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Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy

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ABSTRACT

The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III–V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn–Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.

No MeSH data available.


(a) STM image obtained at 8 K (Vs = −3.0 V, It = 1.0 nA) with 8 × 8 mesh in which time-dependent STM measurements were carried out. (b) Sequence used in measurement of temporal change of the tunneling current (ti: electron injection time). At first we opened the STM feedback loop and the sample bias voltage was changed to a positive value of Vs = +1.5 V (red arrow 1). Then, we closed the feedback loop at the set point with a tunneling current of +0.03 nA (green arrow) to start injection of electrons from the tip to the sample (injection). Almost at the same time, we opened the feedback loop again to fix the tip and started measurement of tunneling current. After an electron injection, the bias voltage was returned to Vs = −2.0 V (red arrow 2). (c) Measurement of temporal change of the tunneling current obtained for the 8 × 8 mesh shown in (a). (d) Three typical plots in a magnified scale selected from those in (c). The spectra shown in green, blue and red respectively correspond to those in the squares in (c) indicated by the same colors. (e) STM image obtained after time-resolved STM measurements shown in (c) (Vs = −3.0 V, It = 1.0 nA).
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Figure 3: (a) STM image obtained at 8 K (Vs = −3.0 V, It = 1.0 nA) with 8 × 8 mesh in which time-dependent STM measurements were carried out. (b) Sequence used in measurement of temporal change of the tunneling current (ti: electron injection time). At first we opened the STM feedback loop and the sample bias voltage was changed to a positive value of Vs = +1.5 V (red arrow 1). Then, we closed the feedback loop at the set point with a tunneling current of +0.03 nA (green arrow) to start injection of electrons from the tip to the sample (injection). Almost at the same time, we opened the feedback loop again to fix the tip and started measurement of tunneling current. After an electron injection, the bias voltage was returned to Vs = −2.0 V (red arrow 2). (c) Measurement of temporal change of the tunneling current obtained for the 8 × 8 mesh shown in (a). (d) Three typical plots in a magnified scale selected from those in (c). The spectra shown in green, blue and red respectively correspond to those in the squares in (c) indicated by the same colors. (e) STM image obtained after time-resolved STM measurements shown in (c) (Vs = −3.0 V, It = 1.0 nA).

Mentions: Figure 3(a) shows an STM image of the surface with an 8 × 8 mesh in each of which the STM electron-injection sequence shown in figure 3(b) was carried out as follows. (1) during an STM scan with the set-point conditions (sample bias and current) of Vs = −2.0 V and It = −1.0 nA, the tip was held at a certain line crossing in the mesh (t = 0). (2) After opening the STM feedback loop, the sample bias voltage was changed to a positive value of Vs = +1.5 V (red arrow 1), at which the tunneling current usually became very small reflecting the I–V character of this surface. (3) Then, the feedback loop was closed at the set point with a tunneling current of +0.03 nA (green arrow). In this step, the distance between the STM tip and the sample became small and electronic injection from the tip to the sample started to occur (injection). After a very short time, we open the feedback loop again to fix the distance between the tip and the surface and started measurement of tunneling current at the same time. (4) After an electron injection time of ti = 0.3 s, the bias voltage was returned to Vs = −2.0 V (red arrow 2).


Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy
(a) STM image obtained at 8 K (Vs = −3.0 V, It = 1.0 nA) with 8 × 8 mesh in which time-dependent STM measurements were carried out. (b) Sequence used in measurement of temporal change of the tunneling current (ti: electron injection time). At first we opened the STM feedback loop and the sample bias voltage was changed to a positive value of Vs = +1.5 V (red arrow 1). Then, we closed the feedback loop at the set point with a tunneling current of +0.03 nA (green arrow) to start injection of electrons from the tip to the sample (injection). Almost at the same time, we opened the feedback loop again to fix the tip and started measurement of tunneling current. After an electron injection, the bias voltage was returned to Vs = −2.0 V (red arrow 2). (c) Measurement of temporal change of the tunneling current obtained for the 8 × 8 mesh shown in (a). (d) Three typical plots in a magnified scale selected from those in (c). The spectra shown in green, blue and red respectively correspond to those in the squares in (c) indicated by the same colors. (e) STM image obtained after time-resolved STM measurements shown in (c) (Vs = −3.0 V, It = 1.0 nA).
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Figure 3: (a) STM image obtained at 8 K (Vs = −3.0 V, It = 1.0 nA) with 8 × 8 mesh in which time-dependent STM measurements were carried out. (b) Sequence used in measurement of temporal change of the tunneling current (ti: electron injection time). At first we opened the STM feedback loop and the sample bias voltage was changed to a positive value of Vs = +1.5 V (red arrow 1). Then, we closed the feedback loop at the set point with a tunneling current of +0.03 nA (green arrow) to start injection of electrons from the tip to the sample (injection). Almost at the same time, we opened the feedback loop again to fix the tip and started measurement of tunneling current. After an electron injection, the bias voltage was returned to Vs = −2.0 V (red arrow 2). (c) Measurement of temporal change of the tunneling current obtained for the 8 × 8 mesh shown in (a). (d) Three typical plots in a magnified scale selected from those in (c). The spectra shown in green, blue and red respectively correspond to those in the squares in (c) indicated by the same colors. (e) STM image obtained after time-resolved STM measurements shown in (c) (Vs = −3.0 V, It = 1.0 nA).
Mentions: Figure 3(a) shows an STM image of the surface with an 8 × 8 mesh in each of which the STM electron-injection sequence shown in figure 3(b) was carried out as follows. (1) during an STM scan with the set-point conditions (sample bias and current) of Vs = −2.0 V and It = −1.0 nA, the tip was held at a certain line crossing in the mesh (t = 0). (2) After opening the STM feedback loop, the sample bias voltage was changed to a positive value of Vs = +1.5 V (red arrow 1), at which the tunneling current usually became very small reflecting the I–V character of this surface. (3) Then, the feedback loop was closed at the set point with a tunneling current of +0.03 nA (green arrow). In this step, the distance between the STM tip and the sample became small and electronic injection from the tip to the sample started to occur (injection). After a very short time, we open the feedback loop again to fix the distance between the tip and the surface and started measurement of tunneling current at the same time. (4) After an electron injection time of ti = 0.3 s, the bias voltage was returned to Vs = −2.0 V (red arrow 2).

View Article: PubMed Central - PubMed

ABSTRACT

The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III–V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn–Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.

No MeSH data available.