Self-powered broadband photodetection enabled by facile CVD-grown MoS2/GaN heterostructures

Achieving self-powered photodetection without biasing is a notable challenge for photodetectors. In this work, we demonstrate the successful fabrication of large-scale van der Waals epitaxial molybdenum disulfide (MoS2) on a p-GaN/sapphire substrate using a straightforward chemical vapor deposition (CVD) technique. Our research primarily centers on the characterization of these photodetectors produced through this method. The MoS2/GaN heterojunction photodetector showcases a broad and extensive photoresponse spanning from ultraviolet A (UVA) to near-infrared (NIR). When illuminated by a 532 nm laser, its self-powered photoresponse is characterized by a rise time (τr) of ∼18.5 ms and a decay time (τd) of ∼123.2 ms. The photodetector achieves a responsivity (R) of ∼0.13 A W-1 and a specific detectivity (D*) of ∼3.8 × 1010 Jones at zero bias. Additionally, while utilizing a 404 nm laser, the photodetector reaches a maximum R and D* of ∼1.7 × 104 A/W and ∼1.6 × 1013 Jones, respectively, at Vb = 5 V. The operational mechanism of the device can be explained by the diode characteristics involving a tunneling current in the presence of reverse bias. The exceptional performance of these photodetectors can be attributed to the pristine interface between the CVD-grown MoS2 and GaN, providing an impeccably clean tunneling surface. Additionally, our investigation has unveiled that MoS2/GaN heterostructure photodetectors, featuring MoS2 coverage percentages spanning from 20% to 50%, exhibit improved responsivity capabilities at an external bias voltage. As a result, this facile CVD growth technique for MoS2 photodetectors holds significant potential for large-scale production in the manufacturing industry.

Dual-mode frequency multiplier in graphene-base hot electron transistor

Since quantum computers have been gradually introduced in countries around the world, the development of the many related quantum components that can operate independently of temperature has become more important for enabling mature products with low power dissipation and high efficiency. As an alternative to studying cryo-CMOSs (complementary metal-oxide-semiconductors) to achieve this goal, quantum tunneling devices based on 2D materials can be examined instead. In this work, a vertical graphene-based quantum tunneling transistor has been used as a frequency modulator. The transistor can operate via different quantum tunneling mechanisms and generates, by applying the appropriate bias, voltage-resistance curves characteristic of variable nonlinear resistance for both base and emitter voltages. We experimentally demonstrate frequency modulation from input signals over the range of 100 kHz to 10 MHz, enabling a tunable frequency doubler or tripler in just a single transistor. This frequency multiplication with a tunneling mechanism makes the graphene-based tunneling device a promising option for frequency electronics in the emerging field of quantum technologies.

PADAr: physician-oriented artificial intelligence-facilitating diagnosis aid for retinal diseases

Purpose: Retinopathy screening via digital imaging is promising for early detection and timely treatment, and tracking retinopathic abnormality over time can help to reveal the risk of disease progression. We developed an innovative physician-oriented artificial intelligence-facilitating diagnosis aid system for retinal diseases for screening multiple retinopathies and monitoring the regions of potential abnormality over time. Approach: Our dataset contains 4908 fundus images from 304 eyes with image-level annotations, including diabetic retinopathy, age-related macular degeneration, cellophane maculopathy, pathological myopia, and healthy control (HC). The screening model utilized a VGG-based feature extractor and multiple-binary convolutional neural network-based classifiers. Images in time series were aligned via affine transforms estimated through speeded-up robust features. Heatmaps of retinopathy were generated from the feature extractor using gradient-weighted class activation mapping++, and individual candidate retinopathy sites were identified from the heatmaps using clustering algorithm. Nested cross-validation with a train-to-test split of 80% to 20% was used to evaluate the performance of the screening model. Results: Our screening model achieved 99% accuracy, 93% sensitivity, and 97% specificity in discriminating between patients with retinopathy and HCs. For discriminating between types of retinopathy, our model achieved an averaged performance of 80% accuracy, 78% sensitivity, 94% specificity, 79% F1-score, and Cohen's kappa coefficient of 0.70. Moreover, visualization results were also shown to provide reasonable candidate sites of retinopathy. Conclusions: Our results demonstrated the capability of the proposed model for extracting diagnostic information of the abnormality and lesion locations, which allows clinicians to focus on patient-centered treatment and untangles the pathological plausibility hidden in deep learning models.

An Efficient ECG Classification System Using Resource-Saving Architecture and Random Forest

This paper presents a resource-saving system to extract a few important features of electrocardiogram (ECG) signals. In addition, real-time classifiers are proposed as well to classify different types of arrhythmias via these features. The proposed feature extraction system is based on two delta-sigma modulators adopting 250 Hz sampling rate and three wave detection algorithms to analyze outputs of the modulators. It extracts essential details of each heartbeat, and the details are encoded into 68 bits data that is only 1.48% of the other comparable methods. To evaluate our classification, we use a novel patient-specific training protocol in conjunction with the MIT-BIH database and the recommendation of the AAMI to train the classifiers. The classifiers are random forests that are designed to recognize two major types of arrhythmias. They are supraventricular ectopic beats (SVEB) and ventricular ectopic beats (VEB). The performance of the arrhythmia classification reaches to the F1 scores of 81.05% for SVEB and 97.07% for VEB, which are also comparable to the state-of-the-art methods. The method provides a reliable and accurate approach to analyze ECG signals. Additionally, it also possesses time-efficient, low-complexity, and low-memory-usage advantages. Benefiting from these advantages, the method can be applied to practical ECG applications, especially wearable healthcare devices and implanted medical devices, for wave detection and arrhythmia classification.

High-Frequency Graphene Base Hot-Electron Transistor

The integration of graphene and other two-dimensional (2D) materials with existing silicon semiconductor technology is highly desirable. This is due to the diverse advantages and potential applications brought about by the consequent miniaturization of the resulting electronic devices. Nevertheless, such devices that can operate at very high frequencies for high-speed applications are eminently preferred. In this work, we demonstrate a vertical graphene base hot-electron transistor that performs in the radio frequency regime. Our device exhibits a relatively high current density (∼200 A/cm²), high common base current gain (α* ∼ 99.2%), and moderate common emitter current gain (β* ∼ 2.7) at room temperature with an intrinsic current gain cutoff frequency of around 65 GHz. Furthermore, cutoff frequency can be tuned from 54 to 65 GHz by varying the collector-base bias. We anticipate that this proposed transistor design, built by the integrated 2D material and silicon semiconductor technology, can be a potential candidate to realize extra fast radio frequency tunneling hot-carrier electronics.

High-performance gallium nitride dielectric metalenses for imaging in the visible

Metalens is one of the most promising applications for the development of metasurfaces. A wide variety of materials have been applied to metalenses working at certain spectral bands in order to meet the requirements of high efficiency and low-cost fabrication. Among these materials, wide-bandgap gallium nitride (GaN) is one of the most promising materials considering its advantages especially in semiconductor manufacturing. In this work, GaN has been utilized to fabricate the high-performance metalenses operating at visible wavelengths of 405, 532, and 633 nm with efficiencies up to 79%, 84%, and 89%, respectively. The homemade 1951 United State Air Force (UASF) resolution test chart has also been fabricated in order to provide resolvable lines with widths as small as 870 nm. As shown in the experimental results for imaging, the metalens designed at 405 nm can provide extremely high resolution to clearly resolve the smallest lines with the nano-sized widths in the homemade resolution test chart. These extraordinary experimental results come from our successful development in design and fabrication for the metalenses composed of high-aspect-ratio GaN nanoposts with nearly vertical sidewalls.

Generation of Concentric Space-Variant Linear Polarized Light by Dielectric Metalens

Miniaturized flat and ultrathin optical components with spatial and polarization degrees of freedom are important for optical communications. Here, we use nanostructures that act as tiny phase plates on a dielectric metalens to generate a concentric polarization beam with different orientations along the radial direction. The important discoveries are that (1) the circularly polarized light can be converted into linearly polarized states with a different orientation at near field and that (2) this orientation is strongly correlated to the rotation of the nanostructures on the metalens. Stokes parameters are utilized to investigate the comprehensive polarization states embedded in the optical intensity along the propagation direction. The variation of the spatial polarization states transformed by the dielectric metalens can be properly mapped onto the Poincaré sphere. We believe that the variety of spatial polarizations within a miniaturized configuration provides a new degree of freedom for diverse applications in the future.

Responsivity and detectivity enhancements by graphene overlay on normal-incident multicolor quantum grid infrared photodetectors

An efficient and effective method to achieve high responsivity and specific detectivity, particularly for normal-incident quantum well infrared photodetectors (QWIPs), is proposed in this study. By combining superlattice (SL) structure, grating structures, and graphene monolayer onto traditional QWIP designs, a graphene-covered multicolor quantum grid infrared photodetector (QGIP) with improved optoelectrical properties is developed. The enhancements of the device's responsivity and specific detectivity are about 7-fold and 20-fold, respectively, which resulted from an increase in the charge depletion region and the generation of extra photoelectrons due to graphene-semiconductor heterojunction. This method provides a potential candidate for future high-performance photodetectors.

Pre-treatment quality of life as a predictor of distant metastasis-free survival and overall survival in patients with head and neck cancer who underwent free flap reconstruction

PURPOSE

This study examined the prognostic associations of pre-treatment quality of life (QoL) with overall survival (OS) and distant metastasis-free survival (DFMS) among patients with head and neck cancer (HNC) who underwent free flap reconstruction.

METHODS

A cohort of 127 HNC patients who received free flap reconstruction between November 2010 and June 2014 at a hospital were recruited. Pre-treatment QoL was measured by the University of Washington Quality of Life Questionnaire, which contains six physical domains, including speech, swallowing, appearance, saliva, taste and chewing, as well as the six social-emotional domains of pain, activity, recreation, shoulder, mood, and anxiety. Cox regression analyses were performed.

RESULTS

Results showed that pre-treatment QoL was predictive of OS and DMFS. Of the domains, swallowing, chewing, speech, taste, saliva, pain and shoulder were demonstrated to be significant predictors of OS. Additionally, swallowing, chewing, speech, pain and activity were demonstrated making significant contributions to DMFS.

CONCLUSION

Our data supported that physical domains of pre-treatment QoL were predictors for OS and DFMS in HNC patients with free-flap reconstruction. Longitudinal studies are warranted to clarify the prognostic abilities of social-emotional domains. Information on pre-treatment QoL should be taken into account to individualize care plan for these patients, and hence prolong their survival.

A broadband achromatic metalens in the visible

Metalenses consist of an array of optical nanoantennas on a surface capable of manipulating the properties of an incoming light wavefront. Various flat optical components, such as polarizers, optical imaging encoders, tunable phase modulators and a retroreflector, have been demonstrated using a metalens design. An open issue, especially problematic for colour imaging and display applications, is the correction of chromatic aberration, an intrinsic effect originating from the specific resonance and limited working bandwidth of each nanoantenna. As a result, no metalens has demonstrated full-colour imaging in the visible wavelength. Here, we show a design and fabrication that consists of GaN-based integrated-resonant unit elements to achieve an achromatic metalens operating in the entire visible region in transmission mode. The focal length of our metalenses remains unchanged as the incident wavelength is varied from 400 to 660 nm, demonstrating complete elimination of chromatic aberration at about 49% bandwidth of the central working wavelength. The average efficiency of a metalens with a numerical aperture of 0.106 is about 40% over the whole visible spectrum. We also show some examples of full-colour imaging based on this design.

Breaking Through the Multi-Mesa-Channel Width Limited of Normally Off GaN HEMTs Through Modulation of the Via-Hole-Length

We present new normally off GaN high-electron-mobility transistors (HEMTs) that overcome the typical limitations in multi-mesa-channel (MMC) width through modulation of the via-hole-length to regulate the charge neutrality screen effect. We have prepared enhancement-mode (E-mode) GaN HEMTs having widths of up to 300 nm, based on an enhanced surface pinning effect. E-mode GaN HEMTs having MMC structures and widths as well as via-hole-lengths of 100 nm/2 μm and 300 nm/6 μm, respectively, exhibited positive threshold voltages (V _th) of 0.79 and 0.46 V, respectively. The on-resistances of the MMC and via-hole-length structures were lower than those of typical tri-gate nanoribbon GaN HEMTs. In addition, the devices not only achieved the E-mode but also improved the power performance of the GaN HEMTs and effectively mitigated the device thermal effect. We controlled the via-hole-length sidewall surface pinning effect to obtain the E-mode GaN HEMTs. Our findings suggest that via-hole-length normally off GaN HEMTs have great potential for use in next-generation power electronics.

A comprehensive model for sub-10 nm electron-beam patterning through the short-time and cold development

In this study, we propose a set of single-spot experiment to construct a comprehensive model of electron-beam lithography to describe the relation among the incident electrons, resist, and the development conditions such as durations and temperatures. Through the experiments, small feature can be achieved by performing a short-time development due to the high acceleration voltage and large depth of focus of electron-beam system. The singular point in the beginning of the development is also observed in our model and supported by the experimental data. In addition, we verify the characteristic region of each incident spot induced by the point spread function of the electron-beam system. We further fabricate the single line with narrow groove width by utilizing the results from single-spot experiment at low developing temperatures. The line is formed by arranging a series of incident points with a distance close to the characteristic radius. This method can eliminate the proximity effect effectively and thus the groove width is scaled down to 8 nm. By adopting the successful experience in the single line formation, dense array with narrow linewidth is also demonstrated under well suppression of the proximity effect. The minimum groove width of 9 nm with 30 nm pitch is achieved with 5 s development time at -10 °C. Finally, the exceptional capability of pattern transfer is presented due to the high aspect ratio of the resist.

GaN Metalens for Pixel-Level Full-Color Routing at Visible Light

Metasurface-based components are known to be one of the promising candidates for developing flat optical systems. However, their low working efficiency highly limits the use of such flat components for feasible applications. Although the introduction of the metallic mirror has been demonstrated to successfully enhance the efficiency, it is still somehow limited for imaging and sensing applications because they are only available for devices operating in a reflection fashion. Here, we demonstrate three individual GaN-based metalenses working in a transmission window with extremely high operation efficiency at visible light (87%, 91.6%, and 50.6% for blue, green, and red light, respectively). For the proof of concept, a multiplex color router with dielectric metalens, which is capable of guiding individual primary colors into different spatial positions, is experimentally verified based on the design of out-of-plane focusing metalens. Our approach with low-cost, semiconductor fabrication compatibility and high working efficiency characteristics offers a way for establishing a complete set of flat optical components for a wide range of applications such as compact imaging sensors, optical spectroscopy, and high-resolution lithography, just named a few.

Pure, single crystal Ge nanodots formed using a sandwich structure via pulsed UV excimer laser annealing

In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si-Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm(-2), the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm(-1) at 300.7 cm(-1), which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities.

Enhanced performance of InGaN-based light-emitting diodes grown on volcano-shaped patterned sapphire substrates with embedded SiO2

This paper describes highly efficient InGaN-based light-emitting diodes (LEDs) grown on volcano-shaped patterned sapphire substrates with embedded SiO₂ (SVPSS).

Effect of surface Si redistribution on the alignment of Ge dots grown on pit-patterned Si(001) substrates

Thermally activated redistribution of Si surface atoms is found to be a crucial factor for the growth of aligned Ge dots on pit-patterned Si(001) substrates. A phenomenon of Si accumulation around the edge of pits significantly alters the substrate surface morphology. As the pit spacing is reduced to below 100 nm, a convex morphology developed between adjacent pits causes a chemical potential distribution that drives the Ge dots into the pits. In addition, the pits of an etching depth greater than 60 nm will evolve into truncated inverted pyramids with sharp base corners that provide deep potential wells for the confinement of Ge dots. Perfectly aligned Ge dots are obtained on pit-patterned Si substrates with this range of pit spacing and etching depth. We also find that the initial geometric shape of the pits does not affect the spatial arrangement of Ge dots.

Influence of patterned sapphire substrates with different symmetry on the light output power of InGaN-based LEDs

This paper aims to investigate the light output power (LOP) of InGaN-based light-emitting diodes (LEDs) grown on patterned sapphire substrates (PSSs) with different symmetry. The GaN epitaxial layers grown on the hexagonal lattice arrangement PSS (HLAPSS) have a lower compressive strain than the ones grown on the square lattice arrangement PSS (SLAPSS). The quantum-confined Stark effect (QCSE) is also affected by the residual compressive strain. Based on the experimentally measured data and the ray tracing simulation results, the InGaN-based LED with the HLAPSS has a higher LOP than the one with the SLAPSS due to the weaker QCSE within multiple-quantum wells (MQWs).

Suppressed quantum-confined Stark effect in InGaN-based LEDs with nano-sized patterned sapphire substrates

This paper demonstrates that quantum-confined Stark effect (QCSE) within the multiple quantum wells (MQWs) can be suppressed by the growths of InGaN-based light-emitting diodes (LEDs) on the nano-sized patterned c-plane sapphire substrates (PCSSs) with reducing the space. The efficiency droop is also determined by QCSE. As verified by the experimentally measured data and the ray-tracing simulation results, the suppressed efficiency droop for the InGaN-based LED having the nano-sized PCSS with a smaller space of 200 nm can be acquired due to the weaker function of the QCSE within the MQWs as a result of the smaller polarization fields coming from the lower compressive strain in the corresponding epitaxial layers.

Short-term external buckling with pneumatic retinopexy for retinal detachment with inferior retinal breaks

PURPOSE

To introduce a new approach for short-term external scleral buckling with pneumatic retinopexy for the management of rhegmatogenous retinal detachment with inferior retinal breaks.

DESIGN

Retrospective, noncomparative, interventional case series.

METHODS

A review of 33 consecutive eyes of 31 patients who underwent external buckling with pneumatic retinopexy for uncomplicated rhegmatogenous retinal detachment with inferior retinal breaks from December 2006 through December 2010. An external buckle was made of a 505 sponge sutured along the blunt side of a 279 tyre (MIRA Inc). The buckle was inserted deeply into the inferior fornix without suture after pneumatic retinopexy and was kept in place for 3 days. Primary and final anatomic outcomes, visual acuity, and adverse events were recorded.

RESULTS

All patients tolerated the procedure. The mean follow-up period was 24.0 months (range, 9 to 61 months). Primary success, defined as successful retinal reattachment within 6 months without further treatment, was achieved in 29 (87.9%) eyes. All patients attained final retinal reattachment (100%). Overall, the mean best-corrected visual acuity improved significantly at the end of follow-up (0.30 logarithm of the minimal angle of resolution units; Snellen equivalent, 6/12), compared with the preoperative best-corrected visual acuity (0.82 logarithm of the minimal angle of resolution units; Snellen equivalent, 6/38; P < .001).

CONCLUSIONS

Short-term external buckling with pneumatic retinopexy is a novel and effective treatment for rhegmatogenous retinal detachment with inferior retinal breaks, with a comparable success rate with other treatment methods. This approach also can avoid complications of long-term buckle implantation. Further comparative cohort studies may be necessary to compare the clinical efficacy with other conventional operations.

Well-patterned metal-semiconductor interface improving contact conductance

In an aluminum/silicon system, contact conductance (Gc) and Al crystallization can improve by using the hole array on Si, which is built by electron-beam lithography, and increase with decreasing hole size; this improves Gc from 0.004 microS to 13.390 microS. TEM results show Al crystals located inside and near the holes. The ratio of the total Al grain area over the pad area, defined in short form as Ac, is improved from 0.007 to 0.359. An experimental model demonstrates that Gc is proportional to Ac, divided by the square of the interfacial oxygen content. The well-known Al/Si system, chosen as a vehicle, verifies this paper's methodology and provides an alternative to a highly doped or annealing process for Gc improvement. Most significantly, it yields a more robust and well-controlled interface and overcomes obstacles in the newly introduced material system. It also addresses devices with the size narrowed into the deep nanoscale domain. The methodology prevents an inherently non-planar Al/Si interface.

Magnetic field enhanced resonant tunneling in a silicon nanowire single-electron-transistor

We report fabrication, measurement and simulation of silicon single-electron-transistors made on silicon-on-insulator wafers. At T-2 K, these devices showed clear Coulomb blockade structures. An external perpendicular magnetic field was found to enhance the resonant tunneling peak and was used to predict the presence of two laterally coupled quantum dots in the narrow constriction between the source-drain electrodes. The proposed model and measured experimental data were consistently explained using numerical simulations.

Thermally induced morphology evolution of pit-patterned Si substrate and its effect on nucleation properties of Ge dots

We demonstrate the effect of the pre-growth heat treatment process on the nucleation properties of Ge dots grown on pit-patterned Si(001) substrates. The prefabricated 200 nm diameter pits inherently evolve into truncated inverted pyramids (TIPs) with (110) base edges and a 7°-9° sidewall slope during heat treatment; this morphology transformation is robust against variations in shape and orientation of the pit patterns. Uniform Ge dots with an areal density of 4 × 10(9) cm(-2) were obtained on the Si substrates having TIPs. Each TIP contains four aligned Ge dots locating symmetrically with respect to (110). These dots exhibit an elliptical dome shape with major axis oriented along (100). The nucleation position, shape and spatial orientation of these Ge dots coincide with the calculated surface chemical potential distribution of the TIP.

Fabrication method of high-quality Ge nanocrystals on patterned Si substrates by local melting point control

The local melting point of a Ge thin film can be controlled by a hole-array pattern on the host Si substrate due to the variations in the stress distribution and the surface morphology induced by the pattern. A simple annealing process is developed from this effect to produce Ge NCs with a single-domain-crystal size over 20 nm, confirmed by transmission electron microscopy and Raman spectroscopy, from an electron-gun-evaporated Ge thin film on the patterned Si substrate. The effect of the dimensions of the hole array is also investigated. Photoluminescence observed around 1157 nm from some of the samples shows the possibility of improving the infrared emission capability by this proposed method.

Electromagnetic energy vortex associated with sub-wavelength plasmonic Taiji marks

The Taiji symbol is a very old schematic representation of two opposing but complementary patterns in oriental civilization. Using electron beam lithography, we fabricated an array of 70 × 70 gold Taiji marks with 30 nm thickness and a total area of 50 × 50 µm(2) on a fused silica substrate. The diameter of each Taiji mark is 500 nm, while the period of the array is 700 nm. Here we present experimental as well as numerical simulation results pertaining to plasmonic resonances of several Taiji nano-structures under normal illumination. We have identified a Taiji structure with a particularly interesting vortex-like Poynting vector profile, which could be attributed to the special shape and dimensions of the Taiji symbol.

Electroluminescence enhancement of SiGe/Si multiple quantum wells through nanowall structures

The enhancement of light extraction from Si(0.5)Ge(0.5)/Si multiple quantum wells (MQWs) with nanowall structures fabricated by electron cyclotron resonance (ECR) plasma etching is presented. It is shown that the ECR plasma treatment does not damage the crystalline quality. At a driving current of 5.5 × 10(6) A m(-2), the light output intensity of the MQWs with nanowall structures shows an enhancement of about 50% compared with that of the original MQWs. In addition to the enhanced light extraction, the improved optoelectronic properties are also attributed to the strain relaxation in nanowall structures.

Enhancement and tunability of active plasmonic by multilayer grating coupled emission

The effect of coupled mode surface plasmon polaritons (SPPs) on the active emission of a nanostructure grating with organic semiconductor material, Alq(3), on the surface was investigated in this study. We report surface plasmon grating coupled emission (SPGCE) from excited organic layer on metal grating in both organic/metal (2-Layer) and organic/metal/organic/metal (4-Layer) structures. The dispersion relation was obtained from angle-resolved photoluminescence measurement. The resultant emission intensity can have up to 6 times enhancement on the 4- Layer device and the Full-Width Half-Maximum (FWHM) is less than 50 nm. The combination of SPPs on organic/metal interface allows specific directional emission and color appearance of Alq(3) fluorophores. Potential applications of such an active plasmonics with enhanced resonant energy emission due to interactions on the organic/metal nano-grating as biosensor were presented and discussed.

Static conformation and dynamics of single DNA molecules confined in nanoslits

Nearly thirty years ago, Daoud and de Gennes derived the scaling predictions for the linear polymer chains trapped in a slit with dimension close to the Kuhn length; however, these predictions have yet to be compared with experiments. We have fabricated nanoslits with vertical dimension similar to the Kuhn length of ds-DNA (110nm) using standard photolithography techniques. Fluorescently labeled single DNA molecules with contour lengths L ranging from 4 to 75 microm were successfully injected into the slits and the chain molecules undergoing Brownian motions were imaged by fluorescence microscopy. The distributions of the chain radius of gyration and the two-dimensional asphericity were measured. It is found that the DNA molecules exhibit highly anisotropic shape and the mean asphericity is chain length independence. The shape anisotropy of DNA in our measurements is between two and three dimensions (2D and 3D). The static scaling law of the chain extension and the radius of gyration <R parallel>, <Rg> approximately L(nu) were observed with nuR(parallel)=0.65+/-0.02 and nu(Rg)=0.68+/-0.05. These results are close to the average value between two (nuR parallel,Rg=0.75) and three (nuR parallel,Rg=0.6) -dimensional theoretical value. The scaling of the extensional and rotational relaxation time are between Rouse model in nanoslits and Zimm model in the bulk solution, respectively. We show that the conformation and chain relaxation of DNA confined in a slit close to Kuhn length exhibit the quasi-two-dimensional behavior.

Beaming light from a subwavelength metal slit surrounded by dielectric surface gratings

In this article, we demonstrate that a subwavelength metal slit surrounded by dielectric surface gratings possesses a directional beaming effect. We propose a surface plasmon diffraction scheme to explain the three kinds of beaming conditions. The numerical simulations of the illustrative structures undertaken used a Finite Difference Time Domain (FDTD) Method and a Rigorous Coupled Wave Analysis (RCWA) Method. Our simulations were found to be consistent and in agreement with the experimental results. In comparison with other metal structures, we find that dielectric metal structures offer better performance as well as the advantage of being able to be efficiently mass produced for large volume industrial applications.

Removal of 2,4-dichlorophenol by suspended and immobilized Bacillus insolitus

In this experiment, Bacillus insolitus was isolated and selected from a mixed culture that have been acclimated to chlorophenols. Decomposition of chlorophenolic compounds will be studied using this pure culture in both suspended and immobilized form. The results are: at lower initial concentrations of 2,4-dichlorophenol (10-50 mg/l), immobilized Bacillus insolitus shows a higher removal of 2,4-dichlorophenol than Bacillus insolitus in suspended growth. When the 2,4-dichlorophenol concentration becomes higher (50-200 mg/l), both immobilized and suspended Bacillus insolitus have approximately the same efficiency for removal of 2,4-dichlorophenol. Higher concentrations of 2,4-dichlorophenol are inhibitive to the growth of either suspended or immobilized Bacillus insolitus. At lower concentrations of 2,4-dichlorophenol, immobilized mixed culture may have the same removal efficiency of 2,4-dichlorophenol as immobilized pure culture of Bacillus insolitus. But with regard to the overall 2,4-dichlorophenol removal efficiency, immobilized pure culture is considered to be superior to immobilized mixed culture.