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Cite this: Chem. Soc. Rev., 2018,47, 7203
Tellurene: its physical properties, scalablenanomanufacturing,
and device applications
Wenzhuo Wu, *abcd Gang Qiu,ce Yixiu Wang,abc Ruoxing Wangabc and
Peide Ye*ce
Tellurium (Te) has a trigonal crystal lattice with inherent
structural anisotropy. Te is multifunctional, e.g.,
semiconducting, photoconductive, thermoelectric, piezoelectric,
etc., for applications in electronics, sensors,
optoelectronics, and energy devices. Due to the inherent
structural anisotropy, previously reported synthetic
methods predominantly yield one-dimensional (1D) Te
nanostructures. Much less is known about 2D Te
nanostructures, their processing schemes, and their material
properties. This review focuses on the synthesis
and morphology control of emerging 2D tellurene and summarizes
the latest developments in understanding
the fundamental properties of monolayer and few-layer tellurene,
as well as the recent advances in
demonstrating prototypical tellurene devices. Finally, the
prospects for future research and application
opportunities as well as the accompanying challenges of 2D
tellurene are summarized and highlighted.
Key learning points(1) Design and scalable-synthesis of 2D
tellurene with controlled yield and dimensions.(2) Key physical
properties of 2D tellurene.(3) Application of 2D tellurene in
nanoelectronics: field-effect transistors.
1. Introduction
Group VI tellurium (Te) belongs to the chalcogen elementfamily
and is chemically related to selenium and sulfur. Itsrarity in the
earth’s crust is comparable to that of platinum,while tellurium is
far more common in the universe. Te hasappealing properties, e.g.,
semiconducting,1 photoconductive,2
thermoelectric,3 topological,4 and acoustic-optic properties5
forapplications in electronics, sensors, optoelectronics, and
energydevices. Te is also a crucial component of many
functionalmaterials, e.g., tellurides, for numerous
societally-pervasivetechnologies, such as photovoltaics,
thermoelectric devices,infrared imaging, etc. Bulk Te has a
trigonal crystal lattice inwhich individual helical chains of Te
atoms are stacked togetherby weak bonding and spiral around axes
parallel to the [0001]
direction at the center and corners of the hexagonal
elementarycell6 (Fig. 1a). Each tellurium atom is covalently bonded
with itstwo nearest neighbors on the same chain.
Due to the inherent structural anisotropy, previously
reportedsynthetic methods predominantly yield one-dimensional (1D)
Tenanostructures.7–9 Much less is known about 2D Te
nanostructures,
Fig. 1 (a) The crystal structure of tellurium. (b–d) The various
1D Tenanostructures shown in previous reports through (b) solution
phasesynthesis. Reproduced with permission from ref. 7. Copyright
2002, RoyalSociety of Chemistry. (c) PVP-assisted hydrothermal
growth. Reproducedwith permission from ref. 9. Copyright 2006,
American Chemical Society.(d) Hydrothermal reduction method.
Reproduced with permission fromref. 8. Copyright 2002, WILEY-VCH
Verlag GmbH & Co. KGaA, Weinheim.(e) Physical vapor deposition
process. Reproduced with permission fromref. 26. Copyright 2013,
IOP Publishing.
a School of Industrial Engineering, Purdue University, West
Lafayette,
Indiana 47907, USA. E-mail: [email protected] Flex
Laboratory, Purdue University, West Lafayette, Indiana 47907, USAc
Birck Nanotechnology Center, Purdue University, West Lafayette,
Indiana 47907,
USA. E-mail: [email protected] Regenstrief Center for Healthcare
Engineering, Purdue University, West Lafayette,
Indiana 47907, USAe School of Electrical and Computer
Engineering, Purdue University, West Lafayette,
Indiana 47907, USA
Received 25th July 2018
DOI: 10.1039/c8cs00598b
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their processing schemes, and their material properties. As
oneof the newest members of the 2D materials’ family, the
existenceof tellurene, in its monolayer or few-layer form, has only
beenrecently confirmed by experimental work10–13 and
theoreticalcalculations.14,15 Inspired by the limited number of
experimentalstudies available to date, there have been a few recent
theoreticalexplorations16–23 which predict the intriguing
properties of 2Dtellurene, e.g., extraordinary carrier mobility,
significant opticalabsorption, high stretchability, etc.
In the following sections of this review, we intend tosummarize
and highlight the recent theoretical and experi-mental advances in
studying 2D tellurene. Firstly, we will brieflyreview the progress
in synthesizing Te nanostructures since theknowledge gained from
these prior efforts provides valuableinsights and guidance for the
synthesis of 2D tellurene. Secondly,we will review and discuss the
up-to-date understanding of theintriguing properties of 2D
tellurene. The recent demonstration
of tellurene devices, e.g., transistors, will also be discussed.
Lastbut not least, we will provide our outlook and perspectives
forthe future opportunities and challenges in the research
andapplication of 2D tellurene. It is expected that the
intriguing,versatile material properties and technological
potential oftellurene will open up numerous exciting opportunities
in both thefundamental exploration and technological application of
tellurene.
2. Synthesis of telluriumnanostructures2.1 Synthesis of
one-dimensional Te nanostructures
A number of synthetic methods have been developed to deriveTe
nanostructures with various morphologies during the pasttwo
decades, e.g., through solution phase reactions7–9,24,25 andvapor
phase deposition.26,27 The products from these synthetic
Wenzhuo Wu
Dr Wenzhuo Wu is the Ravi andEleanor Talwar Rising StarAssistant
Professor in School ofIndustrial Engineering at PurdueUniversity.
He received his BS inElectronic Information Scienceand Technology
in 2005 fromthe University of Science andTechnology of China
(USTC),Hefei and his ME in Electricaland Computer Engineering
fromthe National University ofSingapore (NUS) in 2008. Dr
Wureceived his PhD from Georgia
Institute of Technology in Materials Science and Engineering
in2013. Dr Wu’s research interests include design,
manufacturing,and integration of 1D and 2D nanomaterials for
applications inenergy, electronics, optoelectronics, and wearable
devices.
Gang Qiu
Gang Qiu received his BS degree inmicroelectronics from
PekingUniversity, Beijing, China in2014. He is currently
workingtowards his PhD degree at Schoolof Electrical and
ComputerEngineering in Purdue University,West Lafayette, Indiana,
USA,under the supervision of Prof.Peide. D. Ye. His current
researchinterests focus on novel low-dimensional material
synthesisand characterization, potentialelectronic device
applications andlow-temperature magneto-transport.
Yixiu Wang
Yixiu Wang received his MSdegree in Materials Science
andEngineering from the Universityof Science and Technology ofChina
(USTC) under the super-vision of Prof. Shu-Hong Yu in2014. He is
currently pursuinghis PhD in the School ofIndustrial Engineering
under thesupervision of Prof. Wenzhuo Wu.His main research activity
focuseson low dimensional materialsynthesis and novel 2D
atomiccrystals targeting nanoelectronics
and energy conversion devices together with the exploration
offundamental phenomena in nanoscale systems.
Ruoxing Wang
Ruoxing Wang received her BSdegree in Chemistry in 2011 fromthe
University of Science andTechnology of China (USTC). Sheis
currently a PhD student inIndustrial Engineering at
PurdueUniversity under the supervision ofProf. Wenzhuo Wu. Her
researchinterests mainly focus on nano-manufacturing including the
designof functional nanomaterials andfabrication of nanodevices
forvarious applications.
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efforts are predominantly 1D nanostructures, such as nano-wires,
nanotubes, and nanobelts, growing along the [0001]chiral-chain
direction because of the inherent structural aniso-tropy in
tellurium6 (Fig. 1).
2.1.1 Vapor-phase processes. Furuta and co-authors pioneeredthe
synthesis of Te whiskers a few microns in length through
thesublimation of metallic Te on solid substrates using a
vapor–solid(VS) process at various temperatures, and have
investigated themorphology evolution of the Te whiskers and the
roles of thesubstrate temperature as well as the axial dislocation
in relatedprocesses.28 They further explored the growth of Te
whiskers bya vapor–liquid–solid (VLS) process using various metal
catalysts,e.g., Tl, Zn, and Se.29 Later, Geng et al. demonstrated a
chemicalvapor deposition process for synthesizing 1D Te nanobelts
byreacting Al2Te3 powder with H2O in a horizontal tube furnace
at500 1C.30 A few studies have also been reported on the growthof
1D Te nanostructures by physical vapor deposition. Forexample, Li
and colleagues used the physical evaporationmethod to prepare
hollow prismatic Te microtubes, showingthat the reaction
temperature and the gas flow rate playedcritical roles in the
growth control.27 Employing a VS mechanism,He and co-authors
reported a catalyst-free physical vapor depositionprocess for
growing aligned 1D Te nanostructures with certaincontrol over the
nucleation density, size, and structures of theformed
materials.26
2.1.2 Solution-phase processes. The requirement for highgrowth
temperature and delicate control in the growth atmospherelimit the
scale-up potential of the vapor-phase approaches. Incontrast, the
solution-phase synthetic routes are more relevant forthe potential
large-scale synthesis of Te nanomaterials andhave attracted
extensive attention during the past two decades.
For example, Xia and colleagues reported the first synthesis
of1D trigonal-Te (t-Te) nanowires through a solution-phase,
self-seeding process where the orthotelluric acid or tellurium
dioxidewas reduced by hydrazine at various refluxing temperatures.7
Qianand co-workers subsequently reported the hydrothermal
synthesisof Te nanobelts through the disproportionation of sodium
tellurite(Na2TeO3) in aqueous ammonia solution
8 and revealed that thereaction parameters such as pH,
temperature, and precursorconcentration dictate the formation of
the Te nanobelts. Yu andcolleagues reported the large-scale
synthesis of Te nanowiresand nanobelts with uniform morphologies
and high yieldthrough a poly(vinyl pyrrolidone) (PVP)-assisted
hydrothermalprocess.9 Inspired by these early work, to date, the
solution-based strategies for synthesizing 1D Te nanostructures
typicallyrely on the reduction of a Te precursor in the presence of
asurfactant, e.g., PVP or cetyltrimethyl ammonium bromide(CTAB).
The morphology control for the product materialstrongly depends on
the nucleation and growth conditions,such as the choice of
surfactants, pH values, precursors, reactiontime and so on. A
comprehensive review of the solution-phasesynthesis of Te
nanostructures has been recently provided by Yuand colleagues.31
The morphology-selective synthesis of 1D Tenanomaterials
demonstrated in these prior works suggested thatthe
surfactant-assisted modulation of the growth rates of
relevantcrystalline planes could be utilized to precisely control
thereaction kinetics, and potentially enable the further
morphologyengineering of the as-synthesized Te nanomaterials.
2.2 Prior efforts in preparing 2D Te nanostructures
In contrast to the fruitful progress achieved in synthesizing
1DTe nanostructures, much less is known about the 2D
Tenanostructures, their processing schemes, and their
relatedproperties. He and colleagues reported the synthesis of
2Dhexagonal Te nanoplates (Fig. 2a) on the chemically inertsurface
of mica through the van der Waals epitaxy (vdWE),32
during which the grown materials and the substrate are bondedby
weak vdW interactions. The derived 2D Te nanoplates inHe’s report
have small lateral dimensions (6–10 mm), large thick-ness (30–80
nm), and non-uniform surface/edge roughness.32 Thesubstantial
thickness of these Te nanoplates is well beyond theatomic scale and
may diminish their potential material relevanceand interest for
fundamental exploration and technologicalapplication in the 2D
limit. Huang and colleagues recentlyreported the vdWE of monolayer
and few-layer Te films on agraphene/6H-SiC(0001) substrate by
molecular beam epitaxy(Fig. 2b).13 The authors identified that the
epitaxy Te filmsconsist of in-plane helical Te chains, which is
different from thestructures of Te nanoplates in the study of He
and colleagues32 aswell as the structural models theoretically
proposed for monolayertellurene.14 Chen and co-authors also
demonstrated the growth ofepitaxial Te thin films on highly
oriented pyrolytic graphite (HOPG)substrates (Fig. 2c)33 with a
higher growth rate and a highersubstrate temperature than that used
in Huang’s work.13 In additionto these efforts in the epitaxial
growth of Te thin films, Zhang andcolleagues recently reported the
liquid-phase exfoliation of Tenanocrystals with small lateral
dimensions (B100 nm) (Fig. 2d).34
Peide Ye
Dr Peide Ye is Richard J. and MaryJo Schwartz Professor of
Electricaland Computer Engineering atPurdue University, USA.
Hereceived his PhD from the MaxPlanck-Institute of Solid
StateResearch, Stuttgart, Germany, in1996. Before joining the
Purduefaculty in 2005, he worked forNTT Basic Research
Laboratory,NHMFL/Princeton University, andBell Labs/Lucent
Technologies/Agere Systems. His currentresearch work is focused
on
atomic layer deposition technology and its device integration
onnovel channel materials including III–V, Ge, 2D materials
andcomplex oxides. He has authored and co-authored more than
200peer reviewed articles and 350 conference presentations
includingmany invited, keynote and plenary talks. He has also
served as achairman and a program committee member on top
internationalconferences and symposia. He is a Fellow of IEEE and
the APS(American Physical Society).
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It should be noted that these demonstrated efforts in
preparing2D Te nanostructures are limited by the difficulty in
deriving large-scale monolayer or few-layer 2D Te with uniform
thickness,restrictions in the growth substrates and conditions
(e.g., hightemperature, vacuum), and the vague potential in
scaling-up. Forinstance, top-down liquid-phase exfoliation shows
potential inproducing large quantities of Te nanocrystals.
Nevertheless, thepoor control in thickness uniformity and the small
size of thederived materials undermine the viability of such
approaches.The epitaxy approaches are also proved challenging, in
particularfor device implementation, due to the process-inherent
demandsfor high growth temperature, delicate control in growth
atmo-sphere, pressure and the epitaxy substrates. There has been a
lackof feasible synthetic strategies for the scalable,
substrate-freeproduction of large-area, single-crystal 2D Te with
process-tunable structural and material properties. Such
fundamentalknowledge and technological capability are essential for
exploringthe intriguing properties of 2D Te and implementing
relateddevice technologies.
2.3 Scalable solution synthesis of large-area free-standing
2Dtellurene
To address these challenges, Wu and colleagues developed
asubstrate-free solution process to synthesize for the first
timelarge-area, free-standing, high-quality monolayer, and
few-layertellurene crystals (Fig. 3).10 The samples were grown
throughthe reduction of sodium tellurite (Na2TeO3) by
hydrazinehydrate (N2H4) in an alkaline solution at temperatures
from160 to 200 1C, with the presence of a crystal-face-blocking
ligand PVP. Due to the substrate-free nature of the processand
the use of the aqueous solution in the reaction, the 2D Teflakes
can be transferred and assembled at a large scale,through a
Langmuir–Blodgett process onto various substratesfor
characterization and device integration. The derived 2D Teflakes
from this process have edge lengths ranging from 50 to100 mm, and
thicknesses from a monolayer to tens of nm(Fig. 3a). Structural and
material characterization of all the2D Te samples indicates that
all samples grow laterally alongthe h0001i and h1%210i directions,
with the vertical stacking alongthe h10%10i directions. This is the
first experimental realization oflarge-area, free-standing,
high-quality 2D Te crystals through alow-temperature, scalable
substrate-free solution process.
The authors further systematically studied and revealed
thesynthetic pathway for deriving the 2D tellurene through
thesolution process. The controlled PVP concentration is the key
toobtaining 2D tellurene. A closer examination of reactions
withdifferent PVP concentrations reveals an intriguing
morphologyevolution in growth products with time. For each PVP
con-centration, the initial growth products are dominantly 1D
nano-structures, similar to previous reports.7–9 After a certain
periodof reaction, structures possessing both 1D and 2D
characteristicsstart to emerge. Finally, the ratio of 2D tellurene
flakes whichhave a straight {1%210} edge increases with a reduction
in 1D andintermediate structures and reaches a plateau after an
extendedgrowth. The observed morphology evolution suggests that
thebalance between the kinetic and thermodynamic growth dictatesthe
transformation from 1D structures to 2D forms. In the
initialreaction, PVP is preferentially adsorbed on the {10%10}
surfacesof the nucleated seeds,9 which promotes the
kinetic-driven1D growth. When the growth continues, the {10%10}
surfacesof the formed structures become partially covered due to
theinsufficient PVP capping. Since {10%10} surfaces have the
lowestfree energy in tellurium, the growth of {10%10} surfaces
along the
Fig. 2 Previously reported 2D Te materials. (a) vdWE-grown
hexagonal Tenanoplates. Reproduced with permission from ref. 32.
Copyright 2014,American Chemical Society. (b) vdWE-grown monolayer
and few-layertellurene on a graphene/6H-SiC(0001) substrate.
Reproduced with permissionfrom ref. 13. Copyright 2017, American
Chemical Society. (c) Epitaxial Te thinfilm on an HOPG substrate.
Reproduced with permission from ref. 33.Copyright 2017, Royal
Society of Chemistry. (d) Liquid-phase exfoliated Tenanocrystals.
Reproduced with permission from ref. 34. Copyright 2017,WILEY-VCH
Verlag GmbH & Co. KGaA, Weinheim.
Fig. 3 (a) AFM images of 2D Te with different thicknesses; (b)
STEM imageof the few-layer tellurene lattice; (c) optical image of
2D Te. Inset: Dispersed2D Te solution; (d) 3D illustration of
few-layer tellurene’s structure. Reproducedwith permission from
ref. 10. Copyright 2018, Springer Nature.
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h1%210i direction significantly increases through the
thermodynamic-driven assembly, leading to the 1D/2D intermediate
structures.Wu and colleagues further demonstrated the engineering
andoptimization over the production yield of the process, and
thedimensions and thicknesses of tellurene. Such capability
inmaterials synthesis enables potential modulation of
deviceperformance through tuning the electronic structures, e.g.,
aprocess-tunable bandgap (0.3–1 eV) covering the spectral rangefrom
mid-infrared to near-infrared in tellurene.
3. Physical properties of tellurene
Tellurene is an emerging member of the 2D materials’ family,and
there have been only a few experimental studies10–13 andtheoretical
calculations.14,16–23 More advances are expected tooccur from the
efforts of the material research communityin probing the
fundamental properties of the emerging 2Dtellurene and implementing
novel devices.
3.1 Structural phase transition in monolayer and
few-layertellurene
Recent theoretical calculations suggest that, at
equilibriumunder normal conditions, the a-phase derived from the
bulktrigonal structure is the most stable phase for few-layer
tellurene16
(Fig. 4), and the tetragonal b-phase is more stable for
monolayertellurene due to the structural relaxation14 (Fig. 4). The
recentexperimental efforts in deriving atomically-thin 2D Te also
provideinteresting and insightful results. The vdWE monolayer Te
filmgrown by Chen and co-authors on highly oriented pyrolytic
graphite(HOPG) substrates33 have a crystal structure and in-plane
latticeconstants consistent with the predicted b-phase.14
Nevertheless, thevdWE monolayer Te films grown on graphene layers,
as reported byHuang and colleagues,13 were characterized to have a
largerlattice of 4.42 � 5.93 Å2, more consistent with the bulk
trigonalconfiguration, where parallel-packed Te helical chains
areflat-lying in the substrate plane. The structural
characterizationin Wu and colleagues’ work10 confirmed that these
solution-grown, free-standing few-layer tellurene crystals possess
the bulktrigonal structure (Fig. 3). This is consistent with Ji and
colleagues’calculation results that a-phase derived from the bulk
trigonalstructure is the most stable phase for few-layer
tellurene.16
The structural discrepancy seen in the 2D tellurium derivedfrom
different processes suggests the complexity of the under-lying
mechanism that drives the structure formation of mono-layer or
few-layer tellurene, and necessitates the devotion ofmore efforts
in advancing both the theoretical understandingand the experimental
investigation of the atomically-thin 2Dtellurium, e.g., the role of
growth kinetics in its fundamentalstructural phase transition.
Moreover, the substrate is expectedto also play a critical role in
dictating the structure and propertiesof the supported
tellurene.
3.2 Electronic band structure and carrier mobility inmonolayer
and few-layer tellurene
The electronic band structure in monolayer and few-layer
tell-urene has been recently explored using various
theoreticalschemes such as density functional theory (DFT).14,16,17
Ji andcolleagues report an indirect bandgap of 1.17 eV for
bilayertellurene and an expected bandgap reduction with an
increasedlayer thickness in few-layer tellurene.16 When the layer
numberof 2D Te increases, the valence band maximum (VBM)
signifi-cantly changes from �4.98 to �4.35 eV, roughly three
timesthat of the conduction band maximum (CBM), which suggeststhe
formation of a p-type contact between few-layer tellurenewith most
metal electrodes. This is consistent with the devicecharacteristics
of field-effect transistors made from solution-grown tellurene.10
Interestingly, the band structures of few-layertellurene are
predicted to have a four-fold valley degeneracy in thefirst
Brillouin zone for the valence band, likely due to the(pseudo) spin
non-degeneracy as a result of the strong spin–orbitcoupling in
Te.16 Such a ‘‘camel’s back’’ shaped valence band isusually found
in topological insulators with band inversion andplays a key role
for high-performance thermoelectrics.3 By per-forming hybrid DFT
calculations, Zhu and colleagues predictedthat the monolayer a- and
b-tellurene exhibit indirect bandgapsof 1.15 and 1.79 eV,
respectively.14 The electronic gaps and bandprofiles for monolayer
and few-layer tellurene have also beenexperimentally probed. Huang
and co-workers report a gap of0.92 eV for monolayer epitaxial
tellurene on graphene13 and athickness-dependent bandgap evolution
consistent with thetheoretical predications.14,16,17 The smaller
monolayer bandgapobserved could be due to the finite density of
states of theunderneath graphene near the Fermi level.13 The
scanningtunneling microscopy (STS) mapping of the real space
bandprofiles shows that the epitaxial monolayer and few-layer
tell-urene are p-type semiconductors with the Fermi levels
locatingbelow the middle of the bandgap.13 A similar bandgap
evolutionhas also been reported for the epitaxial few-layer
tellurene on aHOPG substrate.33
In addition to the thickness-dependent bandgap from mid-infrared
to the red range which is of great interest to manyemerging
technologies in mid-infrared and terahertz applications,2D Te has
also been predicted to possess extraordinarily
largeroom-temperature carrier mobilities ranging from hundreds
tothousands of cm2 V�1 s�1, much larger than those of 2D TMDCsand
few-layer BP.14,16 Electrical characterization of the
few-layertellurene transistor devices yields hole mobilities
consistent with
Fig. 4 Structural allotropes for 2D Tellurium. (a–d) Crystal
structures ofbulk (a) and bilayer a-Te from the top- (b) and
side-views (c and d); (e and f)crystal structures of bilayer b-Te
from the top- (e) and side-views (f); (g andh) crystal structures
of bilayer g-Te from the top- (g) and side-views (h).Reproduced
with permission from ref. 16. Copyright 2018, Elsevier.
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the predicted ranges.10 Such large room-temperature mobility
in2D Te is promising for constructing high-speed,
energy-efficientelectronics. An anisotropy in carrier mobility and
electronic trans-port is expected for 2D Te, considering its
structural anisotropyand the assumed different degrees of
interaction along the Techain directions (strong, covalent-type)
and that between chains(weak, vdW-like).35 However, experiments
have shown only a smalldegree of anisotropy (1.13) for few-layer
tellurene.10 Such anunexpected weak anisotropy in the electronic
transport inspiresa more profound understanding of the nature of
the inter-chaininteractions in 2D tellurene. Recent theoretical
study22 suggeststhat the delocalization of Te lone-pair electrons
lowers the effectivemass and changes the potential in the
inter-chain region, henceenhancing the transport across the chains
as well as the inter-chain interactions. The lone-pair electrons
are delocalized bydepletion of the density in their original
positions and enhance-ment of the density in the inter-chain
region, which adds ‘‘metallicbonding’’ or ‘‘covalent-like
quasi-bonding’’ characteristics into theinter-chain
interaction.16,22 This could also be understood bythe relatively
weak nucleus attraction and multi-valence natureof Te, which is a
metalloid element with dual characteristics ofboth metal and
nonmetal.14
3.3 Optical properties and Raman spectroscopy of 2D Te
Recent theoretical studies suggest a similar isotropic
scenariofor light absorption in few-layer tellurene,16 showing a
strongbroadband absorbance almost twice to three-times those
ofblack phosphorus for normal incident light linearly
polarizedalong the two principal in-plane directions.
Interestingly, thecalculation results also indicate a
layer-dependent absorbancewhere the absorption efficiency (i.e.,
the absorbance per layer)substantially increases with the decreased
thickness of few-layer tellurene.16 This is thought to be due to
the thickness-dependent interlayer electronic hybridization and
band dispersion,both of which become stronger as the layer
thickness increases.This predicated high, isotropic
optical-absorbance with thehigh mobility suggests the potential of
tellurene for photonicsand optoelectronics applications.
The fundamental light–matter interaction in 2D materialscan also
be probed and understood using spectroscopy techniquessuch as Raman
scattering. In their recent report,10 Wu andcolleagues performed
room-temperature angle-resolved polarizedRaman spectroscopy for
solution-synthesized tellurene crystalswith controlled thicknesses,
and observed striking thickness-dependent variations (e.g., shifts,
appearance, and disappearance) inthe Raman vibrational modes (Fig.
5a). For instance, the thick 2D Tesamples (thicker than 20.5 nm)
exhibit three Raman-activemodes consistent with the previous
observations in bulk andnanostructured tellurium,32,36 indicating
the ‘‘bulk’’ symmetriccharacteristics despite their 2D morphology.
For the 2D telluriumcrystals within the ‘‘intermediate’’ thickness
range (e.g., 9.1 nm to20.5 nm), the E1 longitudinal (LO) phonon
mode appears inthe Raman spectra because the deformation potential
in thetellurene lattice increases while the electro-optic effect
weakens.When the 2D Te thickness further reduces to the few-layer
range(smaller than 9.1 nm), degeneracy in the E1 transverse (TO)
and
longitudinal (LO) phonons occurs with peak broadening,
possiblydue to the thickness-dependent intra-chain atomic
displacement,electronic band structure changes and symmetry
assignments foreach band. Also, significant peak shifts were also
observed in theRaman spectra, e.g., blue-shifts for the A1 and E2
modes, when 2Dtellurene’s thickness decreases, which may be
attributed to theenhanced interlayer interactions when thinned
down. Such apeculiar behavior is thought to be closely related to
the uniquechiral-chain structure of tellurene. The effects of
mechanicalstrain on the Raman spectroscopy for nanobelt-like 2D
Tesamples has further been studied, showing an anisotropic
strainresponse along the two principal in-plane crystal
directions(Fig. 5b).11 The theoretical Raman intensity of bi-layer
tellureneas a function of vibrational frequency has also been
recentlyreported,16 showing the splitting and anomalous shifts
offrequency consistent with the experimental findings.10
3.4 Magnetotransport in 2D Te
Bulk tellurium has been a material of interest for
elucidatingfundamental quantum phenomena, e.g., scattering
mechanismsof carriers, surface quantum states, magnetoresistance
effect,quantum oscillation, topological insulator, etc.4,37,38
Recently,Du et al. carried out magnetotransport studies for the
solution-synthesized 2D Te samples with magnetic fields applied
alongthree principle axes.11 The temperature-dependent phase
coher-ence length extracted from the weak anti-localization effect
(WAL)indicates its 2D transport behavior when an applied
magneticfield is perpendicular to the [10%10] plane of 2D
tellurene. TheWAL effect vanishes with the applied magnetic field
parallel tothe h1%210i direction (perpendicular to the Te chains).
When theapplied magnetic field is along the h0001i chain direction
of 2DTe, the corresponding phase coherence length extracted from
the
Fig. 5 (a) Raman spectra of 2D Te with different thicknesses.
Reproducedwith permission from ref. 10. Copyright 2018, Springer
Nature. (b) Ramanspectra of Te thin film for both tensile and
compressive c-axis strains.Reproduced with permission from ref. 11.
Copyright 2017, AmericanChemical Society.
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universal conductance fluctuations (UCF) indicates the nature
ofthe 1D transport mechanism. The atomically thin 2D Te crystalwith
its intriguing properties is expected to provide an
attractiveplatform for exploring the quantum physics at the
frontier ofcondensed matter research.
3.5 Environmental stability of 2D Te
The environmental instability of many 2D materials, e.g.,
blackphosphorus, has severely limited the application prospects
ofrelated materials. In sharp contrast, great air-stability has
beendemonstrated in solution-grown 2D Te crystals for almost
theentire thickness range from thick flakes down to a
few-layerthickness. No significant degradation has been observed in
theelectrical performance of the prototypical 2D tellurene
transistorsthat were exposed to air for two months without any
encapsulation.13
Theoretical studies suggest that an energy barrier exists for
therelated oxidation pathways, sufficient to prevent the
few-layertellurene being oxidized under ambient conditions. Such
goodenvironmental stability is critical for exploring the
fundamentalproperties and realizing the technological prospects of
2D tellurene.
4. Device applications of 2D Te4.1 2D tellurene field-effect
transistors
Wu et al. demonstrated the prototypical 2D tellurene
field-effecttransistors (FETs) with a good all-around figure of
merit comparedto known 2D materials.10 The long channel devices
(channellength 3 mm) exhibit large drain current over 300 mA mm�1,
highroom-temperature mobility B700 cm2 V�1 s�1, and high
on/offratio on the order of B105 (Fig. 6). The thickness dependence
ofthe on/off ratios and field-effect mobilities in 2D tellurene
longchannel devices with thicknesses ranging from over 35 nm downto
a monolayer (B0.5 nm) has also been explored to elucidate
thetransport mechanism of 2D Te FETs. A benchmark comparisonwith
black phosphorus shows that the solution-synthesized 2Dtellurene
has B2–3 times higher mobility than black phosphoruswhen the same
device structure, geometry, and mobility extraction
method are adopted. By further exploring the channel scaling
andintegration with atomic-layer-deposition (ALD) grown
high-kdielectric for the 2D tellurene transistors, Wu and
colleaguesachieved record high drive current of over 1 A mm�1 and
goodon/off ratios B103 at relatively low drain bias.10 The
maximumdrain current achieved is 1.06 A mm�1, which is comparable
tothat of conventional semiconductor devices and the highestvalue
among all 2D material transistors. This is significantfor potential
design and implementation of high-performancetellurene-based
electronics. The in-plane electrical transportalong different
crystal directions was also studied at roomtemperature, and the
average anisotropic mobility ratio is1.43 � 0.10, which is slightly
lower than the reported valuesfor bulk tellurium,35 possibly due to
the enhanced surfacescattering in our ultrathin Te samples.
5. Conclusions and outlook
Despite being one of the newest members to the 2D
materialsfamily, 2D tellurene has attracted extensive interest for
its intriguing,versatile material properties and technological
potential, usheringin new research opportunities in both
theoretical and experimentalstudies. Tellurene possesses a few
unique characteristics andadvantages compared to the
state-of-the-art 2D materials. Forinstance, the negligible bandgap
of graphene leads to compromisedpower gains and limited
applications for energy-efficient electronics,while tellurene has a
process-modulated bandgap (B0.35–1.2 eVfrom mid-IR to visible
light); transition metal dichalcogenides’ lowroom-temperature
mobilities limit their prospects for high-speeddevices, while
tellurene possesses a high room-temperature carriermobility (B103
cm2 V�1 s�1); the air-instability of silicene and blackphosphorous
limits their potential for practical applications, whiletellurene
shows a good air-stability for almost the entire thicknessrange. In
terms of synthesis control, free-standing tellurene withlarge
lateral dimensions (B100 mm) and process-controlledthickness (from
a monolayer to tens of nm) can be scalablyproduced with high yield
(495%). Nevertheless, the majority of
Fig. 6 2D tellurene FET performance. (a) Transfer curves of a
typical 2D tellurene transistor with a thickness of 15 nm and
stability measured for 55 days.(Inset: False-colored SEM image of a
tellurene transistor. The scale bar is 10 mm.); (b)
thickness-dependent on/off ratio (orange triangles) and
field-effectmobility (gray circles) for 2D Te transistors; (c) high
on-state current density in a 11.1 nm-thick short-channel tellurene
transistor with 300 nm channel.Reproduced with permission from ref.
10. Copyright 2018, Springer Nature.
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Royal Society of Chemistry 2018
efforts in the state-of-the-art 2D materials are restricted by
factorssuch as growth substrates, synthetic conditions, and small
crystalsize of the obtained materials. For instance, top-down
liquid-phase exfoliation shows potential in producing large
quantitiesof various atomically-thin layered materials, e.g.,
graphene,transition metal dichalcogenides, and boron nitride.
However,the poor control in thickness uniformity and small size of
thederived materials undermine the viability of such approaches.The
bottom-up chemical vapor deposition process can lead tohigh-quality
crystals of graphene and MoS2 with controlledthickness over a large
area. However, the requirement for highgrowth temperature and
delicate control in growth atmospherelimit the potential for
scale-up. Epitaxy growth of 2D materialswith exotic properties,
e.g., silicene, borophene, and stanene,have also been explored,
though it has proved challenging dueto the process-inherent
requirements for epitaxy substrates andhigh vacuum. Still, much
work remains to be done to attain acomprehensive fundamental
understanding of tellurene’sproperties and to realize its full
potential, with the followingopportunities and challenges.
Fundamental exploration
Recent theoretical studies suggest that few-layer tellurene
ishighly stretchable along the Te chain direction.16 This
couldenable high-performance flexible and stretchable devices
withgood lifetime and mechanical durability using the
solution-grown 2D tellurene, through scalable assembly and
integrationapproaches, e.g., ink-jet printing.13 Despite being an
elementalmaterial, the trigonal Te lacks the centrosymmetry in its
crystalstructure and has hence been predicted to exhibit
piezoelectricity.39
Nevertheless, few studies have been reported on Te’s
piezoelectricproperty, possibly due to the narrow bandgap of bulk
Te. Thereduction of dimensionality in tellurene could lead to
strong,accessible piezoelectricity compared to its bulk
counterpart.12
The exploration of tellurene’s piezoelectricity is
potentiallysignificant in the sense that the origin for tellurene’s
piezo-electric characteristics is expected to be fundamentally
differentfrom the ion polarization process for the known
piezoelectricmaterials.40,41 Furthermore, the coupling of
tellurene’s piezo-electricity with its appealing semiconductor
characteristics sug-gests the potential of 2D tellurene as a good
candidate materialplatform for emerging areas such as piezotronics
and piezo-phototronics.42–44 The absence of inversion symmetry
combinedwith the strong spin–orbit interaction in manufacturable
2Dtellurene may also offer interesting opportunities in
exploringthe manipulation of the valley degree of freedom for
practicalvalleytronics devices.45 Moreover, due to the lack of
inversionsymmetry, the spin splitting of the bulk band could give
rise to acurrent-induced magnetization in the nonmagnetic
bulktellurium.46 It would, therefore, be interesting to explore
thefeasibility of 2D tellurene as a new class of
magnetoelectricmaterials which could potentially exhibit both
current-inducedspin magnetization and current-induced orbital
magnetization,47
considering as well the chiral nature of 2D tellurene.3,4 A
recenttheoretical work also predicted that few-layer tellurene
surprisinglyexhibits in-plane ferroelectricity due to the
interlayer interaction
between lone pairs.19 This coupled with the nontrivial
valley-dependent spin-textures for holes in few-layer tellurene
couldenable novel electronic and spintronic applications. The
anisotropicand layer-dependent electron and hole pockets found for
few-layertellurene16 indicate that 2D tellurene possesses more
suitableelectronic structures than that of 1D Te nanostructures
forhigh-performance thermoelectric devices.20,21 For
electronicdevice applications, it is expected that the mobility of
tellurenecan be further improved through approaches such as
improvinginterface quality with high-k dielectric or h-BN
encapsulation toreduce the substrate phonon scattering and charge
impurity.Meanwhile, a comprehensive examination of the
interfacialcharacteristics between 2D tellurene and electrode
materials isnecessary for providing the fundamental understanding,
e.g.,the effects of metals and electrode configurations on the
carriertransport in the metal-tellurene contact.23 Such knowledge
iscritical for the rational design and optimization of future
tellurene-based devices. The exploration of the fundamental
dopingmechanism and defect chemistry in 2D tellurium is not
onlyessential for providing versatility in modulating its
materialproperties by design but may also enable novel device
conceptsand applications. All these intriguing properties
demonstrate2D tellurene as a highly promising elementary 2D
semiconductorfor diverse applications and inspire us to explore the
novelphysics and unusual phenomena in the relatively
uncharteredareas of 2D non-layered materials, in particular, those
withstructural similarity to 2D tellurene and that consist of
weaklybonded atomic chains.48,49
Technological implementation
Among all the demonstrated approaches to synthesize Te
nano-structures, as have been reviewed in the previous
sections,hydrothermal processing emerges as a potential economic
methodfor nanomanufacturing 2D tellurene, due to its energy saving,
cost-effectiveness, low working temperature, and feasibility for
scale-upproduction, and the potential for deriving 2D tellurene
withuniform thickness and dimensions. The room-temperature
air-stability of 2D Te crystals also makes it feasible and
convenientto produce, package, transport, and utilize the
as-fabricated 2DTe materials. The as-fabricated tellurene could
also be used astemplates for deriving large-area, free-standing 2D
tellurideswith tailored dimensions and properties50 as well as a
versatileclass of heterostructures for functional devices. In order
to realizethe manufacturing and production potential of
solution-synthesized2D Te, more efforts are required to reveal and
identify the scientificnature of hydrothermal processing for 2D Te,
particularly on thespatial distribution of nucleation and growth,
patterning, andself-assembly into device forms, which directly
impact the growthrate, assembly yield, performance uniformity, and
batch-to-batchreproducibility for future practical production and
application of2D tellurene.
The rapid and exciting progress achieved in many emergingand
‘‘traditional’’ disciplines, e.g., nanomanufacturing, data
science,condensed matter physics, materials science, solid-state
chemistry,etc., is expected to excite a confluence of collective
efforts from theresearch community and lead to more
theoretical/experimental
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advances in probing the fundamental properties of 2D
tellureneand implementing novel devices. 2D tellurene adds a new
classof nanomaterials to the large family of 2D crystals.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
W. Z. W. acknowledges the College of Engineering and Schoolof
Industrial Engineering at Purdue University for the startupsupport.
W. Z. W. was partially supported by the Oak RidgeAssociated
Universities (ORAU) Junior Faculty EnhancementAward Program. W. Z.
W. was partially sponsored by theNational Science Foundation under
grants CMMI-1663214 andCNS-1726865. W. Z. W. and P. D. Y. were
partially supported byArmy Research Office under grant no.
W911NF-15-1-0574 andW911NF-17-1-0573. P. D. Y. was supported by
NSF/AFOSR2DARE Program and SRC.
Notes and references
1 V. E. Bottom, Science, 1952, 115, 570.2 J.-W. Liu, J.-H. Zhu,
C.-L. Zhang, H.-W. Liang and S.-H. Yu,
J. Am. Chem. Soc., 2010, 132, 8945–8952.3 H. Peng, N. Kioussis
and G. J. Snyder, Phys. Rev. B: Condens.
Matter Mater. Phys., 2014, 89, 195206.4 L. A. Agapito, N.
Kioussis, W. A. Goddard and N. P. Ong,
Phys. Rev. Lett., 2013, 110, 176401.5 D. Souilhac, D. Billerey
and A. Gundjian, Appl. Opt., 1990,
29, 1798–1804.6 A. von Hippel, J. Chem. Phys., 1948, 16,
372–380.7 B. Mayers and Y. Xia, J. Mater. Chem., 2002, 12,
1875–1881.8 M. Mo, J. Zeng, X. Liu, W. Yu, S. Zhang and Y. Qian,
Adv.
Mater., 2002, 14, 1658–1662.9 H.-S. Qian, S.-H. Yu, J.-Y. Gong,
L.-B. Luo and L.-f. Fei,
Langmuir, 2006, 22, 3830–3835.10 Y. Wang, G. Qiu, R. Wang, S.
Huang, Q. Wang, Y. Liu, Y. Du,
W. A. Goddard, M. J. Kim, X. Xu, P. D. Ye and W. Wu,
Nat.Electron., 2018, 1, 228–236.
11 Y. Du, G. Qiu, Y. Wang, M. Si, X. Xu, W. Wu and P. D. Ye,Nano
Lett., 2017, 17, 3965–3973.
12 S. Gao, Y. Wang, R. Wang and W. Wu, Semicond. Sci.Technol.,
2017, 32, 104004.
13 X. Huang, J. Guan, Z. Lin, B. Liu, S. Xing, W. Wang andJ.
Guo, Nano Lett., 2017, 17, 4619–4623.
14 Z. Zhu, X. Cai, S. Yi, J. Chen, Y. Dai, C. Niu, Z. Guo, M.
Xie, F. Liu,J.-H. Cho, Y. Jia and Z. Zhang, Phys. Rev. Lett., 2017,
119, 106101.
15 Lede Xian, Alejandro Pérez Paz, Elisabeth Bianco, PulickelM
Ajayan and Angel Rubio, 2D Mater., 2017, 4, 041003.
16 J. Qiao, Y. Pan, F. Yang, C. Wang, Y. Chai and W. Ji,
Sci.Bull., 2018, 63, 159–168.
17 B. Wu, X. Liu, J. Yin and H. Lee, Mater. Res. Express,
2017,4, 095902.
18 X. H. Wang, D. W. Wang, A. J. Yang, N. Koratkar, J. F. Chu,P.
L. Lv and M. Z. Rong, Phys. Chem. Chem. Phys., 2018,
20,4058–4066.
19 Y. Wang, C. Xiao, M. Chen, C. Hua, J. Zou, C. Wu, J. Jiang,S.
A. Yang, Y. Lu and W. Ji, Mater. Horiz., 2018, 5, 521–528.
20 S. Sharma, N. Singh and U. Schwingenschlögl, ACS Appl.Energy
Mater., 2018, 1, 1950–1954.
21 Z. Gao, F. Tao and J. Ren, Nanoscale, 2018, 10,
12997–13003.22 Y. Liu, W. Wu and W. A. Goddard, J. Am. Chem. Soc.,
2018,
140, 550–553.23 J. Yan, X. Zhang, Y. Pan, J. Li, B. Shi, S. Liu,
J. Yang, Z. Song,
H. Zhang, M. Ye, R. Quhe, Y. Wang, J. Yang, F. Pan and J. Lu,J.
Mater. Chem. C, 2018, 6, 6153–6163.
24 Z. Tang, Y. Wang, K. Sun and N. A. Kotov, Adv. Mater.,
2005,17, 358–363.
25 T. Yang, H. Ke, Q. Wang, Y. a. Tang, Y. Deng, H. Yang,X.
Yang, P. Yang, D. Ling, C. Chen, Y. Zhao, H. Wu andH. Chen, ACS
Nano, 2017, 11, 10012–10024.
26 M. Safdar, X. Zhan, M. Niu, M. Mirza, Q. Zhao, Z. Wang,J.
Zhang, L. Sun and J. He, Nanotechnology, 2013, 24, 185705.
27 X.-L. Li, G.-H. Cao, C.-M. Feng and Y.-D. Li, J. Mater.
Chem.,2004, 14, 244–247.
28 N. Furuta, H. Itinose, N. Maruyama and Y. Ohasi, Jpn.J. Appl.
Phys., 1972, 11, 1113.
29 Noboru Furuta and Norio Wada, Jpn. J. Appl. Phys., 1972,11,
1753.
30 Baoyou Geng, Yu Lin, Xingsheng Peng, Guowen Meng andLide
Zhang, Nanotechnology, 2003, 14, 983.
31 Z. He, Y. Yang, J.-W. Liu and S.-H. Yu, Chem. Soc. Rev.,
2017,46, 2732–2753.
32 Q. Wang, M. Safdar, K. Xu, M. Mirza, Z. Wang and J. He,
ACSNano, 2014, 8, 7497–7505.
33 J. Chen, Y. Dai, Y. Ma, X. Dai, W. Ho and M. Xie,
Nanoscale,2017, 9, 15945–15948.
34 Z. Xie, C. Xing, W. Huang, T. Fan, Z. Li, J. Zhao, Y.
Xiang,Z. Guo, J. Li, Z. Yang, B. Dong, J. Qu, D. Fan and H.
Zhang,Adv. Funct. Mater., 2018, 28, 1705833.
35 L. Rothkirch, R. Link, W. Sauer and F. Manglus, Phys.
StatusSolidi B, 1969, 31, 147–155.
36 A. Pine and G. Dresselhaus, Phys. Rev. B: Solid State,
1971,4, 356.
37 K. von Klitzing and G. Landwehr, Solid State Commun., 1971,9,
2201–2205.
38 K. Nakayama, M. Kuno, K. Yamauchi, S. Souma, K. Sugawara,T.
Oguchi, T. Sato and T. Takahashi, Phys. Rev. B, 2017,95,
125204.
39 G. Arlt and P. Quadflieg, Phys. Status Solidi B, 1969, 32,
687–689.40 W. Wu, X. Wen and Z. L. Wang, Science, 2013, 340,
952–957.41 W. Wu, L. Wang, Y. Li, F. Zhang, L. Lin, S. Niu, D.
Chenet,
X. Zhang, Y. Hao, T. F. Heinz, J. Hone and Z. L. Wang,Nature,
2014, 514, 470–474.
42 W. Wu and Z. L. Wang, Nat. Rev. Mater., 2016, 1, 16031.43 Z.
L. Wang and W. Z. Wu, Natl. Sci. Rev., 2014, 1, 62–90.44 Z. L.
Wang, Piezotronics and Piezo-Phototronics, Springer, 2012.45 J. R.
Schaibley, H. Yu, G. Clark, P. Rivera, J. S. Ross, K. L.
Seyler,
W. Yao and X. Xu, Nat. Rev. Mater., 2016, 1, 16055.
Chem Soc Rev Tutorial Review
Publ
ishe
d on
17
Aug
ust 2
018.
Dow
nloa
ded
by P
urdu
e U
nive
rsity
on
10/1
2/20
18 9
:08:
03 P
M.
View Article Online
http://dx.doi.org/10.1039/c8cs00598b
-
7212 | Chem. Soc. Rev., 2018, 47, 7203--7212 This journal is©The
Royal Society of Chemistry 2018
46 T. Furukawa, Y. Shimokawa, K. Kobayashi and T. Itou,
Nat.Commun., 2017, 8, 954.
47 T. Yoda, T. Yokoyama and S. Murakami, Sci. Rep., 2015,5,
12024.
48 G. Liu, B. Debnath, T. R. Pope, T. T. Salguero, R. K. Lake
andA. A. Balandin, Nat. Nanotechnol., 2016, 11, 845.
49 J. O. Island, A. J. Molina-Mendoza, M. Barawi, R. Biele,E.
Flores, J. M. Clamagirand, J. R. Ares, C. Sánchez, HerreSJ van der
Zant, R. D’Agosta, I. J. Ferrer and A. Castellanos-Gomez, 2D
Mater., 2017, 4, 022003.
50 G. D. Moon, S. Ko, Y. Min, J. Zeng, Y. Xia and U. Jeong,
NanoToday, 2011, 6, 186–203.
Tutorial Review Chem Soc Rev
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ishe
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17
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Dow
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by P
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2/20
18 9
:08:
03 P
M.
View Article Online
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