Carbon nanotubes (CNTs) are materials with exceptional electrical, thermal, mechanical, and optical properties. Ever since it was demonstrated that they also possess interesting thermoelectric properties, they have been considered a promising solution for thermal energy harvesting. In this study, we present a simple method to enhance their performance. For this purpose, thin films obtained from high-quality single-walled CNTs (SWCNTs) were doped with a spectrum of inorganic and organic halide compounds. We studied how incorporating various halide species affects the electrical conductivity, the Seebeck coefficient, and the Power Factor. Since thermoelectric devices operate under non-ambient conditions, we also evaluated these materials' performance at elevated temperatures. Our research shows that appropriate dopant selection can result in almost fivefold improvement to the Power Factor compared to the pristine material. We also demonstrate that the chemical potential of the starting CNT network determines its properties, which is important for deciphering the true impact of chemical and physical functionalization of such ensembles.

The effect of hydrostatic pressure on the paramagnetic -ferromagnetic phase transition has been studied in (Ga,Mn)As. The variation of the Curie temperature (T C ) with pressure was monitored by two transport methods: (1) -measurement of zero field resistivity versus temperature ρ(T), (2) -dependence on temperature of the Hall voltage hysteresis loop. Two specimens of different resistivity characteristics were examined. The measured pressure-induced changes of T C were relatively small (of the order of 1K/GPa) for both samples, however they were opposite for the two.(Ga,Mn)As is one of the most intensively investigated diluted magnetic semiconductors during last decades. The understanding of physical phenomena governing its magnetic properties is crucial for increasing Curie temperature (T C ) and thus for possible application of this material in spintronic devices. The origin of ferromagnetism in (Ga,Mn)As was quantitatively explained within the p-d Zener model assuming magnetic interaction between the localized magnetic moments of Mn 2+ ions mediated by holes in the valence band [1][2][3] . This model, in the case of semiconductors, where the carrier density is smaller than the magnetic ion concentration is equivalent to the Ruderman-Kittel-Kasuya-Yosida (RKKY) approach employed in the diluted magnetic metals 4 . Within this picture the ferromagnetic ordering temperature, T C depends in particular on the local p-d exchange interaction and a free hole concentration. It was demonstrated that indeed an increase of the hole concentration in a field effect transistor structure led to an enhancement of the ferromagnetic state 5. On the other hand it was found that the exchange energy scales with the lattice constant as, N 0 β ~ a 0 -3 , 1 and therefore an external hydrostatic pressure could influence the exchange coupling. Although the studies of (In,Mn)Sb diluted magnetic semiconductor under hydrostatic pressure provided an evidence for an increase in carrier-mediated magnetic coupling 6,7 , giving rise to higher Curie temperature, the effect of hydrostatic pressure on (Ga,Mn)As semiconductor is not as clear.6 Therefore additional study was performed in order to clarify the role of external hydrostatic pressure in the paramagneticferromagnetic phase transition in (Ga,Mn)As. p-type Ga 1-x Mn x As layers were grown by molecular beam epitaxy (MBE) on (100) GaAs substrate. In our studies two different samples were used: A777 and A963. The former sample had 20 nm thick layer of (Ga,Mn)As with Mn content x = 7%. After the MBE growth this sample was capped with amorphous As and annealed in the MBE growth chamber at the temperature of 210 ºC (controlled by the IR pyrometer) for two hours (see Ref. 8 for details). The Curie temperature determined from SQUID magnetometry was close to 85 K (Fig. 1, open symbols). The latter sample had a (Ga,Mn)As layer of 50 nm and x = 6%. This sample was not annealed after the MBE growth. The Curie temperature for A963 sample was approximately 50 K (Fig. 1, solid symbols). Since the amount o...

Thin layers of transition metal dichalcogenides have been intensively studied over the last few years due to novel physical phenomena and potential applications. One of the biggest problems in laboratory...

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The lattice mismatch between interesting 2D materials and commonly available 3D substrates is one of the obstacles in the epitaxial growth of monolithic 2D/3D heterostructures, but a number of 2D materials have not yet been considered for epitaxy. Here, we present the first molecular beam epitaxy growth of a NiTe2 2D transition-metal dichalcogenide. Importantly, the growth is realized on a nearly lattice-matched GaAs(111)B substrate. Structural properties of the grown layers are investigated by electron diffraction, X-ray diffraction, and scanning tunneling microscopy. Surface coverage and atomic-scale order are evidenced by images obtained with atomic force, scanning electron, and transmission electron microscopy. Basic transport properties were measured confirming that the NiTe2 layers are metallic, with a Hall concentration of 1020 to 1023 cm–3, depending on the growth conditions.