Kinetic energy, disordered

Dias FB, Kamtekar KT, Cazati T et al (2009) Exciton diffusion in polyfluorene copolymer thin films kinetics, energy disorder and thermally assisted hopping. Chem Phys Chem 10 2096-2104... 

Radiation Damage. It has been known for many years that bombardment of a crystal with energetic (keV to MeV) heavy ions produces regions of lattice disorder. An implanted ion entering a soHd with an initial kinetic energy of 100 keV comes to rest in the time scale of about 10 due to both electronic and nuclear coUisions. As an ion slows down and comes to rest in a crystal, it makes a number of coUisions with the lattice atoms. In these coUisions, sufficient energy may be transferred from the ion to displace an atom from its lattice site. Lattice atoms which are displaced by an incident ion are caUed primary knock-on atoms (PKA). A PKA can in turn displace other atoms, secondary knock-ons, etc. This process creates a cascade of atomic coUisions and is coUectively referred to as the coUision, or displacement, cascade. The disorder can be directiy observed by techniques sensitive to lattice stmcture, such as electron-transmission microscopy, MeV-particle channeling, and electron diffraction. 

Primitive considerations convince us that such secondary forces exist. For example, gases consist of disordered molecules, whether they be polyatomic like chlorine or ether vapour, or single atoms like helium or mercury vapour. But all gases, even helium, ultimately condense to liquids — and then to solids — if they are cooled and/or compressed sufficiently. When the molecules are forced into close proximity and have their kinetic energies diminished, the weak intermolecular forces are able to take control. Liquefaction results. The strength of these forces can be measured by the latent heat necessary to evaporate the liquid, or to sublime the solid. The equation,... 

In the motion of a material body composed of a large number of molecules, all the molecules have a common component velocity in the direction of motion of the body. If the motion of the body is arrested, by collision with an inelastic screen for example, its kinetic energy is converted into heat, and the ordered motion is converted into chaotic motion of the molecules, the total kinetic energy of the molecules remaining constant. We shall have reconciled the irreversibihty of such processes with the principles of mechanics if we can show that in the motion of material bodies the ordered motion always tends of its own accord to become more disordered or chaotic, while chaotic motion never of its own accord becomes more ordered. 

An increase in the temperature of a substance is always accompanied by an increase in the random motion of its particles. Recall that the kinetic energy of molecules increases with temperature. Increased kinetic energy means faster movement, more possible arrangements, and increased disorder. Therefore, the entropy of any substance increases as its temperature increases, and > 0. 

The growth of films via SCBD can be viewed as a random stacking of particles as for ballistic deposition [33,34]. The resulting material is characterized by a low density compared to that of the films assembled atom by atom and it shows different degrees of order depending on the scale of observation. The characteristic length scales are determined by cluster dimensions and by their fate after deposition. Carbon cluster beams are characterized by the presence of a finite mass distribution and by the presence of different isomers with different stabilities and relativities. Due to the low kinetic energy of clusters in the supersonic expansion stable clusters can survive to the deposition, while reactive isomers can coalesce to form a more disordered phase [35]. 

---