Reading PDFs on the go with a kindle!

Postings have been a bit slow due to the holidays kicking in! Anyway, I often carry a couple of research papers or books in my backpack and read them on the train and/or buses. My wife found that I carry too much stuff everyday, on my way to work, and decided to offer me an amazon kindle. I must say that it's not only a great gift but also a sound investment. I got rid of my research papers and started uploading the PDFs on my kindle and reading them on the go. As a bonus, I have my time magazines delivered to the device for only $1.49 a month!

Encrypt your data in a shared facility

Whenever you're using a shared facility, you have to realize that everybody has access to your data, including your competitors. It's your duty to protect your data. I often hear students complaining that people viewed their SEM images on a shared PC or that their macro code was *stolen*.

If you have proprietary code that you must use on shared machines or if you have data images which you wouldn't want to see ending up on some other research group's PC, then my advice is to encrypt your data.

A nice encryption software that I use is AxCrypt. I even requested some systems administrators/ dedicated staff to install it on PCs where I've written a lot of proprietary code for running tools or where I have a lot of confidential data.

This advice is relevant especially if you are funded by the Air Force Research Labs, ARO, DARPA or any other defense funding agencies. You do not want your data to be floating around!

Article Highlight: Subwavelength nanoimaging in 3-D

I just stumbled upon an interesting article published in Phys. Rev. Lett. by A. Govyadinov et al., entitled "Phaseless three-dimensional optical nanoimaging". Actually, the preprint is on arxiv.

The authors proposed a method in which the subwavelength details of a 3D structure can be recovered in the far-field. It is a very well-thought method which is based on the solution to the inverse scattering problem for a system consisting of a weakly-scattering dielectric sample and a strongly-scattering nano-particle tip. Interestingly, their nano-scale optical tomography technique relies neither on phase-measurements of the scattered field nor on phase-control of the illuminating field.

On the fundamental flaws of cloaking by metamaterials

Invisibility cloaking, using metamaterials, excites the scientific community, the general public, amateurs of sci-fi and most importantly the funding agencies. If you think about it, it is indeed mind-boggling to be able to realize a Harry Potter type cloak!

The metamaterials community, in particular John Pendry and Ulf Leonhardt have thought and pioneered the first invisibility schemes by using metamaterials. The first demonstration of the invisibility cloak was demonstrated by David Smith's group. And subsequently, several researchers have been actively working (both theoretically and experimentally) on cloaking.

Funding agencies and the general public assume that we're close to cloaking military tanks, fighter airplanes, etc... And accordingly, with this type of technology, we could effortlessly win the war in Afghanistan or any war for that matter!

Well the reality is far from our wild imagination! Cloaking by using metamaterials suffer from two fundamental flaws:

1. We can only cloak objects which are of the same size as the wavelength of light.

For instance a typical human eye will respond to wavelengths from 400nm to 600 nm or so (+/- a few nm of course). It means that if you want to cloak an actual object from humans, it cannot be larger than 600 nm!!! This implies that using metamaterials, we can only cloak nanometer size objects, and if you think about it, these objects are so tiny that they are already cloaked!

2. Metamaterials cloaks are extremely sensitive to loss.

In theory, we can design lossless materials where the cloak works out of the box. But in the real world, we have to use materials which are lossy (suffer from energy dissipation). Thus, realistic materials will kill the cloak! However, in the future, we will be in a position to develop robust gain compensation schemes to compensate for losses.

2009 MRS Fall Meeting (Metamaterials Session)

The Metamaterials session of the 2009 MRS Fall Meeting started today, at the Hynes Convention center, in Boston.

Good opening talk by Martin Wegener, who talked about his Gold Helix Metamaterial, and showed impressive ray tracing images of the carpet cloak. Like me, he's a fan of 3D ray tracing.

Overall, it was a very productive day. I also gave a talk entitled "Superresolution Imaging Using Bulk Nanowires Metamaterials at Optical Frequencies" in lieu of my colleague who couldn't present his own talk on transformation optics since he was sick.

I presented the first demonstration of the reconstruction of subwavelength features of an object, over a record distance of more than 6 times the wavelength by a nanolens made up of bulk metamaterials of nanowires, and with a resolution of at least wavelength/4. This is considered a significant breakthrough and was well received by the metamaterials community. We recently submitted the paper and are impatiently awaiting its publication. We strongly believe that this piece of work will get extensive media coverage.

Kudos to the session organizers/chairs Nader Engheta and Minas Tanielian.

Video of Zheludev's group at the University of Southampton

Propaganda for the metamaterials research, led by Nicolay Zheludev, at the Optoelectronics Research Centre ORC (University of Southampton):

Showcasing your research on arXiv

arXiv is an e-print service in the fields of physics, mathematics, non-linear science, computer science, quantitative biology and statistics. arXiv is owned, operated and funded by Cornell University and also partially funded by the National Science Foundation.

It is NOT peer-reviewed and researchers often use it to *temporarily* showcase their work (in the form of an online published article) to the world, after having formally submitted the manuscript to a journal and awaiting publication. The peer review process in some journals usually take time (it can take several months to years in some cases!), and researchers want their work to be known as soon as possible. They want to let the community know that they were the first to come up with the idea! And, arXiv allows them to do just that.

Please note that it is not advisable to submit your manuscript to arXiv without having first submitted it to a journal, as somebody else can reproduce your work and submit it, before you, for publication in an official journal.

Also, bear in mind that some high impact factor journals will prematurely reject your paper if you have published it online on arXiv.

Is your name too common? Consider getting a Researcher ID.

It might happen that you have the same exact name as some other researcher(s). And, when fellow scientists try to look up your publications, they are often swamped by other irrelevant papers (from the other researchers) popping up on their screen. Thomson Reuters created the ResearcherID, which is a unique identifier that expressly associates each participating researcher with his or her published work, thereby standardizing and clarifying author names and citations.

With the ResearcherID system, publications can be added from diverse platforms ranging from ISI Web of Knowledge to EndNote Web and RIS files. Additionally, citation metrics can be created and your h-index is computed automatically.

As a bonus, your unique ResearcherID can be used as a ResearcherID Link on your website to direct others to your publication list.

It'd probably worth it if your name is too common!

Thanksgiving in th U.S.!

Happy Thanksgiving!

(Sent from my mobile device)

Keeping track of patents using RSS feeds

The hard way of keeping tracks of patents is to physically check it from time to time. The smart way of staying up to date is to use RSS feeds. A good RSS feed reader is the Google RSS reader. There are others.

Let's say you want to keep up to date on "metamaterials" patents. First, you go on Google patents search and then query google with the word 'metamaterials'. This will lead you to here. If you now scroll to the bottom, you'll discover the feed URL, which is this.

Simply add the link to your RSS feed reader and you'll be among the first ones to know when patents are popping up!

The latest metamaterials patent which appeared 6 days ago is on "ACTIVE TERAHERTZ METAMATERIAL DEVICES" and belongs to H. T. Chen et al., best known for their paper in Nature.

Dual screen: The way to boost productivity!

Screenshot of my office desk:



Taking advantage of technology can help boost productivity!

Making cheap photolithography masks!

To produce high-quality microstructures in photolithography, we often buy expensive (3 inch mask for 675 USD) chromium masks on quartz / soda lime glass. In academic research, it may happen that we are not really sure if something would work out and might not want to spend that kind of money for a mask in the first place.

I often come across grad students who purchased expensive masks to find out that their final device do not work as expected. It turns out that many people are not aware that we can make or buy cheap masks.

A fast turnaround alternative to chromium masks are mylar transparency masks. First draw your design in a CAD program and then simply print it to scale on a transparency with a high resolution printer. Bear in mind that the dark field will block the light, so watch out for the polarity!

Alternatively, if you don't have a good printer, you can place an order for a transparency mask from the following vendors for ~30 USD or so:

1. Advance reproduction
2. Artnet Pro
3. CAD/Art Services, Inc
4. Infinite Graphics (boasts 50,000 DPI printing!)

Blogging test from my mobile!

Mobile blogging test. This post was created with my blackberry on the go.

Pretty cool!

Cleaning your shoes before stepping into the cleanroom at CFN, BNL

The Center for Functional Nanomaterials (CFN) at Brookhaven National Labs (BNL) has an interesting apparatus for cleaning cleanroom users' shoes (see photo below). I have worked at 5 different national labs and it's the only one which actually catered for the dirty shoes of users!





The other labs in the USA had the traditional blue shoe cover only, while in Asia, users were required to remove their shoes completely and wear cleanroom boots.

Loss compensation schemes to compensate for losses in metal-dieletric structures

An interesting paper appeared 2 weeks ago in Phys. Rev. A :

M. A. Vincenti et al. Loss compensation in metal-dielectric structures in negative-refraction and super-resolving regimes, Phys. Rev. A 80, 053807 (2009). [...]

The authors show that the introduction of gain improves the resolving characteristics of the lens and leads to gain-tunable super-resolution.

The metamaterials which are made up of metallic elements are extremely sensitive to loss. Studies such as those are crucial, before even thinking about practical applications.

We also submitted a related study entitled "Storing light in active optical waveguides with single-negative metamaterials" and eagerly awaiting its publication!

Getting on top of things

In a more senior position in an academic or industry environment, people are overburdened by so many responsibilities that it becomes nontrivial to respond to all emails, remember appointments, and so on without the use of a blackberry or other corporate tools. After being hired in a more senior role at Northeastern, my responsibilities increased and I had to keep up with the latest technology. Nowadays, in order to get on top of things, I have a blackberry curve 8900 which I optimize to the fullest. And, I also use a myriad of online tools, which I'll discuss later, to boost productivity.

My blackberry is wired for my corporate emails, calendar, Google Maps, Gmail, Google Search, Google voice/Skype, Mobile banking application, weather app (need this when you're in Boston!), among others.

My boss prof. Sridhar is also an advocate of modern technology, and a few months ago, started to use Skype combined with the desktop sharing tool yuuguu to disseminate scientific information.

On reviewing scientific manuscripts for scholarly journals

When somebody submits a manuscript to a journal, it will be sent to referees for peer review (of course, provided that the editor likes it in the first place!). The editor would normally ensure that your manuscript is being routed to some expert who's in the same field as yours, although sometimes it might not be necessarily the case.

I review papers for like 7 journals and the list is growing. At some point, 1 or 2 journals did send me some manuscripts which were outside my area of expertise. I had to decline because it would take me too long to keep abreast of the literature in other fields. But I find it sad that (1) journals do make that mistake of sending manuscripts to the wrong person, and worst that (2) some researchers rarely decline to review them. Often, the result, in this case, is that you get poorly reviewed manuscripts. I did encounter in the past reviewers who didn't really understand what was going on.

On the bright side, as I mentioned in an earlier posting, ad hoc referees are subjected to statistics. If a reviewer declines 3-4 papers without sending a genuine report, he'll be rejected by the system and his name won't appear on the referee database. Similarly, if a reviewer accepts blindly 4-5 papers, he's most likely to disappear from the referee database. In brief, there must be some balance and genuine review of a manuscript.

As a referee, if you genuinely review manuscripts and demonstrate that you really know your field, you get high scores from the system. And, you'll be invited to review other journals, in which you may have never published in.

A good guideline to review manuscripts can be found on the Small journal website. And, there's also lots of good advice on Google. The bottom line is that if you accept to review a paper, make sure that it's within your area of expertise and remember that you have a duty to do a good job!

The best lithography software for ion beam systems

Having been affiliated and/or worked in 5 national facilities in Singapore and the United states, I came across a number of lithography software for ion beam systems (SEM, FIB, etc...). The best lithography software that I ever came across, in my opinion, is Joe Nabity's Nanometer Pattern Generation System [NPGS].

NPGS is user-friendly and simply works out of the box! Joe Nabity is a one man company. He's known to answer all his emails and provides very good support. I had the chance to interact with him and he does genuinely listen to user's concerns, and makes every effort to address them.

The other major competing software (Raith150, Elphy, etc...) on the market is from Raith. Although some researchers have successfully mastered it, the control system has bugs and a superfluous alignment of the writefield is necessary before patterning. Also, there's poor software support. I talked to the engineers at Raith concerning improving some of the features of the elphy for Harvard's FIB and they were pretty reluctant to change anything. Personally, the software is bloated and needs a complete rewrite. It has also become too esoteric and needs a lite version.

It's analogous to facebook which has way too many things that a facebook lite was needed. Fortunately they realized it. Along the same line, this is the reason why Google created Chrome instead of trying to fix firefox!

The internal scoring system of high impact factor journals like Science and Nature

Many people do not realize that high impact factor journals like Science/Nature and others have an internal scoring system where they rate both authors (as well as reviewers!). The huge number of papers being sent to these journals force the editors to use some statistical methods to rapidly eliminate a big chunk of manuscripts.

I often hear people complaining that they send lots of manuscripts to these journals and got turned down even when their work was considered a breakthrough. The thing is that if an author has sent manuscripts 3-4 times and got rejected, the next set of papers being sent, by the same author, will automatically get rejected without even being read. Of course, the editor of the journal will always respond with a standard reply saying that you're unlikely to succeed in the competition for limited space and they have to make harsh choices, and so on. But the truth is that you have been statistically eliminated.

So the advice is that if you sent 2 manuscripts and got rejected, STOP SENDING! Wait for 2 years before sending them another one.

Similarly if you have 2-3 papers already published in prestigious journals, the likelihood that your subsequent ones are going to be sent blindly to referrees is pretty high.

The hierarchical structure of academia

Comic taken from PhD Comics says it alls.


[original link]

When it comes to describing academia in humor, nobody can beat Jorge Cham!

Dose matrix in electron beam lithography

In academia, PIs wants results and their grad students want lithography recipes! The newbies often want to know the exact dose which would preserve the geometrical dimensions of their CAD drawing. Telling newbies that the area dose for a particular resist thickness on some substrate fall between 80-200 µC/cm^2 generally irritates them.

They do not appreciate the dynamics of developing processes. The best way to obtain the correct dose in electron beam lithography is to start with a ballpark range and then do a dose calibration to determine the most appropriate dose.

The way to do that is to program the electron beam write to write an array of patterns, starting with an low dose and ending with a very high dose, with judicious increments, as shown below.



In the schematic, we see that the electron beam writer moved in a serpentine manner (e.g. Joe Nabity's NPGS lithography software) with underexposed patterns to overexposed patterns. By carrying some SEM imaging on these patterns, it is possible to determine the exact dose!

Metamaterials for biosensing applications

An interesting paper by Anatoly Zayats group. I had the opportunity to meet A. Zayats at the APS meeting in 2008, in New Orleans.

A. V. Kabashin et al. Plasmonic nanorod metamaterials for biosensing. Nature Materials 8, 867 - 871 (2009).

The authors demonstrate an improvement in biosensing technology using a plasmonic metamaterial that is capable of supporting a guided mode in a porous nanorod layer. [...]

Here, we notice that there's not much innovation as far as design is concerned, but the concept is new. We have entered in an era where we have complete understanding how to design metamaterials. Our limitation resides in the ability to manufacture (micro-/nanofabricate) them. And, the future of metamaterials lies in applications, in particular life sciences applications .

Compilation of Metamaterials theses and research groups working in photonics

I applaud Ki Young Kim's effort in having compiled a comprehensive list of metamaterials theses, as well as a list of all the research groups working in electromagnetics and photonics.

Hossein Mosallaei, now assistant professor at Northeastern University was among the first (together with R. A. Shelby) to specialize in metamaterials and completed his dissertation in 2001.

Materials Discovery: Finding the optical properties of materials

In my job, we're always searching for new materials to engineer, in order to manufacture better metamaterials.

Often, we need to rapidly look up the optical properties of existing materials. There's always Edward Palik's handbook of optical constants in the library but resources on the internet can be faster.

My favorite resources are:


1. Luxpop

2. RefractiveIndex.INFO

3. Photonics Lab at BYU

Bilayer design: The secret to a good lift-off process

I often come across researchers who struggle with a lift-off process: They usually write decent patterns with electron beam lithography, do a good metal evaporation, but when it comes to lifting off the polymer, everything gets ripped apart including their metallic structures.

Most of the time, it's because the evaporated metal coats the polymer sidewalls. To do a better lift-off, it's best using a bilayer design where you have a higher molecular weight polymer on top of a lower molecular weight polymer, as shown in the figure below.



When you expose the bilayer with ebeam, an undercut is formed. Due to the undercut, you avoid coating the sidewall of the resist when you evaporate metal. Lift-off then becomes a breeze!

Probing the magnetic field of light and Acoustic hyperlens

There are two papers on metamaterials worth highlighting this week:

(1) M. Burresi, et al. Probing the Magnetic Field of Light at Optical Frequencies. Science 326, 550 (2009).

The authors used concepts from the field of metamaterials to probe the magnetic field of light with an engineered near-field aperture probe. [...]

There's also a complimentary perspective article titled "Glimpsing the Weak Magnetic Field of Light" by Harald Giessen and Ralf Vogelgesang with some insights on Heinrich Hertz mind.

(2) And, another paper from Xiang Zhang's group:

Jensen Li et al. Experimental demonstration of an acoustic magnifying hyperlens. Nature (Advance publication online) DOI: 10.1038/NMAT2561.

The authors report the experimental demonstration of an acoustic hyperlens that magnifies subwavelength objects by gradually converting evanescent components into propagating waves. [...]

Nanoskiving: A slight variant of it!

Nanoskiving is a new technique pioneered by George M. Whitesides group that combines thin-film deposition of metal on a topographically contoured substrate with sectioning using an ultramicrotome. G. M. Whitesides is best known to have pioneered soft lithography.

Microtomes have been used since 1800 by biologists to cut thin slices of specimen. The ultramicrotome cuts routinely 200 nm slices.

And, it was very clever to use it for nanofabricating structures! I used a variant of the Nanoskiving technique to manufacture extreme high aspect ratio nanowires.

The moral of the story is to learn from the masters who are inspired in devising lithographic techniques to produce awesome nanostructures, which would otherwise be challenging with conventional lithographic techniques. One of my favorite lithographic masters is Teri W. Odom. Very creative!

How to add color or false color SEM images?

Nowadays, for publishing manuscripts in high impact factor journals like Science and Nature, Scanning Electron Microscope (SEM) images need to be false colored for enhancing visual illustration. There are several hypothetical ways of adding color to the SEM images.

Among the myriad of solutions, one could either buy expensive software to do the trick or use MATLAB codes.

I coded a matlab script here that you could use.

To use it, simply convert your SEM image file (.jpg/.png/.gif/.tiff) to a text file (.txt) using a program like ImageJ and then use the script to add color your SEM image. You can play with the MATLAB's colormap GUI to add various colors to the SEM image.

The scientific impact of a scientist: the h-index

In academia, we often want to know the scientific impact of a researcher. Basically, the academic community wants to know if anybody cares about what you have published. In brief, your scientific impact depends on the number of citations you have received for your work. The higher the citations, the more significant your work is.

However, there is a useful metric known as the Hirsch index or h-number which is used nowadays to gauge this scientific impact. And often, universities use this metric to assess potential faculty candidates or use it as a guideline for tenure decisions. Typically, for top universities, assistant professors would have an h-index of around 5+, tenured professors would have it around 10-12 and a full professor would have a value of 20 or more. An average recent PhD graduate would have an h-index of 1-2. But of course, there are always exceptions! There are faculty members with h-index lower than 5!

Michael Nielsen correctly pointed out that it is possible to estimate one's h-index without all the math simply by computing the following:

h ~ √(T)/2, where T is the total number of citations.

To have a more accurate value, you can use prof. Harzing's "Publish or Perish" software.

Just for curiosity, I have an h-index of 6!

Well, h-index, like most things, is not foolproof. It has it's flaws. It can also be tweaked by writing a review article. But nevertheless, it is a good approximation of a researcher's scientific impact on the community.

Welcome To My Blog!

I have been delving (Designing/Simulating, Micro-/Nanofabricating and Characterizing) in micro-/nanophotonics R&D for the past 8 years and made significant breakthroughs. I have lived in Singapore and the United States and thus possess a broad perspective (both academically and socially) of the East and West. Also, I have acquired a unique skill set and experience by working at national facilities in both countries. Additionally, I have been heavily involved in the past in open source software coding.

I am often giving advice to undergrads, grad students and postdocs from schools that are striving to make a name for themselves, to top Ivy league schools like Harvard and MIT. And, I have always been urged to write my thoughts down somewhere.

This blog is about sharing my thoughts and my personal experience to the world. :)