## 3 Synthesis of Transition-Metal-Sulfide-Based Nanomaterials
### Chemical Vapor Deposition (CVD)/Physical Vapor Deposition (PVD)/Plasma Synthesis  
CVD and PVD techniques as well as plasma techniques were utilized for the synthesis of TMS for multiple purposes. PVD consists of vaporizing a solid for deposition under vacuum, which showed to have great control in synthesis. While CVD is a vapor deposition technique from a thin film, the two techniques are very similar, however, the major difference is the deposition material in PVD is a solid and in CVD, it is a gaseous molecule. Additionally, the temperatures used in CVD are typically higher than PVD. Plasma deposition is generally a process defined as the deposition of a material from the action of a plasma. [PERSON] et al. synthesized a bimetallic Ni\({}_{3}\)S\({}_{2}\)/MnS\({}_{2}\) composite nanomaterial using PVD [99]. The authors used metal nitrates in conjunction with CS\({}_{2}\), in a two-step synthesis process. A thiocarbamate precursor was synthesized and decomposed in a tube furnace in an inert atmosphere and Ni\({}_{3}\)S\({}_{2}\)/MnS\({}_{2}\) nanoparticles were synthesized. [PERSON] et al. utilized atmospheric pressure CVD to synthesize CdS, ZnS, Cu\({}_{7.2}\)S\({}_{4}\), NiS, CoS, Fe\({}_{7}\)S\({}_{8}\), MnS, Cr\({}_{2}\)S\({}_{3}\), and WS\({}_{2}\) nanowires [100]. The nanoparticles synthesized through the CVD process averaged between 20 and 30 nm on the low end to 100-150 nm on the high end and ranged in length from 1 to 40 \(\upmu\)m. [PERSON] et al. used CVD to deposit 2-D TMS nanoparticles on carbon paper for electrocatalytic hydrogen evolution [139]. The authors grew MoS\({}_{2}\), NbS\({}_{2}\), and WS\({}_{2}\) nanosheets, where WS\({}_{2}\) showed the highest HER activity with an average size between 100 and 200 nm. The MoS\({}_{2}\) had an average size of 500 nm while the NbS\({}_{2}\) had an average size of 500 nm. [PERSON] and [PERSON] used CVD to synthesize NiS nanoplates, the authors used diethyl amine and CS\({}_{2}\) which synthesized a Ni-dithiocarbamate complex. The compound was decomposed in an inert atmosphere at 400 \({}^{\circ}\)C to generate NiS [140]. [PERSON] et al. used a CVD technique to synthesize CdS nanorods [141]. The authors used a Cd dithiocarbonate which was decomposed in a tube furnace at 450 \({}^{\circ}\)C in nitrogen. The CdS nanoparticles had a tetrapodal geometry with an average size between 4 and 5 nm. [PERSON] et al. synthesized phase-pure CuS nanostructures using a CVD technique [142]. The authors used a single precursor Bis(O-isobutyldithiocarbono)copper(II) complex [Cu(SCSCOCH\({}_{2}\)CH(CH\({}_{3}\))\({}_{2}\))\({}_{2}\)] and decomposed the material at temperatures from 250 to 350 \({}^{\circ}\)C. The CuS formed at 250 \({}^{\circ}\)C was spherical in morphology, at 300 \({}^{\circ}\)C, the nanoparticles had plate-like morphology, and at 350 \({}^{\circ}\)C the authors noted a flower morphology. [PERSON] et al. used non-thermal plasma deposition for the synthesis of a MoO\({}_{3}\)@MoS\({}_{2}\)-CuS composite nanomaterial for light harvesting [101]. The authors used sodium molybdate in conjunction with MoO\({}_{3}\) nanorods and ultrasonic treatment. The authors added MoO\({}_{3}\) and Cu(NO\({}_{3}\))\({}_{2}\) and dried and placed them in a plasma to be sulfided using H\({}_{2}\)S/Ar at 100 W for 40 min. The results showed the formation of nanomaterials with an average grain size of 50 nm for the MoS\({}_{2}\) and micron sized MoO\({}_{3}\) particles. The CuS size was not discussed. [PERSON] et al. used cold plasma (non-thermal plasma) to synthesize Cr-doped ZnS catalysts for H\({}_{2}\)S decomposition [143]. The authors prepared an impregnated Al\({}_{2}\)O\({}_{3}\) support with Zn and Cr in an aqueous solution to prepare the precursor, which was calcined at 450 \({}^{\circ}\)C in air. The calcined sample was then sulfurized in a cold plasma (400 \({}^{\circ}\)C) using a mixture of (Ar:H\({}_{2}\)S 90%:10%) resulting in 8 nm nanoparticles. [PERSON] et al. used low-temperature plasma for the synthesis of 2D TMS, TiS\({}_{2}\), and TiS\({}_{3}\) nanolayers [144].