Low‐Temperature, Template‐Free Synthesis of Single‐Crystal Bismuth Telluride Nanorods

Abstract

High-efficiency, solid-state thermoelectric energy conversion requires materials with a large thermoelectric figure of merit (ZT), defined as [1] rS 2 T/j, in which S is the Seebeck coefficient, r the electrical conductivity, j the thermal conductivity, and T the absolute temperature. The state of the art materials for thermoelectric cooling applications are alloys based on Bi 2 Te 3 /Sb 2 Te 3 and Bi 2 Te 3 /Bi 2 Se 3 with ZT ∼ 1, while a value of ZT ∼ 4 is necessary to surpass competing technologies.[2] Nanostructuring these thermoelectric materials has recently emerged as a successful strategy to gain factorial enhancements in ZT, [3][4][5][6] owing to quantum and classical size effects of the charge and heat carriers, respectively. [2,5] Quantum confinement of the charge carriers is believed to enhance the Seebeck coefficient S and electrical conductivity r owing to an increased density of states at the Fermi level. [7][8][9] . Moreover, intense boundary and interface scattering of heat carriers decreases thermal conductivity, [2,5,[10][11][12][13] exemplified in the Bi 2 Te 3 /Sb 2 Te 3 nanolayer superlattices [3] exhibiting ZT ∼ 2.3.Further increases in ZT are expected due to the presence of stronger quantum confinement and thermal conductivity reduction effects as the dimensionality of the nanostructures is decreased. Sub-nanometer-diameter nanorods of bismuth telluride are predicted to yield ZT values as high as 14, which is nearly threefold higher than the value predicted for two-dimensional (2D) quantum wells. [14][15][16] However, if the diameter is > 5 nm the electrical transport properties of the nanorods approach bulk properties. These studies have sparked a flurry of activity to produce nanorods and nanowires with small diameters from materials that have high ZT values in the bulk form. Most work to date on synthesizing nanorods or nanowires of bismuth telluride based materials has been by surfactantmediated solvothermal techniques [17][18][19] [27]Here, we describe a simple one-step, template-free, lowtemperature (100°C), aqueous-phase synthesis approach to obtain single-crystal bismuth telluride nanorods with diameters in the range 27-130 nm. These diameters are smaller than previously reported, and can be controlled by adjusting the reaction time and the molecular passivating agent, offering promise for realizing high-ZT thermoelectric nanostructures.In a typical synthesis procedure, either thioglycolic acid or L-cysteine was added to bismuth chloride solution, transforming the initially transparent solution to a yellow color due to thio-ligation of the bismuth ions. This solution was mixed with orthotelluric acid in water preheated to 80°C and then refluxed with excess hydrazine monohydrate at 100°C. The reaction was quenched with water at different time intervals to extract 5 mL of the refluxed mixture for microanalysis. Scanning electron microscopy (SEM) images in Figure 1 reveal the bismuth telluride nanorods obtained from a 5 h synthesis. The rods are straight with curved tips; there is no...

Topological insulator nanostructures

“…Chemical synthesis of TI nanomaterials, primarily the noncentro-symmetric zincblende HgTe-type family and the hexagonal centrosymmetric Bi 2 Se 3 family of compounds, has been achieved with a diverse set of methods: colloidal [64][65][66], solvothermal [67][68][69], hydrothermal co-reduction [70], mechano-chemical [71,72], photochemical [73], galvanic displacement [74], and a microwave-assisted synthesis [75].…”

“…With these mild synthesis requirements, significant control both in morphology and chemical modification of the surface can be achieved, which will be useful in designing device architectures ideal for enhancing the surface effects. Extensive morphological control of TI nanostructures has been demonstrated using synthetic chemistry, such as nanoribbons [75], nanorods [65], nanowires [66], nanotubes [74], nanoplates [77], nanorings [75], nanospheres [78], and quantum dots [79]. The crystalline quality of the chemically synthesized TI nanomaterials is high (Fig.…”

Low temperature reduction route to synthesise bismuth telluride (Bi2Te3) nanoparticles: structural and optical studies

“…Sub-nanometer-diameter nanorods of bismuth telluride are predicted to yield ZT values as high as 14, which is nearly threefold greater than the value predicted for two-dimensional (2D) quantum wells [17,19,20]. These studies have sparked a flurry of activity to produce nanorods, nanoparticles and nanowires with small diameters from materials that have high ZT values in the bulk form [21].…”

High density p-type Bi0.5Sb1.5Te3 nanowires by electrochemical templating through ion-track lithography

“…1,11 These materials are therefore one of the best targets for the preparation of 1D nanostructures. A variety of approaches have been reported to prepare n-type Bi 2 Te 3 1D nanostructures, including templated electrodeposition using anodic alumina, [12][13][14][15][16] surfactant-mediated solvothermal techniques, 17,18 step edge selective electrodeposition, 19 high-temperature organic solution synthesis, 20 low-temperature and templatefree synthesis 21 and most recently the galvanic displacement reaction. 22 However, there are only very few reports on the preparation of p-type Bi 0.5 Sb 1.5 Te 3 1D nanostructures.…”