bluuebunny/crossref_metadata_2025_split huggingface dataset:
Label-Free and Real-Time Photonic Sensors As Analytical Platforms for Environmental Monitoring of Pollutants and Medical Diagnosis
Authors: Marsal Lluis F. , Alba Maria , Macias Gerard , Formentin Pilar , Ferre-Borrull Josep , Pallares Josep , Santos Abel 
Published: February 2020

Nowadays, most diagnostic techniques employ labelled samples with fluorescent markers, making analyses time-consuming and expensive. Recently, the development of highly sensitive and label-free nanoporous-based sensors has shown promising results for applications in areas such as environmental science, biomedical research and medical diagnostics [1-2]. Among the variety of possible materials, nanoporous anodic alumina (NAA) and nanoporous silicon (NPSi) have demonstrated to be excellent sensing platforms by their outstanding set of properties and cost-effective fabrication processes [3-4]. Optical and photonic properties as reflectance, transmittance, absorbance and photoluminescence can be structurally engineered by modifying the effective medium of these nanoporous materials [5-6]. Furthermore, further chemical functionalization endows these nanoporous platforms with chemical selectivity for detection of specific analytes.
In this scenario, herein, we present some strategies for the production of label-free optical sensors based on NAA and NPSi. These strategies are based on the design and fabrication of specific nanoporous structures with enhanced optical response (e.g. microcavities, Fabry-Pérot structures, filters, etc.) and additional chemical functionalization of the inner surface to make these nanostructures sensitive to specific analytes. Figure 1 shows some scanning electron microscopy (SEM) images of NPSi and NAA structures. Furthermore, we analyze and discuss different detection techniques such as reflectometric interference spectroscopy, photoluminescent spectroscopy and test their performance in the detection of proteins and heavy metal ions. Finally, we discuss about the future and potential applications of these sensing platforms in areas such as environmental monitoring, biotechnology, medical diagnostics, drug screening, food safety and security.

References

[1]Amarie, D., Glazier, J.A., Sensors, 2012, 12, 17262.
[2] Rapp, B.E., Gruhl, F.J., Länge, K., Analytical and Bioanalytical Chemistry, 2010, 398, 2403.
[3] Sailor, M.J., Wu, E.C., Advanced Functional Materials, 2009, 19, 3195.
[4] Md Jani, A.M., Losic, D., Voelcker, N.H., Progress in Materials Science, 2013, 58, 636.
[5] Santos, A., Macias, G., Ferré-Borrull, J., Pallarés, J., Marsal, L.F., ACS Applied Materials & Interfaces, 2012, 4, 3584.
[6] Kumeria, T., Santos, A., Losic, D., ACS Applied Materials & Interfaces, DOI: 10.1021/am403465x.

Acknowledgements

This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under grant No. TEC2012-34397 and AGAUR 2009 SGR 549.
Design of Extremely Proximity Gettering Using Hydrogen Ion Implantation for Si CMOS Image-Sensor
Authors: Kim Il-Hwan , Park Jun-Seong , Song Seung-Hyun , Park Joo-Hyeong , Park Jea-Gun 
Published: February 2020

As the pixel size in CMOS image-sensor has scaled down less than 1 μm, photo sensitivity which is a ratio of photo and dark current has been important. To improve photo sensitivity in CMOS image-sensor, the achievement of lower dark current is essential. Leakage current is influenced by crystallographic, trapped charge at the SiO2/Si interface, structural defects, and especially metallic contaminant impurities. Also, these contaminant impurities degrade the minority-carrier recombination lifetime.
Thus, we investigated the dependency of the properties of CMOS image-sensor on metallic contamination. Standard aqueous solutions of metallic ion were dropped on the surface of silicon wafers and the wafers were spin dry. They were heated to drive the metallic ion contaminants into the silicon bulk. After that, we fabricated 4-Tr CMOS image-sensor cells. In silicon bulk wafer, the minority-carrier recombination lifetime decreased with increasing a metallic contaminant concentration. These contaminations result in degradation of dark current, sensitivity of photodiode and sensing margin of CMOS image-sensor. These results indicate that metallic contaminants are critical for increasing dark current because metallic contaminants remain inside the photo-diode region, ~3 μm.
In our study, we applied a proximity relaxation-type gettering method. We formed the nano-cavities close to the depletion region using hydrogen ion implantation, as shown in Fig 1. These cavities getter metallic impurities on the cavities wall. Sensing margin of CMOS image-sensor implanted by hydrogen ion was dramatically improved, as shown in Fig 2. In addition, although metallic contaminant concentration increased, the device performances of CMOS image-sensor were constant compare with that of bulk wafer which were not implanted (Fig. 3). These results indicates that proximity gettering by using hydrogen ion implantation was effective in metal gettering for image-sensor. We investigated the correlation of metallic contaminant and sensing margin of CMOS image-sensor. Finally, we will suggest an extremely proximity gettering method for removing metallic contaminants of CMOS image-sensor.
* This work was financially supported by the Brain Korea 21 Plus Program in 2013 and SiWEDS (Silicon Wafer Engineering and Defect Science).
(Invited) High Brightness, Large Scale GaN Based Light-Emitting Diode Grown on 8-Inch Si Substrate
Authors: Lee Seung-Jae , Park Hyung-Jo , Park Jun-Beom , Jeon Dae-Woo , Baek Jong Hyeob , Li Hongwei , Krishnan Balakrishnan , Su Jie , Paranjpe Ajit , Lee Dong S. 
Published: February 2020

GaN based light-emitting diodes(LEDs) grown on a Si substrate is one of promising future technologies in LED industry due to its scalability and costeffectiveness compare to the conventional sapphire based LEDs.One of major technical issues in GaN/Si LED is the severemismatch oflattice and thermal expansion coefficientsbetween GaNand Si, which induces significant tensile strain in the GaNepilayer that often leads to wafer cracking. Optical loss by the absorbing Si substrate is another barrier to overcome for realizing high-brightness LEDs competitive to those on sapphire or SiC substrates.
In this study, we demonstrated blue LEDs grown on 8-inch diameter Si substrate and fabricated high brightness devicesutilizing vertical chip process Thecrack-free InGaN/GaN LED waferswith strain-engineered buffer structure were grown on 8-inch diameter Si(111) substrates by metalorganic chemical vapor deposition (MOCVD) system (Veeco TurboDisk k465i).The optimized growth conditions of AlN buffer layer improved the crystalline quality of GaNepilayers. The FWHM of (002) and (102) ω-scan is 280 and 420 arcsec, respectively. These values are comparable to the best reported so far for GaN on silicon. The surface morphology of GaN layer investigated using atomic force microscopy (AFM) exhibits very smooth surface and clear atomic step flow patterns. The root-mean-square (RMS) roughness is 0.15 nm in a 5x5 μm2 scan area.For LED on 8-inch Si, MQW PL wavelength uniformity of ~0.5% (2.4 nm) has been achieved using the proper strain/curvature engineering with optimized wafer carrier designs. These are among the lowest values reported to date.
After the epitaxial growth with silicon substrate, a 1mm × 1mm sized vertical type LED(VLED) was fabricated using both wafer bonding process and Si removing process. While the GaN on sapphire employs a laser lift-off technique to remove the substrate, we developed the wet etching process in order to remove the silicon substrate without any damageon the surface of LED structure. The electro-optical characteristics of the fabricated VLED in this work shows good efficiency(almost 1W light power at 1A inject current) with operating voltage of 4.0V.
(Invited) Spatially Resolved Study of the EQE Droop in InGaN QW LEDs: Interplay of Point Defects, Extended Defects, and Carrier Localization
Authors: Lin Yue , Zhang Yong , Liu Zhiqiang , Wei Tongbo , Chen Zhong 
Published: February 2020

Spatially-resolved electroluminescence (as a function of injection current) and spatially-resolved photoluminescence (as a function of excitation power) are used to investigate the external quantum efficiency (EQE) droop in InGaN QWs based blue LEDs. The spatially-resolved EL mapping allows us to study two most commonly observed but distinctly different droop behaviors on a single device, minimizing the ambiguity trying to compare independently fabricated devices. We conclude that the EQE ~ current curve reflects the interplay of three effects: nonradiative recombination through point defects, carrier localization due to either In composition or well width fluctuation, and nonradiative recombination of the extended defects, which is in fact common to various optoelectronic devices.[1] By comparing EL and PL mapping data, we show that individual singular sites exhibiting either particularly strong or weak emission in PL do not usually play any significant and direct role in the EQE droop. We introduce a two-level model that can capture the basic physical processes that dictate the EQE ~ current dependence and describe the whole operating range of the device from 0.01 – 100 A/cm2.
[1] Y. Lin, Y. Zhang, Z. Q. Liu, L. Q. Su, J. H. Zhang, T. B. Wei, and Z. Chen, Appl. Phys. Lett. 101, 252103 (2012).
In collaboration with Yue Lin, Zhiqiang Liu, Liqin Su, Jihong Zhang, Tongbo Wei, and Zhong Chen.
Analysis of InGaN/GaN Multiple Quantum Well Heterostructures by Means of Photoconductivity Measurements
Authors: Krause John Robert , Stokes E. B. , Deguzman Panfilo C , Mizuyama Yosuke , Kolli Rajesh 
Published: February 2020

A novel method for the characterization of multiple quantum well(MQW) light emitting diodes(LEDs) is investigated. This method involves the measurement of photocurrent generation in an LED when irradiated with photons of energy near the absorption edge of the quantum wells. In this situation the I-V curve of the LED reveals a number of photocurrent oscillation zones corresponding to spatial variations in the heterostructure (Figure 1).
The mechanism leading to the voltage-bias dependence of these features is hypothesized to be the expansion of the depletion (space-charge) region. Electrons and holes, from the N and P regions respectively, are drawn to the P-N junction as the reverse bias-voltage is increased. The area occupied by the ionized dopant atoms left behind by these charges is referred to as the ‘depletion region’. As the magnitude of the bias increases this area of depleted atoms becomes larger, engulfing the quantum wells in series. An electric field forms between the charges gathered at the P-N junction and the ionized atoms, giving rise to a potential gradient across the depletion region. The I-V features are then caused by the dynamics of the excited electrons as the potential gradient traverses each quantum well.
A preliminary model is constructed by using the SIMS data (Figure 2) for the LED heterostructure supplied by Veeco. The spatial extent of the depleted region is calculated as a function of the applied bias using a doping profile derived from the SIMS data. This allows the estimation of the voltage at which each quantum well will become depleted and thus when a feature will be expected. The resulting curve is compared to the experimentally determined I-V feature spacing.
The wavelength and temperature dependencies of this phenomenon are discussed, citing examples from existing literature. The benefits of this method of analysis are examined in terms of acquisition speed, measurement resolution and hardware cost with respect to current techniques such as capacitance-voltage measurement.
Further research into this effect would involve the spectral transmission of the MQW devices as a function of voltage bias and the possible applications in spectrometry or optical filtering. A more complete picture of the quantum mechanical interaction between the incident photons, quantum wells, and potential gradient would also be valuable for the interpretation of the I-V curves and possible engineering applications.
Ti/Al/Ni/Cu Ohmic Contact with Low Contact Resistance and Smooth Surface Morphology for AlGaN/GaN HEMT
Authors: Wong Yuen-Yee , Chang Edward Yi , Chen Yu-Kong , Liu Shih Chien , Lin Yueh-Chin , Maa Jer-Shen 
Published: February 2020

The feasibility of replacing the Au layer in Ti/Al/Ni/Au ohmic contact for AlGaN/GaN structure with Cu has been investigated. In this study, the thicknesses of Ti, Al and Cu layers were fixed at 200 Å, 1200 Å and 1000 Å, respectively. On the other hand, Ni layer with different thicknesses were used to examine its influence on the Cu-based ohmic contacts. The results showed that the Ni layer played an important role in the Ti/Al/Ni/Cu metallization for achieving low contact resistance, smooth morphology and excellent edge acuity. With a 50-Å Ni layer, a low specific contact resistance of 1.35x10-6 ohm-cm2 has been realized. This result is comparable with the conventional ohmic contact of Ti/Al/Ni/Au (1.19 x 10-6 ohm-cm2). Furthermore, in the absence of Au, the surface roughening caused by Au-Al alloy in the conventional ohmic contact was also prevented. As a result, the root-mean-square roughness of the optimized Cu-based contact was only 7.62 nm as compared to 134 nm for the conventional structure.
The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results suggest that the formation of TiN at the Ti/semiconductor interface has played an important role in achieving low contact resistance similar to the case for the Ti/Al/Ni/Au structure. In addition, the formation of more stable Ti-Al-Cu based alloys in the Cu-based ohmic contact had successfully confined the Cu within the ohmic contact. Both TEM and Auger electron spectroscopy (AES) results confirmed that no Cu was detected in the semiconductor layers. Finally, high electron mobility transistors (HEMTs) were fabricated using the Cu- and Au-based ohmic contacts. Both devices showed the similar DC characteristics suggesting that the Ti/Al/Ni/Au metallization has a great potential to be used as the ohmic contact for AlGaN/GaN devices.
(Invited) Novel Luminescent Materials Based on Semiconductor Nanowires
Authors: LaPierre Ray R , Gustafsson Anders , Kuyanov Paul , Haapamaki Chris 
Published: February 2020

We report novel luminescent materials based on group III-V compound semiconductor nanowires. Semiconductor nanowires are essentially one-dimensional rods with length of several microns and diameter below 100 nm. Hence, nanowires exhibit interesting quantum confinement and carrier transport properties. Nanowires are grown using metal seed particles by the vapor-liquid-solid (VLS) process in a molecular beam epitaxy or metalorganic chemical vapor deposition system. By varying the material deposition during growth, axial or radial nanowire heterostructures and p-n junctions may be formed for various device applications including light emitting diodes, lasers, and photodetectors. Due to the large surface area to volume ratio of a nanowire, lattice mismatch strain may be accommodated by elastic distortion of the nanowire without detrimental misfit dislocations, which gives a much greater ability to perform bandgap engineering in nanowires as compared to thin films. Hence, unique heterostructures are possible in nanowires that would be impossible in thin films, opening up new device applications and possibilities in condensed matter physics.
We will report our recent work on the photoluminescence properties of InAsP/InP nanowires. InP nanowires were grown on <111> Si substrates by the Au-assisted vapor-liquid-solid process in a gas source molecular beam epitaxy system. InAsyP1-y segments were grown in the middle of the InP nanowires, creating a multiple quantum dot structure or superlattice. The quantum dot dimensions and composition were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX). Photoluminescence (PL) from the quantum dot structure could be tuned by the InAsyP1-y composition (y), or by the size of the quantum dot via the quantum confinement effect. Cathodoluminescence (CL) measurements confirmed localized emission from the quantum dots. To reduce detrimental surface states, the nanowires were passivated with an AlInP shell, which resulted in strong PL emission.
The growth mechanism of the quantum dots were inferred from the InAsP and InP segment lengths as a function of nanowire diameter. Short InAsP segment lengths were found to grow by depletion of In from the Au particle as well as by direct impingement, while longer segments of InAsP and InP grew by diffusive transport of adatoms from the nanowire sidewalls. The present study offers a manner to engineer the lengths of InAsP quantum dots embedded in InP barriers to better control the PL or CL emission. A novel group III and V gas switching sequence is presented to improve compositional control of the QD.
Green Emission of Terbium Doped Silicon Rich Silicon Oxide Films Obtained By Chemical Vapor Deposition
Authors: Podhorodecki Artur , Zatryb Grzegorz , Golacki Lukasz W , Misiewicz Jan , Wojcik Jacek , Willson Patric R.J. , Masher Peter , Wang J , Jadwisienczak Wojciech 
Published: February 2020

The effect of silicon concentration, annealing temperature and influence of post-growth hydrogen incorporation on terbium (Tb3+) luminescence was investigated for thin silicon rich silicon oxide films (SRSO). The structures were deposited by means of plasma enhanced chemical vapor deposition (ECR-PECVD). The structural properties of these films were investigated by Rutherford backscattering spectrometry, transmission electron microscopy, FTIR and Raman scattering. The optical properties were investigated by means of photoluminescence, cathodoluminescence and photoluminescence decay spectroscopy.
In this poster, we present a detailed discussion of these issues and determine the optimal conditions of the SRSO films from the point of view of Tb3+ emission properties.
An increase in the Si concentration in SRSO influences the emission properties in two ways. First of all, the refractive index of the film increases which enhances the oscillator strength of the optical transitions. On the other hand, the non-radiative recombination also increases, limiting the PL intensity. Therefore, from the point of view of emission efficiency, the optimal Si concentration in the film is about 35 at.% Si. Besides the Si concentration, another effect investigated in this work was the influence of the annealing temperature on Tb3+ emission. It was found that the PL intensity increases as a function of the annealing temperature. This effect was ascribed to the structural changes of the SRSO matrix. At early stages of the annealing (up to annealing temperature equal to 900oC) the most important factor enhancing the Tb3 emission intensity is a reduction in the number of non-radiative recombination centers. However, as shown by Raman measurements, starting from Ta =1100oC structural changes occur in the matrix (crystallization and formation of the Si nanocrystals) and the Tb environment significantly changes. Therefore, the further increase in the PL intensity obtained for high annealing temperatures (temperatures in the 1100–1200 oC range) can be ascribed to the increasing oscillator strength of the intra-4f transitions, induced by the change of the crystal field around the ions.
Fluorinated Graphene-Based High Performance Electrodes for Primary Lithium Batteries
Authors: Damien Dijo , Sudeep Parambath M , Narayanan Tharangattu , Anantharaman Maleimadam R , Ajayan Pulickel M , Shaijumon Manikoth M 
Published: February 2020

Though rechargeable Li ion battery has become the dominant power source for portable electronics applications, primary batteries are used in applications like military and defense tools, medical implants, long time spatial exploratory missions, cameras etc.1 By virtue of the low molecular weight and high redox potential of the constituting elements, Li/CFx primary battery has clear dominance over any other competing primary battery technologies like Li/MnO2 or Li/SOCl2 in terms of its energy density, exceptionally long shelf life and a wide operating temperature window.2, 3 However, with its poor rate capability, owing to low electrical conductivity and diffusion limited kinetics, Li/CFx battery system is less preferred compared to other battery chemistry like MnO2 based systems.2 Different strategies have been developed specifically for improving energy density, power density and faradic yield of Li/CFx batteries.1 However, a single step strategy capable of improving all the electrochemical parameters still remains to be challenge. Here, we demonstrate the use of fluorinated graphene (FG) as high performance cathode for Li primary battery. FG, obtained through chemical exfoliation of fluorinated graphite polymer (CF0.25)n using improved method,4 exhibited enhancements in energy density and power capability along with exceptional faradaic yield, all in a single step. The obtained specific capacity for FG derived from (CF0.25)n in the present work, is comparable to the theoretical capacity of (CF0.75)n. Further improvements in electrochemical performance could be achieved by optimizing the fluorine content in the starting material. The excellent electrochemical performance achieved here using fluorinated graphene with a very low fluorine content (x= 0.22) could lead to the development of highly efficient primary battery systems with low cost and minimum environmental impact.

Figure 1. Comparison of specific capacities of (CF0.25)nand FG electrodes when galvanostatically discharged against lithium at different current rates.

References

1 K. Guérin, M. Dubois, A. Houdayer and A. Hamwi, J. Fluorine Chem., 134 (2012), 11
2 P. Lam and R. Yazami, J. Power Sources, 153 (2006), 354
3 Z. Sheng , D. Foster and J. Read, J. Power Sources, 188 (2009), 601
4 A. Mathkar, T. N. Narayanan, L. B. Alemany, P. Cox, P. Nguyen, G. Gao, P. Chang, R. Romero-Aburto, S. A. Mani and P. M. Ajayan, Part. Part. Syst. Charact., 30 (2013), 266
Thin and Flexible Solid State Electrolytes for Ambient and Middle Temperature Storage Systems
Authors: Ahlbrecht Katharina , Hupbauer Cornelius , Tübke Jens , Hoffmann Michael J 
Published: February 2020

Solid state electrolytes are generally used in high-temperature systems such as fuel cells or sodium/sulfur batteries. They are common in stationary energy storage applications. The benefit of the solid state electrolytes is their high ion selective conductivity, even exceeding the value of most liquid electrolytes at elevated temperatures. But a widespread use is hindered by their brittleness and fragility. To use the solid state electrolyte in next generation systems, such as in Li/S, Li/Air or sodium-based systems at ambient or middle temperature, the solid state electrolyte is embedded in a flexible, ductile and non-metallic material by using a recently developed manufacturing process. The advantage of those composite materials is the possibility of their plastic deformation under stress. The connection between the solid state electrolyte and the ductile material can be established for example by surface bonding.
By using adjusted and optimized electrolytes for each electrode in the Li/S battery, intrinsic parasitic effects like the polysulfide shuttle mechanism or electrolyte degradation at the side of the alkaline metal anode could be prevented. As an alternative to commercialized lithium-based batteries sodium-based systems become more and more popular. Due to the low melting temperature of sodium (about 100 °C), it is conceivable to use molten sodium as an anode separated with a thin, flexible and stable solid state electrolyte from a cathode. With this design a formation of dendrites and a reaction with the liquid electrolyte could be reduced and improved cycling stability can be obtained.