Study of Properties of Lead Selenide （PbSe） Thin Films Deposited on TiO2

The study of nano properties of PbSe （lead selenide） thin films deposited on TiO2 semi conductor film prepared by sol gel method was a new work destined to perfect the nano materials used in photovoltaic energy. The growth of the first group of the fihns （Set 1： P（9）） ＆ P（14）） was based on the decomposition of lead citrate and sodium selenosulphite in the presence of sodium citrate and sodium hydroxide with ammonia and triethalamine （TEA） acting as the complexing agents and P.H stabilizers; while in the second group （Set 2： Pc15~）, the reaction bath was made up of solutions of lead nitrate Pb（NO3）2, PVA （polyvinyl alcohol）, H20 （distilled water）, NH3 （ammonia）, sodium selenosulphite （Na2SeSO3） and Triethalamine [N（CH2CH2OH）], which was used as the complexing agent. The deposited materials were identified by X-ray diffraction. In addition, nano optical and morphological investigations were also performed. The sample P9 has the lowest absorbance of about 0.3 nm in the ultra-violet region. It was found that there was a reduction in the optical absorbance as the wavelength increases. The optical band gap shows a range of 1.26-2.00 eV with sample PcIs~ having the lowest direct band gap.

Selective formation of ultrathin PbSe on Ag(111)

Two-dimensional(2D)semiconductors,such as lead selenide(PbSe),locate at the key position of next-generation devices.However,the ultrathin PbSe is still rarely reported experimentally,particularly on metal substrates.Here,we report the ultrathin PbSe synthesized via sequential molecular beam epitaxy on Ag(111).The scanning tunneling microscopy is used to resolve the atomic structure and confirms the selective formation of ultrathin PbSe through the reaction between Ag5Se2 and Pb,as further evidenced by the theoretical calculation.It is also found that the increased accumulation of Pb leads to the improved quality of PbSe with larger and more uniform films.The detailed analysis demonstrates the bilayer structure of synthesized PbSe,which could be deemed to achieve the 2D limit.The differential conductance spectrum reveals a metallic feature of the PbSe film,indicating a certain interaction between PbSe and Ag(111).Moreover,the moirépattern originated from the lattice mismatch between PbSe and Ag(111)is observed,and this moirésystem provides the opportunity for studying physics under periodical modulation and for device applications.Our work illustrates a pathway to selectively synthesize ultrathin PbSe on metal surfaces and suggests a 2D experimental platform to explore PbSe-based opto-electronic and thermoelectric phenomena.

Incubation of PbSe Thin Films in a Tin(Ⅱ) Salt Aqueous Solution:Modification and Ion-Exchange Reactions

Topochemical ion-exchange reactions between solid micro- and nanostructured metal chalcogenides and aqueous salt solutions are generally used for formation of composite structures based on initial metal chalcogenides and products of their ion-exchange transformation. However, ion exchange has promises as a route to obtaining both composites and solid solutions based on the initial and the end chalcogenide phases. With the help of the ion-exchange technique, single-phase films of Phi xSnxSe substitutional solid solutions with a tin content up to -2 at.%, which are promising for mid- and long-wavelength infrared radiation （IR） optoelectronics, have been obtained at the interface between PbSe poly- crystalline thin films and SnCl2 aqueous solutions containing sodium citrate. It has been shown that the pH value and temperature of the reaction system play an important role in the ion-exchange process. Incubation of lead selenide （PbSe） films in a tin（II） salt aqueous solution also leads to their modification with oxygen-containing tin compounds to a depth of-3 nm. Differences in the film structure, such as changes in the coherent scattering region sizes and orientation of crystallites along the [220] direction, which arise during the contact with citrate-containing SnCl2 solutions, have also been revealed. For the first time, an idea of the existence of a relatively wide reaction zone of an intragranular topochemical ion-exchange reaction in an aqueous solution, within which substitutional solid solutions can form in micro- and nanostructured systems, has been set forth.