## 2 Materials and Methods
### Sample Preparation
The Au underlayer was the working electrode and a platinum (Pt) strip acted as the auxiliary electrode (Figure 1c). Electrodeposition duration was adjusted to 250-300 s to avoid the nanoporous AAO template overfilling and obtain the Cu NWs in a free-standing vertical orientation on the Au-coated Si substrate. The obtained cathodic reduction current curve for Cu electrodeposition inside the AAO nanopores is presented in Figure 2b, resembling to the typical behavior of an AAO-assisted chronoamperometric process. It can be seen that fast diffusion of cations occurs first towards the bottom of the nanopores. This is suggested by the sharp negative increase in the current, subsequently followed by a current plateau when the gradient of ion concentration in the solution reaches an equilibrium, which mainly relates to the vertical growth of NWs within the AAO nanopores. The vertically-standing arrays of Cu NWs were revealed by entirely dissolving the AAO template in a 2 M NaOH solution for 10 min at room temperature, then gently rinsing the samples with DIW and leaving them to dry in a vacuum desiccator to prevent the superficial oxidation of the Cu NWs under ambient conditions before further manipulation. The optimized preparation conditions determined the formation of dense and robust arrays of vertically-standing Cu NWs with an average diameter value around 90 nm, a center-to-center distance of about 150 nm, and typical lengths of 350 nm (see Section 3.1). Figure 1: Schematic representation of the fabrication process for obtaining CdTe-embedded interfaces based on Cu NWs: (**a**) substrate preparation by in-situ DC magnetron sputtering of Ti (5 nm)/Au (50 nm)/Ti (5 nm)/Al (1 μm) layers on a \(<\)100\(>\) p-doped Si substrate (Ti ultra-thin films are not represented for convenience); (**b**) supported nanoporous Al\({}_{2}\)O\({}_{3}\) template fabrication through anodization of the entire Al film and subsequent chemical widening of the nanopores; (**c**) electrochemical synthesis of Cu within the aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) nanopores; (**d**) complete removal of the Al\({}_{2}\)O\({}_{3}\) template and CdTe deposition on top of the Cu NW array. In a second stage, the prepared arrays of vertically-oriented Cu NWs were covered with thin CdTe films, employing three different deposition methods (Figure 1d): (i) vacuum thermal evaporation (VTE); (ii) radio-frequency magnetron sputtering (RF-MS); and (iii) electrochemical deposition (ECD). The evaporated CdTe thin films were obtained at a working pressure of \(8\times 10^{-4}\) torr, a substrate temperature of 260 \({}^{\circ}\)C, and a source (CdTe powder) temperature of 650 \({}^{\circ}\)C, while the evaporation time was set to 3 min using a Balzers BA 510 evaporation system (Oerlikon Balzers Limited, Balzers, Liechtensen). The VTE process was followed by thermal treatment of the samples at 320 \({}^{\circ}\)C for 10 min, mainly to improve the CdTe intrinsic morphology and crystallinity. For the CdTe RF-MS procedure, a commercial CdTe target (PI-KEM Limited, Wilnecotte, Tamworth, United Kingdom) was employed, and the RF plasma was engaged at 90 W in an Argon (Ar) atmosphere kept at \(4.4\times 10^{-3}\) mbar for a duration of 90 min using a tectra Sputter-Coater (tectra GmbH, Frankfurt, Germany). The substrate temperature during the RF-MS process was maintained at 250 \({}^{\circ}\)C.  
A commonly-established CdTe ECD protocol was performed according to the existing literature reports [28; 29; 30; 31] and subsequently adapted to be applied on the particular Cu NWs-based Au-coated Si substrate. The ECD process used here relied on a chronoamperometric technique applied in a Te-diluted electrolytic solution consisting of 0.5 M 3 CdSO4 -8H2O, 0.5 mM TeO2, and 25 mM H2 SO4 (95% concentrated).