blog.rahivarsani.com

An awesome wallpaper of self-assembled nanoparticles

Rahi — Tue, 29 Nov 2011 03:57:27 +0000

Want a brand new wallpaper of magnetic nanoparticles? Look here.

The image is based on a TEM image I took this year of self-assembled magnetic nanoparticles.

Magnetite nanoparticles self-assembling in a drying droplet - 1920 x 1080

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1280 x 800

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Size-dependent self-assembly of nanoparticles in drying solvent

Rahi — Mon, 28 Nov 2011 07:03:14 +0000

Combining two differently sized magnetic nanoparticles can lead to interesting self-assembly effects. This follows on neatly from my previous self-assembly post. So how do 7 nm particles combined with 15 nm particles self-assemble?

The high surface-tension of evaporating water droplets push the particles together, forcing them to assemble in a space-efficient array. Interestingly, the particles appear to self-assemble based on size, where 7 nm particles and 15 nm particles separate so that they can pack together more efficiently. If the size ratio changes, different effects could be seen such as small particles fitting in between spaces left by larger particles. Some neat images:

7 nm and 15 nm diameter magnetic nanoparticles self-assembling

Self-assembly of nanoparticles in drying solvent

Rahi — Wed, 21 Sep 2011 04:17:51 +0000

Nanoparticles have a very cool way of self-assembling (science talk for arranging themselves) in a drying solvent. At the right concentrations, the solvent surface-tension draws particles together into a monolayer. These TEM images show the awesome self-assembly of 10-nm magnetite nanoparticles suspended in water. Water has a high-surface tension and relatively low boiling point, which helps drive the self-assembly.

Cool self-assembly patterns of magnetite. Almost seem to resemble fractals don't they?

Another awesome image. You can almost get a feeling of how the water was drying.

A low magnification image

A medium magnification image.

A close up, showing the arrangement of individual 10 nm magnetite nanoparticles.

Read “Clustering behaviour of magnetic nanoparticles” to find out why solvent drying effects might be an issue when studying magnetic nanoparticles.

Atomic-Resolution TEM vs. Electron Diffraction

Rahi — Fri, 22 Apr 2011 17:31:31 +0000

There are essentially 2 different experimental approaches to investigating the atomic structure of a material; scattering and imaging based techniques. Most information known today about atoms comes from scattering experiments, where a high-energy beam of particles or photons is fired into the target. The resultant beam is then collected and analyzed, hopefully providing some useful information on the material.

Electron Diffraction is a scattering technique that fires a very energetic beam of electrons towards a material. Crystalline materials with ordered atomic structures cause electrons to reflect along particular directions (Bragg angles). This results in an image with spots or rings, depending on whether the material is single-crystal or multi-domain. Nanoparticles tend to have single crystals, but if there are several particles at different orientations they behave similarly to multi-domain crystals and create diffraction rings. The sizes of the rings give us an indication of how the atomic planes are spaced out, which is generally different for most materials. These d-spacings are the same as those from Powder X-ray Diffraction (XRD).

Atomic-resolution imaging is only a relatively recent development in science. Atomic-resolution TEM (also known as HRTEM) generally involves firing a beam of parallel electrons towards the sample and collecting the electrons to form an image. At the atomic scale however, Bragg scattering causes interference effects which result in alternating light and dark patterns. These patterns give us the same d-spacings and plane directions as measured from diffraction. The key difference is that atomic resolution imaging can acquire structural information from a single nanometer-sized object, where as this proves very difficult if not impossible to achieve in electron diffraction.

Images apparently speak 1000 words, so I’ll save my keyboard from all that and show you some diffraction rings.

A diffraction pattern from magnetite nanoparticles

The biggest spacings (smallest rings) have been indexed with data from [1]. The inset is an atomic-resolution TEM image of a single magnetite nanoparticle on-axis.

Both the diffraction rings and atomic resolution image were coloured and manipulated with GIMP/InkScape (my new hobby).

While you are at it, check out some other posts on atomic-resolution TEM:

[1] Swanson, H.E., Morris, M.C., Stinchfield, R.P. & Evans, E.H. Standard X-ray diffraction powder patterns. (National Bureau of Standards, Washington, DC: 1962).

Magnetite-Nanoparticles Firefox Persona

Rahi — Wed, 30 Mar 2011 01:27:20 +0000

Here’s a great opportunity to showcase magnetite-nanoparticles.

I’ve created a Firefox Persona based on the HAADF-STEM image posted previously.

A firefox persona based on magnetite nanoparticles.

Link to ‘wear’ it: Magnetite Nanoparticles Firefox Persona

Do your bit for nanotechnology awareness.

Seriously.

False-coloured darkfield image of nanoparticles

Rahi — Fri, 31 Dec 2010 06:34:02 +0000

If the astrophysicists at NASA can use false-colour for artistic reasons, I see no reason why nanoscientists can’t jump on the bandwagon.

Here’s a nice colourful start to the new year: 10 nm superparamagnetic magnetite nanoparticles blended with an artificially generated background.

A false-coloured dark-field image of magnetite nanoparticles

Note that colour has no correlation to real values/information (unlike some false-colour images, which are actually representing real data as colours). Image obtained using HAADF-STEM, and manipulated with GIMP.

Top 5 requests for Xmas

Rahi — Fri, 24 Dec 2010 04:22:54 +0000

A request to Santa from (selfish) nanoscientists everywhere.

Dear Santa,

Please give me the technology behind your flying reindeers.
Please teach me how to make a billion toys using the self-assembly of nanoparticles – I know this is how you do it.
Please give me the technical diagrams detailing the subatomic resolution microscope you have in your lab.
Please get me a Nature Nanotechnology paper, in which I am first author.
Please get me a Nobel prize for my work or my students work.

The Nano-Dragon

Rahi — Wed, 03 Nov 2010 02:12:07 +0000

I felt compelled to share this nanodragon I found while looking around my magnetite-silica nanomaterial. Consider this a scientists alternative to cloud-watching, a pastime that has been a part of human culture for centuries.

Pictured above is a magnetite-silica nanocomposite that quite clearly resembles a nanodragon (head towards the top-right). The image was obtained using HAADF-STEM which produces positive contrast (white) from the projected mass. Magnetite (iron oxide) is much denser than silica (silicon oxide) and hence the magnetite nanoparticles are brighter than the surrounding silica.

Why I use LyX/LaTeX

Rahi — Sun, 31 Oct 2010 04:28:45 +0000

LaTeX is a tool that uses markup language to generate scientific documents. The philosophy behind LaTeX is completely different to something like Microsoft Word or Open Office Writer. It takes control of formatting allowing you to focus on writing the document. LyX is a friendly front-end for LaTeX, that allows you to get away from the hard-core LaTeX language. Here are my top 5 reasons for using LyX/LaTeX:

It lets you focus on writing instead of playing with font properties (size, bold) and layout (“Should I place a Figure here or on the next page?”). You can also change the overall look of the document simply by selecting a relevant class such as ‘thesis’, ‘report’ or ‘article’.
LyX/LaTeX is structured, so each Chapter, Section, Subsection, Figure and Table is automatically numbered in order even if you insert things later. In-text references are dynamic so this also means that you don’t have to update them (e.g. from “Figure 6 is…” to “Figure 7 is…”).
Following from above, you can instruct it to generate a Table of Contents/List of Figures/List of Tables automatically, without having to manually insert page numbers and those dots.
If you use maths a lot, LyX/LaTeX will make your life easy. It is a piece of π to insert even the most complicated maths and it looks absolutely beautiful in the final PDF output.
It can generate advanced PDFs with bookmarks, and links between citations and reference lists/bibliographies.

See some of my LyX classes and layouts.

Clustering behaviour of magnetic nanoparticles

Rahi — Wed, 29 Sep 2010 07:47:53 +0000

Magnetic nanoparticles of magnetite (Fe₃O₄) are an exciting class of nanomaterials with application in medical imaging and drug delivery. However, the clustering behaviour of these nanoparticles is not well understood, and has direct implications on their application.

Pictured below is a dark-field image of a cluster of magnetic nanoparticles. High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) images have enhanced mass contrast, and heavier iron-based nanoparticles stand out from the supporting carbon film.

A cluster of magnetite nanoparticles imaged using HAADF-STEM. (Particles from Haw Choon Yian)

Understanding this clustering behaviour is important as it can affect the performance of the magnetic nanoparticles in the body. Magnetic clusters are formed predominantly through a combination of magnetic and van der waal interactions. An added complication is the introduced structure from sample preparation which introduces capillary forces that draw the particles together as the solvent evaporates. Eliminating this will be one of the goals in my PhD, and will enable better understanding and application of magnetic nanoparticles.