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Thermomechanical and Martensitic Transformation Stresses of NiTi/Si Thin Film Composites
Kim, T S,Roytburd, A L,Su, Quanmin,Wuttig, Manfred 대한금속재료학회(대한금속학회) 1997 METALS AND MATERIALS International Vol.3 No.1
The thermomechanical properties of Ni_(50)Ti_(50) deposited on Si substrates was studied focusing on the thermoelastic stress, martensitic transformation stress and interaction of the film and substrate. Ni_(50)Ti_(50)/SiO₂/Si film composites display a two-way shape memory effect without training. The stresses giving rise to this effect are the thermoelastic stress evolving upon cooling from the temperature at which the amorphous as-deposited Ni_(50)Ti_(50) was crystallized and martensitic transformation stress. It is shown how the thermoelastic bending can be compensated for in a (crystalline Ni_(50)Ti_(50)/SiO₂/Si/(amorphous Ni_(50)Ti_(50)) trimorph. The experimentally determined temperature dependence of the stress outside the transformation region agrees with the calculated value of the thermoelastic stress; in the vicinity of the Ms and Af temperatures, which are equal to each other, it also agrees with the theoretical prediction based on the equilibrium thermodynamics of the sum of the film, substrate and film/substrate elastic (interaction) energies. The film/substrate interaction energy is derived from martensitic transformation characteristics through interface accommodation and mechanical constraints exerted by the substrate stiffness. This knowledge has been applied Io fabricate a two way shape memory micro composite switch.
Zhou, Chongjian,Yu, Yuan,Lee, Yong Kyu,Cojocaru-Miré,din, Oana,Yoo, Byeongjun,Cho, Sung-Pyo,Im, Jino,Wuttig, Matthias,Hyeon, Taeghwan,Chung, In American Chemical Society 2018 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.140 No.45
<P>From a structural and economic perspective, tellurium-free PbSe can be an attractive alternative to its more expensive isostructural analogue of PbTe for intermediate temperature power generation. Here we report that PbSe<SUB>0.998</SUB>Br<SUB>0.002</SUB>-2%Cu<SUB>2</SUB>Se exhibits record high peak <I>ZT</I> 1.8 at 723 K and average <I>ZT</I> 1.1 between 300 and 823 K to date for all previously reported n- and p-type PbSe-based materials as well as tellurium-free n-type polycrystalline materials. These even rival the highest reported values for n-type PbTe-based materials. Cu<SUB>2</SUB>Se doping not only enhance charge transport properties but also depress thermal conductivity of n-type PbSe. It flattens the edge of the conduction band of PbSe, increases the effective mass of charge carriers, and enlarges the energy band gap, which collectively improve the Seebeck coefficient markedly. This is the first example of manipulating the electronic conduction band to enhance the thermoelectric properties of n-type PbSe. Concurrently, Cu<SUB>2</SUB>Se increases the carrier concentration with nearly no loss in carrier mobility, even increasing the electrical conductivity above ∼423 K. The resulting power factor is ultrahigh, reaching ∼21-26 μW cm<SUP>-1</SUP> K<SUP>-2</SUP> over a wide range of temperature from ∼423 to 723 K. Cu<SUB>2</SUB>Se doping substantially reduces the lattice thermal conductivity to ∼0.4 W m<SUP>-1</SUP> K<SUP>-1</SUP> at 773 K, approaching its theoretical amorphous limit. According to first-principles calculations, the achieved ultralow value can be attributed to remarkable acoustic phonon softening at the low-frequency region.</P> [FIG OMISSION]</BR>
Sb-Se-based phase-change memory device with lower power and higher speed operations
Yoon, Sung-Min,Lee, Nam-Yeal,Ryu, Sang-Ouk,Choi, Kyu-Jeong,Park, Y.-S.,Lee, Seung-Yun,Yu, Byoung-Gon,Kang, Myung-Jin,Choi, Se-Young,Wuttig, M. IEEE 2006 IEEE electron device letters Vol.27 No.6
A phase-change material of Sb<SUB>65</SUB>Se<SUB>35</SUB> was newly proposed for the nonvolatile memory applications. The fabricated phase-change memory device using Sb<SUB>65</SUB>Se<SUB>35</SUB> showed a good electrical threshold switching characteristic in the dc current-voltage (I-V) measurement. The programming time for set operation of the memory device decreased from 1 μs to 250 ns when Sb<SUB>65</SUB>Se<SUB>35</SUB> was introduced in place of the conventionally employed Ge<SUB>2</SUB>Sb<SUB>2</SUB>Te<SUB>5</SUB> (GST). The reset current of Sb<SUB>65</SUB>Se<SUB>35</SUB> device also dramatically reduced from 15 mA to 1.6 mA, compared with that of GST device. These results are attributed to the low melting temperature and high crystallization speed of Sb<SUB>65</SUB>Se<SUB>35</SUB> and will contribute to lower power and higher speed operations of a phase-change nonvolatile memory.