Supplementary information: Mapping of Axial Strain in InAs/InSb Heterostructured Nanowires

Supplementary information:Mapping of Axial Strain in InAs/InSbHeterostructured Nanowires

Atanu Patra, Jaya Kumar Panda, and Anushree Roy,

Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur 721 302, India

Mauro Gemmi and Jérémy David,

Center for Nanotechnology Innovation @ NEST, Istituto Italiano di Tecnologia, Piazza S. Silvestro 12, I-56127 Pisa, Italy

Daniele Ercolani and Lucia Sorba

NEST-Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, I-56127 Pisa, Italy
S1. Growth parameters
InSb NWs were grown by CBE technique in a Riber Compact 21 system. The system employs pressure control in the metalorganic (MO) lines to determine precursor fluxes during the sample growth. The precursors involved in the NW growth are tri-methylindium (TMIn), tertiarybutylarsine (TBAs) and tris(dimethylamino)antimony (TDMASb). No carrier gas is employed. A nominally 1 nm–thick Au film was first deposited on InAs(111)B wafers by thermal evaporation. Before the growth was initiated, the samples were heated at 560±10 °C under TBAs flow for 20 min in order to dewet the Au film into nanoparticles and to remove the surface oxide from the InAs substrate. InAs stems were grown at a temperature of 430±10 °C for 90 min with MO line pressures of 0.3 and 1 Torr for TMIn and TBAs, respectively. MO precursor fluxes are controlled by regulating the MO line pressure via a needle valve receiving feedback from a capacitive pressure gauge. A calibrated orifice at the injector insures the proportionality between line pressure and precursor flow through the injector. During the growth the pressure in the chamber was in range of 10^-6 Torr. The temperature was lowered to 410±10 °C and InSb segments were grown for 120 min with MO line pressures of 0.4 and 0.7 Torr for TMIn and TDMASb, respectively. We have optimized the growth temperature of the InSb segments in order to limit the very large lateral growth that we observe in long InSb segment. In order to reduce the lateral growth, after 120 min of growth the temperature was then increased to 445±10 °C and the InSb segments were grown for an additional 270 min.

S2. Morphology of NWs
It is believed that during the InAs growth the In content of the catalyst particle is between 22 and 38 atomic percent.^1,2 Group-III content increases to 50-75 atomic percent during the growth of antimonides, suggesting that the change in particle volume due to the uptake of group-III atoms is the main reason of the increase in the diameter of the InSb top segment.^3,4
S3. Details of the Raman spectrometer

A 514 nm line of Ar⁺ laser (Inova 70C, Coherent USA) was used as an excitation source. Laser power was kept at ~ 50 W to avoid the effect of local heating (more will be discussed later). The integration time for each spectrum was kept at 400 sec. Raman spectra were recorded using triple monochromator (model T64000, JY, France). For this monochromator with 1800 grooves/mm grating, by taking into account the dispersion of 514 nm excitation wavelength, we estimate the spectral step resolution as 0.6 cm^-1.

S4.Temperature estimation along the axis of NWs
The integral intensity ratio of the Stokes (I_s) and anti-Stokes (I_AS) Raman lines depends on the sample temperature, T, by .  is the frequency of the Stokes line. A depends on the optical absorption constant and the cross sections for Stokes and anti-Stokes Raman scattering of the material. It also includes the contribution of Rayleigh scattering at Stokes and anti-Stokes wavenumber. Stokes and anti-Stokes Raman spectra were measured along the length of the NWs (Fig. S1). Inset of Fig. S1 shows the estimated value of T derived from the ratio I_S/I_AS in Fig. S1.The value of A has been kept constant for all spectra recorded at different points. We obtain a mean temperature of the system of 29410K.


294±10K

Figure S1. Stokes and anti-Stokes Raman spectra recorded along the length of the NW. The inset of the figure shows the calculated temperature along the NWs. The mean temperature is estimated to be 294± 10 K.

S5. SAED and EDT patterns of NWs

Figure S2. (a) SAED pattern taken at the bottom of an InSb segment. Arrows show the measured distances between 333 and -3-3-3 spots used for estimating d₁₁₁ along the two equivalent directions. (b) 3-dimensional reconstruction of the reciprocal space of the InAs/InSb NW.

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