Accordingly, we adopted

the Γn, physically defined as the

Accordingly, we adopted

the Γn, physically defined as the product of η, τ, and μ (i.e., Γn = ητμ) [45, 48]. As the τμ product is an intrinsic quantity determining photocarrier transport efficiency [42], for a constant η, Γn offers the same www.selleckchem.com/products/tpca-1.html physical meaning as τμ, and its intrinsic property can exclude the effects of selleck kinase inhibitor device dimension and experimental condition. In addition, Γn with the factor of η could take the real light absorption efficiency into account, whose importance has been demonstrated to further understand the PC process in 1D nanostructures [49]. Γn can be obtained by the following equation [45, 48]: (1) The calculated Γn versus I using the data of Γ (Figure  2c) or i p (Figure  2b) for the V2O5 NW measured at V = 0.1 V under 325-nm (E = 3.82 eV) and 808-nm (E = 1.53 eV) illuminations are illustrated in Figure 

4c. One data point of hydrothermal-synthesized selleckchem V2O5 NWs calculated according to the data in [2] (E = 2.76 eV) is also plotted for comparison. After excluding the artificial contributions of l and V, the Γn of our PVD-grown V2O5 NWs at approximately 6 × 10-3 cm2 V-1 is two orders of magnitude higher than that (Γn ~ 5 × 10-5 cm2V-1) of the hydrothermal-synthesized ones for the similar I = 25 ± 5 W m-2. This result indicates the PVD-grown NWs exhibit a higher efficiency for photocarrier transport and photocurrent generation than the hydrothermal ones. The PVD (or thermal evaporation) approach usually provides better control for crystal growth, and the growth temperature at 550°C is also relatively high in comparison

with that in the hydrothermal method (synthesis at 205°C). Accordingly, it is inferred that the higher PC efficiency (or Γn) originated from a higher crystalline quality in this PVD-grown V2O5 nanostructure. In addition, Figure  4c also shows that the Γn at 325-nm excitation is also much higher than that at 808-nm excitation. The optimal (saturation) Γn at λ = 325 nm is 1.7 ± 0.2 × 10-2 cm2 V-1 which is over three orders of magnitude higher than that (Γn = 4.7 ± 0.6 × 10-6 cm2 V-1) at λ = 808 nm in air ambience. The Γn enhanced in the vacuum can also be observed therein. The analysis quantitatively demonstrates the difference of PC efficiency induced by above- and below-bandgap excitations. As Γn linearly depends on η and τ and the volume Bcl-w for optical absorption (or η) of the bulk by inter-bandgap excitation is much higher than that of the surface under sub-bandgap excitation, it is proposed that η plays an important role on the Γn difference for the wavelength-dependent PC. The relatively long photoresponse time (or τ) could also contribute to the higher Γn under inter-bandgap (325 nm) excitation. Finally, it is noted that the PC mechanism based on the small polaron hopping transport has been proposed by Lu et al. [21]. The very short lifetimes in the range of 1 to 1,000 μs are usually one of the criteria to manifest the polaron hopping mechanism.

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