Significance Due to the unique mechanical, electrical, thermal and optical properties, one-dimensional nanomaterials have a wide range of applications in micro- and nano- electro-mechanical systems, flexible transparent conductive devices, and sensors. Different from zero-dimensional and two-dimensional nanomaterials, one-dimensional nanomaterials have larger ratios of length to diameter. To build nano-structures or nano-devices with one-dimensional nanomaterials, both the position and posture (or rotation angle) need to be considered. Therefore, how to precisely control the pose of one-dimensional nanomaterials and then connect them with nanoscale, microscale, or bulk materials is crucial to realize the functionalization and deviceization of nanostructures.

Although one-dimensional nanomaterials have a variety of applications, precise manipulation of their pose and forming a reliable nanoscale interconnection with other materials are still great challenges. It is well known that nanomaterials have a small size, which makes them difficult to manipulate their poses. Manipulation methods, such as mechanical clamping, can easily cause damage to nanomaterials. In addition, the small size of nanomaterials results in a large specific surface area and high surface energy, which significantly reduces the melting point of nanomaterials and makes the nanomaterials susceptible to oxidation. How to connect nanomaterials and other materials without affecting the non-connection parts of nanomaterials is crucial for preparing high-performance nano-joints. To connect nanomaterials, many methods have been proposed, including mechanical pressing, thermal annealing, chemical treatment, cold welding, and light-induced plasmonic nanojoining. One of the potential nanojoining technologies is light-induced plasmonic nanojoining, which utilizes white light or laser to excite local surface plasmon resonances, thereby resulting in local heating. By precisely adjusting the intensity of the incident laser, the connection position of nanomaterials can be slightly melted, resulting in nanojoining of nanomaterial with other materials. Light-induced plasmonic nanojoining is a high-efficiency and low-damage nanojoining method.

In the past few years, various methods have been developed to manipulate the pose of one-dimensional nanomaterials, and then to join them by laser. According to the principle of nano-manipulation, these nano-manipulation methods are summarized into three types: probe method, self-assembly, and optical tweezers. Combining the pose manipulation with laser-induced plasmonic nanojoining of one-dimensional nanomaterials, we introduce the principles and characteristics of pose regulation of one-dimensional nanomaterials in detail, as well as the new development in laser-induced plasmonic nanojoining.

Progress The probe method utilizes probes to move and rotate one-dimensional nanomaterials to adjust their poses precisely. Due to the small size of one-dimensional nanomaterials, the probe tip is generally on the nanoscale. In addition, to manipulate the poses of one-dimensional nanomaterials, the probe method usually requires high-resolution microscope to locate nanomaterials. The microscopes used in the probe method include optical microscope (Fig.1), atomic force microscope (Fig.3), and scanning electron microscope (Fig.4), and these probes include nano-fiber probes, atomic force microscope probes, and nano-tungsten needles.

Joining larger-scale one-dimensional nanomaterials is one of the keys for the realization of deviceization. A potential manipulation method is self-assembly. According to the principle of self-assembly of nanomaterials, there are three types of self-assembly methods. First, nanomaterials are subject to gravitational or repulsive force in solutions, and then self-assembly is realized under dynamic equilibrium. Second, nanomaterials are self-assembled through the Langmuir-Blodgett technology by the surface tension of liquid-gas or solid-liquid interfaces. Third, under the action of external fields, such as electric field, magnetic field, and light field (Fig.6), the polarized nanomaterials are moved along the gradient direction, and the moving direction of polarized nanomaterials is determined by the relative permittivity of the solution and the nanomaterials (Fig.5).

To further improve the precision and efficiency of nano-operation, optical tweezers are used to manipulate the poses of one-dimensional nanomaterials. Single-beam optical tweezer has been used to manipulate the poses of semiconductor nanowires (Fig.7). To improve the stability of nano-manipulation, holographic optical tweezers or optical tweezer arrays are used for nano-manipulation (Fig.8). Photons have momentum. The exchange of momentum between photons and nanomaterials produces scattering forces. Unless the gradient force generated by the optical tweezers can overcome the scattering force acting on nanomaterials, or the nanomaterials are pushed away by the scattering force. For wide-bandgap semiconductor materials, infrared lasers can pass through one-dimensional nanomaterials. Therefore, the scattering force acting on one-dimensional nanomaterials is very weak. But for metal nanomaterials, the scattering force acting on them increases significantly due to their good conductivity. As a result, it is difficult to use conventional optical tweezers to manipulate the poses of one-dimensional metal nanomaterials. To manipulate the poses of metal nanomaterials, plasma tweezers are developed (Fig.9).

Conclusions and Prospects According to the characteristics of the aforementioned nano-manipulation technology, it is observed that the probe technology can be used to manipulate the pose of one-dimensional nanomaterials, to test the conductivity and reliability of the laser-prepared nanostructures. However, the probe technology has a low efficiency of nano-manipulation efficiency. Self-assembly technology has unique advantages in the larger-scale operation of one-dimensional nanomaterials, but the commonly used dielectrophoresis methods need to be performed under a specific electrode structure, and the precision of nano-manipulation is relatively low. Optical tweezer technology has high nano-operation accuracy. The laser source can be used for nano-operation and nanojoining, but it needs to be carried out in solutions. These problems indicate that improving the compatibility of self-assembly and optical tweezer technology with the existing microelectronic processes is the focus of future research. Based on the above research results, we believe that multi-technology integration is the future development trend. It is found that nano-manipulation technology is merging with laser, microscopy, and nano-testing technology to realize nano-observation, nano-operation, nano-joining, and nano-testing. This kind of multi-functional technology and equipment will further promote the development and application of nano-technology, promote multi-disciplinary cross, and produce more innovative applications.