Low temperature synthesis of InP nanocrystals

Materials Chemistry and Physics 112 (2008) 1120–1123

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Materials Chemistry and Physics

journal homepage: www.elsevier.com/locate/matchemphys

Low temperature synthesis of InP nanocrystals

Ung Thi Dieu Thuya, Tran Thi Thuong Huyena,b, Nguyen Quang Liema,∗,1, Peter Reiss c

a Institute of Materials Science (IMS), Vietnamese Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Cau Giay, Hanoi, Viet Nam

b National University of Thai Nguyen, 2 Luong Ngoc Quyen, Thai Nguyen, Viet Nam

c DSM/INAC/SPrAM (UMR 5819 CEA-CNRS-Université Joseph Fourier)/LEMOH, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France

article info

Article history:

Received 18 February 2008

Received in revised form 2 July 2008

Accepted 9 July 2008

PACS:

61.46.Df

61.10.Nz

81.05.Ea

81.16.Be

81.20.Ym

Keywords:

Semiconductors

Chemical synthesis

Raman spectroscopy and scattering

abstract

We present a simple method for the chemical synthesis of InP nanocrystals, which comprises several

advantages: (i) the use of simple reagents, namely InCl3·4H2O and yellow P as the In and P precursors,

respectively, and NaBH4 as the reducing agent in a mixed solvent of ethanol and toluene; (ii) a short reac￾tion time (1–5 h) and low temperature (<75 ◦C); (iii) a high reaction yield approaching 100%. InP NCs in

the zinc-blende structure have been obtained as confirmed by powder X-ray diffraction and Raman scat￾tering measurements. Their mean size of 4 nm has been determined by transmission electron microscopy,

Raman scattering and absorption spectroscopy.

© 2008 Elsevier B.V. All rights reserved.

1. Introduction

In the past decades, nanocrystals (NCs, also termed “quan￾tum dots”) of various II–VI and III–V semiconductors have been

synthesized and studied intensively. Due to their unique opti￾cal properties, they are of high interest for both fundamental

and applied research. Among their most promising applications

their use as fluorescent probes in biological labelling [1,2] and

as light emitters or absorbers in opto-electronic devices, such as

light emitting diodes and solar cells, can be cited [3–8]. In the

latter case, the absorption spectrum and electron affinity can be

adjusted and adapted to the solar emission spectrum by varying

the NCs’ size due to quantum confinement. III–V semiconductors

exhibit a higher degree of covalency in the chemical bonding of

their crystal lattice and larger excitonic Bohr radii as compared

to II–VI compounds. Therefore it can be expected that quantum

size effects are more pronounced in this class of materials, making

them attractive compounds for investigations on the nanoscale. A

particularly interesting material is InP, having a direct band-gap

∗ Corresponding author. Tel.: +84 4 7912835; fax: +84 4 8360705.

E-mail address: [email protected] (N.Q. Liem). 1 Also at College of Technology, Hanoi National University, 144 Xuan Thuy, Hanoi,

Viet Nam.

of 1.35 eV and an excitonic Bohr radius of 11 nm [9]. While the

synthesis of II–VI semiconductor quantum dots such as CdS, CdSe

and CdTe experienced remarkable progress triggered by the sem￾inal work of Murray et al. [10,11], the development of III–V NCs

has taken place on a slower time scale because of difficulties in

the materials preparation [12]. Concerning the synthesis of InP

NCs, the hot-injection method used for cadmium chalcogenides has

been adapted by the groups of Nozik and Peng [13–16]. In these

procedures, carried out in either a coordinating (trioctylphosh￾pine oxide) [13–15] or a non-coordinating (1-octadecene) [16]

solvent at high temperature (300–350 ◦C), the phosphorus pre￾cursor (tris[trimethylsilyl]phosphine, P(TMS)3) is quickly injected

into the solution containing the indium precursor (indium chlo￾ride or indium acetate, respectively). While providing a relatively

good control of the NCs size, these methods suffer from the use

of stringent experimental conditions related to the injection of the

pyrophoric phosphorus precursor and the high reaction tempera￾tures, impeding on the large-scale production of InP NCs. Moreover,

the synthesis in coordinating solvents is very time-consuming, as

reaction times of several days are needed to obtain products of good

crystallinity [13–15,17]. Xie et al. developed a different strategy,

which relies on the use of indium chloride and yellow (i.e. white)

phosphorus in the presence of the reducing agent KBH4 [18,19].

When the reaction was carried out at 80–160 ◦C in ethylenedi￾amine solvent, 11–20 nm InP NCs and large-sized nanorods were

0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved.

doi:10.1016/j.matchemphys.2008.07.051