Filled carbon nanotubes (CNTs) and methods of synthesizing the same are provided. An in situ chemical vapor deposition technique can be used to synthesize CNTs filled with metal sulfide nanowires. The CNTs can be completely and continuously filled with the metal sulfide fillers up to several micrometers in length. The filled CNTs can be easily collected from the substrates used for synthesis using a simple ultrasonication method.

A method of performing heteroepitaxy comprises exposing a substrate to a carrier gas, a first precursor gas, a Group II/III element, and a second precursor gas, to form a heteroepitaxial growth of one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN on the substrate; wherein the substrate comprises one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN; wherein the carrier gas is Hz, wherein the first precursor is HCl, the Group II/III element comprises at least one of Zn, Cd, Hg, Al, Ga, and In; and wherein the second precursor is one of AsH.sub.3 (arsine), PH.sub.3 (phosphine), H.sub.2Se (hydrogen selenide), H.sub.2Te (hydrogen telluride), SbH.sub.3 (hydrogen antimonide), H.sub.2S (hydrogen sulfide), and NH.sub.3 (ammonia). The process may be an HVPE (hydride vapor phase epitaxy) process.

A method for making a transition metal dichalcogenide crystal having a chemical formula represented as MX.sub.2 is provided, wherein M represents a central transition metal element, and X represents a chalcogen element. The method includes providing a MX.sub.2 polycrystalline powder, a MX.sub.2 seed crystal, and a transport medium. The MX.sub.2 polycrystalline powder and the transport medium are placed in a first reaction chamber. The first reaction chamber and the MX.sub.2 seed crystal are placed in a second reaction chamber having a source end and a deposition end opposite to the source end. The first reaction chamber is placed at the source end, and the MX.sub.2 seed crystal is placed at the deposition end.

A method for making a transition metal dichalcogenide crystal having a chemical formula represented as MX.sub.2 is provided, wherein M represents a central transition metal element, and X represents a chalcogen element. The method includes providing a MX.sub.2 polycrystalline powder, a MX.sub.2 seed crystal, and a transport medium. The MX.sub.2 polycrystalline powder and the transport medium are placed in a first reaction chamber. The first reaction chamber and the MX.sub.2 seed crystal are placed in a second reaction chamber having a source end and a deposition end opposite to the source end. The first reaction chamber is placed at the source end, and the MX.sub.2 seed crystal is placed at the deposition end.

The present disclosure relates to P-type SnSe crystal capable of being used as thermoelectric refrigeration material and a preparation method thereof. The material is a Na-doped and Pb-alloyed SnSe crystal. A molar ratio of Sn, Se, Pb and Na is (1-x-y):1:y:x, where 0.015≤x≤0.025 and 0.05≤y≤0.11. The P-type SnSe crystal provided by the present disclosure is capable of being used as the thermoelectric refrigeration material. A power factor PF of the P-type SnSe crystal at a room temperature is ≥70 μWcm.sup.−1K.sup.−2, and ZT at the room temperature is ≥1.2. A single-leg temperature difference measurement platform built on the basis of the obtained SnSe crystal may realize a refrigeration temperature difference of 17.6 K at a current of 2 A. The present disclosure adopts a modified directional solidification method and uses a continuous temperature region for slow cooling to grow a crystal to obtain the large-sized high-quality SnSe crystal.

The present disclosure relates to P-type SnSe crystal capable of being used as thermoelectric refrigeration material and a preparation method thereof. The material is a Na-doped and Pb-alloyed SnSe crystal. A molar ratio of Sn, Se, Pb and Na is (1-x-y):1:y:x, where 0.015≤x≤0.025 and 0.05≤y≤0.11. The P-type SnSe crystal provided by the present disclosure is capable of being used as the thermoelectric refrigeration material. A power factor PF of the P-type SnSe crystal at a room temperature is ≥70 μWcm.sup.−1K.sup.−2, and ZT at the room temperature is ≥1.2. A single-leg temperature difference measurement platform built on the basis of the obtained SnSe crystal may realize a refrigeration temperature difference of 17.6 K at a current of 2 A. The present disclosure adopts a modified directional solidification method and uses a continuous temperature region for slow cooling to grow a crystal to obtain the large-sized high-quality SnSe crystal.

A method for preparing a large-size two-dimensional layered metal thiophosphate crystal includes the following steps: 1) weighing raw materials of indium spheres, phosphorous lumps and sulfur granules according to a predetermined amount and proportion, mixing them, and using iodine as a transport agent and potassium iodide as a molten salt; 2) adding the raw materials, the iodine and the potassium iodide to a reaction vessel together, and vacuum sealing it under a certain pressure, and then subjecting it to a high-temperature reaction; 3) taking out the products after the reaction, and washing the products to remove the residual iodine and potassium iodide and obtain large-size two-dimensional layered metal thiophosphate crystals. This method is simple and highly efficient.

A method for preparing a large-size two-dimensional layered metal thiophosphate crystal includes the following steps: 1) weighing raw materials of indium spheres, phosphorous lumps and sulfur granules according to a predetermined amount and proportion, mixing them, and using iodine as a transport agent and potassium iodide as a molten salt; 2) adding the raw materials, the iodine and the potassium iodide to a reaction vessel together, and vacuum sealing it under a certain pressure, and then subjecting it to a high-temperature reaction; 3) taking out the products after the reaction, and washing the products to remove the residual iodine and potassium iodide and obtain large-size two-dimensional layered metal thiophosphate crystals. This method is simple and highly efficient.

Methods and systems are provided for a homogenous, single crystal, electrically conductive, and narrow bandgap PbSe nanostructure is synthesized using a chemical bath deposition on, for example, quartz substrates, and includes a tunable iodine doping process to select the size and/or shape of the nanostructures. The single crystalline PbSe nanostructure can be exposed following an isolation process (e.g., etching process), and the concentration and/or distribution of iodine across multiple PbSe nanostructures (e.g., on a quartz substrate) can be adjusted during post processing steps, including heat treatments.

Methods and systems are provided for a homogenous, single crystal, electrically conductive, and narrow bandgap PbSe nanostructure is synthesized using a chemical bath deposition on, for example, quartz substrates, and includes a tunable iodine doping process to select the size and/or shape of the nanostructures. The single crystalline PbSe nanostructure can be exposed following an isolation process (e.g., etching process), and the concentration and/or distribution of iodine across multiple PbSe nanostructures (e.g., on a quartz substrate) can be adjusted during post processing steps, including heat treatments.