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Summary form only given. The field emission (FE) characteristics were investigated for the cone-shaped multi-walled carbon nanotube (MWCNT) bundles which were fabricated under the oxygen plasma treatment. The mechanism of the cone-shaped MWCNT bundle formation was explained in previous paper by a model explaining the interaction between the induced dipole moment of the MWCNT and the sheath electric field.1 Formation of C-O or C=O bonds at the dangling bonds of the apex of MWCNT enhances induced dipole moment on the MWCNT, producing attractive dipole force between MWCNTs. Because the MWCNTs tried to be aligned with the sheath electric field, the size of the cone-shaped MWCNT bundles is determined by the force balance between the attractive dipole force and the repulsive aligning force. As a result, vertically aligned MWCNTs which were treated by plasma ion irradiation is composed of the cone-shaped MWCNT bundles at the top region and the vertically aligned MWCNTs at the low region. Because the force balance between the attractive dipole force and the repulsive aligning force generates the cone-shaped MWCNT bundles, the tips of the cone-shaped MWCNT bundles are distributed uniformly with equal distance. In addition, the uniformly distributed cone-shaped MWCNT bundles with various ratios of diameter to height were obtained with control of the irradiated plasma ion energy and dose, corresponding to control of field-screening effect without using patterned electrode. Cone-shaped MWCNT bundles are also expected for the enhanced emission stability due to sustainability of the bundle structure. Consequently, structural deformation of the cone-shaped MWCNT bundle with its FE characteristics was controlled and explained by plasma treatments.