In the recent paper: “Strongly enhanced and tunable photovoltaic effect in ferroelectric-paraelectric superlattices (Jun 2021)”, researchers found a way to engineer a superlattice of ferroelectric BaTiO3 sandwiched between paraelectric SrTiO3 and CaTiO3 resulting in 1000 times higher photovoltaic (PV) effect than measured in regular BaTiO3 of a similar thickness. The result is intriguing since neither SrTiO3 nor CaTiO3 has a PV effect, except for SrTiO3 under extremely large strain gradients.

The PV effect is what is used in solar cells to create electricity from the sunlight. Whether a material is paraelectric or ferroelectric has to do with its polarization curve.

Furthermore, the paper investigates the PV effect across different temperatures and over long time periods. It shows a persistent enhancement over these variations and thereby robustness. Perhaps this technique can be used for creating more efficient solar cells in the future and contribute to a greener energy grid.

The paper, including a STEM image of the structure, can be found here:

https://www.science.org/doi/10.1126/sciadv.abe4206

If you’d like to learn more about nanotechnology, please subscribe to our newsletter and stay tuned for upcoming posts. Credit to Thomas Conrad for bringing the scientific paper to our attention.

The post An Innovative Way to Enhance the PV Response of a Ferroelectric Material appeared first on The Nano Future.

Illustration by Armin Kübelbeck, showing the different types of transportation through the blood-brain barrier. https://commons.wikimedia.org/wiki/File:Blood-brain_barrier_transport_ca.png

So how can you use nanotechnology to effectively deliver medicine to the central nervous system, CNS?

The reason why researchers are interested in using nanomaterials to deliver drugs to the brain, is due to their small size and because they can be functionalized to be more site-specific. Nanomaterials is a very broad term that covers nanocarriers, which can function as transport vehicles for substances such as drugs. There exist many different kinds of nanocarriers such as polymers, liposomes, quantum dots, metallic nanoparticles etc. So let’s take a look at the research that has been conducted in recent years to understand how the drug-delivery problem has been approached using some of these different nanomaterials. 

Liu R. et al investigated whether nanoparticles could be used to treat Alzheimer’s disease in mice. There are several physical changes in the brain related to the pathology of Alzheimer’s disease. One of them is an increase in production and deposition of plaques that consists of peptides. It is also suggested that neuronal support cells called microglia play a role in the pathology of the disease due to an increase in neuroinflammatory responses which can harm the neuronal cells. In this study, the aim was to reduce the harmful peptides and normalize the function of microglia. The nanoparticles used consisted of four different components: 
(1) A zwitterionic polymer, which increases the cell uptake into the microglia and protects the nanoparticles from being destroyed by the disposal system of the cell (called lysosomes). (2) A sugar analogue which increases the permeability of the nanoparticle through the BBB by targeting specific receptors. (3) Zinc oxide which is encapsuled inside the nanoparticle together with (4) fingolimod. The fingolimod is a drug that can reduce inflammation inside the microglia while zinc oxide is used to further normalize these cells. The resulting size of the nanoparticle is around 100 nm in diameter. The effects of the nanoparticles were tested in mice. After four weeks of treatment, the results showed an increase in the removal of harmful peptides related to Alzheimer’s disease and a normalization of dysfunctional microglia. The treated mice showed an improvement in both spatial learning and memory [3]. 

Illustration from article by Liu, R. et al., showing the components of the nanoparticle and its final structure and mechanism. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6974948/

Kim D. et al. investigated whether graphene Quantum dots (GQD) can prevent the accumulation of alpha-synuclein proteins that aggregate forming fibrils in neurons which is seen in Parkinson’s disease, a devastating progressive nervous system disorder that currently cannot be cured [4].
Quantum dots are very small semiconductor crystals that can obtain many different properties depending on the material it is made of and its size and shape. Carbon based quantum dots such as the GQD’s are less toxic and more biocompatible compared to quantum dots made with heavy metals. Quantum dots can serve as a nanocarrier of medicine through modifications and functionalizations [5]. The pathophysiology of Parkinson’s disease is not completely understood but consists among others of: mitochondrial dysfunction and degeneration of dopamine neurons. Using an in vitro BBB model the researchers showed that the GQD’s could permeate the BBB due to their small size. The GQD’s were able to bind to the alpha-synuclein and stop them from aggregating and they could also break down the already existing fibrils. Moreover, seven days of treatment in mice models with the GQD’s resulted in neuroprotective effects preventing dopamine neuronal death, synaptic loss and improved dysfunctional mitochondria. The treated mice showed improvement in their motor skills, and after six months of GQD injections no long-term toxicity was observed in vitro or in vivo [4].

3. A Japanese research group investigated whether nanocarriers and macromolecules could cross the BBB by attaching cyclic peptides (a chain of amino acids that is circular in shape) to nanoparticles and a larger molecule called phage M13. Liposomes were used as nanocarriers, which were coated with the cyclic peptide. They used in vitro rat, monkey and human cell lines as BBB models to control the permeation of the nanocarrier and phage M13. In all models, they saw an increase in BBB permeability for both the nanocarrier and the phage M13 in vivo. 
The researchers point out the importance of using human cell lines and/or cell lines from several different species in order to increase the translation of research into clinical application [6].

As we can see from the mentioned research, the use of nanotechnology in medicine shows promising results for permeating the BBB and alleviating neurodegenerative diseases by functionalizing the nanocarriers to target specific brain sites. But even though nanocarriers have shown effectiveness in both preclinical and clinical studies, there is still a long way until they can be translated to the bedside and directly benefit patients [7]. A main concern regarding nanomaterials is their potential risks of harming the body. Therefore in order to bring nanomedicine closer to clinical practices, several aspects must be investigated to make nanomedicine safer for the body. There is a need of creating standardized nanotoxological studies and strict monitorization, to better understand potential adverse effects such as oxidative stress, accumulation, immune responses and neuronal death[8]. 
Moreover, the surface modifications made to nanomaterials must be carefully considered to make treatment as effective as possible. Luckily there is an increased interest in developing more biocompatible nanomaterials amongst researchers [9]. In summary the prospects for nano-neuromedicine are promising but contain challenges regarding ensuring safety and the need for further development and advancement of the current methods to benefit patients in the (hopefully) near future. 

If you’d like to learn more about nanotechnology, please subscribe to our newsletter and stay tuned for upcoming posts.

References

[1]   Cascione, M., Matteis, V. D., Leporatti, S. & Rinaldi, R. 2020. The New Frontiers in Neurodegenerative Diseases Treatment: Liposomal-based Strategies, Frontiers in Bioengineering and Biotechnology, vol 8, pp. 1-17. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7649361/
[2]   Kandel, E. R. et al. 2012, Principles of Neural Science, pp. 1565-1578.

[3]   Liu, R. et al., 2020. An “Amyloid-β Cleaner” For the Treatment of Alzheimer’s Disease by Normalizing Microglial Dysfunction, Advanced Science, vol. 7, Issue 2, pp. 1-12. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6974948/ 

[4]   Kim, D., 2018, Graphene quantum dots prevent α-synucleinopathy in Parkinson’s Disease, Nature nanotechnology, vol. 13, pp. 812-818. Available at:  https://www.nature.com/articles/s41565-018-0179-y 

[5]   Matea, C. T., 2017, Quantum dots in imaging, drug delivery and sensor applications, International Journal of Nanomedicine, vol 12, pp. 5421-5431. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5546783/ 

[6] Yamaguchi, S., 2020, Novel cyclic peptides facilitating transcellular blood-brain barrier transport of macromolecules in vitro and in vivo, Journal of Controlled Release, vol. 321, pp. 744-755. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0168365920301401?via%3Dihub

[7]   Naqvi, S., Panghal, A. & Flora, S. J. S., 2020, Nanotechnology: A promising Approach for Delivery of Neuroprotective Drugs, Frontiers in Neuroscience, vol. 14, s. 1-26. Available at: https://www.frontiersin.org/articles/10.3389/fnins.2020.00494/full#T1 

[8]   Teleanu, D. M., 2020, Impact on Nanoparticles on Brain Health: An Up to Date Overview, Journal of Clinical Medicine, vol. 7, Issue 7, pp. 1-14.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6306759/

[9]   Hanif, M., 2020, Nanomedicine-based immunotherapy for central nervous system disorders, Acta Pharmacological Sinica, vol. 41, pp. 936-953. Available at:
https://www.nature.com/articles/s41401-020-0429-z#Sec12

The post The prospects for neuromedicine within nanotechnology appeared first on The Nano Future.

Context

–          Why use nano food additives?

–          Are nano food additives safe?

–          What are regulations on nano food additives?

–          Conclusion

Why use nano food additives?

When you shrink the size of something, you increase the surface area to volume ratio, meaning that there is a larger area that can interact with its surroundings; thus giving you more flavor for fewer amounts of ingredients. This for example allows the use of less table salt in processed foods which could help reduce harmful overconsumption. Furthermore, nanosized additives can be used to change the texture or appearance of food. [ii]

Another benefit is the encapsulation of different nutrients such as vitamins, antioxidants, and proteins to control when and where they are released to the body [i]. Better vitamin delivery can have a huge positive impact. When eating non-encapsulated vitamins, a large amount does not make it to the parts of our bodies that need them. This is due to them being affected by the acidic environment of the stomach. 690 million people in the world suffer from undernutrition and far more from malnutrition [iii], so nano-encapsulation can help tackle an important issue.

While the positive benefits speak highly in favor of nanotechnology in food, there is a flip side to the coin.

Are nano additives safe?

The nature of nanoparticles can vary greatly based on size, shape, composition, aggregation state, and electrical charge. This means that risk assessment is necessary on a case-by-case basis. In general, what makes nanoparticles risky is their small size, which makes them both more reactive and allows them to pass through biological boundaries such as cell membranes. If they are bio-accumulating this, in the worst case, could lead to cellular dysfunction. [iv] 

To give an example: some inorganic nanoparticles, such as zinc oxide (ZnO), which could be used as a source of zinc in supplements and functional foods, are considered bad in large amounts as they can cause an excess of reactive oxidative species (ROS) [ii]. ROS have important bodily functions, but can be bad in large amounts. One solution could be to ensure a proper balance in the food by adding dietary antioxidants [iv].

Another example of an inorganic nano food additive is titanium dioxide (TiO2) which is used as a colorant in for instance chewing gum. There is a size distribution when adding particles, so even when aiming for the optimal particle size of 100-300 nm (above the nanoscale), smaller particles are added as well [ii]. Whether they are toxic or not may depend on the specific form in which they are added.

In general, there seems to be a bigger concern about inorganic nanoparticles over organic nanoparticles with the main reason being that organic ones are often completely digested. However, more research is needed into both types of particles to establish their toxicity [ii]. Luckily, regulations are in place in many countries to ensure the safety of consumers.

What are the regulations?

In the EU, EFSA (European Food Safety Authority) is the one to issue guidelines about what can be added to food products. Nanosized additives in food fall into the category of novel foods which must undergo a safety assessment and be approved before they can be traded in the EU. Additionally, food contact materials such as plastic packaging are regulated to be safe for consumers [v]. Packaging would for example not be allowed if unsafe chemicals or nanoparticles leak into the food.

One concern with regulating this is that nano-sized particles are particularly hard to detect. It could therefore be possible for dishonest companies to avoid regulations by not informing about the nano additives. Advancements in sensing technologies could be one of the solutions to ensure rules are being adhered to. Another thing that would help could be larger transparency about the production process of food using nano additives.

Conclusion

Nanotechnology is a rapidly growing field, and its effects on our every-day life are numerous. On one hand, it advances many fields – improving lives and addressing global issues such as hunger and malnutrition. On the other hand, it may have unforeseeable consequences if we are not careful. These can however be addressed by regulation and proper information to consumers. Otherwise, there is a danger that a bad case of unregulated use of nano food additives not representing the whole spectrum could mitigate the positive aspects and give nano food additives a bad reputation. Luckily, at least in the EU, the regulation on novel food products is strict to ensure consumer safety.

If you’d like to learn more about nanotechnology, please subscribe to our newsletter and stay tuned for upcoming posts.

References

[i] María Ximena et al., Nanoencapsulation: A New Trend in Food Engineering Processing. 2009. Accessed at https://link.springer.com/article/10.1007/s12393-009-9012-6

[ii] David Julian McClements & Hang Xiao, Is nano safe in foods? Establishing the factors impacting the gastrointestinal fate and toxicity of organic and inorganic food-grade nanoparticles, 2017, Accessed at https://www.nature.com/articles/s41538-017-0005-1

[iii] Global Hunger Index, https://www.globalhungerindex.org/

[iv] Benedette Cuffari, Nanotechnology in Food, accessed at https://www.azonano.com/article.aspx?ArticleID=4069

[v] European Union Observatory for Nanomaterials, Food, accessed at https://euon.echa.europa.eu/food

The post Nano Food Additives, Good or Bad? appeared first on The Nano Future.

In this interview article, Emil Højlund-Nielsen, Ph.D., CEO, and co-founder of cphnano, shares the inspiring story of the company’s journey in the pursuit of making advanced lab analysis more affordable and disrupting an industry with digitalization. Additionally, he gives valuable advice to people considering a start-up carrier within tech.

 Content

–          What is cphnano?

–          How did it start?

–          Challenges of building a tech start-up

–          Advice for future tech entrepreneurs

What is cphnano?

“A labtech company that develops digital laboratory analysis and diagnostics for the smart lab of the future”. cphnano offers solutions for spectrophotometers and spectrophotometry by digitalizing the process of doing lab analysis.

Using a nanofabricated photonic crystal, their lab cuvette, NanoCuvette One, allows for advanced measurements with only a simple set-up. This drastically increases the analytical capabilities of a spectrophotometer, which is one of the most widely used equipment to investigate liquids.

Ordinarily, liquids can be investigated by sending a spectrum of light through a plastic or glass container with it, known as a “cuvette”. Depending on the type of liquid, light at specific wavelengths will be absorbed more than at others. This can be measured in a spectrophotometer and then be translated to other valuable properties such as the concentration of an analyte. However, in other cases the refractive index is a more informative number to look at.

The refractive index can be measured with NanoCuvette One by combining the nanofabricated photonic crystal and a standard lab cuvette. By simply turning the cuvette 90 degrees, both the absorbance and the refractive index can be measured in a spectrophotometer.

How did it start?

When doing research within academia, many new technologies can seem an appealing way to solve the world’s issues or create exciting new products. The technology does, however, need to be economically feasible and work outside a complex lab set-up if it is to be implemented commercially. It is important to consider not only the end product, but also the production and implementation process. Sometimes, while building a completely new machine can cost millions, there are alternative ways to integrate the technology into already existing products, offering the same result at a much lower cost.

Emil explains how cphnano has followed the latter tactic. The idea of building a company first came from Kristian Tølbøl Rasmussen, another co-founder, during his Ph.D. at the Technical University of Denmark in 2015. At that time, he was working on a mature technology that had undergone thorough research from several other Ph.D. students. Together with Emil, the two engineers came up with a way to use the technology in a product that itself would not break the bank.

The idea was first to create a machine by making a compact version of what worked extremely well in the lab. This machine, however, would at least cost 5 million DKK to build. Thus, a customer would have to pay a large amount upfront.

“At some point, we looked at the lab set-up and saw that it was extremely similar to a spectrophotometer, apart from the unique nanostructured crystal. Next morning, we taped the crystal to a regular lab-cuvette and performed measurements that worked right away”.

Emil explains how this made the business case intriguing as the cost would then drop enormously while creating a large value for the customer. “Starting with something simple is a good thing. It will easily get complex with technical and logistical challenges along the way”. Another advantage is that it is possible to iterate the lab-cuvette and software each year to improve it in newer versions. This is simply not possible when building an expensive machine which the customer uses for many years.

Lastly, what made the business case interesting was that the roadmap to get the product to the market initially seemed short because strict regulatory approvals are only needed for the spectrophotometers and not the cuvettes.

Challenges of building a tech start-up

While there might have been many years of research within this field prior to cphnano, one thing is a lab set-up that researchers can use, another is the consumer-friendly product that is durable and lives up to the expectations every time. Emil puts this point concisely:

“In the scientific community, the best chip on your wafer is evaluated. In the industry, you are evaluated based on your worst chip.”

Another important point he brings up is that each face of a start-up’s journey has its own set of challenges. Some of these challenges might be larger than anticipated, which causes a longer road to market.

The obvious first challenge for cphnano was to optimize the fabrication of the photonic crystal. However, as they succeeded, it turned out that an even bigger challenge was to make their product work across different spectrophotometers and work with the different data formats they present.

“In Denmark, there are around 200 different models of spectrophotometers that our technology needs to facilitate”.

To solve these challenges a company needs the right set of competencies. However, since start-ups’ budgets are limited, it is crucial only to hire the people with the right skills needed.

A big challenge is that the skills needed change over time. cphnano, who integrates physics and nanotechnology with chemistry, biology, and software development, has therefore had to shift employees in and out to match the competencies needed.

While their team started out with mainly clean room competencies, today the company consists of just as many competencies within biotech and software development. Furthermore, Emil explains how skills within marketing and sales have been added in the process of the company becoming commercial ready. Naturally, the skills needed will vary depending on the type of company, but it is important to keep in mind what tasks need to be solved at the time.

Advice for future tech entrepreneurs

The first piece of advice is: “don’t do a start-up”. Do not build a start-up unless it is something you are extremely passionate about. In Denmark, a job with a salary is a far better option economically, as success is not guaranteed. Nevertheless, a start-up requires a full-time commitment and a big responsibility towards one’s employees, so it is not for everyone.

The second piece of advice is: Do your research and ask people who have a lot of experience within the industry that you are considering. It is quite easy to convince oneself that a business idea is good, but reality can be another story. Hence, planning is extremely important.

The third piece of advice is: Learn from other people’s mistakes. There is extremely small room for making mistakes in a start-up, and many can be avoided simply by asking people with experience. Emil compares how larger companies can invest in research projects without going bankrupt if they fail, whereas in a start-up you often have just a single shot to make it work.

The last piece of advice is: Understand the funding game. This varies depending on which country you start a company in, but it can certainly pay off to do some research on where to seek funding to get started. High wages in Denmark is especially a challenge for tech start-ups. Moreover, the tax on investments is high (42 %), which means that the capital available is a lot smaller than in other countries.

If you’d like to learn more about nanotechnology, please subscribe to our newsletter and stay tuned for upcoming posts.

The post cphnano Interview: Building a Strong Start-up within Nanotechnology appeared first on The Nano Future.

Vaccination is one of the strongest tools with regards to fighting infectious diseases. Vaccination is a method of introducing immunization in an individual. It greatly reduces the burden of infectious diseases as it reduces symptomatic disease development as well as prevent further transmission of the vira [1]. This reduces the burden of disease on the national health care systems.

Immune System Response

In all simplicity, immunization is a stimulation of the immune system. This stimulation induces the production of antibodies that can neutralize the stimulus [2]. A vaccine utilizes the immunization that happens when the immune system is exposed to new antigens. However, the infectious agent is replaced with a modified agent that poses as the infectious agent. The modification ensures that no harm or disease is developed. 

The immune stimulation is begun by introducing a modified pathogen (disease inducing organism) to the immune system. This can be done by e.g. injecting an inactivated virus. Different proteins are present on the surface of the pathogen. These allow the pathogen to e.g. adhere to cells in the body and infect the cells [3]. 

Some of these surface proteins are unique for the pathogen in question. These are known as antigens. [4]. These are the particles that the immune system will react to by producing antibodies that are specific to each type of antigen. Each antibody enables the immune system to quickly identify and neutralize any organism that contains the specific antigen on its surface [5].

However, the immune system needs time to react and develop specific antibodies when first exposed to a new antigen. This delay is where the live pathogen has time to multiply and cause symptomatic disease [4]. However, no or only mild disease development occurs if the immune response is triggered by an attenuated or inactivated pathogen as part of a vaccine. If the immune system encounters the antigen again, it is able to immediately confine and destroy the invading organism [6, 7]. This means that any subsequent infection with the same pathogen will result in no or a mild, short course of the disease.

Active Immunization and Vaccine Development

Active immunization has been applied for multiple centuries with the first examples documented in China in the 16th century during a smallpox outbreak [8]. Active immunization at that time was the deliberate exposure of a disease to an individual without modification of the infectious agent. The goal was to induce a mild disease progression while, simultaneously, activating the immune system. This would immunize the subject and prevent smallpox from developing due to any future exposure [8].

A second breakthrough in active immunization arose in the 18th century where vaccines with live, attenuated organisms saw first light [8]. This later progressed into vaccine development based on virus or cell cultures with inactivated disease vectors [8]. 

One of the latest technological approaches to vaccine development is the use of genetic engineering. Genetic manipulation enables the expression of surface proteins from any pathogen, e.g. a virus [2]. The proteins will activate the immune system and immunization process when injected into an individual. The use of genetic engineering thus enables vaccination without introducing the actual pathogen to the vaccine recipient.

mRNA Vaccine Used Against COVID-19

The target antigens of COVID-19 are 180-200 kDa, which corresponds approximately to a size of 5 nm [9]. This means that nanotechnology is needed in order to design a vaccine against COVID-19.

A radically new approach to vaccination has been developed recently. It relies on genetic engineering of mRNA and does not entail introducing any proteins or attenuated pathogens into the body [10]. This means that the vaccine does not cause any disease during the immunization process [11]. This type of vaccine was one of the first COVID-19 vaccine types to be approved for use.

The vaccine consists of a DNA-sequence that encodes the antigen or antigens that are unique to the target pathogen. However, the sequence is injected in the form of mRNA (messenger RNA) which prevents the sequence from permanently integrating itself into the genome of the individual [11,12]. Instead, it only acts as a transient carrier of the genetic information and will degrade over time.

The mRNA in the vaccine enables in situ production of the antigen. This means that the antigen for which the immune response is desired is produced directly in the body of the vaccinated individual. The produced antigen will then trigger the same immune response as if the individual had been exposed to the actual pathogen [11,12]. 

This means that no pathogen – either attenuated or inactivated will ever have entered the body. Instead, the natural protein production environment in our body is used to build the immunization that enables protection against e.g. COVID-19. This also removes the potential side effects of mild symptoms during the immunization process.

If you’d like to learn more about nanotechnology, please subscribe to our newsletter and stay tuned for upcoming posts.

Bibliography

[1] World Health Organization (WHO). “Vaccination greatly reduces disease, disability, death and inequity worldwide.” Bulletin of the World Health Organization, WHO, 2008, Accessed, January 2021, at https://www.who.int/bulletin/volumes/86/2/07-040089/en/.

[2] Murray, Kenneth, et al. “Genetic engineering applied to the development of vaccines.” Philosophical Transactions of the Royal Society of London, B. Biological Sciences, vol. 324, no. 1224, 1989, pp. 461-476.

[3] Science Direct. “Surface Proteins.” Science Direct Topics, Science Direct, 2020, Accessed, January 2021, at https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/surface-proteins.

[4] The Immunisation Advisory Centre. “The immune system and immunisation.” Immunisation, January 2020, accessed, January 2021, at https://www.immune.org.nz/immunisation/immune-system-vaccination.

[5] Britannica. Antibody, accessed, January 2021, at https://www.britannica.com/science/antibody.

[6] Siegrist, Claire-Anne. “Vaccine immunology.” Vaccines, 5 ed., Saunders, 2008, pp. 17-36.

[7] World Health Organization(WHO). “DNA Vaccines.” who.int, WHO, 2007, Accessed, January 2021, at https://www.who.int/teams/health-product-and-policy-standards/standards-and-specifications/vaccines-quality/dna.

[8] Plotkin, Stanley A. History of Vaccine Development. Springer Science & Business Media, 2011.

[9] Huang, Yuan, et al. “Structural and functional properties of SARS-CoV-2 spike protein: potential antivirus drug development for COVID-19.” Acta Pharmacologica Sinica, vol 41, no 9, 2020, pp. 1141-1149.

[10] Bert Hubert, Reverse Engineering the source code of the BioNTech/Pfizer SARS-CoV-2 Vaccine, December 2020, accessed, January 2021, at https://berthub.eu/articles/posts/reverse-engineering-source-code-of-the-biontech-pfizer-vaccine/

[11] Okay, Sezer, et al. “Nanoparticle-based delivery platforms for mRNA vaccine development.” AIMS Biophysics, vol. 7, no. 4, 2020, pp. 323-338.

[12] Schlake, Thomas, et al. “Developing mRNA-vaccine technologies.” RNA Biology, vol. 9, no. 11, 2012, pp. 1319-1330.

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The great aspect of solar cells is that they are producing non-polluting renewable energy by absorbing photons i.e. sunlight, and by extension converting the energy  of the photon to electrical energy for applications or conservation. 

One of the main challenges in the photovoltaic industry is the 33% efficiency limit for any traditional solar cell [1], which is where quantum dot solar cells (QDSCs) come into the spotlight as a solution to break the efficiency limit. 

The efficiency limit is due to excess energy lost to heat (thermalization loss), which could have been utilized [2]. The QDSC solves this issue with “quantum confinement” which will be elaborated further in the following.

What are quantum dot solar cells?

Quantum dot solar cells utilize crystalline nanoparticles known as quantum dots (QDs) as the absorbing photovoltaic material, and are investigated to replace common bulk materials such as silicon. QDs are typically in the size of 1-10 nanometers and are made from semiconductor materials or metals, e.g. cadmium selenide (CdSe) and lead sulfide (PbS). 

One of the biggest attractive attributes of QDSCs, is that they can cover the whole spectrum of wavelengths from sunlight. This is possible since the band gap i.e. the absorption spectrum is related to the size of QDs due to the quantum confinement effect. Therefore, the band gap can be tuned to match the solar radiation spectrum by adjusting the size of QDs, thereby providing great flexibility of light absorption and better efficiency in solar power generation [3]. 

Quantum dots made from lead sulfide are of most interest due to its great tunability [4]. In the case of bulk materials, the band gap is fixed in terms of what material is used, which makes thermalization loss inevitable.

Due to the very small size of QDs, it is also possible to print them into thin flexible sheets and make transparent solar cells more of a reality. These could possibly be incorporated into screens or windows as a form of electricity generation. The technology has also improved substantially in terms of efficiency, from 2.7% in 2010 to a reported 16.6% in 2020 [5].

Technical specifications of QDSCs

The QDSC is typically sandwich structured, with a photoanode, a counter electrode and an electrolyte. The photoanode consists of a transparent conducting electrode (TCE, typically indium tin oxide glass) and a metal oxide semiconductor (usually TiO2) coated with a layer of quantum dots [3]. 

The photoanode is where the sunlight is absorbed and as a result generates both positively charged electron vacancies (holes) and negatively charged electrons in the solar cell. The positive charges are transferred between the photoanode and the counter electrode with the use of an electrolyte. 

The purpose of the counter electrode is to transfer electrons from the external circuit (the electrical device) to the electrolyte, which results in catalyzing the redox reactions of the electrolyte [3]. A schematic of the QDSC is shown on Figure 1. 

Figure 1: A schematic of the quantum dot solar cell, which shows all the main components of a QDSC. The electrons transfer from the photoanode through the external circuit to the counter electrode. 

Outlook on Market

QDSCs are currently yet to be commercially viable in mass scale due to substantial challenges, such as reducing QD material cost and developing high-throughput deposition methods for mass production [6]. Although, several small companies have begun to produce QDSCs with the most notable ones being QD Solar, and Solterra Renewable Technologies, a subsidiary of the QD mass-manufacturer Quantum Materials Corp. 

Solterra gets a headstart in the immature market currently and has accordingly the proprietary technology to mass-produce QDSCs at hundreds of meters per minute using roll-to-roll printing technology. [7]

End note

QDSCs are currently seen as the next generation of photovoltaic devices, which has the most potential to break the thermodynamic efficiency limit of 33% with its excellent optoelectronic properties and the use of quantum confinement. QDSCs also have a maximum potential conversion efficiency of 66%, which is double the possible efficiency of traditional single junction solar cells [8], demonstrating that quantum dots could be the future of solar power.

If you’d like to learn more about nanotechnology, please subscribe to our newsletter and stay tuned for upcoming posts.

Sources

[1] Rühle, Sven “Tabulated values of the Shockley–Queisser limit for single junction solar cells”, published in ScienceDirect (2016).

[2]  Semalti, Pooja et. al.  “Advancements in Quantum Dot Solar Cells: Synthesis and Applications”, published in Sigma-Aldrich (2020). 

[3] Technical University of Denmark (DTU): Department of Chemistry. “Chemistry at the Nanoscale: Chapter 4”. (2020)

[4] Lutfullin, Marat et. al. (King Abdullah University of Science and Technology) . “Quantum Dots for Electronics and Energy Applications”, published in Sigma-Aldrich (2020)

[5] Hutchins, Mark. PV Magazine. “A quantum dot solar cell with 16.6% efficiency”. (2020)

[6] Jean, Joel. “Getting high with quantum dot solar cells”. Published in Nature (2020).

[7] Solterra. “Solterra: Business Objective”. (2020)

[8] NREL. “Quantum Dots Promise to Significantly Boost Solar Cell Efficiencies” (2013).

The post Revolutionizing Solar Cells with Quantum Dots appeared first on The Nano Future.

In order to create different structures, the semiconductor industry uses different bottom-up and top-down methods to deposit and remove materials at the nanoscale. Thermal ALE is one of the latter. By using this technique, researchers at MIT have built the smallest 3D transistor yet of only 2.5 nm across [i].

How does it work? [ii]

Thermal ALE was first reported in 2015 and can be viewed as the reverse of another important process known as atomic layer deposition (ALD). ALD was developed in 1977 and is used to add thin layers of compounds such as ZnS to a surface through controlled self-limiting steps [iii]. In ALE, the opposite happens where different materials can be etched away atomic layer by layer using mainly two processes. 

For materials such as Al2O3, HfO2, and ZrO2, a fluorination process is firstly used. This first process depends on the material, and in other cases needs a conversion or oxidation step. It can be viewed as a way to prepare the surface for the second process which uses ligand exchange reactions to remove the material.

Figure 1: Schematic illustration of an ALE cycle. Step (I) shows the fluorination process, while step (III) shows the ligand exchange interactions to remove a layer from the surface. The purge steps (II&IV) are used to remove excess reagents or products.

On the one hand, the widely used etching technique, reactive ion etching (RIE) which uses plasma, is a lot quicker, requires lower temperatures, and has the desired properties of being selective and directional. On the other hand, the plasma does some damage to the surface and is not as reliable as thermal ALE. 

A sort of in-between method developed in 1988 [iv], plasma ALE, has some of the same advantages as thermal ALE. Plasma ALE is a directional etch (only removing material in one direction), whereas thermal ALE is isotropic (etching in all directions at a time). Both etching types are needed and for certain 3d structures, the latter becomes especially important.

Outlook

As semiconductor devices become smaller, both thermal ALE and plasma ALE are becoming increasingly attractive methods to reach the demands of reliability and precision. Currently, they are expensive options, but this could be less of a concern with the increasing demand for more powerful electronic devices. Additionally, as a big research area, new ALE techniques are being developed for a range of materials that supports the wider use of the methods.

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References

[i] MIT News, Engineers produce smallest 3-D transistor yet, Dec 2018, accessed at https://news.mit.edu/2018/smallest-3-d-transistor-1207

[ii] Chang Fang et. al, Thermal atomic layer etching: Mechanism, materials and prospects, Dec 2018, accessed at https://www.sciencedirect.com/science/article/pii/S1002007118304623

[iii] Richard W. J. et al., A brief review of atomic layer deposition: from fundamentals to applications, June 2014, accessed at https://www.sciencedirect.com/science/article/pii/S1369702114001436

[iv] Keren J. K., et al., overview of atomic layer etching in the semiconductor industry, 2015, accessed at https://avs.scitation.org/doi/10.1116/1.4913379

The post Removing Atomic Layers from Nanostructures with Thermal ALE appeared first on The Nano Future.

The lithium sulfur (Li-S) battery chemistry where sulfur, and lithium metal, are used as the cathode and anode, respectively, is very promising due to its high theoretical energy density of 2600 Wh kg^-1. The sulfur is very attractive as cathode material due to its high theoretical specific capacity of 1675 mAh g^-1 which is six times higher than that of the common LiCoO₂ cathode. Likewise lithium metal is attractive as anode material because of its specific capacity of 3860 mAh g^-1 which is about ten times that of graphite which is used in most commercial lithium ion batteries. [i, ii, iii]
     Some of the challenges that keep Li-S batteries from commercialization are trying to be solved by employing nanostructured graphene and sulfur particles. The results are promising and have led to significant improvements in the last ten years.

Content

–          The working principle of the Li-S battery

–          Challenges with Li-S batteries and possible solutions

–          Concluding remarks

The Inner Workings of the Li-S Chemistry

The lithium sulfur battery cells are commonly composed of a sulfur cathode, a lithium metal anode, a separator, and an organic liquid electrolyte. When the cell is in its charged state, the sulfur will mainly be on the form: Octasulfur since it is the most stable configuration at room temperature [ii]. As the cell discharges, lithium ions and electrons move internally and externally, respectively, from the anode to the cathode. The electrons are inhibited from flowing through the electrolyte because of the separator as it is electrically insulating. When the lithium ions and electrons approach the sulfur cathode, the cyclic octasulfur molecules undergo reduction reactions i.e., the octasulfur molecules accept the electrons which reduces their oxidation level. These reductions result in structural changes in the sulfur molecules which facilitate the formation of lithium polysulfides. At first, these polysulfides will in the early stages of the discharge be on the form Li₂S₈ and Li₂S₆, but as the cell discharges further, more lithium ions and electrons arrive at the cathode which reduces the lithium polysulfides to Li₂S₄ and Li₂S₃. When the cell is completely discharged the cathode will consist of Li₂S molecules [i, ii, iv].
    The sulfur is a conversion cathode material since it converts from cyclic octasulfur to the linear Li₂S molecules. This is different from the intercalation mechanism being utilized in the common commercial lithium ion batteries.

The Intrinsic Challenges of the Li-S Chemistry

The lithium sulfur chemistry is subject to several issues that must be overcome or at least mitigated before commercialization is possible. One of the issues is that both sulfur and Li₂S are electrical insulating which lowers the amount of sulfur/Li₂S that partakes in the charging/discharging of the battery. The result of this issue is a lower capacity. Another issue is that the intermediate compounds, Li₂S₈, Li₂S₆, Li₂S₄, and Li₂S₃ are soluble in the organic electrolyte and will therefore, alongside lithium, shuttle between the anode and cathode where they participate in side reactions. These side reactions deteriorate the anode and the cathode. A third issue is the change in volume when the cathode converts between sulfur and Li₂S which may result in structural degradation of the cathode. [i]
    These issues can be solved by encapsulating the nanosized sulfur particles with a material that can enhance the electrical conductivity, trap the soluble lithium polysulfides, and buffer the volume changes. Graphene and graphene oxide (GO) have both been shown to meet these requirements.[i]
    Graphene is a sheet of carbon atoms arranged in a honeycomb lattice. Graphene oxide is obtained by treating graphene with oxidizers which introduces oxygen and hydrogen groups, and structural defects into the lattice. The oxygen and hydrogen form functional groups which increase the trapping capability of lithium polysulfides. However, the electrical conductivity of graphene and GO is reduced when defects and functional groups are introduced. Another approach is to enhance the physical trapping by constructing porous graphene or GO structures. The pores can be divided into micro- (<2 nm), meso- (2-50 nm), and macropores (>50 nm). Micropores inhibit the diffusion of the lithium polysulfides, while the mesopores trap the polysulfides and increase the amount of sulfur/Li₂S that partakes in the charging/discharging. The macropores do not trap the lithium polysulfides but act as a buffer for the volume change instead. [i]

Sulfur and graphene can be combined into different nanostructures. Three of the possible structures are shown in the figure below. The first structure is the in plane configuration where sulfur is deposited onto a sheet of graphene. This structure does not facilitate a strong trapping of the soluble polysulfides. The entrapment can be enhanced by using a sandwich structure where the sulfur is deposited between layers of graphene. This also ensures great electrical conductivity. The polysulfides can however escape through the edges of the sandwich structure. This leakage can be overcome by wrapping the sulfur with a graphene sheet as seen in the core-shell structure. The last structure is very promising as it traps the polysulfides to a great extent, can buffer the volume changes, and provides high sulfur loadings. The electrical conductivity is however lower compared to the in plane- and sandwich structure. This is due to the larger sulfide particles.

Schematic of three configurations of Li₂S and graphene. Lithium and sulfur are depicted as orange and yellow, respectively. 

Porous 3D foams of graphene oxide have also been utilized. They show great sulfur loading but due to the increased weight of the cathode, the specific capacity is reduced. The structure can also be combined to achieve e.g., high electrical conductivity and great entrapment of the polysulfides. This complicates the production process which in turn increases the cost. [i]

Besides the challenges with the cathode, the lithium metal anode also poses a serious issue. Lithium is highly reactive and will therefore participate in undesired side reactions some of which consume electrolyte. When the Li-S battery charges, lithium ions are shuttled from the cathode to the anode where they form dendrites that can grow through the separator and cause an internal short circuit.
    These issues can be solved in multiple ways. One technique is to coat the surface of the lithium metal with a carbonaceous material such as carbon nanotubes, carbon nanofibers, or graphite particles. Other techniques involve changing from a liquid electrolyte to a solid or gel polymer-based one, or modifying the separator such that it blocks the soluble lithium polysulfides. [i, v]

Conclusion

The Li-S battery chemistry is promising due to the high theoretical energy density of 2600 Wh kg^-1, their low cost, and environmental friendliness, but some major issues must be overcome before they can be commercialized [i]. Graphene and graphene oxide are promising candidates to solve the issues.
    Before the way for commercialization is paved the issues with the lithium polysulfides, the sulfur loading, and the stability of the lithium anode must be solved. However, since 2010 the lifespan and the capacity fade per cycle has increased and decreased, respectively, for Li-S batteries significantly showing that progress is being made. [i]

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References

[i] Yunya Zhang et al., “Graphene and its derivatives in lithium-sulfur batteries”, Materials Today Energi, 9, 2018, pp. 319-335
https://www.sciencedirect.com/science/article/abs/pii/S2468606918300728?via%3Dihub 

[ii] Arumugam Manthiram, Yongzhu Fu, and Yu-Sheng Su, “Challenges and Prospects of Lithium-Sulfur Batteries”, Accounts of Chemical Research, 46, 2013, pp. 1125-1134
https://pubs.acs.org/doi/10.1021/ar300179v 

[iii] Wei Zhao, Woosung Choi, and Won-Sub Yoon, “Nanostructured Electrode Materials for Rechargeable Lithium-Ion Batteries”, Journal of Electrochemical Science and Technology, 11, 2020, pp. 195-219
https://www.jecst.org/journal/view.php?number=335

[iv] Seung-Ho Yu et al., “Understanding Conversion-Type Electrodes for Lithium Rechargeable Batteries”, 51, Accounts of Chemical Research, 2018, pp. 273-281
https://pubs.acs.org/doi/10.1021/acs.accounts.7b00487

[v] Xiaosong Xiong et al., “Methods to Improve Lithium Metal Anode for Li-S Batteries”, Frontiers in Chemistry, 7, 2019, 827
https://www.frontiersin.org/articles/10.3389/fchem.2019.00827/full

The post Lithium Sulfur the Next-Gen Lithium Ion Battery? appeared first on The Nano Future.

Content

–          Top-down approaches

–          Bottom-up approaches

–          Outlook

Top-down Approaches[i]

A good analogy to top-down approaches is a sculptor carving out a statue from a template and thus removing material. An important top-down method in the semiconductor industry is photolithography. Here, short wavelength light (or electrons in e-beam lithography) is used to form the desired pattern in a photoresist to afterward use etching to form a nanostructure by removing material underneath. Different etching methods include chemical, plasma, or reactive ion etching.

Other top-down methods used are chemical- or electropolishing to smoothen a surface, or nano-imprint techniques (using a miniature stamp pressed down into a material) to form the wanted nanostructure.

A disadvantage of top-down approaches is that they are often done layer by layer and are thus 2D techniques which can be a limitation for creating certain 3D structures.

Bottom-up approaches

A bottom-up approach can be described by assembling a larger object from smaller pieces. An analogy here could be making a car. If the car represents the nanostructure, the individual pieces such as screws and wires can be thought of as molecules and atoms.

Nature does this very well and most processes in our bodies work by self-assembly and self-organization. Chemical bonds that are favorable guide the formation of complex structures such as proteins.

Inspired by nature, a big research area is the self-assembly of nanostructures with desired properties. An example is the self-assembly of monolayers of molecules on certain metals such as cysteine on gold surfaces which result in highly ordered structures. In some cases, this gives a useful coating to the material. 

In the industry, self-assembled monolayers are used to make quantum dots stable while preserving their optical properties used in QLED displays. [ii] In addition, quantum dots can themselves be synthesized by the bottom-up method known as colloidal synthesis.

Outlook

New methods are being developed and commercialized in both categories. Start-up companies such as Atlant 3D Nanosystems [iii] are part of creating more choices when it comes to making products with nanostructures. The start-up enables atomic layer 3D printing with certain materials making prototyping faster and cheaper. This method is considered a bottom-up approach.

Today some of the smallest nanostructures (7 nm) on mobile chips are made using extreme ultraviolet (EUV) lithography. This top-down method, used by Samsung and other companies, is thought to enable even smaller nanostructures soon. [iv]

There will likely be a continuous need for different methods as each method offers its own benefits and disadvantages, matching the needs of different products. For complex structures, a combination of methods is likely to provide the best results.

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References

[i] Britannica, Nanofabrication, accessed 2020-11-30 at https://www.britannica.com/technology/nanotechnology/Nanofabrication

[ii] Department of Chemistry – Technical University of Denmark, Chemistry at the Nanoscale, 2020

[iii] Atlant 3D Nanosystems, accessed at https://www.atlant3d.com/

[iv] Samsung, Samsung Electronics Begins Mass Production at New EUV Manufacturing Line, accessed at https://news.samsung.com/global/samsung-electronics-begins-mass-production-at-new-euv-manufacturing-line

The post Nanofabrication: The Top-down and Bottom-up Approaches appeared first on The Nano Future.

Today it is hard to imagine a world where smartphones, laptops, smartwatches, and electric vehicles are not rechargeable. This indispensable attribute is thanks to the lithium-ion battery (LIB) which was first commercialized by Sony and Asahi Kasei in 1991 [i]. Our demand for LIBs does not seem to decrease or stagnate as more personal devices and especially electric vehicles are introduced to the market. The global electric vehicle stock increased exponentially from 1.18 million in 2016 to 4.79 million in 2019 [ii] and the trend is expected to continue. Therefore, continuous development and improvement of LIBs are of great importance.

Content

–          The working principle of lithium-ion batteries

–          Nanostructured anode and cathode materials

–          Outlook at commercial products and the successor to lithium-ion batteries

Working Principle of Lithium-Ion Batteries

The common present-day LIBs are similar to the ones commercialized in 1991 and are composed of two electrodes, a separator, and a liquid electrolyte, as seen in the figure below.

The positive electrode (cathode) is commonly a lithium metal oxide such as LiCoO₂ while the negative electrode (anode) is made from graphite. When the LIB is charged the lithium ions shuttle from the cathode to the anode while electrons are moved away from the cathode and supplied at the anode.
    When the LIB is discharged the process is reversed and the lithium ions shuttle internally from the anode to the cathode where they intercalate. The electrons move externally from the anode to the cathode and as they move, they can be used to power a device such as a smartphone. The capacity of the LIB is hence limited by the amount of lithium that can be stored in the cathode and the anode structure. It can be increased by enlarging the batteries but since this is often not desired, much attention is given to increase the capacity per kilogram of battery i.e. the specific capacity.
    This can be done by creating new cathode and anode compounds which can accommodate more lithium per kilogram. However, this often comes with great challenges e.g. silicon as an anode material has about ten times higher specific capacity compared to graphite but it suffers from drastic volume changes during charge/discharge [iii]. Another way to increase the specific capacity is to optimize the structure of the anode and cathode material such that a larger portion of it participates in the intercalation process.

Nanostructured Anode and Cathode

The anode in commercial LIBs is based on graphite which is the same material used in pencils. It is used due to its price, availability, and relatively good theoretical specific capacity of 372 mAh g^-1 [iv]. Despite the success graphite has had, it is still relevant to improve the anode in terms of e.g. the specific capacity. Some of the promising nanostructured carbon allotropes that could be used instead are: Carbon nanotubes (CNTs), graphene nanosheets, and carbon with nanosized pores. [iv]
    It has been demonstrated that the CNTs, which are rolled sheets of graphene, can accommodate lithium ions both on the inside and outside, and that they have excellent electronic conductivity. It was also reported that by introducing defects into the CNTs the capacity improved. [iv]
    Another option is graphene nanosheets, which can be prepared by exfoliation from bulk graphite since it is composed of stacked layers of graphene. Similar to the CNTs the surface area is greater compared to graphite and since both the plane and the edge of the nanosheets can accommodate lithium ions the theoretical specific capacity can reach 744 mAh g^-1. Furthermore, it can be increased to over 1000 mAh g^-1 by introducing defects. One of the difficulties with graphene is its low density and hence it requires a larger anode volume which ultimately leads to a larger battery. Another difficulty is that it participates in undesired reactions leading to irreversible loss of capacity. [iv]
    A third alternative is to create nanosized pores in carbonaceous materials. One approach is to make hollow spheres with a double-shelled nanostructure which increases the surface area and thus the specific capacity. The specific capacity for such a structure has been reported to reach 920 mAh g^-1. However, the increased surface area inevitably results in obstacles and defects which may trap lithium ions which in turn causes an irreversible capacity loss. [iv]

While the anode material is based on carbon, the cathode material in common commercial LIBs is in general either a lithium metal oxide such as LiCoO₂ (which was introduced by J. B. Goodenough and was the first commercial cathode) and LiNiMnCoO₂,  or a phosphate-based compound such as LiFePO4. These cathode materials are used today along with multiple other types depending on the desired voltage and working environment. LiCoO₂ and LiNiMnCoO₂  are some of the most common cathode materials due to their great specific capacity of about 150 mAh g^-1, and good cyclability. They, however, rely on cobalt which is expensive, toxic, and poses both environmental and health concerns due to the conditions in which it is mined and extracted.
    In order to lower the amount of cobalt and increase the specific capacity, it has been proposed to substitute some of the cobalt with manganese (Mn) and Nickel (Ni). It has been reported that a nanosheet structure of LiNi_1/3Co_1/3Mn_1/3O₂ with width and thickness of 0.7-1.5 µm and 10-100 nm, respectively, delivered an increased specific capacity of 193 mAh g^-1. This is due to the high surface area of the nanosheets. [iv]

Outlook

Many of the nanostructured cathode and anode materials are still in the research phase but some have already been commercialized. An example is a LiFePO₄/Graphite based LIB from LithiumWerks which utilizes their trademarked Lithium Nanophosphate technology [v]. Another example is the porous carbon material usable in both the anode and cathode developed by Graphene Batteries [vi].

Lithium-Ion batteries have and will be important for our transition to green energy but as our demand for inter alia higher capacities and higher power output keeps increasing we may have to look towards other materials for both the anode, cathode, and the electrolyte. This will give us new problems which we have to overcome, perhaps through nanostructuring?

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References    

[i] George Crabtree, Elizabeth Kócs, and Lynn Trahey, ”The energy-storage frontier: Lithium-ion batteries and beyond”, MRS Bulletin, 40, 2015, pp. 1067-1078
https://www.cambridge.org/core/journals/mrs-bulletin/article/energystorage-frontier-lithiumion-batteries-and-beyond/A0CE1F1D2F344EB6B362DA3C29DC2BD1/core-reader

[ii] International Energy Agency, “Global EV Outlook 2020 – Entering the decade of electric drive?”, Technology report, 2020
https://www.iea.org/reports/global-ev-outlook-2020

[iii] Xuefeng Song, Xiaobing Wang, Zhuang Sun, Peng Zhang, and Lian Gao, “Recent Developments in Silicon Anode Materials for High Performance Lithium-Ion Batteries”, Merck, [Accessed on: 08/11-2020]
https://www.sigmaaldrich.com/technical-documents/articles/materials-science/recent-developments-in-silicon-anode-materials.html

[iv] Wei Zhao, Woosung Choi, and Won-Sub Yoon, “Nanostructured Electrode Materials for Rechargeable Lithium-Ion Batteries”, Journal of Electrochemical Science and Technology, 11, 2020, pp. 195-219
https://www.jecst.org/journal/view.php?number=335

[v] LithiumWerks, [Accessed on: 08/11-2020]
https://lithiumwerks.com/

[vi] Graphene Batteries, [Accessed on: 08/11-2020]
https://www.graphenebatteries.no/

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