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Piezoelectric effect in chemical vapour deposition-grown atomic-monolayer triangular molybdenum disulfide piezotronics.

Qi J, Lan YW, Stieg AZ, Chen JH, Zhong YL, Li LJ, Chen CD, Zhang Y, Wang KL - Nat Commun (2015)

Bottom Line: Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation.The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams.Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical-electronic nanodevices.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Science and Engineering, University of Science and Technology Beijing, Xueyuan Road 30, Beijing 100083, China.

ABSTRACT
High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation. The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation. These polarization charges alter the Schottky barrier height on both contacts, resulting in a barrier height increase with increasing compressive strain and decrease with increasing tensile strain. The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams. In addition, a new type of MoS2 strain/force sensor built using a monolayer MoS2 triangle is also demonstrated. Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical-electronic nanodevices.

No MeSH data available.


Related in: MedlinePlus

Band diagrams of the triangle monolayer MoS2 piezotronic device.(a) Energy band diagram of the device without bias voltage. Schottky barrier has similar barrier heights at the S and D contacts. (b) Energy band diagram of the device with an external bias. The quasi-Fermi level is raised at the source contact. (c) Negative polarization charges induced on three zigzag edges of MoS2 under a local isotropic compressive strain, depleting free electrons near the contact interface and increasing the SBHs at both contacts. The asymmetry of band diagram is the result of the bias. (d) Positive polarization charges induced on three zigzag edges of MoS2 under a local isotropic tensile strain, attracting free electrons near the contact interface and decreasing the SBHs at both contacts. The red arrows represent the directions of polarization. EF is Fermi level of monolayer MoS2, EC is conduction band, EV is valence band, Vbias is the external bias and Δ is the piezopotential induced the change of barrier height.
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f6: Band diagrams of the triangle monolayer MoS2 piezotronic device.(a) Energy band diagram of the device without bias voltage. Schottky barrier has similar barrier heights at the S and D contacts. (b) Energy band diagram of the device with an external bias. The quasi-Fermi level is raised at the source contact. (c) Negative polarization charges induced on three zigzag edges of MoS2 under a local isotropic compressive strain, depleting free electrons near the contact interface and increasing the SBHs at both contacts. The asymmetry of band diagram is the result of the bias. (d) Positive polarization charges induced on three zigzag edges of MoS2 under a local isotropic tensile strain, attracting free electrons near the contact interface and decreasing the SBHs at both contacts. The red arrows represent the directions of polarization. EF is Fermi level of monolayer MoS2, EC is conduction band, EV is valence band, Vbias is the external bias and Δ is the piezopotential induced the change of barrier height.

Mentions: It has been theoretically reported that due to lack of centrosymmetry in crystal structure, MoS2 with an odd number of layers under strain will give rise to in-plane piezoelectric polarization charges induced at the zigzag edges24. Here, an AFM tip has been used to apply controlled, local isotropic strain rather than uniaxial strain. In-plane charge polarization radiates circularly from the centre towards the zigzag edges in the case tensile strain, or in an opposite way under compressive strain, instead of along one direction as in the case of uniaxial strain38. In the case of a triangular monolayer MoS2 under local isotropic strain, the induced polarization charges are in the presence of three discrete zigzag edges. Band diagrams of triangular monolayer MoS2 piezotronic devices are provided in Fig. 6, to explain the underlying working mechanism. First, the presence of metal contacts with the semiconducting monolayer of MoS2 establishes the same Schottky barriers height (SBH) at both sides of contacts, as shown in Fig. 6a. When connected to an external power supply for electrical measurements, the quasi-Fermi level of the MoS2 device is raised at one of the contacts as seen in Fig. 6b. However, the barrier heights at the metal sides on both contacts remain the same. Next, placing the AFM tip in contact with the centre of the triangular MoS2 device produces local isotropic compressive strain in the monolayer and negative polarization charges are induced at three zigzag edges of the triangular MoS2, as shown in Fig. 6c. Finally, an induced negative piezopotential at the MoS2 side depletes free electrons near its interface with the metal, thereby increasing SBHs at both contacts and producing a decrease in the measured current under compressive strain. In contrast, positive polarization charges are induced at the three zigzag edges of the MoS2 triangle under a local isotropic tensile strain as shown in Fig. 6d. In the tensile condition, positive-induced polarization charges attract free electrons near the interface between the metals and the MoS2, resulting in decreased SBHs at both contacts and an increase in the measured current. The conductivity of the MoS2 device is clearly sensitive to changes in SBH and the measured current can be readily modulated by strain-induced charge polarization. It is noteworthy that the induced polarization charge with the same sign around three zigzag edges of the triangle MoS2 is expected to observe symmetrical modulation of carrier transport between any two contacts in this experiment. This was evidently verified in the observed I–Vb curves (shown in Fig. 3c). Based on the proposed mechanism, the piezoelectrically induced transport behaviour has been shown to be robust and reproducible. However, the piezoelectricity of nanomaterials may be affected by many factors, including the geometric size, crystal orientation, temperature, surface piezoelectricity and non-local effects. Although new electromechanical theories have been proposed in recent years234950, great efforts are still required to understand the new physics of piezoelectricity in nanomaterials.


Piezoelectric effect in chemical vapour deposition-grown atomic-monolayer triangular molybdenum disulfide piezotronics.

Qi J, Lan YW, Stieg AZ, Chen JH, Zhong YL, Li LJ, Chen CD, Zhang Y, Wang KL - Nat Commun (2015)

Band diagrams of the triangle monolayer MoS2 piezotronic device.(a) Energy band diagram of the device without bias voltage. Schottky barrier has similar barrier heights at the S and D contacts. (b) Energy band diagram of the device with an external bias. The quasi-Fermi level is raised at the source contact. (c) Negative polarization charges induced on three zigzag edges of MoS2 under a local isotropic compressive strain, depleting free electrons near the contact interface and increasing the SBHs at both contacts. The asymmetry of band diagram is the result of the bias. (d) Positive polarization charges induced on three zigzag edges of MoS2 under a local isotropic tensile strain, attracting free electrons near the contact interface and decreasing the SBHs at both contacts. The red arrows represent the directions of polarization. EF is Fermi level of monolayer MoS2, EC is conduction band, EV is valence band, Vbias is the external bias and Δ is the piezopotential induced the change of barrier height.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4491182&req=5

f6: Band diagrams of the triangle monolayer MoS2 piezotronic device.(a) Energy band diagram of the device without bias voltage. Schottky barrier has similar barrier heights at the S and D contacts. (b) Energy band diagram of the device with an external bias. The quasi-Fermi level is raised at the source contact. (c) Negative polarization charges induced on three zigzag edges of MoS2 under a local isotropic compressive strain, depleting free electrons near the contact interface and increasing the SBHs at both contacts. The asymmetry of band diagram is the result of the bias. (d) Positive polarization charges induced on three zigzag edges of MoS2 under a local isotropic tensile strain, attracting free electrons near the contact interface and decreasing the SBHs at both contacts. The red arrows represent the directions of polarization. EF is Fermi level of monolayer MoS2, EC is conduction band, EV is valence band, Vbias is the external bias and Δ is the piezopotential induced the change of barrier height.
Mentions: It has been theoretically reported that due to lack of centrosymmetry in crystal structure, MoS2 with an odd number of layers under strain will give rise to in-plane piezoelectric polarization charges induced at the zigzag edges24. Here, an AFM tip has been used to apply controlled, local isotropic strain rather than uniaxial strain. In-plane charge polarization radiates circularly from the centre towards the zigzag edges in the case tensile strain, or in an opposite way under compressive strain, instead of along one direction as in the case of uniaxial strain38. In the case of a triangular monolayer MoS2 under local isotropic strain, the induced polarization charges are in the presence of three discrete zigzag edges. Band diagrams of triangular monolayer MoS2 piezotronic devices are provided in Fig. 6, to explain the underlying working mechanism. First, the presence of metal contacts with the semiconducting monolayer of MoS2 establishes the same Schottky barriers height (SBH) at both sides of contacts, as shown in Fig. 6a. When connected to an external power supply for electrical measurements, the quasi-Fermi level of the MoS2 device is raised at one of the contacts as seen in Fig. 6b. However, the barrier heights at the metal sides on both contacts remain the same. Next, placing the AFM tip in contact with the centre of the triangular MoS2 device produces local isotropic compressive strain in the monolayer and negative polarization charges are induced at three zigzag edges of the triangular MoS2, as shown in Fig. 6c. Finally, an induced negative piezopotential at the MoS2 side depletes free electrons near its interface with the metal, thereby increasing SBHs at both contacts and producing a decrease in the measured current under compressive strain. In contrast, positive polarization charges are induced at the three zigzag edges of the MoS2 triangle under a local isotropic tensile strain as shown in Fig. 6d. In the tensile condition, positive-induced polarization charges attract free electrons near the interface between the metals and the MoS2, resulting in decreased SBHs at both contacts and an increase in the measured current. The conductivity of the MoS2 device is clearly sensitive to changes in SBH and the measured current can be readily modulated by strain-induced charge polarization. It is noteworthy that the induced polarization charge with the same sign around three zigzag edges of the triangle MoS2 is expected to observe symmetrical modulation of carrier transport between any two contacts in this experiment. This was evidently verified in the observed I–Vb curves (shown in Fig. 3c). Based on the proposed mechanism, the piezoelectrically induced transport behaviour has been shown to be robust and reproducible. However, the piezoelectricity of nanomaterials may be affected by many factors, including the geometric size, crystal orientation, temperature, surface piezoelectricity and non-local effects. Although new electromechanical theories have been proposed in recent years234950, great efforts are still required to understand the new physics of piezoelectricity in nanomaterials.

Bottom Line: Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation.The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams.Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical-electronic nanodevices.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Science and Engineering, University of Science and Technology Beijing, Xueyuan Road 30, Beijing 100083, China.

ABSTRACT
High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation. The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation. These polarization charges alter the Schottky barrier height on both contacts, resulting in a barrier height increase with increasing compressive strain and decrease with increasing tensile strain. The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams. In addition, a new type of MoS2 strain/force sensor built using a monolayer MoS2 triangle is also demonstrated. Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical-electronic nanodevices.

No MeSH data available.


Related in: MedlinePlus