Band Definition and 481 Threads

In crystalline material, bands arise due to the interaction of electron waves with periodic potentials. Can anyone please explain the origin of energy bands in non-crystalline material..couldn't find relevant links on Google.

I'm reading a paper on photovoltaic hydrogen production and the author claims that for reasonable solar efficiencies the band gap must be less than 2.0eV. This I understand. My question is how will it effect the photon absorption if the band gap is much smaller. Say the band gap energy is...

Hello! If I run an agarose gel of undigested DNA of an organism with more than one chromosome, and obtain one band (slightly smeared), what does this mean? The chromosomes aren't all the same length (some might be approximately half the size of others). Is it because they all become...

Hello, I just watched this video, where Dr Brattain talk about semiconductor physics and I thought about what I learned in my solid state physics course, namely band theory. I have several questions : 1)The explanation in terms of chemical bonds given by Dr Brattain (around 10mins) seems a...

I am considering making a yagi antenna for a wifi adapter and I have been warned about some possible side effects that I wanted confirmed or disproved.. I read somewhere that the 2.4GHz band also is the resonant frequency of water and is used by microwave ovens, but at a more powerful rate...

I don't understand the fibre bundle structure of the Mobius band, described by my textbook. "The base space ##X## is a circle obtained from a line segment L as indicated in Fig. by identifying its ends. The fibre ##Y## is a line segment. The bundle ##B## is obtained from the product ##L \times...

Hello Forum, I am looking at the energy levels between the n and p regions of a diode. The p-side has a conduction band that starts at a higher energy (same for the valence band). The n-side has the valence and condution bands that are at lower energy. The Fermi energy line is the same...

Why the voltage drop across the insulator is linear in the band diagram of a MOSFET??

hello, i have a question related to metallic bonding. As far as i know, valence band is defined as the highest filled level in the band and conductionband as the 1st unfilled level. So, if I have 100 Li, we will have 100 orbitals which form a band. Since we have 100electrones, 50 pairs, so we...

Hello, do you know why no electron can stay in the band gap? Is it impossible at every energy? Thank you!

Dear forum people, I just learned how to get a tight-binding dispersion for graphene: E = +- \sqrt{1+4\cos((\sqrt{3}a/2) k_x)\cos((a/2) k_y)+4\cos^2((a/2) k_y)} But i can not figure out how can I plot that. I want to plot that in the following path: K \rightarrow \Gamma \rightarrow M...

Hi and thanks for reading, I don't really understand the valleys in the conduction band, in the E vs. k diagram, there is the L-valley, r-valley and X-valley. Each has a different momentum... and are at different energy levels. I understand that at any temperature above absolute zero, a...

I've been having a very difficult time understanding why band structure is expressed in terms of momentum/crystalline directions. I've included a picture of the band structure of silicon so that you can better understand my question. I think I understand basic crystalline structures and the...

I'm thinking mainly within the context of the useful semiconductors here (Si, GaAs, etc.)... What does it mean for an electron to be in the L or X valley instead of the Gamma valley? If Gamma is the k = 0 point, then momentum p = 0. Does that mean being in L or X means all the electrons...

Hi, thanks for reading my questions. I've been reading and reading and reading and reading and I'm trying to understand the difference between conductors, semiconductors, and insulators at an atomic level. When reading about electricity I often find that metals have a "sea" of "free"...

Homework Statement For a stretched rubber band, it is observed experimentally that the tension f is proportional tot he temperature T if the length L is held constant. Prove that: (a) the internal Energy U is a function of temperature; (b) adiabatic stretching of the band results in an...

Hi I've been searching on the web for this two topics, band structure and fermi surface, both of copper. I can't find any of them from a free source, I am doing just a report of my class of introduction to solid state and I just have found this two things in articles that must be bought. If...

Might be an easy question (or not). What determines the band gap of an element? As far as I know, silicon is the most efficient single-element semiconductor because of it's small (but nonzero) bandgap. Next (as far as I know) is Selenium. I'm aware there are more efficient compounds, but...

How to sketch the band diagram of intrinsic semiconductors including the fermi level with the electric field present verses distance? Its not a homework question.

Homework Statement Write a Java program to solve the following problem. An elastic rope starts out with length 100 meters. The start of the rope is fixed to a pole and a worm is placed on the rope at the start and the worm starts crawling towards the end. Each day the worm crawls 6 meters...

I am reading about solid state electronics(semiconductors). I've read that when atoms of many many atoms are brought close each other,as in a solid, the energy levels of energy states of different atoms get split up into different closely lying energy states collectively forming a band...

Homework Statement Calculate Efi with respect to the center of the bandgap in silicon for t= 200, 400, 600 kelvin. Homework Equations ni = Nc e^-((Ec- Ef)/(kt)) k = boltzman constant t= temperature in kelvin Ec = energy level of the conduction band ef= fermi energy level ni=...

So I've cut the isolated band of my earphones to see what's inside (my cheap earphones quit working). I expected to see copper. And I have. But, there is also a red wire and a blue wire amongst the copper. At they dyed copper, or a different metal...

Hi, I understand for metals the conduction band is usually partially filled. However, at absolute zero, is the conduction band empty (for metals)? I'm asking this because as far as I know, the definition of valence band is "the highest occupied band at absolute zero" However, I have...

Hi All, There is a simple question in my mind. A band with energy Ek has dispersion in k space. Then what it looks like in the real space?

When a n-type semiconductor is brought into contact with a metal, then alignment of the chemical potentials of both systems leads to band bending within the depletion layer, e.g on the semiconductor side. does the amount of band bending (change of potential) also depend on the donor...

why band gaps occur according to bloch theory?

how is the relationship between fermi level and band structure of solids can effect electrical conduction properties of a material?

Metal nanoparticles (Au, Ag, Al or ...) can coat on porous silicon, the particles can be located inside the pores or on the silicon micro/nano structures. By applying this type of coating is there any change in band structure of porous silicon? As I've measured the band gap has changed.

Hiya, been given this question which I am having problems with. Semi conductor quantum well structure contains a 100A thick layer of GaAs between thick AlGaAs layers. Find the band gap for the structure, where GaAs has the following parameters; conduction band effective mass 0.067 me, heavy...

Hi everyone, I'm working on random materials which are coincidencely oxides and showing semiconductor behaviour... Some of these are metals and i suddenly realize MOS (which are practically everywhere). I know them, i know how they work and behave still i can't get to understand the effect of...

Hi all, I'm working on some image analysis as a part of my research, specifically trying to match images. The method I am using transforms the image into the frequency domain and then applies a band pass (or mesa) filter to eliminate noise and the dc component of the image. I have never...

Homework Statement The Gibbs free energy of an elastic band satisfied dG = -SdT - LdF where F is the tension and L the string's length. At fixed temp the entropy is given by S = So - a(L-Lo)^2 + b(L-Lo)^2 Where Lo is the length of the elastic at zero tension and a and b are positive...

The band gap discontinuity in DFT? Hi everybody... I've read about the band gap problem of Density functional theory, there is a discontinuity of the band gap when an electron add to the Kohn-Sham system I have two questions could anybody answer me? please 1- why this discontinuity happens...

We know in silicon a valence electron can be excited to conduction band if it absorbs one photon(one photon absorption) or two photon(two photon absorption),my question is that it must need a certain amount of time for the electron to 'travel' from the valence band to the conduction band(I...

I am not able to understand how a bandgap voltage reference works. The simplest ckt I found was here - (figure 2) - http://www.national.com/rap/Application/0,1570,24,00.html You have 2 branches of diodes, in one branch rich (high) current flows and in the other lean (small) current flows...

We really need help naming our band, I just found this forum and it seems like an excellent place to try, so a little contest: If we choose a name you come up with you will receive $200 usd by paypal. The ideal name should grab people's attention. If it helps: we’re inspired by sci-fi...

Hi everybody, I would like to know if someone could explain to me what happens to the refraction index of gold at grazing angle (X-ray applications), and particularly the band structure explanation (if you have it!)... Indeed, I heard that the x-ray telescopes were made of parallel mirrors...

Dear All I am having problems with how to draw band diagrams with band bending for Schottky Barriers and PN junctions. My issue is that I don't know how you determine which Fermi level remains fixed at its equilibrium level and which Fermi level moves to align with it when the two materials...

Does a PNA show FFT If I'm looking at gain across a band on a PNA could one say that I'm looking at an FFT or is that complete nonsense?

Elastic Potential Energy of Elastic Band* Homework Statement A stretched elastic band of mass 0.55 g is released so that its initial velocity is horizontal, and its initial position is 95 cm above the floor. What was the elastic potential energy stored in the stretched band if, when it lands...

Hi! Is anyone familiar with generating band structures from DFT simulations? I am using graphene, and am trying to plot the electronic structure at the high symmetry points (K, M, and gamma). Grappling to understand this theory, my questions are: 1. Is the location of the high symmetry...

When we say generally TiO2 band gap energy, is it meaning direct or indirect band energy? Some papers show only direct BG or indirect BG or both. Is it right that one semiconductor has one of direct and indirect BG. I am a little bit confused.

ok let's say i have a semiconductor like germanium with band gap of around 0.67eV at rtp. so this means that i need around 0.67 x 10-19 J of energy to cause valence electrons to jump to conduction band right? do i use the formula E = 1/2 kT to relate this energy to temperature? so i...

Hey I am doing a practical on the spring constant of a rubber band, we have studied hooke's law and from that found that the spring constant of a spring is well F = -kx so F is proportional to x. While i did the same experiment with a rubber band, hung it on a clamp connected to a retort...

I need to calculate the density of states for a dispersion relation which is like the free electron dispersion, but with one effective mass in the kx, ky directions, and a different effective mass in kz. So I need to integrate the inverse gradient of E(k) over a surface of constant energy, ie...

Situation: I'm having issues with the iliotibial band in my left leg, and it is preventing me from running. I've been icing it daily and doing lateral leg raises along with various stretching exercises. I've also just purchased a foam roller (didn't know what the heck they were until now)...

Warning: I'm not a practicing chemist. Answers in as-simple-as-possible language (but not oversimplified!) would be greatly appreciated! I'd like to know if the chemical properties of a solid can be affected by conduction band electrons. I assume that, in the majority of cases (and perhaps...

Hi, I have a question regarding Energy band. The energy band of a simple cubic semiconductor crystal with a lattice constant b can be represented as in the following function: E(k) = E0 + E1[cos(kxb) + cos(kyb) +cos(kzb)] where E0 and E1 are independent of the wave vector k. i)...

Hi, I've encountered some problem during solved the band pass filter and twin-T notch filter. I don't really understand what the question exactly meant...hope can get some idea in here..thx 1.) A signal conditioning system uses a frequency variation from 6 kHz to 60 kHz to carry...