Category Archives: Packaging Materials

The 2015 market for electronic gases totaled $3.65B, up 4.3% over the prior year, according to a new report from Techcet Group, “Critical Materials Report: Electronic Gases 2016.” The 2016 outlook is for 6.8% growth overall, with the electronic specialty gases segment leading the way with 8.9% growth to $2.53B and bulk gases increasing 4.3% to $1.37B. Single digit growth is expected to continue to be the norm, with looming shortages in neon and helium threatening to retard the pace.

In bulk gases, Air Liquide increased its share by 3% and now dominates the market at 31% share. In specialty gases, market shares underwent major shifts, including former leader Air Products slipping in position behind Air Liquide. Air Liquide has taken the lead position at 27%, with Air Products dropping to 17% after repositioning themselves as an independent entity, now recognized as Versum. Praxair, Linde and TNSC-Matheson, followed by SK Materials (formerly OCI) continue to round out the other global share leaders.

Concerns about the availability of Neon continue to plague the industry. Over 70% of the global supply of neon is sourced from Iceblick in Odessa, Ukraine, where the political unrest has resulted in a 60% reduction in output in 2015. New capacity is being installed in Texas, Indiana, Ukraine, China and Dubai, but takes two years to come online. The shortfall has sent DUV laser manufacturers scrambling to develop strategies for neon use reduction, but these are not yet considered to be adequate. Meanwhile, the shortage has contributed to the further delay of EUV implementation from 2016-17 to 2020.

The scramble for new commercial sources for helium is being driven by the decision of the US Bureau of Land Management to stop supplying to the merchant market by 2021. This represents 30-40% of the US supply and 15-20% of the global supply. A new source or He has just been discovered in Tanza- nia, but any extraction and purification plant will take 2+ years to come on line. While helium supply is not an immediate concern, pricing has continued inching upward. By 2021, new sources/expansions will need be in full production in order to compensate for the BLM exiting the commercial market. See TECHCET’s Gases Report for actual timelines and details.

TECHCET’s 2016 Gases Report and 2016 Neon Report provide strategic information to ensure business continuity and support category management of the specialty and bulk gas markets and their sup- ply chains. Included are supplier issues, raw material concerns and supplier profiles. Current issues sur- rounding helium, neon, nitrogen trifluoride, tungsten hexafluoride, krypton, xenon, and several more are provided in the Gases Report. High demand applications and forecast on supply vs demand are highlighted in the Neon Report. Global supply chain issues and regulatory changes that impact gases are also discussed in this year’s reports.

TECHCET CA LLC is an advisory service firm focused on Process Materials Supply Chains, Electronic Materials Technology, and Materials Market Analysis for the Semiconductor, Display, Solar/PV, and LED Industries. The Company has been responsible for producing the SEMATECH Critical Material Reports since 2000. For additional information about these reports or about CMC Fabs membership please contact Lita Shon-Roy or Jerry Yang at [email protected] +1-480-332-8336, or visit our websites at www.techcet.com and www.cmcfabs.org.

Other reports released this quarter include:

  •   ALD & High-κ Metal Precursors
  •   Silicon Wafers
  •   Photoresist
  •   Sputter Targets

For additional information about these reports, contact Lita Shon-Roy, [email protected], +1- 480-336-2160, or visit our website at www.techcet.com.

By Pete Singer, Editor-in-Chief

A new roadmap, the Heterogeneous Integration Technology Roadmap for Semiconductors (HITRS), aims to integrate fast optical communication made possible with photonic devices with the digital crunching capabilities of CMOS.

The roadmap, announced publicly for the first time at The ConFab in June, is sponsored by IEEE Components, Packaging and Manufacturing Technology Society (CPMT), SEMI and the IEEE Electron Devices Society (EDS).

Speaking at The ConFab, Bill Bottoms, chairman and CEO of 3MT Solutions, said there were four significant issues driving change in the electronics industry that in turn drove the need for the new HITRS roadmap: 1) The approaching end of Moore’s Law scaling of CMOS, 2) Migration of data, logic and applications to the Cloud, 3) The rise of the internet of things, and 4) Consumerization of data and data access.

“CMOS scaling is reaching the end of its economic viability and, for several applications, it has already arrived. At the same time, we have migration of data, logic and applications to the cloud. That’s placing enormous pressures on the capacity of the network that can’t be met with what we’re doing today, and we have the rise of the Internet of Things,” he said. The consumerization of data and data access is something that people haven’t focused on at all, he said. “If we are not successful in doing that, the rate of growth and economic viability of our industry is going to be threatened,” Bottoms said.

These four driving forces present requirements that cannot be satisfied through scaling CMOS. “We have to have lower power, lower latency, lower cost with higher performance every time we bring out a new product or it won’t be successful,” Bottoms said. “How do we do that? The only vector that’s available to us today is to bring all of the electronics much closer together and then the distance between those system nodes has to be connected with photonics so that it operates at the speed of light and doesn’t consume much power. The only way to do this is to use heterogeneous integration and to incorporate 3D complex System-in-Package (SiP) architectures.

The HITRS is focused on exactly that, including integrating single-chip and multi­chip packaging (including substrates); integrated photonics, integrated power devices, MEMS, RF and analog mixed signal, and plasmonics. “Plasmonics have the ability to confine photonic energy to a space much smaller than wavelength,” Bottoms said. More information on the HITRS can be found at: http://cpmt.ieee.org/technology/heterogeneous-integration-roadmap.html

Bottoms said much of the technology exists today at the component level, but the challenge lies in integration. He noted today’s capabilities (Figure 1) include Interconnection (flip-chip and wire bond), antenna, molding, SMT (passives, components, connectors), passives/integrated passive devices, wafer pumping/WLP, photonics layer, embedded technology, die/package stacking and mechanical assembly (laser welding, flex bending).

Building blocks for integrated photonics.

Building blocks for integrated photonics.

“We have a large number of components, all of which have been built, proven, characterized and in no case have we yet integrated them all. We’ve integrated more and more of them, and we expect to accelerate that in the next few years,” he said.

He also said that all the components exist to make very complex photonic integrated circuits, including beam splitters, microbumps, photodetectors, optical modulators, optical buses, laser sources, active wavelength locking devices, ring modulators, waveguides, WDM (wavelength division multiplexers) filters and fiber couplers. “They all exist, they all can be built with processes that are available to us in the CMOS fab, but in no place have they been integrated into a single device. Getting that done in an effective way is one of the objectives of the HITRS roadmap,” Bottoms explained.

He also pointed to the potential of new device types (Figure 2) that are coming (or already here), including carbon nanotube memory, MEMS photonic switches, spin torque devices, plasmons in CNT waveguides, GaAs nanowire lasers (grown on silicon with waveguides embedded), and plasmonic emission sources (that employ quantum dots and plasmons).

New device types are coming.

New device types are coming.

The HITRS committee will meet for a workshop at SEMICON West in July.

What do you use to handle thin wafers and thin reconstituted wafers?  Increasingly miniaturized electronic devices require decreased profile heights, reduced foot-prints and ultimately, the perpetual thinning of wafers.  Initially, working with thin wafers typically required temporary bonding of the wafer to a carrier and use of a temporary coating layer for wafer protection.

For fan-out wafer-level packaging and 3D packaging, thin wafer handling is critical; the wafer must not warp, bend or shift during any wafer-processing steps.  These wafer processing steps may involve different temperature ranges and exposure to a variety of chemicals depending on the processing steps such as etching, metallization, CMP, PVD, RDL in embedded, fan-out, and 3D wafer-level packaging.

AI Technology, Inc. (AIT) manufactures a series of temporary bonding materials for processing temperatures up to 150 Cº. They are well accepted for grinding, dicing, etching, and deposition.  AIT customers prefer AIT bonding materials over conventional wax materials specifically because AIT’s products feature ease of use and quick removal, especially for very delicate compound wafers and photonics.

For higher temperature processing, AI Technology, Inc. (AIT) developed high temperature wafer processing adhesives (WPA) that can withstand processing temperature up to 330ºC. Also important is the chemical resistance of these WPA materials to acids and bases during the etching processes.  The thermal and chemical stability allows these adhesive to maintain its chemical integrity allowing the thin wafer be separated from the wafer handler/carrier by heat-sliding or by laser de-bonding equipment.  The WPA adhesive layer is designed to absorb UV breaking chemical bonds at the interface allowing for ease of separation.  After separation, the WPA adhesive layer can be removed by peeling with minimum stress or solvent cleaning.

Besides supplying these WPA products in spin coating liquid, AI Technology, Inc. (AIT) also provides WPA as a thin film. This unique and innovative WPA-film minimizes processing time and total waste produced compared to a typical spin-coating process allowing higher through-put.  In high volume manufacturing, some fan-out packaging involves reconstituted panels with larger dimensions compared to the traditional circular and small wafer size. For these high volume manufacturing panels, adhesive film in sheet format may provide the most efficient productivity.  Typically heat-laminated onto a wafer first and followed by vacuum lamination of the wafer onto the carrier, AIT’s WPA thin film processing conditions and debonding techniques resemble the spin coating process used in WPA products.

AI Technology, Inc. (AIT) understands that different types of wafers, Si, GaAs, GaN, InP, glass, and sapphire are used in different applications and, depending on wafer processing conditions, demand highly specialized tools and equipment.  AIT is committed to working closely with our customers and equipment suppliers to satisfy customer needs.

Intermolecular, Inc. today announced IMI Labs for Semiconductor, a materials innovation service to help semiconductor companies explore, discover and characterize new materials. With IMI Labs, semiconductor manufacturers now have broad access to Intermolecular’s experimentation platform, materials expertise and data to accelerate materials decisions that have the potential to unlock substantial innovations.

Early identification of new, suitable materials gives semiconductor companies a significant competitive advantage. The pace of materials exploration in the semiconductor industry has increased exponentially since the 1980s, when only a handful of materials were used. Since 2000, 50 new materials have been developed for semiconductor applications, often in complex compounds or stacks. At the same time, semiconductor manufacturers often conduct R&D on production lines, potentially incurring significant risks when introducing a new material.

“The industry is facing major challenges ranging from architecture choices to materials selection. The next wave of semiconductors will require inventing over 40 materials,” said Dr. Scott E. Thompson, IEEE fellow, U. Florida.

“The future of innovation in the semiconductor industry is highly dependent on the discovery and selection of new complex materials,” said Bruce McWilliams, president and chief executive officer, Intermolecular, Inc. “With IMI Labs, semiconductor manufacturers can experiment with various material combinations without bringing new materials into their production fabs. By leveraging our high-throughput platform, expertise and analytics, customers can reduce the time and risk of new materials research and accelerate the materials decision-making process.”

Services available today from IMI Labs for Semiconductor take their roots from work Intermolecular started for the fast growing $77 billion memory market, specifically DRAM and non-volatile memory (NVM). The company is also expanding its offering to address the global $229 billion digital integrated circuits market.  IMI Labs for Semiconductor provides the following benefits for semiconductor materials research:

  • Evaluate and experiment with new materials such as Chalcogenides
  • Experiment with combined stacks or new elements interfacing with multiple layers
  • Expanded empirical data
  • Ability to predict or validate experimental physical and electrical properties with simulation & empirical modeling
  • R&D equipment ready to perform experiments
  • Ability to test new materials before introducing them into production environments

Examples of IMI Labs for Semiconductor services include:

  • High-throughput site-isolated ALD and PVD deposition of multiple materials with in-situ anneal
  • Comprehensive PVD and ALD-based evaluation of several different dielectric, electrode, or interlayer materials in a MIM capacitor film stack
  • Comprehensive PVD-based evaluation of multinary materials (> 5 elements) and metal/metal nitride electrodes
  • Extensive physical and electrical characterization
  • In-depth evaluation of promising materials candidates with temperature dependent testing, stress testing, and Internal Photon Emission (IPE) testing

“Advanced materials are essential to economic security and human well being, with applications in industries aimed at addressing challenges in clean energy, national security, and human welfare, yet it can take 20 or more years to move a material after initial discovery to the market,” according to the Materials Genome Initiative website. “Accelerating the pace of discovery and deployment of advanced material systems will therefore be crucial to achieving global competitiveness in the 21st century.” 

The Semiconductor Industry Association (SIA), representing U.S. leadership in semiconductor manufacturing, design, and research, commended congressional approval of the Frank R. Lautenberg Chemical Safety for the 21st Century Act, bipartisan legislation that updates the Toxic Substances Control Act of 1976, the primary federal law pertaining to the production and use of chemicals. The Senate passed the legislation last night on a voice vote, and the House of Representatives overwhelmingly approved it on May 24. President Obama is expected to sign the legislation into law.

“The sound regulation of chemicals is critically important to the U.S. semiconductor industry, which relies on certain chemicals and materials to manufacture the semiconductors that underpin modern technology,” said John Neuffer, president and CEO, Semiconductor Industry Association. “This legislation improves chemical safety, protects the environment, and provides the semiconductor industry and other sectors with needed certainty in manufacturing products that drive economic growth.”

The legislation would strengthen the authority of the Environmental Protection Agency (EPA) to evaluate, prioritize, and take action on chemicals that pose risks to health and the environment, while providing industry with increased assurance in their selection of chemicals. The bill directs EPA to assess chemicals based on their conditions of use and potential for exposure, and where EPA takes action on chemicals that pose an unreasonable risk, the bill would allow EPA to consider costs and the feasibility and safety of alternatives in setting a safety standard.

“TSCA was first passed when Gerald Ford was president, “Rocky” won the Academy Award, and Apple was still operating out of a garage,” Neuffer said. “We applaud Congress for approving this much-needed and long-overdue legislation, and especially appreciate Senators Inhofe, Vitter, and Udall, and Congressmen Shimkus and Pallone for introducing the legislation and moving it forward. We urge President Obama to quickly sign it into law.”

An ultrathin film that is both transparent and highly conductive to electric current has been produced by a cheap and simple method devised by an international team of nanomaterials researchers from the University of Illinois at Chicago and Korea University.

Highly conductive ultrathin film on skin between clips. Credit: Sam Yoon, Korea University

Highly conductive ultrathin film on skin between clips.
Credit: Sam Yoon, Korea University

The film — actually a mat of tangled nanofiber, electroplated to form a “self-junctioned copper nano-chicken wire” — is also bendable and stretchable, offering potential applications in roll-up touchscreen displays, wearable electronics, flexible solar cells and electronic skin.

The finding is reported in the June 13 issue of Advanced Materials.

“It’s important, but difficult, to make materials that are both transparent and conductive,” says Alexander Yarin, UIC Distinguished Professor of Mechanical Engineering, one of two corresponding authors on the publication.

The new film establishes a “world-record combination of high transparency and low electrical resistance,” the latter at least 10-fold greater than the previous existing record, said Sam Yoon, who is also a corresponding author and a professor of mechanical engineering at Korea University.

The film also retains its properties after repeated cycles of severe stretching or bending, Yarin said — an important property for touchscreens or wearables.

Manufacture begins by electrospinning a nanofiber mat of polyacrylonitrile, or PAN, whose fibers are about one-hundredth the diameter of a human hair. The fiber shoots out like a rapidly coiling noodle, which when deposited onto a surface intersects itself a million times, Yarin said.

“The nanofiber spins out in a spiral cone, but forms fractal loops in flight,” Yarin said. “The loops have loops, so it gets very long and very thin.”

The naked PAN polymer doesn’t conduct, so it must first be spatter-coated with a metal to attract metal ions. The fiber is then electroplated with copper — or silver, nickel or gold.

The electrospinning and electroplating are both relatively high-throughput, commercially viable processes that take only a few seconds each, according to the researchers.

“We can then take the metal-plated fibers and transfer to any surface — the skin of the hand, a leaf, or glass,” Yarin said. An additional application may be as a nano-textured surface that dramatically increases cooling efficiency.

Yoon said the “self-fusion” by electroplating at the fiber junctions “dramatically reduced the contact resistance.” Yarin noted that the metal-plated junctions facilitated percolation of the electric current — and also account for the nanomaterial’s physical resiliency.

“But most of it is holes,” he said, which makes it 92 percent transparent. “You don’t see it.”

Almost two years after GTAT’s bankruptcy, the sapphire industry is still there. Its decor and characters have, of course, changed but the story is still unfolding. Survival strategies, emerging applications and niche markets, mergers and acquisitions. All the protagonists are contributing to altering the landscape, trying to identify new business opportunities to absorb the sapphire overcapacity. China is a major contributor to the story with new investments and emerging companies in this already saturated industry. What is the impact on the sapphire supply chain? What are the strategies to be adopted to succeed? What are the long-term perspectives?

Figure 1

Figure 1

In this tense economic environment, Yole Développement (Yole) and its partner CIOE are organizing a 1.5 day conference to learn more about the status of the sapphire industry. The event will provide an opportunity for all the participants to discuss the future of this industry and to find answers. Sapphire is now more affordable than ever and new capabilities have enabled the manufacturing of components for very diverse applications. The 2nd International Forum on Sapphire Market & Technologies is the place to be to understand today’s economic and technical challenges and build tomorrow’s industry.

The Yole & CIOE Forum will take place from September 6 to 7 in Shenzhen, China, alongside the 18th China International Optoelectronic Expo 2016. To find out more about this event, visit: Sapphire Forum Agenda – Sapphire Forum Registration.

Figure 2

Figure 2

 The LED sector still has the highest demand for sapphire, but the expected volumes cannot sustain the one hundred or so sapphire producers currently competing in the industry.
Some sapphire companies are leaving the most commoditized markets and shifting their development strategies toward niche markets with higher added-value such as medical, industrial and military applications. Other business opportunities could materialize, including microLED arrays and other consumer applications.

Most sapphire companies are chasing any opportunity to survive and optimize their cost structure within a market which is currently characterized by a relentless price war. In Q1- 2016, the sapphire price plunged to its lowest ever level and most companies experienced a drastic decrease in revenue.

In this highly competitive market with significant economic constraints, Yole and CIOE are organizing the 2nd International Forum on Sapphire Market & Technologies (Shenzhen, China – September 6&7, 2016).

“The Sapphire Forum is an opportunity for the entire supply chain to come together to assess the current status of the industry, understand what lies ahead and determine the best strategies to make it through the crisis”, comments Dr. Eric Virey, Senior Technology & Market Analyst, Yole.

EPFL researchers are pushing the limits of perovskite solar cell performance by exploring the best way to grow these crystals.

This is a Perovskite solar cell prototype. Credit: Alain Herzog / EPFL

This is a Perovskite solar cell prototype. Credit: Alain Herzog / EPFL

Michael Graetzel and his team found that, by briefly reducing the pressure while fabricating perovskite crystals, they were able to achieve the highest performance ever measured for larger-size perovskite solar cells, reaching over 20% efficiency and matching the performance of conventional thin-film solar cells of similar sizes. Their results are published in Science.

This is promising news for perovskite technology that is already low cost and under industrial development.

However, high performance in pervoskites does not necessarily herald the doom of silicon-based solar technology. Safety issues still need to be addressed regarding the lead content of current perovskite solar-cell prototypes in addition to determining the stability of actual devices.

Layering perovskites on top of silicon to make hybrid solar panels may actually boost the silicon solar-cell industry. Efficiency could exceed 30%, with the theoretical limit being around 44%. The improved performance would come from harnessing more solar energy: the higher energy light would be absorbed by the perovskite top layer, while lower energy sunlight passing through the perovskite would be absorbed by the silicon layer.

From dye solar cells to perovskite

Graetzel is known for his transparent dye-sensitized solar cells. It turns out that the first perovskite solar cells were dye-sensitized cells where the dye was replaced by small perovskite particles.

His lab’s latest perovskite prototype, roughly the size of an SD card, looks like a piece of glass that is darkened on one side by a thin film of perovskite. Unlike the transparent dye-sensitized cells, the perovskite solar cell is opaque.

How to make a perovskite solar cell

To make a perovskite solar cell, the scientists must grow crystals that have a special structure, called “perovskite” after Russian mineralogist Lev Perovski who discovered it.

The scientists first dissolve a selection of compounds in a liquid to make some “ink”. They then place the ink on a special type of glass that can conduct electricity. The ink dries up, leaving behind a thin film that crystallizes on top of the glass when mild heat is applied. The end result is a thin layer of perovskite crystals.

The tricky part is growing a thin film of perovskite crystals so that the resulting solar cell absorbs a maximum amount of light. Scientists are constantly looking for smooth and regular layers of perovskite with large crystal grain size in order to increase photovoltaic yields.

For instance, spinning the cell when the ink is still wet flattens the ink and wicks off some of the excess liquid, leading to more regular films. A new vacuum flash technique used by Graetzel and his team also selectively removes the volatile component of this excess liquid. At the same time, the burst of vacuum flash creates seeds for crystal formation, leading to very regular and shiny perovskite crystals of high electronic quality.

Nanomaterials have the potential to improve many next-generation technologies. They promise to speed up computer chips, increase the resolution of medical imaging devices and make electronics more energy efficient. But imbuing nanomaterials with the right properties can be time consuming and costly. A new, quick and inexpensive method for constructing diamond-based hybrid nanomaterials could soon launch the field forward.

University of Maryland researchers developed a method to build diamond-based hybrid nanoparticles in large quantities from the ground up, thereby circumventing many of the problems with current methods. The technique is described in the June 8, 2016 issue of the journal Nature Communications.

The process begins with tiny, nanoscale diamonds that contain a specific type of impurity: a single nitrogen atom where a carbon atom should be, with an empty space right next to it, resulting from a second missing carbon atom. This “nitrogen vacancy” impurity gives each diamond special optical and electromagnetic properties.

By attaching other materials to the diamond grains, such as metal particles or semiconducting materials known as “quantum dots,” the researchers can create a variety of customizable hybrid nanoparticles, including nanoscale semiconductors and magnets with precisely tailored properties.

“If you pair one of these diamonds with silver or gold nanoparticles, the metal can enhance the nanodiamond’s optical properties. If you couple the nanodiamond to a semiconducting quantum dot, the hybrid particle can transfer energy more efficiently,” said Min Ouyang, an associate professor of physics at UMD and senior author on the study.

Evidence also suggests that a single nitrogen vacancy exhibits quantum physical properties and could behave as a quantum bit, or qubit, at room temperature, according to Ouyang. Qubits are the functional units of as-yet-elusive quantum computing technology, which may one day revolutionize the way humans store and process information. Nearly all qubits studied to date require ultra-cold temperatures to function properly.

A qubit that works at room temperature would represent a significant step forward, facilitating the integration of quantum circuits into industrial, commercial and consumer-level electronics. The new diamond-hybrid nanomaterials described in Nature Communications hold significant promise for enhancing the performance of nitrogen vacancies when used as qubits, Ouyang noted.

While such applications hold promise for the future, Ouyang and colleagues’ main breakthrough is their method for constructing the hybrid nanoparticles. Although other researchers have paired nanodiamonds with complementary nanoparticles, such efforts relied on relatively imprecise methods, such as manually installing the diamonds and particles next to each other onto a larger surface one by one. These methods are costly, time consuming and introduce a host of complications, the researchers say.

“Our key innovation is that we can now reliably and efficiently produce these freestanding hybrid particles in large numbers,” explained Ouyang, who also has appointments in the UMD Center for Nanophysics and Advanced Materials and the Maryland NanoCenter, with an affiliate professorship in the UMD Department of Materials Science and Engineering.

The method developed by Ouyang and his colleagues, UMD physics research associate Jianxiao Gong and physics graduate student Nathaniel Steinsultz, also enables precise control of the particles’ properties, such as the composition and total number of non-diamond particles. The hybrid nanoparticles could speed the design of room-temperature qubits for quantum computers, brighter dyes for biomedical imaging, and highly sensitive magnetic and temperature sensors, to name a few examples.

“Hybrid materials often have unique properties that arise from interactions between the different components of the hybrid. This is particularly true in nanostructured materials where strong quantum mechanical interactions can occur,” said Matthew Doty, an associate professor of materials science and engineering at the University of Delaware who was not involved with the study. “The UMD team’s new method creates a unique opportunity for bulk production of tailored hybrid materials. I expect that this advance will enable a number of new approaches for sensing and diagnostic technologies.”

The special properties of the nanodiamonds are determined by their nitrogen-vacancies, which cause defects in the diamond’s crystal structure. Pure diamonds consist of an orderly lattice of carbon atoms and are completely transparent. However, pure diamonds are quite rare in natural diamond deposits; most have defects resulting from non-carbon impurities such as nitrogen, boron and phosphorus. Such defects create the subtle and desirable color variations seen in gemstone diamonds.

The nanoscale diamonds used in the study were created artificially, and have at least one nitrogen vacancy. This impurity results in an altered bond structure in the otherwise orderly carbon lattice. The altered bond is the source of the optical, electromagnetic and quantum physical properties that make the diamonds useful when paired with other nanomaterials.

Although the current study describes diamonds with nitrogen substitutions, Ouyang points out that the technique can be extended to other diamond impurities as well, each of which could open up new possibilities.

“A major strength of our technique is that it is broadly useful and can be applied to a variety of diamond types and paired with a variety of other nanomaterials,” Ouyang explained. “It can also be scaled up fairly easily. We are interested in studying the basic physics further, but also moving toward specific applications. The potential for room-temperature quantum entanglement is particularly exciting and important.”

Marianna Kharlamova (the Lomonosov Moscow State University Department of Materials Science) examined different types of carbon nanotubes’ “stuffing” and classified them according to the influence on the properties of the nanotubes. The researcher’s work was published in the high-impact journal Progress in Materials Science (impact factor — 26.417).

An 87 pages long overview summarized the achievements of scientists in the field of the investigation of the electronic properties of single-walled carbon nanotubes (SWNTs). ‘A detailed systematic study of 430 works was conducted, including 20 author’s works, most of which had been published during the last 5 years, as the area under study is actively developing,’ says Marianna Kharlamova. Apart from analytical systematization of the existing data, the author considers the theoretical basis of such studies — the band theory of solids, which describes the interaction of the electrons in a solid.

The Many Faces of carbon: diamonds, balls, tubes

Carbon has several forms of existence (allotropic modifications) and can be found in different structures. It forms coal and carbon black, diamond, graphite, from which slate pencils are made, graphene, fullerenes and others. The whole organic chemistry is based on carbon which forms the molecular backbone. In diamonds the carbon atoms are kept on a strictly specified positions of the crystal lattice (which leads to its hardness). In graphite, the carbon atoms are arranged in hexagonal layers resembling honeycombs. Each layer is rather weakly interacting with the one above and the one below, so the material is easily separated into flakes which look to us like a pencil mark on the paper. If you take one such layer of hexagons and roll it into a tube, you get what is called a carbon nanotube.

A single-walled nanotube is a single rolled layer, and a multi-walled looks like the Russian ‘matryoshka’ doll, consisting of several concentric tubes. The diameter of each tube is a few nanometers, and the length is up to several centimeters. The ends of the tube are closed by hemispheric “caps” — halves of fullerene molecules (fullerenes are another form of elemental carbon resembling a soccer ball stitched together from hexagons and pentagons). To make and fill the carbon nanotube is much more challenging than to stuff a wafer curl : to tailor these structures scientists use laser ablation techniques, thermal dispersion in an arc discharge or vapor deposition of hydrocarbons from the gas phase.

SWNT is no cookie

What is so special about them then? The properties of the graphite (electrical conductivity, ductility, metallic shine) remind metals, yet carbon nanotubes have quite different properties, which can be used in electronics (as components of prospective nanoelectronic devices — gates, memory and data transmission devices etc.) and biomedicine (as containers for targeted drug delivery). The conductivity of carbon nanotubes can be changed depending on the orientation of the carbon hexagons relative to the tube axis, on what is included in its wall besides carbon, on which atoms and molecules are attached to the outer surface of the tube, and what it is filled with. Besides, single-walled carbon nanotubes (or SWNTs) are surprisingly tear-proof and refract light in a particular way.

Marianna Kharlamova was the first to classify types of nanotubes’ “stuffing” according to their impact on the electronic properties of SWNTs. The author of the review considers the method of filling SWNTs as the most promising for tailoring their electronic properties.

‘This is due to four main reasons,’ Marianna Kharlamova says. ‘Firstly, the range of substances that can be encapsulated in the SWNT channels is wide. Second, to introduce the substances of different chemical nature into the SWNT channels several methods have been developed: from the liquid phase (solution, melt), the gas phase, using plasma, or by chemical reactions. Third, as a result of the encapsulation process, high degree of the filling of SWNT channels can be achieved, which leads to the significant change in the electronic structure of nanotubes. Finally, the chemical transformation of the encapsulated substances allows controlling the process of tailoring the electronic properties of the SWNTs by selecting an appropriate starting material and conditions of the nanochemical reaction.’

The author herself conducted experimental studies of the filling of nanotubes with 20 simple substances and chemical compounds, revealed the influence of “stuffing” on the electronic properties of nanotubes, found the correlation between the temperature of the formation of inner tubes and the diameter of the outer tubes, and explained which factors influence the degree of the nanotubes’ filling.