# Tag Info

8

It's not simply a matter of size. Generally nanoparticles are a few nm to 100 nm and most molecules are smaller. But, for example, single chain of a high molecular weight polymer or a DNA molecule can easily be much larger than 100 nm which would put it outside the conventional "nano" range. The distinction is somewhat fuzzy. Is a fullerene a molecule or a ...

7

Quite likely, the two materials would stick together and form a seamless bond. If you have two two identical crystal lattices, and each one is bond-deficient at the surface, it will be energetically favorable for the surfaces to bond. Moreover, by making the surfaces as flat as possible, you have made it likely that large-scale alignment will occur. Think ...

5

The second law holds on average for systems of any size, large or small. If you have an isolated contraption containing just a few atoms, and you run it through some procedure (maybe as simple as waiting 5 seconds, or maybe more complicated), there is some probability that the atoms will wind up in a lower-entropy configuration at the end of the procedure ...

5

A nanoparticle as typically used in nanotechnology refers to a particle with diameter on the order of 1-100 nanometers, or $10^{-9}$ to $10^{-7}$ meters. However, it's not just a matter of size. These particles are not typically "molecular" in the sense that they are not stoichiometric units made out of atoms held together by covalent bonds. Indeed, most ...

5

It has to do with size. A molecule is in the range of picometers. A carbon-carbon bond is 154 picometers, so you expect most molecules to fall within the range 100-1000 picometers = 0.1 to 1 nanometers. A big molecule, such as a ribosome, or DNA, falls in the range of 10-1000 nanometers. Everything that falls in this range is "nano" by very nature. ...

4

I think the real answer is that when it comes to nanorobots, the materials we're using readily oxidise. Put them out of a vaccum and they're toast the instant they come into contact with the atomosphere. Biology manages to deal with this by using a different material set, and encapsulating everything pretty well so that the environment doesn't damage cell ...

4

The website is clearly supported by lots of money which doesn't guarantee that it reflects the most accurate scientific information. The very page you quoted says under the picture: The material is graphene, also known as graphite... Well, no. Graphene is not the same thing as graphite. Graphite is a 3-dimensional material used to produce pencils - and ...

4

In the picure below, you can see how the row-column grid correspond to the graphene structure. To have a (n,m) nanotube, you "just" have to roll your graphene sheet so that the (0,0) hexagon coincides with the (n,m) hexagon. Of course, it is much easier said than done !

4

A carbon nanotube can be seen as a sheet of graphene that is "rolled up". Now, graphene is a two-dimensional lattice and hence has two lattice vectors, $\vec{a}_1$ and $\vec{a}_2$. (If you are unfamiliar with lattice vectors let me know and I will expand on this). The numbers $(n,m)$ simply state that your tube is obtained from taking one atom of the ...

4

Your approach appears to be incompatible with your assumptions; namely, are not using the correct energy spectrum. Judging by the expression for the wave function that you have given ($\psi_{n}(x)=\sin(k_{n}x)$), it appears as if you are solving an infinite square well problem in 1-D. The different $n$’s label the discrete energy eigenstates in your square ...

3

Now I'm wondering if a perpetual motion machine of the second kind (a machine gaining energy by cooling down the environment) would be possible in nanotechnology. As a result such microchips would lower the entropy of the universe. A thousand times no. If a concept lowers the entropy of the universe in a non-superficial sense it is always false. As ...

3

Laws of classical mechanics cannot just be scaled down to the nano-regime, as alot of additional forces come up (chemical interaction, friction must be inspected newly, cannot be described by rough material parameters as in classical mechanics). Also microfabrication is a highly tricky process, especially if u want to do it in a parallel style fabrication ...

3

The numbers will greatly vary depending on the kind of nanotube. The following are some examples from cursory Google searches. Electrical conductivity was increased by 50 percent to 1,230 siemens per meter. http://news.ncsu.edu/releases/wms-zhu-cnt-composites/ And that’s not all: colossal carbon tubes are ductile and can be stretched, which ...

3

A nanoscope in the sense you're talking about would be physically impossible, because things which are smaller than the wavelength of light don't reflect light. They do scatter light, but that's a different process which doesn't form a coherent image. Visible light has wavelengths between about 400 and 700 nanometers, so anything smaller than that - ...

2

Depends on your definition of a quantum dot. Usually they are understood to be a collection of excitons (bound states of electrons and holes) confined to a small volume. But the smaller the volume, the higher the energy of the system and eventually you would destroy the exciton bonds (besides, there would be a technical problem of how to maintain such a ...

2

This is a footnote to Chris' answer (+1 BTW :-) The microsocopic source of friction is exactly the cold welding mentioned by Chris and DJBunk. When you touch two rough surfaces together their real area of contact will be much less than the total area because only the high spots touch. At these high spots the surfaces adhere due to the same forces that act ...

2

The reason is that you have periodic boundary conditions in the azimuthal direction while there are no special constraints along the cylinder axis (note that, as in the radial direction we have the $\pi$ bonds of the carbon lattice the electron's wavefunction must be strongly confined). Other way to see this, in the azimuthal direction you must have an ...

2

Interesting question. I'm not completely convinced by Cristi Stoica's argument that this is equivalent to Maxwell's demon, since the traditional analysis of Maxwell's daemon assumes that the second law applies to the daemon, whereas we know that the second law has a significant probability of being violated for systems with small numbers of particles. But ...

2

That's a great idea. Maxwell also had an idea to break the second law of thermodynamics. He imagined a demon who would sort the fast from slow molecules. As you can see on Wikipedia, at Maxwell's demon > Criticism and development, Leó Szilárd and Léon Brillouin, and later others, proved that the demon, or equivalently a nanobot, when doing this sorting, ...

2

As far as resolution goes, right now the best in practice are high resolution transmission electron microscopy (which involves firing high energy electrons), high resolution scanning force microscopy (which involves a very sharp tip vibrating above a surface), and the classic scanning tunneling microscopy (which involves conduction through a very narrow ...

2

It's been a decade since I last used an SEM, but back then you would start using a fast scan that was real time i.e. you could move the sample around, change focus, etc and see the effect in real time. However the realtime image is noisy because the numbers of electrons being captured is small. Once you had the picture you wanted you would record them image ...

2

Nanotechnology is a part of science and technology about the control of matter on the atomic and molecular scale - this means things that are about 100 nanometres or smaller. Nanotechnology includes making products that use parts this small, such as electronic devices, catalysts, and sensors etc. Nanotechnology is defined as the study of structures ...

1

I am by no means an expert on this subject, but the following might be helpful. The properties sampled and imaged using the various forms of scanning probe microscopy (SPM) are related to electronic structure. Electronic structure calculations rely on a quantummechanical treatment of the electronic degrees of freedom (the dynamics of the electrons in ...

1

I recall doing this many years ago as a graduate student. I don't think there's any special reason for using a gaussian. It's just a convenient curve that gives a good approximation to the peak shapes in powder XRD patterns. Fitting a gaussian is just a more accurate way of measuring the peak position than estimating by eye. It's especially useful where to ...

1

Ok, let's take a gaussian profile, and we'll repeat it every $2\pi$ to turn it into a function for which we can calculate the Fourier coefficients. The resulting function looks like this: I've written a spreadsheet to calculate the Fourier components for this function and use the components to recalculate the function (I can put the spreadsheet somewhere ...

1

Sure - the relativistic doppler effect means that light which is scattered off a moving object can be redshifted or blueshifted. And there can be more redshifted photons than blueshifted photons, or vice-versa, depending on where the object is, and how it's moving, relative to the center of the trap. But since the object is moving much much much less than ...

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I used an arc-welder to make thermocouples from wires like your starting materials. Your desired objective looks like some of my 'failures.' Try loading a wire in tension and then break it with an arc (i.e. heat and melt a short section.) The ends might draw to the fine diameters you're trying to achieve. I'd try using one of the welders that are designed ...

1

1) Not at all! There are many applications and examples not needing three PhDs to understand. Gosh, where to start... 2) Too many to list here, and I'm not expert, but one important general method is depositing layers onto a material, for example how transistors and other semiconductor devices are made. Vapor deposition, ion bombardment, and more. ...

1

Resistivity is the relevant parameter for three-dimensional materials. Sheet resistance (less commonly called "sheet resistivity") is the relevant parameter for two-dimensional materials, and its inverse is called "sheet conductance" or "sheet conductivity". In the Novoselov paper you cited, they talk about sheet resistance and sheet conductance. Please ...

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