## 1 Introduction  
Titanium dioxide (TiO\({}_{2}\)) is one of the most important functional materials with promising electronic and optical properties. It has a band gap of \(\sim\)3.2 eV for anatase and brookite phases and \(\sim\)3.0 eV for rutile phase, with n-type semiconducting properties [1]. Additionally, TiO\({}_{2}\) is transparent and has a high refractive index [2]. Accordingly, it is extensively used for different applications such as gas sensing [3], fuel cells [4], photocatalysis [5, 6], photovoltaics [7, 8], and photonics [9]. Owing to the high surface-to-volume ratio of one-dimensional (1-D) nanomaterials, TiO\({}_{2}\) nanostructures with 1-D morphology such as nanorods [10], nanowires [11], nanotubes [12], and nanofibers (NFs) [13] are generally utilized for applications requiring a high surface-to-volume ratio, resulting in the enhanced performance of the fabricated device. However, most applications require the size of TiO\({}_{2}\) to be controllable for better performance, which is not easily realized. Among the aforementioned morphologies, NFs have the advantage of easy synthesis using the cost-effective and facile electrospinningning (ES) method [14]. By using the ES method, the diameter of the synthesized NFs can be adjusted by controlling the processing variables [15]. In a typical process of ES, under the effect of an electric field, a viscous solution is extruded from a needle to form a small droplet. If the electric field is sufficiently large, a liquid jet is formed and it accelerates toward a grounded conductive collector, which is at a given distance from the needle, and thus NFs can be produced [16]. The NFs are often deposited without preferred alignment. The morphology and diameter of the synthesized NFs are affected by the intrinsic properties of the solution and operational conditions such as the strength of the applied field and needle-to-collector distance. By controlling these variables, it is possible to control the diameter, length, and alignment of the synthesized NFs [17]. Well-aligned and highly ordered NFs can lead to a higher molecular orientation and degree of crystallinity and, as a result, better mechanical properties [18]. Furthermore, due to the existence of a long 1-D current path, the electrons can flow faster within aligned NFs relative to non-aligned NFs, where there are more junctions among NFs. Therefore, aligned NFs have enhanced electronic transport properties. [19]. Accordingly, the alignment of NFs is important for various applications. For example, microelectronics and photonics devices often require well-aligned and highly ordered structures to demonstrate their best performances [18]. Field-emission sources with highly aligned architectures are highly efficient [20]. Nanosensors with an aligned structure can offer better sensitivity [21]. Optical properties of devices with an aligned structure can be enhanced [22]. In tissue engineering, aligned NFs significantly enhance cell response [23]. Accordingly, many researchers have investigated different strategies to control the parameters of ES in order to obtain aligned NFs [24; 25; 26]. A simple method to generate uniaxially aligned NFs is to introduce a small gap into a charged collector [16]. The as-spun NFs produced via normal ES are highly charged. As the bending instability of a charged jet initiates its movement, as-electrospun NFs are generally randomized. Further, in the presence of a single grounded conductive plate used as the collector, electrostatic forces (strong external field, collector, and any adjacent charged NFs) affect the motion of the ejected fiber and there is no preferential direction of the as-spun NFs in the collector. Consequently, NFs are randomly collected on the surface of the collector. In contrast, when an insulating gap (air) is introduced into the conductive collector, the configuration of the electric field is changed.