Laser-Forged Nanotube-GaSe Hybrids Show Dramatically Tuned Light Response

Scientists have combined one of the most versatile laser synthesis techniques with first-principles quantum simulations to create and understand a hybrid nanomaterial that could reshape how engineers design polarization-sensitive optoelectronic devices. In a study published in Results in Optics, a research team led by A.M. Aliyeva and Vusala Nabi Jafarova reports the synthesis of multi-walled carbon nanotube/gallium selenide (MWCNT/GaSe) nanocomposites using pulsed laser ablation in liquid, together with density functional theory (DFT) calculations that reveal how the interface between the two materials fundamentally rewrites their anisotropic optical behavior. The work stands out because it bridges a persistent gap in nanoscience: experimentalists can measure how a composite absorbs and emits light, but the microscopic electronic origins of those changes often remain hidden.

The choice of ingredients is deliberate. Multi-walled carbon nanotubes are concentric cylinders of graphene that combine excellent electrical conductivity, mechanical robustness, thermal stability, and a broadband optical response. Their one-dimensional electronic structure gives rise to van Hove singularities in the density of states, sharp peaks where optical absorption is dramatically enhanced, and their optical behavior depends strongly on whether the electric field of incoming light is polarized along the tube axis or around its circumference. Gallium selenide, meanwhile, is a layered III-VI semiconductor with a quasi-direct bandgap of roughly 2.0 electronvolts, strong excitonic effects, and pronounced optical anisotropy arising from its van der Waals crystal structure. Combining the two, the researchers reasoned, could produce light-matter interactions unavailable in either material alone.

Synthesis relied on pulsed laser ablation in liquid, a technique prized for producing high-purity nanomaterials without surfactants, reducing agents, or high-temperature chemical treatments that can contaminate delicate interfaces. The team used an Nd:YAG laser operating at 1064 nanometers, with pulses roughly 10 nanoseconds long carrying about 135 millijoules of energy at a 10-hertz repetition rate, reaching a power density of approximately 12 megawatts per square centimeter. The beam was focused through a lens onto targets immersed in distilled water within a quartz cuvette. When the intense pulses strike the target, rapid energy deposition evaporates and ejects atoms, clusters, and plasma species, which then cool and condense into nanoscale particles and hybrid structures. The surrounding liquid confines the expanding plasma plume far more than vacuum or gas would, generating extreme local temperatures and pressures that shape nucleation and growth dynamics.

The experimental procedure unfolded in two stages. First, multi-walled carbon nanotubes from Sigma-Aldrich, with carbon purity above 98 percent, outer diameters of roughly 6 to 13 nanometers, and lengths of 2.5 to 20 micrometers, were ablated in distilled water for about ten minutes to form a colloidal dispersion. Then freshly cleaved plates of GaSe single crystals, grown by the Bridgman technique and verified by X-ray diffraction and Raman spectroscopy, were immersed in that colloid and subjected to identical laser irradiation. This second pass promoted surface functionalization and laser-induced nonequilibrium interactions that welded the two materials into a hybrid interface, all without a single chemical additive.

Structural characterization confirmed the marriage. X-ray diffraction of pristine nanotubes showed characteristic features at 2-theta angles of 15.09, 17.81, and 26.91 degrees, the last corresponding to the graphitic (002) reflection of ordered sp2-bonded carbon layers. After composite formation, the diffraction profile broadened considerably and lost intensity, signaling reduced long-range crystalline order, a common signature of nanocomposites synthesized under pulsed laser irradiation. Debye-Scherrer analysis of the peak broadening yielded coherent crystallite-domain sizes of roughly 7 to 15 nanometers. Energy-dispersive X-ray spectroscopy detected carbon alongside gallium and selenium in nearly equal atomic percentages, 7.60 and 7.99 respectively, indicating the GaSe phase retained its approximately 1:1 stoichiometry through the laser process. Scanning electron microscopy revealed an entangled network of nanotubes decorated with GaSe-containing clusters, and elemental maps showed substantial spatial overlap of gallium and selenium throughout the carbon network.

Transmission electron microscopy pushed the resolution further and delivered the study’s most visually compelling evidence. High-resolution imaging distinguished the multilayer graphitic walls of a representative nanotube, with an outer diameter near 32 nanometers, an inner diameter near 16 nanometers, and about 7 to 9 walls separated by roughly 0.34 nanometers, the classic spacing of graphitic carbon. In the GaSe-containing regions, well-resolved lattice fringes with interplanar spacings of approximately 0.33 to 0.334 nanometers confirmed crystallinity, and critically, the images captured direct nanoscale contact between crystalline GaSe domains and the graphitic nanotube walls, proof that a genuine hybrid interface had formed. A selected-area electron diffraction pattern with rings and discrete reflections rounded out the structural case.

The optical consequences were striking. Ultraviolet-visible absorption and Tauc analysis showed the optical absorption edge shifting dramatically after hybridization: the estimated optical gap fell from about 2.15 electronvolts for pristine nanotubes to 1.39 electronvolts for the composite, a redshift of roughly 0.76 electronvolts. Photoluminescence measurements, excited by the second harmonic of an Nd:YAG laser at 2.34 electronvolts, showed pristine GaSe emitting near 576 nanometers and pristine nanotubes near 887 nanometers. The composite, however, produced a broadband emission spanning approximately 576 to 887 nanometers, covering both parent emission regions in a single continuous profile, with an approximately fivefold enhancement in relative steady-state intensity. The authors are careful to note this figure reflects relative intensity under their conditions, not an absolute quantum-yield increase, and that steady-state spectra alone cannot pin down the exact recombination mechanism.

To explain what was happening at the atomic scale, the team turned to DFT calculations using the QuantumATK package with the local density approximation and Perdew-Zunger parameterization. Because the experimental material contains nanotubes of varying diameters, wall numbers, and orientations, the theorists built an idealized model: an armchair double-walled nanotube, DWCNT(5,5)@(10,10), laid with its axis parallel to a crystalline GaSe surface. After structural optimization, the minimum interfacial distances settled at about 2.31 to 2.53 angstroms. The calculations tracked the absorption coefficient and reflectivity along three polarization directions, xx, yy, and zz, revealing how quantum confinement and electronic symmetry govern direction-dependent light absorption.

The simulated spectra told a coherent story. Pristine GaSe displayed strong anisotropy, with a sharp zz-polarized absorption peak near 1.3 electronvolts exceeding 80,000 per centimeter, a yy peak near 2.5 electronvolts, and a nearly negligible xx response, a direct consequence of its layered bonding. The pristine double-walled nanotube showed the opposite pattern: strong transverse absorption between 1.5 and 4.5 electronvolts from interband transitions between van Hove singularities, with weaker axial response, and a circumferential reflectivity peak of about 0.38 at 3.5 electronvolts. In the hybrid, everything changed. Absorption was strongly suppressed, broadened, and redistributed toward lower energies, with the xx component becoming dominant and new low-energy features appearing below 1 electronvolt. Reflectivity flipped as well, with the xx direction reaching about 0.20 near 0.3 electronvolts while the other directions fell below 0.02, suggesting the hybrid is highly reflective to radially polarized light, a property absent in either constituent.

Electronic-structure analyses filled in the mechanism. The total density of states of the hybrid showed finite electronic states at and around the Fermi level, indicating metallic or strongly conducting character rather than a conventional semiconducting gap, with a degree of spin asymmetry between channels. Electron difference density maps revealed spatially nonuniform redistribution of charge concentrated at the interface, and Mulliken population analysis quantified it: approximately 0.17 elementary charges migrate from the nanotube toward the GaSe component upon interface formation, with gallium atoms accumulating electrons and selenium atoms donating them in a strongly atom-dependent pattern. Together, these results establish that interfacial electronic coupling and charge redistribution, not merely physical mixing, drive the modified optical response. The authors emphasize that the polarization-dependent anisotropy remains a theoretical prediction awaiting direct experimental test, since the colloidal measurements average over randomly oriented nanotubes. Future work with aligned nanotube arrays, single-nanotube spectroscopy, time-resolved photoluminescence, and polarization-resolved measurements on oriented films could confirm the predicted directional behavior. If validated, the combination of broadband emission, a tunable absorption edge, and engineered polarization selectivity positions these laser-forged hybrids as intriguing candidates for polarization-sensitive photodetectors, optical filters, directional mirrors, and infrared photonic devices.

Subject of Research: Synthesis and anisotropic optical properties of multi-walled carbon nanotube/gallium selenide nanocomposites

Article Title: Laser-ablation synthesis and DFT investigation of anisotropic optical properties in multi-walled carbon nanotube/GaSe nanocomposites

Article References: Aliyeva, A., Jafarova, V. N., Hasanova, K. A., Sh., A. S., Guliyeva, A. A., Salmanov, V., Asad, J. H., Mamedov, R., & AlShaikh Mohammad, N. F. (2026). Laser-ablation synthesis and DFT investigation of anisotropic optical properties in multi-walled carbon nanotube/GaSe nanocomposites. Results in Optics, 25, Article 101181. https://doi.org/10.1016/j.rio.2026.101181

Image Credits: AI Generated

DOI: 10.1016/j.rio.2026.101181

Keywords: carbon nanotubes, gallium selenide, nanocomposites, laser ablation in liquids, density functional theory, optical anisotropy, photoluminescence, van der Waals heterostructures, polarization-sensitive optoelectronics, charge transfer, photodetectors, band gap engineering