Molecular beams alignment

In terms of beam delivery, the DLW method is based on optical microscopy, confocal microscopy [4,6,13] and laser tweezers [14] (for reviews on laser tweezers see [ 15,16]). These techniques allow for a high spatial 3D resolution of a tightly focused laser beam with optical exposure of micrometric-sized volumes via linear and nonlinear absorption. In addition, mechanical and thermal forces can be exerted upon objects as small as 10 nm molecular dipolar alignment can be controlled by polarization of light in volumes of with submicrometric cross-sections. This circumstance widens the field of applications for laser nano- and microfabrication in liquid and solid materials [17-22]. 

Fig. 6.2. Alignment of a molecular beam in collisions with a medium of spherically symmetric particles.

Such a method of producing and detecting alignment in a molecular beam was proposed and effected by Sinha, Caldwell and Zare [352] by using Q t Q type fluorescence in the B1nu — transition of... 

Another promising method for producing not only alignment but also orientation in a molecular beam uses spatial effects in collisions with the surface of a crystalline solid (see [208, 247, 281, 299, 354, 355] and references therein). These and other spatial effects are being studied intensely in the laboratories of Auerbach, Zare, Stolte and others, beginning in the 1980s. The idea of the method may be visualized as the bank shot of a billiard ball. 

Fig. 6.4. Alignment of J in interaction between a molecular beam and a surface (a) cartwheel type with preferred rotation in the scattering plane yz (b) helicopter type with preferred rotation parallel to the surface plane xy.

Hefter, U., Ziegler, G., Mattheus, A., Fischer, A. and Bergmann, K. (1986). Preparation and detection of alignment with high m selectivity by saturated laser optical pumping in molecular beams, J. Chem. Phys., 85, 286-302. 

In Ref. [257], Sii- Cx alloy films with x< 0.1 were deposited on Si by molecular beam epitaxy (MBE) to use them for the substrates of heteroepitaxial diamond films. It was expected that when x = 4.33%, a perfect lattice match of Sii C c D = 2 3 occurs and the degree of orientational alignment could be improved. An EIOD film, grown to a thickness of 20 pm using the BEN process, successfully resulted in a (100)-oriented film with (100) faces at the film surface, but the FWHM of the (111) XPF was 6°, the same value as when the direct nucleation of diamond was done on Si using BEN. The results of Raman spectroscopy and XRD of the diamond films were not dependent on the x value. It was thus confirmed that the orientational characteristics of the HOD films had no significant dependence on the C content of the Sii C,v layers. This work can be compared with that of Ref. [258], where layers with x= 1.4 and 3.5% were deposited on Si(lOO) by... 

Figure 1 - The two experimental arrangements used to probe the alignment of benzene molecules in a seeded supersonic beam by direct polarized IR laser absorption (upper device) and molecular beam scattering (lower device). For further details see Ref. [1].

When an electric field gradient is applied on a molecular beam of molecules with a dipole moment or high polarizability, they can be focused or defocused, depending on their J, M (and K for symmetric top sjjecies) quantum states. This method was applied in studying the sjjectroscopy of vdW molecules or in aligning molecules before reacting them. - ... 

A continuous-wave green laser beam (argon ion laser, all lines) with a maximum power of up to 28 W is focused to the beam width of only 4 fim. As shown in Fig. 1, the vertically aligned laser beam runs orthogonal to the molecular beam. All molecules that pass the laser beam at or very close to the focus are heated to an internal temperature above 3000 K and ionize. The positive fullerene ions are then accelerated towards an electrode at 10 kV where they induce the emission of electrons. The electrons in turn are again multiplied and the charge pulses are subsequently counted. The overall molecule detection... 

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