Promise For Several Applications Research Articles

(Invited) Processing of Perovskite Materials for Optoelectronic Devices

Among materials used for thin film technologies, perovskite materials have emerged as one of the rising stars for optoelectronic applications. They show great promise for several applications like e.g. photovoltaics, lasers, light emitting diodes or X-ray detectors. Their success is founded on the feature of some perovskite materials to be largely tolerant to the formation of defects, which enables functional layer deposition from liquid precursor inks. In order to exploit the extraordinary optoelectronic properties, it is necessary to adapt the material processing to the requirements of the application. For a large spectrum of devices, homogeneous, high quality, large grain poly-crystalline perovskite layers are required. Accordingly, our work strives to cover the whole spectrum of the layer formation ranging from the perovskite precursor ink chemistry, the deposition process to post-processing and re-crystallization.Regarding the precursor ink, we spotlight the complex formation of the lead halide species by nuclear magnetic resonance and electrical conductivity measurements. We found a strong and systematic impact of the choice of (Lewis base) solvent on the formation of lead complexes in the precursor solution. Surprisingly, a strong difference in the complex formation, not necessarily translates to notable differences in the resulting layers. Indeed, the difference observed in solvation and coordination appears to become less for increased concentrations of the precursor ink. As such we assume, that throughout the drying process, the impact of lead-solvent complexes observed in the ink might diminish. To add another parameter, we also included Lewis-base additives into our investigations, that evidently modify the shape and size of the crystallites in the resulting layers. Despite their far higher donor number, we found the additive to only marginally impact on the lead core in the liquid precursor. Rather, by in-situ GIWAXS characterization, we could show that the intake of thermal energy during the annealing process proves crutial for changes in the crystal formation. After a gas-quenching process, where the perovskite phase is already present, the formation process with and without additive did not show notable differences. Subsequent thermal annealing of the deposited layers on the other hand allows the coordination between lead and the additive and affords a re-organization of the perovskite phase. During the deposition process, anyhow, the process technology (like gas quenching) is still important to form a homogeneous and pinhole-free initial film, which then can reorganize to form a high-quality perovskite layer.In the second part of the presentation, we will show, that the strategy of thermally assisted reorganization is not limited to the initial annealing step. By using a thermal hot-pressing process, we are also able to trigger the perovskite re-organization and re-crystallization even if the perovskite deposition and formation process is already finished. We performed post-processing by providing thermal energy, while simultaneously limiting the available space where potential perovskite decomposition products could leak, by pressing it with a flat stamp. As a result, the perovskite recrystallizes and forms extremely smooth layers that comprise large grains and express remarkable optical quality. We show this strategy to be applicable to a large variety of different hybrid as well as all-inorganic perovskite materials. Employing patterned stamps, we also utilize this strategy to directly imprint photonic nanostructures (e.g. Bragg gratings) into the perovskite layers.We will show how additive driven reorganization and thermal imprint enable a variety of optoelectronic devices ranging from light harvesting (single-junction and tandem perovskite based solar cells) to stimulated light emission (perovskite lasers).

Wafer‐Scale Integration of Single Layer Graphene Electro‐Absorption Modulators in a 300 mm CMOS Pilot Line

AbstractGraphene‐based devices have shown great promise for several applications. For graphene devices to be used in real‐world systems, it is necessary to demonstrate competitive device performance, repeatability of results, reliability, and a path to large‐scale manufacturing with high yield at low cost. Here, single‐layer graphene electro‐absorption modulators are selected as test vehicles, and their wafer‐scale integration is established in a 300 mm pilot complementary metal‐oxide–semiconductor (CMOS) foundry environment. A hardmask is used to shape graphene, while tungsten‐based contacts are fabricated using the damascene approach to enable CMOS‐compatible fabrication. By analyzing data from hundreds of devices per wafer, the impact of specific processing steps on the performance could be identified and optimized. After optimization, modulation depth of 50 ± 4 dB mm−1 is demonstrated on 400 devices measured using 6 V peak‐to‐peak voltage. The electro‐optical bandwidth is up to 15.1 ± 1.8 GHz for 25 m‐long devices. The results achieved are comparable to lab‐based record‐setting graphene devices of similar design and CVD graphene quality. By demonstrating the reproducibility of the results across hundreds of devices, this work resolves the bottleneck of graphene wafer‐scale integration. Furthermore, CMOS‐compatible processing enables co‐integration of graphene‐based devices with other photonics and electronics building blocks on the same chip for high‐volume, low‐cost manufacturing.

Comparative Volatilomic Profile of Three Finger Lime (Citrus australasica) Cultivars Based on Chemometrics Analysis of HS-SPME/GC-MS Data.

Finger lime is receiving growing attention as an ingredient of gastronomic preparations of haute cuisine for its delicious flavor and fragrance and for its appealing aspect. Volatile compounds play a crucial role in determining the organoleptic characteristics of the fruit and its pleasantness for consumers. The aim of the present study was to investigate the volatile profiles by headspace solid phase micro-extraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) in the peel and, for the first time, in the pulp of three Australian finger lime cultivars grown in Sicily (southern Italy): Pink Pearl, Sanguinea, and Faustrime, allowing to overall identify 84 volatile organic compounds (VOCs). The analytical data showed that the three cultivars were characterized by distinct volatile chemotypes: limonene/sabinene/bicyclogermacrene in the Pink Pearl, limonene/γ-terpinene/bicyclogermacrene in the Sanguinea, and limonene/β-phellandrene/γ-terpinene in the Faustrime. Moreover, some volatiles, found exclusively in one cultivar, could be considered potential markers of the individual cultivar. PCA allowed us to clearly discriminate the samples into three clusters: the first related to the Sanguinea peel, the second to the Faustrime peel, and a third group associated with the Pink Pearl peel along with the pulp of the three cultivars. Accordingly, the VOCs that mostly contributed to the differentiation of the three finger lime cultivars were also identified. Among them, D-limonene, sabinene γ-terpinene, α-pinene, α-phellandrene, β-myrcene, p-cymene, linalool, δ-elemene, ledene, bicyclogermacrene β-citronellol, α-bergamotene, α-caryophillene, and β-bisabolene, have been previously reported to exhibit important biological activities, suggesting that these cultivars, in addition to possessing unique volatile profiles, can show promise for several applications in pharmaceutical and food industry, namely for development of functional foods.

Self-driven highly responsive p-n junction InSe heterostructure near-infrared light detector

Photodetectors converting light signals into detectable photocurrents are ubiquitously in use today. To improve the compactness and performance of next-generation devices and systems, low dimensional materials provide rich physics to engineering the light–matter interaction. Photodetectors based on two-dimensional (2D) material van der Waals heterostructures have shown high responsivity and compact integration capability, mainly in the visible range due to their intrinsic bandgap. The spectral region of near-infrared (NIR) is technologically important, featuring many data communication and sensing applications. While some initial NIR 2D material-based detectors have emerged, demonstrations of doping-junction-based 2D material photodetectors with the capability to harness the charge-separation photovoltaic effect are yet outstanding. Here, we demonstrate a 2D p-n van der Waals heterojunction photodetector constructed by vertically stacking p-type and n-type indium selenide (InSe) flakes. This heterojunction charge-separation-based photodetector shows a threefold enhancement in responsivity in the NIR spectral region (980 nm) as compared to photoconductor detectors based on p- or n-only doped InSe. We show that this junction device exhibits self-powered photodetection operation, exhibits few pA-low dark currents, and is about 3–4 orders of magnitude more efficient than the state-of-the-art foundry-based devices. Such capability opens doors for low noise and low photon flux photodetectors that do not rely on external gain. We further demonstrate millisecond response rates in this sensitive zero-bias voltage regime. Such sensitive photodetection capability in the technologically relevant NIR wavelength region at low form factors holds promise for several applications including wearable biosensors, three-dimensional (3D) sensing, and remote gas sensing.

Atomic Layer Deposition of AlN on Graphene

Graphene is a material with great promise for several applications within electronics. However, using graphene in any such application requires its integration in a stack of thin layers of materials. The ideal structure of graphene has a fully saturated surface without any binding sites for chemisorption of growth species, making film growth on graphene highly challenging. Herein, an attempt to deposit very thin layers of AlN using an atomic layer deposition approach is reported. It is demonstrated using X‐ray photoelectron spectroscopy that Al–N are formed in the films deposited on graphene and shown by scanning electron microscopy and atomic force microscopy that the films have an island morphology. These results may be considered promising toward the development of a growth protocol for AlN on graphene and possibly also for 2D AlN fabrication.

(Invited) Processing and Applications of Monodisperse Two-Dimensional Nanomaterial Inks

Two-dimensional nanomaterials have emerged as promising candidates for next-generation electronics and optoelectronics [1], but advances in scalable nanomanufacturing are required to exploit this potential in real-world technology. This talk will explore methods for improving the uniformity of solution-processed two-dimensional nanomaterials with an eye toward realizing dispersions and inks that can be deposited into large-area thin-films [2]. In particular, density gradient ultracentrifugation allows the solution-based isolation of graphene [3], boron nitride [4], montmorillonite [5], and transition metal dichalcogenides (e.g., MoS2, WS2, ReS2, MoSe2, WSe2) [6,7] with homogeneous thickness down to the atomically thin limit. Similarly, two-dimensional black phosphorus is isolated in organic solvents [8] or deoxygenated aqueous surfactant solutions [9] with the resulting phosphorene nanosheets showing field-effect transistor mobilities and on/off ratios that are comparable to micromechanically exfoliated flakes. By adding cellulosic polymer stabilizers to these dispersions, the rheological properties can be tuned by orders of magnitude, thereby enabling two-dimensional nanomaterial inks that are compatible with a range of additive manufacturing methods including inkjet [10], gravure [11], screen [12], and 3D printing [13]. The resulting printed two-dimensional nanomaterial structures show promise in several applications including photodiodes [14], anti-ambipolar transistors [15], gate-tunable memristors [16], and heterojunction photovoltaics [17,18]. [1] D. Jariwala, et al., ACS Nano, 8, 1102 (2014). [2] E. B. Secor, et al., Journal of Physical Chemistry Letters, 6, 620 (2015). [3] A. A. Green, et al., Nano Letters, 9, 4031 (2009). [4] J. Zhu, et al., Nano Letters, 15, 7029 (2015). [5] J. Zhu, et al., Advanced Materials, 28, 63 (2016). [6] J. Kang, et al., Nature Communications, 5, 5478 (2014). [7] J. Kang, et al., Nano Letters, 16, 7216 (2016). [8] J. Kang, et al., ACS Nano, 9, 3596 (2015). [9] J. Kang, et al., Proc. Nat. Acad. Sci. USA, 113, 11688 (2016). [10] E. B. Secor, et al., Journal of Physical Chemistry Letters, 4, 1347 (2013). [11] E. B. Secor, et al., Advanced Materials, 26, 4533 (2014). [12] W. J. Hyun, et al., Advanced Materials, 27, 109 (2015). [13] A. E. Jakus, et al., ACS Nano, 9, 4636 (2015). [14] D. Jariwala, et al., Proc. Nat. Acad. Sci. USA, 110, 18076 (2013). [15] D. Jariwala, et al., Nano Letters, 15, 416 (2015). [16] V. K. Sangwan, et al., Nature Nanotechnology, 10, 403 (2015). [17] D. Jariwala, et al., Nano Letters, 16, 497 (2016). [18] T. A. Shastry, et al., ACS Nano, 10, 10573 (2016).

Nanometer resolution optical coherence tomography using broad bandwidth XUV and soft x-ray radiation.

Optical coherence tomography (OCT) is a non-invasive technique for cross-sectional imaging. It is particularly advantageous for applications where conventional microscopy is not able to image deeper layers of samples in a reasonable time, e.g. in fast moving, deeper lying structures. However, at infrared and optical wavelengths, which are commonly used, the axial resolution of OCT is limited to about 1 μm, even if the bandwidth of the light covers a wide spectral range. Here, we present extreme ultraviolet coherence tomography (XCT) and thus introduce a new technique for non-invasive cross-sectional imaging of nanometer structures. XCT exploits the nanometerscale coherence lengths corresponding to the spectral transmission windows of, e.g., silicon samples. The axial resolution of coherence tomography is thus improved from micrometers to a few nanometers. Tomographic imaging with an axial resolution better than 18 nm is demonstrated for layer-type nanostructures buried in a silicon substrate. Using wavelengths in the water transmission window, nanometer-scale layers of platinum are retrieved with a resolution better than 8 nm. XCT as a nondestructive method for sub-surface tomographic imaging holds promise for several applications in semiconductor metrology and imaging in the water window.

Prospects of Colloidal Copper Chalcogenide Nanocrystals.

Over the past few years, colloidal copper chalcogenide nanocrystals (NCs) have emerged as promising alternatives to conventional Cd and Pb chalcogenide NCs. Owing to their wide size, shape, and composition tunability, Cu chalcogenide NCs hold great promise for several applications, such as photovoltaics, lighting and displays, and biomedical imaging. They also offer characteristics that are unparalleled by Cd and Pb chalcogenide NCs, such as plasmonic properties. Moreover, colloidal Cu chalcogenide NCs have low toxicity, potentially lower costs, and excellent colloidal stability. This makes them attractive materials for the large-scale deployment of inexpensive, sustainable, and environmentally benign solution-processed devices. Nevertheless, the synthesis of colloidal Cu chalcogenide NCs, especially that of ternary and quaternary compositions, has yet to reach the same level of mastery as that available for the prototypical Cd chalcogenide based NCs. This review provides a concise overview of this rapidly advancing field, sketching the state of the art and highlighting the key challenges. We discuss recent developments in the synthesis of size-, shape-, and composition-controlled NCs of Cu chalcogenides, with emphasis in strategies to circumvent the limitations arising from the need to precisely balance the reactivities of multiple precursors in synthesizing ternary and quaternary compositions. In this respect, we show that topotactic cation-exchange reactions are a promising alternative route to complex multinary Cu chalcogenide NCs and hetero-NCs, which are not attainable by conventional routes. The properties and potential applications of Cu chalcogenide NCs and hetero-NCs are also addressed.

Five-star transportation: using online activity reviews to examine mode choice to non-work destinations

Information and communication technologies are generating unprecedented quantities of data with potential applications in transportation planning and research. Because of their focus on non-work activities, crowdsourced activity reviews such as Yelp reviews have the potential to inform how individuals make travel choices to a range of activities with significant economic impacts. Substantial numbers of Yelp reviews include transportation content, including mode choices. I use content analysis to extract and understand statements on mode from a dataset of more than 225,000 Yelp reviews in the Phoenix metropolitan area. Spatial analysis of the results shows that access to non-work destinations varies significantly by mode across the region and within neighborhoods. The findings address ongoing questions in accessibility research, including preferences for transit around rail stations and local variability in walking preferences. Yelp data do not replace travel surveys, but they provide significantly more information and spatial detail on mode choice to many non-work destinations. Though this and similar datasets show promise for several applications in transportation planning and research, the issues of potential sampling biases and data ownership and access must also be addressed for these data to become widespread tools for practioners and researchers.

Differences in compositional properties of a hulless barley cultivar grown in 23 environments in eastern Canada

Abdel-Aal, E. M. and Choo, T.-M. 2014. Differences in compositional properties of a hulless barley cultivar grown in 23 environments in eastern Canada. Can. J. Plant Sci. 94: 807–815. Barley grains hold a promise for several applications in food, feed, energy and malting industries due to their diverse components and functionalities. The current study aimed to investigate compositional and 2, 2-diphenyl-1-picrylhydrazyl radical (DPPH) scavenging properties of a newly developed hulless barley cultivar, AAC Azimuth. The cultivar was grown at 11 sites in 2010 and 12 sites in 2011 in Ontario and Quebec, Canada. The results showed that most of the nutrients examined in barley varied significantly among locations. In addition several components varied by year such as β-glucan, protein and phenols. There were significant year×location interactions for all of these nutrient components. The application of fungicides increased the content of moisture, but it decreased the content of phenols. The new cultivar contained relatively low amount of dietary fiber, average amount of β-glucan, and high levels of starch and protein, which could improve the feed and energy value. The cultivar also had total phenols and DPPH antioxidant capacity within the range of yellow and color barleys showing its antioxidant potential. The absence of hulls along with reasonable levels of protein, total antioxidant phenols and DPPH antioxidant capacity would promote the cultivar for food use subject to flour characteristics and functionality.

Novel polymer–polyphenol beads for encapsulation and microreactor applications

Novel structures with controllable morphology made from natural materials hold promise for several applications in pharmaceuticals, foods and biotechnology field. In this paper, we utilized the strong interactions between epigallocatechin gallate (EGCG), a polyphenol obtained from green tea, and water soluble cellulose ethers like methyl cellulose (MCE) and hydroxyl propyl methylcellulose (HPMC) to fabricate novel beads with controllable core–shell morphology. The novel polymer–polyphenol beads were prepared by simply adding polymer solution dropwise into an aqueous solution of polyphenol. Effect of process variables like concentration and viscosity grades of polymer, reaction time and concentration of EGCG on bead formation was evaluated. Spherical milky white beads with average diameters ranging from 600–2500 µm were obtained that retained shape after freeze drying. Internal structure of beads was studied using automated light microscopy and cold stage scanning electron microscopy (Cryo-SEM). Percent loading of EGCG in the beads was above 25% w/w in all the cases. The release study in simulated intestinal fluid revealed burst release of EGCG (20% in first 5 minutes) followed by sustained release with more than 90% release at the end of 300 minutes. The antioxidant power of EGCG in the beads was effectively maintained in the alkaline conditions with 5–6 fold activity as compared to free EGCG. Further, the temperature triggered release characteristic of beads was explored by encapsulating eucalyptus oil and studying the release of oil using hot stage microscopy. Enzyme immobilisation application of beads was demonstrated by immobilising α-amylase onto the beads and studying its enzyme activity after several washings.

Capability of Raman lidar for monitoring the variation of atmospheric CO2 profile

Lidar (Light detection and ranging) has special capabilities for remote sensing of many different behaviours of the atmosphere. One of the techniques which show a great deal of promise for several applications is Raman scattering. The detecting capability, including maximum operation range and minimum detectable gas concentration is one of the most significant parameters for lidar remote sensing of pollutants. In this paper, based on the new method for evaluating the capabilities of a Raman lidar system, we present an evaluation of detecting capability of Raman lidar for monitoring atmospheric CO2 in Hefei. Numerical simulations about the influence of atmospheric conditions on lidar detecting capability were carried out, and a conclusion can be drawn that the maximum difference of the operation ranges caused by the weather conditions alone can reach about 0.4 to 0.5km with a measuring precision within 30ppmv. The range of minimum detectable concentration caused by the weather conditions alone can reach about 20 to 35 ppmv in vertical direction for 20000 shots at a distance of 1 km on the assumption that other parameters are kept constant. The other corresponding parameters under different conditions are also given. The capability of Raman lidar operated in vertical direction was found to be superior to that operated in horizontal direction. During practical measurement with the Raman lidar whose hardware components were fixed, aerosol scattering extinction effect would be a significant factor that influenced the capability of Raman lidar. This work may be a valuable reference for lidar system designing, measurement accuracy improving and data processing.

Novel photochemical/photoelectrochemical systems based on metal hexacyanoferrates

Abstract Electrolyte modification is realized to be a promising route to achieve better efficiencies in solar energy conversion in photoelectrochemical cells. Recent reports by Bocarsly et al. [1,2] and Licht et al. [3,4] have amply demonstrated this aspect wherein maximum efficiency received so far viz. 16.4% has been reported using chalcogenides of Cd as semiconductors in contact with a solution of a mixture of ferro/ferricyanide containing added cyanide ions. Surface modification of the semiconductor, cadmium sulphide/selenide, that takes place as a result of interaction with the redox, giving rise to cadmium hexacyanoferrate, has been considered important in yielding the improved energy efficiency. But interestingly, no attempt to ascertain the role of modifying hexacyanoferrate film formed as a possible photo-energy converter (also) has been made. Many metal hexacyanoferrates themselves semiconductors, being intervalent compounds, are subjects of intensive current research as they hold promise in several applications of sensors, electrochromic devices, catalysis, and most importantly in photo-energy conversion. In this context we report the results of photoresponse studies on indium hexacyanoferrate films on conducting carbon in contact with solutions of Fe(CN) −3 6 . We conclude from these studies that such interfaces under light irradiation indeed give rise to measurable and significant photocurrents whose nature is distinctly different from that obtained in the absence of a redox in solution. The article describes the observations and explains them taking into account photo/photoelectrochemical effects.

Nondestructive ion-implant monitoring using laser Raman spectroscopy

A new Raman technique for monitoring low-dose ion implants is described. The capability for detection of implants of 20– 50 keV B+ (or equivalent [Formula: see text] energies) at doses as low as ~1010 cm−2 is of particular interest. Currently, there are few other noncontact, nondestructive methods of evaluating implant doses below 1013 cm−2 (e.g., Vt-adjust, field, and p-well implants) in patterened production wafers. The feasibility of using the technique for monitoring Vt-adjust implants is demonstrated.Low-energy B+ and [Formula: see text] ion implants in silicon were studied to determine the detection limits of the technique. Samples were analyzed immediately after implantation, without annealing. Implant doses in the range from 3 × 1016 cm−2 to the detection limit of 3 × 1010 cm−2 were characterized in this way. The presence of a surface layer of SiO2 (≤ 100 nm thick) did not interfere with the measurements. A tunable laser was used to optimize the sensitivity to implants of different energies.Since the frequency spectrum of Raman scattering can also provide information on the structure of the damaged region or on the distribution of activated boron and residual ion damage after annealing, Raman spectroscopy shows promise in several applications for in situ process monitoring of ion implantation for very large scale integration technology.

Optical Properties and Applications of Photochromic Glass

Corning Glass Works has recently developed a series of inorganic bulk photochromic materials. The present paper is concerned with the results of an extensive laboratory investigation of their properties. It is shown that the fatigueless reversibility and the optical characteristics of these glasses hold definite. promise for several applications.