Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic‐scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer‐like atomic‐scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III‐V, or II‐VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.

Phosphorene—the monolayered material of the element allotrope black phosphorus (Pblack)—and SnIP are 2D and 1D semiconductors with intriguing physical properties. Pblack and SnIP have in common that they can be synthesized via short way transport or mineralization using tin, tin(IV) iodide and amorphous red phosphorus. This top‐down approach is the most important access route to phosphorene. The two preparation routes are closely connected and differ mainly in reaction temperature and molar ratios of starting materials. Many speculative intermediates or activator side phases have been postulated especially for top‐down Pblack/phosphorene synthesis, such as Hittorf's phosphorus or Sn24P19.3I8 clathrate. The importance of phosphorus‐based 2D and 1D materials for energy conversion, storage, and catalysis inspired us to elucidate the formation mechanisms of these two compounds. Herein, we report on the reaction mechanisms of Pblack/phosphorene and SnIP from P4 and SnI2 via direct gas phase formation.

SnIP, an atomic-scale inorganic double helix compound is composed by a hexagonal rodpacking of double helices in the bulk phase. A racemic mixture of Pand M-SnIP double helices is energetically most-favored and present in the solid. In order to evaluate if enantiomer-pure SnIP might be realizable three different stacking models of seven chiral double helices, an enantiomer pure, a 2:1 and a racemic 1:1 ratio were investigated according to their energies of formation. While a top down approach didn't lead to single isolated double helices the development of a bottom up approach might be beneficial.Motivated by templating strategies in confined geometries we performed first-principles density functional theory calculations (DFT) using Carbon nanotubes (CNT) featuring different electronic properties and suitable sizes as matrices to accommodate chiral SnIP double helices. With the aid of DFT, we determined the ideal diameter, stability and electronic properties of different SnIP@CNT systems. Appropriate molecular starting materials and a feasible formation mechanism are identified based on chemical considerations. An interaction between the CNTs and the SnIP units is evident, causing structure and property modifications of the hybrids. The intercalation of SnIP into a suitable CNT leads to a gain in total energy compared to the isolated systems. Based on our findings a straight forward way to introduce chirality in suitable CNTs via SnIP@CNT hybrids is feasible.

SnIP could be the first of a new class of inorganic double-helix materials. [7][8][9] With strong intra-helix covalent bonds and weak inter-helix dispersion forces, SnIP belongs to the group of newly emerging 1D van der Waals (vdW) materials with potential applications in nanoelectronics and photonics. [10][11][12][13] In contrast to the DNA structure, which consists of two equal radius helices, SnIP forms with an outer [SnI] + helix wrapping around an inner [P] − helix, as pictured in Figure 1a. SnIP crystallizes monoclinically with a unit cell containing two opposite-handed double helices so that there is no net chirality. It is composed of abundant and non-toxic elements and can grow uninhibited to cm-length needles with a low-temperature synthesis [6,14] (Sections S1 and S2, Supporting Information) or in nanotubes using vapor deposition. [15,16] Its 1.86 eV band gap, as determined by band structure calculations (Figure 1b,c) and verified experimentally (see ref.[ 6 ] and Section S3, Supporting Information), is well situated for solar absorption and photocatalytic water splitting. [8,10,15] SnIP is also an extremely soft and flexible semiconductor and is therefore a promising material for applications in flexible electronics, [6,10] where these properties are highly desirable. [17] It is predicted to have a high carrier mobility; [8] however, as-grown SnIP is highly resistive so that the current lack of doped samples has made it difficult to explore its electronic properties. [6] Moreover, despite the exciting properties and unique structure of SnIP, there have been no investigations probing its ultrafast photophysical properties.Here, we use time-resolved terahertz (THz) spectroscopy (TRTS) to study picosecond charge carrier dynamics in SnIP nanowire films, as shown in Figure 1d. TRTS, a powerful non-contact ultrafast probe, has been used extensively to probe carrier dynamics in low-dimensional materials, accelerating scientific understanding of transport mechanisms and enabling materials optimization for potential applications. [18,19] From analysis of the photoconductivity spectra, along with insight into the highly anisotropic energy landscape from density functional theory (DFT), we make the first measurement of the carrier mobility in SnIP. We find a maximum electron mobility of 280 cm 2 V −1 s −1 along the double-helix axis, an extraordinarily high mobility for a material as soft and flexible as SnIP. On Tin iodide phosphide (SnIP), an inorganic double-helix material, is a quasi-1D van der Waals semiconductor that shows promise in photocatalysis and flexible electronics. However, the understanding of the fundamental photophysics and charge transport dynamics of this new material is limited. Here, time-resolved terahertz (THz) spectroscopy is used to probe the transient photoconductivity of SnIP nanowire films and measure the carrier mobility. With insight into the highly anisotropic electronic structure from quantum chemical calculations, an electron mobility as high as 280 cm 2 V −1 s −1 along the doub...

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