FORMATION OF MANGANESE SILICIDE THIN FILMS BY SOLID PHASE REACTION

Manganese silicide MnSi_(2-x) thin films have been prepared on n-type siliconsubstrates through solid phase reaction. The heterostructures were analyzed by X-ray diffraction,Rutherford backscattering spectroscopy, Fourier transform infrared transmittance spectroscopy andthe four-point probe technique. The results show that two manganese silicides have been formedsequentially via the reaction of thin layer Mn with Si substrate at different irradiation annealingstages, i.e., MnSi at 450 deg C and MnSi_(1.73) at 550 deg C. MnSi_(1.73) phase exhibits preferredgrowth after irradiation with infrared. In situ four-point probe measurements of sheet resistanceduring infrared irradiation annealing show that nucleation of MnSi and phase transformation of MnSito MaSi_(1.73) occur at 410 deg C and 530 deg C, respectively; the MnSi phase shows metallicbehavior, while MnSi_(1.73) exhibits semiconducting behavior. Characteristic phonon bands ofMnSi_(2-x) silicides, which can be used for phase identification along with conventional XRDtechniques, have been observed by FTIR spectroscopy.

Improving electrical and thermal properties synchronously via introducing CsPbBr_(3)QDs into higher manganese silicides

Higher manganese silicide(HMS)is a P-type medium temperature thermoelectric(TE)material,which has attracted widespread attention over the past few decades due to its remarkable mechanical properties,excellent chemical and thermal stability,as well as the non-toxicity,abundance and competitive price.The peak power factor(PF)of HMS is as high as~1.50×10^(-3)W m^(-1)K^(-2)because of its intrinsic high electrical conductivity and Seebeck coefficient.However,the thermal conductivity of HMS is also high,resulting in relatively low z T values.Introducing nano-dispersion in the matrix is one of the most effective methods to enhance the TE properties via reducing the lattice thermal conductivity significantly without drastic changes on the other parameters.In this study,Cs Pb BrQDs with uniform size were synthesized and introduced into HMS bulks.The PF(at 823 K)was enhanced to 1.71×10^(-3)W m^(-1)K^(-2),which is improved 14.0%approximately compared with that of pure HMS owing to the combined effect of element doping and energy filtering.The lattice thermal conductivity(at 823 K)decreased from 2.56W mKto 1.99 W mKsynchronously(~22.0%)due to the intensive phonon scattering caused by Cs doping,and the embedding of Pb riched CsPbBr_(3)QDs and Pb QDs.A maximum z T value of 0.57(823 K)is achieved in Cs Pb BrQDs/HMS composites,which is 36.0%higher than that of pure HMS.Predictably,for other TE materials,it is also feasible to improve the TE properties via introducing metastable quantum dots.

Incorporating element doping and quantum dot embedding effects to enhance the thermoelectric properties of higher manganese silicides

Element doping and nano-inclusion embedding are effective approaches to enhance the electrical conductivities and decrease the lattice thermal conductivities of thermoelectric(TE)materials,respectively.However,the intrinsic low electrical thermal conductivities and high electrical properties are severely sacrificed,and the final figure of merit(ZT)is usually restricted.In this study,Ag doping and Pt quantum dot(QD)embedding were synchronously achieved via embedding Ag/Pt alloy QDs into the higher manganese silicides to avoid the conventional single-element doping strategy.The power factor(at 823 K)was enhanced from 1.57×10^(-3) W m^(-1) K^(-2) to 1.82×10^(-3) W m^(-1) K^(-2)(-16%)due to the-18%increase in carrier concentration that was derived from the Ag doping effect.Simultaneously,the lattice thermal conductivity(at 823 K)decreased from 2.65 W m^(-1) K^(-1) e1.92 W m^(-1) K^(-1)(-28%)because of the broadband phonon scattering effect that resulted from the residual Pt QDs inclusions.Synthetically,the optimal ZT value increased by-52%from 0.42 to 0.64 at 823 K.This study demonstrated that incorporating metastable alloy QDs to obtain element doping and nano-inclusion embedding effects is a novel and feasible means to enhance the ZT value of HMS.This method is also possibly applicable to other alloy QD/TE composites.