An ideal type-Ⅲnodal point is generated by crossing a completely flat band and a dispersive band along a certain momentum direction.To date,the type-Ⅲnodal points found in two-dimensional(2D)materials have been most...An ideal type-Ⅲnodal point is generated by crossing a completely flat band and a dispersive band along a certain momentum direction.To date,the type-Ⅲnodal points found in two-dimensional(2D)materials have been mostly accidental and random rather than ideal cases,and no one mentions what kind of lattice can produce ideal nodal points.Here,we propose that ideal type-Ⅲnodal points can be obtained in a diamond-like lattice.The flat bands in the lattice originate from destructive interference of wavefunctions,and thus are intrinsic and robust.Moreover,the specific lattice can be realized in some 2D carbon networks,such as T-graphene and its derivatives.All the carbon structures possess type-ⅢDirac points.In two of the structures,consisting of triangular carbon rings,the type-ⅢDirac points are located just on the Fermi level and the Fermi surface is very clean.Our research not only opens a door to finding the ideal type-ⅢDirac points,but also provides 2D materials for exploring their physical properties experimentally.展开更多
目的探讨成人骨型Ⅲ类患者矫治前后上下前牙区牙槽高度和宽度变化以及前牙区牙根位置变化。方法选取2020年5月—2022年11月在中山市小榄人民医院口腔科正畸掩饰治疗的成人骨型Ⅲ类患者50例,比较正畸治疗前后患者上下颌前牙牙槽骨厚度和...目的探讨成人骨型Ⅲ类患者矫治前后上下前牙区牙槽高度和宽度变化以及前牙区牙根位置变化。方法选取2020年5月—2022年11月在中山市小榄人民医院口腔科正畸掩饰治疗的成人骨型Ⅲ类患者50例,比较正畸治疗前后患者上下颌前牙牙槽骨厚度和高度,其中包括上前牙槽骨厚度(upper anterior alveolar bonethickness,UA)、上后牙槽骨厚度(upper posterior alveolar bone thickness,UP)、上牙槽骨总厚度(upper alveolar bone width,UW)、下前牙槽骨厚度(lower anterior alveolar bone thickness,LA)、下后牙槽骨厚度(lower posterior alveolar bone thickness,LP)、下牙槽骨总厚度(lower alveolar bone width,LW)、根中水平上前牙槽骨厚度(upper anterior alveolar bone thickness at the mid-root level,UA-m)、根中水平上后牙槽骨厚度(upper posterior alveolar bone thickness at the mid-root level,UP-m)、根中水平上牙槽骨总厚度(upper alveolar bone thickness at the mid-root level,UW-m)、根中水平下前牙槽骨厚度(lower anterior alveolar bone thickness at the mid-root level,LA-m)、根中水平下后牙槽骨厚度(lower posterior alveolar bone thickness at the mid-root level,LP-m)、根中水平下牙槽骨总厚度(lower alveolar bone thickness at the mid-root level,LW-m)以及上前牙槽骨高度(upper anterior alveolar bone height,UAH)和下前牙槽骨高度(lower anterior alveolarbone height,LAH)。结果正畸治疗前后患者UA、UP-m测量值比较,差异无统计学意义(P>0.05)。与正畸治疗前比较,正畸治疗后患者UP、UW、UA-m、UW-m测量值均显著降低(P<0.05)。正畸治疗后患者LP、LA-m测量值与正畸治疗前比较,差异无统计学意义(P>0.05)。与正畸治疗前比较,正畸治疗后患者LA、LW、LP-m、LW-m测量值均降低(P<0.05)。与正畸治疗前比较,正畸治疗后患者UAH、LAH测量值均显著降低(P<0.05)。正畸治疗后,患者上下颌前牙解剖牙根长度分别为(10.62±0.57)mm、(9.65±0.48)mm,正畸治疗前患者上下颌前牙解剖牙根长度分别为(11.01±0.58)mm、(10.37±0.48)mm,与正畸治疗前比较,患者上下颌前牙解剖牙根长度明显减小(P<0.05)。结论成人骨型Ⅲ类患者进行正畸掩饰治疗后,牙槽形态会发生相应改变,患者上下前牙牙槽骨厚度和高度会一定程度地减少。因此,在矫治过程中应当对患者牙槽形态的变化给予密切关注,尽量避免上下前牙发生代偿性移动,从而降低不良反应情况发生的风险。展开更多
Broken-gap(type-Ⅲ)two-dimensional(2D)van der Waals heterostructures(vdWHs)offer an ideal platform for interband tunneling devices due to their broken-gap band offset and sharp band edge.Here,we demonstrate an efficie...Broken-gap(type-Ⅲ)two-dimensional(2D)van der Waals heterostructures(vdWHs)offer an ideal platform for interband tunneling devices due to their broken-gap band offset and sharp band edge.Here,we demonstrate an efficient control of energy band alignment in a typical type-ⅢvdWH,which is composed of vertically-stacked molybdenum telluride(MoTe2)and tin diselenide(SnSe2),via both electrostatic and optical modulation.By a single electrostatic gating with hexagonal boron nitride(hBN)as the dielectric,a variety of electrical transport characteristics including forward rectifying,Zener tunneling,and backward rectifying are realized on the same heterojunction at low gate voltages of±1 V.In particular,the heterostructure can function as an Esaki tunnel diode with a room-temperature negative differential resistance.This great tunability originates from the atomicallyflat and inert surface of h-BN that significantly suppresses the interfacial trap scattering and strain effects.Upon the illumination of an 885 nm laser,the band alignment of heterojunction can be further tuned to facilitate the direct tunneling of photogenerated charge carriers,which leads to a high photocurrent on/off ratio of>105 and a competitive photodetectivity of 1.03×1012 Jones at zero bias.Moreover,the open-circuit voltage of irradiated heterojunction can be switched from positive to negative at opposite gate voltages,revealing a transition from accumulation mode to depletion mode.Our findings not only promise a simple strategy to tailor the bands of type-ⅢvdWHs but also provide an in-depth understanding of interlayer tunneling for future low-power electronic and optoelectronic applications.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12174157,12074150,and 11874314)。
文摘An ideal type-Ⅲnodal point is generated by crossing a completely flat band and a dispersive band along a certain momentum direction.To date,the type-Ⅲnodal points found in two-dimensional(2D)materials have been mostly accidental and random rather than ideal cases,and no one mentions what kind of lattice can produce ideal nodal points.Here,we propose that ideal type-Ⅲnodal points can be obtained in a diamond-like lattice.The flat bands in the lattice originate from destructive interference of wavefunctions,and thus are intrinsic and robust.Moreover,the specific lattice can be realized in some 2D carbon networks,such as T-graphene and its derivatives.All the carbon structures possess type-ⅢDirac points.In two of the structures,consisting of triangular carbon rings,the type-ⅢDirac points are located just on the Fermi level and the Fermi surface is very clean.Our research not only opens a door to finding the ideal type-ⅢDirac points,but also provides 2D materials for exploring their physical properties experimentally.
文摘目的探讨成人骨型Ⅲ类患者矫治前后上下前牙区牙槽高度和宽度变化以及前牙区牙根位置变化。方法选取2020年5月—2022年11月在中山市小榄人民医院口腔科正畸掩饰治疗的成人骨型Ⅲ类患者50例,比较正畸治疗前后患者上下颌前牙牙槽骨厚度和高度,其中包括上前牙槽骨厚度(upper anterior alveolar bonethickness,UA)、上后牙槽骨厚度(upper posterior alveolar bone thickness,UP)、上牙槽骨总厚度(upper alveolar bone width,UW)、下前牙槽骨厚度(lower anterior alveolar bone thickness,LA)、下后牙槽骨厚度(lower posterior alveolar bone thickness,LP)、下牙槽骨总厚度(lower alveolar bone width,LW)、根中水平上前牙槽骨厚度(upper anterior alveolar bone thickness at the mid-root level,UA-m)、根中水平上后牙槽骨厚度(upper posterior alveolar bone thickness at the mid-root level,UP-m)、根中水平上牙槽骨总厚度(upper alveolar bone thickness at the mid-root level,UW-m)、根中水平下前牙槽骨厚度(lower anterior alveolar bone thickness at the mid-root level,LA-m)、根中水平下后牙槽骨厚度(lower posterior alveolar bone thickness at the mid-root level,LP-m)、根中水平下牙槽骨总厚度(lower alveolar bone thickness at the mid-root level,LW-m)以及上前牙槽骨高度(upper anterior alveolar bone height,UAH)和下前牙槽骨高度(lower anterior alveolarbone height,LAH)。结果正畸治疗前后患者UA、UP-m测量值比较,差异无统计学意义(P>0.05)。与正畸治疗前比较,正畸治疗后患者UP、UW、UA-m、UW-m测量值均显著降低(P<0.05)。正畸治疗后患者LP、LA-m测量值与正畸治疗前比较,差异无统计学意义(P>0.05)。与正畸治疗前比较,正畸治疗后患者LA、LW、LP-m、LW-m测量值均降低(P<0.05)。与正畸治疗前比较,正畸治疗后患者UAH、LAH测量值均显著降低(P<0.05)。正畸治疗后,患者上下颌前牙解剖牙根长度分别为(10.62±0.57)mm、(9.65±0.48)mm,正畸治疗前患者上下颌前牙解剖牙根长度分别为(11.01±0.58)mm、(10.37±0.48)mm,与正畸治疗前比较,患者上下颌前牙解剖牙根长度明显减小(P<0.05)。结论成人骨型Ⅲ类患者进行正畸掩饰治疗后,牙槽形态会发生相应改变,患者上下前牙牙槽骨厚度和高度会一定程度地减少。因此,在矫治过程中应当对患者牙槽形态的变化给予密切关注,尽量避免上下前牙发生代偿性移动,从而降低不良反应情况发生的风险。
基金the National Natural Science Foundation of China(No.62004128)Fundamental Research Foundation of Shenzhen(No.JCYJ20190808152607389)the technical support from the Photonics Center of Shenzhen University.
文摘Broken-gap(type-Ⅲ)two-dimensional(2D)van der Waals heterostructures(vdWHs)offer an ideal platform for interband tunneling devices due to their broken-gap band offset and sharp band edge.Here,we demonstrate an efficient control of energy band alignment in a typical type-ⅢvdWH,which is composed of vertically-stacked molybdenum telluride(MoTe2)and tin diselenide(SnSe2),via both electrostatic and optical modulation.By a single electrostatic gating with hexagonal boron nitride(hBN)as the dielectric,a variety of electrical transport characteristics including forward rectifying,Zener tunneling,and backward rectifying are realized on the same heterojunction at low gate voltages of±1 V.In particular,the heterostructure can function as an Esaki tunnel diode with a room-temperature negative differential resistance.This great tunability originates from the atomicallyflat and inert surface of h-BN that significantly suppresses the interfacial trap scattering and strain effects.Upon the illumination of an 885 nm laser,the band alignment of heterojunction can be further tuned to facilitate the direct tunneling of photogenerated charge carriers,which leads to a high photocurrent on/off ratio of>105 and a competitive photodetectivity of 1.03×1012 Jones at zero bias.Moreover,the open-circuit voltage of irradiated heterojunction can be switched from positive to negative at opposite gate voltages,revealing a transition from accumulation mode to depletion mode.Our findings not only promise a simple strategy to tailor the bands of type-ⅢvdWHs but also provide an in-depth understanding of interlayer tunneling for future low-power electronic and optoelectronic applications.
