How exciting. My first "scribbles" post! The topic I want to share today is about different techniques of contacting 2D semiconductors. This is quite a broad topic and a lot of interesting techniques have been used in the past to achieve electronically transparent interfaces between TMDs and electrodes. It almost sounds trivial to speak about making contacts to semiconductors. However, it is far from trivial when you are dealing with 2D materials, especially in their monolayer form (~3 atoms thick). Several works such as 1 and 2 have shown that evaporating the electrodes directly onto TMDs can cause damage to the TMD layers. 

To overcome this, graphene was being used to contact TMDs for a long time. According to 3, graphene-MoS2 interface proved to be ohmic, which allowed the researchers to measure the intrinsic properties of MoS2 even in a 2-terminal geometry. However, exfoliating TMDs alone is hard but to combine TMDs with graphene? It sounds like a long, tedious and challenging job. There are several other variations of this such as using RuCl3 in proximity (4) and MoNx (5), which is particularly super cool because this can be converted from MoS2 by annealing, but this is a topic for another day.

Contacting the TMDs with another 2D material is cool, but isn't quite scalable. Big tech companies like TSMC and Samsung are looking to TMDs for their next generation semiconductors to go beyond Moore. We can't really suggest mechanical exfoliation and transfer to these companies when they are planning to build gazillion transistors on a single chip. In terms of scalability, evaporation or sputtering still makes sense. The authors in 1 and 2 have shown that instead of depositing the metals by e-beam/thermal evaporation directly onto the TMD layers which may damage the interface, or graphene which is cumbersome to deal with and not scalable (yet), one can evaporate the metal contacts onto a dummy chip, and then transfer the electrodes on top of the TMDs! This is directly opposite to what is typically done in labs. We usually prepattern the electrodes on a pre-defined chip, exfoliate the 2D material on PDMS or on a dummy SiO2/Si, and transfer the 2D material onto the electrodes. By thinking creatively, the authors flipped the approach, and as a result, have nearly reached the Schottky-Mott limit. Whether or not the transfer of metal contacts are scalable is still a question, but with automation and mechatronics nowadays, automatic transfer of contacts could be achieved with good overlay - similar to this work from Japan on automated assembly of 2D heterostructures.

There are a few variations of this technique, especially one that is relevant to air-sensitive materials in frontier research, where one would first pattern VIA contacts (analogous to those in multi-layer PCB designs) into the capping layer, hBN, and transfer the VIA contacts along with the hBN using various polymer-assisted transfer techniques (6, 7). This is perhaps a topic for another day.

Finally, there have been recent developments in combining the best of both worlds. In 8 and 9, the authors evaporated semi-metallic 2D materials Sb and Bi to make ohmic contacts to TMDs. Sb (antimonene) and Bi (bismuthene) are 2D semimetals similar to graphene, but can be evaporated in large scales at CMOS compatible procedures. In particular, Sb does not degrade in air below 250C (10), epitaxially grows on MoS2 (9) and its crystalline orientation can be controlled by heating the substrate to a gentle temperature (8). From the cross-sectional TEM images, it also seems that the TMDs are not damaged by the evaporation process. All in all, I think semimetallic contacts to TMDs will be an interesting and powerful technique for both academics and industry.

Printed Circuit Boards (PCB) are an integral part of our lives, and also in experimental science too. Experiments involving electrical probing/control require carefully designed PCBs that allow the users to conduct their experiments as precisely as possible. PCBs are the components bridging between the measurement electronics such as source measure units (SMU), lock-in amplifiers and digital multimeters (DMM) all the way to your sample. Today, I will briefly talk about the PCB design considerations and some of the jargons used in the manufacturing of PCBs. I am, in no stretch of imagination, an expert on this, but I like sharing my knowledge and have just enough experience to help out an undergrad/ grad student who is just starting out. 

Let see if we can get something done together!

I'm sure electrical engineers would have a much better breadth and depth of understanding when it comes to PCB designs and circuits in general. For 'simple' transport experiments as those performed in experimental condensed matter physics, PCBs tend not to have such elaborate designs and considerations. For low temperature transport, for example, what is more important is the thermal properties, rather than the actual design of the PCBs. For UHV applications, degassing may be more important than the thermal properties. It all depends on the situation.

From here on, I am going to be writing about DC transport strictly because the requirements for RF is quite different to that of DC transport. In some sense, RF is easier, since the absolute value of the AC voltage offset is often not very important (often times you want to zero that out and add your own DC offset via a bias tee). For low temperature DC transport (I call f<1kHz DC), i.e. quantum tunneling experiments, the exact levels of voltage and current are critically important.  If you measure a superconductor, and the grounding of the cryostat is poorly done, then you may get a finite voltage offset in the superconducting state (which is supposed to have exactly zero resistance) or whenever you do a forward/backward sweep, you may get unreproducible hystereses. 

Anyways, lets get to the practicalities. 

General suggestions: 

What I have done in the past and recently too, is that I've used FR-4 type PCBs for room-temperature-to-150C setups. For these intermediate temperatures, normal PCBs work fine. What I recommend is that you have ground planes everywhere. Have the 'hot' leads embedded in the middle layers and protect them with copper-pour (will be discussed later) in plane as well. This will create microwave shieldings from the top, bottom and sides. If you're running very sensitive experiments, then I would also add a bunch of multilayer VIA channels throughout the PCB connecting the GND Nets (will be discussed later) such that there aren't any sort of charge gradients anywhere on the PCB, even for a split second. Depending on your requirements, these may be overkills or may not be compatible with your experiments. But I hope these give you something to think about.

Material selections for your needs: 

For UHV, FR-4 type of PCBs may not be the best. I've used the FR-4 for a HV setup, which went down to 5e-6 mbar (it was not limited by the PCB) but UHV is an entirely different beast. For those, you should go for materials which do not degass. FR-4 is a fiberglass-epoxy laminate, and is not UHV compatible.  Apparently, Ceramic-PTFE composites from Rogers are much better in regards to degassing. [*update: a former colleague of mine confirmed that with a PCB made of FR-4 inside the chamber, he was able to push the vacuum down to ~3e-8 mbar.] For high temperature experiments (>400C), ceramic PCBs are better. However, often times, the solders start to give out before the PCB does. For applications in these extreme conditions, I recommend using high performance conductive adhesives from TedPella. They have a few varieties, including silver and carbon which can withstand beyond 800C. They tend to be a bit expensive for the volume, so if you are on a budget, you can buy an industrial scale product for cold welding (i.e. JB extreme heat).

Now for the low temperature cryostats. Ceramics and some plastics such as polyimide PCBs can be suitable for low temperatures, unlike FR-4 (recommended only down to -50C). However, we are often dealing with a finite cooling power, especially in this day and age of dry fridges. Therefore, it is important that all the components cool down as efficiently as possible. Since the thermal conductivity has both electric and phononic components, metals tend to have much better thermal conductivities than dielectrics. Therefore, building a PCB out of copper core or aluminium core PCBs should be considered. For best results, all the connections should be oxide free, gold coated and the PCB should be mounted with some thermal grease like Apiezon N. I have used FR-4 PCBs inside a wet dilution cryostat, so in principle, FR-4s should still work in a dry setup as well. Something to consider is that for operations in cryostats, having copper grounding planes in the PCBs may not be necessary, since the entire cryostat is a giant metal can, shielding the sample from the external microwaves. This is great, since copper core/ aluminium core PCBs usually have a single layer (usually copper still) on top with a chunk of metal taking up most of the volume. This means that having vias may be difficult or impossible. Also, keep in mind that copper does not superconduct while aluminium does below ~1K. 

For the production of PCBs, these are the typical steps: 

One creates the designs using cad programs specific for PCBs, such as kicad or easyEDA. I've recently found out even Fusion360 from Autodesk can be used. So far, I've been using easyEDA, because their online software is quite easy to use, the designs can be directly transferred to their sister companies who take care of PCB fabrication, and I didn't need very special PCB designs which would force me to consider other dedicated softwares. They (JLCPCB, a sister company of easyEDA) tend to produce the PCBs fast and also offer electrical component soldering services, so I've been happy with the outcomes. (But I've also heard negative reviews as well.) After the design is complete, one can send the resulting Gerber file as a .zip format to the company who will produce the PCBs. In the submission process for the quotation, the details about the PCBs will need to be specified. One needs to specify the material, number of conductive layers, thickness, finish (HASL/ENIG), etc. Just for clarity, HASL stands for Hot Air Solder Levelling and is the most common way of plating the top most layer of copper, where ever the solder mask is defined. This process involves tin/lead and gives the solder pads the silver color. ENIG stands for Electroless Nickel Immersion Gold and give the exposed solder pads a yellowish hue. My guess is that for some magnetotransport experiments, HASL will be better than ENIG due to the presence of Nickel in ENIG . If oxidation is an issue, or if gold-gold bonding is preferred, then ENIG is the way to go. Finally, if there are any errors, the company will probably reach out before production. The base line price of PCBs take up the bulk of the price, meaning that ordering 100 will be more cost efficient per piece than ordering 10. But who needs that many.

Technical terms like nets, copper flow, vias and silklayers can be daunting at first. Here is a bit of jargon to help you get through. 

• Nets: this is the individual ID for each connection. All the PCB lines and pins of ICs should be under the same net, if they are sharing the same connection. One special net is the GND. GND is the ground which in principle should be shared by all the grounding planes of the PCB which are defined by the copper flow.

• Copper flow: this is the term used to fill up the remainder of the PCBs while being isolated from the hot lines. Define the clearance to control the spacing between the copper flow area (GND net) and hot lines (active nets). Make sure to have grounding vias that connect the copper flow areas of different layers together.

• Vias are vertical connections in the form of holes. Vias allow lines in different layers to be connected. They are not equivalent to holes, which do not connect the layers.

• Silk layer: this is the top/bottom most layer which is used for organization. You can write words, guidelines and part numbers here.

• Solder mask: this is the area where the dielectric coating on the top/bottom most layers (just beneath the silk layer) get removed. Defining the areas in this layer will expose the underlying conductor, so that circuit components like resistors, amplifiers and even wires can be soldered on. 

I think I've rambled on long enough about something as 'trivial' as PCBs. However, it's good to keep in mind that once you have a working design of a PCB in your measurement setup, it is more or less gonna stay for the duration of your PhD. If upgrades or modifications are needed, it takes about a week to order a new set. I quite enjoy designing chips, devices, fabrication protocols and PCBs, so I quite enjoyed writing this too. 

Enjoy! and good luck!

There's a reason why the industry has shifted away from wedge-wedge bonding, to ball-wedge bonding.

Industry is all about yield. If the yield of devices reduce because at the final step before packaging, the devices die, then the price of individual devices need to be increased, which drives the consumers away to cheaper sources. Ball bonding is a gentler, and faster method of bonding and because of this, the industry has shifted from thermocompression bonding, to aluminium wedge-wedge bonding to gold ball-wedge bonding in the late 1900s. Now, about 90% of all wirebonds are made with ball bonders. If the industry has done it, why shouldn't we, as academics?

This is a bit of a rant from my years of frustration. Al wedge-wedge bonding uses high force and ultrasonic powers to squish aluminium wires to bond pads. As a result, it has been known to cause cracks in the underlying substrate, leading to breakdowns and shorts. Therefore, the rule of thumb was that the bond pad should be at least 1000 nm thick, in order to prevent any damages to the dielectric layer. In condensed matter physics, we are often dealing with bond pads on our chips that are ~50 nm - 200 nm thick, because we typically use evaporators to do the deposition in small scale. If the bonder is miscallibrated (which happens often), tip broken (shouldn't happen but it does occasionally), or accidentally in a wrong setting (this would be my fault for not checking before bonding), it can puncture through the bondpad and the underlying dielectric layer. I've been to several groups, where they are so scared of shorting due to the wirebonding step, that they manually make contacts with silver paint and thin wires. These are painstaking processes requiring highly trained hands, patience, air-stable samples and JUST the right amount of caffeine. 

Since wirebonding is the final step before loading the device, after all the nanofabrication steps, I would argue that this is the most critical step, and should be reliable. As my father says, when you're golfing, the most important swing isn't the big and impressive swing that will get you the farthest, it's the most precisely controlled one. He's referring to the driver vs a putter, but I think the analogy works here. Even if you have a billion dollar lithography machine, and a fancy cleanroom, the device is going to be trashed if the wirebonding step goes wrong. So why cheap out with the wire bonder? 

Gold ball-wedge bonding is the main driver in the industry. [Now, it is being shifted to copper ball-wedge bonding due to the cost of gold but you get my point.] By creating a soft gold ball prior to bonding, one can reduce the amount of force & power needed to make a successful bond. However, despite the lower force&power requirements, the ball bond is quite strong. In the ball-wedge bond, the part that is difficult to remove is the ball from the contact pad not the wedge bond, which is made to the chip carrier. Therefore, ball bonders are more reliable and let you have higher yield of living devices over all. 

During my PhD, I've spent several years fighting with fabrication and bonding, because just before loading into the cryostats, the devices would die at the bonding stage. There must have been something wrong with the bonder, because even with various different settings, it kept happening. I even tried depositing 600 nm of Al on top of the contact pads to prevent the leakage, but it kept happening. It was a really frustrating set of years. Since then, I've convinced the department to purchase a ball bonder, and my successors seem to be happy with the result. After leaving the department, I've come across several labs where they invested in "new" wire bonders, but they were all wedge-wedge! The sad thing in academia is that people tend to stick to one company, one method or one tool. Since the wedge bonders were standard in academia for the past several decades, researchers are used to them and are not willing to try the "new" technology. Ultrasonic bonding (wedge-wedge) was developed in the 1960s and thermosonic (ball-wedge) in 1970s[1] it's hardly modern.

I can see a good reason to keep a wedge-wedge bonder though, for specific occasions. Often times, bonds need to be made to a layer beneath the surface. For example, if you want to intentionally crack the native oxide of a Si wafer to access a global gate, then wedge bonding is a great way to do that. Another example would be if you have a 2DEG in systems like LaAlO3/SrTiO3, then the wedge bonding is quite useful to crack the LaAlO3 layers in order to directly contact the 2DEG.

My message to researchers in academia is this. Check if your university has a ball bonder. If not, convince the faculty/department to invest in one. It will save you many years of frustration, anger and sadness.

[1. See WIRE BONDING IN MICROELECTRONICS, 3/E, George Harman]

This is a bit of a touchy subject and I think my opinion can be quite controversial, but as the title says, personality is more important than competence. WAY MORE. 

I am of course, speaking strictly from my limited experience as an academic with absolutely no "real world" experience working in the private sector. Therefore, I will only speak about academia here and how I would determine the rubric with which I would hire future students. 

I can immediately think of examples where the personality traits are not as important as the competence, for example, in medicine. I'd rather have a competent ass of a surgeon than a nice imbecile cutting me or my family open. But I'm strictly going to speak about academia, perhaps more towards experimental physics, since that's all I know.

In my opinion, when looking to hire students or researchers for a group, I would first and foremost, value their personality, character traits, communication styles, the ability to work in a team, etc - all the 'soft skills' that are not given as big of a magnitude as the hard skills in academia. I strongly believe, that all the requirements of a good researcher such as the technical skills, the ability to program, the ability to write and even the ability to think critically, can be taught, trained and honed. No one is born a scientist. Therefore, all these skills, which are great if one already has them, are not very important in the hiring process. 

In contrast, one's personality, eagerness to learn, eagerness to become a better version of one's self, mental stability through stressful times, etc. are perhaps much more difficult to shape, hone and to already find in a student. Personality traits are developed over a long time and there is no way that a toxic personality can become a pleasant one in a matter of a few months, whereas teaching a 'bad student' to be competent is a likely possibility.

In academia, the unfortunate and honest truth is that everyone is overworked - sometimes by force from top-down, and sometimes by self-drive. In any case, everyone is in this together, spending 50~100 hours a week in a lab, and battling through together like comrades. As a good supervisor, be it a principle investigator or a project leader, it is your responsibility to create a productive and healthy atmosphere for the people involved. It would be unfortunate if your project causes so much drama that the morale of the group deteriorates. There is a Chinese proverb called "근묵자흑" (in Korean) which means that someone who is close to ink, also finds themselves turning dark. This is a lesson to keep a positive company around, as your surroundings (people and things) have strong influence on you. I think this is mostly true. They say, the people you hang around says a lot about you, but you are 'forced' to hang around your colleagues ~100 hours a week. Wouldn't you want them to be nice people?

I've seen academic research groups where one bad apple, be it the PI or a student, completely disrupt the morale of the group. It's unfortunately not so rare. It's perhaps inevitable, since the interview process for academic positions at all levels are done in such a short time, that one can't really probe the real personality of the interviewee. Or perhaps, the hiring committee wasn't even looking into that. Maybe the personality traits were all overshadowed by the publications and grades...

So, consider this a 'note to self' statement. Martin, if and when you become a PI... well I hope you become a PI some day, but I digress. When you get to the position where you have the authority to make hiring decisions, to hire students or postdocs or colleagues to work with me, hire nice people Martin. Hire the enthusiastic, excited, eager-to-learn student who brings positive energy to the group. As a PI, I am responsible for the training of the student, to teach the student how to do science correctly, how to think critically at every step, to help them become a better conveyor of science and to help them become educators for the next generation. If a student under your supervision fails to become better, the onus is on you.

Wow, what a happy thought. It's like thinking and planning for a long vacation. It's like saying, "I want to go to Las Vegas, I want to see the Grand Canyon, I want to taste the authentic Schweinshaxe, etc." but for research. 

Chances are, everyone who is starting out struggles with money. There is never enough to buy the most technologically advanced measurement equipment. So lets try to be a bit thrifty. These are the things I would still invest in, even if I had a very modest budget.

1. Stamping setup (A. Castellanos-Gomez style, ~2-3k)

2. Used SR830 or 2ch lockins from Salukitec or Sine scientific (~few k each)

3. Used Keithley sourcemeters, or Keysight SMUs (~few k each)

4. Used Optical table (~few k each)

5. Optical cryostat (with or without magnet i.e. Montana Cryocore or FourNine SK100)

6. used VNA from Keysight (~20k) or Rohde&Schwarz ZNH (~12k)

7. *Spectrometer (maybe in the next run of grants)

8. *Cobolt Lasers

9. *Optical components (polarizers, beamsplitters, mirrors, mounts, screws, powermeters, etc)

10. Make our own breakout boxes, resistor boxes, filters, fischer cables, nanopositioners, scaners, etc.

11. Consumables (NGS Graphite, hBN from Japan, MoS2 from SPI, etc).

One of the reasons why I admire the works of Andres Castellanos-Gomez is that he thinks of creative ways to develop research equipment for less and openly shares absolutely all the information on open-access platforms such as Zenodo. It's super admirable.

Let's now assume that there is no restriction in the budget (oh goodie) and what's keeping us grounded is finite lab space, limited students, time and creativity. A guy can dream can't he?

1. 3 Suped-up stamping setups with manual+motorized stages.

   1. integrated pulsed laser for cutting

   2. automatic sample stage with long range for automatic flake identification and sample image stitching

2. High quality AFM for immediate determination of flake thicknesses

   1. with upgrades to include electric characterization (cAFM, PFM, etc)

3. Plasmapreen or a similar plasma asher in the lab for pretreatment of SiO2 for exfoliation

4. Pulsed laser deposition

   1. Should be able to reach 1000C via infrared laser from behind

   2. more than 5 targets inside

   3. RHEED

   4. O2 and Ar input

5. XRD

6. high temperature furnaces

   1. 1 RTA for sample cleaning in Forming gas, air or high vacuum

   2. 1 tube furnace for CVD graphene

   3. 2 tube furnaces for flux growth

7. Suped-up Witec Raman

   1. motorized polarizer/analyser

   2. SHG

   3. Particle scout

8. Glovebox 

   1. fully automated transfer setup from HQ graphene or Manchester

   2. AFM/QTM

   3. Raman

   4. Coldplate

   5. Wirebonder

   6. Evaporator 

   7. Vacuum jacket

9. In-house He liquefier and recovery

10. Wet cryostats (I LOVE wet cryostats. I think they are beautiful and fun to work with)

    1. Dilution with vector magnet for workhorse measurements on QTM.

    2. 1.5 K VTI cryostat with 14T magnet (i.e. Oxford Teslatron) for quick test measurements 

11. Dry cryostats (Super useful and don't need to come in during the weekend to fill)

    1. Optical cryostat with magnet (i.e. Opticool by Quantum Design) for work horse nanomechanics/ strain engineering/ Raman  experiments

       1. fully decked out optics table 

    2. Kiutra fastloading fridge (if all the current issues are ironed out) for REALLY quick checks

    3. Bluefors LD400 with 9-1-1 vector magnet for workhorse measurements on strain engineering and transport.

12. High end electronics

    1. Delft electronics DEMO SPI3 + matrix modules for all setups

    2. SMU

       1. 2 Keithley 6430 sub-fA 

       2. 10 Keithley 2400 standard SMU

       3. 2 Keithley 2470 1100V SMU for gating through SrTiO3

    3. 20 SR860 lockins

    4. 4 Zurich Instruments Lockins

       1. 2 MFLI with upgrades for higher harmonic measurements

       2. 1 UHFLI 

       3. 1 SHFLI

    5. QDevil electronics

       1. QFilters RC+RF for all fridges

       2. Fischer cables

    6. Rohde Schwarz VNA

       1. ZVA 110 GHz for 6G FBARs

       2. ZNB 43 GHz for high frequency experiments

       3. ZND 8.5 GHz for Shapiro step, nanomechanics measurements

13. Software

    1. AutoDesk 

       1. Fusion 360 (parts design and quick FEM)

       2. AutoCAD (sample design)

    2. COMSOL

    3. Labber

14. Ball bonder (i.e. tpt HB 10)

I think this covers pretty much everything. :)

It looks like a lot, and it's a lot. This is probably an entire department's worth of equipments. 

Having gone through the academic life, and still in it currently, I have so many tips and tricks and suggestions I want to share. These stem from the mistakes, trial and errors, regrets and hardships I faced over the years. They say, hind sight is 20/20, so I can clearly see where I could have chosen a better path, or what I could have done to strengthen my knowledge and my CV. When/if I had a child, I would tell her/him all these insider secrets, so that she/he never has to suffer and can take full advantage of the academic system. As often said by a smart philosopher Francis Bacon, "scientia potentia est", which translates to "knowledge is power". [I always thought this was a Korean phrase, because I heard it on Korean shows a lot but I stand corrected.]

1. Do your absolute best in class. 

I didn't fully grasp how important class was until I reached my MSc. I often hear from highschoolers complaining about calculus or the trig rules, saying that they will "never use it in life". That's mostly true. Statistically, outside of academia, an average person rarely needs to remember the cosine law to get out of a sticky situation. In my undergrad, I felt the same way about the "old physics". I was always complaining about thermodynamics, as it was "old" and "figured out already". I was most eager to learn about quantum mechanics which I heard so much about. When I got to the quantum classes, I was let down because the topic was not what I expected it to be, so I lost interest. 

Actually, I lost interest in physics entirely by my third year. What got me back to physics was the final year's bachelor project. The excitement I got from working with the state-of-the-art material graphene, which I heard for the first time in my monthly subscription of Scientific American about, reignited my love for science. It could be rather the feeling of intimacy or secrecy that I got while working at the edge of scientific breakthrough that really got my inner spirit fired up. Then I started my master program, and that is when I lost my mind. I was obsessed with working in the lab. I woke up in the middle of the night to go to the lab to stop the growth, read countless papers on a daily basis, worked on 4-5 projects simultaneously, fabricated devices, ran my own experiments, and took master level theory courses all at the same time. Not to mention, I had just started dating at the time, so I was barely getting 4-6 hours of sleep on average. Not to mention not having any weekends. 

I was doing all this, not only because I fell in love with experimental physics, the excitement and the feeling of being at the edge of what is known, and being the secretive member of the scientists at the outer frontier of knowledge. No, no. It was because I was insecure. I was insecure about not having a solid theoretical foundation, which I would have had, if I paid close attention to the lectures. Instead of trying to take the most prettiest set of notes, if I just LISTENED, and took it all in, the concepts would have stayed with me well past the final exam. To this day, I am still having to re-learn important physics concepts, because they always pop up!

When I say, do your absolute best in class, I don't mean in terms of grades. Once you hit your MSc and PhD, your grades mean nothing. It's all about papers from then on anyways. But how are you going to produce those papers, if you lack the foundational knowledge. This was the reason why I had to work extra hard. I can proudly say that I worked much more than the average MSc student to compensate for my lack of knowledge. Luckily I smartened up and started working really hard, never sleeping in and never skipping class. I still had the tendency to obsess over notes, thinking that writing things verbatim will allow me to prepare better for the exams but this was fixed during my PhD. Again, don't focus on taking the best notes. Absorb the train of thought the professor is guiding you in. Learn the though process, and important concepts as they pop up over and over again in your research. Relax about the grades for now.

2. Don't be shy. You are valuable.

Research experience is an enormous asset. You should apply to research assistant positions or volunteer to work in a lab to gain research experience whenever you get the chance. The topic actually doesn't really matter so much in your BSc. Even if the job is lightyears away from your real interests, you should try it out. The fact that you have such experience, that you know how research works, how publications work, how this entire system functions, is already a HUGE advantage. Moreover, having a widely varying research experience in your bachelors (4 years, 4 summers, 4 different projects in 4 different labs, 4 different fields, 4 different techniques) will make you an outstanding MSc researcher.

The BIGGEST factor prohibiting me from getting any semester/summer research experience was because I thought the professors would see me as an idiot who had no experience and would directly reject me. Or worse, spread rumors about "this particularly stupid student" who dared to apply for a summer internship in his/her group. But let me tell you. This is absolutely never going to happen. I wish I knew what I know now. Summer research assistants/interns are super valuable. They come, work for free for 3 months, get "menial" and time consuming tasks to completion which end up being pretty useful for the group and also give the PhD students the opportunity to supervise. And on the flip side, as a research assistant/intern, you would learn the art and process of science, the state of the art research, cool scientific tools, deepen your understanding, have an early peek at the concepts and topics coming in a couple years, and may have a chance to end up in a publication. As I said above, after your MSc, publications speak more than your grades.

On a similar topic, approach your professors. If you see them in the kitchen, talk to them. Ask them about what they are working in that is interesting to you. If you catch them at a bad time, then you may not get a heartwarming welcome. But, as a scientist myself, I LOVE talking about my research. It gives me great joy to talk to students about my research, and talking to other researchers always opens up exciting new avenues for possible collaborations. I can't think of any scientist passing the opportunity to talk about their research.

3. Apply for anything at any point in time.

There are opportunities for scholarships, small equipments, or poster prizes etc. Apply to these whenever possible. Don't think that you will have "no chance anyways" or that it's a waste of time. Even just the act of applying will teach you so much about the art/ process of science. And as they say, you have 0% chance of success only when you don't try.

4. Ask questions at conferences. There are stupid questions, but you are allowed to ask stupid questions.

When you are in your MSc or PhD or Postdoc, you will have the chance(s) to attend conferences [Unfortunately for me, I couldn't attend any during the final two years of my PhD due to the pandemic]. You will hear great talks on amazing science, new discoveries and new techniques. You will have the chance to ask your questions, and you will probably stay silent, thinking that you don't know enough to be asking questions. Don't think like this. Contrary to the popular cliche "there aren't any stupid questions", there are stupid questions. But you are allowed to ask stupid questions. The tax payers are paying for you to attend the conference, to learn as much as possible. Learn as much as possible. When you ask questions, the memory sticks, so you will retain the information longer. Ask your stupid questions. Get embarassed. Learn.

As my favorite lecturer, Prof. Keshav Dasgupta said, "As you advance in your career, you will have less and less chance to ask questions. When you're a professor, everyone assumes you know everything. And you SHOULD know everything!". I am in my postdoc right now, and I feel that I am FAR from knowing everything. Therefore, when I attend any poster presentations, oral presentations or keynote talks, I try to ask as much questions as possible. I feel that I don't know so much about science, so I'm doing my best to learn. If I cannot ask the questions myself, due to the situation, or the atmosphere, I would at least write it down and try to search for the answer myself, or talk to the presenter after the QnA session. I wish I did this throughout my academic career. I would be a much better researcher if I did this, and would have formed a much larger network, I think. I attended a GRC conference last year. I flew to the U.S. for the first time in my life, all the way from Germany. Of course, the conference fee was expensive, the hotel fee was expensive, and the flights were expensive. So I got the money's worth by asking at least one question per talk (this was only possible thanks to the intimate nature of the conference). I ended up getting a name for myself as "Martin from Munich", and had a chance to meet so many great people at the conference. It was honestly the best conference I attended so far, in terms of what I learned, and how many people I met.

5. When you apply for your next position, get in contact with the alumni.

This is a lesson I learned from one of the postdocs I worked with during my PhD, Dr. Edouard Lesne. He is an absolute genius, knows everything and is extremely hard working. He was the postdoc who my group never had. He taught me a lot of physics and measurement techniques as well as how to navigate in the world of academia. As a wise man he is, he taught me this trick to talk to the former members of the group I am applying to, not just the current ones. After spending 1.5 years away from my PhD group, I can fully understand why he told me this now. If someone is currently in a group, it is difficult for him/her to have unbiased appraisal about the group, the PI and the infrastructure. When that person leaves to the next position, they will have one more data point to compare, will have no consequences in speaking positively/negatively about the group and will have a more indifferent analysis of the group. During my PhD, I didn't really think much about my group, and the institute(s) I was a part of. It was work. All the pros were diluted away in the name of 'daily routine'. Now that I spent some time away from my previous group in TU Delft, I can fully appreciate the magical opportunity I had. I can elaborate here in the next "scribbles", in case someone wants to apply to their groups. [I can't unfortunately elaborate about my current group/institute in Munich since I still work here. My current opinions could be biased in either good or bad ways.]

I think I have many more tips and suggestions. I just need to dig deeper into my notes. 

Maybe I will do a ver.2 of this post some time later in the future...

This might be a post-PhD syndrome or Stockholm syndrome or some sort of syndromes but I deeply miss living in the Netherlands and working in TU Delft. I miss it as much as my real home, Canada.

As promised in the previous "scribbles" post, here is what I think about my previous group in Delft. I can wholeheartedly recommend anyone to apply to the group and to the institute in general. I hope this information is useful for your search for the next academic position.

Supervision

My PhD supervisors are incredible scientists and more than that, incredible leaders. As scientists, they have accumulated great knowledge over the years, are critical thinkers, and make great effort in educating the next generation scientists. As leaders, they are impeccable. Although they have quite different leadership styles, they, each in their own ways, are great leaders. I fortunately had the opportunity to experience both of their leadership styles. Both of them genuinely care about their students and that was one of the main reasons why I successfully completed my PhD. I deeply feel that they care more about successfully promoting their PhD students than their own fame and accomplishments. Being Dutch, they can sometimes say things directly without euphemism. And sometimes, their words caught me off guard, but they mean to guide students in the right path, and don't hesitate to act as the devil's advocate. 

Non-academic staff

Apart from my supervisors, TU Delft also has immaculate and efficient organization. The HR and the secretarial staff take their jobs seriously and perform at their highest efficiency. This can be translated to the entirety of the Netherlands as well. Like, somehow, the entire country runs so smoothly. I am currently in Germany, where it's supposedly the most efficient countries in Europe, and I must say, Germany has to give up that title. The train here is always delayed, sometimes by several hours and everything needs to be signed stamped and physically mailed. No one uses Adobe Reader's digital signature function. [it's arguably more secure than a physical signature! C'mon!]. For making purchases for research, I currently have to write on carbon papers to make 4 copies, sign them, stamp them and scan them. It's rather medieval, than 'high tech' but I digress. 

The services and support offices in TU Delft is also phenomenal. Their patent office is great and helpful in getting your research into the real world. The HR takes things serious and steps in when something is not appropriate in a professional environment. The technology transfer from academia to startup is amazing. Delft is becoming a startup hub. There are a lot of startups popping up especially in quantum. Delft is by far, the leading quantum hub of Europe.

Cleanroom

TU Delft has an incredible cleanroom maintained by the staff that really take professional care of the equipment and organization. It is one of the largest academic nanofabrication cleanrooms in Europe (as far as I remember, the second biggest) and they are making an even bigger one soon. The cleanroom at the Kavli institute is among the best in the world. I've visited the cleanrooms in MIT, Harvard, Boston college, IBM Zurich, Geneva, Manchester, ICFO, TUM, etc. for work. MIT and Harvard indeed had state of the art cleanrooms which had impressive size and capabilities. They were easily twice as big (or bigger) as the one in Delft. However, the Harvard cleanroom has 1700 active users, while Delft had ~200. In Harvard, due to the sheer number of users, EBL slot always had to be arranged at least a week in advance. The cleanroom in Delft had pretty much the same capabilities and equipments (less copies of the same machines), but due to the low traffic, and work-life balanced lifestyle shared by all the users, the cleanroom was pretty much empty by 6pm. On the weekends, there were barely 1 or 2 people. In my PhD, I utilized this to my advantage. I maximized my efficiency by performing as much cleanroom work during the "off hours" as possible, which allowed me to be super efficient. I often had access to both of the 100kV EBL machines during the weekends, so I would load 4 large chips worth 36 dies in total and perform multiple lithographies in parallel. 

What could be better

I can also in an unbiased manner, speak about how my PhD experience in TU Delft COULD have been better. 

First, the food. You don't go to Delft (or the Netherlands for that matter) for food. You go there to do cutting edge science. Unlike most people, I've grown to love some of the local cuisine. Here's a few: Friet Speciaal, Bitterballen, Ollieballen, Stamppot, Kapsalon, Gehaktballen sandwich, Kaas sandwich (the plain ones from Albert Heijn), etc. Most of all, I fell in love with the Dutch cheese. I sometimes get cravings for Old Amsterdam, which has become my personal the top 3 favorites of all time. I still eat plain cheese sandwiches on a daily basis. On campus, there is very little to choose from. I did have some incredible, fresh European breads at the canteen, but in general, the food on campus was overpriced for what you get. Towards the end of my PhD, a mini grocery store and a doner shop opened up nearby, so I could survive on those, but otherwise, there is not much. For some of my fellow foreign colleagues, the lack of food option (on campus, in town and in the country in general) was a killer for them. I should probably stop talking about food. 

Second, I should have asked for more interactions and guidance from my supervisors. It's not like they were too busy to make time for me. They always made time for me if I asked. but I guess it's the Korean in me resurfacing. I really didn't want to bother them unless I had a groundbreaking result. In the end, I didn't get any 'groundbreaking' results but rather...'cement cracking' ones? 

Stop and think. TU Delft is a magical place with so much possibilities, and efficiently run scientific research. One can get carried away, as I have. A PhD is when you really dig deep into a single topic and become a master of that field. For this, you have to stop and think. Afford to 'lose' or 'sacrifice' a few days just to think. There is a bit of a stigma towards 'wasting time' to read, or think. But if you want to dig deep, you have to be able to risk wasting a few days or weeks just to get to the bottom of things. I think I had this stigma. And I also had too broad of an interest. I touched on so many different topics during my PhD: ferroelectricity, phase transitions, charge density waves, pressure sensors, gas sensors, pulsed laser deposition, 2D exfoliation methods, superconductivity, magnetism, Moire physics, transport, optics, Coulomb Blockade, Josephson junctions, Andreev reflections, p-wave superconductivity, Shubnikov de Haas, Anomalous Hall, etc. At a certain point, I had more than 20 on-going projects simultaneously, which all needed long time investments in the cleanroom or in the lab. Naturally, I was not able to sit down and think deeply. 

There are times when I told myself that I would NEVER do ____. I am NEVER gonna use this information. I am just not that kind of a person interested in ______. 

Ohhhh boy. Was I stupid. I could not be more wrong about this. 

Learn from my mistakes - my short sightedness. Keep an open mind about science.

#1. Biology

As Sheldon Cooper illustrated, "it was a warm summer evening in Ancient" Canada when I told myself, a young high-school student at the cross road between different scientific disciplines, that I will NEVER take anything to do with biology. Biology in highschool was the STEM class I struggled to get. Physics, chemistry and math came naturally to me, but boy oh boy, Biology was tough. I had nightmares about highschool biology well into my university. Naturally, I shied away from it. When I was given the choice to choose to or not to take it in grade 12, I of course cried out in happiness and ran as far away from biology classes as I could - into the next room where they were teaching physics. 

Little did I know, my fear of biology came to bite me back in my MSc. I worked on chemical vapour deposition of graphene for my BSc project. Then during the MSc, I decided to stay in the same group. But, my MSc wasn't so 'simple' as growing single atomic layer thick of graphene. No NO. It was to take it several steps further, and use its properties for BIOphysical applications. 

My heart sank. 

I thought I ran away far enough (my last biology class was the freshman course on introductory biology and I think I even took only the first-semester of the two-semester course) to escape from its grasp. Nope. I was back to DNA and neurons and cell cultures and warm room with funky smells and pink solutions and weird looking pipettes and real need for gloves. But I had no choice. I wanted to stay in the field of graphene, especially CVD graphene and this was the only group in my university capable of growing CVD graphene. So I started re-learning about DNAs and RNAs and neurons and pink solutions and weird looking pipettes. 

It didn't take long. Maybe I was ~6 months into my project before I had a gradual realization that I liked all that stuff. To my surprise, I started thinking about biophysics a lot, and read a lot of biophysics papers on my own time. It was fun to think about the properties of graphene, and how it can be used in biology. It was really fun. It was so fun, that after my MSc, I decided to apply to one of the best biophysics groups in the world! I wanted to continue on with the fun thought experiments and to see how graphene and I could be used to help others. In the end, I didn't land the position but I think that was for the better. I was really devastated at the time when I was rejected from the biophysics group, but I instead, landed in a world leading group in the nanomechanics of 2D materials. Thinking back, I don't think I would have had the same amount of fun and gained as much knowledge as I did during my PhD had I landed that job in the biophysics group. 

Although my short-lived career in biophysics came to a halt (now I really don't think I can go back) I am grateful that I have this experience under my belt. I have the tiniest sliver of an experience to pretend like I know what they are talking about in conferences. This helps me network really easily, and allows me to ask interesting questions, identify areas of potential collaborations, etc. 

so, never say never to biology.

#2. Organic Chemistry

In a similar sense, I kept a safe distance from organic chemistry. Oh boy. when you start naming hexagons with one leg differently to hexagons with two legs, I start panicking. All hexagons should be treated equally. 

Frankly, I never really experienced organic chemistry. I never took a course, never read any papers, and never took interest in it. until recently.

In experimental physics, you run into a lot of chemicals. Chemicals like N-Methyl-2-pyrrolidone or tetraethyl orthosilicate, which I can barely pronounce. These are chemicals used in nanofabrication and as an 'expert' in nanofabrication, I am ashamed to say that I don't exactly know how these chemicals work. I don't really know how ANY chemicals work. When I look through the list of chemicals we use on a daily basis in our labs, I am at awe some times. How did we discover/create all these chemicals, purified them to 99.99% and use them to do specific tasks?? 

Specifically in 2D research, you run into many organic chemicals, such as polycarbonate (PC), polypropylene carbonate (PPC), polycaprolactone, polymethylmethacrylate, etc. These are some of the polymers used for the transfer of 2D materials (see Useful things page). I've used them for more than a decade, but I BARELY know how these things work! I know that PPC has a much lower glass transition temperature and is less sticky than PC, but I have NO CLUE why. This naturally brought me to the realization that if physicists and chemists collaborated more often, had more interactions then chemists would have been able to point us towards these transfer polymers a decade earlier than they were reported. We would have made an even better progress in discovering twistronics, and novel device structures which are very difficult to achieve without these transfer methods. If we haven't already, we should talk to chemists. Tell them the sort of problems we are having and ask them to help us find/synthesize the ultimate transfer polymer, which will not leave residues, can release flakes without leaving a puddle, can pick up monolayers just fine, etc. 

Just saying. We need to make more friends with chemists.

#3. Exfoliated graphene

When I discovered graphene through Prof. Philip Kim's article in the Scientific American, I knew I was going to work on it eventually. I also knew that I would be working on the LHC due to another issue of the Scientific American, but I digress. And when I discovered that you can 'grow' these monolayer graphene sheets controllably just by putting in a copper foil into a furnace, I thought I would never work with exfoliated tapes. We are doing science, not kindergarten art project. The furnace that goes up to 1200 C is SO much sexier than the scotch tape from 3M. The RCA method I used to clean the surface of copper was so much more fun than peeling the tape. 

So I told myself that I am NEVER going to work with exfoliated graphene.

OHHH boy. Was I wrong. 

After my MSc, I stopped growing my CVD graphene (I did for a little bit in the earlier days of my PhD) and exclusively worked with exfoliated graphene. For some reason, exfoliated graphene from natural graphite is still more reliable than CVD grown graphene. Since I was working with pressure sensors, I could not risk any atomic defects or wrinkles or punctures in my graphene membranes. That was the reason why I used exfoliated graphene. It was just easier to convince the reviewers that the permeation we see in our measurements had to be extrinsic, since we were using multilayered graphene exfoliated from natural graphite. 

Now, I wish that I had both capabilities. Sometimes, for some applications, CVD graphene is better than exfoliated. But, for low temperature transport, graphene exfoliated from NGS natural graphite has become the gold standard.

#4. Low temperature experiments

The lab I was in during my MSc, was more into low temperature quantum transport. Before I joined, the group was doing more magnetotransport than biophysics. So I had some of my senior colleagues loading their ultrahigh mobility samples into the cryostats every now and then while I was making graphene based neural probes in the corner of the room. The cryostats were very big, had many knobs, electrical lines, pipes and gauges, and was apparently very expensive. It looked like a black box to my untrained eyes and the manipulation of the long dipstick seemed too cumbersome. So I told myself that I would NEVER work with cryostats. What's the point of low temperature physics anyways. It's a lot of money, we need both liquid nitrogen and liquid helium, and helium escapes our gravity anyways, so they are not recyclable once they escape. Biophysics is so much more fun, and as an interdisciplinary field, it is a blue ocean.

My perspective and opinion towards low temperature physics changed 180 degrees during my PhD. After my PhD, while I was looking for postdoc positions, one of the many criteria I considered while choosing the lab, was the number of available cryostats. I still think biophysics is interesting but there is something that makes low temperature physics so dang "cool" - pun intended. The ability to change the sample temperature while probing its properties by light, transport or other means is so powerful. I can go on forever about all the different aspects of cryostats, different types, manufacturers, etc. but I think that's a topic for another scribbles.

#5. 3D materials.

After discovering graphene and its family of 2D materials, I thought the entire field of condensed matter physics was going to shift their gears from 3D and 1D to 2D. At the time, I thought 1D was limiting in geometry, and 3D was old physics. 2D was where cutting edge physics was really at. I started working on graphene but I quickly discovered that graphene isn't really that special. There is MoS2, phosphorene, silicene, etc. Eventually, everything we can think of was going to be replaced by 2D materials. Graphene was going to replace metals used in CPUs, semiconductors were going to be replaced with MoS2, dielectrics were going to be replaced with hBN, etc. It was a matter of time before all the physicists working in 3D abandon ship, jump onto 2D materials and commandeer a material as their niche. 

Of course, I was very naive. 

2D materials haven't revolutionized the everyday lives of our civilization and the physics of 3D crystals are still producing interesting results. 

I luckily had a nice opportunity to work with cool 3D systems like PLD grown complex oxides, and cleaved single crystal flakes. At a certain point, these systems also undergo a 3D to 2D transition depending on how you define the dimensionality. The dimensionality in 2D van der Waals materials is simple. Each layer can be isolated, so crystallographically, they are regarded 2D materials. Ultrathin films of 3D materials can also be regarded as 2D materials when the with the thickness of the layer smaller than the electronic mean free path. I am fascinated by thin films of single crystals but I digress.

3D crystals are interesting, and at the end of the day, we use the same methodology to quantify their quality. XRD, Raman, transport, mechanics, STM, etc. If you know how to employ these techniques for one system, you can easily translate them to the other.

#6. XRD

Related to the above section, I really thought X-ray diffraction (XRD) was an ancient technology that we don't use anymore. In solid state physics textbooks like Ashcroft-Mermin (the solid state physics bible), there is always a section on structure factor, Laue scattering, Bragg scattering and XRD. Just judging by the age of the book, I thought that this section of the book was old, and that XRD was an outdated technique.  Since I was going to work on CVD graphene for the rest of my life, I thought I was NEVER going to use XRD and learning about XRD was a bit of a chore. 

Then I started my PhD, and started growing my freestanding complex oxide samples. How do I tell if what I grew is a high quality single crystal or a polycrystalline mess on top of my precious single crystal SrTiO3 substrate? How do I know if there is residual strain? How do I know if the lattice relaxes after being freed from the growth substrate? 

with the XRD of course.

Oh my. Getting used to the XRD took a LOT of time. I deeply thank my colleagues who trained me on the growth and XRD characterization because since I didn't really pay attention to the XRD section of the solid state physics course, I was so lost. Whenever they talked about diffraction angles, omega, two theta and phi scans, my mind was a mess! I really wished that I paid more attention in the solid state physics class when we went through XRD. I of course learned with a steep learning curve during the research process but that was more painful than it had to be. Now I miss having to grow my own samples and characterizing them with the XRD. 

As I progressed in academia, I came to realize that XRD is so much more than that. There are many groups in the world using soft and hard X-rays facilitated by synchrotrons to make ground breaking discoveries about nature. 

XRD is far from an obsolete methodology from the 20th century.

#7. Scanning probe microscopy

This is interesting. I learned of the scanning probe microscopy techniques in a nanotechnology course. Having the ability to move single atoms, seeing the wave-like interference pattern of confined atom, resolving crystal structures in real-space with sub-atomic precision were all fine and dandy. But they never appealed to me. I am not the most meticulous person nor the most patient. I couldn't imagine myself working with an invisible tip moving at an unnoticeable speeds. So I NEVER imagined myself working with ANY scanning probe microscopy techniques. And I didn't need to when I was working with CVD grown graphene. Since the CVD growth process is so well developed for graphene, you always get a single layer graphene, and almost never any bilayer or trilayer. This changed of course when I transitioned to the exfoliation method. 

When you exfoliate graphene, there are generally three techniques to identify the number of layers. 1) Optical contrast. Graphene is the monolayer form of graphite, so you will never find anything more transparent than graphene, when you exfoliate graphite onto SiO2/Si. So if you train your eyes or use an image processing program, you can exactly quantify the number of layers in the few layer regime. 2) Optical spectroscopy. Raman scattering and photoluminescence (PL) are two methods commonly used to quantify the number of layers in 2D materials. Since the phonon spectra change with the number of layers (in the few layer limit), especially drastically between the mono and bilayer limit of graphene, it is easy to distinguish the number of layers using the shape of the 2D peak in graphene. In materials with a small enough bandgap, PL can be used in conjunction with Raman spectroscopy. For example the Mo(W)S(Se)2 family of TMDs have a large direct bandgap in the monolayer and the band gap reduces and also becomes indirect as the number of layers increases. PL measures the exciton (electron hole pair excited with the incident laser) recombination and therefore is sensitive to the direct bandgap of monolayer TMDs. 3) Scanning probe microscopy. Atomic force microscopy (AFM) is a very powerful tool to quantify the thicknesses of exfoliated 2D materials. By using topography modes (tapping/contact/peak force/etc) one can measure the height of an exfoliated 2D flake with respect to the underlying substrate. It is however unreliable in the few layer limit, as it can give false impression of the height. Monolayer graphene has a theoretical height of ~0.34 nm, so one would expect a step-height of ~0.34 nm. In my experience, I was never able to get ~0.34 nm with the AFM. I always had 1-2 nm (after confirming with Raman) which is an order of magnitude larger than expected. This isn't because AFMs are not accurate enough. It's rather that exfoliated graphene is more complicated than thought. According to Shearer et al. there is always a bit of a 'buffer layer' beneath the graphene that increases the apparent thickness of graphene to be much larger than the theoretical value. By using peak-force microscopy which operates by sweeping the force and recording the deflection response at every pixel, they accurately measured the thickness of graphene. This is not the same as contact mode. In contact mode, the threshold deflection is maintained to be constant by PID, while the piezoscanners move the cantilever across the sample. For monolayer 2D materials, contact mode can be destructive.

In my postdoc, I am now building several custom scanning probe microscopy setups. The main purpose of these scanning probe microscopy setups are not to look at the topography of a sample using x and y piezoscanners. Rather, these setups are intended to scan the rotation angle between neighboring layers of 2D materials. This novel scanning probe microscopy technology called the Quantum Twisting Microscope (QTM) is an invention by Inbar et al. of the Weizmann institute of science. Thanks to the inventors, who graciously shared all the details openly, we are building our own QTM setups.

#8. Piezoelectrics

I first learned about piezoelectrics through this work by Wu et al.. I had to choose a paper to present to my colleagues, and this caught my eye. Again, I was working in CVD graphene, and MoS2 was a close cousin which was going to revolutionize semiconductors, so I was curious about this work. Initially, the fact that mechanical motion (bending) can generate power from these ultrathin crystals fascinated me. I immediately thought that we could make our clothes coated with this material to generate electricity to charge our phones while we are walking. However, they report power generation of 2mW/m^2, which made my idea unrealistic. You would need to bend 500 square meters of this material to generate 1W. I lost interest in piezoelectricity soon after that and thought I would not study piezoelectrics ever.

Then in my PhD I ran into ferroelectrics, which is a subset of piezoelectric materials that not only generate a voltage when mechanical stress is applied, they retain the voltage in the absence of the stress. In principle, it could be used for both piezoelectric generation AND mechanical memory. The ferroelectric I studied is freestanding BaTiO3, a perovskite ferroelectric which I grew using PLD and characterized using XRD. We used piezoelectric actuation to study its polarization switching while being sandwiched between graphene electrodes exfoliated from the bulk. We also used Piezoresponse force microscopy (PFM) a form of scanning probe microscopy to extract its piezoelectric properties. 

Summary

It's interesting how life plays out. 

You never know if you will be working in a field that never interested you before. You might also say A,B & C are boring and uninteresting and that's fine. You don't need to find everything interesting. Actually, as academics who need to publish, and to be world leading experts on their own topics, we are incentivized to focus on the topic at hand. It's difficult enough to stay up to date with your own field of study in this day and age of rapidly evolving science let alone other fields of study that are seemly completely irrelevant to your own. 

I think it's important, though, that we need to keep an open mind.

* indicates my software of choice

GUI:

Matlab*

Labview

Python PyQT5

Nicos

Labber

Data processing:

Matlab*

Python

Sample layout design:

AutoCAD*

KLayout

LEdit

Figures:

Blender*

Adobe Illustrator*

Gimp

Inkscape

Fusion 360

VESTA

Avogadro

Machining/ 3D printer prototyping:

Fusion 360*

Blender

DFT package:

Quantum Espresso (with Burai) *

Gaussian

Gamess

Abinit

Siesta

Vasp

FEM:

COMSOL*

Ansys

Fusion 360*

PCB design:

Easyeda*

KiCad

Fusiono 360

Circuit simulation:

LT Spice*

Matlab Simulink

Math:

Mathematica*

Image processing:

Matlab

Python

Fiji*

ImageJ

Audio Processing:

Pro Tools*

Manuscript writing:

Texmaker*

Remote desktop:

Anydesk

Teamviewer

VNC viewer

Google Remote Desktop