Materials Connect

Match with a Laureate!

I have been following the Nobel Prizes awarded in physics for about 10 years now, and in those 10 years, 2018 was the first time that a woman, Donna Strickland was awarded this honor “for their method of generating high-intensity, ultra-short optical pulses”. It caught my attention for two reasons – I claim to be a physicist at heart and am a woman in science.  So, I decided to look up the history of the Nobel Prize. For anyone who has not looked at the official Nobel Prize website, you should (it is full of amazing science factoids and stories). The first Nobel was awarded in 1901 after Alfred Nobel’s death in 1895. Between 1901 and 2018 there have been 590 Nobel prizes and 935 Nobel laureates in total. Of these, only 52 have been women and only 3 in physics. While these numbers are concerning, they are not unheard of. 

This little trip of procrastination from writing my dissertation and job applications led me to the website: women who changed the world. I think everyone remotely connected to science should look up this fascinating website! (https://www.nobelprize.org/womenwhochangedscience/) You click on the website and answer three simple questions to match with a laureate. I was matched with Maria Goeppert Mayer who won a Nobel prize in physics for “discoveries concerning the nuclear shell structure” in 1963, the second woman ever after the very well-known Marie Curie. My claim of being a physicist at heart was restored! Reading her story from a time when women were not allowed to go to college and yet achieving the greatness that she did, purely because of her commitment to science gave me a sense of inspiration. Now in 2019, I think we have come a long way since 1963 and still have a long way to go. But I would like to imagine that things are changing for the better, however slow it might seem, and that we are an integral part of this change. Nobel Laureate Rosalyn Yalow once said: “The world cannot afford the loss of the talents of half of its people if we are to solve the many problems which beset us.” 

(PS: Rosalyn Yalow was also a physicist who won the Nobel prize in physiology in 1977 for a method to  measure concentrations of substances in the blood ) 

 

Science inspirations to your earbuds

I dived into the world of podcasting to, initially, improve my English. It turns out that I have gained more than just picking up the language. By listening to a podcast, I feel immersed in a community of like-minded listeners. The science podcasts, in particular, remind me of why I wanted to become a scientist in the first place, and show me how to effectively communicate science.    

If you are new in this world, keep in mind that it is subjective whether the shows are good or not. Even though you find yourself unsubscribing from a bunch of shows because the tone does not work for you, it is okay. Here are my top five playlists in terms of materials science and science communications, and I want to give you an idea of what to expect before you start listening.

(Photo by Juja Han on Unsplash)

 

Chemistry & materials:

 

1. MRS Bulletin Materials News Podcast 

This is the very own Materials Research Society News show. Through a very short form of interview each week, the podcast gives “the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology.” And by saying a short form, I mean less than six minutes per episode, which is an easy fit within a busy experiment schedule. This show is a relatively young broadcast, running since this January, and I am looking forward to the benefits it brings to all of our materials scientists.

 

2. C&EN's Stereo Chemistry

This monthly podcast by Chemical & Engineering News is a must-hear, as materials research is closely related to chemistry. Launched in early 2018, the podcast is dedicated to “sharing the voices of chemists worldwide to tell stories that we hope will surprise, inform, and inspire everyone who loves the central science.” The show is crisp and sharp, and nicely keeps me informed about wide-ranging fields centered around the fascination with chemistry. 

 

#PhDlife:

 

3. Hello PHD 

Ph.D. students and postdocs face unique challenges in many ways. Therefore, I recommend this podcast for it addresses a diverse range of topics such as mental wellness and career options. (They even touched on financial management. Who would think about it since graduates have no money to spare anyway?) The discussion of “the human side of science and life in the lab” brings insights and practical tips to these issues in a very thoughtful and cheerful way.

 

4. Passionate PhDs 

The show involves one question, “What does a Ph.D. mean to you?” in conversing with guests from various professionals. Their conversation reminds me of why I signed up for a graduate program, and, most importantly, why I wanted to become a scientist. I resonate hugely with the host’s philosophy that the Ph.D. is “a research process; not only for science but researching process of (one’s) personality and mission.” Listening to the podcast purely “brings you the passion of PhDs.”    

 

The personal side of science:

 

5. Lady Science

This podcast is actually beyond being feminist, if you assume the content merely based on the title. The show covers a broad range of the history of science, technology, and gender while making it relevant to the present. I discovered this show very recently and got hooked. After a long day in the lab, the ladies offer me space to freshly reflect and appreciate science.  

 

Please send more of your favorites in the comments! 

The Order of the Dot

Quantum dots (QDs) are semiconductor single crystals of nanoscale dimensions. These nanomaterials can be solution-synthesized in a low-cost manner. QDs are home to a wide array of tantalizing optical and electronic properties, such as strong and tunable optical absorption and fast charge transport, absent from their corresponding bulk forms. These surprising characteristics are a virtue of a quantum mechanical phenomenon, the ‘quantum confinement effect’, which comes into play when materials are reduced in dimensions below a certain size.

This size limit is defined by the material’s properties. When below this limit, electrons (and holes) start experiencing the physical boundaries of the confined matter. The charges stop behaving as free particles giving rise to exotic properties, the most prominent among which is the size-tunable band gap: changing the size of the particle changes the color it absorbs and emits. Another related property is the sharp emission linewidths. It is primarily for these two properties that QDs have been widely pursued with intense vigor over the past two decades for applications in third generation photovoltaics and as a low-cost flexible display technology. In particular, tunability of light absorption can help absorb and manage sunlight in a better way by also absorbing the infrared radiation that makes up 50% of the spectrum and cannot be absorbed by the current silicon solar cell technology, due to the latter’s fixed band gap.

Figure 1: Quantum confinement effect. Tuning the QD size tunes their optical bandgaps, without the need to change their chemical composition or synthesis protocol. (Credit: https://area-info.net/quantum-dots-market-2016-2023-research-report-by-decisiondatabases/)

QDs have a large surface-to-volume ratio. Comprising of a few-hundred to a few-thousand atoms, they are usually capped with organic surfactants. Chiefly, the surfactants keep the QDs from aggregating, render them soluble in organic solvents, and protect their pristine surfaces from the environment. There is another very exciting thing these surfactants do – they allow the QDs to self-assemble. When the QD ink is cast into a thin film, for example, the interaction of these surfactants with the drying solvent defines the long-range order that the QD ensemble will achieve. This long-range order, however, has thus far been of limited application for researchers studying charge transport as the long-range ordered ensemble contains these organic, long-chain surfactants that impede the flow of charges and the ensemble behaves as an insulator. Enter the shorter-chain molecules…

If this QD film with insulating surfactants is soaked briefly in a solution containing shorter-chain molecules (ligands), an exchange reaction occurs on the QD surfaces. The shorter ligands clip-off the surfactants and replace them, bringing the QDs closer for improved charge transport. Electrical conductivity increases by several orders of magnitude, however, at the cost of the long-range order. What remains is a glassy, amorphous QD film – with tremendous charge transport properties (compared to the initial insulating film). The resulting disorder is expected since the solid film undergoes a sudden volume reduction due to the exchange reaction.

Figure 2: Effect of ligand exchange. a) Cubic perovskite quantum dots initially capped with long-chain organic surfactants are made to undergo ligand exchange. The initial long-range order is lost. b) These exchanged QD films are used as absorbers in the latest high-performing QD solar cells.

The exchange process described above is called the solid-state exchange, since it is performed on a solid film. There is another chemical route to achieving this, the solution-phase exchange. To perform the latter, the QD ink is mixed with the shorter ligand solution leading to exchange in solution-phase. Since this is carried out in the solution-phase, it is expected to preserve the initial long-range order, at least, to some extent. Against expectation, however, these QDs also have failed to show any long-range order to date.

This brings us to the question: of what use is the long-range order? Order in the final conductive film has thus far remained elusive. Quantum mechanics tells us that having order in the final, exchanged QD film can have interesting implications for charge transport. Carriers can flow faster allowing ‘band-like transport’ – the charge transport mechanism common in atomic solids with excellent charge mobilities. New research is beginning to reveal the fruitful consequences of preserving order in QD films. Balazs et al (https://onlinelibrary.wiley.com/doi/full/10.1002/adma.201802265) recently reported electron mobilities of 24 cm²V^-1s^-1 from lead chalcogenide QD films exhibiting substantial order  (lead chalcogenide QDs are a family of QDs that have garnered the most attention due to their superior electronic properties). Mobilities in these QDs had not been reported to exceed 5 cm²V^-1s^-1 prior to this report, highlighting the importance of long-range order.

Disorder in QD films impedes the flow of electrons and holes in these materials. This means that charge carriers generated inside QD solar cells ‘die’ before they could be extracted in the form of useful electrical power. This is one of the major reasons that threatens further progress toward QD solar cell technology. Further improvements in QD optoelectronics are on offer if a method is found to suppress disorder, and Balazs’ results are a step in the right direction. It is time to search for the order of the dot!

 

 

The Story Behind A Digital Artist and Materials Researcher

Recently a LinkedIn post caught my attention: Armin VahidMohammadi, a Ph.D. candidate and research assistant at Auburn University, U.S., who I met in 2018 MRS Meeting in Boston, won the MRS Science as Art competition again. It is the third time Armin wins, and he is the only graduate student who achieves this hat trick as the first and leading author of the artwork. Last year, Armin was the Grand prize winner of JEOL USA’s scanning electron microscopy (SEM) image contest.

 (Credit: Armin VahidMohammadi)

Armin VahidMohammadi, the Alabama NASA EPSCoR (GRSP) Ph.D. Fellow and a Research Assistant of Materials Engineering in the Department of Mechanical & Materials Engineering, Auburn University, U.S.

Nano Nemo MXene: Grand Prize Winner of the 2017 JEOL SEM Image Contest

(Credit: Courtesy of Armin VahidMohammadi at Auburn University, U.S., and JEOL USA)

The nano-sized layers of a Ti₂C particle represent the Nemo character in the Pixar’s animation, Finding Nemo, and its reflection in the water.

The MXene Yoda: Second Place Winner of 2019 MRS Spring Meeting

(Credit: Courtesy of Armin VahidMohammadi at Auburn University, U.S., and the Materials Research Society)

A colored SEM image of an oxidized two-dimensional (2D) V₂CT_x (T_x represents terminal elements, e.g., O, F and OH) resembling the Yoda character in the Star Wars Movie series.

The MXene Turtle: First Place Winner of the 2018 MRS Fall Meeting

(Credit: Courtesy of Armin VahidMohammadi at Auburn University, U.S., and the Materials Research Society)

A colored SEM image of a 2D V₂CT_x particle showing similarities to the head of an imaginary giant turtle. V₂CT_x is synthesized by selective etching Al atoms from V₂AlC and is a promising electrode material for energy-storage devices.

Nano Lord Voldemort: First Place Winner of the 2016 MRS Fall Meeting

(Credit: Courtesy of Armin VahidMohammadi at Auburn University, U.S., and the Materials Research Society)

A colored SEM image of a layered Ti₂C particle mimicking the face of Lord Voldemort, a character in the Harry Potter movie series. Ti₂C is synthesized by selective etching Al atoms from Ti₂AlC and is a promising electrode material for energy-storage devices.

Inspired by his outstanding images and impressive presentations, and as a beginner struggling in rendering breath-taking three-dimensional (3D) illustrations, I am eager to know how this young materials scientist falls in love with digital art. I finally fulfilled my curiosity by having a conversation with Armin a week ago. With his permission, I am sharing the story about how he acquired, developed, and practiced the skills of scientific drawing.

The Early Days

Creating and animating 3D models fascinated Armin, a then high school student. "Making 3D models and computer-generated graphics is amazing, particularly when making photo-realistic models." says Armin, "Whenever I show 3D artworks to other people and they think the images are real, it makes me excited!" The capability of the computer graphics and 3D modeling in designing and creating photo-realistic images further stimulated Armin to expand his knowledge in this field.

Armin, and his brother, Aidin, managed to teach themselves how to work with different 3D software by reading the manuals and instructions of them. “Aidin was so passionate in 3D artworks and we always were discussing new things. I am sure we could never do what we can do today without learning and working together. Aidin had a big role in mastering the skills”, Armin says. The two passionate learners soon reached a reasonable level of skills and developed their first portfolio of sample works. Impressed by their high-quality pictures, local television companies approached and hired Armin and his brother to work on different animation projects. It was only 16 years old that Armin got his first job offer to design 3D models and create 3D animations. In 2011, Armin entered the Sharif University of Technology in Iran as an undergraduate student; there he continued to work as a freelance artist. Notably, he and his brother served as 3D modelers for the TV series of "Alavi Detector-Part 2" and a few other TV commercials. These experiences had deeply sharpened Armin's 3D modeling skills.

Materials Research Embraces Art

Armin's research focuses on electrochemistry and applications of novel nanomaterials in monovalent (e.g., Li⁺) or multivalent (e.g., Al³⁺) ion batteries and supercapacitors (a.k.a. ultracapacitors). He chose this research field because he believes that energy storage devices are increasingly important for modern society, particularly in the next few years when electric cars will start to dominate the vehicle market. In the Sharif University of Technology, Armin investigated the syntheses and characterizations of nanomaterials in addition to his interest. "To be honest, I have always wished to make truly high-performance and reliable batteries that will make a difference in our lives," says Armin. After moving to Auburn University, Armin started working on 2D metal carbides and nitrides (MXenes) and 2D metal oxides as battery and supercapacitor electrodes.

Armin always enjoys leveraging his 3D modeling skills to help with his research, by both making schematics to illustrate the working mechanisms of his energy-storage devices and delineating the procedures of material syntheses. Armin believes that a major problem of scientific presentations is the lack of eye-catching and informative images to make people excited and interested. "I have frequently noticed that many researchers have done pretty cool and significant works, but they fail to deliver their ground-breaking discoveries in a visually appealing way to impress the audience," says Armin. To avoid the pitfalls, Armin supplies his presentations with vivid illustrations (examples below). "Sometimes, my scientific illustrations attract more attention than my works themselves. For example, after one presentation in the past MRS meeting, some fellow researchers asked me how I made my slides or the graphics, instead of talking about the science of my research. It’s not a negative thing though, because it indicates that at least the audience paid attention to my slides and listened to my talk. The main purpose of using eye-catching illustrations in science is to attract people and facilitate understanding of your works."

Armin used this scheme to show the synthesis procedures of the cation-assisted assembly of stable V₂CT_x MXene nanosheets. Credit: VahidMohammadi et al., Adv. Mater. 2019, 31, 1806931.

Armin rendered this illustration to show the working mechanism of an Al-ion battery consisting of a V₂CT_x cathode, an Al anode, and an AlCl₃-containing ionic liquid electrolyte. Credit: VahidMohammadi et al., ACS Nano 2017, 11, 11135-11144.

How to Start Learning 3D Drawing

Armin believes perseverance is essential. You need to set your mind that whatever software you learn, it is going to be a non-trivial task and a long journey, particularly if you want to render sophisticated 3D models. It may take a year or more of constant practice to master only a small portion of only one advanced drawing software. Nowadays, tutorial articles and videos are widely available for various drawing software and learners of different levels, but you always need your dedication and persistence to support you through the challenging yet encouraging learning processes.

Tianyu Liu

The author of the post appreciates Armin VahidMohammadi of Auburn University (U.S.), Xiaozhou Yang of Virginia Tech (U.S.), and Hortense Le Ferrand of Nanyang Technological University (Singapore) for their careful proofread.

The Bandgap Abnormality of Nano-sized Hematite Crystals

Bandgap is one of the characteristic properties of semiconductors. It represents the energy gap between electronic orbitals (or more rigorously speaking, electronic bands) filled with electrons (the valence bands) and the ones with no electrons (the conduction bands). The bandgap largely determines the optical and electrical properties of a semiconductor.

Though the bandgap is a semiconductor's intrinsic property, its value does not always remain constant. Quantum mechanics reveal that, when the size of a semiconducting material falls in the nanometer range, its bandgap starts to broaden. This behavior is due to the increased quantum confinement effect imposed by size reduction, which shrinks the available space for electrons (sometimes are positively charged holes) in semiconductors to move around. This increasingly confined space leads to the enlarged bandgap, as predicted by Schrödinger Equation (a fundamental equation that every student must master in order to survive a Quantum Mechanics 101 class).

However, my knowledge on quantum mechanics has been completely thrown up after I came across a paper recently published in The Journal of Physical Chemistry C 2018, 122, 9292-9301. Sharma et al. reported an anomalous trend of how the bandgap of hematite (the alpha phase-iron oxide), a semiconducting material, changes with crystal size. The bandgap of hematite indeed increased when the crystal size reduced from 75 nm to 30 nm. However, when further decreasing the size from 30 nm to 15 nm, the bandgap decreased (see the figure below, the blue curve). How come what I learned is not true here?

Figure. Variation of electrical conductivity (the black curve) and bandgap (the blue curve) with crystallite size of hematite. Credit: American Chemical Society.

It turned out that what I learned touches only the basic but the real world is always more complicated. The authors of the article studied the evolution of the electronic structure of different sized hematite nanoparticles using X-ray absorption spectroscopy. It reveals that the observed "abnormal" observation, in a nutshell, is because of the change in bond nature between Fe and O atoms. This bond change alters the width of the valence band and consequently modifies the bandgap of hematite. My quantum mechanic class assumes the width of the valence band is constant and, hence, the conclusion derived there is no longer valid for this case.

This experience reminds me about the difference between textbook knowledge and cutting-edge research: Textbooks help us to form general yet somewhat blurred images, but it is the insight gained from state-of-the-art experimental works that render pictures with much improved resolution. It is why I feel extremely excited when reading cutting-edge research works both within and beyond my research expertise.