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ABSTRACT: The electronic properties of silicon, such as the conductivity, are largely dependent on the density of the mobile charge carriers, which can be tuned by gating and impurity doping. When the device size scales down to the nanoscale, routine doping becomes problematic due to inhomogeneities. Here we report that a molecular monolayer, covalently grafted atop a silicon channel, can play a role similar to gating and impurity doping. Charge transfer occurs between the silicon and the molecules upon grafting, which can influence the surface band bending, and makes the molecules act as donors or acceptors. The partly charged end-groups of the grafted molecular layer may act as a top gate. The doping- and gating-like effects together lead to the observed controllable modulation of conductivity in pseudometal-oxide-semiconductor field-effect transistors (pseudo-MOSFETs). The molecular effects can even penetrate through a 4.92-mum thick silicon layer. Our results offer a paradigm for controlling electronic characteristics in nanodevices at the future diminutive technology nodes.
Journal of the American Chemical Society 08/2009; 131(29):10023-30. · 9.91 Impact Factor
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Advanced Materials 10/2008; 20(23):4541 - 4546. · 13.88 Impact Factor
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ABSTRACT: We have controllably modulated the drain current (I(D)) and threshold voltage (V(T)) in pseudo metal-oxide-semiconductor field-effect transistors (MOSFETs) by grafting a monolayer of molecules atop oxide-free H-passivated silicon surfaces. An electronically controlled series of molecules, from strong pi-electron donors to strong pi-electron acceptors, was covalently attached onto the channel region of the transistors. The device conductance was thus systematically tuned in accordance with the electron-donating ability of the grafted molecules, which is attributed to the charge transfer between the device channel and the molecules. This surface grafting protocol might serve as a useful method for controlling electronic characteristics in small silicon devices at future technology nodes.
Journal of the American Chemical Society 12/2006; 128(45):14537-41. · 9.91 Impact Factor
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ABSTRACT: Nanoelectronic molecular and magnetic tunnel junction (MTJ) MRAM crossbar memory systems have the potential to present significant area advantages (4 to 6F(2)) compared to CMOS-based systems. The scalability of these conductivity-switched RAM arrays is examined by establishing criteria for correct functionality based on the readout margin. Using a combined circuit theoretical modelling and simulation approach, the impact of both the device and interconnect architecture on the scalability of a conductivity-state memory system is quantified. This establishes criteria showing the conditions and on/off ratios for the large-scale integration of molecular devices, guiding molecular device design. With 10% readout margin on the resistive load, a memory device needs to have an on/off ratio of at least 7 to be integrated into a 64 x 64 array, while an on/off ratio of 43 is necessary to scale the memory to 512 x 512.
Nanotechnology 10/2005; 16(10):2251-60. · 3.98 Impact Factor
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ABSTRACT: We have demonstrated a new planar edge defined alternate layer (PEDAL) process to make sub-25 nm nanowires across the whole wafer. The PEDAL process is useful in the fabrication of metal nanowires directly onto the wafer by shadow metallization and has the ability to fabricate sub-10 nm nanowires with 20 nm pitch. The process can also be used to make templates for the nano-imprinting with which the crossbar structures can be fabricated. The process involves defining the edge by etching a trench patterned by conventional i-line lithography, followed by deposition of alternating layers of silicon nitride and crystallized a-Si. The thickness of these layers determines the width and spacing of the nanowires. Later the stack is planarized to the edge of the trench by spinning polymer Shipley 1813 and then dry etching the polymer, nitride and polysilicon stack with non-selective RIE etch recipe. Selective wet etch of either nitride or polysilicon gives us the array of an aligned nanowires template. After shadow metallization of the required metal, we get metal nanowires on the wafer. The process has the flexibility of routing the nanowires around the logic and memory modules all across the wafer. The fabrication facilities required for the process are readily available and this process provides the great alternative to existing slow and/or costly nanowire patterning techniques. (P.D. Franzon).
01/2005; 8116.
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Jorge M Seminario,
Yuefei Ma,
Luis A Agapito,
Liuming Yan,
Roy A Araujo,
Sridhar Bingi,
Nagendra S Vadlamani,
Krishna Chagarlamudi,
Tangali S Sudarshan,
Michael L Myrick,
Paula E Colavita,
Paul D Franzon, David P Nackashi,
Long Cheng,
Yuxing Yao,
James M Tour
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ABSTRACT: Reproducible negative differential resistance (NDR)-like switching behavior is observed in NanoCells. This behavior is attributed to the formation of filaments and clusters between the discontinuous gold films. Control experiments are performed by self-assembly of insulating molecules between the gold islands and conducting molecules on these islands. Additional control experiments are performed by removing the filaments and clusters between islands using a piranha bath. The results are consistent with theoretical predictions and extend the domain of molecular electronics based in organic molecules to include nanosized clusters as active units. This facilitates a scenario where synthetically accessible organic molecules, with defined characteristics, can be adjusted by metallic nanoclusters as an in situ fine-tuning element, able to compensate for the lack of addressing in the nanosize regime.
Journal of Nanoscience and Nanotechnology 10/2004; 4(7):907-17. · 1.56 Impact Factor
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ABSTRACT: NanoCells are disordered arrays of metallic islands that are interlinked with molecules between micrometer-sized metallic input/output leads. In the past, simulations had been conducted showing that the NanoCells may function as both memory and logic devices that are programmable postfabrication. Reported here is the first assembly of a NanoCell with disordered arrays of molecules and Au islands. The assembled NanoCells exhibit reproducible switching behavior and two types of memory effects at room temperature. The switch-type memory is characteristic of a destructive read, while the conductivity-type memory features a nondestructive read. Both types of memory effects are stable for more than a week at room temperature, and bit level ratios (0:1) of the conductivity-type memory have been observed to be as high as 10(4):1 and reaching 10(6):1 upon ozone treatment, which likely destroys extraneous leakage pathways. Both molecular electronic and nanofilamentary metal switching mechanisms have been considered, though the evidence points more strongly toward the latter. The approach here demonstrates the efficacy of a disordered nanoscale array for high-yielding switching and memory while mitigating the arduous task of nanoscale patterning.
Journal of the American Chemical Society 10/2003; 125(43):13279-83. · 9.91 Impact Factor
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ABSTRACT: Recently, several mechanisms have been proposed as a basis for designing molecular electronic logic switching elements. Many two terminal molecular devices functioning as diodes have been synthesized with responses similar to silicon devices such as rectifying and resonant tunneling diodes. In this paper, the feasibility of integrating these molecular diodes into current circuit architectures is explored. A series of logic gates and a memory element are simulated based on the voltagecontrolled current flow method using the Tour-Reed molecular diode exhibiting negative differential resistance (NDR). HSPICE simulation results are used to illustrate the performance of these devices and to quantify additional component and interconnect requirements. Finally, future system design approaches using molecular components are discussed. Keywords: Computer architecture, molecular circuit design, molecular electronics, negative differential resistance, resonant tunneling diode 1.
01/2001;
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ABSTRACT: An important component to the nanocell, among other self-assembled networks, is the fabrication of a framework by which molecular elements can be interconnected. This framework must be nanometric in scale, created in a material suitable for attachment chemistries and remain electrically discontinuous until molecular attachment. Utilizing the Volmer-Weber mechanism by which gold grows on silicon dioxide surfaces, nanometric islands of gold are fabricated to provide this framework. Using standard photolithography techniques, the regions where these islands are located are well defined. A two-layer photoresist stack is developed that prevents edge shorting around the boundaries of each region. The discontinuous gold films fabricated in this study are repeatable, offer a fill factor of 63%, and are easily patterned down to the one-micron scale.
