“…1a). Only peaks for hexagonal crystal structure of β-InSe 29, 35 appear without any other extra peaks, thus indicating the high crystalline purity of the as-grown InSe crystal. From the XRD profiles, the calculated lattice constants are a = b = 4.005 ± 0.004 Å and c = 16.660 ± 0.004 Å, in excellent agreement with previous crystallographic results 36 .Figure 1( a ) XRD spectra of β-InSe.…”
We have investigated the electronic response of single crystals of indium selenide by means of angle-resolved photoemission spectroscopy, electron energy loss spectroscopy and density functional theory. The loss spectrum of indium selenide shows the direct free exciton at ~1.3 eV and several other peaks, which do not exhibit dispersion with the momentum. The joint analysis of the experimental band structure and the density of states indicates that spectral features in the loss function are strictly related to single-particle transitions. These excitations cannot be considered as fully coherent plasmons and they are damped even in the optical limit, i.e. for small momenta. The comparison of the calculated symmetry-projected density of states with electron energy loss spectra enables the assignment of the spectral features to transitions between specific electronic states. Furthermore, the effects of ambient gases on the band structure and on the loss function have been probed.
“…1a). Only peaks for hexagonal crystal structure of β-InSe 29, 35 appear without any other extra peaks, thus indicating the high crystalline purity of the as-grown InSe crystal. From the XRD profiles, the calculated lattice constants are a = b = 4.005 ± 0.004 Å and c = 16.660 ± 0.004 Å, in excellent agreement with previous crystallographic results 36 .Figure 1( a ) XRD spectra of β-InSe.…”
We have investigated the electronic response of single crystals of indium selenide by means of angle-resolved photoemission spectroscopy, electron energy loss spectroscopy and density functional theory. The loss spectrum of indium selenide shows the direct free exciton at ~1.3 eV and several other peaks, which do not exhibit dispersion with the momentum. The joint analysis of the experimental band structure and the density of states indicates that spectral features in the loss function are strictly related to single-particle transitions. These excitations cannot be considered as fully coherent plasmons and they are damped even in the optical limit, i.e. for small momenta. The comparison of the calculated symmetry-projected density of states with electron energy loss spectra enables the assignment of the spectral features to transitions between specific electronic states. Furthermore, the effects of ambient gases on the band structure and on the loss function have been probed.
“…Several growth techniques have been used for growing indium-selenide compounds: vacuum evaporation [ 42 ], molecular beam epitaxy (MBE) [ 43 ], colloidal methods [ 44 , 45 ], flash evaporation [ 46 ], chemical vapour deposition [ 47 ], van der Waals epitaxy [ 48 ], radiofrequency sputtering [ 49 ], Czochralski [ 50 ] and the Bridgman-Stockbarger technique [ 37 , 51 , 52 ].…”
Section: Growthmentioning
confidence: 99%
“…Three highly distinct polytypes of the InSe crystal have been identified [ 35 , 36 ] (β, ε, and γ, see Figure 1 ), in which In and Se atoms are differently arranged. The β (space group symmetry ) and ε polytypes (space group symmetry ) are characterized by a hexagonal lattice consisting of eight atoms in the unit cell, and their extension over two layers [ 37 ]. Rhombohedral γ polytype (space group symmetry ) contains two cations and two anions distributed on four adjacent layers [ 35 , 38 ].…”
Section: Introductionmentioning
confidence: 99%
“…While ε-InSe has an indirect band gap of 1.4 eV [ 36 ], both β- and γ-InSe have a direct band gap [ 36 ] with closely matching values (1.28 eV [ 37 ] and 1.29 eV [ 40 ], respectively). Accordingly, only β and γ phases of InSe could supposedly be employed in optoelectronics, for which finite and direct band gaps are beneficial [ 41 ].…”
Among the various two-dimensional semiconductors, indium selenide has recently triggered the interest of scientific community, due to its band gap matching the visible region of the electromagnetic spectrum, with subsequent potential applications in optoelectronics and especially in photodetection. In this feature article, we discuss the main issues in the synthesis, the ambient stability and the application capabilities of this novel class of two-dimensional semiconductors, by evidencing open challenges and pitfalls. In particular, we evidence how the growth of single crystals with reduced amount of Se vacancies is crucial in the road map for the exploitation of indium selenide in technology through ambient-stable nanodevices with outstanding values of both mobility of charge carriers and ON/OFF ratio. The surface chemical reactivity of the InSe surface, as well as applications in the fields of broadband photodetection, flexible electronics and solar energy conversion are also discussed.
“…Indium monoselenide (InSe) is a potential candidate for photovoltaic applications owing to its advantageous characteristics like chemical stability, low cost, ready availability, and anisotropic and non-hazardous nature (Č elustka & Popović, 1974;Chevy et al, 1977;Gurbulak et al, 2014;Ma et al, 2013). It crystallizes in a layered hexagonal structure with the stacking sequence Á Á ÁSe-In-In-SeÁ Á Á.…”
The present work demonstrates a novel use of physical vapour deposition for grain‐growth engineering by optimizing supersaturation, which led to the evolution of stoichiometric indium monoselenide crystals, employing a custom‐fabricated dual‐zone furnace. The growth zone was kept at a constant temperature for different experimental runs (673–883 K), while the source zone was kept at a stable temperature of 1123 K. In this way, the temperature difference ΔT = 240–450 K resulted in a significant increase of the mass transport between the zones so as to accomplish bulk crystallization. At comparatively low supersaturation (ΔT = 240 K), the presence of nodules and flakes was observed. When ΔT = 250 K, multiple grains were formed owing to temperature asymmetry at the rough vapour–solid interface. A further increase in supersaturation (ΔT = 330 K) facilitated polyhedral grain growth, with distinct grain boundaries. A subsequent increment in ΔT (400 K) led to evolution of the polycrystalline morphology to well developed hexagonal platelets owing to adsorption of atoms on surface steps and kinks in accordance with the leading‐edge growth mechanism. Energy‐dispersive analysis by X‐rays and X‐ray diffraction experiments were carried out to confirm the structure and phase of crystals. Microindentation studies were done to assess the hardness and mechanical stability of the as‐grown crystals in response to external loads in order to explore their suitability for solar cell applications. The investigations of bulk vapour phase transport, morphology and strengthening of InSe platelets provide pathways for the production of crystalline textures with versatile properties.
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