STM 8

Black Phosphorus n-type Doping by Cu: A Microscopic Surface Investigation

Despite the interest in surface science studies of this layered semiconductor in its few-layer form, there have been few studies up to now due to sample preparation challenges, because of the high reactivity of bP with oxygen and moisture. We developed a protocol to efficiently prepare samples of exfoliated bP for STM experiments, exfoliating bP in an inert atmosphere and using graphene as a flat, conducting substrate. The obtained surface is clean (without resist residues or oxidation), and bP flakes can be clearly identified in atomic resolution images, as shown in Fig. 1(a). We studied the surface evolution with temperature, focusing on the regime in which sublimation starts (Fig. 1(b)) and monolayer-deep (Fig. 1(d)) craters, which show a preferential orientation, appear on the surface. Thanks to the atomic resolution provided by STM, we were able to demonstrate that these craters are aligned along one of the crystallographic axis i.e. the zig-zag direction (Fig 1(c)).


Figure 1: (a) bP flake on graphene; insets: left: cross section providing thickness, and right: atomic resolution image of bP. (b) bP surface after annealing at 400°C for 2h. (c) Atomic resolution image of the region marked by the black box in (b), and (d) cross-section along the black dashed line in (b).

Next, we study surface charge transfer doping of exfoliated black phosphorus flakes by copper using scanning tunneling microscopy and spectroscopy (STS) at room temperature. The tunneling spectra reveal a gap in correspondence of Cu islands, which is attributed to Coulomb blockade phenomena. Moreover, using line spectroscopic measurements across small copper islands, we exploit the potential of the local investigation, showing that the n-type doping effect of copper on bP is short-ranged. These experimental results are substantiated by first-principles simulations, which quantify the role of cluster size for an effective n-type doping of bP and explain the Coulomb blockade by an electronic decoupling of the topmost bP layer from the underlying layers driven by the copper cluster. Our results provide novel understanding, difficult to retrieve by transport measurements, of the doping of bP by copper, which appears promising for the implementation of ultra-sharp p-n junctions in bP.


Figure 2: (a) 11 μm × 11 μm STM image showing two bP flakes on a graphene substrate after 20 min of copper deposition. Scan parameters: (− 3.0 V, 0.33 nA). Inset: height profile across the larger flake along the dashed blue line. (b) 100 nm × 100 nm STM image on the larger flake, showing copper islands on bP. Inset: 5 nm × 5 nm STM image obtained upon further zoom-in, showing a copper island on top of the atomically resolved bP surface. Scan parameters for both images: (− 1.0 V, 0.33 nA).

Publications:

  1. Abhishek Kumar, F. Telesio, S. Forti, A. Al-Temimy, C. Coletti, M. Serrano-Ruiz, M. Caporali, M. Peruzzini, F. Beltram, and S. Heun: STM Study of Exfoliated Few Layer Black Phosphorus Annealed in Ultrahigh Vacuum, arXiv:1808.09164 [cond-mat.mes-hall].
  2. Abhishek Kumar, F. Telesio, S. Forti, A. Al-Temimy, C. Coletti, M. Serrano-Ruiz, M. Caporali, M. Peruzzini, F. Beltram, and S. Heun: STM Study of Exfoliated Few Layer Black Phosphorus Annealed in Ultrahigh Vacuum, 2D Mater. 6 (2019) 015005.
  3. Abhishek Kumar: Black Phosphorus: Pristine and doped surface investigations using Scanning Tunneling Microscopy, PhD Thesis, Scuola Normale Superiore, Pisa, Italy, 2019.
  4. Francesca Telesio and Stefan Heun: Black Phosphorus: Pristine and doped surface investigations using Scanning Tunneling Microscopy, CNR Nano Activity Report 2020 [Page 64].
  5. Abhishek Kumar, Francesca Telesio, Deborah Prezzi, Claudia Cardoso, Alessandra Catellani, Stiven Forti, Camilla Coletti, Manuel Serrano-Ruiz, Maurizio Peruzzini, Fabio Beltram, Stefan Heun: Black Phosphorus n-type doping by Cu: a microscopic surface investigation, arXiv:2201.00610 [cond-mat.mtrl-sci].
  6. A. Kumar, F. Telesio, D. Prezzi, C. Cardoso, A. Catellani, S. Forti, C. Coletti, M. Sarrano-Ruiz, M. Peruzzini, F. Beltram, and S. Heun: Black phosphorus n-type doping by Cu: a microscopic surface investigation, J. Phys. Chem. C 125 (2021) 13477 – 13484.
  7. Surface properties and doping of few layer black phosphorus, Cnr Nano Activity Report 2022. [Pages 82-83]

Presented at:

  1. A. Kumar, F. Telesio, A. Al Temimy, S. Forti, C. Coletti, M. Serrano-Ruiz, M. Caporali, M. Peruzzini, F. Beltram, and S. Heun: STM studies of exfoliated black Phosphorus, Phosphorene and 2D Companions Workshop, Rome, Italy, 08 May 2017 (oral). [Abstract] [Talk]
  2. S. Heun: Optimization of few-layer black phosphorus for low-temperature magneto-transport studies, Iconsat 2018, Bangalore, India, 21 – 23 March 2018 (invited). [Abstract] [Talk]
  3. S. Heun: Optimization of few-layer black phosphorus for low-temperature magneto-transport studies, AGH University of Science and Technology, Krakow, Poland (Prof. B. Szafran), 12 June 2018 (invited). [Abstract] [Talk]
  4. Abhishek Kumar, F. Telesio, S. Forti, A. Al-Temimy, C. Coletti, M. Serrano-Ruiz, M. Caporali, M. Peruzzini, F. Beltram, and S. Heun: STM Study of Exfoliated Few Layer Black Phosphorus Annealing in Ultrahigh Vacuum, International conference on Novel 2D materials explored via scanning probe microscopy & spectroscopy, Donostia-San Sebastián, Spain, 25 – 29 June 2018 (poster). [Abstract] [Poster]
  5. S. Heun: Optimization of few-layer black phosphorus for low-temperature magneto-transport studies, École Polytechnique de Montréal, Quebec, Canada (Prof. O. Moutanabbir), 13 September 2018 (invited). [Abstract] [Talk]
  6. S. Heun: Optimization of few-layer black phosphorus for low-temperature magneto-transport studies, Materials.it 2018, Bologna, Italy, 22 – 26 October 2018 (invited). [Abstract] [Talk]
  7. F. Telesio, Abhishek Kumar, D. Prezzi, S. Forti, A. Al-Temimy, C. Coletti, M. Serrano-Ruiz, M. Caporali, M. Peruzzini, F. Beltram and S. Heun: Exfoliated black Phosphorus Surfaces investigated by Scanning Tunneling Microscopy, NanoMeeting 2018, Pisa, Italy, 29 – 30 October 2018 (oral). [Abstract] [Talk]
  8. A. Kumar, F. Telesio, S. Forti, A. Al Temimy, C. Coletti, M. Serrano-Ruiz, M. Caporali, M. Peruzzini, F. Beltram, and S. Heun: STM Study of Exfoliated Few Layer Black Phosphorus Annealed in Ultrahigh Vacuum, E-MRS Spring Meeting 2019, Nice, France, 27 – 31 May 2019 (poster). [Abstract] [Poster]
  9. Abhishek Kumar: Black Phosphorus: Pristine and doped surface investigations using Scanning Tunneling Microscopy, Thesis Defense, Scuola Normale Superiore, Pisa, Italy, 15 October 2019. [Talk]
  10. S. Heun: Surface Engineering of two-dimensional black Phosphorus, Israel-Italy Workshop on 2D Materials, Bar-Ilan University, Israel, 25 – 27 November 2019 (invited). [Program] [Abstract] [Talk]
  11. S. Heun: Black phosphorus n-type doping by Cu: a microscopic surface investigation, New Times, 1st International Virtual Conference, 14 – 18 June 2021 (invited). [Abstract] [Talk]
  12. A. Kumar, F. Telesio, D. Prezzi, C. Cardoso, A. Catellani, S. Forti, C. Coletti, M. Serrano-Ruiz, M. Peruzzini, F. Beltram, and S. Heun: Black phosphorus n-type doping by Cu: a microscopic surface investigation, International Symposium on Nanoscale Research, Leoben, Austria, 20 – 21 September 2021 (oral). [Abstract] [Talk]