It is confirmed that the work contained in the diploma thesis entitled "NEW CONFIGURATIONS OF ATOMIC BEAMS AND LASER BEAMS FOR MICRO". The present work mainly focuses on two lithographic techniques, viz. selective laser ablation lithography and atom lithography using dipole force. Dipole atom lithography work deals with the simulation of atomic trajectories under dipole force using a semi-classical technique for various configurations of atomic beams and light fields to focus the atomic beam down at the submicron level.
We proposed the use of square arrays of multiple atomic lenses produced by the interference of four nearly collinear optical beams in atomic lithography using the dipole force. A new configuration of microscopic square arrays of atomic beams (microoven array) is proposed in the presence of a TEMoo-mode laser acting as an atomic lens for lithography of atoms via dipole force to obtain AI2 subperiodic structures. Therefore, we have developed a new technique for generating a cold atom beam with low divergence.
The axial velocities and divergence of the atomic beam were investigated as a function of laser energy. The proposed configuration of array of microwaves for obtaining a large number of periodic atomic beams is realized experimentally via selective laser ablation lithography i.
Experimental realization of matrix of micro-ovens 109
Basic principle of atom lithography using dipole force in presence of stand
Atomic beam generation by focused laser ablation of thin film 14
Intensity distribution is as shown in the bottom of the figure 34 3.9 Trajectories of initially collimated cold rubidium atomic beam in optics.
Trajectories of rubidium thermal atomic beam at intensity, Io=l W/m^ and
Launching position of rubidium atoms in presence of interfering optical
Final positions of initially collimated rubidium atoms after interacting with
Final positions of thermal rubidium atoms after interacting with TEMqo
Final positions of thermal rubidium atoms after interacting with TEMoo
Energy level digram of uranium showing isotopic shifts and laser detuning 3.27 Proposed experimental scheme for isotopic separation of uranium
68 4.10 Intensity distribution in the interference pattern 70 4.11 Experimental setup for selective laser ablation lithography in one dimension.
Schematics of experimental set-up used for generation of sculpted atomic
Deflection signals corresponding to (a) Atomic beam and (b) Ionic beam at
LIST OF FIGURES ™
Micrograph of Indium thin film exposed by two beam interferometric pat- tem showing single ablated spot. Distance between the lens and the thin
Atomic force microscope picture of Indium thin film exposed to four beam
Optical micrograph of target and deposited atomic beam 99
Q is the average angular divergence with an unfocused laser and no aperture, 6\ is the average angular divergence with an aperture and an unfocused laser, and 02 is the average angular divergence with and without a focused laser.
Chapter 1
- Lithographic techniques
- Optical lithography
- Electron and Ion beam lithography
- Scanning probe lithography
- Atom lithography using dipole force
Atomic lithography via dipole force is another emerging scheme to write the entire periodic structure in one step. The resolution of the optical lithography technique is limited to the wavelength of the radiation and to the numerical aperture (NA) of the optics used for this lithography technique. Using a lens with a higher NA will result in better resolution of the image, but since the depth of field of a lens is inversely proportional to the square of the NA, improving resolution by increasing the NA reduces the depth of field of the lens. system.
These techniques offer higher patterning resolution than optical lithography due to the shorter wavelengths of the charged particles used. With such lithographic systems, there is also the possibility of damage to the substrate due to the involvement of a beam of charged particles with high energy (10-50 keV). Atomic lithography using dipole force [28-31] is a new upcoming technique that can overcome some limitations of already existing techniques.
Since the de Broglie wavelength of neutral atoms is very small (<0.1 nm for thermal atom beam), this lithographic technique has the potential for high resolution. Furthermore, the low-energy atomic beam used in this lithography does not damage the substrate. With the correct configuration of the atomic beam and the laser beam, the trajectories of the atoms can be manipulated to focus down on the atoms in the periodic nano-sized structures of desired geometry.
40] reported the focusing of the sodium atomic beam in the presence of the TEMoo mode laser in 1978 for the first time experimentally. 43], where the sodium atomic beam was launched perpendicular to the standing wave of the resonant radiation field at approximately wavelength A as shown in Fig. Each period of the standing wave acts as a cylindrical lens to focus the atomic beam.
Since then, there have been a large number of experimental reports on the focusing of atomic beams of chromium [44–48], cesium [49], aluminum [50], ytterbium [51] and iron [52, 53] using the dipole force of generated by cw optical standing waves. The width of the structure reported by the author was in the range of 80 nm. The dependence of laser power on structure width and focusing depth was also discussed [55, 56].
A periodicity smaller than Af2 can also be achieved by switching the light field announcement during deposition [60], It has been shown that the material selective characteristics of the atom-light interaction can be used for structural doping [61], Atomic beam focusing has also been reported for cesium via a pulsed standing wave dipole force [62, 63]. Since the pulsed laser can be conveniently converted to the short wavelength region via harmonic generators, it offers advantages when using atomic lithography with blue or UV resonance elements. lines, thereby reducing the periodicity of writing. Theoretical simulations of trajectories under the dipole force are necessary to understand the process as well as to access the optimal parameters of the atom-light interaction for the deposition of the required nanostructures. The trajectories of atoms under a given configuration of an atomic beam as well as a light beam under a dipole force can be calculated [65] either by a semi-classical approach or by solving the Bloch equations [32] in quantum mechanical formulations.
The atomic trajectories via dipole force have been reported for the TEMoo mode of laser [66], for standing wave configuration with the Gaussian envelope for chromium [67] and He [68] atoms and for Laguerre Gauss and Bessel light.
