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Various biomaterial scaffolds have been developed for improving stem cell anchorage and function in tissue constructs for in vitro and in vivo uses. Growth factors are typically applied to scaffolds to mediate cell differentiation. Conventionally, growth factors are not strictly localized in the scaffolds; thus, they may leak into the surrounding environment, causing undesired side effects on tissues or cells. Hence, there is a need for improved tissue construct strategies based on highly localized drug delivery and a homeostatic microenvironment. This study developed an injectable nanomatrix (NM) scaffold with a layer-by-layer structure inside each nanosized fiber of the scaffold based on controlled self-assembly at the molecular level. The NM was hierarchically assembled from Janus base nanotubes (JBNTs), matrilin-3, and transforming growth factor β−1 (TGF-β1) via bioaffinity. JBNTs, which form the NM backbone, are novel DNA-inspired nanomaterials that mimic the natural helical nanostructures of collagens. The chondrogenic factor, TGF-β1, was enveloped in the inner layer inside the NM fibers to prevent its release. Matrilin-3 was incorporated into the outer layer to create a cartilage-mimicking microenvironment and to maintain tissue homeostasis. Interestingly, human mesenchymal stem cells (hMSCs) had a strong preference to anchor along the NM fibers and formed a localized homeostatic microenvironment. Therefore, this NM has successfully generated highly organized structures via molecular self-assembly and achieved localized drug delivery and stem cell anchorage for homeostatic tissue constructs.

RNA delivery into deep tissues with dense extracellular matrix (ECM) has been challenging. For example, cartilage is a major barrier for RNA and drug delivery due to its avascular structure, low cell density and strong negative surface charge. Cartilage ECM is comprised of collagens, proteoglycans, and various other noncollagneous proteins with a spacing of 20nm. Conventional nanoparticles are usually spherical with a diameter larger than 50-60nm (after cargo loading). Therefore, they presented limited success for RNA delivery into cartilage. Here, we developed Janus base nanotubes (JBNTs, self-assembled nanotubes inspired from DNA base pairs) to assemble with small RNAs to form nano-rod delivery vehicles (termed as “Nanopieces”). Nanopieces have a diameter of ~20nm (smallest delivery vehicles after cargo loading) and a length of ~100nm. They present a novel breakthrough in ECM penetration due to the reduced size and adjustable characteristics to encourage ECM and intracellular penetration.

A 2.5–5.6 GHz low-phase-noise subharmonically injection-locked sub-sampling all-digital phase-locked loop with a dual-edge complementary switched injection technique is presented. While previously reported injection-locked phase-locked loops (ILPLLs) require additional circuitry for resolving a phase alignment mismatch between the PLL loop and injection path, the presented ILPLL exhibits a simplified architecture owing to the proposed injection technique and sub-sampling bang-bang phase detector (SSBBPD). Because the proposed injection technique exploits dual-edge injection, we analyze the performance impact of dual-edge injection when inaccurate injection timing occurs. This paper also offers an analysis of the injection technique based on the charge transfer and derives the realignment factor of the injection. With the proposed injection technique and the direct connection of the digitally controlled oscillator (DCO) clock to the SSBBPD, the timing mismatch between the PLL loop and injection path becomes insensitive to voltage and temperature drift. The proposed ILPLL prototype is fabricated in a 65-nm CMOS process and achieves a 168-fs integrated rms jitter over 1 kHz to 40 MHz at a 5-GHz output frequency with 156.25-MHz reference clock while consuming 15.4 mW with an active area of 0.06 mm2.

The extent of subsurface damage on (0001) GaN wafers post different polishing treatments was quantified using depth-resolved cathodoluminescence spectroscopy (DRCLS). The band edge emission spectra were obtained from CLS with different electron energies, which manifested a significant non-radiative recombination resulted from polishing-induced subsurface damage. Cross-sectional transmission electron microscopy (XTEM) was also used to diagnose the extent of the subsurface damage layer. For the GaN polished with 1.00 and 0.25 μm diamonds abrasive, the extent of non-radiative subsurface damage is about 250 and 100 nm, corresponding to the calculated electron penetration depth at the accelerating voltage for the onset of band edge emission. In this study, the depth of subsurface damage estimated from CL spectra compared well with direct XTEM measurements in GaN substrate.

We develop a novel multi-level nanoimprinting mold fabrication methodology realizing the uniform pattern height of each level with the deviation less than 2.6%, by applying the unique ‘top-to-bottom’ level patterning protocol in contrast to typical bottom-to-top patterning sequence. This is implemented by performing sequential dry etching of the stack of etch stop layers and organic insulation layers of desired thicknesses, with proper photolithographic masking in between. We demonstrate that the fabrication can be conducted on a flexible substrate without deformation of pattern profile, which then can be utilized in continuous roll-to-roll nanoimprinting of multi-level nanoarchitectures in a single imprinting process without resorting to alignment of each level. Many applications will benefit from our method, particularly requiring large-area multi-level nanoarchitectures such as thin-film transistor arrays in flexible displays.

This paper depicts efforts for fabricating GaN on diamond microstructure through direct bonding between Ga and C, while excluding the use of adhesive interlayer during spark plasma sintering (SPS) process. The resulting GaN on diamond architecture is seemingly successful, as suggested by macroscopic morphological observations. The microscopic inspection using high-resolution transmission electron microscopy (HRTEM), however, shows a unique, off-the-chart interlayer configuration, wherein the components are migrated, etched, or fused to tentatively form multiple crystal phases. These phases can be constructed based on their utmost stabilities among all possible phases thermodynamically driven under or near the SPS conditions.

With increasing demand for means of controlling surface adhesion in various applications, including the semiconductor industry, optics, micro/nanoelectromechanical systems, and the medical industry, nano-engineered surfaces have attracted much attention. This study suggests a design methodology for nanostructures using the Derjaguin approximation in conjunction with finite element analysis for the control of adhesion forces. The suggested design methodology was applied for designing a nano-engineered surface with low-adhesion properties. To verify this, rectangular and sinusoidal nanostructures were fabricated and analyzed using force-distance curve measurements using atomic force microscopy and centrifugal detachment testing. For force-distance curve measurements, modified cantilevers with tips formed with atypical particles were used. Subsequently, centrifugal detachment tests were also conducted. The surface wettability of rectangular and sinusoidal nanostructures was measured and compared with the measured adhesion force and the number of particles remaining after centrifugal detachment tests.

To achieve sensitive plasmonic biosensors, it is essential to develop an efficient method for concentrating analytes in hot spots, as well as to develop plasmonic nanostructures for concentrating light. In this study, target analytes were delivered to the surface of double-bent Au strip arrays by a multiple dip-coating method; they were self-aligned in the valleys between neighboring Au strips by capillary forces. As the valleys not only accommodate target analytes but also host strong electromagnetic fields due to the interaction between adjacent strips, sensitive measurement of target analytes was possible by monitoring changes in the wavelength of a localized surface plasmon resonance. Using the proposed plasmonic sensor and target delivery method, the adsorption and saturation of polystyrene beads 100 nm in size on the sensor surface were monitored by the shift of the resonance wavelength. In addition, the pH-dependent stability of exosomes accumulated on the sensor surface was successfully monitored by changing the pH from 7.4 to 4.0.

Liquid scintillation counters are common instruments used in the measurement of pure beta-emitting radionuclides, and while they represent a conventional radiometric technique, they are still competitive for their potential to measure multiple radionuclides simultaneously. In this work, we propose an algorithm based on an artificial neural network (ANN) for the simultaneous analysis of the beta-ray spectra of 3H and 14C in dual beta-labeled samples using a liquid scintillation counter. We achieved percentage deviations below 5.0% using the proposed algorithm in 16 out of 18 cases, with RMSDs below 1.5% in 17 out of 18 cases. The trained ANN also produced activity ratios with high accuracy even while having to deal with highly fluctuating spectra. Results demonstrate that the rapid predictions with a short measurement time from our proposed ANN method are compatible with the calculated ones from previous studies that were obtained with long measurement times.

In this report, we investigated a single-step process for formation of high crystallinity Y2O3:Eu3+ red nanophosphor by flame spray pyrolysis (FSP) without post-heat treatments. Crystallinity of as-formed nanophosphor particle was improved by addition of urea to the nitrate-based liquid precursor. Urea increased the temperature in the flame zone thus ensuring Y2O3:Eu3+ formation at higher flame temperature. Higher temperature reached during combustion of urea promoted the formation of better crystallinity, nano-sized and spherical-shaped particles. The effect of urea in the precursor to obtain high-efficiency Y2O3:Eu3+ nanophosphor was studied.

We demonstrate the use of a parallel detection system with a nanograting-based microarray to accomplish high-throughput analysis of bio-molecular interactions in a label-free manner. Well-type label-free microarrays were fabricated to eliminate the risk of cross-contamination and to minimize sample volumes. Parallel analysis without the use of spectrometer arrays or a moving platform was accomplished by using scanning multiple optical probes generated by a spatial light modulator and microlens array. Additionally, multiple optical probe spots focused by the microlens array reduced detection errors while enhancing the signal-to-noise ratio within a high-density microarray. Finally, we verified the feasibility of the parallel detection system by analyzing the peak wavelength value (PWV) shift of human salivary cortisol and anti-cortisol in a competitive binding experiment.

The super resolution near-field structure (Super-RENS) which is composed of a thin layer of a thermally responsive optical phase change material (PCM) between two dielectric layers, can be a means of resolving the limited resolution of the laser beam for direct laser lithography. In Super-RENS, incident laser irradiation induces the direct, reversible opening and closing of a nanoaperture in the PCM layer, and a nanoscale pattern is realized in the lithography system. Here, we first introduce the complete modeling procedures and optimization methodology for Super-RENS in nanolithography based on a rigorous analysis of near-field structure, thermal analysis in the finite-element method, and analysis of the corresponding feature size on the photoresist (PR) layer. Multiple combinations of the PCM layer and the two dielectric layers with varying dimensions are considered as design parameters to achieve the required resolution in the nanolithography system. The feasible line profiles are investigated at the general operating conditions of the pulsed laser beam, based on varying dimensions of the PCM layer (5–30 nm) and the two dielectric layers (10–200 nm). This work will provide a detailed methodology for the design and optimization of the Super-RENS for applications in the nanolithography system. Keywords: Maskless nanolithography, Phase change material, Super-resolution near-field structure (Super-RENS), Photo-thermal simulation

Durable drag-reduction surfaces have recently received much attention, due to energy-saving and power-consumption issues associated with harsh environment applications, such as those experienced by piping infrastructure, ships, aviation, underwater vehicles, and high-speed ground vehicles. In this study, a durable, metallic surface with highly ordered hierarchical structures was used to enhance drag-reduction properties, by combining two passive drag-reduction strategies: an air-layer effect induced by nanostructures and secondary vortex generation by micro-riblet structures. The nanostructures and micro-riblet structures were designed to increase slip length. The top–down fabrication method used to form the metallic hierarchical structures combined laser interference lithography, photolithography, thermal reflow, nanoimprinting, and pulse-reverse-current electrochemical deposition. The surfaces were formed from nickel, which has high hardness and corrosion resistance, making it suitable for use in harsh environments. The drag-reduction properties of various metal surfaces were investigated based on the surface structure: a bare surface, a nanostructured surface, a micro-riblet surface, and a hierarchically structured surface of nanostructures on micro-riblets.

Infrared-to-visible upconversion devices made by integrating an infrared quantum dot photodetector with an organic light-emitting diode potentially offer a route to low-cost, pixel-free infrared imaging. However, making such devices sufficiently efficient for practical use is a challenge. Here, we report a high-gain vertical phototransistor with a perforated metallic source electrode having an EQE up to 1 × 105% and a detectivity of 1.2 × 1013 Jones. By incorporating a phosphorescent organic light-emitting diode in this phototransistor, an infrared-to-visible upconversion LEPT with a photon-to-photon conversion efficiency of over 1,000% is demonstrated. An optoelectronic device that efficiently converts infrared light to visible light could prove useful for imaging applications.

Recently, the development of durable hydrophobic surfaces has received much attention, with anti-icing applications in harsh environments such as aircrafts, wind turbines, power lines, and marine vessels. In this paper we describe a design methodology employing a lattice Boltzmann method to determine the optimal geometry of microstructures to achieve superhydrophobicity. We describe a top-down fabrication method to form superhydrophobic micro-hierarchical metal surface using photolithography, nanoimprinting, and continuous metal-to-metal replication using pulse-reverse-current electrochemical deposition. The surfaces were formed of nickel, which has a large hardness and is resistant to corrosion, making it suitable for use in harsh external conditions. We compared the measured wettability of fabricated micro-hierarchical metal surface with that from numerical simulations. The contact angle and contact angle hysteresis of four metal surfaces were measured (i.e., a bare surface, a random nanostructured surface, an engineered nanostructured surface, and an engineered hierarchical structured surface), and the anti-icing properties of these four metal surfaces were investigated.

In an organic light-emitting diode (OLED), only about 20-30% of the generated light can be extracted because of the light lost to the thin film guided modes and surface plasmon. Using corrugated high-index-refractive substrates, the thin film guided modes can be effectively out-coupled from the device because of the high index substrate and the loss to the surface plamon is suppressed due to the corrugated structure. With an additional macro lens attached to the substrate to extract the substrate mode, we finally demonstrated a green phosphorescent OLED with an extremely high external quantum efficiency of 63%.

The microstructural properties of an aluminum nitride (AlN) layer grown on a silicon (Si(110)) substrate were studied in detail using transmission electron microscope techniques to determine atomic structure and dislocation behavior. AlN islands elongated along the [11 2 ¯ 0]AlN//[ 1 ¯ 10]Si direction were observed at the initial growth stage on the Si(110) substrate. The threading dislocations with a Burgers vector vertical to the interface, most probably be = [0001] of the wurtzite structure, were frequently observed in the AlN thin film. Due to anisotropic biaxial strain distributions, two different atomic structure behaviors were observed along the two in-plane directions; a coherent interface was observed along the [11 2 ¯ 0]AlN//[ 1 ¯ 10]Si direction and a semicoherent interface, including periodic extra-half planes, was observed along the [ 1 ¯ 100]AlN//[001]Si direction. The extra-half planes were observed at approximately two monolayers above the interface, and not at the exact interface.

The crystallization of lead zirconate titanate (PZT) thin films was evaluated on two different platinum-coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO2 adhesion layer. The Pt deposited on TiO2 exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order (IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X-ray diffraction at a synchrotron source. The intensity of the Pt3Pb phase indicated that deposition on a highly oriented Pt/TiO2 substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO2 substrate than on the Pt/Ti substrate.

Low temperature wet etching using various etchants was investigated to reveal sub-surface damage in sapphire wafer induced during lapping. Surface scratches during wafer preparation is conveniently observed using optical or atomic force microscopy whereas sub-surface damage to crystal requires techniques such as X-ray diffraction, Raman spectroscopy etc. In this study, sub-surface damage in sapphire was revealed as shallow scratches by etching in H 2 SO 4 at temperatures ∼125 °C and 3:1 H 2 SO 4 –H 3 PO 4 at temperatures ∼75 °C. These etching conditions showed no measurable etch rate of sapphire and also did not affect the pristine sapphire surface. The heavily damaged and sub-surface damaged layer was determined to be 1.6 ± 0.1 and 2.2 ± 0.1 μm deep by repeated chemical mechanical polishing and etching of sapphire wafer lapped with 1 μm diamond abrasive.

In order to improve the electrical conductivity of LiFePO4 (LFP) cathode, ZnO/Carbon was incorporated in the cathode by wet vibratory ball milling ZnO, Polyethylene glycol (PEG) and LFP particles together. Herein, polyethylene glycol (PEG) was used as both dispersant during ball milling and carbon source after calcination process. The uniformly dispersed carbon and ZnO on the surface of LFP led to a good electronic contact between the LFP grains. The charge/discharge rate in the range of C/10 to 10C and cycle performance at C/10 for 50 cycles was tested at room temperature. The LFP/ZnO/Carbon composite cathode showed a high capacity of 158.9 mA h g−1, displayed excellent high rate and cyclic performance due to high amounts of graphitic carbon transformed by ZnO used as a catalyst during calcination process. The decrease in capacity was within 31% at a discharge rate of 10C and less than 3% after 50 cycles at C/10 rate. The LFP/ZnO/Carbon composite was characterized using X-ray diffraction (XRD), Scanning electron microscopy (SEM), high resolution Transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Micro-Raman, and specific surface area. Electrochemical properties were measured using electrochemical impedance spectroscopy (EIS), potentiostatic intermittent titration technique (PITT) and galvanostatic measurements.

In this paper, the amount of phase shift with result of the pulse injection is derived mathematically and verified by simulation. The resultant phase shift is proportional to injection pulse width, and inversely proportional to on-resistance of the switch and total capacitance parallel to injection transistor. In addition, phase shift has sinusoidal form with two times the oscillation frequency. Furthermore, locking range can be estimated using the amount of the maximum resultant phase shift. Thereby, it is verified that pulse injection-locked oscillators using shorting scheme have two locking points in one period.

In chemical mechanical polishing (CMP) slurry distribution systems, highly localized shear stresses generated by the pumping devices can cause particle agglomeration, resulting in a significant increase in particle-induced defects. We investigate the role of interparticle forces on stress-induced particle agglomeration in typical silica slurries with various chemicals. Both the maximum interparticle repulsive force and the critical distance at which attractive forces overcome repulsive forces increased with pH for silica slurries. Addition of salt to the slurry led to decrease in both maximum repulsive force and critical distance. These results can be directly correlated to the stability of slurry under shear stress. The degree of agglomeration on particle-induced defectivity was assessed through the CMP of low-k dielectrics.

Improving the front metallization quality of silicon solar cells should be a key to enhance cell performance. In this work, we investigated a two-layer metallization scheme involving light-induced plating (LIP) and tried to quantify its impact on the series resistance of the front grid metals and FFs on finished cells. To estimate the effect of LIP processing on a printed and fired seed layer, individual components of series resistance were measured before and after LIP processing. Among them, grid resistance and contact resistance were closely observed because of their large contribution to series resistance. To optimize the plating on the seed metal grid, the grid resistance of the two-layer metal grid structure was calculated as a function of cross section area of the plated layer. Contact resistivity of the grid before and after LIP processing was analyzed to understand the contact resistance reduction, as well. As a result, the efficiency of solar cells with 80 μm seed metal grid width increased by 0.3% absolute compared with conventional solar cells of 120 μm metal grid width. The total area of electrodes in conventional cells was 1800 mm 2 and electrodes area of LIP processed solar cells was 1400 mm 2 . The efficiency gain was due to reduction of shadowing loss from 7.7% to 6.0% without the increase of resistance due to two-layer front metallization.

The continuous demand on miniaturized electronic circuits bearing high power density illuminates the need to modify the silicon-on-insulator-based chip architecture. This is because of the low thermal conductivity of the few hundred nanometer-thick insulator present between the silicon substrate and active layers. The thick insulator is notorious for releasing the heat generated from the active layers during the operation of devices, leading to degradation in their performance and thus reducing their lifetime. To avoid the heat accumulation, we propose a method to fabricate the silicon-on-diamond (SOD) microstructure featured by an exceptionally thin silicon oxycarbide interlayer (∼3 nm). While exploiting the diamond as an insulator, we employ spark plasma sintering to render the silicon directly fused to the diamond. Notably, this process can manufacture the SOD microarchitecture via a simple/rapid way and incorporates the ultra-thin interlayer for minute thermal resistance. The method invented herein expects to minimize the thermal interfacial resistance of the devices and is thus deemed as a breakthrough appealing to the current chip industry.

An ALD (Atomic Layer Deposition) system is constructed. It has multi-channel shower head to deliver sequentially separated source pulses, and it also has a load-lock chamber to develop high vacuum in main chamber efficiently. In this system, Ru (Ruthenium) layers are deposited on 8-inch silicon wafer. A new Ru-precusor, Ru(CO)3(C4H6), is used as a Ru source. NH3 is used as a reactant, and Ar, a conventional purge gas, is used as a carrier gas. For each one cycle period, one second pulses of the source and the reactant with Ar are injected to the system separately, and Ar purge gas is injected for three second between the source and the reactant pulse. The mechanism and the process of Ru deposition by the new Ru- precursor are completely understood, and Ru is deposited successfully on the silicon wafer in our system. The physical properties and phase of the deposited Ru film are investigated by changing the physical variables including Ru flow rate. Our AES result of Ru thin film by using our new Ru precursor is shown in this paper. The oxygen impurity is barely detected. The proper control of the impurity is discussed. From our results, our ALD system with the new Ru-precursor is expected to be one of the future candidates for fabricating Ru electrode for capacitors below 50nm technology.

The adhesion force and removal of alumina particles on Cu, Ta, TEOS, SILKTM, Aurora and FSG wafer surfaces were experimentally and theoretically investigated in slurry solutions of different pHs. These wafer surfaces showed negative zeta potentials in the investigated pH ranges with exception of FSG and Ta. However, the zeta potentials of FSG surface drastically decreased with increasing pH. The lowest adhesion force and smallest number of alumina particles were measured between alumina particle and FSG surface in a slurry solution of pH 11. Alkaline slurry was much more desirable in controlling the level of particle contamination during Cu CMP. The pH of the slurry and zeta potentials of the surfaces played important roles in controlling the interaction force.

Negative skin friction is perhaps one of the most common problems in the design of pile foundations in soft soils. The development of dragload on single piles and piles in groups in consolidating ground was investigated from 2D and 3D elasto-plastic numerical analyses. Conventional no-slip continuum analysis and slip analysis were conducted for comparison. The parametric analyses showed that dragload for single piles and their reductions in pile groups were substantially over-estimated by the continuum analyses. Axial loading of about 125–325% of the maximum dragload was required to eliminate dragload, depending on the stiffness of the bearing layer. Dragload development heavily depended on the interface friction coefficient, surface loading, and axial load, governing soil slip behavior at the pile–soil interface. The application of axial loads on piles in groups resulted in reductions in group effects. An example analysis and two previous experimental observations of dragload and group effects were back-analyzed. The slip analysis estimated reasonable dragload and group effect, whereas unrealistic computations were obtained from the no-slip continuum analysis.

We fabricated OLEDs on corrugated high-refractive-index substrates with an EQE of 63%. The high efficiency was achieved by suppressing the thin film guided modes and efficiently extracting the surface plasmon mode with the corrugated structure.

Fluorinated polyimides have attracted much attention as potential materials for optical waveguide fabrication due to their high thermal stability, humidity resistance, as well as low optical loss in the wavelength region of optical communications. For the fabrication of optical waveguide structures, reactive ion etching (RIE) has been widely used. According to our study, the highest etch rate obtained with vertical profile for RIE of fluorinated polyimides with O2 plasma was 300 nm/min. Inductively coupled plasma (ICP) etching of Ultradel® 9020D fluorinated polyimide has been conducted to obtain waveguide channels with higher etch rate and more vertical profile than is possible with RIE. The etch rate and the etch profile have been investigated as a function of ICP power, r.f. chuck power, O2 flow rate, and chamber pressure. Etch rates of 1700 nm/min to 2200 nm/min with vertical profile and smooth sidewall were obtained by ICP etching at an ICP power of 500 W, r.f. chuck power of 150 W to 350 W, chamber pressure of 5 mTorr and O2 flow rate of 40 sccm. Under these conditions there was no appreciable change in the etch rate with chamber pressure in the range 5–20 mTorr.

Sapphire is uniquely suitable for sensor windows of electro-optical systems due to its high transparency, high mechanical strength, and chemical inactivity. Unfortunately, these same characteristics also cause polishing of sapphire windows to be extremely difficult and slow. Hence the challenge is to develop a process for affordable production of large area sapphire windows with low-roughness, low-stress and without surface and subsurface damage. Here we report a novel rapid chemical mechanical polishing process that increases the material removal rate during polishing of sapphire by greater than twofold over conventional processes. Such a process can also produce angstrom level surface finish.

We fabricated OLEDs on corrugated high-refractive-index substrates. With a macro lens to extract the substrate mode, we were able to achieve an EQE of 63.2%. The high efficiency was achieved by suppressing the thin film guided modes and efficiently extracting the surface plasmon mode with the corrugated structure.

The increasing demand for lightweight, miniaturized electronic devices has prompted the development of small, high-performance optical components for light-emitting diode (LED) illumination. As such, the Fresnel lens is widely used in applications due to its compact configuration. However, the vertical groove angle between the optical axis and the groove inner facets in a conventional Fresnel lens creates an inherent Fresnel loss, which degrades optical performance. Modified Fresnel lenses (MFLs) have been proposed in which the groove angles along the optical paths are carefully controlled; however, in practice, the optical performance of MFLs is inferior to the theoretical performance due to fabrication errors, as conventional design methods do not account for fabrication errors as part of the design process. In this study, the Fresnel loss and the loss area due to microscopic fabrication errors in the MFL were theoretically derived to determine optical performance. Based on this analysis, a design method for the MFL accounting for the fabrication errors was proposed. MFLs were fabricated using an ultraviolet imprinting process and an injection molding process, two representative processes with differing fabrication errors. The MFL fabrication error associated with each process was examined analytically and experimentally to investigate our methodology. (C) 2015 Optical Society of America

Hot embossing has been widely accepted as an alternative to photolithography in generating patterns on polymer substrates. The optimization of embossing process should be accomplished based on polymer surface properties. Therefore, in this paper, polymers with different surface characteristic were selected and the surface properties of each polymers such as surface energy and adhesion force were investigated by contact angle and AFM. Based on these results, the imprinted nano patterns were compared. Silicon molds with nano size patterns were fabricated by e-beam direct writing. Molds were coated with self-assembled monolayer (SAM) of (1, 1, 2, 2H –perfluorooctyl)-trichlorosilane to reduce the stiction between molds and polymer substrates. For embossing, pressure of 500 psi, embossing time of 5 min and temperature of above transition temperature were applied. Mr-I 8010 polymer (Micro Resist Technology), Polymethylmethacrylate (PMMA 495k) and LOR (polyaliphatic imide copolymer) were used as substrate for hot embossing process development in nano size. These polymers were spun coated on the Si wafer with the thickness of 150 nm. The nano size patterns obtained by hot embossing were identified by atomic force microscopy without breaking the pattern and compared based on the polymer surface properties. The mr-I 8010 which has the lowest surface energy and adhesion force shows the best demolding property.

Laser interference lithography (LIL) is a technique that allows maskless patterning of large areal periodic nano/micro structures. The LIL pattern is often used as an etch barrier to pattern SiO2 intermediate layer in the fabrication process of high aspect ratio silicon nano/micro structures by deep reactive ion etching process (DRIE) with SiO2 etch barrier. In this study, a method to fabricate high aspect ratio nanograting structures by direct DRIE process of silicon substrate using LIL pattern without intermediate layer was developed as a simple and cost-effective fabrication process. To fabricate high aspect ratio silicon nanograting with high pattern fidelity, a simulation method to predict the cross sectional profile of photoresist (PR) pattern after exposure and development processes was investigated, and the LIL processing conditions were selected to obtain optimized cross sectional profile of PR pattern without residual layer based on the simulation results. To minimize the side wall defects during the DRIE process due to the deterioration of LIL pattern etch barrier, the processing conditions of DRIE process including etching gas, etching gas ratio, passivation time and power were optimized. Finally, a silicon nanograting with a grating pitch of 780 nm and height of 2.42 µm (aspect ratio: 6) was fabricated via the developed direct DRIE process with LIL pattern.

We report a continuous wave laser output of a spiral-shaped InGaAs microcavity laser. When the boundary of the cavity is selectively pumped by current injection with a dc current, the laser generates a directional emission around the notch. We investigate the characteristics of the cw laser operation and observe whispering gallery type modes, whose Q factor is about 7000.