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ScienceDaily

Going small for big solutions: Sub-nanoparticle catalysts made from coinage elements as effective catalysts

Due to their small size, nanoparticles find varied applications in fields ranging from medicine to electronics. Their small size allows them a high reactivity and semiconducting property not found in the bulk states. Sub-nanoparticles (SNPs) have an extremely small diameter of around 1 nm, making them even smaller than nanoparticles. Almost all atoms of SNPs are available and exposed for reactions, and therefore, SNPs are expected to have extraordinary functions beyond the properties of nanoparticles, particularly as catalysts for industrial reactions. However, preparation of SNPs requires fine control of the size and composition of each particle on a sub-nanometer scale, making the application of conventional production methods near impossible.

To overcome this, researchers at the Tokyo Institute of Technology led by Dr. Takamasa Tsukamoto and Prof. Kimihisa Yamamoto previously developed the atom hybridization method (AHM) which surpasses the previous trials of SNP synthesis. Using this technique, it is possible to precisely control and diversely design the size and composition of the SNPs using a “macromolecular template” called phenylazomethine dendrimer. This improves their catalytic activity than the NP catalysts.

Now, in their latest study published in Angewandte Chemie International Edition, the team has taken their research one step further and has investigated the chemical reactivity of alloy SNPs obtained through the AHM. “We created monometallic, bimetallic, and trimetallic SNPs (containing one, combination of two, and combination of three metals respectively), all composed of coinage metal elements (copper, silver, and gold), and tested each to see how good of a catalyst each of them is,” reports Dr Tsukamoto. 

Unlike corresponding nanoparticles, the SNPs created were found to be stable and more effective. Moreover, SNPs showed a high catalytic performance even under the milder conditions, in direct contrast to conventional catalysts. Monometallic, bimetallic, and trimetallic SNPs demonstrated the formation of different products, and this hybridization or combination of metals seemed to show a higher turnover frequency (TOF). The trimetallic combination “Au4Ag8Cu16” showed the highest TOF because each metal element plays a unique role, and these effects work in concert to contribute to high reaction activity.

Furthermore, SNP selectively created hydroperoxide, which is a high-energy compound that cannot be normally obtained due to instability. Mild reactions without high temperature and pressure realized in SNP catalysts resulted in the stable formation of hydroperoxide by suppressing its decomposition.

When asked about the relevance of these findings, Prof Yamamoto states: “We demonstrate for the first time ever, that olefin hydroperoxygenation can been catalyzed under extremely mild conditions using metal particles in the quantum size range. The reactivity was significantly improved in the alloyed systems especially for the trimetallic combinations, which has not been studied previously.”

The team emphasized that because of the extreme miniaturization of the structures and the hybridization of different elements, the coinage metals acquired a high enough reactivity to catalyze the oxidation even under the mild condition. These findings will prove to be a pioneering key in the discovery of innovative sub-nanomaterials from a wide variety of elements and can solve energy crises and environmental problems in the years to come.

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ProgrammableWeb

Top 10 Countries APIs

Developers wishing to create applications supplied with data about individual countries and other international data may be interested in these APIs found in the Countries category of ProgrammableWeb.

What is a Countries API?

A Countries API, or Application Programming Interface, is an interface that connects developers to software featuring data concerning countries around the world.

APIs in the Countries category may provide data about demographics, geography, culture, flags, airport codes, postal codes, capital cities, universities, natural history, currency and financial markets, environment and any number of regional features.

This article focuses on the 10 favorite Countries APIs of ProgrammableWeb readers.

1. REST Countries API

REST Countries APITrack this API provides information about the world’s nations via REST calls. These calls allow users to retrieve all available countries or to retrieve a given country’s currency, capital city, calling code, region, sub-region, ISO 639-1 language, name, or country code.

2. Nutritics API

Nutritics APITrack this API supports the extraction and manipulation of nutrition and food-related data from the official national databases of countries around the world. It operates as a multilingual gateway portal to country-specific nutrition and dietetics data. The API is useful for developing analytical addons applications for recipes, diets, and meal planning, in addition to customizing access to academic research and collaboration resources.

Nutritics API provides nutrition of products from specific countries. Image: Nutritics

3. University Domains and Names Data List API

The University Domains and Names Data List APITrack this API from Hipo Labs retrieves JSON files with domains, names, and countries of national and international universities.

4. Open AQ API

OpenAQ uses a combination of open data and open source tools as well as a global, grassroots community to fight air inequality in different locations across the world. Use the Open AQ APITrack this API to build apps that power a variety of air quality measurement tools. The API convey responses in JSON format.

5. Numbeo Cost of Living API

The Numbeo Cost of Living APITrack this API integrates living conditions comparisons between two cities or countries. Methods include cities, price items, currency exchange, hotel prices, indices, crime, healthcare, pollution, traffic, and climate.

6. GeoDataSource Neighbouring Countries API

The GeoDataSource Neighbouring Countries Web ServiceTrack this API enables users to get the associated land border countries (the neighboring countries) based on the input of country code in ISO3166-2 format.

7. World Bank Country API

The World Bank Country APITrack this API returns country data including region, income level, ISO codes, lending type, capital city, longitude, and latitude. Data is provides in JSON or XML formats.

8. Graph Countries GraphQL API

The Graph Countries APITrack this API is a free GraphQL API to query country-related data like currencies, languages, flags, regions+subregions, bordering countries, and distance to other countries.

9. The Basetrip API

The Basetrip APITrack this API offers a variety of travel information by country including currency information, electricity (sockets & plugs), ATM locations, credit and debit cards information, driving data, dial codes, health related information, and emergency numbers. Additionally, Basetrip offers GeoJSON formatted data.

Add travel information about various countries to apps via this API

Add travel information about various countries to apps via this API. Image: The Basetrip

10. Tuxx EU Country API

The Tuxx EU Country APITrack this API checks whether a given country is a country in the European Union. A country in the European Union is a country that belongs to the economic and political union of 28 member states which are primarily located in Europe.

Head over to the Countries category for more than 40 APIs, SDKs, and Source Code Samples.

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Author: <a href="https://www.programmableweb.com/user/%5Buid%5D">joyc</a>

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ScienceDaily

Breaking molecular traffic jams with finned nanoporous materials

Thousands of chemical processes used by the energy industry and for other applications rely on the high speed of catalytic reactions, but molecules frequently are hindered by molecular traffic jams that slow them down. Now an entirely new class of porous catalysts has been invented, using unique fins to speed up the chemistry by allowing molecules to skip the lines that limit the reaction.

This discovery was published in Nature Materials.

The breakthrough focused on reducing barriers for molecules accessing the interior pores of catalysts, called zeolites — aluminosilicates with pores smaller than a nanometer. Zeolites are widely used in commercial processes as solid catalysts for the production of gasoline and value-added chemicals and other products.

In these applications, chemistry within the zeolite pores first requires molecules to find the small number of openings on the outside surface of catalyst particles. This creates a queue of molecules that must “wait in line” to enter the particle, diffuse to the active site involved in the chemical reaction, and then exit the particle.

One approach to address these transport problems has been to synthesize small nanoparticles. As zeolites become smaller, the amount of surface area exposing the pores increases per amount of catalyst material, which grants increased access for molecules entering the pores. Smaller particles also reduce the internal distance molecules must travel through the particle.

However, the synthesis of these smaller zeolite particles is expensive, and the resulting particles are often too inefficient for practical applications.

Researchers at the University of Houston, led by Jeffrey Rimer, Abraham E. Dukler Professor of chemical and biomolecular engineering, developed a way to induce larger catalyst particles to behave like nanoparticles — that is, to allow molecules to enter, spark a reaction and exit quickly, by growing protrusions, or fins, on the surfaces of catalyst particles. By adding nanoscale fins that protrude from the external surface of large particles, the roughened exterior of the particle significantly increased in surface area, granting molecules increased access and reducing the transport limitations that frequently plague conventional zeolite materials.

“Our new synthesis approach capitalizes on work we have been doing in our group for many years, focused on controlling zeolite crystallization in ways that enable the growth of fins,” Rimer said. “This new class of materials bypasses the need to directly synthesize nanoparticles, creating a new paradigm in zeolite catalyst design.”

Rimer worked with a team of international experts in materials synthesis, characterization and modeling to demonstrate the capability of finned zeolites to improve the performance of this unique family of solid catalysts. By comparing finned zeolites with conventional catalytic materials, they showed that zeolites with fins lasted almost eight times longer. Rimer said the incorporation of fins leads to shorter internal diffusion pathways and ensures molecules efficiently reach the reaction sites while reducing the propensity of carbon-based species to become immobilized. That build up ultimately deactivates the catalyst.

Xiaodong Zou, professor of inorganic and structural chemistry at Stockholm University, and members of her laboratory conducted advanced 3D electron microscopy characterization to unravel the pore structures of the finned crystals and confirmed that the fins were extensions of the underlying crystal and did not create impediments for internal diffusion.

“It is amazing to see how well all these hundreds of individual nanofins are aligned with the parent crystal,” Zou said.

Additional state-of-the-art techniques for characterizing zeolite catalysts in real time were performed at Utrecht University by the research group of Bert Weckhuysen, professor of catalysis, energy and sustainability. These measurements confirmed the exceptional ability of finned zeolites to prolong catalyst activity well beyond that of larger catalysts.

Weckhuysen said the use of operando spectroscopy clearly showed how the introduction of fins lowered the amount of external coke deposits during catalysis. “That substantially increased the lifetime of finned zeolite crystals,” he said.

Jeremy Palmer, assistant professor of chemical and biomolecular engineering at UH, used computational methods to model finned materials and explain how the new design works to improve catalysis.

Researchers had expected the fins would perform better than a standard-sized zeolite catalyst, he said. “But we found it was not just a 10% or 20% improvement. It was a tripling of efficiency. The magnitude of the improvement was a real surprise to us.”

Additional work at the University of Minnesota by the research group of Paul Dauenhauer, professor of chemical engineering and materials science, and by Michael Tsapatsis, professor of chemical and biomolecular engineering at Johns Hopkins University, confirmed the enhanced mass transport properties of finned zeolites. Using a new method to track molecule diffusion by infrared light, the UM researchers demonstrated that the fins enhanced molecule transport between 100 and 1,000 times faster than conventional particles.

“The addition of fins allows molecules to get inside the channels of zeolites where the chemistry happens, but it also lets molecules quickly get out of the particle, which lets them operate for a much longer period of time,” Dauenhauer said.

The discovery has immediate relevance to industry for a host of applications, including the production of fuels, chemicals for plastics and polymers, and reactions that make molecules for food, medicine and personal care products.

“The beauty of this new discovery is its potential generalization to a wide range of zeolite materials, using techniques that are easy to incorporate in existing synthesis processes,” Rimer said. “The ability to control the properties of fins could allow for much greater flexibility in the rational design of zeolite catalysts.”

This work was supported by and is part of a larger mission of the U.S. Department of Energy, with additional support provided by various international funding agencies.

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ScienceDaily

Scientists discover new class of semiconducting entropy-stabilized materials

Semiconductors are important materials in numerous functional applications such as digital and analog electronics, solar cells, LEDs, and lasers. Semiconducting alloys are particularly useful for these applications since their properties can be engineered by tuning the mixing ratio or the alloy ingredients. However, the synthesis of multicomponent semiconductor alloys has been a big challenge due to thermodynamic phase segregation of the alloy into separate phases. Recently, University of Michigan researchers Emmanouil (Manos) Kioupakis and Pierre F. P. Poudeu, both in the Materials Science and Engineering Department, utilized entropy to stabilize a new class of semiconducting materials, based on GeSnPbSSeTe high-entropy ourchalcogenide alloys, a discovery that paves the way for wider adoption of entropy-stabilized semiconductors in functional applications.

Entropy, a thermodynamic quantity that quantifies the degree of disorder in a material, has been exploited to synthesize a vast array of novel materials by mixing eachcomponent in an equimolar fashion, from high-entropy metallic alloys to entropy-stabilized ceramics. Despite having a large enthalpy of mixing, these materials can surprisingly crystalize in a single crystal structure, enabled by the large configurational entropy in the lattice. Kioupakis and Poudeu hypothesized that this principle of entropy stabilization can be applied to overcome the synthesis challenges of semiconducting alloys that prefer to segregation into thermodynamically more stable compounds. They tested their hypothesis on a 6-component II-VI chalcogenide alloy derived from the PbTe structure by mixing Ge, Sn, and Pb on the cation site, and S, Se, and Te on the anion site.

Using high throughput first-principles calculations, Kioupakis uncovered the complex interplay between the enthalpy and entropy in GeSnPbSSeTe high-entropy chalcogenide alloys. He found that the large configurational entropy from both anion and cation sublattices stabilizes the alloys into single-phase rocksalt solid solutions at the growth temperature. Despite being metastable at room temperature, these solid solutions can be preserved by fast cooling under ambient conditions. Poudeu later verified the theory predictions by synthesizing the equimolar composition (Ge1/3Sn1/3Pb1/3S1/3Se1/3Te1/3) by a two-step solid-state reaction followed by fast quenching in liquid nitrogen. The synthesized power showed well-defined XRD patterns corresponding to a pure rocksalt structure. Furthermore, they observed reversible phase transition between single-phase solid solution and multiple-phase segregation from DSC analysis and temperature dependent XRD, which is a key feature of entropy stabilization.

What makes high-entropy chalcogenide intriguing is their functional properties. Previously discovered high-entropy materials are either conducting metals or insulating ceramics, with a clear dearth in the semiconducting regime. Kioupakis and Poudeu found that. the equimolar GeSnPbSSeTe is an ambipolarly dopable semiconductor, with evidence from a calculated band gap of 0.86 eV and sign reversal of the measured Seebeck coefficient upon p-type doping with Na acceptors and n-type doping with Bi donors. The alloy also exhibits an ultralow thermal conductivity that is nearly independent of temperature. These fascinating functional properties make GeSnPbSSeTe a promising new material to be deployed in electronic, optoelectronic, photovoltaic, and thermoelectric devices.

Entropy stabilization is a general and powerful method to realize a vast array of materials compositions. The discovery of entropy stabilization in semiconducting chalcogenide alloys by the team at UM is only the tip of the iceberg that can pave the way for novel functional applications of entropy-stabilized materials.

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3D Printing Industry

Interview: AMT and DTI on how they created new 3D printing food-contact applications

“Food-contact applications are definitely a place where 3D printing will take a bigger piece of the cake, it’s only the tip of the iceberg for us with surface treatment. It’s a market that will grow a lot in the coming years, so there’s a big potential there.” That’s how Mads Østergaard, Team Manager at The […]

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Author: Paul Hanaphy

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ProgrammableWeb

Five Major Vulnerabilities in GraphQL

GraphQL (GQL) is a data query language used commonly in modern web and mobile applications as a key part of the technology stack. GQL simplifies fetching data from a server to a client via an API call. This article recaps some thoughts from a post by carvesystems.com, covering the five most common GraphQL vulnerabilities, how to use a GQL “goat” to exemplify vulnerabilities, and some tooling to evaluate GQL implementation.

Understanding a little more about what GQL is will help clarify the concepts in this article. CarveSystems contributor Aiden elaborates:

“GraphQL is a standardized language for describing and making queries to APIs. Originally built by Facebook in 2015 for use in their mobile applications, GraphQL provides a number of benefits to application developers when compared to a traditional REST API”:

  • “Client applications are able to request only the information they need, minimizing the amount of data sent.”
  • “GraphQL allows for more complicated queries to be represented, reducing the number of API requests that must be made.”
  • “All input data is type-checked against a schema defined by the developer, assisting with data validation.”
  • Benefits accompanying GQL come with a corresponding level of complexity and associated security vulnerabilities.

Explore a Demo API

To illustrate these vulnerabilities, Carve has built a sample API with the issues built-in for exemplification, using minimal notes service (this allows API clients to create their own public and private notes, as well as allowing them to see other users’ public posts). You can find the source code for the API sample here. You can run your own instance locally with Node, or with a Docker container (this is available at carvesystems/vulnerable-graphql-api on Docker Hub. “The demo application exposes a webserver with an instance of the GraphiQL IDE for experimentation, which is available on port 3000.”
 

Vulnerability 1: Inconsistent Authorization Checks

The most commonly found issue in GraphQL-based applications is flawed authorization logic. Carve elaborates, “While GraphQL helps implement proper data validation, API developers are left on their own to implement authentication and authorization methods on top. Worse, the “layers” of resolvers typical to a GraphQL API make doing this properly more complicated – authorization checks have to be present not only at the query-level resolvers, but also for resolvers that load additional data (for example, to load all of the posts for a given user).”

GQL API flaws usually come in one of two forms. Carve explains, “The first, and more common, occurs when authorization functionality is handled directly by resolvers at the GraphQL API layer. When this is done, authorization checks must be performed separately in each location, and any instance where this is forgotten could lead to an exploitable authorization flaw. The likelihood of this occurring increases as the complexity of the API schema increases, and there are more distinct resolvers responsible for controlling access to the same data.”

The demo API created by Carve portrays several methods for retrieval of listing Post objects: a client can retrieve a list of users, then retrieve all their public posts, or simply retrieve a post by its numeric ID. One vulnerability exposed in the demo API exposes the opportunity to retrieve a post by ID, where there are no authorization checks. Vulnerabilities in this vein are simple and commonly found in real-world GQL deployments. 

GraphQL design guides advise how to securely perform authorization: the logic should be applied by the business-logic layer, thereby smoothing the way for consistently applied authorization constraints. 

Vulnerability 2: Flimsy REST Proxy Layers

An underlying API adapted for use by GraphQL clients with REST proxies can be “implemented in the GraphQL proxy layer by making a request to GET /api/users/1 on the backend API. If implemented unsafely, an attacker may be able to modify the path or parameters passed to the backend API, presenting a limited form of server-side request forgery.” 

Properly URL encoding and validating parameters passed to another service can protect against this kind of vulnerability. Leveraging the GraphQL schema to require a number for the file name would be one way to troubleshoot this vulnerability. An alternative tactic would involve implementing validation of input values. “GraphQL will validate the types for you, but leaves format validation to you. A custom scalar type (for example, a AssetId scalar) could be used to consistently apply any custom validation rules that apply for a commonly-used type.”

Vulnerability 3: Skipping Custom Skalar Validation

Raw data with GQL is represented with a Skalar type, and is ultimately passed as input data or returned as output. Carve breaks it down, explaining that there are five built-in scalar types – Int, Float, Boolean, String, and ID (which is really just a string). This basic set of scalar types is sufficient for many simple APIs, but for scenarios where additional raw datatypes are useful, GraphQL includes support for application developers to define their own scalar types. For example, an API might include its own DateTime scalar type, or an extended scalar type that provides extended input validation, such as “odd integers” or “alphanumeric strings.”

If a developer implements their own Skalar type, they will then be responsible for keeping up with sanitization and type validation. A demo pulled in the graphql-type-json library is available here.

Vulnerability 4: Disorganized Rate-Limiting

Implementing rate-limiting and other denial-of-service protections mirror GraphQL APIs in their complexity and difficulty. The number of actions GQL query takes is by nature mutable, and thus takes an erratic amount of server resources. This is why rate-limiting techniques used for REST APIs are not meant to be used for GQL APIs – the REST API strategies are insufficient for GQL APIs. 

Vulnerability 5: Introspection Feature Unmasks Public Data

Tacking on veiled features to API endpoints is an appealing prospect to developers who want a bit of functionality tucked away from public view. These features could be shielded from public view with admin-access protection, or with another API endpoint. Carve advises that “a GraphQL feature called introspection makes discovery of hidden endpoints trivially easy. As part of an effort to be developer-friendly, the introspection feature, which is enabled by default in most GraphQL implementations, allows API clients to dynamically query information about the schema, including documentation and the types for every query and mutation defined in the schema. This is used by development tools, like the GraphiQL IDE, to dynamically retrieve the schema if not provided one.” The demo API developed by Carve further illuminates these ideas with a hidden mutation. 

Final Thoughts

Using a more complex solution like GraphQL comes with more complex problems. With that in mind, it solves many of the fundamental issues with data validation commonly found in REST APIs. These commonalities are available for exploration with the Carve demo API.

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Author: <a href="https://www.programmableweb.com/user/%5Buid%5D">Katherine-Harrison-Adcock</a>

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ProgrammableWeb

Flutter v1.17 Released

Flutter; Google’s UI toolkit for building native applications for mobile, web, and desktop; has announced the release of v1.17. This is Flutter’s first stable release of 2020, and the Flutter team indicated that it plans on new releases arriving on a quarterly basis. In addition to the more than 3,000 PRs included in this release, v1.17 brings increased performance and many new features including Metal support on iOS, new Material components, new Network tracking, and more.

Simply by upgrading to v1.17, the Flutter team reports that developers will see immediate improvements including 20%-37% speedup in navigation and a 40% reduction in CPU/GPU usage. The biggest performance improvements come from iOS support for Metal. Metal is now used by default in Flutter and increases app speed by 50% on average.

New Material components include NavigationRail, DatePicker, and more. NavigationRail is a widget that provides a new responsive app navigation model. It easily swaps in for BottomNavigator and is, therefore, a good candidate for apps that switch between mobile and desktop. DatePicker has been redesigned with new Material guidelines, visuals, and inputs. For a complete list, check out the DatePicker redesign specification. Other components updates include Flutter text theming, Google fonts for Flutter, accessibility, and internationalization, and new tooling.

Finally, new network tracking tools are available on the network tab. Once the record button is selected, developers can track network traffic on an app. For more details on all new features, check out the blog post announcement.

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Author: <a href="https://www.programmableweb.com/user/%5Buid%5D">ecarter</a>

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Hackster.io

Get Started with TinyML Webinar

TinyML is opening up incredible new applications for sensors on embedded devices, from predictive maintenance to health applications using vibration, audio, biosignals and much more! 99% of sensor data is discarded today due to power, cost or bandwidth constraints.

This webinar introduces why ML is useful to unleash meaningful information from that data, how this works in practice from signal processing to neural networks, and walks the audience through hands-on examples of gesture and audio recognition using Edge Impulse.

// 🧠 https://www.edgeimpulse.com
// 👉 https://www.hackster.io/news/tinyml-for-all-developers-with-edge-impulse-2cfbbcc14b90

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ProgrammableWeb

Apple Extends Application Update Deadline

Apple has announced an extension of its deadline for developers to update their applications in accordance with the latest design guidelines. The deadline to update existing applications on the app store is now June 30, 2020.

The new application standards include a requirement that apps for iPhone or iPad be built on iOS 13 SDK or later. Additionally, these apps are required to use an Xcode storyboard for the applications launch screen. These apps will also be required to support all possible device screen sizes. 

Apple Watch applications will now be required to use watchOS 6 SDK or later. Apple is also requiring that many applications that set up user accounts support Sign in with Apple. These apps are specified in guideline 4.8 of the App Store Review Guidelines.

Additional standards are mentioned for Kids apps and apps using HTML 5. Check out the full post for additional details

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Author: <a href="https://www.programmableweb.com/user/%5Buid%5D">KevinSundstrom</a>

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ScienceDaily

Double-walled nanotubes have electro-optical advantages

One nanotube could be great for electronics applications, but there’s new evidence that two could be tops.

Rice University engineers already knew that size matters when using single-walled carbon nanotubes for their electrical properties. But until now, nobody had studied how electrons act when confronted with the Russian doll-like structure of multiwalled tubes.

The Rice lab of materials theorist Boris Yakobson has now calculated the impact of curvature of semiconducting double-wall carbon nanotubes on their flexoelectric voltage, a measure of electrical imbalance between the nanotube’s inner and outer walls.

This affects how suitable nested nanotube pairs may be for nanoelectronics applications, especially photovoltaics.

The theoretical research by Yakobson’s Brown School of Engineering group appears in the American Chemical Society journal Nano Letters.

In an 2002 study, Yakobson and his Rice colleagues had revealed how charge transfer, the difference between positive and negative poles that allows voltage to exist between one and the other, scales linearly to the curvature of the nanotube wall. The width of the tube dictates curvature, and the lab found that the thinner the nanotube (and thus larger the curvature), the greater the potential voltage.

When carbon atoms form flat graphene, the charge density of the atoms on either side of the plane are identical, Yakobson said. Curving the graphene sheet into a tube breaks that symmetry, changing the balance.

That creates a flexoelectric local dipole in the direction of, and proportional to, the curvature, according to the researchers, who noted that the flexoelectricity of 2D carbon “is a remarkable but also fairly subtle effect.”

But more than one wall greatly complicates the balance, altering the distribution of electrons. In double-walled nanotubes, the curvature of the inner and outer tubes differ, giving each a distinct band gap. Additionally, the models showed the flexoelectric voltage of the outer wall shifts the band gap of the inner wall, creating a staggered band alignment in the nested system.

“The novelty is that the inserted tube, the ‘baby’ (inside) matryoshka has all of its quantum energy levels shifted because of the voltage created by exterior nanotube,” Yakobson said. The interplay of different curvatures, he said, causes a straddling-to-staggered band gap transition that takes place at an estimated critical diameter of about 2.4 nanometers.

“This is a huge advantage for solar cells, essentially a prerequisite for separating positive and negative charges to create a current,” Yakobson said. “When light is absorbed, an electron always jumps from the top of an occupied valence band (leaving a ‘plus’ hole behind) to the lowest state of empty conductance band.

“But in a staggered configuration they happen to be in different tubes, or layers,” he said. “The ‘plus’ and ‘minus’ get separated between the tubes and can flow away by generating current in a circuit.”

The team’s calculations also showed that modifying the nanotubes’ surfaces with either positive or negative atoms could create “substantial voltages of either sign” up to three volts. “Although functionalization could strongly perturb the electronic properties of nanotubes, it may be a very powerful way of inducing voltage for certain applications,” the researchers wrote.

The team suggested its findings may apply to other types of nanotubes, including boron nitride and molybdenum disulfide, on their own or as hybrids with carbon nanotubes.

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