## 3 Results and Discussion
### A Model for the Tunnel Photocurrent within the Structure  
In contrast to traditional metal photosensors with a flat radiation receiver, the surface of the sensitive element being investigated has a two-dimensional structure, where the depth of topological irregularities can be compared with the radiation wavelength. Therefore, as a result of the direct and reflected wave interference, we find a complex pattern of standing waves, particularly near the tip of the emitter blade (see Figures 2 and 3). The calculations also showed that, when the emitter is irradiated by electromagnetic radiation of the visible or near IR range, the penetration depth of electromagnetic waves into the molybdenum blade (the skin depth) can be about 30 nm (distribution of the normalized specific absorption power at the depths up to 20 nm is shown in Figure 4). In this case, the diffraction effects of the fields in the vacuum form significant spatial inhomogeneity of the optical field and inside the emitter along the blade perimeter, as shown in Figure 4. This leads to substantial inhomogeneity of the specific absorption power not only along the depth of the skin layer, but also along the perimeter of the tip of the blade. In the external strong electrostatic field, the height of the potential barrier over the metal surface decreases by  
\[\Delta\varphi=(e^{3}F)^{1/2}=1.2\ (F(\mathrm{V/nm}))^{1/2}, \tag{3}\]  
where \(e\) is the absolute value of electron charge. Figure 5: Dependencies of the squared modulus of the optical field along the generatrix 0–5 of the emitter molybdenum blade section inside (**a**) and outside (**b**) the surface; dependence of electrostatic field at the unit potential \(\mathrm{U}_{g}\) along the perimeter of the generatrix 0–5 (**c**) and a two-dimensional vicinity of the emitter blade tip (**d**). Then, the tunneling probability of the hot electrons from the emitter surface when exposed to optical radiation in both the visible and near-IR ranges increases exponentially. This happens despite the low photon energy, which is noticeably less than the work function \(\varphi_{0}\). The results provided in the recent works [5; 12; 13; 25; 26] demonstrate the experimental observation of the tunnel photoemission. As follows from the analysis of strength distribution in the electrostatic field presented in Figure 5c,d, the localization zone in the emitter is limited to the part of the segment designated by the points 3 and 4. According to (3), it is only in this zone that the Schottky barrier decreases to the maximum, whereas the permeability increases, respectively, and conditions can arise for the tunneling of photoelectrons into the vacuum. A generalized scheme and mechanisms for sequential irradiation of the tip of the blade, generation of hot electrons at the volume of the molybdenum emitter skin layer, the transport of hot electrons from the layer with \(L_{\tau}\) thickness to the surface of the emitter, and their tunneling into the vacuum in the localization zone of the electrostatic field are given in Figure 6.  
The probability of tunneling of nonequilibrium photoelectrons generated in the surface layer of molybdenum with the thickness \(L_{\tau}\) with the energy \(E_{F}+h\
u\) and the momentum directed normally to the surface of the emitter is determined by the following relationship [13; 21]:  
\[D_{\lambda}=\exp\left[-\frac{8\pi/3\cdot(\sqrt{2m}/h)(\varphi-h\
u)^{3/2}}{eF }\vartheta(y)\right] \tag{4}\]  
Here, \(h\
u\) is the energy of irradiating photons, \(y\equiv(e^{3}F)^{1/2}/(\varphi-h\
u)\) is the relative decrease in the potential barrier height for nonequilibrium photoelectrons, \(\vartheta(y)\) is the Nordheim elliptic function, the range of the argument variation is \(1>y\geq 0\), \(m\) is the effective mass electron, and \(F\) is intensity of the electrostatic field.