^{1,a)}, S. Le Roy

^{2}, M. Foldyna

^{3}, M. Kildemo

^{1}and E. Søndergård

^{2}

### Abstract

Inclined GaSbnanopillars prepared by low energy ion sputtering with oblique ion beam incidence have been characterized by two different Mueller matrix ellipsometric tools. The optical properties of the nanopillars were found to be well described by a uniaxial anisotropic graded effective medium model. The pillar height and inclination angle were determined by fitting the parameters of the effective medium model to spectroscopic (1.44–2.88 eV) Mueller matrix measurements at multiple azimuth sample orientations. A set of different samples with various average pillar height and inclination angle was studied; results from the optical characterization correspond well with those from scanning electron microscopy analysis. For samples with nanopillars inclined by 45° or less, the height could be determined from a single Mueller matrix measurement at only one azimuth orientation, allowing real-time *in situ* observation of the formation. The nanopillars were also studied using a single wavelength angle resolved Mueller polarimeter, which also can be used to determine height and inclination of the pillars, in addition to validating the optical model over a wide range of incident and azimuth angles.

We are thankful to Horiba Jobin Yvon and Antonello De Martino at LPICM for access to scientific instruments, and acknowledge support from the Aurora mobility program. In addition, S.L.R. and E.S. acknowledge support from the ANRT and Saint-Gobain. We are thankful to Christina McClatchey at Queen’s University Belfast for giving comments on the manuscript.

I. INTRODUCTION

II. THEORY AND OPTICAL MODELING

III. EXPERIMENTAL DETAILS

IV. RESULTS AND DISCUSSION

V. CONCLUSION

### Key Topics

- Nanostructures
- 26.0
- Sputtering
- 22.0
- Scanning electron microscopy
- 21.0
- III-V semiconductors
- 17.0
- Height measurements
- 16.0

## Figures

Sketch of the optical model, dependent on four parameters, the height , the bottom, and top relative diameters and , and the inclination angle .

Sketch of the optical model, dependent on four parameters, the height , the bottom, and top relative diameters and , and the inclination angle .

Cross section SEM image of nanopillars sputtered at 45° ion incidence, for 10 min exposure time.

Cross section SEM image of nanopillars sputtered at 45° ion incidence, for 10 min exposure time.

SEM images of nanopillars sputtered with 45° ion incidence, for various exposure times (10, 5, 4, and 2 min), taken at a 45° view angle.

SEM images of nanopillars sputtered with 45° ion incidence, for various exposure times (10, 5, 4, and 2 min), taken at a 45° view angle.

SEM images of nanopillars sputtered with various ion incidences (10°, 22.5°, and 60°), for 5 min ion exposure time, 45° view.

SEM images of nanopillars sputtered with various ion incidences (10°, 22.5°, and 60°), for 5 min ion exposure time, 45° view.

Measured (dotted line) and simulated (solid line) Mueller matrix elements for sample 2, 3, and 5, prepared by sputtering for 5, 4, and 2 min at 45° ion incidence. This resulted in approximately 120, 60, and 35 nm high pillars, respectively. The measurements were performed at an azimuth orientation with the pillars inclined in a plane normal to the ellipsometric plane of incidence .

Measured (dotted line) and simulated (solid line) Mueller matrix elements for sample 2, 3, and 5, prepared by sputtering for 5, 4, and 2 min at 45° ion incidence. This resulted in approximately 120, 60, and 35 nm high pillars, respectively. The measurements were performed at an azimuth orientation with the pillars inclined in a plane normal to the ellipsometric plane of incidence .

Measurened (dots) and simulated (solid) Mueller matrix elements for sample 2 vs azimuth orientation , at a photon energy of 2.6 eV and 70° angle of incidence.

Measurened (dots) and simulated (solid) Mueller matrix elements for sample 2 vs azimuth orientation , at a photon energy of 2.6 eV and 70° angle of incidence.

(a) Experimental AR-MME measurements (532 nm) of sample 1. The 16 images represent polar plots of the 16 normalized Mueller elements. The polar coordinate represent the angle of incidence (, where is the angle of incidence), while the polar angle represents the azimuth sample orientation. A horizontal line through the center of the polar plots correspond to the pillars being inclined parallel to the plane of incidence, a vertical line through the center correspond to the pillars being inclined along a direction orthogonal to the plane of incidence. (b) Simulated angle resolved Mueller matrix, with parameters given for sample 1 in Table I.

(a) Experimental AR-MME measurements (532 nm) of sample 1. The 16 images represent polar plots of the 16 normalized Mueller elements. The polar coordinate represent the angle of incidence (, where is the angle of incidence), while the polar angle represents the azimuth sample orientation. A horizontal line through the center of the polar plots correspond to the pillars being inclined parallel to the plane of incidence, a vertical line through the center correspond to the pillars being inclined along a direction orthogonal to the plane of incidence. (b) Simulated angle resolved Mueller matrix, with parameters given for sample 1 in Table I.

## Tables

Comparison of SEM characterization and parameters found by the effective medium fit to the spectroscopic Muller matrix measurements (MM16, 1.44–2.8 eV) at five azimuth orientations , at an angle of incidence 70°. *Incl*. denotes the angle of ion incidence during sputtering (set manually by rotating the sample holder), is the sputtering exposure time, is the pillar height determined from SEM images, , , and are the fitted parameters of the effective medium model, and is a measure of the goodness of fit. The height of this sample was obtained using AFM.

Comparison of SEM characterization and parameters found by the effective medium fit to the spectroscopic Muller matrix measurements (MM16, 1.44–2.8 eV) at five azimuth orientations , at an angle of incidence 70°. *Incl*. denotes the angle of ion incidence during sputtering (set manually by rotating the sample holder), is the sputtering exposure time, is the pillar height determined from SEM images, , , and are the fitted parameters of the effective medium model, and is a measure of the goodness of fit. The height of this sample was obtained using AFM.

Comparison of SEM characterization and effective medium parameters found from fitting the optical model to spectroscopic measurements of two Mueller elements and at the azimuth orientation , with the inclination angle fixed to be equal to the angle of ion incidence. is the pillar height determined from SEM images, is the height found from fitting to multiple azimuth orientations (Table I), , and are the fitted parameters of the effective medium model, and is a measure of the goodness of fit. The height of this sample was obtained using AFM.

Comparison of SEM characterization and effective medium parameters found from fitting the optical model to spectroscopic measurements of two Mueller elements and at the azimuth orientation , with the inclination angle fixed to be equal to the angle of ion incidence. is the pillar height determined from SEM images, is the height found from fitting to multiple azimuth orientations (Table I), , and are the fitted parameters of the effective medium model, and is a measure of the goodness of fit. The height of this sample was obtained using AFM.

Comparison of SEM characterization and effective medium parameters found from fitting the optical model to angle resolved Mueller matrix measurements at a single wavelength of 532 nm. *Incl*. denotes the angle of ion incidence during sputtering (set manually by rotating the sample holder), is the sputtering exposure time, is the pillar height found from SEM images, , , , and are the fitted parameters of the effective medium model, and is a measure of the goodness of fit. The height of this sample was obtained using AFM.

Comparison of SEM characterization and effective medium parameters found from fitting the optical model to angle resolved Mueller matrix measurements at a single wavelength of 532 nm. *Incl*. denotes the angle of ion incidence during sputtering (set manually by rotating the sample holder), is the sputtering exposure time, is the pillar height found from SEM images, , , , and are the fitted parameters of the effective medium model, and is a measure of the goodness of fit. The height of this sample was obtained using AFM.

Article metrics loading...

Full text loading...

Commenting has been disabled for this content