the Nucleosomes and H1 Defects on Properties of Chromatin

We present a model improving the two-angle model for interphase chromatin (E2A model). This model takes into account the cylindrical shape of the histone octamers, the H1 histones in front of the nucleosomes, and the distance d between the in and outgoing DNA strands orthogonal to the axis of the corresponding nucleosome cylinder. Factoring these chromatin features in, one gets essential changes in the chromatin phase diagram: Not only the shape of the excluded-volume borderline changes but also the orthogonal distance d has a dramatic influence on the forbidden area. Furthermore, we examined the influence of H1 defects on the properties of the chromatin fiber. Thus, we present two possible strategies for chromatin compaction: The use of very dense states in the phase diagram in the gaps in the excluded-volume, borderline, or missing H1 histones can lead to very compact fibers. The chromatin fiber might use both of these mechanisms to compact itself at least locally. Line densities computed within the model coincident with the experimental values.

Enhancement and suppression of spontaneous emission by temperature tuning InAs quantum dots to photonic crystal cavities

We report on the control of the spontaneous emission rates in InAs self-assembled quantum dots weakly coupled to the mode of a modified H1 defect cavity in a two-dimensional photonic crystal slab. Changes in sample temperature are used to spectrally tune the exciton emission from a single quantum dot to the monopole mode of the microcavity. A Purcell enhancement of the spontaneous emission rate of up to a factor of 11.4 is seen on-resonance, while suppression by up to a factor of 4.4 is seen off-resonance. Also, a two orders of magnitude increase in the intensity of light detected from the exciton is measured when compared to a quantum dot in bulk GaAs.

Novel molecular defects of the δ-aminolevulinate dehydratase gene in a patient with inherited acute hepatic porphyria

Cloning and expression of the defective gene for delta-aminolevulinate dehydratase (ALAD) from the second of 2 German patients with ALAD deficiency porphyria (ADP), who had been originally reported by Doss et al. in 1979, were performed. Cloning of cDNAs for the defective ALAD were performed using Epstein-Barr virus (EBV)-transformed lymphoblastoid cells of the proband, and nucleotide sequences of cloned cDNA were determined. Two separate mutations of ALAD cDNA were identified in each ALAD allele. One was G457A, termed "H1," resulting in V153M substitution, while the other was a deletion of 2 sequential bases at T(818) and C(819), termed "H2," resulting in a frame shift with a premature stop codon at the amino acid position of 294. Using allele-specific oligonucleotide hybridization, the mother of the proband was shown to have an H1 defect, while using genomic DNA analysis, the father was shown to have an H2 defect. Expression of H1 cDNA in Chinese hamster ovary cells produced an ALAD protein with only a partial activity (10.65% +/- 1.80% of the normal), while H2 cDNA encoded no significant protein. These data thus demonstrate that the proband was associated with 2 novel molecular defects of the ALAD gene, 1 in each allele, and account for the extremely low ALAD activity in his erythrocytes ( approximately 1% of normal).

Multifrequency EPR,1HENDOR, and saturation recovery of paramagnetic defects in diamond films grown by chemical vapor deposition

Paramagnetic defects in free-standing polycrystalline chemical vapor deposition (CVD) diamond films have been studied using multifrequency electron paramagnetic resonance (EPR) (1--35 GHz), electron-nuclear double resonance (ENDOR), saturation recovery, and infrared absorption. The results confirm the ${}^{1}$H hyperfine parameters for the recently identified H1 defect [Zhou et al., Phys. Rev. B 54, 7881 (1996)]. However, in the CVD diamond samples studied here, H1 is always accompanied by another defect at $g=2.0028(1)$. Saturation recovery measurements are consistent with two defects centered on $g=2.0028$. At temperatures below 100 K the spin-lattice relaxation rate of H1 is determined by the direct process and is a factor of 10--100 times more rapid than the single substitutional nitrogen center, which is known to be incorporated into the bulk diamond. ${}^{1}$H matrix ENDOR measurements indicate that the H1 center is in an environment with hydrogen atoms 0.2--1.0 nm from the center. The near-neighbor hydrogen identified by multifrequency EPR was not detected in the ENDOR experiments. The concentration of H1 correlates with the total integrated CH stretch infrared absorption in the samples studied here. All the evidence is consistent with H1 being located at hydrogen decorated grain boundaries (or in intergranular material) rather than in the bulk diamond. A third EPR resonance at $g=2.0028(1)$ has been observed in some of the CVD diamond samples studied. The resonance is distinguished by its temperature-dependent linewidth: above 50 K the line is exchange narrowed, but below 50 K it broadens rapidly with decreasing temperature.

Studies of deep-level defects in flash lamp annealing of ion-implanted silicon

The spatial uniformity and in-depth profile of phosphorus-ion-implanted silicon annealed by flash lamps were studied with Hall effect, spreading resistance and minority-carrier lifetime measurements. Deep levels in flash-lamp-annealed n+p diodes were examined using deep-level transient spectroscopy (DLTS) and reverse current measurements. The annealing lamp energy densities used were 20-28 J cm-2. A uniformly annealed area, about 40*40 mm2, was obtained, which coincided with the uniformly light-irradiated area of the flash lamp annealing system. In n+p diodes, two hole traps H1(Ev+0.39 eV) and H2(Ev+0.46 eV) were observed at 26 J cm-2, and two hole traps H1(Ev+0.39 eV) and H3(Ev+0.47 eV) were observed at 20 J cm-2. The spatial reverse current distributions within the wafer were similar to those of H2 defects. To remove these residual defects in diodes, effects of the additional furnace annealing and the multiple-shot irradiations were also investigated. H1 defects were annealed out with 700 degrees C additional furnace heating for 30 min. H1 and H2 defects of 26 J cm-2 flash-lamp-annealed samples were annealed out by two-shot flash lamp irradiations.