Fabrication of "bio-electronic nano-sensors" using the theory of activation of metal nano-tube hybridization

Note:   There  are several  problems with the methods  of making bioelectronic nanosensors using metal nanotube hybridization functionalization  . First of all, most of the nanotubes are functionalized  and as a result the electronic structure  of SWCNTs is defective. Second, due to  the strong reaction,  it is difficult to purify the product from amorphous carbon. The most important thing is that  there is no covalent reaction after which  the (m,n) nanotube can be uniquely  purified.

These reactions sometimes destroy the walls of nanotubes and lead to the formation of amorphous carbon or graphite layered structures. By hydrogenation of single-walled nanotubes, the semiconducting nature of SWCNTs increases at room temperature. Strong plasma or reaction at high temperature causes the wall of metal nanotubes to be etched. that semiconductor SWCNTs are not damaged. Therefore, it is very important to control the reaction conditions. In nanotubes, the reaction with methane plasma  removes metal SWCNTs without destroying  semiconductor SWCNTs. In  the method of using  nanomolecular soft hydrogen plasma, in which  hydrogen plasma is used to convert metallic SWCNTs into  semiconducting SWCNTs, and in  this case, the walls of the nanotubes  are not destroyed or etched. These reactions, which are carried out in the gas phase,  cause in-situ and high-scale fabrication of TFTS and  FETS with semiconductor nanotubes,  which is very important for the commercialization of high-efficiency devices  based on nanotubes. By choosing suitable reactive gases, this  method can also be used for selective reactivity with  semiconductor nanotubes. by reacting SWCNTs SO3 as  under neutral gas in the presence of gas; Reactive gas inside the furnace at a temperature of 400 C, semiconductor nanotubes  are preferred  with reactive gas . After that, the nanotube is heated to a temperature of 900°C  to restore the metal nanotubes  with structural defects. This process  is a simple way to enrich the nanotube sample Metal nanotubes. The mass production of metal nanotubes  can be done with a more precise control of the reaction conditions  and finally increase the  production scale of its uses, including conductive films and  transparent electrodes.

In general, based on the reaction rate,  selective covalent electrochemistry of metal nanotubes can  be divided into two categories:

1-  The first is that the metal nanotubes become a type of semiconductor  , which causes  the metal type to be turned off,  and the other is the removal of  the metal nanotubes .  Creates.

2- The second reaction converts  all conjugated systems into a  series of smaller aromatic compounds by  opening CC bonds in the nanotube structure  . The final result of both cases  is obtaining semiconductor nanotubes, which  are suitable for making nanoelectronic equipment  .

3- In selective covalent reactions,  reactant concentration is always important. And when the concentration of the reactant is high  , both types of nanotubes  are affected by the reaction. For example, in the case of FETS, increasing  the reactant concentration decreases the Off current,  and as a result, the Off/On ratio  increases to more than 105. On the other hand, the strong response  reduces mobility, which  is another important parameter for electronic equipment. Therefore, there should  be a balance between the progress of the reaction and the  final efficiency of the equipment.

Note: The electronic properties of carbon nanotubes are highly sensitive to the chemical environment around the nanotubes. This sensitivity is a suitable tool for using nanotubes in the sensing sector.

Nano sensors using single-walled semi-conductor carbon nanotubes, using electronic conduction, which is  grown by CVD on the substrate and  connecting a wire to the nanotubes and creating a metal/nanotube/metal structure, can make a nanotransistor that can be used in The effect of applying different voltages  will change the conductivity. The electrical conductivity of these nanotubes is used in the structure of nanosensors and electronic nanosensors of   single-walled  carbon nanotubes  . A hole-enhanced semiconductor  whose electrical conductivity is reduced by three times due to the application of a positive gate voltage to  this nanosensor system. In the presence of electronic conduction of nanosensors, the capacitance band of the nanotube moves away from the Fermi level.  This leads to a decrease in the number of holes and, as a result, a decrease in electronic conductivity  . The Fermi energy of CNT nanotubes and CNTs is in the valence band. By doing this, the concentration of holes  in the nanotube is increased, and as a result, the electrical conductivity in the nanosensors is improved.

Carbon nanotubes have a fullerene-like structure, whose ends can be closed. The name of these nanostructures is derived from their physical shape, in which a tubular sheet of graphene with different angles of tubularization leads to tubes with different symmetry  . The tube angle and  tube radius determine the appearance of metallic or  semiconductor properties in these nanostructures. Nanotubes  are divided into two categories: single-walled carbon nanotubes  (SWCNTs) and multi-walled carbon nanotubes  (MWCNTs). In multi-walled nanotubes, several graphene sheets are rolled. Carbon nanotubes stick together naturally due to van der Waals attraction.