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

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| National Institute for Materials Science

Science and Technology of Advanced Materials

Sci. Technol. Adv. Mater. 16 (2015) 015002 (8pp)

doi:10.1088/1468-6996/16/1/015002

Dynamic probe of ZnTe(110) surface byscanning tunneling microscopy
Ken Kanazawa, Shoji Yoshida, Hidemi Shigekawa and Shinji Kuroda
Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, Japan
E-mail: kanazawa@ims.tsukuba.ac.jp
Received 7 September 2014
Accepted for publication 18 December 2014
Published 13 January 2015
Abstract

The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promisingmaterial in the research ﬁeld of semiconductor spintronics, was studied by scanning tunnelingmicroscopy/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 aresimilar 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, asurface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale
manipulation of this widely applicable surface of ZnTe.
Keywords: scanning tunneling microscopy, atom manipulation, ZnTe, semiconductor surface

1. Introduction

Comparing to group IV or III–V semiconductors, however, the ZnTe surface has not been well comprehended.
Moreover, reported studies are mainly concerned with static
surface properties such as atomic structure and electronic
ground state, but dynamic phenomena on the surface havebeen largely uncertain. ZnTe(110) surface states, which are
the topic of this paper, have been studied by low-energy
electron diffraction [7], scanning tunneling microscopy(STM) [8, 9], angle-resolved photoelectron spectroscopy(ARPES) [10], electron energy loss spectroscopy (EELS) [11]and density functional theory (DFT) calculations [12]. These
results have revealed that the topmost cationic and anionic
atoms are slightly displaced toward the inside of the crystal
and vacuum from the ideal (110) structures of truncated bulk
crystal, respectively, and the atomic arrangement of ZnTe(110) surface is fundamentally similar to that of III–V semiconductor surfaces (hereafter referred to as the reconstructedsurface). The STM observations, however, showed that thissurface is unstable and friable, i.e., line defects tend to begenerated along the 〈110〉 direction (ﬁgure 1(a)) when a cleansurface is obtained by cleavage [8, 9]. In addition, when thesurface is scanned by STM with a positive sample bias voltage, surface atoms are often desorbed from the surface [8].
These characteristics are unique and markedly different fromthose of IV and III–V semiconductor surfaces.

The characterization of semiconductor surfaces is important
not only for fundamental scientiﬁc research but also for theapplication of nanotechnology. Group IV (Si and Ge) and III–V (GaAs, GaP and InSb) semiconductor surfaces have been
intensively studied, particularly from the viewpoint ofdeveloping novel electronic devices. ZnTe, which we focus
on in this study, is a II–VI semiconductor with a relatively
wide direct band gap and is expected to be applied for opticaldevices such as green light-emitting diodes [1] and THz light
generators and detectors [2, 3]. In addition, ZnTe is also
commonly used as a substrate for CdTe self-assembled
quantum dots [4]. Furthermore, it is used as a host material of
diluted magnetic semiconductors (DMS), which are promising materials in the research ﬁeld of semiconductor spintronics [5, 6]. For example, (Zn,Cr)Te is well known for its
intrinsic room-temperature ferromagnetism, which is realized
when the Cr composition is higher than 20% (Zn0.8Cr0.2Te).

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1© 2015 National Institute for Materials ScienceK Kanazawa et al

Sci. Technol. Adv. Mater. 16 (2015) 015002

Figure 1. (a) STM image of ZnTe(110) surface (Vs = −1.5 V, It = 60 pA). (b) High-resolution image of ZnTe(110) surface (Vs = −2.0 V,
It = 20 pA). (c) Schematic structures of ZnTe(110) surface.

With the reduction of device size, the development ofcomposite materials with multiple functions is required.
Control of the surface atomic and electronic structures, particularly that of atomic-scale defects, has become a key
technology to meet the requirements. Therefore, to exploit thecharacteristics of ZnTe, it is important to clarify the structures
and the associated phenomena of its surface. For this purpose,
we have carried out scanning tunneling microscopy andspectroscopy (STM/STS) analysis of this surface. In addition
to conﬁrming the charge transfer on this surface, oscillation intunneling current, which is considered to reﬂect the positional
ﬂuctuation of the topmost Zn atom induced by charge injection was observed. Furthermore, by applying this mechanism,
we have succeeded in fabricating atomic structures on thesurface. Such fabrication is expected to play a role, forexample, in modulating the local potential of a surface todesign functional devices with various electronic properties.

Figure 2. (a) Normalized differential conductance (NDC)—sample
bias voltage spectra obtained above a Zn atom (blue) and a Te atom(red). The setpoint voltage and current were Vs = −2.0 V and
It = 20 pA, respectively. The peaks shown in the blue (+1.0 eV) andred (−0.8 eV) lines indicate the energy levels of the dangling bondstates of the surface Zn and Te atoms, respectively. (b) Schematic of
the ZnTe band structure derived from the NDC-Vs spectra.

2. Experimental methods
A p-type ZnTe single crystal doped with phosphorus of aconcentration of 1018 cm−3 was used as a sample in this study.
All STM/STS measurements were performed with an Omicron low-temperature scanning tunneling microscope underultrahigh-vacuum conditions (<10−8 Pa) at 8 K and 77 K
using an electrochemically sharpened W tip (ϕ = 0.3 mm). A
ZnTe(110) surface was obtained by cleaving the sample in ahigh vacuum (∼1 × 10−5 Pa).

caused by the absence of topmost atoms and are intrinsic
defects of the ZnTe(110) surface, as mentioned above. From
the different brightness on the both sides of the dark-line
defects, we can determine the indexes of the in-plane crystallographic axes on the surface (the distinction between [110]and [−110] axes), as shown in ﬁgure 1(a) [9]. And we could
determine the correspondence of the STM image to theatomic arrangement on the surface (ﬁgure 1(c)) as shown inﬁgure 1(b).
To investigate the surface electronic structure in moredetail, we carried out STS measurement. Figure 2 shows theresults of normalized differential conductance (NDC) analysis, which reﬂects the local density of states (LDOS). NDC-Vs
curves were measured on topmost Zn (blue) and Te (red)atoms, respectively. There are differences between the two
curves, particularly at the rising edges from the semiconductive gap region near Vs = 0. At the rising edge at a
positive (negative) sample bias voltage, the NDC-Vs spectrum
obtained at the Zn (Te) position exhibits a higher peak thanthat obtained at the Te (Zn) position. These results can be

3. Results and discussion
Figure 1(a) shows a typical STM image obtained at a sample
bias voltage of Vs = −1.5 V. Since occupied lone pair states
are formed on the topmost Te atoms due to charge transferfrom topmost Zn atoms, the Te atoms can be imaged as brightpoints at a negative sample bias voltage. In addition to thebright lines of Te atoms along the 〈110〉 direction, several
dark lines along the same direction were observed. According
to the previous study [8], these dark lines are line defects
2

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Sci. Technol. Adv. Mater. 16 (2015) 015002

original ‘low-current’ state and another ‘high-current’ state.
No damage was observed in the STM image obtained after
sequential measurements, as shown in ﬁgure 3(e), whichindicates that, during the sequence, the charge injection of thiscondition induced only current oscillation without any
destructive contact or scratching of the surface with the
STM tip.
As a possible reason of the current oscillation, we may
consider ﬁrst the simple reﬂection of a temporal occupying
event of electrons at the surface such as the Coulombblockade, which, however, is not consistent with ourexperimental results. If Coulomb-blockade was formed, weshould observe the effect of the ‘staying electron’ as the dropof the tunneling current. However, we observed the jump-up
of tunneling current from the original ‘low-current’ state at
the start of the injection of the tunneling electron.
Comparing the current oscillation with the unstable STM
observation with a positive sample bias voltage as reported by
the earlier study [8], a possible phenomenon to be able toexplain the current oscillation is a structural variation between
the original surface-reconstructed structure and anotherstructure, which causes the ‘high-current’ state, i.e., the STM
sequence induces a structural change of the topmost Zn or Te
atom toward the vacuum side from the reconstructedstructure.
What causes the structural change? A possible mechanism to excite the structural change is the effect of inelastic
tunneling which is widely observed. However, any current
oscillation was not observed in a similar sequence with anegative sample bias voltage, which should appear in the caseof inelastic tunneling: inelastic tunneling occurs at the same
positive and negative bias voltages.
In order to establish a possible interpretation for thesurface dynamics induced by the electron injection of the
STM sequence, we carried out a DFT calculation using thePerdew–Burke–Ernzerhof generalized gradient approximation with the ABINIT code and plane-wave-based normconserving pseudopotentials. A supercell including a slab
model with ﬁve ZnTe(110) layers was used for the calculation. The dangling bonds of atoms in the bottom layer werepassivated by hydrogen atoms, as shown in ﬁgure 4(a). Theenergy cutoff of the calculation was 60 Ry. As the samplingk-points, we used 8 × 8 × 2 grids within the ﬁrst Brillouinzone. Here, we focused on a possibility of the atomic displacement of the topmost Zn atom, because the Zn atom is
considered to be most easily desorbed from the surface,referring to the previous study [9], which reports that thedefects on the cleaved ZnTe(110) surface mainly consist of
the absences of Zn only or Zn–Te pairs and not Te only. As apossible computational model to describe the atomic displacement of the surface Zn atom toward the vacuum sidefrom the reconstructed structure, we consider the ideal (110)
surface structure consisting of a truncated bulk structure. The
stability of the surface was analyzed by comparing the totalenergy difference between the ideal and reconstructed surface
structures in the neutral state and in charged states with up to
six additional electrons per supercell.

comprehensively explained by the mechanism that the empty
and occupied dangling bond states are formed through the
charge transfer from cationic Zn to anionic Te associated withthe surface reconstruction. Similar charge transfer is wellknown to occur on several semiconductor surfaces such as Si(100) dimer and GaAs(110) reconstructed surfaces, which has
been conﬁrmed by STM observation with atomic resolution[13, 14]. The STS analysis has conﬁrmed the surface states ofZnTe(110) in the real space. The observed energy levels
correspond to the surface states studied by ARPES [10],EELS [11], and DFT [12], which have suggested that theanionic Te (cationic Zn) dangling bond state is located near
the valence band maximum (conduction band minimum), as
shown in ﬁgure 2(b). Here, the energy gap of the host ZnTe
was determined from the distance between the Zn (−1.0 V)
and Te (+1.3 V) peaks in the spectra, because we have to
remove the inﬂuence of their surface states. The gap energy
obtained is about 2.3 eV, which is close to the previously
reported energy gap of ZnTe (2.39 eV at 4.2 K).
In this STS measurement, a small current set point (−2 V,
20 pA), which was used to observe the STM image inﬁgure 1(b), was chosen to reduce the effect of the surface
instability reported in an STM measurement for the positive
sample bias voltage region. In fact, no remarkable phenomenon related to the instability was observed during the STS
measurements. However, with a larger tunneling current setpoint, the surface instability appeared. Therefore, next weinvestigated the instability observed during the STM measurement at a positive sample bias voltage in more detail. To
observe the expected dynamics on the surface, we studied theeffect of the electron-injection from the STM tip to the sample
at 8 K with the tip position ﬁxed at meshed points during thetwo-dimensional scan over the surface.
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 washeld at a certain line crossing in the mesh (t = 0). (2) After
opening the STM feedback loop, the sample bias voltage waschanged 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, thefeedback loop was closed at the set point with a tunnelingcurrent of +0.03 nA (green arrow). In this step, the distance
between the STM tip and the sample became small andelectronic 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 andstarted 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).
Figure 3(c) shows the tunneling current as a function oftime measured in each 8 × 8 grid in ﬁgure 3(a). The origin,tmes = 0, is the time when the tunneling current was set to+0.03 nA. Variations in the tunneling current can be seen.
Figure 3(d) shows three typical examples of data selectedfrom ﬁgure 3(c). The current appears to oscillate between the3

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Sci. Technol. Adv. Mater. 16 (2015) 015002

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 carriedout. (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, thebias 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).

Furthermore, in order to discuss the effect of the electrons injected from the STM tip in more detail theoretically,
we calculated partial density of states (PDOS) for the topmost
Zn and Te atoms and the Zn atom located in the third (110)layer, which should correspond to the state far from the
topmost surface, of the reconstructed surface with no and one
additional electron. The results of the PDOS calculations
show that the PDOS of the topmost Zn atom is the largest
near the conduction band minimum in the neutral condition(ﬁgure 4(d)) and the state is occupied by one additional
electron with the shift of the Fermi energy (EF) (dotted lines),
as indicated by a black arrow (ﬁgure 4(e)). In addition, thetheoretical results of the DOS (ﬁgure 4(f)) and spatial distribution of the LDOS integrated over EF−0.2 eV < E < EF(ﬁgure 4(g)) calculated for the ideal surface structure with two
additional electrons, which may cause the inversion of thesurface stability, clearly indicate that the additional electrons
are preferentially located at the topmost Zn atom of the ideal
structure. These results are consistent with those of our STS
measurement, in which we observed the ZnDB state near the
conduction band minimum, suggesting that the injected
electrons tend to be located at the dangling bond states of the
topmost Zn. Upon the occupation of the empty ZnDB states by

Figure 4(b) shows the summary of the results of our DFT
calculation, showing the total energy difference between theideal and reconstructed surface structures (Eide−Erec) as afunction of the number of additional electrons per supercell.
As shown in the ﬁgure, the reconstructed surface is morestable than the ideal surface in the neutral state (without
additional electrons). This result validates the surface reconstruction of this surface with the buckling of the Zn–Te
structure, similar to the cases of the Si dimer and Ga–As
structure appearing upon their surface reconstruction [13, 14].
On the other hand, the surface stability changes with the
charge injection; the ideal conﬁguration becomes more stable
when the number of additional electrons is larger than 1.5.
Considering the result of our theoretical study with the resultof our experiment, in which the variations in the tunnelingcurrent was observed, these results may indicate that theelectrons injected from an STM tip induce modulation of thesurface structure; the charge injection into the surface region
may induce an atomic oscillation of the surface Zn atoms
between the reconstructed structure and a structure with displacement of the Zn atom toward the vacuum side as schematically shown in ﬁgure 4(c).
4K Kanazawa et al

Sci. Technol. Adv. Mater. 16 (2015) 015002

Figure 4. (a) Schematic illustration of the ZnTe structure used for the DFT calculation. (b) Total energy difference between the ideal andreconstructed surface structures (Eide−Erec) as a function of the number of injected electrons. (c) Schematic diagrams showing atom
manipulation by charge injection. Electrons injected from the STM tip induce the displacement of the topmost Zn atoms toward the vacuum
side. (d) and (e) Calculated partial density of states (PDOS) for the topmost Zn and Te atoms and the Zn atom located in the third (110) layerof the reconstructed surface with no (d) and one (d) additional electron. (f) DOS calculated for the ideal surface structure with two additional
electrons. (g) Calculated spatial distributions of the LDOS integrated over EF−0.2 eV < E < EF (EF: Fermi energy) for the ideal surface
structure with two additional electrons.

cases, but at a much greater distance from the Zn atom inother cases.
Next, we consider the relationship between the structural
oscillations and the atomic desorption from the surface
induced by STM observation at a positive sample bias voltage
in the previous study. No damage reﬂecting the atomic desorption was observed with the measurement condition of the
STS measurement (ﬁgure 1) and during the above STM
sequence (ﬁgure 3) in this study. However, the atomic desorption occurred when we used the setpoint tunneling currentof ten times larger, I = 0.3 nA. Figures 5(a) and (c) show the
STM images obtained before and after the electron injection
sequence shown in ﬁgure 3, which was carried out at the grid
points of the mesh drawn in ﬁgure 5(a). Formation of defects
is clearly shown in ﬁgure 5(c). When the surface Zn atom isdisplaced toward to the vacuum by the electron injection,
tunneling current increases. In fact, much larger tunnelingcurrent, which exceeded the detection limits of 5 nA wasobserved during the electron injection as shown in ﬁgure 5(b),which might induce the atomic desorption as a result of anenhancement of the atomic oscillation.
Here, the appearances of the atomic deﬁciencies generated by the desorption process are quite similar to the intrinsic
line defects on the cleaved ZnTe(110) surface recognized as a

the additional electrons, the bonding state of the Zn atom withneighboring Te atoms may change from the ﬂat sp2-like
conformation to the sp3-like tetrahedral coordination. The
distance between the STM tip and the Zn atom decreases
upon the conformational change from the reconstructedstructure to the displaced structure with Zn atom moved
toward the vacuum side, producing the high state observed intunneling current. According to our theoretical study, theconformational change is considered to be a possible
mechanism for producing the current oscillation observed
during the STM electron-injection sequence.
If the STM tip and the surface Zn atom are closely
located, the electrons are injected to the dangling bond with ahigh possibility, and, the displacement should occur frequently. In this case, the ‘high-current’ state is supposed to beobserved continually. Actually, comparing the details of thecurrent oscillations shown in ﬁgure 3(c), the tunneling current
in the top spectrum of ﬁgure 3(d) tends to be high, forexample, and in the bottom spectrum the oscillation occurs
less often. This difference is considered to be due to therelative lateral positions of the STM tip to that of a Zn atom
below the tip. Since the measurement in each mesh wasstarted without checking the relative positions, the STM tip
might be located only slightly above the Zn atom in some5

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Sci. Technol. Adv. Mater. 16 (2015) 015002

Figure 5. (a) STM image before the electron-injection sequence with Vs = +1.5 V and It = 0.3 nA (Vs = −3.0 V, It = 1.0 nA). (b) Temporalchange of the current obtained during the electron-injection sequence carried out on the area indicated by dotted lines. (c) STM image of thesurface defects generated by the electron-injection sequence (Vs = −3.0 V, It = 1.0 nA).

Figure 6. (a) STM image of a ZnTe surface obtained before the electron injection treatment (Vs = −3.0 V, It = 1.0 nA). (b) Typical temporalchange of the current obtained during the treatment. (c), (d), (e) STM images after the treatment with three different electron injection timesof ti ((c) 0.1 s, (d) 0.3 s, (e) 0.5 s, Vs = +1.5 V, It = 30 pA). D1 to D4 are surface defects induced by each treatment. D3 in (d) and (e) indicate
exactly the same defect. Black arrows indicate clusters of atoms desorbed by the manipulation.

STM tip and the surface atom during the electron injection, inorder to induce the desorption of surface atoms. Speciﬁcally,
possible reasons, which may inﬂuence the probability of thedesorption, include the tunneling current, the distance, theelectric ﬁeld between the STM tip and the sample surface, andthe local temperature.
To verify the mechanism, we carried out current injection
under different conditions. Namely, we observed the surface
and placed the STM tip immediately above a Zn atom, andmissing row of Zn atoms or Zn–Te pair, though the length of
the generated defects are quite short. Therefore, it is reasonable to consider that the short defects arise from the positionof the surface Zn atom, corresponding to the theoretical calculation, which supports the model that the charge injection
from the STM tip induces the displacement of the surface
Zn atom.
This result suggests that we should consider the experimental parameters to enhance the interaction between the6

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Sci. Technol. Adv. Mater. 16 (2015) 015002

then the sequence shown in ﬁgure 3(b) was carried out. The
sample temperature was set at 77 K.
Figure 6(a) shows the surface observed before the treatment. Figure 6(b) shows a typical time-resolved spectrum,i.e., the tunneling current as a function of time, in whichtmes = 0 corresponds to the moment when the tunneling current was set to +0.03 nA, similarly to the case shown inﬁgure 3(d). The tunneling current jumped from 0.03 to ∼5 nA
and then disappeared. Figure 6(c) shows the STM image after
the treatment with the injection time of ti = 0.1 s, in which an
atomic-scale defect was generated. Namely, the jump intunneling current shown in ﬁgure 6(b) is considered to correspond to the desorption of the surface Zn atom. To conﬁrm
this result, we carried out the same process with increased
electron injection times ti to 0.3 s and 0.5 s, the results ofwhich are shown in ﬁgures 6(d) and (e), respectively. Larger
defects were generated with increasing ti, and clusters considered to be formed by the removal of atoms were observed,
as indicated by arrows. After the desorption of the Zn atom
immediately below the STM tip, the adjacent Zn atoms may
have been desorbed depending on the injection time. Further
analysis is necessary to determine in detail the conditions
required for desorption. Although the lengths of the defects
were short, their appearances were very similar to the intrinsic
line defect on the ZnTe(110) surface shown in ﬁgure 1(a) inthat they run along the 〈110〉 direction with single-atomicrow-width on the surface.
Here, the atomic manipulations were demonstrated at
77 K with the same parameter as that used in the previous
experiment (ﬁgure 3) at 8 K. The higher environmental temperature of 77 K is only different experimental parameterfrom the former experiment. Considering the two results thatthe ten times larger tunneling current at 8 K and the higher
environmental temperature of 77 K could induce the atomic
desorption, environmental temperature may work as anadditional driving force to overcome the potential hill of thechange in state of the surface Zn atom located just below the
STM tip [15], and the atomic desorption might have been
induced easier at 77 K than at 8 K. Similar temperaturedependence is known for the case of Si(001) surface dimer,where dimer ﬂip-ﬂop motion has temperature dependence[16]. The relationship between atomic desorption and STM
parameters is yet unclear. It involves several factors, such as
local heating by the tunneling current and the relative position
between the tip and surface atoms, which affects the electricﬁeld distribution. Further study is necessary to understand themechanism of the atomic oscillation and desorption.
Finally, we focus on the generated defects. An ellipticaldisk-shaped dark area was observed around the defects, as
shown in ﬁgure 6, which is similar to that around the atomicscale defects and surface steps observed on a GaAs surface[17]. Namely, the results suggest the modulation of theelectronic structure in the region, such as charge doping to thehost semiconductor [18]. Since a dark area is observed at anegative sample bias voltage, a positively charged dopant
center is supposed to be formed here. Although the band
structure must be examined in detail by taking into account a
tip-induced band bending [18, 19], this atomic-scale

fabrication may give a possibility for controlling local electronic structures of this surface.
In fact, in (Ga,Mn)As, for example, activation energy ofMn acceptor was controlled by changing the condition of As
vacancies around the Mn atom [20]. On the other hand, ZnTe
is known to be a host material of (Zn,Cr)Te, one of the mostpromising DMSs with intrinsic room temperature ferromagnetism, as mentioned earlier. According to the results ofprevious studies [21, 22], the magnetic behavior of (Zn,Cr)Te
and the electronic states of the host material ZnTe have aclose relationship; therefore, the manipulation of the surface
electronic states is a key technology for realizing futureadvances in semiconductor spintronics associated with, forexample, nanomagnetism. Although there are many issues toovercome, such as removal of clusters of the desorbed atoms
as indicated by black arrows in ﬁgures 6(c)–(e), for futureapplication with further optimization and improvement of themanipulation techniques, we may be able to fabricate adesired atomic-scale electronic structure, for example, a local
potential modulation, on a surface.

4. Conclusions
The charge transfer associated with the surface reconstructionof ZnTe(110) was conﬁrmed in real space at the atomic scale.
The tunneling current oscillation, which should be concernedwith the positional change of a surface Zn atom between thereconstructed and bulk-like displaced structures as a result of
charge injection, was directly observed using STM and wasfound to be in good agreement with the theoretical calculationof the structural stability. Analysis of the conformationalchange may provide information on the environmental conditions surrounding a Zn atom. In addition, although theconditions required to induce a conformational change must
be clariﬁed, atomic-scale defects were successfully generated
below the STM tip using the atom manipulation process
based on charge injection. Since the generated defects have
similar characteristics to such as the charge dopant in a host
semiconductor, the technique of precise atom manipulation
may be a key factor in the future development of spintronics
or nanomagnetics based on DMS materials.

Acknowledgment
Support from Japan Society for the Promotion of Science inthe form of Grants-in-Aid for Scientiﬁc Research is
acknowledged.

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