# 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 ...

7

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

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 ...

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. ...

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 ...

4

The angle at $C$ is not $120^\circ-\theta$, it's $180^\circ-(120^\circ+\theta)=60^\circ-\theta$. The rest of the algebra is right, and you can quickly see where the sign comes from.

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

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

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

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

Biological processes do not generate atoms or even sub-atomic particles out of thin air. When a cell splits, the number of total atoms in the daughter cells is exactly the number of atoms in the mother cell. Sustained growth is possible since nutrition provides an external source of energy and raw material, allowing the daughter cells to grow and achieve ...

4

Carbon nanotubes, or similarly manmade materials, might be able to accomplish this in the future. The current record is a tensile strength of 63$\times$10$^{9}$ Pa (Pa = pascals = N/m$^{2}$ or force per area). So if we assume a circular cross section, then the area is defined by 4$\pi$r$^{2}$. We can take the tensile strength and the area formula to find ...

3

A CO$_2$ molecule is more like 0.5nm long and 0.25nm wide, so you're not going to create your holes with a laser or any imminent development of nanolithography. A better bet would be to grow a crystal with pores of the correct size. For example you could probably find a zeolite with a suitable pore size.

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

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 - ...

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 ...

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

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

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

I don't believe that the materials we use for engineering on the macroscopic scales, gears and wheels and metals and so forth, will be appropriate for nano-devices. Macroscopic devices are usually built out of chemically homogenous materials, which do not afford flexibility in knowing where to cut and splice to design new shapes, or how to assemble the parts ...

2

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 ...

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

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

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

The specific heat of the bulk is the integral of the specific of all the applicable energy carriers. Let us consider electrons and phonons for simplicity $$C_{v-total} = C_{v-electrons} + C_{v-phonons} = (\frac{\partial U}{\partial T}_{v-electrons}) + (\frac{\partial U}{\partial T}_{v-phonons})$$. Taking into account that energy distributions, we can ...

2

$\text{m}\Omega ^{-1}$, means milli-S, that means the resistivity is in the range of kilo-Ohm. What's the problem? Apparently, the curve in your post shows very low conductivity compared to Cu.

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