Valence electrons and Photonic crystals

[wolf1711]

Hello PF,

I came across a fact that, tungsten, molybdenum and chromium all have 6 valence electrons.

Now,if one uses Molybdenum and Chromium instead of tungsten in photonic crystals for TPV(Thermo PhotoVoltaics) does it mean:

1. All are capable of releasing equal number of photons, because of electron hole diffusion?
2. Is photonic Bandgap dependent on number of valence electrons, in anyway?
3. Tungsten: 5d46s2, Chromium: 3d54s1, Molybdenum: 3d54s1, does the availability of valence electrons at different shell levels going to effect the spectral emissivity? e.g. in Tungsten(W) the 5d has 4 and 6s has 2, they offer 6 valence electrons in all. where as, chromium 3d has 5 and 4s has 1.Molybdenum: 3d has 5 and 4s has 1 to offer. Nnow would that also mean since Mo and Cr's d and s are offering similar electrons, so the properties would also be strikingly similar as compared to Tungsten?
4. Is photonic Bandgap also dependent on valence electrons available at different shells?
Thanks for your replies.
wolf

 

[ZapperZ]

This is a bit puzzling.

Photonic band gap typically has nothing to do with number of valence electrons. It has more to do with the GEOMETRY of the metals being used. It is very much like the metamaterial that has been used to create left-handed material.

Here's an example of a photonic band gap crystal - a "woodpile" structure.

http://www.flickr.com/photos/ames_laboratory/3292950605/

You can make it using copper (which is typical), or other good conductors. In PBG for accelerating cavity, you could even make it using Niobium for a SRF cavity.

Are you sure you want a photonic band gap, rather than an electronic band gap?

Zz.

 

[wolf1711]

This is a bit puzzling.

Photonic band gap typically has nothing to do with number of valence electrons. It has more to do with the GEOMETRY of the metals being used. It is very much like the metamaterial that has been used to create left-handed material.

Here's an example of a photonic band gap crystal - a "woodpile" structure.

http://www.flickr.com/photos/ames_laboratory/3292950605/

You can make it using copper (which is typical), or other good conductors. In PBG for accelerating cavity, you could even make it using Niobium for a SRF cavity.

Are you sure you want a photonic band gap, rather than an electronic band gap?

Zz.

Thanks for your reply, Zz, actually, Copper might not be able to suppress nm waves?
The refractive index of tungsten provides for increased normal emittance at wavelengths shorter than 2μm, and suppressed emittance at longer wavelengths.

I need your opinion if Cu is capable of that, I just found out that the Refractive index of Molybdenum(Mo) is quite tight with the Tungsten(W).
I know that Valence band is effected by Valence Electrons. I would reframe my question a bit, here we go
Does, the Valence Electrons have anything to do with, Spectral Emissivity, strange thing is that I found three publications all of them use tungsten photonic crystals. None cared to explain exactly, why they used Tungsten and no mention is there about Mo and Cr based crystals.
On a second thought, I remember them saying that These crystals are damn difficult to fabricate, is it that this is an unexplored field relatively, when we talk about group 6 elements applying to photonic crystals?
regards
wolf

 

[ZapperZ]

Thanks for your reply, Zz, actually, Copper might not be able to suppress nm waves?
The refractive index of tungsten provides for increased normal emittance at wavelengths shorter than 2μm, and suppressed emittance at longer wavelengths.

I need your opinion if Cu is capable of that, I just found out that the Refractive index of Molybdenum(Mo) is quite tight with the Tungsten(W).
I know that Valence band is effected by Valence Electrons. I would reframe my question a bit, here we go
Does, the Valence Electrons have anything to do with, Spectral Emissivity, strange thing is that I found three publications all of them use tungsten photonic crystals. None cared to explain exactly, why they used Tungsten and no mention is there about Mo and Cr based crystals.
On a second thought, I remember them saying that These crystals are damn difficult to fabricate, is it that this is an unexplored field relatively, when we talk about group 6 elements applying to photonic crystals?
regards
wolf

You didn't answer my question or address the point I was making. The PBG is the result of the GEOMETRY, not the material.

Zz.

 

[wolf1711]

You didn't answer my question or address the point I was making. The PBG is the result of the GEOMETRY, not the material.

Zz.

Yes, so far that's what I have read, I mean its just been 3 days I have stepped into this field.
sorry, I missed your question.

http://www.science.unitn.it/~semicon/archive/2007-OE-Riboli.pdf
seems like they do make that point of your about the Geometry more elaborate.

 

[wolf1711]

You didn't answer my question or address the point I was making. The PBG is the result of the GEOMETRY, not the material.

Zz.

http://www.mit.edu/~ivanc/Publications/2006_ 2D Tungsten as TPV Selective emitters.pdf
but these guys are using tungsten and explaining the reason for using tungsten kindly refer to the page 2 of the publication
regards
wolf

 

[ZapperZ]

http://www.mit.edu/~ivanc/Publications/2006_ 2D Tungsten as TPV Selective emitters.pdf
but these guys are using tungsten and explaining the reason for using tungsten kindly refer to the page 2 of the publication
regards
wolf

And I can show this publication where you only need to insert copper rods into the cavity to create a PBG

http://prst-ab.aps.org/pdf/PRSTAB/v12/i12/e121302

Check out also the references therein from the MIT group headed by Rick Tempkin (i.e. Smirnova et al.).

Zz.

 

[wolf1711]

And I can show this publication where you only need to insert copper rods into the cavity to create a PBG

http://prst-ab.aps.org/pdf/PRSTAB/v12/i12/e121302

Check out also the references therein from the MIT group headed by Rick Tempkin (i.e. Smirnova et al.).

Zz.

Thanks, so what do you suggest? As you might be able to conclude, that the Mo and Cr would have similar structure to W, so going by the Geometry, can we use them as alternatives of W based PhC's for TPV?

 

[Dr Lots-o'watts]

Besides geometry, the relevant material property for a photonic crystal is its index of refraction for the wavelength of interest, or more specifically, the difference in the refractive indices of the two constituing materials (one of which is usually n[air] = 1).

A stack of thin films ABABAB[...], where A and B each have indices and thicknesses chosen to obtain 100% reflection of a specific (incident) wavelength s the simplest of photonic crystals : 1-dimensionnal system.

2- and 3-dimensionnal systems are typically made of stacked cylinders, spheres, or more complex schemes, but are much easier to simulate than to fabricate, especially if you're interested in optical wavelengths.

Valence electrons are referred to in the context of electronic bandgaps, which are a totally different phenomena. Photonic bandgaps are however often compared to electronic bandgaps, somewhat like a water current can be compared to an electric current. There are similarities in the math, but they are mostly unrelated (at least at the introductory level.)