Crystal Definition and 382 Threads

Hi! I'm new to the physics forum but I've read a little bit and I'm impressed with the knowledge a lot of people have here. I've tried searching for any topic on my question without any luck. My question is simply what the algorithm is to determine the band structure for a one dimensional...

I am trying to build something but I’m too stupid to understand this stuff so I need some help. Basically I am trying to create a system that will produce a constant sine wave, frequency of somewhere between 420 – 440 hertz under water with the greatest amount of amp output possible. I...

Powder pattern calculation from single crystal data Hi Kindly, I want to know what the theoretical base of X-ray powder diffraction pattern calculation from single crystal data? and is the obtained pattern same as experimental powder pattern and if not same what the cause of difference? Thanks

Hi, Could someone help to explain that why for the 2 D system, like 2 dimensional electronic gas, the crystal momentum k in 2D band structure is defined on a torus? Thanks a lot.:)

Homework Statement H = -D(S^z)^2 for cases D>0, D<0, where D<0 should remove the degeneracy in the ground state.Homework Equations H = -D(S^z)^2 = -D\hbar^2 (1 0 0; 0 0 0; 0 0 1) (`;' separates rows) det(H-1E)= 0, or by inspection... The Attempt at a Solution I get, for D>0, E_1 = -D...

I just noticed that it's often taken for granted that a macroscopic crystal has a similar geometric structure as in the atomic scale. What is the physical explanation for this (assuming it is true)?

I mean, the system is clearly related to seeing if the sides are of equal length and if the angles equal 90 degrees. If we first exclude the hexagonal, we have three sides and three angles each of which could be either equal/90degree. That gives us 3^2 = 9 possibilities. Then looking at the...

Is it possible to perform x-ray diffraction for 2-D crystal like Graphene? If poossible how does the bragg interference criteria look like here?

Hello all, I already have the answer to my question, but what I would like to know is why. My question is: why in the question below is the plane 111 used to find ao and not another plane? An ordered compound of NiAl has a cubic structure with one formula unit/cell. One Al atom at...

Homework Statement A Czochralski growth process is begun by inserting 1000 moles of pure silicon and 0.01 mole of pure arsenic in a crucible. For this boule, the maximum permissible doping concentration is 1018 cm-3. What fraction (X) of the boule is usable? (k=0.3) Homework Equations...

Good Morning Can anyone help me understand why, apparently the physical length of a monopole end feed wire for a crystal set need to be ½ the wave length of the desired signal. The reason I ask is, that I understood that, if you have a variable coil in series with the antenna, the...

I'm TAing an introductory class, and of course Miller indices and unit cells versus primitive cells and all that crystallographic stuff is a big first week. It's tough for some students to wrap their heads around all the 3-D symmetries, and *really* tough for me to draw all those structures on...

Homework Statement Calculate the density of crystalline NaCl, given that NaCl has a face-centred cubic lattice with a dimension a = 5.64A. Homework Equations 1/8 Cl ion at each corner, 1/2 Cl ion on each face. 1 whole Na in the center, 1/4 Na ion along each edge. The Attempt at a...

I am attempting to construct a device that will vary frequency between MHz and 3200MHz. Does anyone know of a fairly inexpensive crystal that will allow me to use all frequencies in this range? Thanks ~Matt

This might be more of a simple engineering question, but does work hardening (cold worked) of say a metal create smaller, more numerous crystal grains (and thus, more grain boundaries)? or does it just create dislocations in the crystal?

Hi I have a tutorial problem involving determining the ideal methods for identifying material properties of a layered semiconductor structure. The problem states to use either scanning or transmission electron microscopy. THe structure consists of several monolayers (around 5nm) of AlGaAs...

Is fullerene C_{60} elementary crystal cell or the whole crystal? I do not clearly understand it fom the context? Why is considered most perfect point symmetry form?

If I am given that mica has a modulus of 52GPa parallel to the c-axis and 179 GPa perpendicular to the c-axis, how do I figure out the elastic modulus of a polycrystalline mica where grains are oriented randomly?

What is the volume of atom/volume of cell?

Homework Statement In a mock exam I was asked for Q. Two properties associated with a single crystal. Homework Equations The Attempt at a Solution For one answer I gave that they are hard. I think another answer might have been something to do with crystal...

Dear friends, I am doing a Molecular dynamics simulations of a crystal. For this the initial configuration is FCC (face centered cubic) lattice. My problem is that I have to study the system for different orientations of the crystal i.e. (100) plane, (110) plane and (111) planes. For (100), the...

Homework Statement Localize the image of an object situated at 1.2 m from a crystal ball with a diameter of 0.2 m (n=1.5). Homework Equations None given. But Snell's law I believe. The Attempt at a Solution I'm totally stuck at starting. Does the size of the object matters...

The problem said: "Determine the magnitude of the Schmid factor for an FCC single crystal oriented with its [100] direction parallel to the loading axis. " The Schmid factor is the "cos(\phi)*cos(\lambda)" term in the equation for resolved shear stress. I know that the slip planes...

Hello, is there any detailed table about the s,p,d,f,etc level splitting due to various crystal symmetry(like O,Oh,D4h,...). I think it should be somewhere since it is a well established material. Can anyone help?

Hello everyone, I am trying to understand COMSOL 3.5 and I am interested in Photonic crystal fibres and tapered optical fibres. First of all, could you please tell me what is the background of the layout? When you create a design/object, the rest area is air or I need to define another object as...

Metals with what type of crystal lattice less prone to brittle fracture? Why?

When I was a little kid, I met a gemologist who showed me a cool trick with a ring he'd bought for his wife. When he submerged it in water, the crystal disappeared! As I now know, this crystal had an index of refraction of 1.33. Anyone know what this crystal is and/or how I can get my...

1. Homework Statement Using the powder XRD data below, show that the substance has a face centred cubic structure. (xray lamda = 0.154056 nm) Peak No.------2(theta) 1 -------------38.06 2 -------------44.24 3 -------------64.34 4 -------------68.77 5 -------------73.07 2...

Homework Statement Using the powder XRD data below, show that the substance has a face centred cubic structure. (xray lamda = 0.154056 nm) Peak No.------2(theta) 1 -------------38.06 2 -------------44.24 3 -------------64.34 4 -------------68.77 5 -------------73.07 Homework...

Hi, I have this quite basic question regarding photonic crystals. As I understand, a periodic dielectric structure (photonic crystal) has modes (spatial profiles) at discrete frequencies from: \nabla \times \Big( \frac{1}{\epsilon(r)}\nabla \times H(r) \Big) = \frac{\omega^2}{c^2} H(r)...

Can entangled protons be maintained in a crystal lattice for an indefinite period of time? The following papers seem to support this contention. I need the help of the Forum’s readers to critique this research and the assertions the authors are making. Dr. Francois Fillauxa and Dr Alain...

I want to know the basic principle of working for quartz crystal microbalance, how it is used to measure the thickness of the film?And why it can work at room temp (with water cooling) and at higher temp say 65deg ??

Homework Statement Calculate the potential energy, by ion, in an infinite bi-dimensional ionic crystal. Hint : Use the power series expansion of \ln (x+1). Homework Equations \ln (x+1)=\sum _{i=1}^{\infty} \frac{(-1)^{i+1}x^i}{i}. The Attempt at a Solution W=U=k\sum...

Hi, I am having trouble with the following: All I have really done is differentiate the function to give an expression for F(r), but I am a bit clueless about the rest. How can there be equilibrium if the two ions are attracted to each other? Cheers, GeoffreyThelm

Hey. I want to derive the conductivity of graphene. I'm looking for a formula of the sort: J = \frac{e}{\hbar} n \frac{dE}{dk} D(E) \Delta E where \frac{1}{\hbar} \frac{dE}{dk} is the electron velocity, D(E) = \frac{dN}{dE} is the density of states, \Delta E might be the applied voltage...

Setup: I'm trying to make the band structure for a planar photonic crystal with finite thickness, i.e., a quasi-3D problem. I only want the x-direction band structure. So, I'm using variable floquet periodic BCs for the x-direction boundaries, and 0 degree floquet periodic BCs for the...

What can this crystal be? Hello, I have some crystals with the following properties which I am unfortunately unable to find out their chemical formula or name... any other material with the following characteristics will help too. Cubic with octahedral habit. RI : 1.5 - 1.6 Density...

number of electrons leaving crystal surface. any help :)? [b]1. A scanning tunnelling electron microscope (STM) measures a tiny electrical current tunnelling out of the surface of a crystal. The current is 0.30 pA (0.30 x 10-12 A). Calculate the number of electrons per second leaving the...

What difference would you observe about the yield stress, young modulus,etc if your material were a single crystal? Explain the difference.

I heard that it is possible to measure positions of individual atoms in a crystal. Is this true? I understand the principle of measuring crystal orientation and base vectors of Bravais lattice with X-ray, but I have no idea how positions of individual atoms can be obtained. I suppose it is...

Hello, I was wondering if we can deoxidize Iron inside a crystal like Kyanite (Natural form), which contains Fe inclusions (sometimes rusty)... Thanks in advance.

I am new to this website but I would like to know how to build a homemade radio using an electro magnet and a germanium diode crystal. Are ther any other components required to complete the construction of the radio?

Hello, I have this ongoing argument with my professor. I read in a paper (friction and wear) that the crystal structure can affect friction. HCP crystal structures having lower friction coefficients. I have two papers that mention this in passing one, linking FCC crystal structures to have...

Are there stress and strain graphs for different crystal structures?

Homework Statement The distance between the Li+ and Cl- ions in a LiCl is .257 nm. Use this and the molecular mass of LiCl 42.4 g/mol to compute teh density of LiCl.Homework Equations The Attempt at a Solution I am surprisingly having a lot of difficultly with this problem. The LiCl crystal is...

Homework Statement X rays with wavelength 0.10 nm are incident on a crystal with a hexagonal crystal structure. The x-ray diffraction spectrum is shown in the figure. Figure: What is the atomic spacing D of this crystal? (in nanometers) Homework Equations The Bragg...

This was just the coolest thing I have ever seen. I'd love to go there and see it in person. http://news.nationalgeographic.com/news/2007/04/070409-crystal-cave.html

Homework Statement A mono-energetic beam are of neutrons is directed perpendiculary at the surface of a metal crystal whose atom are a constant distance 0.1E-10m apart. The scattered beam of neutrons is found to have maximum intensity at an angle of 25degree to the initial direction. What is...

Homework Statement The atomic mass number of copper is A = 64. Assume that atoms in solid copper form a cubic crystal lattice. To envision this, imagine that you place atoms at the centers of tiny sugar cubes, then stack the little sugar cubes to form a big cube. If you dissolve the sugar, the...

When setting up this derivation one assumes a chain of identical atoms. The interatomic interaction between atoms is short ranged and so only affects neighbouring atoms (see Hook and Hall, "Solid State Physics" chapter 2.3.1). The potential V(r) is expanded as a taylor series about r = a to...