**3.2. Mechanical properties of DNWs**

Tanskanen et al. described the mechanical properties of DNWs through Poisson's ratios, Young's moduli and shear moduli interrogations [66], which proved that (111) DNWs have the highest Young's moduli than the (110) and (111) DNWs. In this report, they suggest that polyicosahedral DNWs have more strain than that of conventional DNWs. In this way, Guo and coworkers presented the mechanical properties of (001) DNWs by means of molecular dynamics simulations [68] and specified that Young's modulus of those DNWs is lower than those of bulk diamond. Similarly, Jiang et al. explored Young's modulus of DNWs in different crystallographic orientations as a function of cross-sectional area [69]. Wherein, Young's modulus has the sequence of (100), (110), (111) and (112) directions and indicated that those values are lower than the bulk value and increase with its cross-sectional area.

than the CNT and depends on the choice of thermostat [73]. Similarly, Guo et al. described that the thermal conductivity of DNWs may rise with respect to the increase in length and cross-sectional areas [74]. Recently, as seen in **Figure 7**, our group also proved the downfall in the conductivity of a single G-DNW with respect to a decrease in temperature [63]. Overall, it has been concluded that between 0 and 1000 K, DNW's thermal conductivities firstly upsurge

Diamond Nanowire Synthesis, Properties and Applications

http://dx.doi.org/10.5772/intechopen.78794

27

**Figure 7.** Temperature-dependent conductivity of DNW L2. Reproduced with permission from [63].

Next, coming to the electrochemical properties, it is well recognized that the planar borondoped diamond (BDD) materials have the unique physical properties and were already been effectively applied as electrodes in many sensing studies. Wherein, compared to glassy carbon electrode, the diamond electrode acts as a potential candidate due to its chemical stability and biocompatibility [75]. Moreover, BDD electrode is not fouled easily and has a low background current with a wide potential window. By altering the surface end of BDD, the electronic and chemical properties can be tuned according to the requirement. Currently, the BDD nanograss array is also involved in electron transport and electrocatalytic utilities [76, 77]. Conclusively, it is well established that the nanotextured DNW surfaces become the suitable

Among the applications of DNWs, the following five utilities have been demonstrated strongly. Those applications are (1) field emission applications of DNWs, (2) DNWs in mass analysis of small molecules, (3) DNWs as nanoelectromechanical switches, (4) DNWs as elec-

The negative electron affinity of DNWs has been used in field emission studies. Recently, reports on the electron field emission (EFE) properties of CVD-developed ultracrystalline

trochemical sensors and (5) DNWs in ultrasensitive force microscopy.

with an increasing temperature and then dropdown.

platform for novel biosensor investigations.

**4.1. Field emission applications of DNWs**

**4. Applications of DNWs**

#### **3.3. Density and compressibility of DNWs**

Initially, Dubrovinskaia and Dubrovinsky reported the density of the aggregated diamond nanorods (ADNRs), which were developed from fullerene C60 by multi-anvil apparatus [61]. The X-ray density of ADNRs is about 0.2–0.4% greater than the bulk diamond, which also corresponds to the measured density of 3.532(5) g cm−3. The higher density of ADNRs may arise from the outerlayer contraction leading to shortening of the C-C bonds inside the diamond. In this work, they have also evaluated the compressibility of ADNRs by using the third-order Birch-Murnaghan equation of state, wherein they established the >11% lesser compressibility of ADNRs than that of usual diamond.

#### **3.4. Phonon optical modes and electronic properties of DNWs**

Trejo and coworkers reported the optical phonons and Raman-scattering properties of DNWs by using a local bond polarization model based on the displacement–displacement Green's function and the Born potential [70]. Further, they have also studied the electronic band structure of DNWs through a semiempirical tight-binding approach and compared with density functional theory (DFT) studies. From the calculations, they have concluded that phonons and electrons tend to show a clear quantum confinement signature. Moreover, this study also establishes that during the DNWs width increase, the Raman peak shifts to lower frequencies due to the phonon confinement, as reported by our group [71]. Subsequently, the band gap also decreases as the width of the DNWs increases.

## **3.5. Thermal conductivity and electrochemical properties of DNWs**

In general, it is recognized that the thermal conductivity of DNWs may not be incredibly affected by surface functionalization. However, at nanometer scale, dimensions of DNWs may reduce the thermal conductivity than that of bulk diamond as demonstrated by Novikov et al. [72]. In this way, Moreland and coworkers explored that the conductivity of DNW is lower

**Figure 7.** Temperature-dependent conductivity of DNW L2. Reproduced with permission from [63].

than the CNT and depends on the choice of thermostat [73]. Similarly, Guo et al. described that the thermal conductivity of DNWs may rise with respect to the increase in length and cross-sectional areas [74]. Recently, as seen in **Figure 7**, our group also proved the downfall in the conductivity of a single G-DNW with respect to a decrease in temperature [63]. Overall, it has been concluded that between 0 and 1000 K, DNW's thermal conductivities firstly upsurge with an increasing temperature and then dropdown.

Next, coming to the electrochemical properties, it is well recognized that the planar borondoped diamond (BDD) materials have the unique physical properties and were already been effectively applied as electrodes in many sensing studies. Wherein, compared to glassy carbon electrode, the diamond electrode acts as a potential candidate due to its chemical stability and biocompatibility [75]. Moreover, BDD electrode is not fouled easily and has a low background current with a wide potential window. By altering the surface end of BDD, the electronic and chemical properties can be tuned according to the requirement. Currently, the BDD nanograss array is also involved in electron transport and electrocatalytic utilities [76, 77]. Conclusively, it is well established that the nanotextured DNW surfaces become the suitable platform for novel biosensor investigations.
